Skeletal and dental effects of maxillary protraction in patients with angle class III malocclusion. A meta-analysis

The aim of this study was a quantitative review of the published results concerning the treatment effects of maxillary protraction in patients with Angle Class III using the meta-analysis method. 85 articles published between 1966 and 1998 were reviewed under strict, pre-defined criteria. Of these, 12 studies presenting results of cephalometric measurements were selected for further analysis. The results of different cephalometric measurements were reviewed with Dstat 1.10 software in order to calculate a standardized treatment effect variable. The homogeneity of the variances of the different effect variables as well as a composite effect were calculated. For the latter, each individual effect variable was weighted by the reciprocal of its variance, with predefined study characteristics being used for categorical model calculations. Our results showed a significant composite effect of the therapy on the skeletal components (SNA: 1.4 degrees, composite effect = 1.11; SNB: -1.3 degrees, composite effect = -0.94; ANB: 2.6 degrees, composite effect = 1.73; lower anterior face height: 1.6 mm, composite effect = 0.85) as well as on the dental components of the face (inclination of upper incisors: 1.6 degrees, composite effect = 0.37; inclination of lower incisors: -3.7 degrees, composite effect = -0.87). However, several of the individual effect variables demonstrated a significant lack of homogeneity. Study characteristics which might possibly account for this variability were the patients' ages at the start of treatment and the combination of maxillary protraction with rapid maxillary expansion. In summary, maxillary protraction was shown to have a significant treatment effect. The meta-analysis method proved to be a valuable tool in judging the current status of a given clinical therapeutic concept.