Changes in incisor relationship over the life course - Findings from a cohort study

Objective: The aim of this longitudinal cohort study was to investigate the changes in incisor relationship over three decades from adolescence to mid-adulthood. Materials and Methods: The sample included 1,037 children (48.4% female) born between April 1972 and March 1973 from the longitudinal birth cohort Dunedin Multidisciplinary Health and Development Study. Overjet and overbite values were assessed at age 15 and 45 years and entered in a regression model as outcome variables. Baseline occlusal variables, sex, history of orthodontic treatment, periodontal data recorded at age 38, and self reported oral parafunction and orthodontic treatment history recorded at age 45 were entered as covariates in the regression analysis. Results: Regression modelling showed that overjet/overbite category (high or low) at age 15 tends to predict overjet/overbite category at age 45, with overjet become slightly larger (around +0.5 mm) and overbite slightly lower (-0.5 mm) over time. Study members with self-reported tooth clenching had a slighter greater overbite (+0.3 mm) at age 45 than those who did not. Additionally, those with signs of periodontal disease at age 38 had a slightly larger overjet (+0.5 mm) at age 45 than those without disease. Sex differences were demonstrated with females having 0.6 mm larger overjet, and 0.4 mm overbite at age 45. Conclusions: Overall, overjet values tend to be higher during mid-adulthood than during adolescence, while the converse is true for overbite. There appears to be a degree of sexual dimorphism in overjet and overbite values later in life. Clinical Significance: Incisor relationships change during the life course and are related to ageing, sex, periodontal health, and parafunctional habits. Clinicians and educators should be aware of these changes when making treatment decisions that alter incisor relationship.