Minimal-Invasive-Monocortical-Angle-System – Load Sharing and Load Bearing Forces

Monocortical fixation of mandibular angle fractures and osteotomies are done by conventional 90° screw plates. Recently a unique fixation system was designed as an intra-oral six-hole 2mm plate in which screws were used at a 60° angle (MIMAS). Objectives: To compare and determine the force resistance of the newly developed angle system (MIMAS) with that of a conventional system when applied in both a load sharing and load bearing situation. Methods: Sets of 12 sheep mandibles were collected from an abbatoir, cleaned, and an angular fracture was simulated on each mandible with a surgical saw. The mandibles were fixated with a conventional screw plate and the MIMAS system respectively and mounted in a specially designed holding device to enable testing in an Instron testing machine. Each system was fixated in a load sharing and a load bearing fracture simmulation. Each sample in the four different groups were mounted in an Instron testing machine and the anterior part of the mandible were compressed with a rounded lever placed on a molar to an arbitrary point of failure (3mm). The force resistance was recorded at 0.5mm travel intervals. Results: With fixation in a load sharing fracture force resistance of the MIMAS system was higher than force resistance obtained with the conventional sytem – this difference was however not statistically significant (p>0.05). With fixation in a load bearing fracture force resistance of the MIMAS system was significantly higher (p<0.05) than force resistance obtained with the conventional system. Conclusion: The MIMAS system gave consistent higher force resistance values when compared with the conventional system and should be the method of choice for the treatment of mandibular angle fractures and osteotomies.