Characterisation of a new plasma-enhanced film to improve shear bond strength between zirconia and veneering ceramic

The aim of this study was to develop and characterise a new plasma-enhanced chemical vapor deposition (PECVD) film for improving shear bond strength (SBS) between yttria-stabilised tetragonal zirconia (Y-TZP) and veneering ceramic. In total, 192 Y-TZP samples (13 x 5.4 x 5 mm) were divided into 6 groups: control - no treatment (C), airborne-particle abrasion with 27 mu m aluminum oxide particles (Al-27), 110 mu m aluminum oxide particles (Al-110), and 250 mu m aluminum oxide particles (Al-250, application of liner for zirconia (L) and the PECVD film application (P). The Y-TZP surface was characterised by means of Scanning Electronic Microscopy (SEM), Energy-dispersive Spectroscopy (EDS), atomic force microscopy (AFM), surface profilometry and surface free energy (SFE). SBS between Y-TZP and veneering ceramic was tested before and after thermocycling (20,000 cycles of 5 and 55 degrees C), and failure mode was also evaluated. Data were analysed by ANOVA and Tukey's HSD test (alpha = 0.05). Data analysis showed that PECVD film had no effect on surface roughness of Y-TZP (p > 0.05 vs control), whilst the other groups presented higher roughness values (p < 0.05). All treatments increased SFE, except the Al-27 group. The highest SBS was presented by the P group (p < 0.05), and values were similar to those of the Al-27 group (p = 0.107). Mixed failures were prevalent in all groups, and premature failures were found only in Al groups after thermocycling. Whilst PECVD treatment did not affect Y-TZP surface roughness, high SBS between Y-TZP and the veneering layer was observed. Therefore, PECVD treatment is a promising alternative to improve the performance of bi-layer zirconia-based restorations.