The American Board of Orthodontics (ABO) released in 1999, objective study cast grading criteria for evaluating cases presented for the phase 3 ABO examination. These criteria could be construed as measures of patient care quality. Objectives: To test if quality of first premolar extraction treatment in an orthodontic training program has changed since the program's inception 40 years ago. Methods: Post treatment study casts of 40 patients completing treatment in the late 1950s (group A) were compared with 40 patients completed in year 2000 (group B). The ABO Grading System criteria provided 15 variables that were measured by a single operator using the ABO measuring gauge. Mean total scores were tallied and compared to the suggested ABO study cast plus radiographic self-assessment guidelines for passing (20) and failure (30). Results: Independent t-testing revealed that treatment time increased in group B (27.8 vs 22.1 months, p=.008). Two of 15 ABO criteria variables were greater in group B than group A: lower posterior alignment (2.3 vs 1.5, p=.004) and lower molar bucco-lingual inclinations (4.1 vs 2.8, p=.000). Three of 15 criteria were greater in group A than group B: upper anterior alignment (1.1 vs 0.3, p=.000), lower anterior alignment (0.9 vs 0.3, p=.002), and upper interproximal contacts (3.9 vs 2.5, p=.002). ABO Grading System total mean score for study casts only (without radiographic appraisal) for group A was 35.8 and group B was 32.4 (p=.104). Conclusions: Of the 15 ABO Grading System criteria used in this study to test the quality of first premolar extraction treatment results, 3 criteria improved, 2 worsened and treatment time increased from orthodontic training program inception four decades ago to present.

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