Somatosensory-evoked potential to evaluate the trigeminal nerve after sagittal split osteotomy

Objective. The purpose of this study was to assess the onset period of trig eminal nerve hypoesthesia during bilateral sagittal split osteotomy, with t he use of the trigeminal somatosensory-evoked potential (TSEP). Study design. Subjects were 10 patients with mandibular prognathism who und erwent setback surgery. Intraoperative TSEP was measured 4 times: just befo re the commencement of the surgery, immediately after the induction of gene ral anesthesia; after the medial periosteal dissection of the alveolar neur ovascular bundle; after the sagittal split of bone; and after semirigid fix ation; with a titanium miniplate with the use of a monocortical screw. Post operative TSEP was measured after the start of postoperative weeks 2, 4, 12 , and 24. Normal records of the TSEP wave comprised peak (13 ms), trough (1 6 ms), peak (22.7 ms), and trough (36 ms) (N1, P1, N2, P2, respectively). T rigeminal hypoesthesia was assessed by the latency of P1 and N2, because th ey indicated the most reproducible waveforms. Results. The change in shape of the spectra indicated that prolonged latenc y was initiated on medial periosteal dissection and was extended further af ter the sagittal bone split and fixation. However, latency recovery was obs erved relatively quickly after the start of: postoperative weeks 2 and 4. Conclusions. Trigeminal hypoesthesia appeared to be induced by direct injur y to the alveolar nerve during the bone split or by compression injury afte r fixation. Accordingly, the occurrence of a long-lasting postoperative tri geminal sensory hypoesthesia seemed to depend on nervous involvement of the split surface, the manner of fixation, or the intraoperative care.