In vitro evaluation of the resistance of three types of fixation to treat fractures of the mandibular angle.

The purpose of this study was to compare the mechanical resistance of three different plates used to treat fractures of the mandibular angle: a regular 4-hole plate, a longer 4-hole plate (both positioned using the Champy technique), and a 3-dimensional plate positioned over the oblique line. Three equal groups of replicas of human dentate mandibles made out of polyurethane resin were used (n=21 in each group). The force was applied perpendicular to the occlusal plane at a rate of 2mm/minute at three different points: the first molar on the sectioned side; the first molar on the contralateral side; and between the central incisors. This was followed by a resistance-to-load test. The two varying factors (type of plate and site-of-load application) were tested by analysis of variance, and probabilities of less than 0.05 were accepted as significant. There were no significant differences between the subgroups, or between the mean values of the different types of plates (p=0.925). The three types of plates showed similar mechanical behaviour, which showed that the 3-dimensional plates positioned over the oblique line can produce mechanical scores similar to those of conventional plates.