Effect of Thickness and Trim Lines on the Magnitude and Distribution of Transverse Forces Exerted by Thermoformed Plastic Aligners During Maxillary Arch Expansion

OBJECTIVE: The study evaluates the impact of thickness and trimming geometry on the magnitude and distribution of transverse forces applied by thermoformed plastic aligners during maxillary arch expansion. METHODS: A randomised experiment evaluated 60 aligners fabricated from PET-G in two distinct thicknesses (0.03 and 0.040 in.) and three different trimming geometries (G1-scalloped margins, G2-straight margins with 5 mm width and G3-straight margins with 10 mm extension). Transverse forces in the canine (C), first premolar (FP), second premolar (SP), first molar (FM), second molar (SM) and third molar (TM) were measured in newtons (N). Three measurement repetitions (original data plus two replicates) were implemented to generate sufficient degrees of freedom for the sum of squares of the error. RESULTS: The maximum transverse force in the canine region was exerted by the PET-G aligner with a thickness of 0.040 in., with no significant difference observed between the G2 and G3 straight trim lines. However, the G1 scalloped trim line exerted significantly lower transverse forces. The G3 geometry with a 0.040-in. Polymer thickness consistently generated the highest forces in the premolar and molar regions. The average transverse forces decreased in an antero-posterior direction, with the highest force observed in the canine region and the least in the molar region. CONCLUSIONS: The thickness and trimming pattern of orthodontic aligners significantly influence force delivery during transverse expansion. Transverse forces during expansion with aligners progressively reduce from the anterior to the posterior region.