SỰ KHÁC BIỆT VỀ ĐỘ DÀY CỦA KHAY CHỈNH NHA TRONG SUỐT ĐỊNH HÌNH NHIỆT: NGHIÊN CỨU IN VITRO

Abstract

Background: In contemporary orthodontics, clear aligner therapy has gained considerable traction due to its aesthetic appeal and convenience for patients. The thermoforming process for in-house aligner fabrication involves two primary stages: generating a 3D dental model using additive manufacturing technology and subsequently thermoforming a plastic material over this model. The thickness of the aligner is a critical factor influencing the magnitude of the force exerted on the teeth, thereby affecting the extent of tooth movement during treatment. During the thermoforming process, several factors can potentially impact the final aligner thickness, including the height of the 3D model base, material sag during heating, the 3D model's position on the forming platform, and the clinical crown height. This study aims to evaluate the variation in aligner thickness post-thermoforming across different tooth groups and at distinct measurement points on individual teeth, with the ultimate goal of refining fabrication techniques to achieve aligners of appropriate thickness, thereby ensuring effective orthodontic treatment outcomes for patients. Materials and methods: This study was conducted on a sample of n = 10 orthodontic aligners fabricated from Zendura FLX orthodontic plastic sheets (Bay Materials, USA) with a pre-thermoforming thickness of 0.76mm. Following thermoforming using a Drufomat Scan machine (Dreve, Germany) on 3D-printed maxillary models created with a Rayshape Edge E2 printer (Rayshape, China), the thickness of each aligner was measured at various locations on different teeth using a Syntek (MTM Precision, China) digital micrometer (0-25mm/0.001mm resolution). The collected data were analyzed using JASP software. Results: Following the thermoforming process, the mean aligner thickness decreased from the initial 0.76mm to 0.43mm, representing a reduction of 43.4% compared to the original sheet thickness. The findings of this study further revealed statistically significant differences in the thickness of in-house fabricated clear aligners across different tooth groups and at various measurement sites on the tooth surface. Specifically, intergroup comparisons of thickness (incisors, canines, premolars, molars) indicated that the molar group exhibited the greatest thickness, with the premolar-molar pair being the only one demonstrating a statistically significant difference (p = 0.031). Analysis of thickness at different locations—mid-buccal (MN), buccal gingival margin (CRN), mid-lingual (MT), and lingual gingival margin (CRT)—revealed statistically significant variations between these sites on the same tooth (F = 134.35, p < .001). Notably, the MT and CRT locations showed significantly greater thickness compared to the MN and CRN sites. The CRN position was identified as the thinnest area of the aligner, with a recorded thickness reduction of up to 62% from the original material thickness. Conclusion: Orthodontic aligners undergo a substantial reduction in thickness after the thermoforming process, and this reduction varies significantly depending on the tooth group and the location on the clinical crown. From a clinical perspective, these discrepancies in thickness directly impact the force exerted by the aligner on the teeth and should be considered as a potential factor influencing the overall effectiveness of orthodontic treatment.