Postoperative stability following bilateral intraoral vertical ramus osteotomy based on amount of setback.

Our aim was to evaluate the postoperative stability associated with differing degrees of mandibular setback and their relations after intraoral vertical ramus osteotomy (IVRO). We planned a retrospective cohort study of 94 patients (mean age (range) 23 (18-46) years) selected from a larger group who had been diagnosed with mandibular prognathism with or without facial asymmetry and who had mandibular setback by IVR osteotomy from 2004 to 2009. The preoperative, 7-day, and 12-month postoperative lateral cephalographs were measured to find out the degree of movement, and the vertical and horizontal positions of menton and pogonion were compared at different time points to measure stability. The mean (SD) setback was 10.5 (5.1) mm, with 0.8 (1.1) posterior relapse at 12 months. The mean surgical change of menton vertically was 3.0 (3.0) mm superiorly, with an additional 1.3 (1.05) mm at 12 months. The amount of posterior relapse was less as the amount of setback increased but not significantly so. The amount of setback therefore has minimal effects on anterior relapse, and cannot be considered singly as a variant that affects the degree of stability. The risk of anterior relapse is low even with a substantial degree of mandibular setback, so overcorrection is not necessary with the IVR osteotomy.