Investigation of the effect of hydrofluoric acid in different concentrations and surface treatments on SHEAR bond strength of three different ceramic/ GLASS polymer CAD/CAM blocks to resin cement

Objective: The aim of the study is to examine the effect of different surface treatments on the shear bond strength of three different polymer-containing CAD/CAM materials to the resin cement. Method: Samples of 2 mm thickness (N=180) were obtained using a precision cutting device from Grandio block (VOCO, GmbH Cuxhaven, Germany), Vita Enamic (Vita Zahnfabrik, Cuxhaven, Germany) and Cerasmart (GC, Tokyo, Japan) which are ceramic/ glass blocks. The prepared samples were divided into six subgroups (n=10), including the control group, according to the applied surface treatments. Cojet, 2W Er,Cr:YSGG laser, 9.5% hydrofluoric acid, 6% hydrofluoric acid and 3% hydrofluoric acid were applied to the surface of the specimens where cement shear bond strength was to be evaluated. After the applied surface treatments, 2 randomly selected sample from each group was subjected to SEM and AFM analysis. Then, dual-cure self-adhesive resin cement RelyX U200 (3M ESPE, St. Paul, USA) was applied to the treated surfaces of all samples. The bond strength of the resin cement was tested with a microtension device, Esetron Mechatronics (Ankara, Turkey), with a force speed of 0.5 mm/min, with a force perpendicular to the sample surfaces. Due to the normal distribution of the obtained data, the "Independent t-test" and "One-Way ANOVA" test, which are parametric methods, were used for comparisons between groups. Statistical significance level was accepted as p<0.005. Fracture types were examined with a stereomicroscope. Results: There was a significant difference in the bonding strength values of Cojet, 2W Er,Cr:YSGG laser and 9.5% HF acid applied Grandio block and Vita Enamic CAD/CAM block samples (p<0.05). All surface treatments applied to Cerasmart samples increased the bond strength value. Adhesive fractures were the most common in stereomicroscopy, while cohesive fractures were found only in 4 specimens. Conclusions: The effectiveness of the applied surface treatments varies according to the material type. Although low concentrations of hydrofluoric acid did not affect all groups, it changed the surface topographies. Key words: CAD/CAM blocks, Surface treatment, Resin cement ,Bond strength