Methods for medical applications

BACKGROUND: Current methodologies in the prevision of post-surgical features of the face in orthognathic surgery are mainly 2-D. An improvement is certainly given by the introduction of CT, but its acceptance is controversial due to its high biological cost. As an alternative, in this study an effective procedure for the construction of a 3-D textured digital model of the face and dental arches of patients with dentofacial malformations using a 3-D laser scanner at no biological cost is presented. METHODS: A 3-D Laser scanner Konica-Minolta VIVID 910 is used to obtain multiple scans from different perspectives of the face of patients with dentofacial malocclusions requiring orthognathic surgery. These multiple views are then recombined, integrating also the maxillary and mandibular arch plaster casts, to obtain the 3-D textured model of the face and occlusion with minimal error. RESULTS: A viable methodology was identified for the face and occlusal modeling of orthognathic patients and validated in a test case, confirming its effectiveness: the 3-D model created accurately describes the actual features of the patient's face; the proposed methodology can be easily applied in the clinical routine to accurately record the steps of the surgical treatment and to perform accurate anthropometric analyses of the facial morphology, and thus constitute the necessary database for the development of previsional tools in orthognathic surgery. CONCLUSIONS: The proposed method is effective in recording all the morphological facial features of patients with dentofacial malformations, to develop a facial modification database and tools for virtual surgery.

Computed tomography is a medical instrument that can be useful not only for diagnostic purposes, but also for surgical planning, thanks to the fact that it offers volumetric information which can be translated in three dimensional models. These models can be visualized, but also exported to Rapid Prototyping (RP) systems, that can produce these structures thanks to the rapidity and versatility of the technologies involved. The literature reports various cases of stereolithographic models used in orthopedic, neurological, and maxillo-facial surgery. In these contexts, the availability of a copy of the real anatomy allows not only planning, but also the practical execution of surgical operations, within the limitations of the materials. Nevertheless, the Rapid Prototyping model also presents some disadvantages that can be reduced if practical simulation is accompanied by virtual simulation, performed on a digital model. The purpose of this work is to examine and present the use of Virtual Reality (VR) and Rapid Prototyping for surgical planning in Maxillo-Facial surgery. ©2008Muntaz B. Habal, MD.

Keywords: Osteogenesis distraction , Rapid prototyping , Reverse engineering , Surgical planning , Virtual reality

Quality of service, in terms of improvement in patient satisfaction, is an increasingly important objective in all medical fields, and is especially imperative in orthodontics due to the high numbers of patients treated. Information technology can provide a meaningful contribution to bettering treatment processes, and we maintain that systems such as CAD, CAM and CAE, although initially conceived for industrial purposes, should be evaluated, studied and customized with a view to use in medicine. The present study aims to evaluate Reverse Engineering (RE) and Rapid Prototyping (RP) in order to define an ideal chain of advanced technological solutions to support the critical processes of orthodontic activity.

Purpose: Low back pain related to intervertebral disc (IVD) degeneration represents a socio-economic problem which affects quality of life. In order to solve this problem the current gold standard techniques such as spinal arthroplasty and arthrodesis (or fusion) are considered. As for spinal arthroplasty, over the past 40 yrs, IVD prostheses have been designed to maintain the correct IVD spacing and to allow for motion, while providing stability. However, there are many difficulties in incorporating important features such as viscoelastic and shock absorber behavior of natural IVDs in a prosthetic disc design. Moreover, in some cases, the use of IVD prostheses does not represent the ideal solution. Consequently, the aim of this study was to improve the design of alternative devices for spinal fusion, which overcome the problems related to metal ones currently available on the market, such as stress shielding, stress concentration effects and eventual bone corrosive or inflammatory reaction. Methods: Accordingly, a novel polyetherimide (PEI)-based cage reinforced with carbon fibers through filament winding and compression molding technologies was realized. Results: The characterization through a porcine model has produced very interesting results. The small values obtained from local compression tests have suggested that a reduction in mobility occurred, whereas distributed compression tests on IVDs prosthesized by employing the PEI-based cage reinforced with carbon fibers have highlighted a compressive stiffness of 100 MPa. This stiffness is lower than that of the IVD prosthesized through the titanium cage (146 MPa), and closer to the stiffness of natural porcine IVDs (90 MPa). Conclusions: Through a suitable composite cage design it is possible to control stress-strain distributions and the mechanical signals to bone, thus avoiding the stress-shielding phenomena, but also corrosion and metal ions release which are typical of the metallic implants. © Società Italiana Biomateriali.

Keywords: Composite interbody fusion device , Intervertebral disc , Mechanical behavior , Porcine model , Prosthesized segments

Morphological and mechanical properties of PCL porous scaffolds for bone tissue regeneration have been analyzed as function of two different preparation techniques : particulate leaching/phase inversion and rapid prototyping technique. © 2008 American Institute of Physics.

Tissue engineered scaffolds must have an organized and repeatable microstructure which enables cells to assemble in an ordered matrix that allows adequate nutriental perfusion. In this work, to evaluate the reciprocal cell interactions of endothelial and osteoblast-like cells, human osteoblast-like cells (MG63) and Human Umbilical Vein Endothelial Cells (HUVEC) were co-seeded onto 3D geometrically controlled porous poly(ε-caprolactone) (PCL) and cultured by means of a rotary cell culture system (RCCS-4DQ). In our dynamic co-culture system, the lack of significant enhancement of osteoblast ALP activity and ECM production indicated that the microgravity conditions of the rotary system affected the cells by favoring their proliferation and cellular cross-talk. These results emphasize how osteoblasts increase endothelial cell proliferate and endothelial cells amplify the growth of osteoblasts but decrease their differentiation. This dynamic seeding of osteoblasts and endothelial cells onto a 3D polymeric scaffold may represent a unique approach for studying the mechanisms of interaction of endothelial and osteoblast cells as well as achieve a functional hybrid in which angiogenesis, furnished by neo-vascular organization of endothelial cells may further support osteoblasts growth. Furthermore, this in vitro model may be useful in examining the applicability of novel material structures for tissue engineering. © SAGE Publications 2008.

Keywords: 3D scaffolds , Dynamic co-culture , Poly-ε- caprolactone , Rapid prototyping , Tissue engineering

In this paper a complex prosthesis of dental implants, inserted in a mandible bone, has been analyzed using a virtual model. The study has been performed by means of a three-dimensional finite element model including the implants, the bridging structure and the bone. The interaction between implant screws and bone has been simulated in detail. Four different load conditions has been implemented to mimic the masticatory phase. The stress distribution in the implants and in the bone has been evaluated. Effects of possible temperature variation and assembling errors have been also taken into account. Moreover, the stiffening effect of the stabilizing bar that connect the implants has been also discussed. Starting from the results of the numerical investigations an optimization of the shape of the implants has been proposed in order to optimize the assembling procedure. © 2008, The Japan Society of Mechanical Engineers. All rights reserved.

Keywords: Dental Biomechanics , Finite Element Modeling , Immediate Loading Implants , Virtual Model

Purpose - The purpose of this paper is to consider surgical robotics, with a focus on technology and design issues for remote-mode operation assistance. The investigation leads to the definition of the technical characteristics of a co-robotic positioning device (CRPD), to be developed in support of a split-duty approach to planning. The expected characteristics and advantages are outlined, including the operation potential of special-purpose devices (e.g. an automatic changer for surgical tools) and of scope-driven enhancers (e.g. the exploration of the intervention theatre). Design/methodology/approach - The paper addresses example developments based on projects performed with the co-operation of other robot laboratories in Munich and Paris. The CRPD concept is applied in relation to the DLR KineMedic® arm (developed by the Munich laboratory), and with the LRP prototype mini-arm (built by the Paris laboratory). Findings - Minimally-invasive surgery deserves increasing attention to reduce post-operative hospital stays and to reduce complications. This leads to new trends in robotics, to facilitate safe, fast and accurate remote manipulation, and integrated computer-aided implements. The features of the example CRPD design are summarised for the two cases. Practical implications - The overall comments consider minimally-invasive robotic surgery as a given intervention practice in the near future, and the split-duty approach, supported by the CRPD technology, as a valuable aid for human-robot co-operation, according to the "best-of-skills" idea, supporting intervention under the surgeon's control. Originality/value - This investigation shows new results aimed at expanding the operation versatility of robotics with integrated intelligence, to enhance scope-driven alternatives and out-of-reach handling with improved dexterity and safe autonomic processing. © Emerald Group Publishing Limited.

Keywords: Remote handling devices , Robotics , Surgery

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

The work presented in this paper refers to the implementation of a product development process based on the use of virtual model of the human body to design specific custom-fit product, such as a prosthesis socket (interface between the residual limb and the mechanical part of the prosthesis). It considers the integration of advanced ICT tools coming from the reverse engineering, the physics-based modelling and simulation, and the rapid prototyping fields. The paper describes problems related to the implementation of each step within a real socket development process. © Springer-Verlag Berlin Heidelberg 2007.

Keywords: Human body modeling , Physics-based simulation , Product customization , Prosthesis design

Mandibular distraction osteogenesis is a clinical procedure used for modifying the mandibular geometry when problems of dental overcrowding and arch shrinkage occur. The objective of this study is to use a computational model of tissue differentiation to examine the influence of the rate of distraction on bone re-growth within the fracture callus of a human mandible submitted to symphyseal distraction osteogenesis. A 3D model of the mandible is reconstructed from CT scan data and meshed into finite elements. Two different mastication loadings have been investigated: a 'full' mastication load and a 'reduced' mastication load where the action of each muscle was reduced by 70%. Four different distraction rates were analyzed: 0.6, 1.2, 2, and 3 mm/day, allowing a total displacement of 6 mm. In the early stages of the distraction process it is predicted that there is a decrease in the amount of bone tissue forming within the center of the fracture gap for all distraction rates. After the initial phases of expansion, the bone tissue within the callus increases for the slower rate of distraction or continues to decrease at the faster rates of distraction. At the end of the simulated maturation period, 47% of the distracted callus was predicted to consist of bone tissue for a distraction rate of 0.6 mm/day, decreasing to 22% for a distraction rate of 3 mm/day. Significantly higher amounts of bone formation were predicted for all distraction rates for the case of reduced mastication loading. Disparities between the model predictions and what is observed in vivo were found. For instance, during the latency period, the distraction period and beyond, the model is predicting larger than expected amounts of cartilage tissue formation within the callus. This and other limitations of the proposed model are discussed and possible specific explanations for these disparities are provided in the paper. The model predicts a distraction rate of around 1.2 mm/day to be optimal as higher rates produce less bone tissue while the risk of a premature bone union is greater at slower rates of distraction because in the latter stages of the distraction process bone tissue is predicted to form between the left and right side of the bone callus. © 2007 Biomedical Engineering Society.

Keywords: Finite element analysis , Mandibular distraction osteogenesis , Mechanobiology , Osteotomized human mandible , Tissue differentiation

Purpose: The purpose of this article is the demonstration of virtual reality (VR) and rapid prototyping (RP) in surgical planning in maxillofacial surgery. The authors emphasize the role of reverse engineering (RE) and RP, suggesting a model of cooperative work, with the interaction of maxillofacial surgeons, radiologists, and engineers. Materials and Methods: Data acquisition is performed using computed tomography. The 3D model is the result of RE practices based on image segmentation, and the real model is produced via stereolithography. Virtual simulations are performed on the 3D model obtained from image segmentation. All these stages require the interaction and collaboration of various experts: maxillofacial surgeons, radiologists, and RE and RP experts. Results: VR and stereolithography models represent a new technology to help the surgeon who has to work in cooperation with engineers and radiologists to improve the results in surgical planning of maxillofacial distraction. Conclusion: When performing the VR simulation, surgeons and engineers operate together in order to optimize the exploitation of the instruments available. Both VR and RP, with different and complementary advantages and limitations, can improve surgical planning activities and this is particularly effective when dealing with complex anatomical structures in maxillofacial surgery. © 2007 American Association of Oral and Maxillofacial Surgeons.

Repairing severe human skull injuries requires customized cranial implants. Trauma, cranial tumors, infected craniotomy bone flaps and neurosurgical external decompression are the main causes for large cranial defects. The success of the reconstructive cranial surgery depends on diverse aspects regarding the preoperative evaluation of the defect, the design and manufacturing of the implant and the execution of the operation. Currently, the design of membranes is mainly a manual work, even with the use of CAD facilities, and results in a time-consuming and user-dependent skull reconstruction. This paper presents an automated design methodology for custom-made cranioplasty plates in a PHANToM®-based haptic environment and the possibility to manufacture the same using Solid Freeform Fabrication technologies.

Keywords: Custom-made cranial plates , Haptic environment , PHANToM®-based tools , Solid freeform fabrication

Over the past years, a tremendous effort has been made to develop an intervertebral disc (IVD) prosthesis with suitable biological, mechanical and transport properties. However, it has been frequently reported that current prostheses undergo failure mainly due to the mismatch between the mechanical properties of the conventional device and the spine segment to be replaced. The aim of the present work was to develop a poly(2-hydroxyethyl methacrylate)/poly(methyl methacrylate) (PHEMA/PMMA) (80/20 w/w) semi-interpenetrating polymer network (s-IPN) composite hydrogel reinforced with poly(ethylene terephthalate) (PET) fibres, and to investigate the static and dynamic mechanical properties. Filament winding and moulding technologies were employed to obtain the composite IVD prostheses with the unique complex structure that is peculiar to the natural IVD. The compressive properties analysis showed the typical J-shaped stress-strain curve which is displayed by natural IVDs. Compressive modulus varied from 84 to 120 MPa, as a function of the strain rate, and stress was higher than 10 MPa. These values are in the range of those of the natural lumbar IVDs. No failure of the prostheses has occurred during fatigue test performed for ten million cycles in physiological solution. Dynamic mechanical tests have confirmed the composite IVD prostheses exhibited appropriate viscoelastic properties. © 2007 Springer Science+Business Media, LLC.

A review of recent literature revealed a very high success rate of implants used to support a mandibular overdenture as an alternative to the conventional removable dentistry. Today there are already several prosthetic solutions for the same clinical situations: in particular, the implant support can be different depending on the type of implants used and their layout. It is well known that the success or the failure of implants interfaced with bone depends, taking into account a favourable biological reaction, on the structural condition of the biomechanical system constituted by the bone structure and the implant. Knowledge of the strain/stress pattern can allow one to establish if bone maintenance, resorption or addition is more likely to take place. In this work two different kinds of implant supports for overdenture retention were compared by means of FEM: they differed in the number of implants, their dimension, their location inside the mandible and, finally, in the presence/absence of a beam connecting all implants and making them all linked. Clinical follow-up was assessed by means of technetium 99m-MDP scintigraphy. The obtained results agree with the clinical experience.

Keywords: Biomechanics , Bone remodelling , Bone scintigraphy , Dental implants , FEM , Nuclear medicine

This work analyzes the mechanical behavior of a human mandible when distraction orthodontic devices are used for correcting problems of dental overcrowding and/or arch shrinkage. The mandible 3D model is reconstructed from CT scan data and meshed into finite elements. The distractor is also modeled. FEM analysis included geometric non-linearity. Displacement field of healthy and osteotomized mandibles are compared. Progressive expansion of the distractor and effects of mastication are also analyzed. Finally, we compare two distraction protocols PROT1 and PROT2 where device is, respectively, expanded by 0.6 or 1.2 mm/day. The global displacement is 6 mm according to clinical recommendations. It came out that mastication forces generate displacements compatible with bone remodeling. However, parasitic rotations of the mandible arms due to mastication may counteract arch expansion induced by the device. Stress concentrations occurred where the device is fixed: stress peaks stay however below yield limit. Finally, PROT2 reduced by about 10% stresses in mandible and reproduces better than PROT1 the displacement field imposed by the device. © 2005 Elsevier Ltd. All rights reserved.

Keywords: 3D FEM analysis , Displacement protocols , Distraction osteogenesis , Orthodontic devices , Osteotomized mandible

Hip prostheses should meet the anatomical and physiological characteristics of patients; this is the rationale for designing modular implants of different sizes. To optimize implant geometry, it is necessary to consider, not only the prosthesis component design, but also the final configuration of the implanted leg. This means the necessity to consider the specific morphological and functional condition of "that" patient and not only of "that" hip to restore, at best, limb functions. Variations in the length of the implanted limb are frequent; therefore, the variations in the three geometrical features of the hip prosthesis neck, which can affect the restoration of the anatomical symmetry of the limbs, were investigated: (i) neck lengths (Ln), between 50.5 and 64.5 mm; (ii) cervico-diaphyseal (CD) angle (γ), between 135 and 125° and; (iii) anteversion (AV) angle (β), between 0 and 15°. Adopting a three-dimensional (3D) simplified biomechanical model, the resultant load acting on the hip was estimated for each different design solution; corresponding stress distributions and contact pressures at the interface between the prosthesis head and the ultra high molecular weight polyethylene (UHMWPE) layer were evaluated by 3D finite element (FE) analyses and using the Strozzi approach. The following values have been assumed as physiological values: γ = γp = 125°, β = βp = 15° and Ln = 57 mm; it was found that to contrast limb lengthening, if the CD angle varies from 135-125° (with neck length Ln = 64.5 mm and AV = 0°), the joint resultant load decreases by 8.8% (7.2% if AV = 15°); the contact pressure decreases by 5.8%, (5% if AV = 15°); the bending moment in the stem neck increases by 10.9% (13.8% if AV = 15°) and the torque increases by 1% (12.8% if AV = 15°). © Società Italiana Biomateriali.

Keywords: Anteversion angle , Cervical-diaphyseal angle , FE , Hip prosthesis , Limb lengthening , Prosthesis neck geometry , UHMWPE wear