Data sources: Medline was the primary data source, with references of identified papers then being reviewed for additional studies.
Study selection: Studies were included if they were clinical trials, in English, of samples of greater than 10 subjects who had undergone fixed appliance orthodontic treatment and who had both pre- and postoperative X-rays available. A measurement of external apical root resorption (EARR) in maxillary incisors was essential as was a measure of displacement with the apex of the root as reference.
Data extraction and synthesis: Variables were coded and articles graded by three independent investigators who subsequently negotiated final coding and assessed the methodological soundness of each study. A cumulative 'meta-analysis factor' was computed for each article. Articles were evaluated on study design; population sample; treatment assignment; documentation of statistics; the accuracy of root resorption measurement and apical displacement of incisor roots. A funnel plot analysis did not identify publication bias.
Results: Eight articles were included in the statistical analysis. Two did not contain data for mean apical displacement and therefore correlations between mean EARR and mean apical displacement could not be calculated for them. The mean meta-analysis factor was 39 (range, 12-78). Mean root resorption was 1.421+/-0.448 mm (n=8), and mean apical displacement was 2.382+/-0.756 mm. The weighted correlation coefficient between mean root resorption and apical displacement was 0.822 and that between mean root resorption and treatment duration was 0.852.
Conclusions: This analysis suggests that treatment-related root resorption is correlated with the distance the apex moves and the length of time the treatment took.