Orthodontic treatment outcome: the relationship between anterior dental relations and anterior inter-arch tooth size discrepancy.

Objective: This study investigated the pre- (T1) and post-treatment (T2) relationship between anterior (canine to canine inclusive) inter-arch tooth size ratio and various dental and skeletal variables.

Design: Retrospective longitudinal clinical study.

Setting: Swedish Health Board Clinic 2000.

Subjects: Random selection of T1 and T2 orthodontic records of 137 Swedish patients (56 male and 81 female). The sample included non-extraction (77), and four premolar extraction (60) cases across a range of dental and skeletal malrelationships.

Main Outcome Measures: Dental cast and lateral cephalogram measurements were recorded. Exploratory modelling investigated whether a significant relationship existed between the anterior inter-arch tooth size ratio and these measurements.

Results: Data was normally distributed with no statistically significant differences between males and females (P = 0.88) and extraction and non-extraction (P = 0.52) treatment modalities with respect to the anterior ratio. T1 bivariate regression analysis failed to show a relationship (p < 0.05) between variables. T2 bivariate analysis showed a statistically significant relation between three variables and anterior tooth size ratio. Multiple regression analysis led to a final model where maxillary inter-canine width (P = 0.002) and upper arch crowding (0.001) were statistically significantly related to the anterior inter-arch ratio. The coefficient of determination was however uniformly low (R(2) < 0.2) for all variables.

Conclusion: The anterior inter-arch tooth size ratio was not associated with any common pre- or post-treatment variables in the population studied, therefore measurement of an anterior tooth size ratio pre-treatment was not clinically beneficial for determining anterior dental relations post-treatment.