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

Abstract

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 (R² < 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.

Keywords:

• Bolton ratio
• inter-arch tooth size ratio
• tooth size
• tooth size ratio

Acknowledgments

We wish to thank the staff of the Public Orthodontic Clinic in Halmstad, Sweden for facilitating the measurement and analysis of their orthodontic records. Thanks also to Dr Alan Kelly and Dr Bernard McCartan for statistical advice, and to Dr Marielle Blake for assistance in the preparation of this manuscript.