To assess the outcome quality of subjects treated with a completely customized lingual appliance (CCLA) in a postgraduate university program, using the ABO Objective Grading System (OGS), by testing the null-hypothesis of a significant proportion of post-treatment cases exceeding an adjusted ‘exam failure’ threshold value of OGS=24.

This retrospective single-arm study included 66 consecutively debonded CCLA cases (m/f 19/47; mean age: 25.1±9 years) treated at Hannover Medical School (MHH, Hannover, Germany). The discrepancy index (DI) was assessed on initial plaster casts. The OGS of the cast-radiograph evaluation was scored for both set-up and post-treatment casts, including the seven components of alignment/rotation, marginal ridges, buccolingual inclination, overjet, occlusal contacts, occlusal relationships and interproximal contacts, to parameterize differences between those.

DI score distribution (≥20, <20) was 25 (37.9%)/41 (62.1%) subjects. Mean initial DI was 17.3±8.5. Mean set-up OGS was 10.4±4.4 (min-max: 3–21), mean final OGS was 17.7±5.9 (min-max: 7–33), and the difference 7.3 (post-treatment - set-up) was statistically significant (p<0.0001; 95% CI [5.8, 8.7]). The null-hypothesis was rejected: A statistically significant proportion of the final casts (n=58; 87.8%) scored below OGS=24 by exact binomial test (P<0.0001; 95% CI [77.5%, 94.6%]). The rate of a final OGS score<24 was not significantly different (P=0.98) between both DI (≥20, <20) groups.

The outcome quality of the CCLA treatment in this postgraduate university setting was high and therefore sufficient for a vast majority of treated cases to pass the ABO-OGS clinical examination.