Stability of orthodontic treatment outcome: follow-up until 10 years postretention.

Dental casts of 1016 patients were evaluated for the long-term treatment outcome using the Peer Assessment Rating (PAR) index. The PAR index was measured at the pretreatment stage (n = 1016), directly posttreatment (n = 783), postretention (n = 942), 2 years postretention (n = 781), 5 years postretention (n = 821), and 10 years postretention (n = 564). The mean absolute change as well as the percentage of change per year (relapse) related to the postretention stage was calculated. An analysis of variance was applied to compare the mean change in the PAR between cases with and without a fixed retainer at the postretention stage and up to 10 years postretention. Drop-out analysis showed that more Class II Division 2 cases were lost to follow-up than cases of other Angle classes. The results indicate that 67% of the achieved orthodontic treatment result was maintained 10 years postretention. About half of the total relapse (as measured with the PAR index) takes place in the first 2 years after retention. All occlusal traits relapsed gradually over time but remained stable from 5 years postretention with the exception of the lower anterior contact point displacement, which showed a fast and continuous increase even exceeding the initial score. The presence of a fixed retainer had a positive effect on the PAR score. In cases with fixed retention, the relapse was 3.6 PAR points less at 5 years postretention and 4.6 points less at 10 years postretention. The results of this type of studies enable clinicians to inform their patients about treatment limitations in order to better meet their expectations.