[Stability of screw fixation following sagittal splitting osteotomy of the mandibular ramus].

Abstract

Recently, sagittal splitting osteotomy of the mandibular ramus is frequently performed in orthognathic surgeries of mandibular deformities. Although the surgical technique has been established. Methods for osteosynthesis following sagittal spitting of mandibular ramus still remain unestablished. Osteosynthesis is usually achieved by circumferencial wiring, interosseous wiring or screw fixation. It is unknown which of these three methods is best suited from dynamic and clinical point of view. The author carried out a simulation study of screw fixation using acrylic resin plate models and sagittally split air-dried human mandibles. The following result were obtained: 1) In the fixation experiment using an acrylic resin plate and AO cortical bone screws, a significantly smaller displacement was recorded by S3E type fixation, compared with other modes of fixation. In determining the amount of stress required for causing displacement, S3D type fixation required a significantly larger stress, compared with other modes of fixation. 2) In the destruction experiment using an acrylic resin plate and AO cortical bone screws, the critical displacement measured was significantly smaller by S3E type fixation compared with other modes of fixation S3C type fixation required a significantly larger amount of stress to cause destruction. 3) In the fixation experiment using the air-dried human mandibles and alumina ceramic screws, a significantly smaller displacement was recorded by 2-alumina ceramic screw fixation, compared with other modes of fixation. In determining the amount of stress required for causing displacement, 3-alumina ceramic screw fixation required a larger stress, compared with other modes of fixation. 4) In the fixation experiment using the air-dried human mandible and AO cortical bone screws, a significantly smaller displacement was recorded by 2-AO cortical bone screw fixation, compared with other modes of fixation. In determining the amount of stress required for causing displacement, 3-AO cortical bone screw fixation required a larger stress, compared with the 2-AO type of fixation. The above experimental results suggest that when the sagittally split proximal cortical plate retains enough thickness for tapping, clinical application of screw fixation either with alumina ceramic or AO cortical bone screws produces an adequately high anti-displacement effect, even if only 2 screws are used. However, when stability is evaluated in terms of the resistance to stress, 3-screw fixation is considered to amply satisfy the resistance required.