Changes in chin position and morphology in response to orthodontic treatment with premolar extraction

Abstract

Objectives Premolar extraction is a common therapeutic strategy in orthodontic treatment, which helps to achieve an aesthetic profile by adjusting the positional relationship between nose, lip and chin. This retrospective study aimed to examine the chin changes in response to premolar extraction and develop predictive models. Materials and Methods A total of 135 adults requiring orthodontic treatments with four premolars extraction were included in the study and the cephalometric indications for their chin changes, as well as other skeletal, dental and soft tissue changes were measured with lateral cephalograms. Morphometric analysis, Pearson’s correlation analysis and multivariate regression analysis were conducted to recognize the potential factors contributing to chin changes. Results Soft tissue pogonion (sPog) point advancement relative to both subnasale (Sn) vert plane and nasion-B (NB) plane was observed. The soft tissue thickness of boney gnathion-soft tissue gnathion (Gn-sGn), Z angle and mentolabial sulcus’s angle increased. Patients with larger ANB angle, longer and thicker upper lips showed less forward movement of chin. Patients with more protruded incisors may have greater changes in chin position and morphology. Additionally, changes of sella nasion point B angle (SNB), occlusion plane and the incisor position by premolar extraction can also influence the post-orthodontic chin position and morphology. Conclusions The position and morphology of chin changed in response to orthodontic extraction. Orthodontists should pay attention to sagittal skeletal pattern, occlusion plane, incisor position, soft tissue morphology and age before and during treatment, which were proved to be related to the chin changes. Clinical Relevance Clarifying and predicting the chin change caused by orthodontic extraction will facilitate treatment planning and physician-patient communication.