Abstract: The design of advanced devices is a paramount goal in the biomedical field. Current challenges include the development of customized devices with improved and tailored properties according to the specific application. Accordingly, the aim of the study was to report some recent efforts in the design of advanced biomedical devices, especially focusing on dental implants and hybrid structures for cranioplasty.

Keywords: Additive Manufacturing | Biomedical Applications | Design for Additive Manufacturing

Abstract: Additive manufacturing (AM) allows to create complex shapes and to improve the performance of critical components in different fields. The characteristics of the as-built parts can be an obstacle in terms of satisfaction of the parts’ quality requirements. Concerning the manufacturing process, the relationship among the process parameters, microstructure and mechanical properties is crucial in different areas and involves innovative and traditional fabrication techniques. Fused Deposition Modeling (FDM) is widely employed to fabricate devices with tailored and enhanced properties. In this context, the process parameters clearly influence the quality of devices fabricated from different polymer-based materials, according to the specific AM technology. As reported in the literature, many theoretical models for the prediction of the surface quality focus on the concept of roughness. Furthermore, several parameters have also been proposed to assess the surface quality. Benefiting from advances in design strategies and methodologies of analysis, the aim of the current research was to provide further insight into the development of models for surface roughness prediction in FDM. The relationship among the layer height, printing speed, flow rate and extrusion width was considered and implemented in the model. Preliminary experimental analyses were also performed.

Keywords: Additive Manufacturing | Prediction Model | Surface Roughness

Abstract: Over the past years, a wide range of dental implants has been proposed. In general, the dentists may find the best solutions according to the specific needs of the patients. A variety of factors influences the level of osseointegration and, consequently, the anchorage of the implant to the bone. The stress transfer mechanism along the bone-implant interface depends upon the surface area of the bone-implant contact. Great efforts have been devoted to the design of 3D porous lattice structures with tailored architectural features in order to reduce the implant stiffness as well as to favour bone ingrowth, thus stabilizing the device. Accordingly, the aim of the current study was to provide further insight into the design criteria for dental implants. In particular, starting from a screw implant (Implant A), different concepts of dental implants were developed: i) Implants B1–B5, with lattice shell surrounding a solid core, without thread; ii) Implant C, with lattice structure; iii) Implant D as topography optimized implant. Finite element analysis on the several models of bone-implant provided interesting information in terms of stress distributions in cortical and trabecular bone. Some differences among the implants may be ascribed to the different design criteria.

Keywords: Dental implants | Design criteria | Finite element analysis | Lattice structure | Topography optimization | Topology optimization

Abstract: Factory acceptance test is the inspection of equipment and components at the supplier’s premises before delivery or final inspection. However, this control can represent a considerable cost for the customer, especially when the manufacturer’s company is geographically far from the customer one and inspections must be frequent. In this paper, the authors present a framework to support the factory acceptance test based on augmented reality (AR) techniques and model-based definition aimed at dimensional checks that does not require the physical presence of the customer at the supplier's premises. The supplier must be previously equipped with an automatic measuring machine. Once the component under inspection is placed inside the machine, this reads the type and the position of the features to be measured along with the related specification limits directly from the annotated 3D model of the component. The results are automatically transmitted to the customer’s site. Through a tablet, the supplier, guided by the customer, reads the results of the measures directly on the measured object through augmented or mixed reality techniques. Any out-of-specification dimension can be remeasured in real time with the customer’s remote assistance using traditional measurement techniques. The proposed architecture, at an advanced stage of experimentation, is discussed with reference to an industrial case study proposed and using an entry level commercial 3D scanner.

Keywords: Augmented reality | Dimensional inspection | Factory acceptance test | Metrology

Abstract: The current best-practice in the assembly process of aircraft skin panels involves several manual measurement-fit-adjust quality loops, such as loading part on the assembly frame, measuring gaps, off-loading parts, adding be-spoke shims and re-positioning parts ready for the fastening operation. The consequence is that the aircraft is re-assembled at least twice and therefore this process has been proved highly inefficient. This paper describes the framework developed under the “Integrated Smart Assembly Factory” (ISAF) project in the “Intelligent Factory” specialisation area in Italy. Taking advantage of the emerging tools brought by Industry 4.0 the ISAF framework spearheads innovation in the assembly process of aircraft skin panels by integrating smart and digital technologies such as in-line measurement systems with highly accurate sensors, large-scale physics-based simulations, multi-disciplinary process optimisation and additive manufacturing. ISAF implements a flexible alignment, which combines both rigid rotations/translations and local deformations to account part deformations. The proposed methodology allows predicting and fabricating shims using in-line measurement data with no need to iterate the measurement-fit-adjust quality loops. This will undoubtedly reduce inspection/measurement time and costs, enabling operators to virtually test assembly operations before installation in the field. The results were demonstrated during the assembly process of a vertical stabiliser for commercial aircrafts, and findings showed a significant time saving of 75%.

Keywords: Additive manufacturing | Digital twin | Flexible alignment | In-line measurement | Physical simulation | Shimming | Smart factory

Abstract: The paper presents a preliminary design activity and virtual prototyping of an innovative boat equipped with hydrofoils and hybrid propulsion, with the aim of extending the foil technology from the field of competition boats to recreational day-cruiser yachts and creating a craft with minimal environmental impact. Hydrofoils allow boats to rise from the water, greatly reducing resistance and increasing performance. The current work dealt with the preliminary design of a daysailer with foil technology and hybrid propulsion that allow to combine green and comfortable navigation both under sail and motor and that, when required, can sail in a more performing way by exploiting the foil technology and the thrust of the wind. After having deepened the theory and physics of sailing on foils, a MATLAB code was created to integrate the stability equations that characterize hydrofoil sailboats: connecting the acting forces and allowing to define the dimensions of the geometries, the code was fundamental in speeding up the iterative preliminary design process. The next step was to model the geometry of the hull and the appendages in the CAD environment and, subsequently, the wing movement mechanism so that it could both manage the incidence of the wings and retract the foils when the boat is moored. The hull, profiles, and wings were subsequently placed in a CFD and VPP virtual environment for testing their resistance. Future developments will include a detailed design and the physical prototyping of a first boat for water testing.

Keywords: Green | Hybrid | Hydrofoil | Virtual prototyping

Abstract: Creative design methods should allow the extraction of novel wisdoms and favour their integration into many technological domains, thus leading to an innovative product. The current research reports some technical considerations on the role of generative design as a “collaborative partner” in supporting the ideation process through the development of design alternatives in agreement with the designer’s criteria. A specific case study was considered and the role of the generative design method was stressed, also focusing on technical features and differences in terms of solutions for the given design problem. The possibility of selecting well defined manufacturing methods (e.g., traditional or advanced – additive manufacturing) was highlighted.

Keywords: additive manufacturing | design methods | development | Generative design | mechanical measurements | product design

Abstract: Additive manufacturing technology allows producing objects layer-by-layer starting from three-dimensional (3D) digital models. These 3D models can be drawn using CAD software or can be obtained starting from a real-world object, through reverse engineering (RE) techniques. RE process is today widely used in numerous industrial applications. It is a powerful tool for additive manufacturing, and their combination can greatly enhance product design as well as shorten the product development cycle. This chapter describes the main reverse engineering techniques – contact and noncontact active and passive systems – and the main phases that allow obtaining a 3D CAD model starting from a physical object.

Keywords: Active and passive methods | Contact and noncontact systems | Industrial CT scanning | Point cloud | STL format

Abstract: Additive manufacturing has become an advanced processing method to fabricate highly customized devices with tailored functional properties, complex geometries, and architectural features. In this scenario, design strategies are currently leading to a wide range of possibilities to search for the optimal solution or a set of optimal solutions for the design of 3D additive manufactured structures with suitable functional properties according to the considered application. Topology optimization and generative design may be considered very powerful tools to create optimized designs. Furthermore, creative solutions to the design problems may be provided by the biological knowledge, which represents a source of inspiration for the designers. A creative bioinspired design method may allow the extraction of innovative wisdoms from biological prototypes and their integration into several technological domains, thus creating an innovative product. Accordingly, the present chapter first introduces some considerations on the role of CAD tools in providing a support for the ideation process through the generation of design alternatives in agreement with the designer’s criteria, and describes the state of the art of the generative design methods in different application fields. The terminology and the application of the biological knowledge in engineering innovation are reviewed, and the potential of biologically inspired design methods is stressed as they go beyond both biomimicry and biomimetics. The importance of combining additive manufacturing and reverse engineering is also briefly emphasized. Furthermore, focusing on a specific case study, the potential of topology optimization and generative design methods are reported, also evidencing technical features and differences.

Keywords: Bioinspired design | Biomimetics and biomimicry | Creativity and innovation | Design strategies | Generative design | Topology optimization

Abstract: A leading challenge in the assembly process of aircraft skin panels is the precise control of part-to-part gaps to avoid excessive pre-tensions of the fastening element which, if exceeded, impair the durability and the response under dynamics loads of the whole skin assembly. The current practice is to measure the gap in specific points of the assembly with parts already at their final location, and then be-spoke shims are machined and inserted between the mating components to fill the gap. This process involves several manual measurement-fit-adjust quality loops, such as loading parts on the assembly frame, measuring gaps, off-loading parts, adding be-spoke shims and re-positioning parts ready for the fastening operation—as a matter of fact, the aircraft is re-assembled at least twice and therefore the current practice has been proved highly cost and time ineffective. Additionally, the gap measurement relies on manual gauges which are inaccurate and unable to follow the actual 3D profile of the gap. Taking advantage of emerging tools such as in-line measurement systems and large-scale physics-based simulations, this paper proposes a novel methodology to predict the part-to-part gap and therefore minimise the need for multiple quality loops. The methodology leverages a physics-driven digital twin model of the skin assembly process, which combines a physical domain (in-line measurements) and a digital domain (physics-based simulation). Central to the methodology is the variation model of the multi-stage assembly process via a physics-based simulation which allows to capture the inherent deformation of the panels and the propagation of variations between consecutive assembly stages. The results were demonstrated during the assembly process of a vertical stabiliser for commercial aircraft, and findings showed a significant time saving of 75% by reducing costly and time-consuming measurement-fit-adjust quality loops.

Keywords: Aircraft skin panels | Digital twin | Morphing mesh | Multi-stage assembly simulation | Physics-based modelling | Virtual shimming

Abstract: This study evaluated the influence of distal implants angulation and framework material in the stress concentration of an All-on-4 full-arch prosthesis. A full-arch implant-supported prosthesis 3D model was created with different distal implant angulations and cantilever arms (30° with 10-mm cantilever; 45° with 10-mm cantilever and 45° with 6-mm cantilever) and framework materials (Cobalt–chrome [CoCr alloy], Yttria-stabilized tetragonal zirconia polycrystal [Y-TZP] and polyetheretherketone [PEEK]). Each solid was imported to computer-aided engineering software, and tetrahedral elements formed the mesh. Material properties were assigned to each solid with isotropic and homogeneous behavior. The contacts were considered bonded. A vertical load of 200 N was applied in the distal region of the cantilever arm, and stress was evaluated in Von Misses (σVM) for prosthesis components and the Maximum (σMAX) and Minimum (σMIN) Principal Stresses for the bone. Distal implants angled in 45° with a 10-mm cantilever arm showed the highest stress concentration for all structures with higher stress magnitudes when the PEEK framework was considered. However, distal implants angled in 45° with a 6-mm cantilever arm showed promising mechanical responses with the lowest stress peaks. For the All-on-4 concept, a 45° distal implants angulation is only beneficial if it is possible to reduce the cantilever’s length; otherwise, the use of 30° should be considered. Comparing with PEEK, the YTZP and CoCr concentrated stress in the framework structure, reducing the stress in the prosthetic screw.

Keywords: Dental implants | Finite element analysis | Polymers | Prosthodontics

Abstract: Additive manufacturing (AM) allows the development of novel and customized products with tailored properties. However, the application of extrusion-based AM techniques (i.e., fused deposition modeling – FDM) in the design of functional parts is often limited because of the poor mechanical performance as a consequence of the nature of the process to build the object in a layer-by-layer fashion. In the current study, the impact resistance of the 3D printed polyethylene terephthalate glycol-modified (PETG) and high impact polystyrene (HIPS) was evaluated as a function of three printing parameters (i.e., printing temperature, layer height and line width). Izod-type test specimens were fabricated and analyzed according to the ASTM D256. The contribution of each factor was properly analyzed. The results also indicated that the printing temperature was the most significant parameter for the impact resistance of 3D printed PETG and HIPS. The obtained findings may be considered as valid only within the limit of parameters and ranges investigated in the current study.

Keywords: Design of experiments | Fused deposition modeling | Impact resistance

Abstract: Titanium alloys (e.g., Ti6Al4V) have been widely considered for the design of biomedical implants. To avoid stress shielding effects, bone atrophy and implant loosening bone, 3D porous devices with controlled geometry and architecture should represent a promising solution. Several cellular structures were already investigated to obtain a wide range of mechanical properties. Many studies focused on the mechanical performance of diamond and body-centered-cubic. Different kinds of porous and semi-porous femoral stems were also proposed and analyzed. Accordingly, the aim of the current research was to provide further insight into the design of solid-lattice hybrid structures through a two-step process involving the classical and lattice topology optimization. A cementless femoral stem was considered as a case study. The solid isotropic material with penalization (SIMP) was used at varying values of the penalty factor and the effect of the geometrical features of each beam forming the lattice structure was also determined. Differences were found in terms of functional and structural performances according to the selected strategy for the design of the solid-lattice hybrid structures, as a consequence of the material distribution/layout and geometrical features.

Keywords: Biomedical applications | Solid-lattice hybrid structures | Topology optimization

Abstract: Titanium and its alloys are widely employed in commercial dental devices. Because the surface morphology and chemical composition of Ti-based dental implants play a relevant role in osseointegration, three different commercial threaded implants have been investigated by scanning electron microscopy and X-ray photoelectron spectroscopy (XPS). The Implants A and C were made of pure Ti whereas the Implant B was made of Ti6Al4V alloy. Obtained results evidenced the common features and differences due to specific process parameters used in the treatments of mordanting and sandblasting for surface roughening. Implant A exhibits a uniform surface covered by very small dimples of about 1–2 μm. The surface of Implant B is not homogeneous: The thread tops present an irregular morphology (dimples size >10 μm) while finer dimples (about 1 μm) are observed along the thread flanks and valleys. Implant C shows an irregular morphology with dimples of different sizes and shapes distributed on thread tops, flanks, and valleys. XPS analyses revealed the presence of metal oxides: TiO2 in all the implants; Al2O3 and V2O5 only in the implant B. Moreover, these results demonstrated that Mg2SiO4 is present on the surface of Implant A, probably due to a specific preparation process. Obtained results have been discussed on the basis of the factors promoting the osseointegration.

Keywords: dental implants | SEM | surface morphology | Ti6Al4V | titanium | XPS

Abstract: Objective: The aim of this study was to evaluate the influence of three different dental implant neck geometries, under a combined compressive/shear load using finite element analysis (FEA). The implant neck was positioned in D2 quality bone at the crestal level or 2 mm below. Methods: One dental implant (4.2 × 9 mm) was digitized by reverse engineering techniques using micro CT and imported into Computer Aided Design (CAD) software. Non-uniform rational B-spline surfaces were reconstructed, generating a 3D volumetric model similar to the digitized implant. Three different models were generated with different implant neck configurations, namely 0°, 10° and 20°. D2 quality bone, composed of cortical and trabecular structure, was modeled using data from CT scans. The implants were included in the bone model using a Boolean operation. Two different fixture insertion depths were simulated for each implant: 2 mm below the crestal bone and exactly at the level of the crestal bone. The obtained models were imported to FEA software in STEP format. Von Mises equivalent strains were analyzed for the peri-implant D2 bone type, considering the magnitude and volume of the affected surrounding cortical and trabecular bone. The highest strain values in both cortical and trabecular tissue at the peri-implant bone interface were extracted and compared. Results: All implant models were able to distribute the load at the bone-implant contact (BIC) with a similar strain pattern between the models. At the cervical region, however, differences were observed: the models with 10° and 20° implant neck configurations (Model B and C), showed a lower strain magnitude when compared to the straight neck (Model A). These values were significantly lower when the implants were situated at crestal bone levels. In the apical area, no differences in strain values were observed. Significance: The implant neck configuration influenced the strain distribution and magnitude in the cortical bone and cancellous bone tissues. To reduce the strain values and improve the load dissipation in the bone tissue, implants with 10° and 20 neck configuration should be preferred instead of straight implant platforms.

Keywords: Dental implants | Finite element analysis | Implant design | Strain distribution

Abstract: Additive manufacturing technologies allow for the direct fabrication of 3D scaffolds with improved properties for tissue regeneration. In this scenario, design strategies and 3D fiber deposition technique are considered to develop advanced scaffolds with different lay-down patterns, tailored mechanical and biological properties. 3D poly(ε-caprolactone) scaffolds are manufactured and surface-modified (i.e., aminolysis). The effect of surface modification on the mechanical and biological performances of the designed 3D scaffolds is assessed.

Keywords: computer-aided design | design for additive manufacturing | mechanical analysis | scaffold design

Abstract: Light-activated resins and composites are used in conjunction with a light curing unit and allow an on-demand process of polymerization. These kinds of materials usually represent the most popular choice in the restorative dental practice. Some works have already highlighted contemporary tendencies in the use of nondegradable scaffolds and mesenchymal stem cells in regenerative medicine. Accordingly, the aim of the current research is to develop 3D porous and light-activated composite structures with optimized functional properties. Preliminary mechanical and biological tests are carried out.

Keywords: composite structure design | computer-aided design | design for photo-curing 3D printing | mechanical and functional properties

Abstract: In the article titled “Design of Additively Manufactured Lattice Structures for Biomedical Applications” [1], there was an error in the author’s name, where “Sverio Maietta” should be corrected to “Saverio Maietta.” e corrected author name is shown in the author group above.

Abstract: A wide range of materials has been considered to repair cranial defects. In the field of cranioplasty, poly(methyl methacrylate) (PMMA)-based bone cements and modifications through the inclusion of copper doped tricalcium phosphate (Cu-TCP) particles have been already investigated. On the other hand, aliphatic polyesters such as poly (e-caprolactone) (PCL) and polylactic acid (PLA) have been frequently investigated to make scaffolds for cranial bone regeneration. Accordingly, the aim of the current research was to design and fabricate customized hybrid devices for the repair of large cranial defects integrating the reverse engineering approach with additive manufacturing, The hybrid device consisted of a 3D additive manufactured polyester porous structures infiltrated with PMMA/Cu-TCP (97.5/2.5 w/w) bone cement. Temperature profiles were first evaluated for 3D hybrid devices (PCL/PMMA, PLA/PMMA, PCL/PMMA/Cu-TCP and PLA/PMMA/Cu-TCP). Peak temperatures recorded for hybrid PCL/PMMA and PCL/PMMA/Cu-TCP were significantly lower than those found for the PLA-based ones. Virtual and physical models of customized devices for large cranial defect were developed to assess the feasibility of the proposed technical solutions. A theoretical analysis was preliminarily performed on the entire head model trying to simulate severe impact conditions for people with the customized hybrid device (PCL/PMMA/Cu-TCP) (i.e., a rigid sphere impacting the implant region of the head). Results from finite element analysis (FEA) provided information on the different components of the model.

Keywords: Composite bone cement for cranioplasty | Design for additive manufacturing | Finite element analysis | Reverse engineering | Temperature profile analysis

Abstract: Recently, a variety of craniofacial approaches has been adopted to enter the skull base, including the endonasal endoscopic technique. An effective watertight technique, the reconstruction can be performed using different materials, both autologous and non-autologous, individually or combined in a multilayer fashion. The current study focuses on the development of new advanced devices and techniques that help to reduce the postoperative cerebrospinal fluid leak rate. Additive manufacturing allows the design of devices with tailored structural and functional features, as well as injectable semi-interpenetrating polymer networks and composites; therefore, specific mechanical/rheological and injectability studies are valuable. Accordingly, we propose new additive manufactured and injectable devices.

Keywords: Additive manufacturing | CSF leakage | Design of injectable systems | Endoscopic endonasal surgery | Reverse engineering | Skull base reconstruction

Abstract: It has been widely reported that breast reconstruction improves the quality of life of women who undergo mastectomy for breast cancer. This approach provides many psychological advantages. Today, different techniques are available for the breast oncoplastic surgeon that involve the use of breast implants and autologous tissues, also offering interesting results in terms of aesthetic and patient-reported outcomes. On the other hand, advanced technologies and design strategies (i.e. design for additive manufacturing, reverse engineering) may allow the development of customised porous structures with tailored morphological, mechanical, biological, and mass transport properties. For this reason, the current study deals with the challenges, principles, and methods of developing 3D additive manufactured structures in breast reconstructive surgery. Specifically, the aim was to design 3D additive manufactured poly(ε-caprolactone) scaffolds with different architectures (i.e. lay-down patterns). Preliminary mechanical and biological analyses have shown the effect of the lay-down pattern on the performances of the manufactured structures.

Keywords: Additive manufacturing | Breast reconstructive surgery | Fat grafting | Functional properties | Mechanical | Pore geometry and lay-down pattern | Reverse engineering | Scaffold design

Abstract: Assembly process of aeronautical skin panels deals with large, thin and compliant components, which are usually joined with rivets. A leading challenge is the control of part-to-part gaps prior to riveting operation, which must be maintained below tight design specification limits to avoid excessive pretensions of the rivets which, if exceeded, impair the durability of the whole skin assembly. Gaps are compensated by number of time consuming and costly manual inspection-repair quality loops, which involve measuring gaps, disassembling parts, adding be-spoke shims, re-assembling parts. This paper proposes a novel methodology to support the inspection-repair quality loops with the aim to model and optimise the shape of the shims with the ultimate goal of reducing/eliminating manual and trial-and-error measurements as per today best practice. The methodology will be discussed in two steps: (1) physics-based variation simulation to model generation and propagation of dimensional and geometrical variations (by using scanning data o morphing mesh model) during multi-stage assembly operations; (2) virtual shimming simulator to model and optimise shimming condition between parts being assembled. The proposed methodology is presented and validated using the assembly process of the vertical stabiliser for commercial aircrafts.

Keywords: Aircraft Skin Assembly | Morphing Mesh | Physics-based Modelling | Scanning Data | Virtual Shimming Simulator

Abstract: In this work is analyzed the possibility to use optical techniques for the characterization of airless radial tire. Electronic Speckle Pattern Interferometry (ESPI), laser scanner based on principle of triangulation and Digital Image Correlation (DIC) have been used to acquire and study this kind of tire. A MICHELIN® X® TWEEL® UTV has been considered as case study. The acquisitions have been used for the measurement of the shape for testing junction areas and to evaluate the structure behavior under a vertical load.

Keywords: Composite laminates | Laser scanner | NDI | Tire

Abstract: The aim of the current work was to analyze the influence of the ferrule effect for hybrid composite endodontic post designs consisting of carbon (C) and glass (G) fiber-reinforced polyetherimide (PEI), in upper canine teeth. Starting from theoretical designs of C-G/PEI hybrid composite posts with different Young's moduli (Post A-57.7 GPa, Post B-31.6 GPa, Post C-graduated from 57.7 to 9.0 GPa in the coronal-apical direction) in endodontically treated anterior teeth, the influence of the ferrule effect was determined through finite element analysis (FEA). On the surface of the crown, a load of 50 N was applied at 45° to the longitudinal axis of the tooth. Maximum principal stresses were evaluated along the C-G/PEI post as well as at the interface between the surrounding tooth structure and the post. Maximum stress values were lower than those obtained for the corresponding models without a ferrule. The presence of a ferrule led to a marked decrease of stress and gradients especially for posts A and B. A less marked effect was globally found for Post C, except in a cervical margin section along a specific direction, where a significant decrease of the stress was probably due to local geometric features, compared to the model without a ferrule. The presence of a ferrule did not generally provide a marked benefit in the case of the graduated Post C, in comparison to other C-G/PEI posts. The outcomes suggest how such a hybrid composite post alone should be sufficient to optimize the stress distribution, dissipating stress from the coronal to the apical end.

Keywords: Computer-Aided Design | Endodontic post design | Finite element analysis | Polyetherimide composites | Reverse engineering

Abstract: In the current research, an optimization design strategy for additive manufacturing processes based on extrusion/injection methods was extended to the fabrication of poly(ε-caprolactone) (PCL)/iron oxide (Fe3O4) scaffolds for tissue engineering. The attention was focused on four parameters: process temperature (PT), deposition velocity (DV), screw rotation velocity (SRV), slice thickness (ST). Specifically, PCL/Fe3O4 scaffolds were manufactured varying iteratively one parameter, while maintaining constant the other three parameters. A further insight into the influence of process parameters on the morphological features and mechanical properties of PCL/Fe3O4 scaffolds was provided.

Keywords: Design for additive manufacturing | Magnetic nanocomposite scaffolds | Mechanical and morphological properties | Tissue engineering

Abstract: The special issue focuses on different features related to the design of additively manufactured lattice structures for biomedical applications. In many cases, the process-structure- property relationship and technical features are discussed from a morphological, mechanical, and functional point of view. In particular, an overview of the Additive Manufacturing processes, software methods, and design criteria, which allow the direct fabrication of 3D porous structures and lattices with tailored properties, are reported. Accordingly, the current special issue aims at providing new insights into the development of advanced devices and illustrates theoretical/experimental approaches used by researchers working in the field.

Abstract: In the last decades a variety of innovative craniofacial approaches has been adopted to entire skull base. The endonasal endoscopic route has emerged as a suitable methodology for several skull base lesions. An effective watertight closure is essential to isolate the intracranial cavity in order to restore the natural intra and extradural compartment division, necessary to prevent postoperative cerebrospinal fluid (CSF) leakage and complications such as meningitis, brain herniation, and tension pneumocephalus. The reconstruction can be performed using different materials, both autologous (autologous grafts) and non-autologous, individually or combined in a multilayer fashion. The harvesting a nasoseptal flap is one of the most effective techniques: it reinforces the skull base closure granting isolation of the surgical field. The current study was focused on the development of new advanced devices and techniques, aiding in reducing postoperative CSF leak, which is one of the most feared complication of this surgical procedure. Additive manufacturing allows to design devices with tailored structural and functional features, in order to satisfy all the requirements. On the other hand, the development of injectable semi-IPNs and composites clearly benefits from specific mechanical/rheological and injectability studies. Accordingly, starting from some basic concepts, innovative principles and strategies were also proposed towards the design of additively manufactured and injectable devices.

Keywords: additive manufacturing | CSF leakage | design of injectable systems | endoscopic endonasal surgery | reverse engineering | skull base reconstruction

Abstract: Products aimed at individuals with disabiliy could not match user requirements under conditions imposed by the user. Also, frequent modifications and adaptation are required to increase the match between user requirements and prototypes. The importance to test different solutions and gain a knowledge base is an important aspect as the time in trials and experimentation is still a limit of personalized devices. An experimentation is conducted to test a solution of hardware interface for an Augmentative and Alternative Communication System which implements visual feedbacks and visual tutorial in training phase. In this study, visual feedbacks demonstrate an improvement of performances due to three main effects: reducing training time through an interactive tutorial, improving automatic behaviour and limiting cognitive load. The prototypes are realized using open-source electronic boards and Additive Manufacturing to realize the housing. A usability test is performed to calculate metrics and benchmark solutions with and without visual aids. Measures of Lostness and Keystroke Level Model estimates the effectiveness of software interface and interaction of users with hardware and software interfaces.Also, this study can lead to the definition of an adaptive switch that modify its status in order to eliminate redundant operations and ineffective actions.Visual feedback has proven some advantages in training user and Additive Manufacturing enabled the study and lead the way for devices that are adaptive on software interface and control and personalized in the hardware interface.

Keywords: augmentative and alternative communication | biomedical devices | usability

Abstract: Many women with early breast cancer undergo mastectomy as a consequence of an unfavorable tumor/breast ratio or because they prefer this option to breast conservation. As reported, breast reconstruction offers significant psychological advantages. Several techniques are currently available for the breast oncoplastic surgeon and offer interesting results in terms of aesthetic and patient-reported outcomes, using both breast implants and autologous tissues. On the other hand, advanced methodologies and technologies, such as reverse engineering and additive manufacturing, allow the development of customized porous scaffolds with tailored architectures, biological, mechanical and mass transport properties. Accordingly, the current research dealt with challenges, design methods and principles to develop 3D additively manufactured structures in breast reconstructive surgery.

Keywords: additive manufacturing | breast reconstructive surgery | design | fat grafting | reverse engineering | scaffold design

Abstract: The current research reports for the first time the use of blends of poly(ε-caprolactone) (PCL) and poly(ester amide) (PEA) for the fabrication of 3D additive manufactured scaffolds. Tailor made PEA was synthesized to afford fully miscible blends of PCL and PEA using different percentages (5, 10, 15 and 20% w/w). Stability, characteristic temperatures and material's compatibility were studied through thermal analyses (i.e., TGA, DSC). Even though DMTA and static compression tests demonstrated the possibility to improve the storage modulus, Young's modulus and maximum stress by increasing the amount of PEA, a decrease of hardness was found beyond a threshold concentration of PEA as the lowest values were achieved for PCL/PEA (20% w/w) scaffolds (from 0.39 ± 0.03 GPa to 0.21 ± 0.02 GPa in the analysed load range). The scaffolds presented a controlled morphology and a fully interconnected network of internal channels. The water contact angle measurements showed a clear increase of hydrophilicity resulting from the addition of PEA. This result was further corroborated with the improved adhesion and proliferation of human mesenchymal stem cells (hMSCs). The presence of PEA also influenced the cell morphology. Better cell spreading and a much higher and homogenous number of cells were observed for PCL/PEA scaffolds when compared to PCL ones.

Keywords: Additive manufacturing | Biological properties | Image analysis | Poly(ester amide) | Scaffold design | Thermal and mechanical properties

Abstract: Light activated composites are the most popular choice in the field of dental restoration. They generally show internal stress even after a prolonged time period. The knowledge of mechanical properties and residual stress should provide interesting information on the clinical performance of such materials. Accordingly, in the current research experimental analyses were carried out to assess the effect of the curing process on the properties of one of the most commonly employed light activated dental composites (Gradia Direct—GC Corporation, Japan). At 10 min, 1 h and 24 h after light curing, the bending modulus (4.7–6.2 GPa) as well as the punching performance (peak load of 12.1–17.5 N) were evaluated for the micro-hybrid composite. Scanning electron microscopy also allowed to analyze the fracture surface. Residual stresses ranging from 0.67 ± 0.15 MPa to 1.12 ± 0.17 MPa were measured by means of the thin-ring-slitting approach reported in the literature, according to measurement time and cutting time.

Keywords: CAD/CAM system | Dental materials | Mechanical and morphological properties | Residual stress

Abstract: The control of the process–structure–property relationship of a material plays an important role in the design of biomedical metal devices featuring desired properties. In the field of endodontics, several post-core systems have been considered, which include a wide range of industrially developed posts. Endodontists generally use posts characterized by different materials, sizes, and shapes. Computer-aided design (CAD) and finite element (FE) analysis were taken into account to provide further insight into the effect of the material–shape combination of metal posts on the mechanical behavior of endodontically treated anterior teeth. In particular, theoretical designs of metal posts with two different shapes (conical-tapered and conical-cylindrical) and consisting of materials with Young’s moduli of 110 GPa and 200 GPa were proposed. A load of 100 N was applied on the palatal surface of the crown at 45◦ to the longitudinal axis of the tooth. Linear static analyses were performed with a non-failure condition. The results suggested the possibility to tailor the stress distribution along the metal posts and at the interface between the post and the surrounding structures, benefiting from an appropriate combination of a CAD-based approach and material selection. The obtained results could help to design metal posts that minimize stress concentrations.

Keywords: Computer-aided design (CAD) | Dental materials | Finite element analysis | Image analysis | Mechanical properties | Metal posts

Abstract: The complexity of the interaction between user and computer can limit usability in products. When products are aimed at individuals with disability, the complexity increases the cognitive load and can reduce performances. The identification of interaction models and usability issues plays a role in product development as it enables designers to reduce this complexity. Methodology to identify lacking areas in products are required and permits to correct issues leading to an improvement of performances. A custom Augmentative and Alternative Communication system was developed for a student of the University of Naples Federico II. The user has complex communication needs and motor impairments and requires a personalized device to communicate. To promote an efficient interaction, hardware and software interfaces were personalized. Several studies were conducted: a usability evaluation, determination of the learning rate and Hardware/Software layout optimization were used to reduce the cognitive demands required by the system in its functioning. In this paper the HW layout optimization is investigated and strategies to reduce the cognitive load modifying order and position of the sensors of the input peripherals are provided.

Keywords: Augmentative and Alternative Communication | Human-Computer Interaction | Usability Testing

Abstract: In a complex case of speech disorder, the communication is entrusted to systems equipped with a speech synthesizer. When the user has a motor disability, in addition, hardware and software interfaces are personalized to make technology more accessible. Interaction design methods can be applied to develop improved assistive systems and, particularly, for Augmentative and Alternative Communication (AAC). Interaction design methods and usability evaluation could have a positive impact in reducing product barriers and improving performances as the effort state associated to its use can be reduced. Minimizing cognitive and physical efforts through the development of new solutions and interface optimization can be challenging. A usability test and an interface optimization of a personalized AAC system developed for a student of the University of Naples Federico II with complex communication needs due to a traumatic injury and motor impairment are discussed to fix usability issues, highlight critical areas and design new prototypes.

Keywords: Augmentative and alternative communication | Biomedical devices | Disability | Interaction design | Learnability | Usability

Abstract: Mechanical and architectural features play an important role in designing biomedical devices. The use of materials (i.e., Ti6Al4V) with Young's modulus higher than those of natural tissues generally cause stress shielding effects, bone atrophy, and implant loosening. However, porous devices may be designed to reduce the implant stiffness and, consequently, to improve its stability by promoting tissue ingrowth. If porosity increases, mass transport properties, which are crucial for cell behavior and tissue ingrowth, increase, whereas mechanical properties decrease. As reported in the literature, it is always possible to tailor mass transport and mechanical properties of additively manufactured structures by varying the architectural features, as well as pore shape and size. Even though many studies have already been made on different porous structures with controlled morphology, the aim of current study was to provide only a further analysis on Ti6Al4V lattice structures manufactured by selective laser melting. Experimental and theoretical analyses also demonstrated the possibility to vary the architectural features, pore size, and geometry, without dramatically altering the mechanical performance of the structure.

Abstract: Nowadays, the quality assurance of aeronautical components is a very crucial issue. Diverse defects can be generated during composite material components manufacturing such as voids, delamination, cracks, etc. The identification of these defects requires the use of different types of inspection methods. In this paper, two diverse non-contact inspection techniques, i.e. a laser-based reverse engineering method and an ultrasonic testing procedure, are integrated to provide a complete quality assessment of carbon fibre reinforced polymer components for applications in the aeronautical field. A custom made software code was developed in order to create a user interface allowing for the visualization and analysis of the reverse engineering and ultrasonic information for the detection of geometrical and internal flaws of the component under inspection.

Keywords: Composite materials | Laser-based reverse engineering | Non-contact testing | Quality control | Ultrasonic non-destructive inspection

Abstract: This paper deals with parenthood perception (maternal and paternal) after the visualization and interaction (touch) with a 3D printed facial fetal model. The model is created using Additive Manufacturing techniques, starting from the image elaboration of routine ultrasound data. In this study, the method used for the elaboration and construction of 3D printable models of fetal faces starting from routine ultrasound images is briefly described. In addition, we present the results of a new survey conducted with future parents at the Altamedica clinic (Rome, Italy) to verify whether there are any benefits derived from the use of 3D printing models with future parents, both regarding the improvement of the parenthood experience, and the improvement of the understanding and collaboration with the physicians in case of fetal malformations, using 3D models coupled with the data of routine ultrasound examinations.

Keywords: 3D ultrasound | Additive manufacturing | Fetal face | Image processing | Parenthood perception | Survey

Abstract: The current research was focused on a further insight into the mechanical properties of 3D parts printed with virgin and recycled polylactic acid (PLA). A first set of specimens was printed with virgin PLA lament and mechanically tested. Such specimens were then ground up and re-extruded into filament using a homemade extruder. The re-extruded filament was employed to manufacture a new set of specimens which were also analysed. Three recycling processes were performed to assess the effect on the mechanical properties. The obtained results suggested that 3D printing with recycled PLA may be a viable option.

Keywords: Additive Manufacturing | Mechanical properties | Recycled polymers

Abstract: Objectives: To evaluate the association between maxillary dental arch transverse dimensions, palatal depths, palatal area and volume with buccally displaced canine (BDC) in mixed dentition subjects when compared to non-BDC subjects using laser scanner 3D technology. Materials and methods: Sixty Caucasian subjects, 8-11 years of age (mean, 9.26 ± 1.48 years), were included. In each group (BDC and non-BDC) 30 children were matched. Digital dental casts were obtained using a 3 Shape D700 laser scanner. Intercanine and intermolar widths (cusp and gingival levels), anterior and posterior palatal depth (cusp level), palatal surface area and volume were measured. An independent sample Student's t-test and an ANOVA were undertaken with significance level set as P < 0.05. Results: Intercanine widths at the cusp (1.76 mm; P = 0.020) and the gingival level (1.6 mm; P = 0.006), palatal area (133 mm2; P = 0.021) and volume (790 mm3; P = 0.046) were significantly lower in the BDC compared to the control group. Limitations: A smaller part of the subjects was in late mixed dentition phase. To overcome this limitation a matched control group was used. Some subjects did not have some teeth because of the transition phase which might have had an influence on the dental measurements. However, these subjects were not excluded to avoid introducing a bias. Conclusions: 3D evaluation of the maxillary arch and palate highlighted significant differences between BDC and non-BDC mixed dentition subjects. Maxillary dental arch dimensions and palate morphology may allow early identification and prevention of maxillary canine impaction.

Abstract: Computational Fluid Dynamics (CFD), as early used in the design stage, helps engineers to come up with the optimum design of a sail in a reasonable timeframe. However, traditional CFD tools are approximate and need to be validated when it comes to predicting the dynamic behaviour of non-developable shape with high camber and massively detached flow around thin and flexible membranes. Some of these approximations are related to the implementation of the constitutive material characteristics and assumption of their isotropic properties, while the sail aerodynamic performance is strongly influenced by the arrangement of sail panels as well as the orientation of the fibres in the composite structure. The present paper offers a methodology that enhances the understanding of the influence of panel arrangement and fibre orientation on sail performance. Fluid-structure-interaction (FSI) in a symmetric spinnaker was studied through an integrated CFD-CSM (Computational Structural Mechanics) analysis. A suitable triangular membrane element formulation of sail was adopted and the constitutive characteristics (elasticity and damping) of the Nylon superkote 75 were implemented in CSM model after being experimentally measured. The aerodynamic performance of sail in terms of drive force and side force was evaluated using both Reynolds Averaged Navier Stokes Simulations (RANS) and Shear Stress Transport (SST) turbulence model with a finite volume approach. A comparison between different panel arrangements was carried out under altered downwind flow conditions of wind speed and wind angle. Digital photogrammetry was employed to create the 3D reconstruction of the sail's flying shape and validate the results obtained by aeroelastic analysis.

Keywords: CFD-CSM analysis | Flying shape photogrammetry acquisition | Sail panel arrangement | SST model | Triangular membrane elements

Abstract: Objective: To investigate the influence of implant design on the change in the natural frequency of bone-implant system during osseointegration by means of a modal 3D finite element analysis. Methods: Six implants were considered. Solid models were obtained by means of reverse engineering techniques. The mandibular bone geometry was built-up from a CT scan dataset through image segmentation. Each implant was virtually implanted in the mandibular bone. Two different models have been considered, differing in the free length of the mandibular branch (‘long branch’ and ‘short branch’) in order to simulate the variability of boundary conditions when performing vibrometric analyses. Modal analyses were carried out for each model, and the first three resonance frequencies were assessed with the respective vibration modes. Results: With reference to the ‘long branch’ model, the first three modes of vibration are whole bone vibration with minimum displacement of the implant relative to bone, with the exception of the initial condition (1% bone maturation) where the implant is not osseointegrated. By contrast, implant displacements become relevant in the ‘short branch’ model, unless osseointegration level is beyond 20%. The difference between resonance frequency at whole bone maturation and resonance frequency at 1% bone maturation remained lower than 6.5% for all modes, with the exception of the third mode of vibration in the ‘D’ implant where this difference reached 9.7%. With reference to the ‘short branch’ considering the first mode of vibration, 61–68% of the frequency increase was achieved at 10% osseointegration; 72–79% was achieved at 20%; 89–93% was achieved at 50% osseointegration. The pattern of the natural frequency versus the osseointegration level is similar among different modes of vibration. Significance: Resonance frequencies and their trends towards osseointegration level may differ between implant designs, and in different boundary conditions that are related to implant position inside the mandible; tapered implants are the most sensitive to bone maturation levels, small implants have very little sensitivity. Resonance frequencies are less sensitive to bone maturation level beyond 50%.

Keywords: Bone properties | CAD | Dental materials | Endosteal implants | Finite element analysis | Implant stability | Material properties | Osseointegration | Reverse engineering

Abstract: The purpose of this paper is to assess the main effects on the geometric errors in terms of flatness, circularity and cylindricity based on the size of the printed benchmarks and according to the position of the working plane of the 3D printer. Three benchmark models of different sizes, with a parallelepiped and cylinder shape placed in five different positions on the working plane are considered. The sizes of models are chosen from the Renard series R40. Benchmark models are fabricated in ABS (Acrylonitrile Butadiene Styrene) using RepRap Prusa i3 3D printer. A sample of five parts for each geometric category, as defined from the R40 geometric series of numbers, is printed close to each corner of the plate, and in the plate center position. Absolute Digimatic Height Gauge 0–450 mm with an accuracy of ± 0.03 mm by Mitutoyo is used to perform all measurements: flatness on box faces, and circularity/cylindricity on cylinders. Results show that the best performances, in terms of form accuracy, are reached in the upper-left printable area while they decrease with the sample size. Being quality a critical factor for a successful industrial application of the AM processes, the results discussed in this paper can provide the AM community with additional scientific data useful to understand how to improve the quality of parts which may be obtained through new generations of 3D printer.

Keywords: Additive manufacturing | Fused deposition modelling | GD&amp;T | Geometric errors

Abstract: Over the past few years, foam materials have been increasingly used in the passive safety of sport fields, to mitigate the risk of crash injury. Currently, the passive safety certification process of these materials represents an expensive and time-consuming task, since a considerable number of impact tests on material samples have to be carried out by an ad hoc testing apparatus. To overcome this difficulty and speed up the design process of new protective devices, a virtual model for the low-velocity impact behaviour of foam protective mats is needed. In this study a modelling approach based on the mesh-free Element Galerkin method was developed to investigate the impact behaviour of ethylene-vinyl acetate (EVA) foam protective mats. The main advantage of this novel technique is that the difficulties related to the computational mesh distortion and caused by the large deformation of the foam material are avoided and a good accuracy is achieved at a relatively low computational cost. The numerical model was validated statistically by comparing numerical and experimental acceleration data acquired during a series of impact events on EVA foam mats of various thicknesses. The findings of this study are useful for the design and improvement of foam protective devices and allow for optimizing sports fields' facilities by reducing head injury risk by a reliable computational method.

Keywords: EFG method | Foam protective mats | Impact testing | Sports safety

Abstract: Objectives: To assess conceptual designs of dental posts consisting of polyetherimide (PEI) reinforced with carbon (C) and glass (G) glass fibers in endodontically treated anterior teeth. Methods: 3D tessellated CAD and geometric models of endodontically treated anterior teeth were generated from Micro-CT scan images. Model C-G/PEI composite posts with different Young's moduli were analyzed by Finite Element (FE) methods post A (57.7 GPa), post B (31.6 GPa), post C (from 57.7 to 9.0 GPa in the coronal–apical direction). A load of 50 N was applied at 45° to the longitudinal axis of the tooth, acting on the palatal surface of the crown. The maximum principal stress distribution was determined along the post and at the interface between the post and the surrounding structure. Results: Post C, with Young's modulus decreasing from 57.7 to 9.0 GPa in the coronal–apical direction, reduced the maximum principal stress distribution in the restored tooth. Post C gave reduced stress and the most uniform stress distribution with no stress concentration, compared to the other C-G/PEI composite posts. Significance: The FE analysis confirmed the ability of the functionally graded post to dissipate stress from the coronal to the apical end. Hence actual (physical) C-G/PEI posts could permit optimization of stress distributions in endodontically treated anterior teeth.

Keywords: CAD | Dental materials | Design | Endodontic treatment | Finite Element analysis | Image analysis

Abstract: In this work is exploited the possibility to use two optical techniques and combining their measurements for the 3D characterization of different tyres with particular attention to the tyre's section. Electronic Speckle Pattern Interferometry (ESPI) and Laser Scanner (LS) based on principle of triangulation have been employed for investigating and studying the tyre's section and 3D shape respectively. As case studies two different racing tyres, Michelin S9H and Pirelli Diablo respectively, have been considered. The investigation has been focused at the aim to evaluate and measure the section's components in order to add to the 3D model obtained by Laser Scanning accurate information about the different layers along through the tyres sections. It is important to note that the assessment about the different layers along the section is a very difficult task to obtain by visual inspection or classical microscopy and even with the LS. Here we demonstrate that the different layers can be easily highlighted and identified by mean of the ESPI.

Keywords: Holography | Laser scanner | Non-destructive testing | Speckle | Tyre characterization | Tyre layer thickness measurement

Abstract: Over the last three decades, it has been frequently reported that the properties of dental restorative composites cured with argon laser are similar or superior to those achieved with conventional halogen and light emitting diode (LED) curing units. Whereas laser curing is not dependent on the distance between the curing unit and the material, such distance represents a drawback for conventional curing units. However, a widespread clinical application of this kind of laser remains difficult due to cost, heavy weight, and bulky size. Recently, with regard to the radiation in the blue region of the spectrum, powerful solid-state lasers have been commercialized. In the current research, CAD (computer-aided design)/CAM (computer-aided manufacturing) assisted solid-state lasers were employed for curing of different dental restorative composites consisting of micro- and nanoparticle-reinforced materials based on acrylic resins. Commercial LED curing units were used as a control. Temperature rise during the photopolymerisation process and bending properties were measured. By providing similar light energy dose, no significant difference in temperature rise was observed when the two light sources provided similar intensity. In addition, after 7 days since curing, bending properties of composites cured with laser and LED were similar. The results suggested that this kind of laser would be suitable for curing dental composites, and the curing process does not suffer from the tip-to-tooth distance.

Keywords: Composites | Computer-aided design/computer-aided systems | Dental materials | Laser | Mechanical properties | Thermal properties

Abstract: Objective: To assess the influence of implant thread shape and inclination on the mechanical behaviour of bone-implant systems. The study assesses which factors influence the initial and full osseointegration stages. Methods: Point clouds of the original implant were created using a non-contact reverse engineering technique. A 3D tessellated surface was created using Geomagic Studio® software. From cross-section curves, generated by intersecting the tessellated model and cutting-planes, a 3D parametric CAD model was created using SolidWorks® 2017. By the permutation of three thread shapes (rectangular, 30° trapezoidal, 45° trapezoidal) and three thread inclinations (0°, 3° or 6°), nine geometric configurations were obtained. Two different osseointegration stages were analysed: the initial osseointegration and a full osseointegration. In total, 18 different FE models were analysed and two load conditions were applied to each model. The mechanical behaviour of the models was analysed by Finite Element (FE) Analysis using ANSYS® v. 17.0. Static linear analyses were also carried out. Results: ANOVA was used to assess the influence of each factor. Models with a rectangular thread and 6° inclination provided the best results and reduced displacement in the initial osseointegration stages up to 4.58%. This configuration also reduced equivalent VM stress peaks up to 54%. The same effect was confirmed for the full osseointegration stage, where 6° inclination reduced stress peaks by up to 62%. Significance: The FE analysis confirmed the beneficial effect of thread inclination, reducing the displacement in immediate post-operative conditions and equivalent VM stress peaks. Thread shape does not significantly influence the mechanical behaviour of bone-implant systems but contributes to reducing stress peaks in the trabecular bone in both the initial and full osseointegration stages.

Keywords: Bone properties | CAD | Dental materials | Endosteal implants | Finite element analysis | Material properties | Osseointegration | Plateau implants

Abstract: Experimental/theoretical analyses have already been performed on poly(ε-caprolactone) (PCL) loaded with organic-inorganic fillers (PCL/TiO2 and PCL/ZrO2) to find a correlation between the results from the small punch test and Young's modulus of the materials. PCL loaded with Ti2 (PCL = 12, TiO2 = 88 wt %) and Zr2 (PCL = 12, ZrO2 = 88 wt %) hybrid fillers showed better performances than those obtained for the other particle composition. In this context, the aim of current research is to provide further insight into the mechanical properties of PCL loaded with sol-gel-synthesized organic-inorganic hybrid fillers for bone tissue engineering. For this reason, theoretical analyses were performed by the finite element method. The results from the small punch test and Young's modulus of the materials were newly correlated. The obtained values of Young's modulus (193 MPa for PCL, 378 MPa for PCL/Ti2 and 415 MPa for PCL/Zr2) were higher than those obtained from a previous theoretical modelling (144 MPa for PCL, 282 MPa for PCL/Ti2 and 310 MPa for PCL/Zr2). This correlation will be an important step for the evaluation of Young's modulus, starting from the small punch test data.

Keywords: Biomedical applications | Composites | Computer-aided design (CAD) | Finite element analysis (FEA) | Mechanical analysis | Organic-inorganic hybrid materials

Abstract: The use of intraoral scanners and Additive Manufacturing (AM) techniques in dentistry is increasing, and such technologies are integrated in daily workflows for the production of various types of dental restorations. Thus, it is clinically sensible to assess the accuracy of these systems. This in vivo study presents a comparison, in term of accuracy, among three commercially available AM systems, used to rapid prototype models obtained from intraoral scans data. Eight patients with a complete dentition were selected. Complete-arch scans of both upper and lower jaws were obtained using the 3Shape Trios 3 color intraoral scanner. The corresponding CAD models were created by means of the 3Shape Dental System software, and three AM systems, Photocentric LC10 (AM1), Zortrax M 200 (AM2) and Prusa I3 (AM3) were used to manufacture them. The manufactured fourty-eight models were scanned with the 3Shape Trios 3 color scanner, by the same operator. Scans of the manufactured models were aligned and compared to the reference intraoral scan by means of a Reverse Engineering software (Geomagic Studio). The comparison between the scans of the manufactured models and the reference intraoral scans, for the eight patients, shows a standard deviation (SD) in the range 0.11 – 0.27 mm for AM1, in the range 0.04 – 0.26 mm for AM2 and in the range 0.07 – 0.26 mm for AM3. The results of this research show that Prusa I3 and Zortrax M 200 are statistically more accurate than Photocentric LC10. Nevertheless, if we consider the amount of difference in accuracy, this may be not relevant from a clinical point of view. Thus, the three AM systems can be used in some dental applications which are compatible with the reported accuracy.

Keywords: Additive manufacturing | Dental models | Dentistry | Intraoral scans | Orthodontic appliances

Abstract: In the past few years, a new generation of additive manufacturing (AM) techniques has rapidly become available due to the expiration of some AM patents which allowed significant cost reductions. This article explores some available techniques fostering products innovation in experimental laboratories for the development of naval propulsion, where high costs represent an important limitation for both basic research and industrial testing, by identifying significant knowledge and variables and by providing reliable and accurate data to support designers and researchers. The propeller INSEAN E779a case study was taken into account and fabricated by direct metal laser sintering in AlSi10Mg aluminium alloy and by fused deposition modeling in acrylonitrile–butadiene–styrene, and UltraT polymeric materials. The study of printing parameters, flexural tests, differential scanning calorimetry and thermogravimetric analysis, allowed to optimize the printing process conditions. A reverse engineering system, Faro-CAM2, and the iterative closest point algorithm of the geomagic control software were used to analyse deviations from the printed propeller and the CAD nominal model. The atomic force microscopy test allowed to assess the morphological features and surface roughness of printed propellers. Towing Tank tests were carried out and the hydrodynamic performance comparison was analysed in terms of torque and drag. The results of this study show differences between the benchmark and AM propellers, as a function of the advance coefficient J, the morphological characteristics and the materials. However this study also shows a substantial adequacy of AM propellers in most studies carried out in Towing Tank.

Keywords: Additive manufacturing (AM) | Marine propeller | Reverse engineering (RE)

Abstract: Additive Manufacturing technologies allow for the direct fabrication of lightweight structures with improved properties. In this context, Fused Deposition Modelling (FDM) has also been considered to design 3D multifunctional scaffolds with complex morphology, tailored biological, mechanical and mass transport properties. As an example, poly(ε-caprolactone) (PCL), surface-modified PCL and PCL-based nanocomposite scaffolds were fabricated and analysed. The effects of structural and morphological features (i.e., sequence of stacking, fiber spacing distance, pore size and geometry), surface modification and nanoparticles on the in vitro biological and mechanical performances were investigated.

Keywords: Additive Manufacturing | Design | Mechanical and Functional Analyses | Scaffolds

Abstract: In this work is exploited the possibility to use Electronic Speckle Pattern Interferometry (ESPI) for the characterization of different tyres with particular attention to the tyres shoulder section. Tyres characterization is of fundamental importance for vehicle dynamics modelling, since they are the main responsible of vehicles dynamical behaviour and thanks to their ability to deform, they allow to drive a vehicle generating the appropriate interaction forces at the interface with the road. Their behaviour is a consequence to their very complex structure. Two different racing tyres, one for car and other for motorcycle, have been considered. The investigation has been focused at the aim to evaluate and measure the section's components in order to get accurate information about the different layers along through the tyres shoulder section. Here we demonstrate that the different layers (rubber, nylon, steel) can be easily highlighted and identified by mean of the ESPI that, thanks to its high sensitivity, is capable to estimate the different out of plane displacement of the different layers that respond in a different way (i.e. with a different deformation) to a thermal stimulus highlighting the layers themselves. Moreover, we introduce a de-noising step in the reconstruction process: In particular we enhance the wrapped phase information by using a suitable algorithm called SPADEDH. It is important to note that the assessment about the different layers along the section is a very difficult task to obtain by visual inspection or classical microscopy. In fact, the condition of the cutted surface, or rather the strong inhomogeneity and the roughness make impossible to obtain good images especially in the shoulder area.

Keywords: Holography | Non-destructive testing | Speckle | Tyre characterization

Abstract: In the field of movement disorders, each disabled person is different for both motor performance for functional requirements and expectations. This paper describes the development of a personalized device for a student with spastic quadriplegia at Federico II. This device is an Alternative Augmentative Communication system and it consists of hardware and software, which have been adapted to the individual characteristics of the student. According to participatory design and using the task analysis, we proceed to the hardware prototyping and to the software interface improving. An approach based on Analytic Hierarchy Process and Multiple-Criteria Decision Analysis is used. Tests under laboratory conditions are performed for evaluating the usability index of the device. Considering the data analysis, some critical issues are identified. The knowledge acquired in the case study is a point of strength of the proposed paper because it can be re-used for other persons with severe motor disabilities to improve their inclusion, integration and participation and to carry out tasks in different areas of application with minimum stress and maximum efficiency and effectiveness.

Keywords: Alternative augmentative communication | Participatory design | Spastic quadriplegia | Usability assessment

Abstract: A computer-aided design (CAD)-based approach and sol-gel chemistry were used to design a multilayer dental post with a compositional gradient and a Young's modulus varying from 12.4 to 2.3 GPa in the coronal-apical direction. Specifically, we propose a theoretical multilayer post design, consisting of titanium dioxide (TiO2) and TiO2/poly("-caprolactone) (PCL) hybrid materials containing PCL up to 24% by weight obtained using the sol-gel method. The current study aimed to analyze the effect of the designed multilayer dental post in endodontically treated anterior teeth. Stress distribution was investigated along and between the post and the surrounding structures. In comparison to a metal post, the most uniform distributions with lower stress values and no significant stress concentration were found when using the multilayer post.

Keywords: Biomedical applications | Composites | Computer-aided design (CAD) | Finite element analysis (FEA) | Hybrid materials | Mechanical analysis

Abstract: Objectives To investigate the influence of specific resin-composite, glass ceramic and glass ionomer cement (GIC) material combinations in a “multi-layer” technique to replace enamel and dentin in class II mesio-occlusal-distal (MOD) dental restorations using 3D-Finite Element Analysis (FEA). Methods Four 3D-FE models (A–D) of teeth, adhesively restored with different filling materials, were created and analyzed in comparison with a 3D model (E) of a sound lower molar. Models A, B & C had “multilayer” constructions, consisting of three layers: adhesive, dentin replacement and enamel replacement. Model A: had a low modulus (8 GPa) composite replacing dentin and a higher modulus (12 GPa) composite replacing enamel. Model B: had a GI cement replacing dentin and a higher modulus (12 GPa) composite replacing enamel. Model C: had a low modulus (8 GPa) composite replacing dentin and a very high modulus (70 GPa) inlay replacing enamel. Model D: had a lithium disilicate inlay replacing both dentin and enamel with a luting cement base-layer. Polymerization shrinkage effects were simulated and a load of 600 N was applied. All the materials were assumed to behave elastically throughout the entire deformation. Results Model A showed the highest stress distribution along all the adhesive interfaces of the shrinking resin-based materials with a critical condition and failure risk marginally and internally. Model D, by contrast, showed a more favorable performance than either of the multilayer groups (A–C). Stress and displacement plots showed an elastic response similar to that obtained for the sound tooth model. Model B and Model C performed according to their bilayer material properties. The use of a non-shrink dentin component simulating a GIC clearly affected the shrinkage stress at the basis of the Model B; while the bulk resin composite having a 12 GPa Young's modulus and linear polymerization shrinkage of 1% strongly influenced the biomechanical response in the bucco-lingual direction. Significance Direct resin-based composite materials applied in multilayer techniques to large class II cavities, with or without shrinking dentin layers, produced adverse FEA stress distributions and displacements. An indirect lithium disilicate inlay used to replace lost dentin and enamel in posterior restored teeth generated lower stress levels, within the limits of the elastic FEA model.

Keywords: CAD | Class II restorations | Finite element analysis | Image analysis | Materials properties

Abstract: Objective To assess the effect of a ferrule design with specific post material-shape combinations on the mechanical behavior of post-restored canine teeth. Methods Micro-CT scan images of an intact canine were used to create a 3-D tessellated CAD model, from which the shapes of dentin, pulp and enamel were obtained and geometric models of post-endodontically restored teeth were created. Two types of 15 mm post were evaluated: a quartz fiber post with conical–tapered shape, and a carbon (C) fiber post with conical–cylindrical shape. The abutment was created around the coronal portion of the posts and 0.1 mm cement was added between prepared crown and abutment. Cement was also added between the post and root canal and a 0.25 mm periodontal ligament was modeled around the root. Four models were analysed by Finite Element (FE) Analysis: with/without a ferrule for both types of post material and shape. A load of 50 N was applied at 45° to the longitudinal axis of the tooth, acting on the palatal surface of the crown. The maximum normal stress criterion was adopted as a measure of potential damage. Results Models without a ferrule showed greater stresses (16.3 MPa) than those for models with a ferrule (9.2 MPa). With a ferrule, stress was uniformly distributed along the abutment and the root, with no critical stress concentration. In all models, the highest stresses were in the palatal wall of the root. Models with the C-fiber post had higher stress than models with the quartz fiber posts. The most uniform stress distribution was with the combination of ferrule and quartz fiber post. Significance The FE analysis confirmed a beneficial ferrule effect with the combination of ferrule and quartz fiber post, with tapered shape, affording no critical stress concentrations within the restored system.

Keywords: CAD | Dental materials | Endodontic treatment | Finite element analysis | Image analysis | Materials properties

Abstract: Purpose: To study the influence of the resin bonding layer thickness and the bulk filling material stiffness in adhesive class II mesio-occlusal-distal (MOD) restorations using numerical finite element analysis (FEA). Methods: Four 3D-FE models of teeth restored with different filling material stiffness and resin bonding layer thickness were built-up and analyzed. The 3D model of a sound lower molar was also analyzed and compared with restored ones. The tooth tissues . (enamel, dentin), dental restoration and bolus on the occlusal surface, was divided into 3D solid CTETRA elements with four grid points. The adhesive bonding around the dental restoration was modeled with shell elements. Polymerization shrinkage was simulated with a thermal expansion approach. Mechanical behavior of restored models in terms of stress and displacement distributions, under the combination effects of polymerization shrinkage and occlusal load (600 N), was analyzed. All the materials were assumed to behave as elastic materials throughout the entire deformation. Results: Numerical results show that the mechanical response of the restored models was very different compared to the sound tooth ones, where the stress was uniformly distributed from enamel to dentin with no critical stress concentration. In the | restored models, the highest stress values were detected in the enamel, near the enamel-dentin interface and in the bulk ' restorative material. Tooth preparations A and B showed lower gradient stresses than corresponding C and D. The value of the vertical displacement components in models A and B were higher than corresponding C and D. The maximum displacement values were mainly located around the groove and were higher by an order of magnitude than the sound models. The results showed better mechanical response with models A and B compared to C and D. It is also evident that resin bonding thickness slightly affected the stress level of the restored teeth.

Abstract: Objectives To study the influence of resin based and lithium disilicate materials on the stress and strain distributions in adhesive class II mesio-occlusal-distal (MOD) restorations using numerical finite element analysis (FEA). To investigate the materials combinations in the restored teeth during mastication and their ability to relieve stresses. Methods One 3D model of a sound lower molar and three 3D class II MOD cavity models with 95° cavity-margin-angle shapes were modelled. Different material combinations were simulated: model A, with a 10 μm thick resin bonding layer and a resin composite bulk filling material; model B, with a 70 μm resin cement with an indirect CAD-CAM resin composite inlay; model C, with a 70 μm thick resin cement with an indirect lithium disilicate machinable inlay. To simulate polymerization shrinkage effects in the adhesive layers and bulk fill composite, the thermal expansion approach was used. Shell elements were employed for representing the adhesive layers. 3D solid CTETRA elements with four grid points were employed for modelling the food bolus and tooth. Slide-type contact elements were used between the tooth surface and food. A vertical occlusal load of 600 N was applied, and nodal displacements on the bottom cutting surfaces were constrained in all directions. All the materials were assumed to be isotropic and elastic and a static linear analysis was performed. Results Displacements were different in models A, B and C. Polymerization shrinkage hardly affected model A and mastication only partially affected mechanical behavior. Shrinkage stress peaks were mainly located marginally along the enamel-restoration interface at occlusal and mesio-distal sites. However, at the internal dentinal walls, stress distributions were critical with the highest maximum stresses concentrated in the proximal boxes. In models B and C, shrinkage stress was only produced by the 70 μm thick resin layer, but the magnitudes depended on the Young's modulus (E) of the inlay materials. Model B mastication behavior (with E = 20 GPa) was similar to the sound tooth stress relief pattern. Model B internally showed differences from the sound tooth model but reduced maximum stresses than model A and partially than model C. Model C (with E = 70 GPa) behaved similarly to model B with well redistributed stresses at the occlusal margins and the lateral sides with higher stress concentrations in the proximal boxes. Models B and C showed a more favorable performance than model A with elastic biomechanics similar to the sound tooth model. Significance Bulk filling resin composite with 1% linear polymerization shrinkage negatively affected the mechanical behavior of class II MOD restored teeth. Class II MOD direct resin composite showed greater potential for damage because of higher internal and marginal stress evolution during resin polymerization shrinkage. With a large class II MOD cavity an indirect composite or a lithium disilicate inlay restoration may provide a mechanical response close to that of a sound tooth.

Keywords: CAD | Composite | FEA | Inlay | Lithium Disilicate | Micro-CT | Stress analysis

Abstract: This paper deals with additive manufacturing techniques for the creation of 3D fetal face models starting from routine 3D ultrasound data. In particular, two distinct themes are addressed. First, a method for processing and building 3D models based on the use of medical image processing techniques is proposed. Second, the preliminary results of a questionnaire distributed to future parents consider the use of these reconstructions both from an emotional and an affective point of view. In particular, the study focuses on the enhancement of the perception of maternity or paternity and the improvement in the relationship between parents and physicians in case of fetal malformations, in particular facial or cleft lip diseases.

Abstract: The use of polymer composites has been increasing over the years and nowadays the requirements for designing high performance and lightweight fabrics and laminates for sail manufacturing have become more stringent than ever. The present paper offers an effective methodology that enhances the understanding of the influence of fibres orientation and arrangement of panels on sail performance. Constitutive characteristics of the ten commonly used sail cloths are experimentally measured and their influence on sail dynamic performance is compared using an aerodynamic approach. As expected also in industry 4.0 the method allows to control the production process and final product optimization.

Keywords: Aerodynamic coefficient | Apparent wind angle (AWA) | Apparent Wind Speed (AWS) | CFD analysis | Digital photogrammetry | RE | Turbulence model

Abstract: A statistical approach for the characterization of Additive Manufacturing (AM) processes is presented in this paper. Design of Experiments (DOE) and ANalysis of VAriance (ANOVA), both based on Nested Effects Modeling (NEM) technique, are adopted to assess the effect of different laser exposure strategies on physical and mechanical properties of AlSi10Mg parts produced by Direct Metal Laser Sintering (DMLS). Due to the wide industrial interest in AM technologies in many different fields, it is extremely important to ensure high parts performances and productivity. For this aim, the present paper focuses on the evaluation of tensile properties of specimens built with different laser exposure strategies. Two optimal laser parameters settings, in terms of both process quality (part performances) and productivity (part build rate), are identified.

Keywords: Additive Manufacturing (AM) | ANalysis of VAriance (ANOVA) | Design of Experiments (DOE) | Direct Metal Laser Sintering (DMLS) | Nested Effects Modeling (NEM)

Abstract: Objective To study the influence of the different class II mesio-occlusal-distal (MOD) cavity shape on the stress and strain distributions in adhesive indirect restorations, using numerical finite element analysis (FEA). To investigate the relationship between restored teeth failure and stiffness of food, three values of Young's modulus were used for the food. Methods A 3D model of a sound lower molar and three class II MOD cavities with different shape were created. Slide-type contact elements were used between tooth surface and food. An adhesive resin-based cement, modeled with fixed-type contact elements, and a single restorative filling materials were considered. To simulate polymerization shrinkage effect, which is basically restricted to the thin composite cement layer, shell elements were employed and the thermal expansion approach was used. A vertical occlusal load of 600 N was applied, while assigning fixed zero-displacements on the cutting surfaces below the crevices. All the materials were assumed to be isotropic and elastic. A static linear analysis was carried out. Results In the lingual cusp, the displacements increased as the values of the stiffness food increased. In the restored teeth, the stress near the restoration-tooth interface was strongly dependent on the MOD cavity shape. The stress peaks were mainly located along the enamel–dentin interface at the lingual side; wedge-shaped MOD cavity with a low angle, in combination with the lowest food stiffness provided the best results. Significance A more complex load application on the occlusal surfaces was introduced. Food stiffness slightly affected the stress distribution of the restored and sound teeth. Teeth with adhesive class II MOD indirect resin composite restorations were potentially more susceptible to damage if the class II MOD cavity-margin-angle was higher than 95°. Restored teeth with a higher cavity-margin-angle led to considerable stress concentration in the lingual cusp along the enamel–dentin interface. These models were more susceptible to fracture in the lingual cusps when compared to the buccal ones.

Keywords: CAD | Endodontics | Finite element analysis | Micro-computed tomography | Stress analysis

Abstract: The purpose of this paper is to assess the main effects on the geometric errors in terms of flatness, circularity and cylindricity based on the size of the printed benchmarks and according to the position of the working plane of the 3D printer. Three benchmark models of different sizes, with a parallelepiped and cylinder shape placed in five different positions on the working plane are considered. The sizes of models are chosen from the Renard series R40. Benchmark models are fabricated in ABS (Acrylonitrile Butadiene Styrene) using Zortrax M200 3D printer. A sample of five parts for each geometric category, as defined from the R40 geometric series of numbers, is printed close to each corner of the plate, and in the plate center position. Absolute Digimatic Height Gauge 0-450mm with an accuracy of ±0.03mm by Mitutoyo is used to perform all measurements: flatness on box faces, and circularity/cylindricity on cylinders. Results show that the best performances, in terms of form accuracy, are reached in the area center printable while they decrease with the sample size. Being quality a critical factor for a successful industrial application of the AM processes, the results discussed in this paper can provide the AM community with additional scientific data useful to understand how to improve the quality of parts which may be obtained through new generations of 3D printer.

Keywords: Additive manufacturing | Fused deposition modelling | Geometric errors

Abstract: Sail manufacture has undergone significant development due to sailing races like the America’s Cup and the Volvo around the World Race. These competitions require advanced technologies to help increase sail performance. Hull design is fundamentally important but the sails (the only propulsion instrument) play a key role in dynamic of sailboats. Under aerodynamic loads, sail cloth deforms, the aerodynamic interaction is modified and the pressure on the sails is variously distributed resulting in performance inconsistencies. The interaction between fluid and structure necessitates a solution which combines aerodynamic and structural numerical simulations. Furthermore, in numerical simulations the aeroelastic sail characteristics must be known accurately. In this paper, the dynamic performance of a Spinnaker was studied. Digital photogrammetry was used to acquire the images, make the 3D reconstruction of the sail and validate the models in Computational Fluid Dynamics (CFD) analysis. Orthotropic constitutive characteristics of ten different sail cloths were measured by experimental test. The methodology allowed to compare dynamic performance in terms of forces, pressure and vibration for the different sail cloths and different fiber orientations.

Keywords: CFD analysis | Detached eddy simulations | Pressure distributions | Sail aerodynamics | Turbulence models

Abstract: 3D inspection process is getting more and more interest for manufacturing industries as it helps to carefully check the expected quality of the released products. Much more attention is oriented to optical devices able to quickly capture the whole shape of the product providing many useful information on the process variability and the deliverability of the key characteristics linked to the quality of the product/process. Although the optical control of 3D scanners is mature enough, many factors may influence the quality of the scanned data. These factors may be strictly related to internal elements to the acquisition device, such as scanner resolution and accuracy, and external to it, such as proper selection of scanning parameters, ambient lighting and characteristics of the object surface being scanned (e.g. surface colour, glossiness, roughness, shape), as well as the sensor-to-surface relative position. For the 3D laser-based scanners, the most common on the market, it would be of great industrial interest to study some scanning factors mainly affecting the quality of the 3D surface acquisitions and provide users with guidelines in order to correctly set them so to increase the massive usage of these systems in the product inspection activities. In this context, by using a commercial triangulation 3D laser scanner, the effects of some scanning factors that may affect the measurement process were analysed in the present paper. Working on a sheet metal test part, more complex than the ones commonly used in laboratory and documented in the literature, the scanner-to-object relative orientation and the ambient lighting, as well as an internal scanner parameter, were tested. Through a Design of Experiments (DoE) approach, and setting root mean square error (RMSE) as response function, the outcomes of the tests mainly pointed out that the scanner-to-object relative orientation as well as its position within the field of view of the measurement device are the key factors mostly influencing the accuracy of the measurement process.

Keywords: 3D inspection process | 3D laser scanner | Design of Experiments | Surface acquisition

Abstract: Polymer-based composites are ideal for applications where high strength-to-weight and stiffness-to-weight ratios are required. In the biomedical field, fiber-reinforced polymers have replaced metals, emerging as suitable alternative. Reverse engineering and additive manufacturing methods are required to achieve the design of customized devices with specific shape and size. At the same time, micro-mechanics and macro-mechanics play an important role in the development of highly functional composite materials. The aim of this research is to develop customized 3D models of a human mandible using reverse engineering, additive manufacturing and composite material technology. Experiments were carried out by loading the models through the condyles and the results show the potential to reproduce the mechanical behavior of a human mandible. Taking into account the curves of the load-arch width decrease, the stiffness of the 3D composite model was 14.1± 1.9 N/mm, which is close to the tested human mandible (17.5 ± 1.8 N/mm).

Keywords: Experimental Testing | Fiber-reinforced composites | Mandible | Reverse Engineering | Stereolithography

Abstract: Nowadays photogrammetric techniques have known important developments and are widely employed for 3D acquisitions in different fields of application. The paper analyzes the effects of different parameters (texturization, ambient light and water turbidity) on the quality of the 3D reconstruction in underwater photogrammetry. Several experimental tests were performed on a wind turbine blade using a common action camera, the GoPro 4 black edition and a commercial software, Photoscan by ©Agisoft. By means of a DoE (Design of Experiments) approach, 3D models were reconstructed varying the chosen parameters. Each of them was compared with a CAD model, used as reference, obtained by more accurate laser scans VI-9i by Konica Minolta. The results showed that blade texturization, ambient light and water turbidity significantly impact on the quality of the 3D reconstruction. Optimal results were obtained with textured blade, morning ambient light (exposure 1/60, f/2.8 and ISO sensitivity 100) and clear water. Moreover, in order to calculate confidence intervals for regression coefficients, even with few acquisitions, a computer-intensive bootstrap procedure was applied to the regression model. Finally, further confirmation experiments carried out in a deeper swimming pool and with poor conditions (e.g., very low ambient light and no blade texturization) in order to reproduce the real submarine environment. In such situations, an additional source of light and one or more grids, which allow a pattern to be created on the edges of the wind turbine blade, may help reconstructions.

Keywords: Bootstrapping | Design of experiments | Passive no-contact techniques | Reverse engineering | Structure from motion | Underwater photogrammetry

Abstract: In the field of additive manufacturing (AM) processes, there is a significant lack of scientific data on the performance of open-source 3D printers in relation to process parameter values. The purpose of this paper is to assess the impact of the main process parameters on the accuracy of a set of typical geometric features, as obtained with an open-source 3D printer, the RepRap Prusa-Mendel I2. For this purpose, a benchmarking part was set up, composed of elementary shapes, representing a series of different geometric features. By means of a DoE approach, it was possible to assess the effects of two process parameters - layer thickness (Lt) and flow rate (Fr) - on five geometric features: cube, sphere, cylinder, cone, and angled surface. A high resolution Laser Scanner was used to evaluate the variation between the acquired geometric feature and the corresponding 3D computer-aided design (CAD) nominal model. On the basis of experimental results, it was possible to analyze and discuss the main effects of the above-mentioned process parameters on each geometric feature. These results can help RepRap users in the correct selection of process parameters with the aim of improving the quality of prototypes.

Keywords: geometric features | laser scanner | open-source 3D Printers | process parameters

Abstract: Purpose - This study aims to quantify the ultimate tensile strength and the nominal strain at break (f) of printed parts made from polylactic acid (PLA) with a Replicating Rapid prototyper (Rep-Rap) 3D printer, by varying three important process parameters: layer thickness, infill orientation and the number of shell perimeters. Little information is currently available about mechanical properties of parts printed using open-source, low-cost 3D printers. Design/methodology/approach - A computer-aided design model of a tensile test specimen was created, conforming to the ASTM:D638. Experiments were designed, based on a central composite design. A set of 60 specimens, obtained from combinations of selected paramers, was printed on a Rep-Rap Prusa I3 in PLA. Testing was performed using a JJ Instruments - T5002-type tensile testing machine and the load was measured using a load cell of 1,100 N. Findings - This study investigated the main impact of each process parameter on mechanical properties and the effects of interactions. The use of a response surface methodology allowed the proposition of an empirical model which connects process parameters and mechanical properties. Even though results showed a high variability, additional ideas on how to understand the impact of process parameters are suggested in this paper. Originality/value - On the basis of experimental results, it is possible to obtain practical suggestions to set common process parameters in relation to mechanical properties. Experiments discussed in the present paper provide a variety of data and insight regarding the relationship among the main process parameters and the stiffness and strength of fused deposition modeling-printed parts made from PLA. In particular, this paper underlines the shortage in existing literature concerning the impact of process parameters on the elastic modulus and the strain to failure for the PLA. The experimental data produced show a good degree of compliance with analytical formulations and other data found in literature.

Keywords: Central composite design | Nominal strain at break | Open-source 3D printers | Polylactic acid | Process improvement | Ultimate tensile strength

Abstract: With a view to enabling additive manufacturing (AM) processes, today, open-source, low-cost 3D printers are systems with great potential. However there is a significant lack of scientific data on the performance of open-source 3D systems and on the selection of adequate process parameters that can help to improve the quality of the parts. The purpose of this paper is to assess the effects of the main process parameters on the dimensional accuracy of a specific open-source 3D printer, the RepRap Prusa-Mendel I2. This study consisted of a benchmarking part, involving elementary shapes representing a series of different features. By means of a full factorial DoE (Design of Experiments), with three factors (layer thickness, deposition speed, and flow rate), three levels, and three replications, 81 parts were obtained. Subsequently, a laser scanner (D700 Laser Scanner-3Shape, Denmark) was used as high resolution reverse engineering system in order to evaluate the variation between real parts and nominal geometry. The impact of the main process parameters was evaluated and optimal combinations were analyzed. On the basis of the results obtained in the experiments, practical suggestions for the settings of common process parameters were formulated. Test results serve to improve the quality of AM parts through the most appropriate selection of the main process parameters.

Abstract: A technique to obtain the kinematic calibration of multilink systems is presented. The technique that is based on a digital photogrammetry vision system and the D-H based kinematic equations, can be considered as a reverse engineering aspect. The most important aspects of this technique consist in that no information on the kinematics chain is needed, it is fast, low cost, non invasive and also friendly for the operator. Tests of the technique on a revolute robot are also reported, showing a good reliability of the technique itself.

Keywords: Digital photogrammetry | Kinematic calibration | Reverse engineering | Robot mechanics

Abstract: Documentation of maritime heritage is essential for its protection, and for reference in restoration and renovation processes. These functions become problematic in the case of historical ships and boats that lack lines drawings. The purpose of this paper is to describe a procedure for creation of lines drawings based on the shape analysis of surviving historical boats or their small-scale models with the help of reverse engineering (RE) techniques. The paper describes how digital photogrammetry and the iterative method were used to analyze the shape of three historical boats: Tomahawk, Refola and Nada. The application of the proposed procedure produced the lines drawings of the boats as its result. The accuracy of the 3D CAD model obtained with the photogrammetric technique was verified by comparing it against a more accurate 3D model produced with the help of a RE laser scanner. The examination of the resulting lines drawings proves that the digital photogrammetry process and the proposed iterative method are adequate tools for developing lines plans of boat models. The research offers the methodological basis for the creation of an archive of lines drawings of historical boats. Such an archive would provide reference for philologically correct restorations, and permit definition and classification of distinctive elements of various types of historical boats, particularly those produced in the Campania Region. © 2014 Springer Science+Business Media New York.

Keywords: 3D CAD models | Digital photogrammetry | Laser scanning | Maritime heritage documentation | Philological reconstruction | Reverse engineering

Abstract: Aim Today Cone Beam Computed Tomography (CBCT) has become an important image technique for dento-maxilla facial applications. In the paper a new method to assess the geometric accuracy of these systems was proposed. It uses a free form benchmark model and a non-contact Reverse Engineering (RE) system. Method The test geometry chosen for this study was designed in such a way that it simulated human spongy bone, cortical bone, gingiva and teeth and it composed of removable free form parts. It was acquired with a high-resolution laser scanner (D700 Scanner - 3Shape, Denmark). The reference 3D surface models obtained with the laser scanner was compared with the 3D models that were created from a CBCT system (Scanora 3D - Soderex, Finland) and from a traditional Multi-Slice Computed Tomography (MSCT) scanner (LightSpeed VCT 64 Slice - General Electric, USA) at different reconstruction settings, using an iterative closest point algorithm (ICP) in Geomagic® software. Results The comparison between the different pairs of CAD models clearly shows that there is a good overlap between the models. Conclusions Although the results obtained in this study could lead to increase the use of CBCT for an increasing number of dental procedures, the publication of the European Commission guidelines represents a baseline on which the clinicians should rely heavily when considering the use of CBCT in their practice. Clinical Significance The results of this research show that the accuracy of CBCT 3D models is comparable to MSCT 3D models. © 2014 Elsevier Ltd. All rights reserved.

Keywords: Benchmark free form model | Cone Beam Computed Tomography (CBCT) | Laser scan | Multi-Slice Computed Tomography (MSCT) | Virtual modelling

Abstract: The artifacts that appear on maxillofacial X-ray CT images are mainly caused by the presence of metallic prosthetic appliances (such as amalgam or gold fillings). They cause problems in the three dimensional virtual reconstruction and in the eventual physical reproduction by rapid prototyping systems. At present the classification of different artifact types, metallic presences or artifacts induced by them, is often left to the experience and sensitivity of the operator. The purpose of this paper is to solve this problem automatically, by using an expert system based on fuzzy logic. Decisional networks were created and tested, using the Hounsfield scale values of each CT image pixel, for the membership functions. Three cases study were considered to evaluate the novel method. The CT images were processed and cleaned automatically leaving the decisional phase to the computer. The data from the three cases study show that the proposed methodology is accurate. The results of this study allow to get correct virtual and physical models in medical applications. © 2012 Springer-Verlag France.

Keywords: CT images | Expert system | Fuzzy logic | Metallic artifacts

Abstract: Current methods to produce 3-dimensional complete tooth (enamel, dentin and pulp) models involve conversion from tomographic data. In the paper a novel approach to obtain the complete 3D reconstruction of a tooth starting from the only 3D crown information is described. Using as reference models, five human posterior molars derived from micro-computed tomography (CT) data, specific computer aided design (CAD) modeling procedures were developed to create, in a simplified way, the surfaces of enamel, dentin and pulp of the teeth, starting from the data of a molar acquired by a non-contact reverse engineering (RE) system. To evaluate the simplified model, finite element method (FEM) simulations were performed and compared. The results from FEM analysis confirm the general validity of the proposed approach. This method allows to generate an efficient complete 3D reconstruction of teeth with a good approximation of the shape, due to the small number of parameters to adjust, and requires little interaction from the user. The described method can be successfully adopted to generate detailed 3D CAD models of teeth starting only from the crown data, acquired by non-contact RE systems (structured-light scanners, laser scanners or intra-oral laser scanners). It could be quickly implemented for other dental or biomechanical applications without the use of more expensive CT and micro-CT. © 2012 Springer-Verlag.

Keywords: CAD procedure | Crown surface | Finite element analysis | Micro-CT | Scanner laser

Abstract: Objectives: Aim of the research is to compare the orthodontic appliances fabricated by using rapid prototyping (RP) systems, in particular 3D printers, with those manufactured by using computer numerical control (CNC) milling machines. 3D printing is today a well-accepted technology to fabricate orthodontic aligners by using the thermoforming process, instead the potential of CNC systems in dentistry have not yet been sufficiently explored. Materials and methods: One patient, with mal-positioned maxillary central and lateral incisors, was initially selected. In the computer aided virtual planning was defined that, for the treatment, the patient needed to wear a series of 7 removable orthodontic appliances (ROA) over a duration of 21 weeks, with one appliance for every 3 weeks. A non-contact reverse engineering (RE) structured-light 3D scanner was used to create the 3D STL model of the impression of the patient's mouth. Numerical FEM simulations were performed varying the position of applied forces (discrete and continuous forces) on the same model, simulating, in this way, 3 models with slice thickness of 0.2 mm, 0.1 mm (RP staircase effect) and without slicing (ideal case). To define the areas of application of forces, two configuration "i" and "i-1" of the treatment were overlapped. 6 patients to which for three steps (3rd, 4th and 5th step) were made to wear aligners fabricated starting from physical models by 3D printing (3DP-ROA) and afterwards, for the next steps (6th, 7th and 8th step), aligners fabricated starting from physical models by CNC milling machine (CNC-ROA), were selected. Results: For the 6 patients wearing the CNC-ROA, it was observed a best fitting of the aligner to the teeth and a more rapid teeth movement than the 3DP-ROA (2 weeks compared to 3 weeks for every appliance). FEM simulations showed a more uniform stress distribution for CNC-ROA than 3DP-ROA. Conclusions: In this research, 6 different case studies and CAD-FEM simulations showed that, to fabricate an efficient clear and removable orthodontic aligner, it is necessary to consider a compromise of several factors. A lower staircase effect (lower layer thickness) and a higher physical prototype accuracy allow a better control of tooth movement. © 2012 Academy of Dental Materials.

Keywords: 3D printers | CNC milling machine | FEM analysis | Modeling and simulation | Non-contact reverse engineering systems | Orthodontic appliances

Abstract: Objective: To evaluate the reliability and accuracy of computer-designed surgical guides in osseointegrated oral implant rehabilitation. Materials and methods: Six implant rehabilitations, with a total of 17 implants, were completed with computer-designed surgical guides, performed with the master model developed by muco-compressive and muco-static impressions. In the first case, the surgical guide had exclusively mucosal support, in the second case exclusively dental support. For all six cases computer-aided surgical planning was performed by virtual analyses with 3D models obtained by dental scan DICOM data. The accuracy and stability of implant osseointegration over two years post surgery was then evaluated with clinical and radiographic examinations. Radiographic examination, performed with digital acquisitions (RVG - Radio Video graph) and parallel techniques, allowed two-dimensional feedback with a margin of linear error of 10%. Results: Implant osseointegration was recorded for all the examined rehabilitations. During the clinical and radiographic post-surgical assessments, over the following two years, the peri-implant bone level was found to be stable and without appearance of any complications. The margin of error recorded between pre-operative positions assigned by virtual analysis and the post-surgical digital radiographic observations was as low as 0.2 mm. Significance: Computer-guided implant surgery can be very effective in oral rehabilitations, providing an opportunity for the surgeon: (a) to avoid the necessity of muco-periosteal detachments and then (b) to perform minimally invasive interventions, whenever appropriate, with a flapless approach. © 2012 Academy of Dental Materials.

Keywords: Minimally invasive approach | Muco-compressive impression | Muco-static impression | Osseointegration | Surgical guides | Virtual modeling

Abstract: Objective: In the paper laser scanning was used to evaluate, by indirect methods, the accuracy of computer-designed surgical guides in the oral implant supported rehabilitation of partially or completely edentulous patients. Materials and methods: Five implant supported rehabilitations for a total of twenty-three implants were carried out by computer-designed surgical guides, performed with the master model developed by muco-compressive and muco-static impressions. For all cases the surgical virtual planning, starting from 3D models obtained by dental scan DICOM data, was performed. The implants were inserted on the pre-surgical casts in the position defined in the virtual planning. These positions were acquired by three-dimensional optical laser scanning and compared with the laser scans of the intraoral impressions taken post-operatively. Results: The comparison between the post-surgical implant replica positions and the positions in the pre-operative cast, for the five patients, shows a maximum distance in the range 1.02-1.25 mm, an average distance in the range 0.21-0.41 mm and a standard deviation in the range 0.21-0.29 mm. Significance: The results of this research demonstrate accurate transfer of implant replica position by virtual implant insertion into a pre-operative cast and a post-operative cast obtained from impressioning. In previous studies the evaluation of the implant positions have required a post-surgical CT scan. With the indirect methods by laser scanning technique, proposed in the paper, this extra radiation exposure of the patient can be eliminated. © 2012 Academy of Dental Materials.

Keywords: Dental implants | Guided implant surgery | Impressions | Laser scan | Virtual modeling

Abstract: Objective: To investigate the influence of implant design factors in terms of bone integrity and implant stability. Materials and methods: A 3D parametric CAD model was developed. Then, once domain settings and boundary conditions were defined, a 3D FEM model was created. To simulate the physical interaction at the bone-implant interface, identity pairs were introduced. After generating different design scenarios with a DOE approach, the most significant design factors were obtained. Results: This study showed that the geometry of the screw thread highly influenced the implant stability. In particular the degree of bone damage became minimal when adopting 0.40 mm for the thread width and 0.05 mm for the thickness. Significance: Thread width and thickness play a crucial role to reduce induced stresses and damage in bone. Considering these preliminary results, future improvements should focus on investigating also two-factor and higher interactions to better understand the implant loading mechanism. © 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Keywords: Bone-stress distribution | Dental implants | DOE design | FEM modeling | Osseo-integration | Thread parameterization | Titanium implants

Abstract: The geometric shape of a dental implant plays an important role on the osteo-integration process. The purpose of this paper is to study the biomechanical behavior of different commercial dental implants and to analyse how thread profile may affect the stress concentration and distribution. Three different commercially-available dental implants were considered and acquired by means of a no-contact reverse engineering system. Stresses at bone-implant interface, in presence of perfect and not-perfect osteo-integration, were numerically evaluated by means of finite element (FEM) analyses applying occlusal and lateral loads. The results show more dangerous stresses at implant-bone interface in the case of not-perfect osteo-integration and stresses gradient enough uniform around the threads in the case of osteo-integration. In particular, the implant with the lowest thread-pitch exhibits the lowest bone damage. This confirms the crucial role of the geometric shape of the implant to reduce bone induced stresses and bone damage. The structural and functional connection between living bone and implant is a key issue in implantology field. When a guest device is installed in the living bone, many clinical responses may arise, such as inflammatory processes or osteo-integration failure. The results of this study can give useful information to understand the influence of the implant features and to appropriately apply it in the science of dental implants with the aim to reduce the potential implant failure. © 2012 Springer-Verlag.

Keywords: Dental implant | Finite element analysis | Osteo-integration | Stress distribution | Thread

Abstract: In this work the design and the technical characteristic of a Moore rotating bending machine are presented. The machine has been realized at the University of Cassino in order to run tests on multiple specimens at different temperature. The user can choose independently the load and the temperature for each specimen. The machine has been designed to produce in short time a several numbers of data of materials fatigue strength at low costs. The machine is in assembling step at the Laboratory of Industrial Design of the University of Cassino.

Keywords: Fatigue | Product design process | Test machine | Wholer

Abstract: Objective: In restored teeth, stresses at the tooth-restoration interface during masticatory processes may fracture the teeth or the restoration and cracks may grow and propagate. The aim was to apply numerical methodologies to simulate the behavior of a restored tooth and to evaluate fatigue lifetimes before crack failure. Materials and methods: Using a CAD-FEM procedure and fatigue mechanic laws, the fatigue damage of a restored molar was numerically estimated. Tessellated surfaces of enamel and dentin were extracted by applying segmentation and classification algorithms, to sets of 2D image data. A user-friendly GUI, which enables selection and visualization of 3D tessellated surfaces, was developed in a MatLab® environment. The tooth-boundary surfaces of enamel and dentin were then created by sweeping operations through cross-sections. A class II MOD cavity preparation was then added into the 3D model and tetrahedral mesh elements were generated. Fatigue simulation was performed by combining a preliminary static FEA simulation with classical fatigue mechanical laws. Results: Regions with the shortest fatigue-life were located around the fillets of the class II MOD cavity, where the static stress was highest. Significance: The described method can be successfully adopted to generate detailed 3D-FE models of molar teeth, with different cavities and restorative materials. This method could be quickly implemented for other dental or biomechanical applications. © 2010 Academy of Dental Materials.

Keywords: 3D fatigue simulation | 3D image acquisition | CAD-FEM modeling | Class II MOD restoration | Micro-CT

Abstract: Objectives: The aim was to evaluate the stress distribution, comparing an anterior sound tooth with post-endodontic restored teeth under mechanical loading. Methods: A three-dimensional finite element analysis was performed based on micro-CT scan images of a maxillary canine. Twelve models with different crown properties and post-configurations were simulated. The model of the maxillary sound canine was also created and investigated. A load of 50 N was applied at a 63° angle with respect to the longitudinal axis of the tooth on the palatal surface of the crown. Principal stresses were registered. Numerical FEA results were statistically analyzed to show the influence of post shape and crown materials. Results: All analyzed models (M1-M12) exhibited a high stress gradient, due to different material stiffnesses present at the various interfaces. The most uniform mechanical behavior of the investigated models, very similar to sound tooth, was the combination of a composite crown and a cylindrical or conical fiber-glass post. Significance: The results of this study facilitate informed clinical choice between possible material combinations in restorative procedures of endodontically treated anterior teeth. © 2011 Academy of Dental Materials.

Keywords: Canine teeth | Dental crown | Fiber-post | Finite element analysis | Mechanical behavior | Stress distribution

Abstract: To design a customized prosthesis that is tailored to the size and the shape of a unique anatomy provides better medical treatments and outcomes along with improved comfort and quality of life for patients. In this paper an innovative approach to spine implant design is proposed which relies on freeform modeling software and a haptic interface. The system mimics working on a physical replica of the patient’s spine and allows the user to model a prosthesis which might represent a promising concept to fix a curved vertebral column.

Keywords: FreeForm | Haptic modeling | Shape memory alloy springs | Spinal deformities | Spinal implants

Abstract: In the paper the design process, from the idea to the manufacturing aspects, with all the technical and technological problems, to develop a new competitive hard antitheft is described. The integrated use of the CAD/CAE and RP techniques made possible to analyse three different solutions in a very short time. The new model has completely designed, developed and patented (patent n. NA2005A000037) at the University of Naples and Cassino, Italy. It has weight and size very limited and some important features such as easiness to handle, high strength and high versatility; all this makes it an exclusive product of its type. The final product, made in AISI 1040 steel, is going to be manufactured and distributed in Europe by BULLOCK® in 2006.

Keywords: Antitheft | CAD | CAE | Lock system | Patent | PhD Researcher | RP Massimo Martorelli

Abstract: This article presents the use of stereolithography in oral implantology. Stereolithography is a new technology that can produce physical models by selectively solidifying an ultraviolet-sensitive liquid resin using a laser beam, reproducing the true maxillary and mandibular anatomic dimensions. With these models, it is possible to fabricate surgical guides that can place the implants in vivo in the same places and same directions as those in the planned computer simulation. A 70-year-old woman, in good health, with severe mandibular bone atrophy was rehabilitated with an overdenture supported by 2 Branemark implants. Two different surgical planning methods were considered: 1) the construction of a surgical guide evaluating clinical aspects, and 2) the surgical guide produced by stereolithographic study. The accuracy of surgical planning can reduce the problems related to bone density and dimensions. Furthermore, the stereolithographic study assured the clinicians of a superior location of fixtures in bone. Surgical planning based on stereolithographic technique is a safe procedure and has many advantages. This technologic advance has biologic and therapeutic benefits because it simplifies anatomic surgical management for improved implant placement. Copyright © 2004 by Lippincott Williams & Wilkins.

Keywords: Anatomic models | Jaw atrophy | Rapid prototyping | Surgical planning

Abstract: When considering the use of rapid prototyping (RP), there are many questions a designer might ask. One such question is "what build orientation should be used to minimise the adverse effects of surface roughness?" At present, this decision is often made in an intuitive way or sometimes overlooked completely. This paper describes a methodology and software implementation that provides the designer with a computer graphics based visualisation of RP model surface roughness. This enables the build orientation to be determined as a result of increased designer knowledge. The surface roughness values were obtained through an extensive empirical investigation of several RP techniques. These are used as the database for a visualisation algorithm that represents varying surface roughness of the RP model as colour shading within a CAD image. The nature of the empirical measurements is analysed and the functionality of the software algorithm is described. Examples are given that demonstrate the use and benefits of the methodology. Finally, conclusions are drawn as to the significance of the work and future research directions are outlined. © 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Material deposition | Rapid prototyping | Rapid technologies | Roughness visualisation | Surface roughness measurements