Orthodontic treatment has been associated with apical root resorption for many years, but a consensus on treatment-related causes of apical resorption cannot be found in the literature. Factors often quoted in orthodontic texts are: magnitude of force application, duration of treatment, morphology of teeth and the nature of the adjacent bone. Radiographic evidence of pretreatment root resorption is also felt to be a significant factor. The problem is that, when reading the literature, reports that support or refute the above claims can be found in equal numbers.

The best way, from a scientific point of view, would obviously be to investigate all of the above factors with a prospective randomised clinical trial, but of course it would be unethical to do so. Indeed, now that the use of postorthodontic treatment radiographs is not considered a routine requirement, retrospective studies will also be more difficult to carry out.

This paper investigated treatment-related aetiological factors of EARR through meta-analytic assessment. Meta-analysis is the statistical analysis of a sample of analyses taken from individual studies for the purpose of integrating findings to produce a greater weight of evidence. The authors found around 150 studies investigating EARR in relation to orthodontics, but only nine met their inclusion and exclusion criteria as detailed in the above summary.

Their results support the anecdotal evidence believed by many clinical orthodontists, that the degree of root resorption is correlated with the distance the apex of an incisor moves and the length of time of the orthodontic treatment. My only criticism of the paper is the decision to exclude patients and studies with a history of prior root resorption. Although I can understand the reason for this, as a clinical orthodontist it would be very useful to have some evidence to support or refute the claim that such patients would be more prone to resorption during orthodontic treatment or indeed whether it is appropriate to treat such cases.

This study highlights two important issues. First is the fact that fewer than 10% of published studies could be included in what I thought were fairly generous inclusion criteria. The need for consistent research methods in this important area of clinical dentistry is once again highlighted. Secondly, factors such as magnitude of the force applied and morphology of teeth, factors that are anecdotally associated with root resorption, cannot be quantified.

Practice point

  • Patients who require prolonged orthodontic treatment or treatment involving a significant degree of tooth movement should be warned about resorption prior to orthodontic treatment.