Recovery of nerve injury after mandibular sagittal split osteotomy. Diagnostic value of clinical and electrophysiologic tests in the follow-up.

The diagnostic value of several clinical, quantitative sensory tests (brush-stroke directional discrimination (BSD), touch detection threshold (TD), warm/cold (W/C) and sharp/blunt discrimination (S/B)), and electrophysiologic tests (mental nerve blink reflex (BR), nerve conduction study (NCS), cold (CDT), and warm (WDT) detection thresholds) in the recovery of inferior alveolar nerve (IAN) injury was evaluated in a prospective 1-year follow-up study of 20 patients after bilateral sagittal split osteotomy (BSSO). The subjective sensory alteration was assessed from patients' drawings. The predictive values of different tests at 2 weeks were determined in relation to the subjective sensory recovery at 12 months. The most pronounced recovery of the nerve damage occurred during the first 3 months according to all measures used. After 3 months, the electrophysiologic tests, especially the NCS, indicated significant further improvement. Except for the TD test, all other clinical test results were normal already at 3 months postoperatively. At early and late controls, the NCS and the thermal quantitative sensory testing could best verify the subjective sensory alteration, and most accurately assess the degree of thick and thin fibre dysfunction. At 1 year, the nerve dysfunction, as revealed by the NCS, corresponded with the figures of sensory alteration reported by the patients (35% R, 40% L). The W/C, BSD, S/B and WDT tests had the best early positive predictive values. Electrophysiologic tests had higher negative predictive values compared to clinical tests.