A three dimensional supposition method to locate the mandibular canal after movement of the distal fragment on sagittal split osteotomy of the mandibular ramus using ceramic screw fixation

Abstract

In sagittal split osteotomy of the mandibular ramus using ceramic screw fixation, contact with or insertion of screws into the mandibular canal is regarded to cause for functional disturbance of the inferior alveolar nerve. In order to reduce the incidence of this disadvantage, the authors have devised a three dimensional supposition method to locate the mandibular canal after movement of the distal fragment.
The authors remodeled a upper member of the articulator into a supposition instrument. This instrument consisted of a mounting frame for a upper dental plaster cast and a metal bar that the condyle region of the mandibular ramus model was fixed to. After mounting the upper dental cast to this instrument, the lower dental cast was fitted, and immobilized, to it. The mandibular ramus model composed of two plates, the outer one was made of clear plastic plate was fixed to the metal bar of the supposition instrument and the inner one was bonded to the lower dental cast. After the two ramus plates were separated, the lower dental cast was moved to the planned position and the safety zone for screw fixation was indicated by the mandibular canal drawn across the inner plate.
This supposition method has been used in 26 cases of ceramic screw fixation in sagittal split osteotomy. The success rate of avoiding contact with the mandibular canal was 82.7%(43 of 52 rami). This method achieved a more favorable result than cases in which this method was not used (61.2%).