Does a Self-etching Ceramic Primer Improve Bonding to Lithium Disilicate Ceramics? Bond Strengths and FESEM Analyses

Objective: To compare the effect of hydrofluoric acid (HF) vs self-etching ceramic primer on resin cement microshear bond strength (mu SBS) and ultramorphology of lithium disilicate (LD) ceramic. Methods and Materials: LD (IPS e.max CAD, Ivoclar Vivadent) blocks (14x4x2 mm(3)) were polished to 1200 grit and assigned to nine groups (n=5): CON: control, no LD surface treatment; IVO: 5.0% HF (IPS Ceramic Etching Gel, Ivoclar Vivadent); VIT: 5.0% HF (Vita Ceramics Etch, VITA Zahnfabrik); FGM: 5.0% HF (Condac Porcelana, FGM); ULT: 9.0% HF (Porcelain Etch, Ultradent); PRM: 9.6% HF (Premier Porcelain Etch Gel, Premier); BIS: 9.5% HF (Porcelain Etchant, Bisco Inc); DEN: 10.0% HF (Condicionador de Porcelanas, Dentsply Brazil); and MEP: self-etching ceramic primer (Monobond Etch & Prime, Ivoclar Vivadent). For all HF groups and control, an MDP-containing silane solution (MB+, Monobond Plus, Ivoclar Vivadent) was applied on rinsing the HF gel and air drying. Three transparent matrices for each specimen were filled with light-cured resin cement (Variolink Veneer, Ivoclar Vivadent). After storage in water for 48 hours at 37 degrees C, specimens were tested in shear mode to measure mu SBS. Mode of failure was analyzed at 50x. Statistical analysis included one-way analysis of variance and the Duncan post hoc test (alpha=0.05). Thirty-six additional LD specimens were assigned to the same experimental groups (n=4) and observed under a field-emission scanning electron microscope (FESEM) at magnifications ranging from 10,000x to 100,000x. Results: IVO resulted in statistically higher mean mu SBS than all the other groups. MEP resulted in statistically lower mu SBS than all HF groups. The failure mode for MEP was predominantly adhesive. The most frequent failure mode for the HF groups was mixed. CON resulted in 100% pretesting failures. For FESEM, no retentive pattern was observed for CON specimens. MEP resulted in the least pronounced etching pattern, few areas around crystals exhibited a slight increase in retention pattern compared to the control group. All HF gels created microporosities on the LD surface with distinct etching patterns. VIT and DEN resulted in an LD ultramorphology that suggested overetching. Conclusions: HF etching followed by a silane solution resulted in higher bond strengths than a self-etching ceramic primer. Some HF gels may cause overetching of the LD intaglio surface.