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 surface. Methods: 100 zirconium oxide ceramic disks fabricated with a rough modified surface (Nobel Bond), which allows more micromechanical interlocking for adhesive cementation, were divided into 5 groups. The groups were contaminated using human saliva (SL), blood (BL), and/or type III dental stone (ST). For cleaning the modified surfaces were either 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). Also a combination of the both cleaning methods was used. The following combinations of contamination and cleaning protocols were chosen: group 1: SL,BL,ST-PA,FU; group 2: SL,BL-PA; group 3: ST-FU; group 4: SL,BL,ST-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). 50 samples were subjected to 20,000 thermal cycles (TC). All samples were tested for SBS. Statistical analysis was performed using a two-way ANOVA with α=0.05. Results: SBS ranged from 16.6 to 18.8 MPa (non-TC) and 10.6 to 21.7 MPa (TC). Only group 2 after TC was significantly lower in SBS than all other groups. XPS showed that saliva and blood contamination produced higher levels of carbon, oxygen, and nitrogen, whereas stone contamination generated elevated levels of sulfur and calcium. Cleaning reduced contamination significantly. Conclusion: A combination of PA, FU can be used as an efficient method for cleaning contaminated modified zirconia surfaces.