Giulia Gay - Post-graduate School of Orthodontics, Lingotto-Dental School, Department of Surgical Sciences, University of Turin, Turin, Italy
Serena Ravera - Post-graduate School of Orthodontics, Lingotto-Dental School, Department of Surgical Sciences, University of Turin, Turin, Italy
Tommaso Castroflorio - Post-graduate School of Orthodontics, Lingotto-Dental School, Department of Surgical Sciences, University of Turin, Turin, Italy
Francesco Garino - Private Practice, Turin, Italy
Giovanni Cugliari - Department of Statistics and Quantitative Methods, University of Milano-Bicocca, Milan, Italy
Andrea Deregibus - Post-graduate School of Orthodontics, Lingotto-Dental School, Department of Surgical Sciences, University of Turin, Turin, Italy

Background Existing literature indicates that orthodontics patients are more likely to have severe apical root shortening, interesting mostly maxillary, followed by mandibular incisors. Objectives The aim of the present study was to investigate the incidence and severity of root resorption (RR) in mandibular incisors of adult patients treated with aligners. Methods The study group consisted of ۷۱ adult healthy patients (mean age ۳۲.۸ ± ۱۲.۷) treated with aligners (Invisalign®, Align Technologies, San Jose, CA, USA) for the intrusion of the lower incisors. Root and crown lengths of a total of ۲۷۹ lower incisors were measured in panoramic radiographs at the beginning (T۰) and at the end (T۱) of aligner therapy. Individual root-crown-ratio (RCR) of each tooth and therefore the relative changes of RCR (rRCR) were determined. Results ۴۴% of the ۲۷۹ measured teeth presented a reduction of the pre-treatment root length. A reduction in percentage of > ۰% up to ۱۰% was found in ۲۶.۷۶% (n = ۷۶), a distinct reduction of > ۱۰% up to ۲۰% in ۱۲.۳۲% (n = ۳۵) of the sample. ۴.۵۸% (n = ۱۳) of the teeth were affected by a clinically relevant reduction (> ۲۰%). Conclusions Orthodontic treatment with Invisalign® aligners could led to RR in cases in which intrusion of the lower incisors is planned. However, the incidence of RR is comparable to data described in case of application of light forces with fixed appliances, and considerably lower than what has been described for traditional comprehensive orthodontic treatments.

Adult Patients, Aligners, Root Resorption