Meta analysis of the treatment-related factors of external apical root resorption.

OBJECTIVE To elucidate possible treatment-related etiological factors--such as, duration of treatment and apical displacement--for external root resorption.

DESIGN Meta-analysis of the available English-language literature.

INCLUSION & EXCLUSION CRITERIA Papers with a sample size > 10, fixed appliances, pre- and post-operative radiographs, and apical displacement recorded were included. History of trauma, prior root resorption and endodontic treatment were excluded. Appropriateness of these selections was tested with a 'funnel plot' analysis.

OUTCOME MEASURE Correlations between root resorption, apical displacement, and treatment duration.

RESULTS Mean apical root resorption was strongly correlated with total apical displacement (r = 0.822) and treatment duration (r = 0.852).

CONCLUSION The treatment-related causes of root resorption appear to be the total distance the apex had moved and the time it took.