Abstract
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).
Highlights
There are a few approaches to treating a Class III malocclusion but in severe cases where skeletal deformity is too great to be masked by orthodontic camouflage alone, orthognathic surgery is recommended
Patients who require combined orthodontic-orthognathic approach will undergo pre-surgical orthodontic treatment to remove this natural compensation which is followed by orthognathic surgery
This study aimed to investigate the relationship between crowding and lower incisor changes upon orthodontic decompensation, and to predict the changes of lower incisor based on the amount of crowding
Summary
There are a few approaches to treating a Class III malocclusion but in severe cases where skeletal deformity is too great to be masked by orthodontic camouflage alone, orthognathic surgery is recommended. It involves surgical repositioning of the maxilla, mandible and dentoalveolar segments to achieve occlusal and facial harmony [1]. Aligning the teeth back to their ideal axial inclination usually leaves the patient looking worse temporarily, with an increase in the reverse overjet This step is necessary so that both the maxillary and mandibular arches will coordinate after orthognathic surgery [4]. In non-extraction cases, space gain in the lower arch is mainly achieved from uprighting of buccal segments and arch lengthening via lower incisor proclination and protrusion
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