O.116 Orthognatic surgery and microvascular reconstruction of maxillo-mandibular defects

Abstract

This in vitro investigation was developed with the purpose of comparing the biomechanical features of 3 different methods of rigid internal fixation for sagittal split ramus osteotomies for mandibular advancement.Rigid internal fixation techniques included a 4-hole plate and 4 monocortical screws (miniplate group), a 4-hole plate and 4 monocortical screws with 1 additional bicortical positional screw (hybrid group), and 3 bicortical positional screws in a traditional inverted-L pattern (inverted-L group). Screws and miniplates were made of titanium and from a 2.0-mm system (MDT, Rio Claro, SP, Brazil). Sixty polyurethane replicas of human hemimandibles (Nacional, Jaú, SP, Brazil) were used as substrates, simulating a 5-mm advancement surgery by a sagittal split ramus osteotomy. They were adapted to a test support, and were submitted to lateral torsional forces on the buccal molar surface and vertical cantilever loading on the incisal edge by an Instron 4411 mechanical testing unit (Instron, Norwood, MA) for recording peak loading at 1 mm, 3 mm, 5 mm, and 10 mm of displacement. Each group was formed by 10 replicas, subjected to a linear noncyclical testing only once. Means and standard deviation were analyzed using analysis of variance and Tukey tests, with a 5% level of significance. Testing failures were also recorded.The miniplate group showed lowest load peak scores (P < .01) when compared with the other fixation techniques, irrespective of the direction of force. The inverted-L group showed higher resistance (P < .01) than the hybrid group when vertical forces were applied. For molar load, the hybrid and inverted-L groups showed no significant difference.For mandibular advancement surgery of 5 mm, it was concluded that the rigid internal fixation technique for sagittal split ramus osteotomies based on 3 bicortical screws in the inverted-L pattern was the most stable in a laboratory environment. Furthermore, the results suggested that installation of a bicortical positional screw in the retromolar region may significantly optimize the resistance of the miniplate and monocortical screw fixation.