The objective of this study was to assess these geometrical changes of the condyle and lower incisors following a unilateral sagittal split osteotomy. A long-term clinical study of patients who received a USSO was also carried out.

Method: (1) Geometry: to determine the condylar changes following USSO, 20 randomly selected mandibles were analyzed. Mandibular asymmetry correction was simulated. The angle changes of the condyle and antero-posterior changes were recorded. (2) Clinical study: 23 who required USSO for correction of asymmetry were included. The vector of the advancement/setbacks was measured at the time of surgery. Patients were followed up for six months and the temporomandibular joints examined for changes.

Results: (1) Geometry: for a mean 1 mm transverse correction the condyle on the un-operated side rotated by a mean of 0.75° with a mean antero-posterior change of 0.66 mm. (2) Clinical study: no post operative adverse effects were found in the patient’s who have undergone USSO.

Discussion: Small mandibular asymmetries can be corrected by means of USSO. Secondary antero-posterior changes as a result of setback or advancement on the operated side should be taken into account when planning treatment. Small rotational changes of the condyle proved not to affect the temporomandibular joints adversely.