Effect of surface finish and acidic medium on hardness and fracture toughness of zirconia reinforced lithium silicate (An In-vitro study)

Aim: To assess the effect of surface finish and acidic beverage (cola beverage) on hardness and fracture toughness of zirconia lithium silicate (Celtra press) Methodology: Total of n=36 samples of zirconia reinforced lithium silicate (Celtra press) plates were divided into two main groups (n=18 glazed samples and n=18 polished samples) and then each group was subdivided into two equal groups according to immersion solution (artificial saliva & cola beverage). Surface hardness and facture toughness measurements were obtained for each specimen, before and after storage in the solutions. Surface micro hardness was measured by Vicker Micro-hardness tester. The fracture toughness was measured by using the indentation method. Results: For Vickers hardness results: For Glazed group, it was found that the values of Vickers hardness were recorded before immersion subgroup followed by artificial saliva immersed subgroup while the lowest values were recorded with Cola immersed subgroup. For Polished group, it was found that the highest values of Vickers hardness were recorded before immersion subgroup followed by artificial saliva immersed subgroup while the lowest values were recorded with Cola immersed subgroup. For fracture toughness results: For Glazed group, it was found that the highest values of fracture toughness were recorded before immersion subgroup followed by artificial saliva immersed subgroup while the lowest values were recorded in Cola immersed subgroup. For Polished group, it was found that the highest values of fracture toughness were recorded before immersion subgroup followed by artificial saliva immersed subgroup while the lowest values were recorded in Cola immersed subgroup. Conclusion: Ageing in acidic medium negatively affected both the surface hardness and the fracture toughness for Celtra press and polished Celtra press had prominent hardness and fracture toughness compared to auto-glazed Celtra press.