Mechanical behavior of an osteotomized mandible with distraction orthodontic devices.

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 1.2mm/day. The global displacement is 6mm 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.