Evaluati̇on of the effects of different surface treatments on repair of fiber-reinforced dentin composite with posterior composite

Objective: The aim of this study is to investigate the effects of different surface treatments applied to the fiber reinforced dentin composite surface on the repair bond strength and to examine how dimethyl sulfoxide (DMSO) application affects the adhesion. Method: 40 composite resin blocks with 4x4x4 mm dimensions were formed by using composite (EverX Posterior,GC Europe), which is recommended to be used under high chewing forces in the clinic. The samples were divided into 8 different groups (n=5) according to the surface preparation methods; (G1) negative control group, (G2) adhesive application, (G3) 50% dimethylsulfoxide application ,(G4) 50% dimethylsulfoxide + adhesive application, (G5) 37% phosphoric acid etch+ adhesive application (G6) air abrasion + adhesive application, (G7) 37% phosphoric acid etch + 50% dimethylsulfoxide application + adhesive application, (G8) air abrasion + 50% dimethylsulfoxide application + adhesive application group. Composite specimens with different surface preparation processes were embedded in acrylic. Afterwards, an adhesive agent (Single Bond Universal, 3M, ESPE,Neuss,Germany) was applied to the surfaces according to the manufacturer's recommendations. The adhesive applied surfaces were repaired in two layers with a posterior composite (Estelite Sigma Quick Posterior,Tokuyama,Tokyo, Japan) 4x4x4 mm in size using silicone guides. Composite sticks with dimensions of 1x1x8 mm were cut with a diamond saw under water cooling. A total of 20 composite sticks were randomly selected for the microtensile bond strength (μTBS) test from each group. Before the μTBS test, the adhesive interface area of each composite bar was measured with a digital caliper. The samples were adhered to the test apparatus of the micro tensile tester with cyanoacrylate adhesive. The μTBS test was applied to 160 composite bars at a head speed of 1.0mm/min under 50 kilogram (kgf) load until failure occurred. The fracture surfaces of the specimens subjected to the μTBS test; examined under a stereomicroscope (x25) to determine the type of failure. Six short fiber reinforced composite samples applied with different surface treatments control (only the bur group), 37% phosphoric acid, air abrasion, dimethylsulfoxide, phosphoric acid+DMSO, air abrasion+DMSO, and one no storaged in water and no surface treatment applied short fiber reinforced composite samples' surface topography was investigated by scanning electron microscope (SEM) analysis. The Shapiro Wilk test was used to test the normality of the microtensile data of surface treatments. As a result of the ANOVA test, it was observed that there was a difference between the mean microtensil bond values of the groups. Differences between groups were determined by Tukey HSD test. Results: The highest average microtensile bond strength values were recorded in the eighth group (air abrasion + DMSO + adhesive). The lowest mean values were found in the negative control group, which was applied only with bur roughening. Statistically significant μTBS values were obtained in all adhesive-applied groups. The negative control group was the group in which the most adhesive failure was detected (100%). When the SEM images were examined, it was seen that the acid etch application partially removed the residues on the composite surface, while the air abrasion application damaged the fiber structures from place to place. Conclusion: In the repair of fiber reinforced dentin composite with posterior composite, it was detected that the adhesive applied groups showed higher average bond strength than the negative control group. It was noted that the application of 50% DMSO without the application of adhesive did not statistically increase the success of the bonding. Acid etch and air abrasion applications on the fiber composite surface roughened with the bur did not provide a statistically significant additional contribution when compared to the group in which only the adhesive was applied.