Effects of one versus two-layer applications of a self-etching adhesive to dentin of primary teeth: a SEM study

Resin composite is increasingly the material of choice for the restoration of primary teeth, and new materials with simplified procedures are increasingly being offered. Self-etching primers have been developed to simplify the bonding procedures. Some manufacturers recommend the application of these materials in two layers. However little is known about the application times. Therefore, this study evaluated the quality of the interfacial seal and the micromorphology of the hybrid layer in composite restorations bonded with one or two layer applications of a self-etching adhesive to the dentin of the primary teeth. The superfacial dentin (within 1-2 mm of dentinoenamel junction (DEJ)) on the occlusal surfaces of fourteen primary molars was exposed by a flat cut perpendicular to the long axis of the tooth. The occlusal surfaces were divided into two halves by a 1 mm deep groove in the labial-lingual orientation. The teeth were randomly divided into two groups: Group 1: Single Bond (control group) was applied according to the manufacturer's instructions on one half of the surface. On the other half of the same tooth, one layer of Prompt-L-Pop (experimental group) was applied according to the manufacturer's instructions. Group 2: the teeth received the same bonding regimes as group 1, but the experimental group had two layer application of Prompt-L-Pop. All samples were analyzed in SEM. Student's t-test was used to compare the width of the gap and hybrid layer thickness generated by experimental groups and control. There was a statistically significant difference between control (Single Bond) and the experimental groups (one or two layer application of Prompt-L-Pop) (p<0.05). Single Bond showed the best results. Two layer application of Prompt-L-Pop showed better sealing ability than one layer application of it (p<0.05). Only Single Bond presented a visible hybrid layer that had an average thickness of 3.7microm.