Comparison of surface hardness values of resin based cements of different structures after static- and dynamic-aging

Indirect ceramic and ceramic-like restoration applications have found widespread use together with the CAD/CAM technique. When it comes to bonding these restorations to dental hard tissues, composite resin luting cement or self-adhesive luting cement materials are used. The mechanical properties of these luting cement materials significantly affect the clinical performance of the indirect restoration. Hardness is defined as the resistance of the material's surface to abrasion and scratching, and it is important for all restorative materials, as well as for resin-based bonding cement materials to support the restoration against forces. There are static- and dynamic-post-aging studies of composite resin restorative materials in the literature. However, there is not enough about composite resin luting cement and self- adhesive resin luting cement. The aim of the present study is to investigate the time- dependent changes in the upper and lower surface hardness values of the composite resin luting cement and self-adhesive resin luting cement in the static and dynamic environment; and to evaluate the possible changes in these values after static- and dynamic-aging in clinical practice, in the cementation phase, to guide clinicians and contribute to new studies. In the present study, test samples were prepared from a 2 mm thick, square prism (20 mm x 20 mm) black plexiglass mold with a 5 mm diameter gap in the middle (n=40). During the preparation of the disk-shaped (5 mm diameter, 2 mm thick) test samples, a black plexiglass mold was placed on the glass on which the transparent tape was placed. After the test material was placed in the cavity with a diameter of 5 mm in the mold, transparent tape and glass coverslip were placed on the upper surface of the mold. The tip of a high light intensity (1400 mW/cm2) LED light source was applied to the disc-shaped part on the upper surface of the test mold from a distance of 0 mm for 20 seconds. In the first stage of the thesis study, test samples were prepared from 1 composite resin restorative material (n=5) and 1 composite resin bonding cement (n=5) in order to decide on the load and duration planned to be applied. The upper and lower surface hardness measurements of the test samples were performed with the HVS-1000 Vickers surface microhardness device. For the measurement, it was decided to apply the lightest projecting load and the least duration (50 g and 10 sec). In the second phase of the thesis work, the decided load and time (50 g and 10 sec), 3 different resin-based cement materials were divided into 2 separate subgroups for static- and dynamic-aging. Before and after aging, upper surface and lower surface hardness measurements were performed. The findings were evaluated with the IBM SPSS Statistics 22 program. The analysis of the data, the conformity of the parameters to the normal distribution were examined by Kolmogorov Smirnov and Shapiro Wilks tests. In evaluating Composite resin restorative material/composite resin luting cement, the joint effect of applied force (grams) and applied time (seconds) on upper surface and lower surface hardness values, Three-way analysis of variance=Three-way ANOVA test, Tukey HSD as post hoc test was used. Among the tested resin-based luting cements, one-way analysis of variance=One-way ANOVA test was used for surface hardness evaluation, and Tukey HSD test was used as post hoc. Among the tested materials, analysis of variance in repeated measurements, Bonferroni test was applied as a post hoc test to examine the change in surface hardness values after static-aging at the measurement intervals after 10 minutes, 1 hour, 24 hours and 1 year. Paired Samples t test was used for comparison of upper surface- 79 lower surface and dynamic-aging before/after dynamic-aging procedure. Significance was evaluated at the p<0.05 level. After 1 year, when the results after static-aging and dynamic-aging, which corresponds to 1 year clinical conditions, were evaluated, statistical differences were found in VHN values depending on the nature of the tested materials. In vitro conditions, dynamic- aging is a more suitable test technique, in which information on material-related surface hardness changes can be obtained in a short time. In the tested materials, especially the changes in the upper surface VHN values, the mean and standard deviation values created very small numerical differences. This is explained by the sufficient amount of polymerization that occurs in the materials due to the application of the LED light source with high light intensity from the closest distance (0 mm).