Abstract
PURPOSE: The aim of this study was to evaluate the effect of hydrofluoric acid (HF) etching duration on the shear bond strength between zirconia-enhanced lithium silicate (ZLS) and enamel. METHODS: Ninety-six extracted human third molars and premolars were used and randomly divided into six groups (n=16). The teeth were sectioned to produce specimens from the buccal and lingual surfaces, polished to achieve smooth bonding areas of 3×3 mm. The ceramic materials used (Celtra Duo, IPS e.max Press) were prepared into 3×3×3 mm blocks, with surfaces treated with or without 4.9% HF for varying durations. Representative specimens from each group were analyzed using field-emission scanning electron microscopy (SEM) to assess etching-induced surface morphology. Silane coupling agent and luting resin (RelyX(TM) Veneer) were then applied to bond the ceramics to the enamel, forming the bonding specimens. These specimens were stored in distilled water at 37°C for either 24 hours or 6 months before shear bond strength testing, which was conducted using a universal testing machine at a crosshead speed of 1.0 mm/min. Failure modes were evaluated under a stereomicroscope. Data were analyzed using two-way ANOVA and Post hoc Tukey tests test (α=.05) as well as Weibull distributions. RESULTS: As etching time increases, the dissolution of ceramic components on the ZLS surface also rises. After 24 hours or 6 months of storage in water at 37°C, the shear bond strength of ZLS etched with 4.9% HF for 40 seconds was significantly greater than that of Lithium disilicate (LS(2)) etched with 4.9% HF for 20 seconds (P<.05), accompanied by a higher Weibull modulus. Aging resulted in a reduction of bond strength across all groups, approximately 20%, alongside lower characteristic strength, and a higher incidence of adhesive failures at the bonding interface. CONCLUSION: HF etching duration has a significant effect on the surface morphology of ZLS and the shear bond strength with enamel. ZLS etched with 4.9% HF for 40 seconds demonstrated the highest shear bond strength, highlighting the importance of optimal etching time for enhancing bonding performance.