Long-term posttreatment changes measured by the American Board of Orthodontics objective grading system

Background: The American Board of Orthodontics (ABO) developed the objective grading system (OGS) to evaluate cases submitted as part of the phase III examination for board certification. This study examines the long-term changes in 6 of the 8 criteria measured by the board, with an emphasis on the relationship between posttreatment results and subsequent improvement or worsening. Material: One hundred subjects were randomly chosen from the postretention archives of the Department of Orthodontics at the University of Washington. Pretreatment peer assessment rating (PAR) scores and posttreatment and postretention OGS scores were measured on study casts. The ABO criteria studied were alignment, marginal ridges, buccolingual inclinations, occlusal contacts, occlusal relationships, and overjet. Interproximal contacts and root angulations were not scored. Results: The mean overall OGS score at posttreatment was 21.5 points. At postretention, this score had improved significantly, by approximately 4 points. When comparing posttreatment scores and long-term changes, similar patterns were seen for all criteria, except alignment; increased posttreatment scores were associated with increased long-term improvement. Well-treated cases tended to deteriorate, and poorly finished cases tended to improve, illustrating a regression to the mean. Alignment was the only criterion associated with a mean long-term worsening, as well as a less predictable pattern of change. Conclusions: The results of this study indicate that settling occurs after orthodontic treatment, and that the attainment of perfect occlusal results does not ensure stability.