Introduction & Objective: The peer assessment rating index (PAR) has been developed to provide a single summary score for all the occlusal anomalies, which may be found in a malocclusion. The score provides an estimate of how it may deviates from normal alignment and occlusion. Reduction of score after treatment reflects the degree of improvement and, therefore, the success of treatment. The aim of this study was assessment of outcome of removable orthodontic treatment performed by under graduated dental students in orthodontic department of Hamadan dental school.

Materials & Methods: In this descriptive- analytical study pre- and post-treatment dental casts of 70 patients were studied. According to PAR Index following variables were evaluated: upper right segment, upper left segment, upper and lower anterior segments, lower right segment, lower left segment, over jet, overbite, midline and right and left buccal occlusion. Weighted PAR score was given to the rough score of every component and final score were compared usingWillcoxon test before and after the treatment.

Results: Results showed the differences between the pre- and post-treatment score of upper anterior segment, midline and left buccal occlusion were not significant (P>0.05). However, the pre- and post-treatment score of lower anterior (P =0.039), overjet (P =0.001), overbite (P=0.004) and right buccal segment (P =0.037) had significant differences. The mean of PAR score showed significant difference between pre-treatment (18.2± 0.94) and post-treatment (10.8 ± 0.68) in dental casts (P =0.001).

Conclusion: According to the results of this study, 38.6% of patients had "worse or non different" degree, 57.1% had "improvement" degree and 4.3% had "greatly improvement" degree.