Comparative analysis of experimental torque behavior and physicochemical properties of commercial and in‑house orthodontic aligners.

OBJECTIVES

Clear aligner performance depends on the magnitude and time-dependent behavior of experimentally generated moments. This study compared polymer identity, local post-thermoforming thickness, and experimental torque behavior of a commercial multilayer aligner (Invisalign) and two in-house thermoformed PETG aligners.

METHODS

Ethical approval and consent were obtained. A digital scan from one patient was used to fabricate a standardized 3D-printed maxillary model. Three systems were evaluated: Invisalign (thermoplastic polyurethane [TPU]-based) and two vacuum-formed PETG systems (BioArt and Forestadent). Polymer identity was determined by ATR-FTIR. SEM assessed local thickness and morphology after thermoforming. Experimental torque, defined as mechanical moment (N·mm), was quantified using a setup programmed to produce a 0.3 mm displacement of the maxillary right central incisor. Short-term torque was recorded from 0 to 3 minutes (n = 5 per group) and analyzed using two-way repeated-measures ANOVA. Seven-day torque decay was monitored under dry, room-temperature conditions (n = 2 per group) and interpreted descriptively.

RESULTS

ATR-FTIR confirmed PETG signatures for BioArt and Forestadent and TPU signatures for Invisalign. Thermoforming reduced local PETG thickness at tooth 11 by 58.6% for BioArt and 45.8% for Forestadent. At baseline and 3 minutes, Invisalign and Forestadent generated higher experimental torque than BioArt. Significant short-term torque reduction occurred for Invisalign and Forestadent, but not for BioArt. In the exploratory 7-day assessment, torque loss was 12.3%, 13.6%, and 20.2%, respectively.

CONCLUSIONS

Material chemistry and local geometry influenced experimental torque magnitude and relaxation under in vitro conditions. Long-term findings were exploratory and require confirmation under clinically relevant conditions.