Neurosensory Alteration in the Lower Lip and Chin Area After Orthognathic Surgery: Bilateral Sagittal Split Osteotomy Versus Inverted L Ramus Osteotomy

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This study investigated neurosensory disturbances in patients after orthognathic surgery in relation to differences in mandibular splitting methods and degree of surgical skill. Forty-five patients who had undergone bilateral sagittal split ramus osteotomies (SSRO), and 21 (group L) who had undergone intraoral inverted L ramus osteotomies (ILRO), were examined for postsurgical neurosensory disturbances. Twenty-two (group S1) of the SSRO patients were treated by 11 surgeons who had little experience, and the others (23 patients; group S2) were treated by 2 skilled surgeons who had considerable experience. One of the 2 skilled surgeons was the only surgeon carrying out the ILRO procedure. The neurosensory tests employed included light touching using a Semmes-Weinstein monofilament tester (SW tester), electrical stimulation, and a questionnaire to determine changes in subjective sensations, at the time of each sensory evaluation. Neurosensory examinations were carried out bilaterally (132 sides) at 1, 3, 6, and 12 months after surgery. More patients showed abnormal thresholds for the 2 measurement techniques in the SSRO group than in the ILRO group, and furthermore there were more such patients in group S1 than in group S2, at each measurement point. At 6 months after surgery, the number of patients with reduced sensitivity was significantly higher in group S1 than in group L (P < .05). In the SSRO group at each measurement point, the thresholds for the lower lip and chin were unrelated to the set-back (or advance) distance. By contrast, in group L only at the 1-month evaluation point, the thresholds for the lower lip and chin were significantly raised in patients whose setback distances were larger than average (P < .05). Postsurgical neurosensory disturbances of the lower lip and chin occur more frequently in SSRO patients treated by surgeons having little experience than in those treated by skilled surgeons, although the difference is not significant. Long-term prognosis for resolution of postsurgical neurosensory disturbances is better in ILRO patients than in SSRO patients. Although the width of movement of the split bone fragments has an influence on postsurgical neurosensory disturbances immediately after ILRO, the relationship becomes less obvious with time.