Apical root resorption six and 12 months after initiation of fixed orthodontic appliance therapy.

The low explained variance of identified risk factors for apical root resorption in orthodontic patients suggests effects of parameters related to individual predisposition. Our purpose was to explore this hypothesis. We evaluated standardized periapical radiographs of the maxillary incisors made before treatment (T1) as well as at about six and 12 months after bracket placement (T2 and T3) of 247 patients aged 10.1 to 57.1 years at T1. The radiographs were converted to digital images, and commercially available software was used to correct for differences in projection. The results showed that 20.2%, 7.7%, and 5.3% of the patients had > or =1 tooth with >2.0, 3.0, and 4.0 mm resorption at T3, respectively. Pearson's correlation revealed an association between resorption from T1 to T2 and from T2 to T3 (P < .01). The risk of > or =1 tooth with >1.0 mm resorption from T2 to T3 was 3.8 times higher (95% CI 2.4-6.0) in patients with > or =1 tooth with >1.0 mm from T1 to T2 than in those without. Also, resorption was more pronounced (P < .001) from T2 to T3 in patients with > or =1 tooth with >1.0 mm and >2.0 resorption from T1 to T2 than in those without. The explained variance of identified risk factors was <10%. Orthodontic patients with detectable root resorption during the first six months of active treatment are more likely to experience resorption in the following six-month period than those without.