Ultrastructural Investigation Of The Enamel-Bonding Interface Using Self-Etching Primers M. Hannig*, H. Bock, B. Bott, W. Hoth (Clinic Of Operative Dentistry And Periodontology, University Of Kiel, Germany) The purpose of this in vitro study was to investigate the micromorphological appearance of 1) the enamel surface and 2) the resin-enamel interface after application of the following self-etching / self priming adhesive systems: Clearfil Liner Bond 2 (LB 2), Clearfil Liner Bond 2V (LB 2V), Clearfil SE Bond (SE), Etch & Prime 3.0 (EP), Resulcin AquaPrime + Monobond (RAP).   The buccal surfaces of extracted human molar teeth were ground flat and polished using 1000-grit and 4000-grit abrasive paper. In the first part of the study, the self-etching primer components of the five adhesive systems were applied to six enamel surfaces each, according to the reaction times specified by the manufacturer, subsequently thoroughly rinsed with water and analysed by SEM. Enamel surfaces treated with the Clearfil LB 2, LB 2V and SE revealed a relatively shallow etching effect, whereas application of EP and RAP resulted in a more distinct etching pattern. However, none of the self-etching primers caused the familiar etching pattern observed after phosphoric acid treatment. In the second part of the study, the adhesive systems were applied to six enamel surfaces each and light-cured.   The morphology of the enamel-bonding zone was evaluated by SEM performed on cross-cut sections of the specimens. In addition, ultrathin sections were cut from the bonded enamel interfaces and analyzed by transmission electron microscopy (TEM). Short tags measuring 1 µm in length were detected sporadically by SEM-analysis of the LB 2, LB V and SE specimens, whereas 3- 5 µm long tags were frequently found in RAP and EP specimens. TEM investigation of non-decalcified bonded specimens prepared from all five materials revealed a 1- 5 µm wide enamel surface layer characterized by a less dense packing of enamel crystallites which were separated from each other by nanometer-sized spaces. A 1- 5 µm wide, netlike resinous structure was observed in corresponding decalcified specimens indicating that the self-etching priming agents have the potential to dissolve the surface of the enamel crystallites while simultaneously promoting inter-crystallite monomer infiltration.   These results provide ultrastructural evidence for an inter-crystallite retention mode in composite-to-enamel bonding with self-etching primers. The observed "nanoretentive“ interlocking between enamel crystallites and resin could explain the potential of self-etching/self priming systems in resin-to-enamel bonding in spite of the less distinct enamel etching pattern observed by SEM.