The long-term benefits of orthodontic treatment

OBJECTIVE

This study aimed to evaluate post-treatment changes at least five years out of retention in a cohort of 100 consecutively started patients treated by a postgraduate student in a UK orthodontic department.

DESIGN

Analysis of study models using recognised occlusal indices. Setting Patients initially treated at Newcastle Dental Hospital were recalled for record collection.

MATERIALS AND METHODS

Study models and clinical photographs were taken for each patient attending for post-retention records. Weighted Peer Assessment Rating (PAR) Index and Index of Orthodontic Treatment Need (IOTN) scores were recorded for cases at the beginning, end and at least 5 years post-retention. Main outcome measures Post-treatment changes were evaluated using PAR Index and IOTN to evaluate extent and likelihood of change and to compare treatment modalities.

RESULTS

Seventy-eight patients attended for post-retention records. Overall PAR reduction immediately post-treatment was 68.6% and at a mean of 6.5 years post-retention was 55.5%. Dual arch fixed appliance treatments achieved the greatest reduction in PAR score, and maintained the reduction beyond the retention period better than other treatment modalities. Eighty-four per cent of the cohort still had some demonstrable improvement after a mean of 6.5 years post-retention. There was a residual need for treatment in 8% of cases on aesthetic grounds and in 24% of cases on dental health grounds.

CONCLUSIONS

Occlusal deterioration after orthodontic treatment is almost universal. Dual arch fixed appliance treatment provides the best post-treatment and post-retention result.

An ex vivo study to investigate bond strengths of different tooth types

This study aimed to identify the presence and pattern of differences in ex vivo shear bond strength between tooth types when bonding orthodontic brackets using Right-On, and took the form of a prospective laboratory study of bond strength on different tooth types, at the Newcastle University Dental School Materials Science Laboratory, 1997-1999. Ex vivo bond strength testing was undertaken using the technique described by Fox et al. (BJO 18, 125-130, 1991) on a total of 120 extracted incisor, canine, and premolar teeth of each dental arch. Analysis was by one-way ANOVA with Tukey's pairwise comparisons, and by Weibull Analysis. Shear stress to failure (measured in MPa) was recorded on Instron 5567 universal testing machine. Significant differences in mean bond strength existed between different tooth-type series. Canine (upper 12.3, lower 12.1) and premolar (upper 11.9, lower 10.9) teeth exhibited higher strengths than incisors (upper 6.9, lower 9.0). The results of this study confirm that ex vivo bond strength is not uniform across all teeth.