Abstract
BACKGROUND AND OBJECTIVES: The curve of Spee is a naturally occurring phenomenon in the human dentition. Leveling the curve of Spee can affect the Frankfort-mandibular plane (FMP) Angle and thus the lower anterior facial height. This study examined the degree of change in FMP angle after leveling the curve of Spee in different malocclusion groups. METHODS: In this study, 75 patients who were aged >14 years and had undergone fixed appliance therapy using a 0.022-slot MBT bracket system were included. The pre- and post-treatment casts and lateral cephalograms of the patients were divided into three groups, namely Class I, II, and III malocclusions, with 25 patients in each group. The curve of Spee and FMP angle were measured before and after orthodontic treatment, and their correlation was evaluated. RESULTS: After leveling the curve of Spee, the FMP angle decreased in Class I and II groups and increased in Class III group. These results were statistically significant except in Class I malocclusion group. A mild positive correlation was observed between the curve of Spee and FMP angle in Class I and III malocclusion groups and a negative correlation in Class II malocclusion group. CONCLUSION: The change in FMP angle, following the leveling of the curve of Spee, in Class II and III malocclusion group, is attributed to alterations in lower anterior facial height. The study observed a mild positive correlation between the curve of Spee and FMP angle in Class I and III malocclusion groups and a negative correlation in Class II malocclusion group.