Therapeutic Yield of Orthodontic Treatment in Acceptability of Occlusal Condition

Fixed orthodontic treatment (FOT) is expensive and time-consuming, but few studies have evaluated long-term outcomes.

Objective: 1) to identify pre-treatment orthodontic characteristics predictive of FOT provision in a representative population of 13-year-olds; 2) to estimate therapeutic yield of FOT among groups classified according to their pre-treatment orthodontic characteristics.

Methods: Prospective, observational cohort study of 3,925 13-year-olds attending the South Australian Dental Service in 1988/89. At enrolment in the study 10 Dental Aesthetic Index (DAI) traits were measured. In 2006 1859 subjects were traced and 632 completed a questionnaire that asked about history of FOT. 421 also were re-examined to record their DAI at 30 years of age. A favourable outcome was defined as a reduction of 5+ in DAI between 13 and 30 years. Probability of a favourable outcome was compared between FOT and non-FOT subjects and number-needed-to-treat (NNT) was computed as a nomogram of therapeutic yield for all people and groups stratified by pre-treatment DAI.

Results: At enrolment, 45% had acceptable (DAI <26), 15% had borderline (DAI 26-30), 10% had unacceptable (DAI 31-35) and 15% had very unacceptable (DAI 36+) occlusal conditions. 35% subsequently received FOT and 34%, 21%, 18% and 28% of treated subjects had acceptable, borderline, unacceptable and very unacceptable pre-treatment DAI scores respectively. Using the threshold of a decrease in DAI of 5 units to define a beneficial yield, NNT for all subjects was 4 (95%CI = 3 to 6). Stratifying subjects by 13-year-old DAI at 36+ vs <36 lead to NNT of 14 (-16 to 4; ns-non-significant benefit or harm)and 6 (4 to 13); stratifying at 31+ vs <31 lead to NNT of 6 (4 to 21) and 9 (5 to 8275); and, stratifying at 26+ vs <26 lead to NNT of 5 (4 to 9) and 17 (-26 to 6; ns)respectively.

Conclusion: A high proportion of FOT was targeted to people with acceptable or very unacceptable occlusal conditions where FOT did not produce a beneficial therapeutic yield in acceptability of occlusal condition. Supported by NHMRC # 299057.