Evaluation of color stability and bond strength of interim restorations fabricated by CAD/CAM and 3D printing: an in vitro study

Mechanical properties of interim restorations, as well as fabrication methods, are important for the integrity of restorations, especially for a long interim period. Interim restorations are subjected to occlusal loads; therefore, an adequate bond strength should be maintained until the final restoration is delivered. Color stability is also crucial in the esthetic zone throughout the long-term treatment phase. Therefore, both color stability and bond strength are dependent on the fabrication methods. to evaluate the color stability and bond strength of 3-D printed and CAD/CAM milled interim restorations, and to compare between different groups regarding their color stability and bond strength. A total of 72 interim PMMA specimens were fabricated in two distinct shapes: disc-shaped (8 mm in diameter × 2 mm in height) and square-shaped (10 mm × 10 mm × 2 mm thick). Half of the specimens (n = 36) were manufactured using CAD/CAM milling, while the remaining half (n = 36) were produced through 3D printing. Within each fabrication method, the specimens were categorized into two subgroups: Subgroup A, which consisted of 12 square-shaped specimens designated for color stability testing, and Subgroup B, comprising 24 disc-shaped specimens intended for shear bond strength testing. In Subgroup B, the discs were further divided based on surface treatment into three groups: surface roughening with a bur (n = 8), sandblasting (n = 8), and an untreated control group (n = 8). Color stability and bond strength measurements were recorded for all relevant specimens. In both CAD/CAM milled and 3D printed groups, there was a significant difference in the color stability of the specimens over time (p < 0.05). They had high discoloration values with CAD/CAM specimens, with a mean of 13.50 (0.10), while 3D printed specimens had a mean of 14.31(0.10). Shear bond strength was also significantly different between the experimental groups with CAD/CAM milled specimens: the control group, 0.53 ± 0.33; the sandblasted group, 1.16 ± 0.25; and the roughened group, 1.00 ± 0.34. In contrast, the 3D printed specimens showed the following results: Control, 1.63 ± 0.90; Sandblasted, 1.44 ± 0.42; and roughened, 1.30 ± 0.43. CAD/CAM milled PMMA exhibited higher color stability compared to 3D printed PMMA, with coffee having a higher staining potential on PMMA than tea beverages. CAD/CAM shear bond strength was higher with surface treatment by aluminum oxide particles, while 3D printed PMMA has a higher shear bond without any surface treatment.