Risk factors associated with external apical root resorption of the maxillary incisors: a 15-year retrospective study

To determine the possible risk factors for external apical resorption (EARR) of the maxillary incisors.

Panoramic radiographs of 132 orthodontic patients with a mean age of 16.9 +/- 3.6 years were selected from two practice centres in Tehran. The radiographs were taken between 1990 and 2005 and 63.6% of the subjects were female. Mean, standard deviation and distribution of EARR for various variables were assessed. Prevalence significance, as well as differences between frequency distributions of clinical EARR (> or = 1.2 mm) between genders, treatment plans (extraction/ non-extraction), initial overjet and overbite magnitude, and incisor types (centrals/laterals) were evaluated by the chi-squared test. The mean resorption rates on central and lateral incisors were compared using the independent-samples t-test. Associations between EARR with the age, duration of treatment, pretreatment overjet and overbite were assessed by the Pearson's correlation test. The reliability of the method was determined by remeasuring 117 randomly selected incisors and determining the associations between both sets of measurements with the Pearson's correlation coefficients.

The prevalence of EARR, and clinical EARR (> or = 1.2 mm) were 91.8% and 44.78% respectively. The average of EARR was 1.377 +/- 1.214 mm, or 8.65 +/- 8.021% of pretreatment root lengths. The prevalence of clinical EARR was significantly higher in extraction cases, cases with greater initial overjet and on lateral incisors. Using the t-test, significant differences (p < 0.05) were observed between the extent of resorption between genders (higher in females), treatment plans (higher in extraction cases) and incisor types (greater on lateral incisors). Longer treatment times and excessive initial overjet were correlated with higher EARR levels (p < 0.05, r < 0.2).

Factors related to premolar extraction, initial ovejet size, treatment time and being female may be correlated with higher EARR. Clinically significant resorption did not occur more in females.