aim of the study: to evaluate and compare the surface roughness (Ra, Rq, Rz), Vickers microhardness (VHN), and thickness of single-layer and multi-layer clear aligner sheets.
material and methods: the study will be conducted on clear aligners fabricated from two commercial thermoplastic materials: single-layer (0.76 mm, ) and multi-layer (0.76 mm, ). Each material will be evaluated at three stages: before thermoforming, after thermoforming on 3D-printed casts, and after 2 weeks of intraoral wear.
Specimen Preparation For each group, specimens will be prepared at three stages: before thermoforming (T0), after thermoforming (T1), and after intraoral wear (T2). At T0, square-shaped specimens (approximately 5 × 5 mm) will be cut directly from the unused raw sheets. At T1 and T2, specimens of the same dimensions will be obtained from the mid-labial surface of the central incisor region of the thermoformed aligners, both immediately after thermoforming and after two weeks of intraoral wear. The full thickness of the material will be preserved in all specimens to ensure consistency across groups.
Outcomes:
Primary Outcome:
Surface Roughness (Ra):
Measured at three stages:
T0: Raw, unused sheet specimens (baseline) T1: After thermoforming on dental casts T2: After 2 weeks of intraoral use
Secondary Outcomes:
Hardness:
Measured at T0, T1, and T2. Tested using Vickers hardness method (ISO 6507 compliant).