The relation between incisal guidance angle and the growth and development of temporomandibular joint: a multi-cross-sectional retrospective study

BACKGROUND The incisal guidance angle (IGA) is related to temporomandibular joint (TMJ), and changes to the IGA are often involved in the prosthetic and orthodontic treatment of anterior teeth. However, the influence of incisal guidance on the growth, development and remodelling of the TMJ is not yet clear. The aim of this study was to investigate age-related morphological differences in the TMJ in subjects with different IGAs. METHODS Cone-beam computed tomography (CBCT) images of 274 patients were included (group 1, IGA   60°). Each group was then divided into 4 age groups (group a, 6-12 years; group b, 13-16 years; group c, 17-25 years; group d, 26-33 years). TMJ morphology was assessed by linear measurements, angular measurements, and subjective evaluations. The IGA and occlusal plane angle were also measured. RESULTS Anterior inclination of condyle (AIC) increased with age in the three IGA groups but decreased from 17 years onward in group 2 (P   0.05). Articular eminence inclination (AEI) decreased with age in group 1 (P = 0.027) but increased with age in group 3 (P = 0.053). The AEI in group 2 was larger than that in group 1 at 17-25 years (P = 0.046), and it was larger in group 3 than in group 1 at 26-33 years (P = 0.047). The IGA had a weak correlation with AEI (P < 0.05). CONCLUSION The articular fossa of patients with shallower incisal guidance changed to a flatter shape with age, whereas the condylar anterior slope and articular eminence of patients with steeper incisal guidance changed towards a steeper alignment. There was a correlation between IGA and TMJ shape.