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The purpose of the study was to investigate the risk of severe apical root resorption after orthodontic treatment with fixed appliances in relation to resorption after initial treatment, 6–9 months; and in relation to apical root form. The risk of severe apical root resorption in relation to resorption after 6–9 months of treatment was studied on 390 upper incisors in 98 consecutive patients (55 boys, 43 girls). Intra-oral radiographs before treatment, after 6–9 months and after treatment were evaluated. The importance of the root form (normal, short, blunt, apically bent, pipette shaped) for root resorption was studied on 610 upper incisors in 153 patients (75 boys, 78 girls). Intra-oral radiographs before and after treatment were evaluated. Treatment was performed with an edgewise or a Begg technique and lasted from 11 to 29 months. An index from 0 to 4 (Fig. 1) was used for the evaluation of the degree of root resorption. Root resorption after treatment was significantly related to the resorption after the initial 6–9 months. The results indicate a risk of severe resorption in teeth with minor resorptions after 6–9 months. Even an irregular root contour after 6–9 months indicates a risk of severe resorption. No-severe resorption was found after treatment in teeth without resorption after 6–9 months. The degree of root resorption in teeth with blunt or pipette shaped roots was significantly higher than in teeth with a normal root form.
Levander et al. (Mon,) studied this question.