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Summary The chemical treatment of enamel surfaces is an approach in obtaining increased bonding of dental materials to tooth surfaces. Three etching solutions commonly used at present are 50% H3PO4, 50% H3PO4 attenuated with 7% zinc oxide and 50% citric acid. The effects of these three conditioning solutions on normal and polished enamel surfaces and on the interfaces between untreated enamel and etched enamel surfaces were studied by scanning electron microscopy. The variable etching pattern observed with each of the acids made a comparative study difficult. This was further complicated by the dependence of the etching action on prism orientation on polished enamel surfaces. Additional factors that have to be considered are the presence of prismless enamel and perikymata. Surface profile recordings of polished and acid-etched polished enamel surfaces provided some quantitative measure of the etching action of the conditioning solutions. The 50% citric acid solution had the mildest etching action while 50% H3PO4 and 50% H3PO4 attenuated with 7% zinc oxide elicited comparable responses.

Summary Conditioning of the enamel surface is an accepted procedure in several disciplines of dentistry to obtain increased bonding of dental materials to tooth surfaces. Three etching solutions commonly in use are 50% phosphoric acid, 50% phosphoric acid attenuated with 7% zinc oxide by weight and 50% citric acid. The effects of these solutions on the contact angle of an uncured epoxy resin on, and the bond strength of an epoxy resin formulation to polished enamel surfaces were investigated and compared with the results obtained on polished, unconditioned surfaces. In addition, the rates of etching of enamel surfaces by these acids were determined. The attenuated phosphoric acid produced the greatest reduction in contact angles and the most marked increase in bond strengths. 50% phosphoric acid etched the enamel surface to a greater extent than the other conditioning solutions.

Summary Phosphoric acid at different concentrations has been extensively used as an etching agent to improve bonding of dental materials to enamel surfaces. Recently attention has been drawn to the possible use of polyfunctional organic acids as conditioning agents. The object of this investigation was to determine the optimal concentration of pyruvic acid as an etching agent. A commercial composite resin with an intermediary bonding system supplied with 37% H3PO4 as an etching agent was used as the control system. In addition, a comparative study was carried out to evaluate 37% H3PO4, 20% lactic acid and the optimal concentration of pyruvic acid as conditioning solutions. Etching enamel surfaces with 10% pyruvic acid resulted in the optimal tensile bond strength of the resin to etched enamel surfaces. The use of 10% pyruvic acid did not adversely affect the bond strength of the resin system when compared to enamel surfaces etched with 37% H3PO4 for the same time period. Significantly lower tensile bond strengths were recorded on enamel surfaces etched with 20% lactic acid. The rate and depth of etching obtained with 37% H3PO4 can be considerably reduced by using 10% pyruvic acid as the conditioning agent.

Summary None of the materials presently available to the dental profession truly dhere to enamel and dentine. Conditioning of the enamel surface with phosphoric acid greatly increases the bonding of dental materials to tooth structure and the etching technique is now an accepted and widely applied procedure in dentistry. During the development and laboratory evaluation of new dental materials, the resin-enamel bond strength is determined by means of tensile loading tests. The site of failure is often recorded as occurring within the test material; partly within the material; at the adhesive-enamel interface; within the enamel; or in a combination of these sites. An epoxy resin formulation developed for the direct bonding of orthodontic attachments was used as the adhesive and enamel etched with 50% phosphoric acid as the adherend surface. Experimental bonds were subjected to tensile stresses to failure and both the enamel and adhesive aspects of the fractured bonds examined by scanning electron microscopy. The results indicate that the sites of failure cannot be reliably classified by visual examination per se or under low magnification. A model is proposed to elucidate the characteristics of interfacial failures. This experimental model was tested by surface roughness profiles and atomic absorption spectrometry.

Summary Low viscosity bonding resins have been introduced for use on etched enamel surfaces prior to the application of the viscous composite resins. In this in vitro study the effects of a low viscosity bonding resin on the bond strength, adaptation and microleakage of a composite resin to etched enamel were evaluated. The low viscosity bonding resin did not improve the tensile bond strength of a composite resin to etched enamel, did not increase resin penetration into etched enamel and did not decrease marginal leakage at the composite resin/etched enamel interface. The continued use of low viscosity bonding resins in clinical dentistry is questioned.