Dental casts of 1016 patients were evaluated for the long-term treatment ou
tcome using the Peer Assessment Rating (PAR) index. The PAR index was measu
red at the pretreatment stage (n = 1016), directly posttreatment (n = 783),
postretention (n = 942), 2 years postretention (n = 781), 5 years postrete
ntion (n = 821), and 10 years postretention (n = 564). The mean absolute ch
ange 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 r
etainer at the postretention stage and up to 10 years postretention. Drop-o
ut 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 pl
ace in the first 2 years after retention. All occlusal traits relapsed grad
ually over time but remained stable from 5 years postretention with the exc
eption of the lower anterior contact point displacement, which showed a fas
t 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 fix
ed 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 limitati
ons in order to better meet their expectations.