Clear Aligners With Two Different Change Schedules vs Traditional Braces for People With Crowded Lower Front Teeth

Overview

The goal of this clinical trial was to compare two clear aligner treatment plans with traditional braces for treating crowded lower front teeth in adults. Clear aligners were removable plastic trays. Traditional braces were metal brackets and wires. The main questions the study aimed to answer were: How fast did the teeth move? How long did treatment take? How much pain did participants feel? Researchers studied 21 adults aged 18 to 40 years. The adults had mild to moderate crowding of the lower front teeth. They did not have teeth removed for treatment. Researchers assigned participants by chance to one of three groups: Aligner I: clear aligners that moved teeth 0.25 mm per step. Aligner II: clear aligners that moved teeth 0.35 mm per step. Control: traditional braces. Participants: Wore clear aligners for 22 hours a day and changed to a new aligner every 2 weeks, or wore traditional braces that were adjusted every month. Visited the clinic for checkups, tooth scans, and pain checks. Were treated for up to 20 weeks. Researchers measured crowding with a score that showed how crooked the lower front teeth were. They recorded how many weeks treatment took. They asked participants to rate pain on a 0 to 10 scale. A score of 0 meant no pain. A score of 10 meant the worst pain. Researchers found that all three treatments straightened the teeth. Traditional braces worked fastest. The typical participant in the braces group finished in 10 weeks. The typical participant in Aligner II finished in 12 weeks. The typical participant in Aligner I finished in 16 weeks. Pain changed over time in all groups. Clear aligners were not always more comfortable than braces. At weeks 8 and 10, both aligner groups reported more pain than the braces group.

This study was a three-arm, parallel-group, randomized clinical trial conducted at the outpatient clinic of the Orthodontics Department, Faculty of Dentistry, Ain Shams University. Twenty-one participants were enrolled and allocated equally to three groups (n = 7 per group) using simple randomization. An allocation sequence was generated with Microsoft Excel by a colleague not involved in the trial. Each participant received a sequential number corresponding to presentation order, and group assignment was determined by matching this number to the pre-generated sequence. For the aligner groups, intraoral scan datasets were imported into 3Shape software (3Shape Ortho System, 3Shape A/S, Copenhagen, Denmark). Models were spatially oriented using three reference points: the central fossae of the maxillary right and left first molars and the contact point between the central incisors. Model bases were created 4-5 mm apical to the gingival margins. Individual tooth segmentation was performed by identifying mesial and distal contact points, refining tooth splines, and adjusting axial orientation. The diagnostic setup involved adjusting the occlusal plane to reproduce any clinical canting, selecting and refining the arch form, and performing a three-dimensional tooth setup to achieve ideal alignment per American Board of Orthodontics criteria without overcorrection. Incremental staging steps were generated. Extrusive and intrusive movements were set at 0.15 mm per step; rotational, tipping, and torquing movements were set at 1 degree per step. Planar translation increments were the group-specific variable: 0.25 mm per step for Aligner I and 0.35 mm per step for Aligner II. Each staging step was inspected for interproximal or occlusal interferences exceeding 0.2 mm, which were resolved within the software. Attachments were placed according to biomechanical needs: vertical attachments for tip or rotation ≥5 degrees and horizontal attachments for extrusion ≥0.5 mm. Attachments were positioned centrally and as incisally or occlusally as possible without interfering with occlusion. Standard dimensions were 3.5 × 1.5 × 0.8 mm, with adjustments based on tooth morphology or occlusal interferences. Finalized digital models were labeled with the patient's name and exported as STL files. For aligner fabrication, STL files were sent to a digital lab. Models were printed using Formlabs Grey resin (Formlabs, Somerville, MA, USA) on a Form 2 3D printer (Formlabs Inc., Somerville, MA, USA). Printed samples were washed in a Form Wash tank (Formlabs) for 20 minutes and post-cured in a Form Cure tank (Formlabs). Aligners were thermoformed from 0.8 mm Erkodur-AL material (Erkodent Erich Kopp GmbH, Germany) using a MiniSTAR S machine (Scheu-Dental GmbH, Iserlohn, Germany). Aligners were trimmed in a straight line terminating 2 mm apical to the gingival margins. Clinically, one week before bonding, patients in the aligner groups received dental prophylaxis. After isolation with cheek retractors, cotton rolls, and suction, enamel surfaces were etched with 37% phosphoric acid for 15 seconds, rinsed, and dried to a frosty appearance. A thin layer of Transbond XT primer (3M Unitek, Monrovia, CA) was applied and light-cured. The attachment template was seated. Flowable composite (Nexcomp Flow, Meta Blomea, Korea) was injected into attachment recesses and light-cured through the template. The template was removed, and excess composite was finished with a carbide bur. Interproximal reduction was performed using metallic abrasive strips as prescribed. Gained space was measured using IPR gauges. Treated surfaces were polished. The first aligner was seated using chewies. For the control group, conventional fixed appliance therapy was initiated. One week after polishing, teeth were isolated and etched with 37% phosphoric acid for 30 seconds. After rinsing and drying, Transbond XT primer was applied. Stainless steel brackets with a Roth prescription and 0.018-inch slot size, along with bondable molar tubes, were bonded using Transbond XT composite. Each bracket was firmly seated, excess adhesive was removed, and adhesive was light-cured for 20 seconds per tooth. Leveling and aligning were performed using a standardized, progressive sequence of nickel-titanium archwires, advancing to rectangular stainless-steel wires. Statistical analysis was performed using IBM SPSS Statistics for Windows (Version 23.0, Armonk, NY: IBM Corp). Normality of numerical data was assessed through visual inspection of distributions and confirmed with Kolmogorov-Smirnov and Shapiro-Wilk tests. Because all variables exhibited non-normal distributions, non-parametric methods were used. Data were summarized as median, range, mean, and standard deviation. Intergroup comparisons among the three groups were performed using the Kruskal-Wallis test, followed by the Mann-Whitney U test for pairwise comparisons. Longitudinal changes within each group were evaluated using the Friedman test. When Kruskal-Wallis or Friedman tests yielded statistically significant results, post hoc pairwise comparisons were conducted using Dunn's test. The threshold for statistical significance was set at P ≤ 0.05.