The purpose of this study is to determine whether sensory retraining exercise could improve lip numbness caused by bilateral sagittal split of mandible.

The study is a prospective randomized controlled trial. The patients receiving bilateral sagittal split osteotomy and having lip numbness or paraesthesia will be included in this study. 80 patients will be included and randomized into two groups and there are 40 patients in each group. The control group is to maintain follow up in clinic and do not receive any sensory retraining exercise. The experimental group is requested to perform sensory retraining at home by themselves.

Inclusion Criteria:

1. Taiwanese adult (18-40 y/o)
2. Developmental dentofacial disharmony (Class III)
3. Patients received orthognathic surgery (BSSO alone or with maxillary procedure)

Exclusion Criteria:

1. Medical condition associated with systemic neuropathy
2. Unwilling to sign informed consent
3. Congenital anomaly or acute trauma affecting the face
4. Previous facial surgery
5. Positive pain sensation at first week of post-surgery
6. Altered sensation before OGS as numbness or unusual feeling
7. Cleft lip and palate