Bonding to Enamel/Dentin Etched with Phosphoric and Hydrofluoric Acids

Objective: To develop an order for using dentin/enamel etchant and the porcelain etchant which yield the highest bond strength to composite resin. Intraoral repair of porcelain requires sequential etching of porcelain, enamel and dentin with different etchants. Reportedly, etching of enamel and dentin with hydrofluoric acid has an adverse effect on bonding to composite resin. Method: Human molars flattened in enamel (E) and dentin (D), embedded in polymethylmethacrylate were used. They were placed in four groups and etched as follows: (I) 37% phosphoric acid (Ultra-etch, Ultradent), (II) 9.5% buffered hydrofluoric acid (Porcelain Etch, Ultradent); (III) phosphoric acid followed by hydrofluoric acid; and (IV) hydrofluoric acid followed by phosphoric acid. Etched surfaces were treated with a dentin bonding system (PQ1, Ultradent) and bonded to a hybrid composite resin (Z100, 3M). The bonds were tested using an Instron testing machine at a crosshead speed of 1 mm/min. Resulting shear bond strength (MPa) for enamel (E), dentin (D) and four etching treatments were: IE = 28.2±71; IIE = 6.1 ± 1.8, IIIE = 13.4 ± 3.5, IVE = 13.2 ± 4.1, ID = 15.0 ± 4.3, IID = 8.9 ± 2.4, IIID =11.7 ± 6.5 and IVD = 11.01 ± 6.5. Results: ANOVA (P<0.05) revealed significant differences between groups. Conclusion: Combined use of hydrofluoric acid and phosphoric acid significantly reduced bonding composite resin to enamel and dentin. The sequence of use of the two etchants had no effect on the bond of composite resin to enamel or dentin. Supported in part by Ultradent Products Inc.