Effects of surface treatment and thermocycling on shear bond strength of zirconia-reinforced lithium silicate ceramic

Abstract

Zirconia-reinforced lithium silicate (ZLS) ceramic is a novel material which combines the outstanding aesthetic of lithium disilicate and mechanical properties of zirconia ceramic. However, there was insufficient information with regards to effective treatment protocol along with the durability of bond strength. This study aimed to investigate the effects of different surface treatments and thermocycling on shear bond strength (SBS) between resin cement ZLS ceramic. Ninety-six ZLS ceramic specimens were prepared and randomly allocated to four different surface treatment groups: etch and silane (ES), etch and universal primer (EUP), self-etching primer (SEP) and sandblasting and silane (SS). Standardized composite cylinders were bonded to treated ZLS ceramic, after which SBS values were obtained via universal testing machine either after 24H water storage only or with additional 5,000 cycles of thermocycling (TC), resulting in eight subgroups (n = 12). After the failure mode was evaluated under a stereomicroscope (30X), representative scanning electron microscopy (SEM) images (40X) were acquired. Additional ZLS specimens were prepared and randomly allocated to: hydrofluoric acid etching, self-etching primer and sandblasting groups for the surface roughness (Sa) test (n = 10). Supplementary specimens were sent for fieldemission scanning electron microscopy (FE-SEM) (n = 2) and atomic force microscopy (AFM) (n = 2) to investigate their surface topographies. ANOVA showed a statistically significant difference in SBS values following different surface treatment protocols after 24H water storage (p < 0.001). However, TC groups revealed no statistically significant difference in their SBS value (p = 0.394). All surface treated groups were significantly affected by TC (p < 0.001), except for the SS group (p = 0.48). Sa was significantly influenced by the different surface treatment protocols (p < 0.001). SEP’s ability to achieve comparable bond strength with a less technique-sensitive approach makes it a favourable alternative to ES for the surface treatment of ZLS ceramic. Future clinical studies are warranted to validate these findings.