Preparation, properties and effects on bond strength of a glass coating method for ultra-translucent zirconia...

This study aimed to develop a SiO₂-Li₂O-Al₂O₃ (SLA) glass-ceramic coating system (GC) for application to ultratranslucent zirconia (5Y-PSZ), compare it with a commercial glass-ceramic coating system (Biomic LiSi Connect, BLSC), and evaluate its effects on shear bond strength and optical properties of 5Y-PSZ.

A total of 110 zirconia specimens were prepared. An experimental SiO₂-Li₂O-Al₂O₃ (SLA) glass-ceramic powder was synthesized by melt quenching, applied to 5Y-PSZ surfaces by brush coating, and subjected to a second heat treatment to form the GC coating system. This coating system was compared with a commercial glass ceramic coating system, Biomic LiSi Connect (BLSC). Before bonding, the performance differences between the two distinct coating systems were characterized by scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), three-dimensional surface morphology analysis, and measurements of translucency parameter (TP), contrast ratio (CR), and opalescence parameter (OP). For the shear bond strength (SBS) test, lithium disilicate glass ceramic was used as the reference control group, and airborne particle abrasion + Z Prime Plus™ (APA+ZP) was used as the positive control group. The effects of the two glass coating systems, combined with 5% hydrofluoric acid (HF) etching for 20 s and 60 s (designated as GC20s, GC60s, BLSC20s, and BLSC60s), on the bond strength to zirconia were investigated both immediately and after 5000 thermal cycles. Failure modes were analyzed with optical microscopy and SEM. Statistical analysis was performed using one-way ANOVA followed by post hoc Bonferroni test, with the significance level set at α = 0.05.

The glass coating (both GC and BLSC) resulted in a uniform, glass-rich surface and a graded glass-zirconia composite interphase and significantly enhanced optical properties. HF etching time (5%, 20 s vs 60 s) significantly affected surface roughness; both GC and BLSC groups exhibited increased SBS with the extension of etching time (p < 0.05). Before thermocycling, the higher SBS was observed in the GC 60 s group (26.1 ± 2.3 MPa) (p < 0.05), which was similar to the LDGC 20 s reference group (28.2 ± 3.8 MPa, p > 0.05). It also demonstrated superior bond stability after thermocycling. Failure mode analysis showed a predominance of mixed and cohesive failures.

This study provided an effective strategy for enhancing the bond strength to ultra-translucent zirconia (5Y-PSZ) without compromising its properties. SLA glass coating has the potential to contribute to improving the SBS of 5-YPSZ zirconia restorations in a clinically applicable manner.