A comparison of lower lip hypoesthesia measured by trigeminal somatosensory-evoked potential between different types of mandibular osteotomies and fixation

Purpose. The purpose of this study was to compare objectively, the recovery of hypoestheia of the lower lip following orthognathic surgery using different procedures ( sagittal split ramus osteotomy [SSRO]) and intra-oral vertical ramus osteotomy (IVRO)) and fixation methods (monocortical plate fixation and bi-cortical plate fixation). Hypoesthesia was evaluated using the trigeminal somatosensory-evoked potential (TSEP). Patients and Methods. The subjects consisted of 174 patients (348 sides) with mandibular prognathism with or without asymmetry, who underwent mandibular ramus osteotomies using different fixation types. The patients were divided into 4 groups. The OAM group consisted of 128 sides who had SSRO using the Obwegeser method with mono-cortical absorbable plate fixation, the ODTM group consisted of 84 sides who had the Obwegeser-Dal Pont method with mono-cortical titanium plate fixation, the OTB group consisted of 32 sides who had the Obwegeser method with bi-cortical titanium plate fixation and the VO group consisted of 104 sides who underwent IVRO according to the Bell method without fixation. Trigeminal nerve hypoestheia at the region of the lower lip was assessed bilaterally by the TSEP method. An electroencephalograph recording system (Neuropack Sigma; Nion Koden Corp., Tokyo, Japan) was used to analyze the potentials. Each patient was evaluated pre-operatively and then post-operatively at 1 and 2 weeks, 1, 3, and 6 months, and 1 year. Results. The mean measurable period and standard deviation of TSEP of the lower lip in the OAM group was 5.2 +/- 9.9 weeks, 10.9 +/- 13.1 weeks in the ODTM group, 7.8 +/- 4.5 weeks in the OTB group, and 2.5 +/- 6.3 weeks in the VO group. There were significant differences between the OAM and ODTM groups (P < .0001), the ODTM and OTB groups (P < .0001), the OTB and VO groups (P < .0221), the OAM and VO groups (P < .0001), and the ODTM and VO groups (P < .0001). Conclusion. This study proved using objective measurements that the recovery period from hypoesthesia of the lower lip following orthognathic surgery was dependent on the surgical procedure. Recovery in lower lip hypoesthesia after IVRO was significantly earlier than SSRO.