Bonding mechanism of three "one-bottle" systems to conditioned and unconditioned enamel and dentin

This in vivo study investigated the formation of hybrid layer, resin tags and adhesive lateral branches, by use of the latest generation of enamel-dentin bonding systems ("one-bottle" systems) on conditioned and unconditioned enamel and dentin.

The dentin adhesives were tested on 24 flat dentin preparations made on facial surfaces of vital, periodontally compromised teeth. The experimental teeth were randomly divided in six groups of four samples each. Group 1: Prime & Bond 2.1 (conditioned dentin, CD); Group 2: Single Bond (CD); Group 3: Syntac Sprint (CD); Group 4: Prime & Bond 2.1 (unconditioned dentin, UD); Group 5: Single Bond (UD); Group 6: Syntac Sprint (UD). In the first three groups, the "one-bottle" systems were applied following the manufacturers' instructions, while in the other three groups the dentin and the enamel were not treated with phosphoric acid and the primer was applied directly on the prepared surfaces. On top of the primer-adhesive, a thin layer of resin was applied and light-cured for 20 seconds. The sample teeth were extracted immediately after the adhesive material was light-cured. All the samples were split-fractured along their long axis. Half of the samples were deproteinized and decalcified at the interface in order to visualize the hybrid layer and the other halves were completely dissolved in order to observe the morphology of resin tags by use of scanning electron microscopy.

Groups 1-3: All the tested products showed the same micromechanical bonding mechanism to conditioned dentin with phosphoric acid: they formed hybrid layer, resin tags and adhesive lateral branches. In the samples of the first three groups, characteristic reverse cone-shaped tags with their corresponding adhesive lateral branches were evident. At the enamel site, traditional pattern of etch enamel was always observed. Groups 4-6: When the bonding systems were applied on unconditioned dentin, hybrid layer was not formed, resin tags were rarely noted and their shape was narrow and they did not completely seal the tubular orifices. The tubules remained mainly closed by smear plugs. At the enamel site, the unetched surface showed absence of characteristic etch pattern and of resin tags.