Introduction: Norms for mandibular growth are well-established, but they have large variances, and no research has been conducted on how practitioners use them in clinical judgment to guide the treatment of individual patients.
Methods: Co-Pog projections of mandibular growth were combined from the Burlington and Michigan growth studies following statistical adjustments. Cervical measures were also evaluated. Photographs of complete records for 2 males and 2 females aged approximately 12 years with mandibular length matched age and sex norms were presented to 29 practicing orthodontics. Initial treatment plans and changes in treatment, if any, were noted across a projected range in 2-year mandibular growth.
Results: A large variance was noted in the growth norms. Stepwise multiple regression found insignificant improvements in predictions when cervical vertebral maturation scores were added to age and sex. Comparably large variation was also observed across practitioners in their initial treatment plans given common patient information. Moreover, 4 in 10 practitioners would not change their initially proposed treatment, given growth projections varying between 0-7 mm over 2 years. Others were sensitive only to small or large changes or used a range smaller than the variance in the norms. Between a quarter and a third of the variance in changed treatment plans was a function of differences between practitioners, whereas almost none was attributable to expected growth in patients.
Conclusions: This study represents the integration of the established literature with practitioner experience called for in the American Dental Association concept of evidence-based dentistry. It was found that there was substantial variance in both established norms for mandibular growth and the role claimed for precise estimates of growth play in treatment planning. The latter appears to be the larger of the two.
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