Long-Term Effect of Acidic Beverages on Dental Injectable Composite Resin: Microhardness, Surface Roughness, Elastic Modulus, and Flexural Strength Patterns

The purpose of this study is to evaluate the effects of different acidic beverages on the surface roughness, microhardness, flexural strength, and elastic modulus of microhybrid, bulk-fill, and injectable composites and the correlations between them. Microhybrid, bulk-fill, and injectable composites were used in this study. One hundred and thirty-five disk-shaped samples were prepared for the microhardness test and the surface roughness measurements, and 675 rectangular prism-shaped samples were prepared for elastic modulus and flexural strength measurements. In each sample, the initial surface roughness, microhardness, flexural strength, and elastic modulus were measured and then randomly divided into three groups (n = 15) in preparation for the immersion procedure in coke, orange juice, and artificial saliva. Relevant measurements were repeated on the first day, first week, first month, and first year after the immersion procedure was performed with each beverage. Moreover, the effects of the beverage on surface morphology were evaluated by scanning electron microscopy at the relevant control times. A three-way analysis of variance was used to compare microhardness, surface roughness, flexural strength, and elastic modulus measurement values according to the material, beverage, and immersion cycle, and Tukey’s test was used for multiple comparisons. Spearman’s rho correlation coefficient was used to examine relationships between parameters. The significance level was p< 0.05. Statistically significant effects were found on the surface roughness values of the materials, beverages, immersion cycle times, as well as the interactions among these parameters (p< 0.001). The highest surface roughness value of 5.28 was obtained in the injectable composite group, which was exposed to a one-year coke immersion cycle. After the immersion cycle, a significant decreasing trend in the microhardness value was detected in all materials (p< 0.001). It was determined that the injectable composite had the highest flexural strength value (173.6 MPa). The lowest flexural strength value was determined to be in the microhybrid composite group (92.9 MPa) before the immersion procedure. Moreover, a significant decrease was observed in the flexural strength and elastic modulus values of all composite groups that were subjected to the immersion cycle with coke, while this change was minimal in artificial saliva. The injectable composite exposed to short- and long-term immersion cycles exhibited a flexural strength value above ISO 4049/2019 standards, which is promising for clinical use.