Scanning microscopy of resin infiltration patterns in acid-etched incisor enamel

Previous studies have described the surface morphologic characteristics of acid-etched enamel. The purpose of this investigation was to examine the patterns of resin infiltration into the etched enamel. Fourteen, human, incisor teeth, extracted because of advanced periodontal disease, were etched on the labial surfaces for 60 seconds with 37% phosphoric acid, washed in tap water, and then air-dried. A self-cured enamel resin was applied to the etched labial surface and supported with epoxy. The teeth were dissolved in formic acid. The resin remnants were cleaned in water, dried, mounted on specimen stubs, coated with sputtered gold, and examined in a Scanning electron microscope (SEM). Resin infiltration patterns were photographed in the SEM at a magnification of 400 in 0.125-mm2 areas of the incisal, middle, and gingival thirds of each labial surface. Resin infiltration patterns were scored according to the correspondence with the rod-core, rod-periphery, and irregular acid-etch patterns seen in enamel. The distribution of resin infiltration patterns was as follows: rod-core, 9.7%; rod-periphery, 40.5%; and irregular, 49.7%. The values were averaged over all the surface areas. Infiltration patterns into the etched enamel exhibited deep interperikymata resin penetration. Subsurface channeling of resin was responsible for the pattern seen in irregular etch and was the most common form of infiltration in the gingival region. Subsurface channeling may be related to the development of micropores observed in incipient carious lesions. Deep monomer penetration and channeling may be important factors in mechanical attachment.