The influence of dentine bonding systems and their handling characteristics on the morphology and micropermeability of the dentine adhesive interface

Objectives: Development of an adequate interfacial seal is fundamental to achieving a good dentine bond. This study investigates the influence of the properties and application of primers and resin adhesives on dentine interfacial morphology and micropermeability, using a fluorescence confocal microscopy technique. Methods: Three commercially available (Optibond, Clearfil Liner Bond 2, Pertac Universal Bond) and four experimental dentine bonding systems based on the total etch technique were used in the study. Approximal cavities were prepared in third molar teeth and restored using the dentine bonding system (DBS) and resin composite. In the interfacial morphology study the primer and adhesive bonding system were labelled with fluorescent dyes, while in the micropermeability study the pulp chambers were filled with fluorescent labelled saline for 3 h. Ten teeth were prepared in each study for each dentine bonding system. Teeth were sectioned longitudinally and viewed with a tandem or laser scanning confocal microscope. Interfacial micropermeability from the pulpal wall was measured using image analysis techniques. Results: All primers and adhesives showed good penetration of the prepared dentine, except Pertac Universal Bond which manifested 100% micropermeability. The lowest micropermeability results were obtained with Clearfil Liner Bond 2, Optibond and a total etch experimental system where the primer was applied with agitation and contained no photo-initiators and the adhesive resin was unfilled. The latter, when used with a photosensitive version of the same primer, demonstrated a detrimental effect on micropermeability. Light activation of primers in the experimental systems coincided with very variable patterns of leakage. Conclusions: This high resolution confocal fluorescence technique enabled both the degree and site of micropermeability within the interfaces to be recorded. Matching of primers and adhesives in DBS is important to minimize micropermeability. The non-polymerized primer system probably retained some elasticity in the hybrid zone and so gave less leakage than experimental primers with photo-initiators.