Evaluation of the bonding mechanism of an adhesive material to primary teeth

Purpose: The aim of this study was to evaluate with scanning electron microscopy (SEM) the bonding mechanism of the one-bottle adhesive Prime&Bond NT (Dentsply, PBNT) to enamel and dentin of deciduous teeth, following different methods of substrate treatment. Methods: Eighteen extracted posterior deciduous teeth were randomly divided into 6 groups (N=3). The experimental groups differed for substrate and method of substrate conditioning prior to bonding with PBNT. Group 1: 36% phosphoric acid (PA)/PBNT on dentin; group 2: PA/PBNT on enamel; group 3: non-rinsing conditioner (NRC) (Dentsply)/PBNT on dentin; group 4: NRC/PBNT on enamel; group 5: PBNT on dentin without any previous conditioning; group 6: PBNT on enamel without any previous conditioning. On all the specimens, following the application of the adhesive solution, Dyract AP was layered on top and light-cured. The bonded specimens were processed for SEM observations. Results: When used in combination with 36% phosphoric acid, PBNT was able to form a hybrid layer with resin tags on both enamel and dentin. Following conditioning with NRC, a thinner hybrid layer with shorter resin tags was developed on dentin; on enamel an etching pattern was still detectable. When only PBNT was applied without any previous conditioning, on dentin neither hybrid layer nor resin tags were visible; no sign of micromechanical bonding could be seen on the untreated enamel. Conclusions: The bonding mechanism of the one-bottle adhesive Prime&Bond NT on enamel and dentin of deciduous teeth is effective only following substrate conditioning with 36% phosphoric acid or NRC.