Post‐etching cleaning influences the resin shear bond strength to CAD/CAM lithium‐disilicate ceramics

Background Bonding to silica-based ceramics requires micro mechanical (hydrofluoric-acid, HFetching) and chemical (silane) coupling [1–5]. The HF-etching provides dissolution of Abstract Statement of problem: The hydrofluoric acid (HF) is able to promote selective dissolution of the glassy phase in silica-based ceramic. However, the etching leaves insoluble silica-fluoride salts in the surface that affects negatively the bond, affirming the need of a post-etching cleaning. Purpose: Evaluate the shear bond strength (SBS) of composite resin to CAD/CAM lithium-disilicate ceramics after different post-etching cleaning and silane treatments. Methods: Twenty-four 2 mm-thick slices of IPS e.max CAD (Ivoclar Vivadent, AG, Schann, Liechtenstein) were crystallized, embedded in acrylic resin, polished and cleaned in an ultrasonic bath. Each specimen was etched with 5% HF for 20 s, rinsed for 60 s, and treatment was completed using surface cleaning and silanization. The cleaning methods were: AW—air/water spray; UB—ultrasonic bath; PA—37% phosphoric acid; and ST—steam cleaning. The cleaned surface received: E—no silane treatment; E/S—silane application for 20 s, air drying for 20 s and hot drying (60 °C) for 20 s; E/S+—silane application for 60 s, air drying for 20 s, hot air drying (60 °C) for 20 s, rinsing with boiling water for 15 s and hot air drying for 20 s. Cylinders of composite resin (n = 12) (Z100, 3M-ESPE, Saint Paul, MN, USA) were bonded using an adhesive resin (Optibond FL adhesive, Kerr Corp, Orange, CA, USA). SBS testing was carried out after 24 h of storage in water. Samples for each post-etching cleaning regimen were analyzed by SEM. Results: According to two-way ANOVA (Bonferroni-corrected post hoc tests, p < 0.05), the SBS was significantly influenced by the post-etching cleaning, with UB yielding the highest SBS (21 MPa for E/S); other post-etching cleaning regimens showed lower SBS values (12–17 MPa). The type of silane application was not significantly different. The SEM analysis showed a cleaner ceramic surface for UB when compared to the other groups. Conclusions: Etching lithium disilicate ceramics following by ultrasonic bath cleaning and regular application of a silane is recommended.