Neurosensory alterations of the inferior alveolar and mental nerve after genioplasty alone or associated with sagittal osteotomy of the mandibular ramus.

[AIMS] The purpose of our protocol is to study neurosensory disturbances following genioplasty, sagittal split mandibular osteotomy, or both procedures in combination. Many authors assessed the incidence and degree of neurosensory disturbances of the inferior alveolar nerve following orthognathic surgery but often results are difficult to interpret and compare due to a lack of standardization of methods.

[PATIENTS] Fifty patients (24 males and 26 females) were tested with qualitative (touch sensation, sharp/blunt test, cold sensation and hot sensation) and quantitative methods (localization test, two point static and dynamic test) at least 1 year after orthognathic surgery. The patients were divided into the following groups: 10 patients in group 1 (controls); 12 patients in group 2 (genioplasty alone or in association with maxillary osteotomy or vertical mandibular ramus osteotomy); 10 patients in group 3 (sagittal split osteotomy alone); 18 patients in group 4 (sagittal split osteotomy with concomitant genioplasty).

[METHOD] On both sides four areas were tested: centre of chin and lip (cutaneous and mucosal sides), 2 cm lateral to the chin centre (cutaneous and mucosal sides), 3 cm lateral to the chin centre i.e. approximately at the mental foramen (cutaneous and mucosal sides) and vermilion. Tests were always performed by the same person. All patients were also asked to indicate whether the altered sensation was considered subjectively as being disabling.

[RESULTS] None of the patients showed persistent anaesthesia in the tested areas according to the qualitative tests. In group 2 the quantitative sensory tests revealed normal or slight hypoaesthesia (17%) in all areas tested; in 30% of the patients of group 3, minimal quantitative sensory disturbances were noted, while the incidence of objective sensory deficits increased in patients who had undergone a concomitant genioplasty (40% among group 4). Among the tested areas the vermilion and oral commissure were affected most often in all groups. Statistical analysis (using STATA 6.0) revealed that these differences were significant (p<0.05). There were also significant differences between group 1 and groups 3 and 4 for tactile sensitivity, location tests and sharp-blunt discrimination, while two point discrimination (quantitative test) showed statistically significant differences between group 1 and all other groups (2-4). No statistically significant differences among the four groups were found for thermal sensation (hot and cold).

[CONCLUSIONS] The combination of genioplasty and sagittal split osteotomy seems to be more detrimental for the lip sensibility than genioplasty or sagittal split alone. Thermal sensation is less affected than tactile sensation, location and two point discrimination tests (static and dynamic). Despite that, sensory deficit was never considered as disabling by the patients subjectively.