Measurement of Aligner Thickness and Gap Width in Two Types of Clear Aligner Sheets Manufactured Using Two Different Thermoforming Machines - A Nano-CT Pilot Study.

Objective: The aim of this study was to compare the effects of two thermoforming machines on the gap width and thickness of passive aligners with the same nominal thickness from different manufacturers by using nano-computed tomography (CT). Methods: An intraoral scan of a patient with Angle's Class I malocclusion was conducted, and a 3D maxillary arch model was printed. The aligners (n=16) were fabricated using two thermoforming machines: Ministar machine (n=8) and a Plastpress machine (n=8). Each group was subdivided on the basis of aligner material: polyethylene terephthalate glycol (PET-G) (Group A) and thermoplastic polyurethane (TPU) (Group B). Sheets with a nominal thickness of 0.75 mm were used. Nano-CT was performed, and the rendered 3D models were sliced into central incisor, canine, and molar regions to assess gap width and aligner thickness in the buccal, incisal, and palatal regions. Results: Comparing thermoforming machines, PET-G (p=0.010) and TPU (p=0.004) aligners showed significant differences in gap width in the molar region. Similar results were found for aligner thickness (TPU, p=0.05; PET-G, p=0.004). Comparing PET-G and TPU sheets thermoformed via the same machine, significant differences were observed only in the molar region (p=0.004), with no differences in the canine and incisor regions. Adaptation in the anterior region was greater than in that of the posterior region, whereas aligner thickness increased from posterior to anterior. Conclusion: Aligner material type significantly affected gap width and thickness only in the molar region, whereas the specific thermoforming machine did not substantially affect these characteristics.