Root resorption (RR) is described as a permanent loss of tooth structure from the root apex. Many reports in the literature indicate that orthodontically treated patients are more likely to have severe apical root shortening, interesting mostly maxillary, followed by mandibular incisors. The aim of the study was to investigate the incidence and severity of RR in adult patients treated with aligners. The study group consisted of 71 class I adult healthy patients (mean age 32.8 ± 12.7) treated with aligners (Invisalign®, Align Technologies, Santa Clara, CA, USA). All incisors, canines, upper first premolars, and first molars were assessed. Root and crown lengths of 1083 teeth were measured in panoramic radiographs at the beginning (T0) and at the end (T1) of clear aligner therapy. Individual root-crown ratio (RCR) of each tooth and therefore the relative changes of RCR (rRCR) were determined. A decrease of rRCR was assessed as a reduction of the root length during treatment. All patients had a minimum of one teeth affected with a reduction of root length, on average 6.38 ± 2.28 teeth per patient. Forty one, 81% of the 1083, measured teeth presented a reduction of the pre-treatment root length. A reduction in percentage of >0% up to 10% was found in 25.94% (n = 281), a distinct reduction of >10% up to 20% in 12.18% (n = 132) of the sample. 3.69% (n = 40) of the teeth were affected with a considerable reduction (>20%). Orthodontic treatment with Invisalign® aligners could lead to RR. However, its incidence resulted to be very similar to that described for orthodontic light forces, with an average percentage of RR < 10% of the original root length.

Among orthodontists and scientists, in the last years, upper molar distalization has been a debated topic in the orthodontic aligner field. However, despite that few clinical studies have been published, no insights on aligners’ biomechanics regarding this movement are available. The aim of this study was to assess, through finite element analysis, the force system resulting in the upper arch during second maxillary molar distalization with clear aligners and variable attachments settings. The average tooth distalization was found to be 0.029, with buccal flaring of the upper incisors in all attachment configurations. The mesial deformation of the aligner was registered to be 0.2 mm on average. Different pressure areas on the interface between aligners and upper molars were registered, with the mesial attachment surface to be directly involved when present. Periodontal ligament pressure was reported to range between 67 g/cm² and 132 g/cm². Configurations with rectangular attachments from second molar-to-canine and from first molar-to-canine present, in an in silico environment, almost equal efficiency in distalizing the upper second molar. However, attachments from the second molar to the canine are suggested to be adopted in clinical environments due to greater feasibility in everyday practice.

This study aimed to evaluate the efficacy of Invisalign First Phase I treatment compared with tooth-borne rapid maxillary expansion (RME) in mixed dentition patients by examining changes in palatal volume, palatal surface area, and maxillary interdental transverse measurements. In this open-label, 2-arm, parallel, randomized controlled trial, patients with a posterior transverse discrepancy ≤6 mm were allocated into the clear aligner therapy (CAT) group (Invisalign First Phase I treatment) and RME group (tooth-borne RME) according to a computer-generated randomization list immediately before the start of treatment. Digital models were obtained before the beginning of the treatment (T0) and at the end of the retention period/treatment (T1) using an intraoral scanner. Palatal volume was measured as the primary outcome, and palatal surface area and intermolar and intercanine transverse widths at the cusps and gingival level were measured as secondary outcomes. Patients and interventionists were not blinded because of the nature of the intervention. Out of 50 patients, 41 (19 males and 22 females; mean age, 8.12 ± 1.53 years) were enrolled and divided into 2 groups: 20 in the CAT group and 21 in the RME group. Two participants did not receive the allocated intervention for different reasons (1 patient discontinued the intervention in the CAT group, and another patient was lost to follow-up in the RME group). Thus, 19 patients (5 males and 14 females; mean age, 8.48 ± 1.42 years) were analyzed from the CAT group, and 20 patients (12 males and 8 females; mean age, 7.83 ± 1.19 years) from the RME group. Regarding intragroup comparisons, all outcome measures significantly increased from T0 to T1 in both groups. In terms of intergroup comparisons, there were no significant differences in the variation (Δ) of outcome measures between the 2 groups from T0 to T1, except for the intermolar width at the gingival level (P <0.005). The change in palatal volume was 532.01 ±540.52 mm³ for the RME group and 243.95 ± 473.24 mm³ for the CAT group (P = 0.310), with a moderate effect size (d = ∼1.136). RME exhibited superior results compared with the Invisalign First Phase I treatment, considering all the assessed outcome measures. The only parameter that showed statistically significant differences between the 2 groups was variation in intermolar width at the gingival level, suggesting the occurrence of buccal tipping in patients undergoing Invisalign First Phase I treatment. The trial was registered at ClinicalTrial.gov (no. NCT04760535).

Since the low level of available evidence and the limited number of studies do not clarify whether clear aligners are a good option for extrusion, finite element (FE) analyses were performed to obtain more accurate biomechanical data about open-bite treatment in the upper arch. The aim of this study is to answer three questions: Are aligners efficient in performing upper incisor extrusion? Does the number, position, and shape of attachments influence the force system? Is posterior anchorage preserved during incisor extrusion? Six different simulations were performed with different attachment patterns. The results of this study were consistent with the biomechanical information obtained from clinical trials, and highlighted the need of better knowing undesired forces during teeth movement with clear aligners. Some attachment configuration seems to lead to a better force system. The presence of rectangular horizontal attachments on the buccal or palatal surface of upper incisors in combination with rectangular vertical attachments on posterior teeth was found to produce the most efficient force system with minimal aligner deformation.