Improvement of Zirconia Shear Bond Strengths by Silica Spray Coating

Objectives: To investigate the effects of silica spray coating on shear bond strengths (SBSs) and bond durability of 3 mol% yttria-stabilized zirconia ceramic (3Y-TZP).
Methods: Forty-eight 3Y-TZP disks were silica-coated by spraying Biomic LiSi (Aidite) and sintered, while forty-eight lithium disilicate glass ceramics (LDGC) served as control. X-ray diffraction (XRD), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray detector (EDX) were used to analyze surface chemical and micro-morphological changes. Silica-coated 3Y-TZP and LDGC disks were etched with hydrofluoric acid (HF) and luted with Variolink N (Ivoclar-Vivadent IPS). The SBSs were determined after water storage (24 h) and thermocycling. The SBSs were analyzed with two-way ANOVA and Weibull analysis. Failure modes and surfaces were determined by optical microscopy and SEM.
Results: XRD, ATR-FTIR and XPS identified formation of lithium disilicate and zirconium silicate on silica-coated 3Y-TZP. Compared with LDGC, silica coating surfaces revealed less micro-porosities with comparatively large lithium silicate crystals after HF etching. The SBSs of silica-coated 3Y-TZP were significantly lower than those of LDGC (P ＜ 0.05). The SBSs of the LDGC gradually decreased from the baseline (34.87±11.02 Mpa) to 10,000 thermocycles (30.72±7.97 Mpa) and to 50,000 thermocycles (27.25±9.03 Mpa), whereas the SBSs of silica-coated zirconia decreased dramatically from the baseline (27.03±9.76 Mpa) to 10,000 thermocycles (21.84±7.03 Mpa), but maintained stable over 10,000 to 50,000 thermocycles (20.77±6.80 Mpa).
Conclusions: A homogeneous silica coating of lithium disilicate prepared on 3Y-TZP surfaces by silica spray coating could achieve two-thirds of bond strengths of LDGC, regardless of thermocycling. And it significantly decreased after 10,000 thermocycles, but maintained stable during 10,000-50,000 thermocycles.