A computer study of fracture mobility and strain on biodegradable plates used for fixation of mandibular fractures.

PURPOSE: This computer-based study was done to determine whether a small biodegradable plate system was suitable for internal fixation of mandibular fractures.
MATERIALS AND METHODS: In a three-dimensional computer model of the mandible, fracture mobility and plate strain were calculated for bite forces applied on 13 bite points on the dental arch. Simulated solitary angle, body, and symphysis fractures were fixed with one titanium miniplate, one polylactide (PLA) midiplate, one PLA maxiplate, or two PLA midiplates. Fractures with and without interfragmentary bone contact were studied. In the case of fractures with bone contact, the loads were transmitted through the fracture surfaces and the plate; when there was no contact, the loads were transmitted only through the plate. Maximum fracture mobility was set at 150 microm. Maximum plate strain was set at the yield strain of PLA and titanium.
RESULTS: For fractures without interfragmentary bone contact, all plate fixations resulted in a fracture mobility and plate strain higher than the limits set, except for the symphysis fracture fixed with two PLA midiplates. Interfragmentary bone contact significantly reduced fracture mobility and plate strain. For the angle fracture with bone contact, all PLA plate fixations resulted in a fracture mobility above the limit, whereas the titanium miniplate fixation had a fracture mobility below the limit. For the body and symphysis fracture with bone contact, only double PLA midiplate fixation resulted in a fracture mobility below the limit.
CONCLUSIONS: From a mechanical point of view, based on the computer model, small PLA plates are only suitable for symphysis fractures with and without interfragmentary bone contact and for body fractures with interfragmentary contact. However, fixation with two PLA plates is always necessary to provide sufficient reduction of fracture mobility and plate strain.