Influence of shoulder margin and feather-edge incisal preparations on the marginal and internal adaptation of laminate veneers fabricated with three manufacturing techniques

Purpose: To compare the marginal and internal adaptation of shoulder margin and feather-edge 3D-printed veneers with milled zirconia and pressed lithium disilicate laminate veneers. Materials and Methods: Veneer preparations were made on the right and left maxillary incisors using shoulder margin and feather-edge designs. The preparations were scanned to create the reference standard tessellation language (STL) file. Ninety laminate veneers were fabricated for each preparation design using 3D-VS (3D-printing Varseosmile), M-Zr (milled zirconia), and P-LD (pressed lithium disilicate). All veneers were digitized to generate test STL files, which were then used to measure 3D deviations from the reference file with a 3D software program. Marginal and internal adaptation, as well as trueness, were assessed. Color maps were produced to quantify the mean ± standard deviation of the 3D deviations between the reference and test STL files. Results: The marginal discrepancy was significantly higher in the feather-edge design than in the shoulder margin design across all groups (p < 0.001). M-Zr exhibited the best marginal adaptation in all four measured areas: cervical (30.2±4.02 µm), mesial (15.8±2.97 µm), distal (16.7±3.23 µm), and incisal (20.6±2.36 µm) for shoulder margin design. For feather-edge designs, M-Zr excelled in all areas: cervical (29.5±2.71 µm), mesial (15.8±2.97 µm), distal (17.2±2.65 µm), and incisal (45.3±3.97 µm). Statistically significant differences in internal adaptation were found among the 3 groups (p < 0.001). M-Zr demonstrated the best internal adaptation in the cervical third (shoulder margin: 25.3±1.49 µm, feather-edge: 19.2±3.52 µm) and middle third (shoulder margin: 14.3±3.09 µm; feather-edge: 14.1±2.31 µm). Trueness of M-Zr was better than that of other groups (p < 0.001) (shoulder margin: 17.4±1.74 µm; feather-edge 20.4±1.33 µm). Conclusions: M-Zr veneers had the best marginal and internal adaptation of the fabrication methods and materials tested. Shoulder margin design consistently exhibited better fit across all three materials. The marginal and internal adaptations for the three materials were within the acceptable clinical range.