Does Thermoforming Setup Affect Thickness in Thermoplastic Orthodontic Appliances? A Comparison of Single vs. Dual-Model Fabrication

Thermoforming remains the predominant fabrication route for clear thermoplastic orthodontic appliances, yet it reduces and redistributes sheet thickness, which governs force delivered to teeth. Simultaneous thermoforming of two models may reduce fabrication time and material waste; however, its effect on final appliance thickness has not been evaluated. This in vitro study compared appliance thickness after thermoforming over a single model or two models simultaneously, using ten commercial aligner brands with different polymer composition and initial thickness. Thickness was measured with a digital caliper at anterior, canine and posterior sites, and analyzed using three-way ANOVA with Tukey post hoc tests. A significant three-way interaction (measurement point × number of models × brand; p < 0.001) was found. Significant single- versus dual-model differences emerged in some brand–region combinations; in most, dual-model appliances were thicker than single-model appliances. Four brands showed no significant difference at any site. Within the limits of this study, simultaneous fabrication of two appliances in a single thermoforming cycle produced appliances with thicknesses comparable to, and often slightly greater than, those fabricated over a single model. Simultaneous thermoforming maintained comparable appliance thickness and may improve manufacturing efficiency.