Effects of Simulated Gastric Juice on CAD/CAM Resin CompositesMorphological and Mechanical Evaluations

Purpose: To evaluate the effects of simulated gastric juice on CAD/CAM resin composites by means of morphological and mechanical (i.e., hardness) evaluations. Materials and Methods: Fourteen specimens of each resin composite (Lava Ultimate and Paradigm MZ100) were prepared according to the manufacturer's instructions. They were submitted to erosive challenges in a simulated gastric juice (pH = 1.2) solution for 6 and 24 hours. Vickers microhardness and surface roughness (R-a, R-q) evaluations were taken before (baseline) and after acid exposure. Morphological analysis was obtained using scanning electron microscopy (SEM). Statistical analysis was performed using two-way repeated measures ANOVA and Student-Newman-Keuls's test (alpha = 0.05). Results: Paradigm MZ100 demonstrated higher microhardness than Lava Ultimate regardless of the storage time period (p <= 0.001), and microhardness was not affected by the acidic challenge (p = 0.58). After 6 hours of acid exposure, a significant decrease in R-a and R-q was seen for Paradigm MZ100 when compared to the baseline (R(a)p = 0.032; R(q)p = 0.013); however, for Lava Ultimate only Rq decreased (p = 0.021), while R-a remained unchanged (p = 0.38). After 24 hours of acid exposure, while Paradigm MZ100 exhibited no additional changes in surface roughness (p >= 0.75), Lava Ultimate became rougher (R(a)p = 0.041; R(q)p = 0.014), as confirmed by SEM imaging. Conclusions: The acidic scenario tested in the present study changed the surface roughness of the resin composites but not their Vickers microhardness. Moreover, both resin composites seem suitable for use under acidic scenarios, although Paradigm MZ100 showed enhanced stability compared to Lava Ultimate.