Lower incisor changes following non-extraction orthodontic decompensation in Class III surgical cases

The amount of incisor decompensation during pre-surgical orthodontics may affect the outcome of Class III orthognathic cases. The purpose of this study was to assess the lower incisor changes post-orthodontic decompensation in Class III surgical cases and to investigate the amount of crowding as a predictive factor. This was a retrospective study reporting on 22 Class III orthognathic cases. The lower incisor angulation (LIA) and distance of the lower incisor edge to the A-Pogonion line (Li-APo) were measured on pre-treatment and pre-surgical lateral cephalograms whereas crowding was measured on digitised pre-treatment study models. Pearson’s correlation (p <0.05) was used to assess the correlation of crowding with LIA and Li-APo changes, and prediction of the lower incisor decompensation was conducted using linear regression analysis. Results showed lower incisors were retroclined at 79.84° ± 7.08° and positioned ahead of APo line by 6.52 mm ± 2.97 mm at the start of treatment. Pre-surgical LIA and Li-APo were found to increase following orthodontic decompensation to 90.43° ± 5.96° and 10.34 mm ± 3.25 mm, respectively. There was a moderate positive correlation (r = 0.592) between crowding and Li-APo changes which was statistically significant, p value = 0.004, and had a strong predictor with 31.8% predictability. However, LIA showed a weak correlation (r = 0.329) with crowding and was not statistically significant (p = 0.135). Li-APo changes during orthodontic decompensation can be predicted with 31.8% predictability using the formula; Li-APo change = 2.064 + 0.503 (crowding).