The success of clear aligner treatment depends largely on how effectively forces are transmitted through the aligner and attachment interface. This research investigated how well two clear aligner materials—Duran+ and Zendura FLX—fit against two attachment configurations—rectangular and optimized—at a microscopic level using scanning electron microscopy (SEM). Fifty-six samples were prepared and divided equally into four groups: Duran+ with rectangular attachments, Zendura FLX with rectangular attachments, Duran+ with optimized attachments, and Zendura FLX with optimized attachments (n = 14 per group). After bonding attachments to bovine incisors under standardized conditions, the aligners were thermoformed at 220 °C for 40 seconds. Cross-sectional analyses were carried out under SEM at 250× magnification, and gap widths were recorded at specific measurement sites (seven for rectangular and five for optimized attachments).
Interfacial gaps ranged from 14.75 ± 1.41 µm to 91.07 ± 3.11 µm. Zendura FLX showed a tighter fit compared with Duran+ in rectangular attachments (42.10 ± 1.07 µm vs. 44.52 ± 1.51 µm, p < 0.001). Optimized attachments generally achieved better conformity than rectangular ones. Across all groups, gaps were widest along gingival margins (67.18–91.07 µm) and narrowest on flat buccal areas (14.75–20.98 µm). None of the evaluated combinations achieved a completely precise fit. Both aligner composition and attachment shape play important roles in microscopic adaptation, with multi-layer materials and optimized geometries providing superior contact. These outcomes help clarify mechanical factors that may contribute to the clinical shortcomings of clear aligner systems.
