Background: To investigate and compare the gap (i.e. fit) and thickness of six aligner systems (Airnivol, ALL IN, Arc Angel, F22, Invisalign and Nuvola) using industrial computed tomography (CT). The null hypothesis was that there would be no detectable differences in either measurement between the aligners investigated. Materials and methods: Passive aligners of each brand were fitted to one single resin cast prototyped from an STL file from a single patient. The samples obtained were examined under high-resolution micro-CT, and the resulting tomographic microphotographs and volumetric data were compared. 3D analysis investigated the gap volume, the mean gap width and the maximum gap width of each sample. A total of 204 linear 2D measurements were made on 18 microtomographic images to investigate the aligner gap and thickness among different systems. Investigated regions were the central incisor, canine and first molar. The resulting measurements were analysed by ANOVA and compared using Tukey’s post hoc analysis (P < 0.05). Results: 3D analysis revealed that the F22 displayed lower gap volume and mean gap width, followed by Airnivol and Invisalign, whereas Airnivol the lowest maximum gap width. 2D analysis showed that F22 had the lowest mean gap and aligner thickness at all teeth investigated. Comparison of the 2D point values revealed statistically significant differences between brands in terms of both measurements (P < 0.05), with the exception of six points in the gap analysis and one in the thickness analysis. Conclusions: There are differences between the six aligner systems examined in terms of 2D and 3D measurements of aligner thickness and gap.

Mario Palone, Mattia Longo, Niki Arveda, Michele Nacucchi, Fabio De Pascalis, Giorgio Alfredo Spedicato, Giuseppe Siciliani, Luca Lombardo. Korean J Orthod 2021;51:135-41. https://doi.org/10.4041/kjod.2021.51.2.135

We aimed to investigate the stress relaxation properties of five different thermoplastic aligner materials subjected to 14 days of constant deflection. Five different thermoplastic aligner materials were selected, whose elastic properties varied: F22 Evoflex, F22 Aligner, Durasoft, Erkoloc-Pro and Duran. The static properties of these materials—in particular, stiffness, stress–strain curve and yield stress—were measured with a three-point bending test. For all the tests that were performed, a minimum of three samples per material were tested. The yield load, yield strength, deformation and particularly the stiffness of each material were found to be similar in the single-layer samples, while the double-layer samples showed far lower stiffness values and were similar one to another. F22 Evoflex and Erkoloc-Pro maintained the highest percentages of stress, 39.2% and 36.9%, respectively, during the 15-day period. Duran and Durasoft obtained the lowest final stress values, 0.5 MPa and 0.4 MPa, respectively, and the lowest percentage of normalized stress, 4.6% and 3.9%, respectively, during the 15-day period. All the materials that we tested showed a rapidity of stress decay during the first few hours of application, before reaching a plateau phase. The F22 Evoflex material showed the greatest level of final stress, with relatively constant stress release during the entire 15-day period. Further research after in vivo aging is necessary in order to study the real aligners’ behavior during orthodontic treatment.

Objectives: To provide clinical information on overcorrection to be included in the initial digital setup to make clear aligner therapy (CAT) more efficient. Materials and Methods: Prescription data for 150 patients (80 women and 70 men; mean age 33.7 ± 12.7 years) treated successfully with CAT (F22 Aligners, Sweden & Martina, Due Carrare, Italy) and requiring only a single, minimal finishing phase were acquired retrospectively. The inclusion criteria were Class I dental malocclusion with only minimal crowding (≤3 mm), 12–20 aligner steps per arch, no use of auxiliaries or interarch elastics, and rotations ≤25° for round-shaped teeth. The prescribed and corrective movements to be achieved in the main and finishing treatment phases, respectively, were quantified by the dedicated clear aligner setup software. The magnitudes of inclination (buccal-lingual crown tipping), angulation (mesial-distal crown tipping), rotation, intrusion, and extrusion were extracted and analyzed by tooth type, maxilla and mandible, and both arches. Descriptive statistics, that is, mean, standard deviation, and percentage, were calculated for each movement investigated. Classification and regression trees (CART) were generated using the model-based recursive partitioning approach, and the corrective movements were correlated with respect to both the amount of the movements prescribed and the tooth type. Statistical significance was set at 5%. Results: Inclination and rotation required the greatest correction, whereas angulation, intrusion, and extrusion required only minimal correction. Expressed as a percentage of prescribed movement, mean corrective movements were 20.5% for inclination, 14.5% angulation, 28.4% rotation, 11.7% extrusion, and 22% intrusion. According to CART, all corrective movements except extrusion depended on both tooth type and the magnitude of prescribed movement. Conclusions: To achieve more efficient CAT, approximately 20% overcorrection should be added to the initial planning phase when planning challenging movements such as inclination and rotation.