Alteration in facial sensibility in adolescents following sagittal split and chin osteotomies of the mandible.

Static two-point discrimination, pressure, and vibratory threshold values were measured bilaterally at standard coordinates in the area of the face innervated by the mental nerve in 115 adolescents (230 nerves). The patients were divided into four groups: normal adolescents who had not undergone any orthognathic surgery (group I controls, n = 134 nerves, mean age 18 years, SD = 3), those 1 year after undergoing bilateral sagittal split osteotomies of the mandible (group II, n = 14 nerves, mean age 19 years, SD = 2), those 1 year after undergoing an osteoplastic genioplasty (group III, n = 40, mean age 19 years, SD = 3), and those 1 year after undergoing a combination of bilateral sagittal split osteotomies and an osteoplastic genioplasty (group IV, n = 42 nerves, mean age 19 years, SD = 3). Subjective residual numbness at the 1 year postoperative interval was reported by 2 of 7 patients in group II, 2 of 20 patients in group III, and 14 of 21 patients (67 percent) in group IV. Long-term subjective numbness involved only the chin skin in 16 of 18 patients experiencing residual numbness and was perceived as problematic in the remaining 2 (group IV) patients whose subjective numbness also was measured objectively in the chin, lower lip (mucosa and skin), and gingiva. Objectively, the mean threshold values of the three sensory modalities tested were higher in group IV patients than in the remaining groups at all coordinates tested, but significant differences (p < 0.05) were found only between the mean two-point discrimination of group IV patients and the control group in the region of the chin skin. The high percentage of patients documented to have subjective and objective sensory disturbance after undergoing a combination of sagittal split osteotomies of the mandible and an osteoplastic genioplasty (group IV) may be explained by the "double crush syndrome."