The Effect of cleaning Saliva-Contaminated Zirconia with Various Sodium Hypochlorite Concentrations on shear bond strength

Abstract

The objective of the study is to investigate and compare the adhesive bond strength between resin cement and zirconia surface after contamination with saliva, as well as to compare how different concentrations of sodium hypochlorite solution used in cleaning affect the bond strength. Additionally, the study aims to compare the bond strength between resin cement and zirconia surface before and after thermocycling. Research Methodology: Test specimens consisted of 103 zirconia pieces in total. Each specimen was embedded into a square-shaped mold made of polyvinyl chloride (PVC), then sandblasted, cleaned, and dried free of any residual material. All except one specimen underwent the contamination process with human saliva, after which the specimens were divided into 6 groups according to the following surface cleaning methods: Group 1: Cleaning with distilled water (the control group) Group 2: Cleaning with isopropyl alcohol Group 3: Cleaning with 1% sodium hypochlorite solution Group 4: Cleaning with 2.5% sodium hypochlorite solution Group 5: Cleaning with 5% sodium hypochlorite solution Group 6: Cleaning with 10% sodium hypochlorite solution One specimen from each group was randomly selected for the microscopic surface examination using Scanning Electron Microscopy (SEM) and the elemental analysis using Energy-Dispersive X-ray Spectroscopy (EDS). The remaining specimens were injected with self-adhesive resin cement (RelyX universal), then immersed in distilled water at 37 °C for 24 hours, and, finally, divided randomly into two subgroups. The specimens in Subgroup 1 were immediately tested for the shear bond strength while those in Subgroup 2 underwent thermocycling at 5 and 55 °C for 10,000 cycles before being tested for the shear bond strength. The shear bond strength testing was performed using two-way ANOVA analysis and Tukey's post-hoc test. Research Findings: The average bond strength of all groups decreased after thermocycling compared from before thermocycling. The highest average bond strength after thermocycling was observed in the group cleaned with 10% sodium hypochlorite solution (27.36 ± 2.38 MPa), albeit not significantly different from the groups cleaned with 2.5% and 5% sodium hypochlorite solutions. After thermocycling, the group cleaned only with distilled water experienced bond failure among all its specimens.