Effects of gastric acid and mechanical toothbrushing in CAD-CAM restorative materials: Mechanical properties, surface topography, and biofilm adhesion

Objective: To evaluate the effects of simulated gastric acid erosion combined with mechanical toothbrushing abrasion on the mechanical properties, surface topography, and biofilm adhesion of different CAD/CAM materials.Material and methods: Specimens of zirconia-reinforced lithium silicate glass-ceramic (ZLS), polymer-infiltrated ceramic network (PICN), feldspathic glass-ceramic (FE), and two nanoceramic resins (RK, RG), were submit-ted to the following challenges: erosion (E), abrasion (A), erosion combined with abrasion (E + A), or remained untreated (control -C). After challenges, flexural strength was evaluated, while microhardness (KHN) and sur-face roughness (Ra) were tested before and after treatments. The biofilm adhesion (Streptococcus mutans ATCC 700610, Streptococcus sanguinis ATCC 10556 e Candida albicans MYA 2876) was determined by the counting of colonies forming units per milliliters (UFC/mL) after erosive and abrasive challenges.Results: FE showed the lowest flexural strengths, while ZLS and RG exhibited the highest, while PICN and RK, had intermediate values. PICN, ZLS, and FE showed lower microhardness after E and E + A challenges than polymer -based materials (RG and RK). FE surface roughness increased after E and E + A challenges and after A and E + A challenges for RK. Biofilm formation after erosive/abrasive challenges was higher on ZLS than FE, RK, and RG, but no different than PICN. RK and RG exhibited the lowest biofilm formation among the groups. Furthermore, E + A challenges held significant changes in the surface of the materials, which were more severe on the surface of glass ceramics and hybrid materials.Conclusion: Erosive challenges combined with abrasion negatively influenced the mechanical properties and surface topography of most CAD/CAM materials and increased the biofilm adhesion on ZLS. Besides, the severity of the damage is related to the type and composition of each material.