Influence of contamination and cleaning on bond strength to modified zirconia

Objective: To evaluate the influence of contamination and cleaning procedures on shear bond strength (SBS) to modified zirconia surfaces. Methods: One hundred zirconium-oxide ceramic disks fabricated with a rough modified surface (Nobel Bond), which allows more micromechanical interlocking for adhesive cementation, were divided into five groups. Groups were contaminated with organic (OC; human blood and saliva) and/or inorganic contaminants (IC; type IV dental stone). For cleaning, modified surfaces were etched with phosphoric acid for 1 min (PA) or fired in a ceramic furnace up to 910 °C and cleaned in an ultrasonic bath in ethanol (FU). Following combinations of contamination and cleaning protocols were chosen: group 1: OC-PA; group 2: IC-FU; group 3: OC + IC-PA + FU; group 4: OC + IC-no cleaning; group 5: no contamination-no cleaning. Level of contamination and efficacy of cleaning were evaluated using X-ray photoelectron spectroscopy (XPS). Composite cylinders were bonded to the disks using dual curing adhesive resin cement (RelyX ARC). Fifty samples were subjected to 20,000 thermal cycles (TC). All samples were tested for SBS. Statistical analysis was performed using one-way ANOVA with α = 0.05. Results: SBS ranged from 16.6 to 18.8 MPa (non-TC) and 10.6-21.7 MPa (TC). TC did not lower SBS, except for group 1. XPS showed that OC produced higher levels of carbon, nitrogen, and silica, whereas IC generated elevated levels of calcium, sulfur, carbon, and potassium. Cleaning with both procedures reduced contamination significantly. Significance: A combination of FU and PA is an efficient method for cleaning contaminated modified zirconia surfaces.