Failure at the dental adhesive—etched enamel interface

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. Copyright © 1974, Wiley Blackwell. All rights reserved