Study of fixation of a mandibular plate for favourable fractures of the mandibular angle: numerical predictions.

Abstract

Fractures of the mandibular angle have been well-described and, in most societies, their incidence is decreasing. In this study we analysed the stabilisation of fractures using a single plate (standard or optimised model). The finite element model was developed based on a mandibular computed tomographic scan, together with a miniplate from DePuy Synthes and an optimised plate. Using the finite element model we looked in turn at the four screws for fixation of the standard plate, and the six screws for the optimised plate, in a complete and an incomplete favourable fracture of the mandibular angle, using two screw diameters, 1.5 and 2 mm. The results indicated that a complete fracture is critical, with 10% more strain at the bone holes. The maximum microstrain was found for the 1.5mm diameter, in screws number 2 and 4, with 7270με and 6872με in the complete fractures, respectively. There were similar microstrains in screws number 1 and 2 of the optimised plate with six screws showing similar strains. Micromovements in the fracture line achieved 60με. The position of the screws influences the microstrains along the fracture line, suggesting that the surgeon places the screws along that line at a distance of 2.5 times the diameter of the screw. The optimised geometry with more screws does not prevent screws from loosening.