Contemporary self-etch adhesives can be classified into 4 categories: aggressive (pH < 1), intermediate (pH ≈ 1.5), mild (pH ≈ 2) or ultra-mild (pH > 2.5), according to their pH.2 The pH of most universal adhesives ranges from 2.3-3.2. For example, All-Bond Universal® and Scotchbond® Universal have pH values of 3.2 and 2.7, respectively. For bonding to enamel, the pH of any self-etch adhesive is not acidic enough (phosphoric acid etchant has a pH of 0.1, which is 1000 times more acidic than an adhesive with a pH of 3) to dissolve and etch enamel. In order to have a maximum mechanical bond, selective etching of the enamel with phosphoric acid is required. For bonding to dentin, more acidic self-etch adhesives will dissolve more of the smear layer, which may result in lower bond strength and higher sensitivity rates.2 Adhesives with low pH cause incompatibility between the acidic adhesive and the self-cure mechanism of a dual-cure resin composites/cements.3,4 The major reason for the incompatibility is because the amine-initiator of the composite/cement is deactivated by the ‘acid-base’ reaction between the acid (H+) from the oxygen-inhibited layer of the cured adhesive and the amine-initiator of the composite/cement. The consequence is no polymerization at the adhesive and composite/cement interface, resulting in no bonding due to the incompatibility.
Published on Aug 11th 2015