American Board of Orthodontics (ABO) Discrepancy Index and peer assessment rating (PAR) index with models versus photographs

•The American Board of Orthodontics Discrepancy Index method on photographs appears to be more reliable than the peer assessment rating for grading pre-treatment and severe malocclusions.•The findings may help encourage peer assessment and self-assessment.•Owing to their lower cost, and the ease of transporting and storing them, photographs sometimes are the only available evaluation tool in epidemiologic studies. The objectives of this study were to determine whether rating systems, such as the Peer Assessment Rating (PAR) and the American Board of Orthodontics Objective Grading System (ABO-OGS) can be applied to intraoral photographs. Models and photographs of 50 cases were graded by 4 raters, and a 20% repeat of randomized cases was completed 2 weeks later. Intraclass correlation coefficients (ICCs) were used to assess inter- and intra-rater agreements, as well as the level of agreement between the ratings on models and photographs. The intra- and inter-rater agreements were considered good to excellent. The paired mean difference (model minus photo) for the PAR index and the ABO Discrepancy Index as a total was 2.405 and 1.156, respectively. Overjet was the subdomain that produced the highest differences between photos and models. The ABO- Discrepancy Index method on photographs was more reliable than the PAR index when grading pre-treatment and more-severe malocclusions. Both methods can be used, but the choice depends on the purpose of the evaluation, and on consideration of the weaknesses and strengths of each relating to its use on photographs.