Depth of resin penetration into enamel with 3 types of enamel conditioning methods: a confocal microscopic study

The clinical efficiency of a bonding material relies on its bond strength and debonding characteristics; the depth of resin penetration into enamel affects both of these factors. The depth of resin penetration has been previously studied by researchers using laborious, indirect methods, including the scanning electron microscope and the optical microscope.

We used a more direct method, confocal microscopy, to visualize the resin tags in enamel. Thirty maxillary first premolars were selected and divided into 3 groups. In group A, the buccal enamel surfaces were conditioned with 37% phosphoric acid; in group B, a self-etching primer was used; and group C was treated with air abrasion. Transbond XT adhesive (3M Unitek, Monrovia, Calif) was used to bond a modified bracket. Transbond XT primer (3M Unitek) mixed with rhodamine B fluorescent dye (Chennai Chemicals, Chennai, India) was applied in groups A and C. In group B, rhodamine was mixed with self-etching primer. After curing, the brackets were debonded, and the teeth were visualized under the fluorescent channel of the confocal microscope.

Maximal resin penetration of 53.9 μm was observed in group A, followed by group B at 40.5 μm and group C at 39.9 μm.

Confocal microscope evaluation showed that enamel conditioning with 37% phosphoric acid produced greater depths of resin penetration than did self-etching primer or air abrasion.