Shermin Lee

Mandibular reconstruction in adults: a review

Mandibular defects may result from trauma, inflammatory disease and benign or malignant tumours. Mastication, speech and facial aesthetics are often severely compromised without reconstruction. The goal of mandibular reconstruction is to restore facial form and function, implying repair of mandibular continuity and muscle attachments. There should also be room for implant insertion so as to allow for rehabilitation of occlusion and articulation, whereas the function of the inferior alveolar nerve should be restored to assure adequate sensitivity of the lips. Mandibular reconstruction principles and techniques have evolved dramatically over the years. Refinements in techniques continue to improve patient quality of life. This paper reviews current techniques of mandibular reconstruction in adults and discusses the strengths and weaknesses of each.

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.

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.

Replacement of the Condyle and Ascending Ramus by a Modular Endoprosthesis in Macaca fascicularis— Part 1: A Clinical and Radiographic Study

PURPOSE To evaluate the feasibility of replacing the condyle and ascending ramus with a novel modular endoprosthesis in Macaca fascicularis. MATERIALS AND METHODS Eight male adult monkeys (Macaca fascicularis) were used in this study. The right condyle and ascending ramus posterior to the lower second molar were resected. An endoprosthesis consisting of 2 modules was inserted to replace the resected segment and fixed in place using polymethylmethacrylate bone cement (Palacos). Four monkeys were sacrificed at 3 months and another 4 at 6 months postoperatively. The operated side of the mandible was then harvested, including the endoprosthesis and the stump of the mandible to which it was attached. Lateral mandibular radiographs were taken using standard settings immediately postoperatively and postsacrifice. RESULTS Two monkeys presented with a fistula at the operated area 1 month postoperatively, but this resolved with a short course of antimicrobial treatment. At the time of sacrifice, no fistulas, dehiscences, or mobility of the endoprostheses was observed. There was no significant change in maximum mouth opening. At 3 months, a linear radiolucency was noted at the cement-bone interface in the 2 monkeys that previously presented with fistulas; whereas at 6 months, none of the 4 animals showed any radiolucency. CONCLUSIONS The use of a cemented modular endoprosthesis for replacement of the condyle and ramus unit was feasible with minimal complications allowing normal mouth opening and occlusion. Further histologic and microfocus computed tomographic studies will be done to confirm the findings.

Replacement of the Condyle and Ascending Ramus by a Modular Endoprosthesis in Macaca fascicularis—Part 2: Microcomputed Tomographic and Histologic Evaluation of the Ramus and Stem

PURPOSE The present study presents the microcomputed tomographic and histologic evaluation of the peri-implant tissues of a modular endoprosthesis used to replace the condyle and ascending ramus in Macaca fascicularis. MATERIALS AND METHODS The right condyle and ascending ramus were resected in 8 adult monkeys and replaced by a modular endoprosthesis, fixed with polymethylmethacrylate bone cement (Palacos). Four monkeys were sacrificed at 3 months and 4 at 6 months postoperatively. Microcomputed tomographic scanning was performed to analyze the bone volume at the bone-cement interface. Histologic and histomorphometric assessments were done using a modified hard and soft tissue grading scale and by studying the total bone contact at the interface. RESULTS The combined (buccal, lingual, and inferior) mean bone volume percentage of the 6-month group was significantly greater than that of the 3-month group (P < .05). The 6-month specimens showed a reduced inflammatory response and more abundant bone formation around the stem. The total soft tissue histologic score was significantly greater in the 6-month group (P < .05). A total bone contact percentage of 15.4% to 85.2% was achieved in 3 specimens. CONCLUSIONS Satisfactory bone growth was found at the bone-cement interface at the stem region, although direct bone contact with the cement was not achieved in all cases. Soft tissue contact with the prosthetic ramus, in the form of a fibrous capsule, was present in some areas. At 6 months, minimal interfacial inflammation was found in this monkey model.

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.

Segmental mandibular bone reconstruction with a carbonate-substituted hydroxyapatite-coated modular endoprosthetic poly(ɛ-caprolactone) scaffold in Macaca fascicularis

A bio-degradable scaffold incorporating osteoinductive factors is one of the alternative methods for achieving the regeneration of a mandibular bone defect. The current pilot study addressed such a bone reconstruction in a non-human primate model, Macaca fascicularis monkeys, with an engineered poly(ɛ-caprolactone) (PCL) scaffold, provided with a carbonate-substituted hydroxyapatite coating. The scaffolds were implanted into unilaterally created mandibular segmental defects in 24 monkeys. Three experimental groups were formed: (1) scaffolds with rhBMP-2 (n = 8), (2) scaffolds with autologous mixed bone marrow cells (n = 8), and (3) empty scaffolds as a control group (n = 8). Evaluation was based on clinical observation as well as micro-CT, mechanical, and histological analyses. Despite a high infection rate, the overall results showed that the currently designed PCL scaffolds had insufficient load-bearing capability, and complete bone union was not achieved after 6 months of implantation. Nevertheless, the group of PCL scaffolds loaded with rhBMP-2 showed evidence of bone-regenerative potential, in contrast to PCL with autologous mixed bone marrow cells and the control group.

Replacement of the condyle and ascending ramus by a modular endoprosthesis in Macaca fascicularis--part 4: evaluation of the temporomandibular joints.

PURPOSE To assess, using cone-beam computed tomography and histologic examination, whether the fixation of a condyle-ascending ramus mandibular modular endoprosthesis results in a physiologic condylar replacement in Macaca fascicularis. MATERIALS AND METHODS The right condyle and ascending ramus were resected in 8 adult monkeys and replaced with a modular endoprosthesis, fixed with polymethyl methacrylate bone cement (Palacos). Four monkeys were sacrificed at 3 months and another 4 at 6 months postoperatively. The reconstructed and contralateral temporomandibular joints were harvested en bloc and studied using cone-beam computed tomography and descriptive histologic examination. Heterotopic bone formation was quantified using a modified grading scale. The condyle cartilage thickness in the contralateral temporomandibular joint was measured using histomorphometric methods. The results were compared with those of the unoperated control monkeys. RESULTS Bone resorption in the glenoid fossa and pathologic changes in the articular disc were noted on the reconstructed side in most specimens. Nevertheless, cone-beam computed tomography findings, histologic findings, and condyle cartilage thickness measurements of the contralateral temporomandibular joint were not significantly different from those of the control specimens. CONCLUSION Replacement of the condyle and ascending ramus using a modular endoprosthesis in Macaca fascicularis resulted in adaptive remodeling of the glenoid fossa at up to 6 months postoperatively. Long-term studies are required to further assess the potential of this mode of reconstruction.

Replacement of the condyle and ascending ramus by a modular endoprosthesis in Macaca fascicularis--part 3: evaluation of peri-implant bone remodeling.

PURPOSE To assess whether the fixation of a condyle-ascending ramus mandibular modular endoprosthesis, using bone cement, will result in stress-related bone resorption in the Macaca fascicularis. MATERIALS AND METHODS The right condyle and ascending ramus were resected in 8 adult monkeys and replaced by a modular endoprosthesis, fixed with polymethylmethacrylate bone cement (Palacos). Four monkeys were sacrificed at 3 months and another 4 at 6 months postoperatively. The bone mineral density was assessed using dual-energy x-ray absorptiometry in the region anterior to the stem and using micro-computed tomography in the buccal, lingual, and inferior regions adjacent to the stem. RESULTS The bone mineral density of the 3-month specimens was greater than that at 6 months in the buccal, lingual, and inferior regions adjacent to the stem. However, the difference was statistically significant only in the inferior aspect. No significant difference was found in the bone mineral density in the region anterior to the stem between the 3- and 6-month specimens. CONCLUSION A minimal reduction in bone density around the stem of the endoprosthesis was observed between 3 and 6 months after placement. This reduction did not result in any adverse clinical events.

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.