A comparison of orthodontic treatment outcomes using the Objective Grading System (OGS) and the Peer Assessment Rating (PAR) index

INTRODUCTION: The use of objective criteria is essential to uniformly quantify and measure the severity of malocclusions and the efficacy of different treatment modalities. The Peer Assessment Rating (PAR) index and, more recently, the American Board of Orthodontics Objective Grading System (OGS) were developed to fulfill this need.

AIM: The aim of this retrospective study was to assess and compare treatment outcomes using the UK and US weighted PAR and the OGS.

MATERIALS AND METHODS: The sample consisted of randomly selected records of 50 patients treated by residents in one postgraduate orthodontic clinic. UK and US weightings for the PAR index were applied and compared with OGS.

RESULTS: There was no statistically significant association between the OGS and the PAR index grading systems. Neither the UK nor the US PAR weightings showed statistically significant correlation with the OGS. All cases were 'greatly improved' or 'improved' according to the PAR index, while most cases (62%) failed according to OGS. There was a statistically significant correlation between the unweighted PAR index and the OGS (r = -0.32, p = 0.024). The US and the UK weightings for the PAR were highly correlated (r = 0.90, p < 0.001). Both weighting systems were also highly correlated with the unweighted PAR (p < 0.001). There were no gender differences found in any of the scoring systems.

CONCLUSIONS: The current PAR index cannot replace the OGS for evaluating treatment outcomes. The current OGS cannot detect the improvement achieved in a treated case.