Predicting thickness distribution of thermoplastic dental aligners via KBKZ-based finite element analysis

This study aims to clarify the thickness distribution and its dynamic evolution during the thermoforming of PET thermoplastic dental film for orthodontic appliances using a numerical simulation system based on the KBKZ integral constitutive model. It establishes a mapping relationship between initial and formed thickness, offering a method to optimize membrane thickness and process parameters at various stages of orthodontic treatment. A nonlinear viscoelastic finite element analysis framework was constructed using the KBKZ integral constitutive model. PET thermoplastic dental film with initial thicknesses of 0.6 mm, 0.8 mm, and 1.0 mm were studied. Thermoforming simulations were conducted using the ASNSY-Polyflow module. Physical membrane thermoforming experiments were also performed. Thickness distribution data of the formed samples were measured with a thickness micrometer. The analysis focused on thickness distribution characteristics in the lingual, buccal, and occlusal functional regions. The numerical simulations and experimental measurements showed significant consistency. The thickness distribution curves exhibited an average Pearson coefficient [Formula: see text] ([Formula: see text]) and Spearman coefficient [Formula: see text] ([Formula: see text]); the thickness change rate curves showed [Formula: see text] and [Formula: see text] ([Formula: see text]). The formed appliances exhibited typical regional heterogeneity. The thickness attenuation rate (η) in the lingual and buccal regions was [Formula: see text], significantly higher than that in the occlusal region ([Formula: see text]). This study shows that the finite element method using the KBKZ integral model can accurately predict the thickness distribution and its changing law of invisible braces during the thermoforming process. In terms of thickness prediction, the accuracy of the error with actual production is successfully achieved to be less than 7%. In future orthodontic plans, combined with the forward-looking "dynamic thickness compensation" strategy concept of this study, the stiffness of the appliance can be controlled by designing the initial diaphragm thickness. This offers a parametric solution for clinical scenarios needing high orthodontic forces, such as molar intrusion, tooth rotation, and sequential treatments. This enhances the biomechanical controllability of the clear aligner system and has important clinical engineering application value for improving the accuracy of orthodontic force control.