Pattern and amount of change of upper front teeth after retention with a bonded retainer : Follow-up one to seven years postretention

Abstract

Objectives: To investigate the amount and pattern of relapse of maxillary front teeth previously retained with a bonded retainer for two to four years. Which teeth are more prone to relapse? Is there any difference in behavior between contact point displacement and rotation? What is the magnitude of the relapse in short-term and long-term? Materials and Methods: The study group originally consisted of 45 patients, and 27 patients on recall for the second study. Recordings from study models before treatment (T1), at debonding (T2), one year after removal of the retainer (T3) and seven years postretention (T4) were present. All patients had been treated with fixed edgewise appliances by the same operator. The irregularity index (sum of contact point displacement [CPD]), and rotations of front teeth in relation to the Raphe line and intercanine distance, were calculated at T1, T2, T3 and T4. Statistical analysis: Paired t-test, Pearson’s product-moment correlation and Pearson’s productmoment correlation coefficient were applied. For all statistical analyses, the statistical significance level was set to 5%. Results: Before treatment (T1), the mean irregularity index was 10.1 (range 3.0– 29.9). The largest displacements were recorded between laterals and centrals followed by the displacement between laterals and canines. The smallest deviations were found between the centrals. After treatment (T2), the mean irregularity index was 0.7 (range 0.0–2.1). There was a significant difference in the index between T1 and T2 (P <.0001). One year postretention (T3), the mean irregularity index was 1.4 (range 0– 5.1). There was a significant difference in the index between T2 and T3 (P <.0001). Results from the second study showed that there were no statistically significant differences between the change in mean CPDs for the contacts canines/laterals, laterals/centrals, or centrals/centrals. The mean irregularity 9����index for the 27 patients examined in the second study was 10.3 (range 3.7- 29.9) at T1, 0.9 (range 0.0-2.1) at T2, 1.3 (range 0.0-3.5) at T3 and 2.0 (range 0.0-5.8) at T4. No correlations were found between the pretreatment and postretention irregularity T1/T3 and T1/T4. There was a significant association between the irregularity index at T3 and T4 (R = 0.938, P < .0001). The irregularity index of the maxillary front teeth changed very little or not at all during the first year postretention. Further changes long-term resulted in an irregularity index of mean 2.0 mm (range 0.0 – 5.8). The contact relationship between the laterals and centrals seems to be the most critical. Forty rotated teeth in 21 patients were corrected more than 20 o. Mean relapse during the first year postretention was 6.7 degrees (range 0.0-14.7). Mean changes during seven years were 8.2 degrees (range 0.0-19.3). Conclusions: Minor or no relapse in short-term follow-up (one year) was noted in the maxillary front after correction of irregularity and a two to four year period of bonded retention. Further, small relapses occurred long-term i.e. at mean seven years postretention. No significant relation was found between the amount of correction of contact point displacement and magnitude of relapse neither in one nor seven years postretention. There was a strong correlation between irregularity one and seven years postretention. Stable cases one year postretention are stable in the longterm and cases with small changes one year postretention tend to deteriorate with time. Most of the rotational relapse was seen one year postretention with small changes long-term. There was a significant positive correlation between the amount of correction of incisor rotation and the magnitude of relapse. Of the over corrected contacts, only 50 percent returned to perfect alignment. Laterals are more prone to relapse. If, after a three year period of retention, a decision is made to use permanent retention of the maxillary front teeth, a retainer bonded to only the incisors seems to be a relevant choice.