Evaluation of changes in clinical crown length of lower anterior teeth after treatment with Frankel-2's appliance.

Purpose: The aim of this study was to test the null hypothesis that there is no change in the lower anterior teeth's crown size when measured just after the treatment with Frankel-2's orthopedic appliance and in a long-term posttreatment follow-up. Materials and Methods: The sample was composed of 34 plaster models belonging to 9 male and 8 female individuals, treated at the College of Health, Methodist University of Sao Paulo, Sao Bernardo do Campo, Sao Paulo, Brazil, with mean age of 12 years and 6 months (standard deviation [SD] =7 months) at T1 (end of the treatment with Frankel-2's function regulator), and 19 years and 8 months (SD = 7 months) at T2 (7.11 years after the end of the treatment). Results: The distance from the incisal edge to the most concave portion of the gingival margin of the lower incisors and canines was measured using a digital caliper. Data analysis was carried out by means of Student's t-test and paired-t test. Among the lower anterior teeth, the teeth 31, 33, 42 and 43 showed a statistically significant increase in their crown length, whereas the teeth 32 and 41 showed no changes. Conclusion: It can be concluded that there is a tendency to increase the clinical crown of lower anterior teeth throughout the years after the mandibular advancement treatment by using functional devices, rejecting the null hypotheisis.