The primary objective of the study was to compare surface roughness changes of thermoformed (Zendura™ FLX) and direct-printed aligners (TA 28 resin) after 10 days of intraoral usage. The secondary objective was to evaluate both line and surface roughness changes between used and unused thermoformed and direct printed aligner.

The study included 48 aligner samples divided into four groups: direct printed control, direct printed used, thermoformed control, and thermoformed used ( n = 12 each). Surface roughness was analysed using atomic force microscopy (AFM), measuring parameters such as Sa, Sq, Sy, Sp, Sv for surface roughness and Ra, Rq, Ry, Rp, Rv for line roughness. Shapiro-Wilk test showed non-normal distribution of data. Median values and interquartile ranges were used for descriptive statistics. Median quantile regression analysis was performed.

Direct-printed control aligners demonstrated higher median roughness values (Sa: 57.76 nm) compared to their used counterparts (49.93 nm). In contrast, thermoformed aligners exhibited significantly lower roughness, particularly under used conditions (Sa = 16.85 nm). Direct-printed unused versus used samples showed significant differences ( P ≤ 0.05) for Sq and Sv parameters, confirming that usage reduces surface roughness. Similar patterns were observed in thermoformed groups (unused vs. used), with significant reductions in Sa, Sq, and Sy parameters ( P ≤ 0.05). Both Direct-printed and thermoformed aligners unused versus used aligners showed significant reductions in Ra, Rq, and Ry parameters ( P ≤ 0.05). Both comparisons showed significant positive coefficients for Rv, indicating shallower valleys after use.

Intraoral use led to decreased surface roughness in both aligner types, with thermoformed aligners showing the smoothest surface post-use. These findings have important implications for aligner fit, patient comfort, and potential effects on oral tissues.