Methods for medical applications

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.

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

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

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

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

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

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

Introduction: Traditional prosthetic solutions expose the amputee to numerous problems that limit his ability to safely perform the normal activities of daily life. In order to eliminate the problems related to the use of the traditional prosthesis with socket, a new technique was developed for fixing the prosthesis to the amputees based on the principle of osseointegration. The aim of this paper is to study and analyze the stress distribution on the interface between a trans-humeral osseointegrated prosthetic implant and the residual bone, identifying the most stressed areas and thus foreseeing possible failure phenomena of the entire prosthetic system and, after, to compare the stress distribution on three different prosthetic designs that differ from each other for some geometric characteristics. Materials and methods: A healthy individual mimics two fall scenarios of which the trans-humeral amputees can most likely be victims: Static fall and Dynamic fall. A force platform (P-6000, BTS Bioengineering) is required for load data acquisition. The CAD model of the trans-humeral osseointegrated implant was created following the guidelines of the OPRA implant. The bone model was created starting from the CAT scan of a left humerus. The FEM simulation was conducted throught a linear analysis. Results: Both during static fall and dynamic fall, similar trends have been observed for the reaction force Fz, the torque moment Tz, the bending moments Mx and My. From the analysis of the von Mises stress distribution it was found that the stress distribution is more homogeneous in the case where the thread of the fixture is made by a triangular profile with height of the thread equal to 0.5 mm. However, it can be seen that, when passing from a thread with height of 0.5 mm to a 1 mm, there is a slight decrease in the stress on the whole contact zone between the fixture and the humerus. The same improvement can also be seen in the case of trapezoidal threading. Conclusion: By modifying the height and/or by varying the thread profile, are obtained slightly better results with respect to the case with a 0.5 mm height triangular thread.

Keywords: Amputees , Finite element method , Osseointegration , Prosthesis , Upper limb

Rising reverse engineering applications require the use of 3D models based on polygonal meshes and a set of modeling operations to shape the final product. Usually, 3D modeling tools do not exploit existing software development kits for developing custom virtual applications. This approach can be very useful for reverse engineering process in the medical field. The paper describes the software development of local mesh modeling algorithms as an extension of the open source library VTK with the aim of shaping 3D triangulated meshes. Then, a case study has been considered to create virtual modeling tools supporting the design process of custom-fit products and, in particular, of lower limb prosthetic socket for amputees. The application has been tested to design a socket for a patient with an above knee amputation. Results reached so far provide a positive feedback on the quality of the designed process and outcome, mainly thanks to the use of the virtual tools based on the developed software modules for 3D mesh modeling.

Keywords: medical devices , Polygonal 3D modeling , prosthesis design , VTK

Using a wheelchair can be a challenging task for people with reduced force and control of muscles of abdomen or lower back. Spinal cord injured (SCI) people are the majority of those who are spending most of the day on a wheelchair and a proper training and chair setup is mandatory to reach a good level of functionality and to avoid harms and side effects. In order to assess the complex motion of a person self-pushing a wheelchair, a motion capture (Mocap) system has been arranged and a group of SCI patients has been acquired in a hospital gym. The Mocap system uses three Microsoft Kinect RGB-D sensors and iPisoft to perform the recording of the 3D motion. The main goal of the research is to provide therapists with a quantitative method to define a preliminary configuration in an objective way once is given the user's medical conditions and his/her way of using the wheelchair. Working side by side with physiotherapists, the main parameters to be evaluated (e.g. pushing angles) have been identified and algorithms have been identified to automatically extract them from the 3D digital avatar model data coming from the Mocap system. The performance of the patients is then analyzed taking into account the wheelchair setup (e.g. position and inclination of the seat and of the back). The influence of geometric parameters on patients' motion is analyzed so that design guidelines for configuration can be found. The overall outcome is to maximize performance and minimize side effects and fatigue, providing users with a better experience on the wheelchair.

A number of pathologies impact on the way a patient can either move or control the movements of the body. Traumas, articulation arthritis or generic orthopedic disease affect the way a person can walk or perform everyday movements; brain or spine issues can lead to a complete or partial impairment, affecting both muscular response and sensitivity. Each of these disorder shares the need of assessing patient's condition while doing specific tests and exercises or accomplishing everyday life tasks. Moreover, also high-level sport activity may be worth using digital tools to acquire physical performances to be improved. The assessment can be done for several purpose, such as creating a custom physical rehabilitation plan, monitoring improvements or worsening over time, correcting wrong postures or bad habits and, in the sportive domain to optimize effectiveness of gestures or related energy consumption. The paper shows the use of low-cost motion capture techniques to acquire human motion, the transfer of motion data to a digital human model and the extraction of desired information according to each specific medical or sportive purpose. We adopted the well-known and widespread Mocap technology implemented by Microsoft Kinect devices and we used iPisoft tools to perform acquisition and the preliminary data elaboration on the virtual skeleton of the patient. The focus of the paper is on the working method that can be generalized to be adopted in any medical, rehabilitative or sportive condition in which the analysis of the motion is crucial. The acquisition scene can be optimized in terms of size and shape of the working volume and in the number and positioning of sensors. However, the most important and decisive phase consist in the knowledge acquisition and management. For each application and even for each single exercise or tasks a set of evaluation rules and thresholds must be extracted from literature or, more often, directly form experienced personnel. This operation is generally time consuming and require further iterations to be refined, but it is the core to generate an effective metric and to correctly assess patients and athletes performances. Once rules are defined, proper algorithms are defined and implemented to automatically extract only the relevant data in specific time frames to calculate performance indexes. At last, a report is generated according to final user requests and skills.

In this chapter, authors provide a description of boundary element method (BEM) applications in biomechanics, with a focus on advantages and limitations of BEM versus other numerical methods such as finite element method, finite difference method, and meshless methods. In addition to a general overview, the chapter focus on how the BEM approach can be advantageous in those biomechanical problems involving fracture mechanics and contact modeling. To this aim, its preprocessing flexibility to tackle sharp geometric changes and complex remeshing is highlighted. The comparison among BEM and other numerical approaches proceeds through the evaluation of inherent accuracy, preprocessing and postprocessing efforts, and run times. Bio-CAD models with complex shapes are usually created from medical images acquisition, computer tomography or magnetic resonance scan, with different modeling techniques, which result in different accuracy and usability of the generated tessellated or surface computer-aided design (CAD) geometry. Special attention must be drawn to the mathematical reconstruction of bio-CAD model to facilitate the meshing process in the BEM environment and reduce the geometrical imperfections generated during the CAD to computer-aided engineering translation phase. BEM is best suited to reproduce accurately high surface stress gradients that are generally a modeling issue (e.g., in bone-implant contact simulations). Working with 3D models, the mesh refinement in the neighboring areas where high stress gradients are expected is much facilitated when using BEM, also because it is possible to use discontinuous elements and circumvent the constraint of a continuous mesh. BEM approach is certainly more accurate for linear analysis but, on the other hand, less versatile in some areas like those of highly nonlinear material behavior. A short description of some case studies showing the described advantages of BEM approach is reported.

Keywords: Bio-CAD , Biomechanics , Boundary element method , Dual boundary element method , Fracture

Background and objective: The purpose of the present paper is to pave the road to the systematic optimization of complex craniofacial surgical intervention and to validate a design methodology for the virtual surgery and the fabrication of cranium vault custom plates. Recent advances in the field of medical imaging, image processing and additive manufacturing (AM) have led to new insights in several medical applications. The engineered combination of medical actions and 3D processing steps, foster the optimization of the intervention in terms of operative time and number of sessions needed. Complex craniofacial surgical intervention, such as for instance severe hypertelorism accompanied by skull holes, traditionally requires a first surgery to correctly “resize” the patient cranium and a second surgical session to implant a customized 3D printed prosthesis. Between the two surgical interventions, medical imaging needs to be carried out to aid the design the skull plate. Instead, this paper proposes a CAD/AM-based one-in-all design methodology allowing the surgeons to perform, in a single surgical intervention, both skull correction and implantation. Methods: A strategy envisaging a virtual/mock surgery on a CAD/AM model of the patient cranium so as to plan the surgery and to design the final shape of the cranium plaque is proposed. The procedure relies on patient imaging, 3D geometry reconstruction of the defective skull, virtual planning and mock surgery to determine the hypothetical anatomic 3D model and, finally, to skull plate design and 3D printing. Results: The methodology has been tested on a complex case study. Results demonstrate the feasibility of the proposed approach and a consistent reduction of time and overall cost of the surgery, not to mention the huge benefits on the patient that is subjected to a single surgical operation. Conclusions: Despite a number of AM-based methodologies have been proposed for designing cranial implants or to correct orbital hypertelorism, to the best of the authors' knowledge, the present work is the first to simultaneously treat osteotomy and titanium cranium plaque.

Keywords: Additive manufacturing , CAD , Cranium surgery , Image processing

Background: Current approaches to quantifying the severity of pectus excavatum require internal measurements based on cross-sectional imaging. The aim of this study is to exploit a novel index evaluated on the external surface of the chest with a three-dimensional (3D) optical scanner. Methods: Fifty-one children (41 male, 10 female) between 2 and 17 years of age were evaluated with a 3D optical scanner. Pectus excavatum severity was calculated by using an ad hoc instant 3D scanner and defining an automatic procedure to generate an optical 3D correction index (CI3D). For the latter, an ideal threshold was derived from a statistical analysis, and five blind surveys were collected from pediatric specialists on chest wall deformities. The CI3D was then correlated with blind clinical assessments of PE severity. Results: The cutoff thresholds were determined to optimally discriminate between six degrees of severity of PE patients by a correlation analysis. The correlation coefficient obtained by matching the CI3D with the average subjective severity shows that the proposed method outperforms traditional approaches. Conclusions: The optical 3D index has a good match with the average subjective assessment in distinguishing patients with mild to severe PE. This innovative approach offers several advantages over existing indices, as it is repeatable and does not require cross-sectional imaging. The index might be particularly suitable for monitoring the efficacy of nonoperative treatment and, in the future, for designing an optimal personalized usage of therapeutic devices.

The percutaneous interventions in the treatment of structural heart diseases represent nowadays a viable option for patients at high risk for surgery. However, unlike during the traditional open heart surgery, the heart structures to be corrected are not directly visualized by the physician during the interventions. The interpretation of the available medical images is often a demanding task and needs specific skills i.e. clinical experience and complex radiological and echocardiographic analysis. The new trend for cardiovascular diagnosis, surgical planning and intervention is, today, mutually connected with most recent developments in the field of 3D acquisition, interactive modelling and rapid prototyping techniques. This is particularly true when dealing with complex heart diseases since 3D-based techniques can really help in providing an accurate planning of the intervention and to support surgical intervention. To help the research community in confronting with this new trend in medical science, the present work provides an overview on most recent approaches and methodologies for creating physical prototypes of patient-specific cardiac structures, with particular reference to most critical phases such as: 3D image acquisition, interactive image segmentation and restoration, interactive 3D model reconstruction, physical prototyping through additive manufacturing. To this purpose, first, recent techniques for image enhancement to highlight anatomical structures of interest are presented together with the current state of the art of interactive image segmentation. Finally, most suitable techniques for prototyping the retrieved 3D model are investigated so as to derive a number of criteria for manufacturing prototypes useful for planning the medical intervention.

Keywords: 3D modelling , Cardiovascular diseases , Heart , Medical imagery , Rapid prototyping , Surgical planning

Pectus Excavatum, one of the most frequent chest wall deformities, is characterized by a depression of the sternum and costal cartilages. Patients with mild deformities are generally treated conservatively by using the so called Vacuum Bell (VB) i.e. a suction cup to be placed on the patient's sternal region. Three different sizes, as well as a model fitted for young women, of VB are available on the market. Unfortunately, the variability of the surface to be treated, the possible asymmetry of the caved-in area and the prolonged use, can make the device uncomfortable and, in some cases, ineffective for the patient. In order to cope with these issues, the present paper proposes a computer-aided method for customized vacuum bell design to be used by non-expert user, e.g. by medical staff. In particular, the present work entails the development of a system comprising: 1) a dedicated software capable of acquiring the 3D chest geometry - by using a low-cost range sensor, i.e. Kinect v2 - and of processing the point cloud so to generate NURBS surfaces of the chest; 2) a procedural CAD modeling of a personalized VB implemented within Siemens NX 11 CAD environment. Using the devised method, the medical staff is required only to use the 3D scanning system for acquiring the patient chest and to sketch, in a CAD-based interface, the boundary of the area to be treated. Once these tasks are performed, the system automatically builds the personalized VB model, ready to be manufactured.

Keywords: design customization , Procedural CAD modeling , reverse engineering , vacuum bell

In tissue engineering, biocompatible porous scaffolds that try to mimic the features and function of the bone are of great relevance. In this paper, an effective method for the design of 3D porous scaffolds is applied to the modelling of structures with variable architectures. These structures are of interest since they are more similar to the stochastic configuration of real bone with respect to architectures made of a unit cell replicated in three orthogonal directions, which are usually considered for this kind of applications. This property configures them as, potentially, more suitable to satisfy simultaneously the biological requirements and those relative to the mechanical strength. The procedure implemented is based on the implicit surface modelling method and the use of a triply periodic minimal surface (TPMS), specifically, the Schwarz's Primitive (P) minimal surface, whose geometry was considered for the development of scaffolds with different configurations. The representative structures modelled were numerically analysed by means of finite element analysis (FEA), considering them made of a biocompatible titanium alloy. The architectures considered were thus assessed in terms of the relationship between the geometrical configuration and the mechanical response to compression loading.

Keywords: Design , FEA , Scaffold , Tissue engineering , TPMS

Background/Aim. We retrospectively investigated the prognostic potential (correlation with overall survival) of 9 shape and 21 textural features from non-contrast-enhanced computed tomography (CT) in patients with non-small-cell lung cancer. Materials and Methods. We considered a public dataset of 203 individuals with inoperable, histologically- or cytologically-confirmed NSCLC. Three-dimensional shape and textural features from CT were computed using proprietary code and their prognostic potential evaluated through four different statistical protocols. Results. Volume and grey-level run length matrix (GLRLM) run length non-uniformity were the only two features to pass all four protocols. Both features correlated negatively with overall survival. The results also showed a strong dependence on the evaluation protocol used. Conclusion: Tumour volume and GLRLM run-length non-uniformity from CT were the best predictor of survival in patients with non-small-cell lung cancer. We did not find enough evidence to claim a relationship with survival for the other features.

Keywords: Computed tomography , Non-small-cell lung cancer , Radiomics. , Shape , Texture

In this paper, we aim at providing results concerning the application of desktop systems for rapid prototyping of medical replicas that involve complex shapes, as, for example, folds of a colon. Medical replicas may assist preoperative planning or tutoring in surgery to better understand the interaction among pathology and organs. Major goals of the paper concern with guiding the digital design workflow of the replicas and understanding their final performance, according to the requirements asked by the medics (shape accuracy, capability of seeing both inner and outer details, and support and possible interfacing with other organs). In particular, after the analysis of these requirements, we apply digital design for colon replicas, adopting two desktop systems. The experimental results confirm that the proposed preprocessing strategy is able to conduct to the manufacturing of colon replicas divided in self-supporting segments, minimizing the supports during printing. This allows also to reach an acceptable level of final quality, according to the request of having a 3D presurgery overview of the problems. These replicas are compared through reverse engineering acquisitions made by a structured-light system, to assess the achieved shape and dimensional accuracy. Final results demonstrate that low-cost desktop systems, coupled with proper strategy of preprocessing, may have shape deviation in the range of ±1 mm, good for physical manipulations during medical diagnosis and explanation.