Contamination of the zirconia surface by components of mixed saliva and its control by X-ray photoelectron spectroscopy. Part 1. Untreated surface (mucin model)
INTRODUCTION. Zirconium dioxide (ZrO 2 ) is among the most widely used materials for fixed dental prostheses, and the reliability of adhesive luting largely depends on surface cleanliness. Contact of the framework with mixed saliva during try-in results in adsorption of organic components that reduces bond strength to resin cements. Conventional cleaning procedures do not always remove the protein film completely, and objective methods for monitoring residual contamination are lacking in clinical practice. AIM. To assess the character of zirconia surface contamination by organic components of mixed saliva using a mucin model and X-ray photoelectron spectroscopy (XPS). MATERIALS AND METHODS. Yttria-stabilized zirconia (Y-TZP) plates were examined in three states: pristine surface, surface after application of a mucin model (snail secretion filtrate), and the same surface after three-fold rinsing with distilled water. XPS was performed on a PREVAC EA15 spectrometer (Al Kα, hν = 1486.6 eV). Atomic concentrations of nitrogen (N) and zirconium (Zr) were quantified and the N/Zr ratio was calculated ( n = 6 per group). Data were analysed by one-way ANOVA with Tukey post-hoc test. RESULTS. The N/Zr ratio was 0.120 ± 0.002 on the pristine surface and increased to 0.181 ± 0.003 after mucin application (+51%; p < 0.001). After rinsing it remained 0.181 ± 0.003, not differing from the mucin group ( p = 0.82) and remaining significantly higher than baseline ( p < 0.001; one-way ANOVA F = 918.3, p < 0.001). CONCLUSION. Organic nitrogen-containing components of mixed saliva adsorb onto zirconia almost irreversibly; threefold water rinsing does not restore the pristine surface state. The N/Zr ratio measured by XPS is an objective and reproducible marker of residual contamination, underlying the developed method for identifying saliva residues on zirconia devices.