Ammonium Hydrogen Fluoride Etchant for Bonding Pretreatment of Glass-Ceramics

Objectives: Hydrofluoric acid (HF) etchant is commonly used for bonding pretreatment of glass-ceramics such as feldspathic porcelain and lithium disilicate glass, while its high toxicity necessitates safer alternatives. This study aimed to develop a low-toxicity etchant for glass-ceramics and evaluate its effect on the bond strength between glass-ceramics and resin cement.
Methods: The experimental etchant (EXP) was prepared by dissolving ammonium hydrogen fluoride and ammonium hydrogen sulfate in distilled water with 1% fluoride concentration. EXP was applied to lithium disilicate glass (e.max CAD, Ivoclar) and feldspathic porcelain (Bloc Mark II, VITA) for bonding pretreatment. Surface morphology and roughness were analyzed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), respectively. Bonding tests involved treating the etched surfaces with a silane-coupling agent, bonding with resin cement (Panavia V5, Kuraray), and subjecting samples to thermocycling. Shear bond strength (SBS) was evaluated and compared with unetched samples (Cont), Porcelain Etchant (HF etchant, Bisco), and Monobond Etch & Prime (MEP, Ivoclar). Statistical analysis was conducted using one-way ANOVA with Tukey’s test (p < 0.05).
Results: SEM observation revealed that the EXP etched the glass phase of both glass-ceramics, demonstrating behavior similar to that of the HF etchant. In contrast, no etching was observed on glass-ceramics treated with MEP. CLSM analysis indicated significantly higher surface roughness for both glass-ceramics in the EXP group compared to Cont and MEP. Regarding SBS results for MARK II, no significant differences were observed among the groups. For e.max, however, the SBS of the EXP group (5.7 MPa) was lower than that of HF (9.3 MPa) but higher than those of Cont (0 MPa) and MEP (1.4 MPa).
Conclusions: The EXP etchant, containing low concentrations of ammonium hydrogen fluoride and ammonium hydrogen sulfate, effectively etched glass-ceramic surfaces and enhanced bond strength to resin cement. EXP etchant shows potential as a low-toxicity alternative to conventional HF etchant for glass-ceramic bonding pretreatment.