The mesiodistal angulation and faciolingual inclination of each whole tooth in three dimensional space post non-extraction orthodontic treatment

Background: In a recent study by Tong et al. (2012), 76 subjects with near-normal occlusion, who were never orthodontically treated, were studied using CBCT to measure the mesiodistal angulation and faciolingual inclination of each whole tooth (crown and root) in 3-dimensional space. The study provided a standard for positioning each whole tooth properly in the arches.;Purpose: In this study, a subset of the 76 subjects was studied after they were orthodontically treated with non-extraction treatment. The purpose of this study is to determine the changes in mesiodistal angulation and faciolingual inclination after orthodontic treatment was rendered.;Methods: Of the 76 patients from the previous study, 24 of them also had CBCT records taken at the completion of the non-extraction orthodontic treatment. Their final CBCT records were digitized using the custom University of Southern California root vector analysis software program. Paired t-tests were used to compare pre- and post-treatment values for mesiodistal angulation and faciolingual inclination.;Results: Results of the paired t-tests showed that there was a statistically significant difference for the mesiodistal angulation value of lower first molars and faciolingual inclination values of upper second premolars and lower first molars after orthodontic treatment was rendered. The range of change was larger and pattern of change was more variable from tooth to tooth in mesiodistal angulation than in faciolingual inclination measurement.;Conclusion: The mesiodistal angulation and faciolingual inclination of each tooth was maintained throughout orthodontic treatment, except upper second premolars and lower first molars. This may be due to difficulty of determining proper band position for lower first molars and poor visibility for bracket position of upper second premolars. Bracket position may affect mesiodistal angulation more than faciolingual inclination in the final outcome of non-extraction treatment. More studies with larger sample sizes are needed.