Biomechanics of Pierre Robin Mandibular Distraction Osteogenesis

Abstract Body : Introduction: Mandibular Distraction Osteogenesis (MDO) is used to treat severe tongue-based airway obstruction secondary to mandibular hypoplasia in Pierre Robin Sequence (PRS) patients. We lack an understanding of the biomechanics and strain patterns in pediatric hypoplastic mandibles.
Objective: The study evaluates how hardware placement for MDO influences the strain regime in the infant PRS hypoplastic mandible.
Material & methods: The study was approved by the research ethics committees of Uchicago and Piracicaba Dental School – State University of Campinas. This study used CT scans of three individuals with PRS mandibular hypoplasia who underwent surgical treatment with MDO. Finite element analysis was used to model effects of distractor activation. The mechanical properties of bone followed our previous study; properties of newly formed bone were calculated from the bone density. Distractor components were composed of titanium alloy and isotropic, with modulus of elasticity equal to 96 gigapascal (GPa) and Poisson's ratio equal to 0.36. The analysis simulated bilateral distractor activation consisting of displacement of the anterior plate in a direction guided by the distractor rail with a displacement of 0.5 mm. As boundary conditions the posterior plate was fixed in the 3 axes of movement to avoid displacements. The mandibular condyle was free displacement in the 3 axes, simulating its position inside the temporomandibular joint.
Results: The application of a 0.5 mm displacement on the anterior plate of the distractor was configured to simulate the resulting force on the bone structure due to the distractor's activation. The plate presented anterior displacement resulting in an action on the anterior bone structure and a reaction on the newly formed bone structure and on the mandibular ramus. All models showed a similar deformation regime with an asymmetric configuration being higher on the right side. The direction of deformation in the body of the mandible was anterior with a slight upward angulation. In the osteotomy region the newly formed bone showed deformation ranging from 0.1 to 0.3 mm on both sides for all models. The models presented a minimum amount of deformation ranging from 0 to 0.002 mε. The newly formed bone area and areas adjacent to the screws showed a greater amount of deformation. The greatest amounts of tensile deformations occurred in the newly formed bone region ranging from 0.005 to 0.05 mε. In areas adjacent to the screws, tensile strains reached up to 0.4 mε.
Conclusion - Pierre Robin Infants mandible presents a specific and unique biomechanics scenario according to the deformation regimes during the hardware activation. Hardware placement and the process of mandibular distraction changes the strain regime of the Pierre Robin Infants mandible.
Significance/Implications: Future research should investigate the effect of the position of the osteotomies and placement of distractors on stress/strain patterns in the mandible, so as to provide insight into the degree to which mandibular hypoplasia affects mandibular strain patterns before and after distraction.
Funding Sources: The authors would like to thank Bernard G. Sarnat, MD.
Foundation and The Institutional Internationalization Program (PRINT) of the Brazilian Coordination for the Improvement of Higher Education Personnel (CAPES).