Scanning electron microscopic analysis of the efficacy of acid etching on cat enamel

The effect of etching on cat enamel made with 40% orthophosphoric acid for different times was evaluated. Twenty-one cat teeth were selected and randomly divided into three groups of seven teeth each. They were subjected to etching on a circular area of the coronal enamel (diameter = 2 mm) for 30 s (group A), 45 s (group B) and 60 s (group C). The samples obtained were observed by a scanning electron microscope focusing on the border area between etched and unetched enamel, to highlight the differences. The micrographs were subjected to blind assessment of three experienced operators. The groups were statistically assessed with the Wilcoxon test. At 30, 45 and 60 s, the acid attack results only in the formation of an irregular enamel surface and without uncovering and attack of the prismatic organisation. Prismatic areas with preferential interprismatic action could be detected in few samples etched for 60 s. Analysis with ImageJ was also used to quantify the efficacy of acid etching in the conditions used for human enamel, by an evaluation of grey levels. In cat enamel the etching times considered are not as effective as in human enamel for the purpose of adhesion and the presence of a thick prismless layer could explain this result.