Objective: The aim of this study was to investigate the incidence and severity of root resorption in patients treated with Invisalign aligners (Align Technology, San Jose, CA, USA) and to examine a larger number of factors with a higher number of patient treatments, in comparison to the current literature, to show correlations between these factors and root resorption.
Materials and methods: The study group comprised 108 patients treated with Invisalign appliances. From these 108 patients, a total of 1,567 teeth were measured twice in panoramic radiographs before (T1) and after (T2) orthodontic treatment. The following teeth (according to FDI notation) were assessed: 16, 14, 13, 12, 11, 21, 22, 23, 24, 26, 36, 33, 32, 31, 41, 42, 43 and 46. The parameters determined from the patient records and examined were as follows: sex, age, arch (mandible or maxilla), side (right or left), tooth position (anterior or posterior), tooth type (central incisor, lateral incisor, canine, first premolar, first molar), position in the arch (anterior mandible, anterior maxilla, posterior maxilla, posterior mandible), Angle Class (I, II, III), reverse articulation, deep bite, open bite, gap position, crowding, use of elastics, use of motion appliances, extrusion, intrusion, translation, rotation, angulation, inclination, number of ClinCheck plans, total number of aligners (treatment time), and number of aligners per ClinCheck. Root resorption was determined by root–crown ratio and calculated according to the Linge-Linge formula.
Results: All patients displayed root resorption, but only 20 of the 1,567 teeth showed clinically relevant root resorption of more than 20%. Three-quarters (75.2%) of the total sample had only mild root resorption (under 9.7% resorption). The following parameters were statistically significant and showed a correlation with the occurrence of root resorption: central incisors, intrusion, posterior maxilla and anterior mandible. Increased angulation also tended to be associated with increased root resorption, but this did not reach the 5% threshold. Finally, the treatment duration (total number of aligners) and the average number of aligners per ClinCheck were significantly associated with increased root resorption.
Conclusions: Orthodontic treatment with Invisalign aligners can lead to root resorption. All patients showed root resorption, but this was mainly mild, without recorded clinical relevance. In order to reduce root resorption during orthodontic treatment, the orthodontist should pay special attention to the movement of the central incisors, movements through the cortical bone, intrusions and angulations, and slower staging. Keywords: aligners, Invisalign, orthodontics, root resorption