Resorption of maxillary incisors after orthodontic treatment--clinical study of risk factors.

INTRODUCTION External apical root resorption (EARR) is one of the major problems associated with orthodontic treatment. Such lesions represent an iatrogenic risk that must be detected as early as possible, with regular radiological follow-up and appropriate therapeutic precautions. The causes and mechanisms leading to susceptibility to root resorption following the application of an orthodontic force are often not clear and are generally said to be of multifactorial origin. The aim of this clinical study was to analyze the factors linked to the occurrence of moderate to severe resorption (MSR) of upper incisors during orthodontic treatment in a group of Moroccan patients treated in the Dento-Facial Orthopedic Department of the Dental Consultation and Treatment Center (Centre de consultation et de traitements dentaires [CCTD]) in Rabat. MATERIAL AND METHODS A total of 82 patients (28% males, 72% females) aged between 12 and 27, with various malocclusions, who had been treated with fixed appliances for at least 1 year and for whom panoramic X-rays at the start, during and at the end of treatment were available, were selected randomly. The reduction in maxillary incisor root length was evaluated using resorption scores. The factors studied in relation to the risk of occurrence of MSR were: age, sex, treatment duration, extraction or non-extraction, type of malocclusion (Class I arch-length discrepancy, Class II, Class III), the vertical diagnosis (normal, supraocclusion, open bite), presence of dysfunction, impacted canines and root morphology. Statistical analysis was performed using SPSS software, version 18.0. Statistical tests used were: Kaplan-Meier analysis and the univariate and multivariate Cox models for the study of factors associated with MSR. The threshold of significance adopted was 0.05. RESULTS The factors that were significantly associated with the occurrence of MSR at the level of the upper incisors were: tooth type, with a greater risk for the lateral incisor (HR=3.2 95% CI [2.3-4.5] P<0.001), treatments with extraction (HR=1.64 95% CI [1.16-2.33] P<0.05), the presence of supraocclusion (HR=2.17 95% CI [1.33-3.53] P<0.05) or open bite (HR=3.12 95% CI [1.66-5.86] P<0.001) and root malformation (HR=1.5 95% CI [1.09-2.07] P<0.05). Age, sex, type of malocclusion, dysfunction and impaction of canines were not associated at a statistically significant level with the risk of occurrence of MSR of the upper incisors. CONCLUSION EARR is difficult to avoid; the orthodontist's role remains crucial in identifying risk factors so as to adopt a treatment strategy taking these factors into account. In our population, the risk of MSR in the upper incisors appeared to increase in treatments with extraction, situations of supraocclusion or open bite, and in the presence of root abnormalities. Finally, clinical recommendations for the prevention of the occurrence of MSR of the maxillary incisors are proposed, taking into account all the risk factors identified.