Mandibular reconstruction with a bioactive-coated cementless Ti6Al4V modular endoprosthesis in Macaca fascicularis.

The titanium mandibular modular endoprosthesis fixed with polymethylmethacrylate cement in the medullary space of the mandible has been introduced in previous studies. However, the internal parts of these devices have been found to be prone to loosening and wound dehiscence. The current study introduces a newly designed bioactive-coated cementless modular mandibular endoprosthesis, which was used for reconstruction in Macaca fascicularis. The devices were coated with hydroxyapatite (HA) and hydroxyapatite/bioglass (HA/BG) and implanted in unilateral mandibular segmental defects in nine monkeys for 6 months. Biomechanical testing found the reconstructed mandible to have a mean stiffness value of 110.43 N/mm. Histologically, there were both fibrous capsule and woven bone around the device body, and histomorphology analysis showed 64.17% bone contact to device stem surface. The percentage bone volume calculated from micro-computed tomography analysis around the stem surface was found to be superior to that reported in previous studies of cemented mandibular endoprostheses. Intermodular connection screw loosening has also been resolved with the dovetail interconnection. In conclusion, the current bioactive-coated cementless mandibular endoprosthesis is feasible for use in mandibular segmental reconstruction. However, insufficient load-bearing capability and a high rate of intraoral wound dehiscence were found in the majority of the study animals. Further device modifications and improvements in the surgical technique need to be addressed in future studies.

Effect of replacement of mandibular defects with a modular endoprosthesis on bone mineral density in a monkey model.

The effect of mandibular modular endoprostheses on bone mineral density (BMD) in the stem regions was studied. Modular endoprostheses were inserted into standardized mandibular condyle or body defects in 16 Macaca fascicularis. Each group of eight monkeys was divided into two groups, one killed at 3 months, the other at 6 months post-surgery. The mandibles were harvested, sectioned and scanned with a micro-computed tomography scanner. The reconstructed slices, made at a right angles to the long axis of the prosthesis, were analysed using software to calculate BMD in regions of interest buccal, lingual and inferior to the stems of the endoprosthesis. Measurements of the contralateral sides of three monkeys that underwent a similar procedure were used as control/baseline BMD. BMD for the condyle replacement group did not differ significantly from the control group. At 6 months, BMD decreased slightly; significant only at the inferior region. BMD for the body replacement group was significantly lower in all regions compared with control and condyle replacement groups probably because of connection screw loosening and infection. Loss of BMD in the peri-implant region of a modular endoprosthesis for mandibular replacement is minimal up to 6 months postoperatively, provided the device remains stable and well-fixed.

Review of biomechanical models used in studying the biomechanics of reconstructed mandibles.

This study looked at computer and physical biomodels used to study the biomechanical performance of mandibular reconstruction, reviews the literature and explains the strengths and limitations of the models. Electronic databases (Pubmed, Medline) were searched. 17 articles were selected. Computer biomodels can be divided into virtual biomodels (mainly used for clinical diagnosis and treatment planning) and computational models (e.g. finite element analysis), they can predict areas most likely to fail based on internal stress distribution and areas of maximum stress concentration. Physical biomodels include: rapid prototyping, animal bone, human cadaveric bone, and bone substitute models. Physical models allow testing on a gross level to give fatigue performance and fracture strength. The use of bone substitutes allows a more consistent specimen size and a reduction in sample size. Some commercially available products can replicate the material properties of bone. The use of any biomodel depends on the question being asked: the bending strength of a reconstruction plate would necessitate a three point bending test; the biomechanical performance of a new method of reconstruction (e.g. the mandibular modular endoprosthesis) would necessitate finite element analysis to predict areas of likely failure and also a physical biomodel to look at fatigue failure.

Temperature changes in a cemented mandibular endoprosthesis: in vitro and in vivo studies.

Using polymethylmethacrylate (PMMA) cement in cemented endoprostheses may cause heat necrosis and prosthesis failure due to the highly exothermic reaction. This study determined the magnitude and duration of temperature change during the cementation of a mandibular endoprosthesis in an in vitro and in vivo Macaca fasicularis model. In the in vivo study the median maximum temperature (T(max)) around the mandible-prosthesis unit (MPU) was 31.0°C with the peak T(max) at hole 1 (1mm from stem). The in vitro study recorded a lower T(max) and indicated a trend that increased spacing (groove) around the prosthesis results in a higher T(max). All the T(max) MPU measurements were lower than normal body temperature (38°C). In the in vivo study the median maximum temperature change (T(maxΔ)) was 1.8°C; in the vitro study, the T(maxΔ) of the 4mm groove width was significantly higher than all others. Temperature increases were transient, with the temperature returning to baseline a median of 6.0min after T(max). Histological analysis showed surrounding tissue at the cement-bone interface with mild inflammation. Within the parameters tested, there was minimal risk of thermal damage. The temperature changes were influenced by the quantity of cement used and the distance from the prosthesis stem.

Biomechanics of mandibular reconstruction: a review.

Knowledge of the biomechanics of the mandible allows the surgeon to understand the forces acting on the mandible during function and the resulting deformation that can occur. This allows the appropriate selection and placement of osteosynthesis plates to neutralize these forces. Many methods have been proposed for mandibular reconstruction, each of which has strengths and weaknesses. Most papers evaluating these techniques have focused on survival rates and the quality of the grafted bones, and there have been few studies of the biomechanics (stress distribution and strength) of the various types of reconstructed mandibles. This paper reviews the biomechanics of the mandible and the various methods of reconstruction reported in past studies.

Peri-implant and systemic release of metallic elements following insertion of a mandibular modular endoprosthesis in Macaca fascicularis.

The aim of this study was to assess the release of metal elements from a Ti6Al4V modular endoprosthesis for mandibular reconstruction. Ten monkeys were included, seven of the animals had an endoprosthesis inserted and three served as controls. Mucosa, regional lymph nodes and distant organs, were assessed after the implant had been in place for 12 months, using light (LM) and transmission electron microscopy (TEM) and inductively coupled plasma optical emission spectroscopy (ICP). Blood was also drawn from all animals for elemental analysis using ICP. LM and TEM evaluation showed no detectable metal particles in the mucosa surrounding the endoprosthesis, nor in the regional lymph nodes and distant organs. Blood analysis revealed that titanium and vanadium were detectable in comparable amounts in the test (Ti: 1.63+/-0.54, Va: 0.42+/-0.08) as well as in the control group (Ti: 2.07+/-0.55, Va: 0.37+/-0.07). The amount of aluminum appeared to be higher in the control group (31.77+/-11.67) compared with the test group (20.41+/-9.13), but this difference was not statistically significant. ICP showed that no titanium, vanadium or aluminum was detectable in the mucosa surrounding the endoprosthesis. In addition, no titanium and vanadium were found in the lymph nodes and distant organs using ICP. On the other hand, using ICP, the aluminum content was found to be higher in the right regional lymph nodes and all examined distant organs as compared to the control group (lymph nodes: 11.55+/-22.15 vs. 0.36+/-0.61, lung: 6.24+/-11.28 vs. 1.40+/-2.15, liver: 1.66+/-0.99 vs. 0, kidney: 15.69+/-24.88 vs 0, spleen: 2.75+/-3.09 vs. 0.49+/-0.43). However, only for the kidney and liver the higher amount of aluminum was statistically significant. In conclusion, this study quantified the release of only aluminum in lymph nodes and distant organs, when using a modular endoprosthesis made of Ti-6Al-4V for mandibular reconstruction.

Modular endoprosthesis for mandibular body reconstruction: a clinical, micro-CT and histologic evaluation in eight Macaca fascicularis.

This paper presents the results of an animal experiment, in which a modular endoprosthesis is tested to replace a resected part of the mandible. The prostheses were fixed with polymethacrylate (PMMA) cement into the medullar space of the stumps. Clinical, radiologic, micro-computed tomographic and histologic evaluations were made after 3 and 6 months on four Macaca fascicularis for each implantation time. The prosthesis had not loosened but there were some loose screws that had caused fistulas in three animals. The stems of the modules were stably fixed with PMMA cement, surrounded by a fibrous capsule with inflammatory cells. This capsule was thinner in the 6-month group and showed less inflammatory infiltrate compared with the 3-month group; this was not statistically significant. There was an increase in woven bone surrounding the modules after 6 months. After 3 months of implantation, there was a considerable inflammatory reaction in the soft tissues surrounding the module, which subsided over following 3 months. The results are encouraging, but a longer period of follow-up is required to assess its application in a clinical setting, and some design drawbacks need to be addressed.

Modular endoprosthesis for mandibular reconstruction: a preliminary animal study.

The use of a mandibular modular endoprosthesis after segmental resection of part of the body of the mandible was studied. This preliminary study was carried out on four pigs and four monkeys. The devices were made of a titanium alloy and were cemented in the prepared medullary spaces with polymethylmetacrylate cement. The prosthesis failed in one pig, but in the other animals the prostheses were stable and firmly fixed to the stumps after 3 months. It was concluded that the endoprosthesis has potential in reconstructive surgery of the mandible, but that further studies are necessary to substantiate this claim. Pigs are not suitable for further studies as the medullary space is too large and filled with fat. They are also too big to handle and the variations in size and shape of the mandibles precludes the use of a modular system.

Experimentally induced unilateral tooth loss: expression of type II collagen in temporomandibular joint cartilage.

PURPOSE: We sought to examine possible changes in pattern and concentration of type II collagen in the condylar cartilage and articular disc of the temporomandibular joint (TMJ) in response to unilateral extraction of mandibular teeth in a rabbit model as a means of elucidating the effects of unilateral mastication on the TMJ. METHODS: A total of 12 experimental rabbits were killed either 3 or 6 weeks after the extractions, and 3 additional rabbits without extractions were used as controls. TMJ blocks from both sides of each of the 15 animals were examined for type II collagen via an immunoperoxidase procedure. RESULTS: Anti-type II collagen antibody (Ab) binding was detected mainly in the hypertrophic chondroblast layer of the condylar cartilage of normal rabbits. At 3 weeks after unilateral extraction of teeth, anti-type II collagen Ab binding to the territorial matrix of the hypertrophic chondroblast layer of the condylar cartilage and to the disc was stronger than normal. The increase in Ab binding appeared more dramatic on the nonfunctional side than on the functional side of TMJ. Variations from the normal pattern of anti-type II collagen Ab binding in terms of distribution through the extracellular matrix and fibrillar appearance were also observed. CONCLUSION: The findings suggest that the condylar cartilage and disc adapt to the imbalance induced by unilateral extraction of teeth through chondrocyte repair responses involving collagen II expression that appear to differ between the functional and nonfunctional sides of the TMJ.

Experimentally induced unilateral tooth loss: histochemical studies of the temporomandibular joint.

Occlusal abnormality may contribute to osteoarthrosis of the temporomandibular joint (TMJ). Since mechanical force may induce changes in the extracellular matrix, we tested the hypothesis that unilateral removal of teeth and the resulting unilateral mastication change the content of glycosaminoglycans (GAGs) in the TMJ condyle and disc. Lower-right-side teeth were extracted from 12 adult male rabbits, which were killed 3 or 6 weeks later. Three normal rabbits served as controls. Sections were analyzed for morphological changes and levels of sulfated GAGs in the condyle and disc. Unilateral removal of teeth led to thickening of the condylar cartilage, alterations in the morphology of chondrocyte nuclei in the condylar cartilage and disc, and increases in levels of negatively charged ions in the hypertrophic layer of condylar cartilage. Small differences were observed, after unilateral removal of teeth, between the functional and non-functional sides of the TMJ. The results suggest that in response to mechanical stress, chondrocytes alter sulfated glycosaminoglycan (GAGs) synthesis and degradation rates, resulting in an elevated level of sulfated GAGs in the condylar cartilage.

Three-dimensional virtual-reality surgical planning and soft-tissue prediction for orthognathic surgery.

Complex maxillofacial malformations continue to present challenges in analysis and correction beyond modern technology. The purpose of this paper is to present a virtual-reality workbench for surgeons to perform virtual orthognathic surgical planning and soft-tissue prediction in three dimensions. A resulting surgical planning system, i.e., three-dimensional virtual-reality surgical-planning and soft-tissue prediction for orthognathic surgery, consists of four major stages: computed tomography (CT) data post-processing and reconstruction, three-dimensional (3-D) color facial soft-tissue model generation, virtual surgical planning and simulation, soft-tissue-change preoperative prediction. The surgical planning and simulation are based on a 3-D CT reconstructed bone model, whereas the soft-tissue prediction is based on color texture-mapped and individualized facial soft-tissue model. Our approach is able to provide a quantitative osteotomy-simulated bone model and prediction of postoperative appearance with photorealistic quality. The prediction appearance can be visualized from any arbitrary viewing point using a low-cost personal-computer-based system. This cost-effective solution can be easily adopted in any hospital for daily use.

The microanatomy of the rhesus monkey temporomandibular joint.

PURPOSE: The objective of this study was to describe and compare the histology of the rhesus monkey temporomandibular joint (TMJ) with that of the human joint. MATERIALS AND METHODS: Seventeen rhesus monkeys (Macaca mulatta) with an age range from 4 to 11 years were used. Both TMJs of the first animal and the left TMJs of the remaining 16 animals were used for this study. The joint specimens were sectioned sagittally and processed for light and electron microscopic studies. RESULTS: The rhesus monkey TMJ consists of the condylar, glenoid fossa, and articular disc components. The histology of these components is described at the light and electron microscopic level. CONCLUSIONS: The monkey TMJ was found to be anatomically similar to the human joint. It was concluded that the rhesus monkey is one of the most suitable animal models for studies involving the TMJ.

Computer-assisted three-dimensional surgical planing and simulation. 3D soft tissue planning and prediction.

The purpose of this paper is to report a new technique for three-dimensional facial soft-tissue-change prediction after simulated orthognathic surgical planning. A scheme for soft tissue deformation, "Computer-assisted three-dimensional virtual reality soft tissue planning and prediction for orthognathic surgery (CASP)", is presented. The surgical planning was based on three-dimensional reconstructed CT visualization. Soft tissue changes were predicted by two newly devised algorithms: Surface Normal-based Model Deformation Algorithm and Ray Projection-based Model Deformation Algorithm. A three-dimensional color facial texture-mapping technique was also used for generating the color photo-realistic facial model. As a final result, a predicted and simulated patient's color facial model can be visualized from arbitrary viewing points.

A comparative study on meniscectomy and autogenous graft replacement of the Rhesus monkey temporomandibular joint articular disc--Part I.

The aims of this study were to compare the effects of meniscectomy and autogenous graft replacement on the functions and histology of the Rhesus monkey temporomandibular joint. Eight matured Rhesus monkeys (Macaca mulatta) were used for the first part of the study to compare firstly the results of meniscectomy without replacement and secondly, replacement of the disc with a fascia lata graft. The results showed that unilateral meniscectomy in Rhesus monkeys did not result in significant morbidity. Degenerative changes (osteoarthritis) were observed in all the experimental joints with and without replacement of the articular discs. Fascia lata did not survive after grafting and did not reliably induce re-formation of an articular disc-like structure.

A comparative study on meniscectomy and autogenous graft replacement of the rhesus monkey temporomandibular joint articular disc--Part II.

This study investigated the effects of free auricular cartilage and pedicled temporalis myofascial flap replacement of the temporomandibular joint articular disc in eight rhesus monkeys (Macaca mulatta). The eight animals were divided into two groups (four animals in each group) for replacement of the disc with either auricular cartilage graft or pedicled temporalis myofascial graft. Degenerative changes (osteoarthritis) were observed in all the experimental joints. Despite degeneration of grafted cartilage tissue, histologic and clinical responses after auricular cartilage grafting were favourable. Pedicled temporalis myofascial flap resulted in re-formation of a disc-like interpositional structure in most of the studied joints with the most favourable histologic response.

Computer-assisted three-dimensional surgical planning and simulation: 3D color facial model generation.

A scheme for texture mapping a 3D individualized color photo-realistic facial model from real color portraits and CT data is described. First, 3D CT images including both soft and hard tissues should be reconstructed from sequential CT slices, using a surface rendering technique. Facial features are extracted from 3D soft tissue. A generic mesh is individualized by correspondence matching and interpolation from those feature vertices. Three digitized color portraits with the "third" dimension from reconstructed soft tissue are blended and texture-mapped onto the 3D head model (mesh). A color simulated human head generated from frontal, right and left real color portraits can be viewed from an arbitrary angle in an inexpensive and user-friendly conventional personal computer. This scheme is the basic procedure in 3D computer-assisted simulation surgery.

Computer-assisted three-dimensional surgical planning and simulation: 3D virtual osteotomy.

A computer-assisted three-dimensional virtual osteotomy system for orthognathic surgery (CAVOS) is presented. The virtual reality workbench is used for surgical planning. The surgeon immerses in a virtual reality environment with stereo eyewear, holds a virtual "scalpel" (3D Mouse) and operates on a "real" patient (3D visualization) to obtain pre-surgical prediction (3D bony segment movements). Virtual surgery on a computer-generated 3D head model is simulated and can be visualized from any arbitrary viewing point in a personal computer system.

Three-dimensional virtual reality surgical planning and simulation workbench for orthognathic surgery.

A new integrated computer system, the 3-dimensional (3D) virtual reality surgical planning and simulation workbench for orthognathic surgery (VRSP), is presented. Five major functions are implemented in this system: post-processing and reconstruction of computed tomographic (CT) data, transformation of 3D unique coordinate system geometry, generation of 3D color facial soft tissue models, virtual surgical planning and simulation, and presurgical prediction of soft tissue changes. The basic mensuration functions, such as linear and spatial measurements, are also included. The surgical planning and simulation are based on 3D CT reconstructions, whereas soft tissue prediction is based on an individualized, texture-mapped, color facial soft tissue model. The surgeon "enters" the virtual operatory with virtual reality equipment, "holds" a virtual scalpel, and "operates" on a virtual patient to accomplish actual surgical planning, simulation of the surgical procedure, and prediction of soft tissue changes before surgery. As a final result, a quantitative osteotomy-simulated bone model and predicted color facial model with photorealistic quality can be visualized from any arbitrary viewing point in a personal computer system. This system can be installed in any hospital for daily use.

[Management of the temporalis flap donor site].

OBJECTIVE: To describe a technique of using a sterilized form of moldable cold cured acrylic, Cranioplastic, for camouflaging the depressed temporalis flap donor site, and to assess the long term morbidity and aesthetic results. METHODS: A retrospective clinical assessment of 50 consecutive patients who had temporalis myofascial flap surgery from 1988 to 1995. Any complications of healing, neurosensory deficit were recorded. The aesthetics of the temporal region was graded by subjective and objective methods. The histology of the tissues around the implant in one patient was examined under light microscopy. RESULTS: There was no major complications noted except immediate postoperative seroma formation and temporary paresis of the temporal branch of facial nerve. A satisfactory restoration of aesthetics at the temporal donor site was achieved with the moldable acrylic technique in 96% of patients. The capsular tissues surrounding the implanted acrylic consisted of hyalinized collagen fibres with scanty inflammatory cells. CONCLUSIONS: The use of moldable acrylic to restore the temporalis donor site is a simple, versatile and effective technique with minimal long term morbidity. The aesthetic result of the camouflage was satisfactory and the material exhibits good biocompability.