Effect of Food Simulating Liquids and Thermo-cycling on flexural strength and surface hardness of a Resin Nano-Ceramic CAD/CAM Material

Abstract

Purpose: Evaluate the effect of food simulating liquids and thermocycling on miniflexural strength and surface micro-hardness of a resin nano-ceramic material (Lava Ultimate) compared to indirect laboratory composite resin material (Nexco Paste) and direct composite resin material (Filtek Z350 XT). Material and Methods:A total number of 180 samples were fabricated. The samples were divided equally into 3 groups (n=60). Group 1 (M 1 ) samples were fabricated from the resin nano ceramic CAD/CAM blocks (Lava Ultimate), group 2 (M 2 ) samples were farbricated form indirect micro-hybrid resin composite (Nexco Paste), while group 3 (M 3 ) samples were fabricated from direct resin composite (Filtek Z350 XT). Thirty bars (12X2X2mm) from each material were fabricated to evaluate the mini flexural strength. Thirty disks (8X2mm) were fabricated from each material to evaluate the surface micro-hardness. The samples of M 1 groups were fabricated by cutting from the CAD/CAM block using low speed diamond disk while samples of M 2 and M 3 samples were fabricated using teflon mold. Each material samples were further subdivided into 6 subgroups; the first subgroup was not immersed into food simulating liquids nor thermocycled, 4 subgroups samples were immersed into food simulating liquids (water, ethanol, heptane and citric acid) and the last subgroup samples were thermocycled. Mini flexural strength test was done using universal testing machine and surface hardness was done using Vickers hardness tester.Results: Lava Ultimate showed the significantly highest mini flexural strength and surface micro-hardness values before and after immersion into food simulating liquids and thermocycling compared to the two other tested materials. Conclusion:According to the results of the present study, Lava Ultimate showed better mini flexural strength and surface micro-hardness compared to the two other tested materials.

Color Stability of three esthetic monolithic block materials after immersion in commonly consumed beverages

“…19 When the composite resin is exposed to a low pH environment, the inorganic fillers tend to fall out from the resin material and the matrix components decompose. 21,46 Generally, water contributes to the color change of composite materials in several ways. Water sorption induced by hydrophilic resinous components as mentioned before could lead to discrepancies in the refractive index of the different components within the organic matrix.…”

“…Thus the fillers become more susceptible to stress corrosion attack and eventually complete or partial filler debonding consequently producing cracks at the resin-filler interface where colorants may penetrate the cracks and cause color changes. 16,21,46,47 The zirconia nanofiller component accentuated the problem as they cannot be effectively silanized due to their high crystallinity. 16,48 In addition, zirconia was shown to exhibit progressive phase transformation in contact with water known as low-temperature degradation (LTD).…”