Acid Effects on the Physical Properties of Different CAD/CAM Ceramic Materials: An in Vitro Analysis

Abstract

Purpose: To evaluate the flexural strength, elastic modulus, microhardness, and surface roughness of monolithic zirconia, lithium disilicate ceramics, and feldspathic ceramics after being exposed to different acidic solutions.

Materials and methods: Rectangular specimens (n = 180) were prepared from three different ceramic materials: lithium disilicate, monolithic zirconia, and feldspathic porcelain. Initial Surface roughness of ninety specimens (n = 30/material) was evaluated using an optical noncontact profilometer. Thirty specimens of each material were immersed in one of the following solutions (n = 10/group): citric acid; acidic beverage; and artificial saliva, which served as the control. Post immersion surface roughness, flexural strength, and elastic modulus were determined using an optical noncontact profilometer and three-point bending test. Another thirty specimens of each material were immersed in the aqueous solutions (n = 10/group) following the same protocol and subjected to microhardness test using a Vickers diamond microhardness tester. A scanning electron microscope (SEM) was used to examine the surface characteristics changes. ANOVA and Post-hoc Tukey's Kramer tests were used for data analysis (α = 0.05).

Results: Immersion in different solutions did not affect the flexural strength and elastic modulus of lithium disilicate or zirconia. Microhardness and surface roughness were significantly affected in all groups (p < 0.05). For feldspathic porcelain groups, the flexural strength and elastic modulus were significantly decreased in the citric acid group (p = 0.045 and p = 0.019). Also, there were significant differences among all feldspathic porcelain groups (p = 0.001) in terms of microhardness and surface roughness values.

Conclusions: The tested acidic agents significantly affected the flexural strength, elastic modulus, surface roughness, and microhardness of feldspathic porcelain. However, the flexural strength and elastic modulus of evaluated lithium disilicate and zirconia did not change significantly.

Keywords: Ceramics; acid immersion; elastic modulus; flexural strength; microhardness; surface roughness.