A Study of the Development of the Adhesive System Exclusively to Er: YAG-lased Dentin

 Purpose: Our previous study revealed that resin-modified glass-ionomer cement (RMGI) as a dentin bonding system exhibited relatively stable bonding behavior to Er: YAG lased dentin. However, the obtained bond strengths of RMGI were lower than those of the bonding resin. In this study, to develop a new dentin bonding system suitable for Er: YAG-lased dentin, conditioning effects of carboxylic acid-metal salt, which is expected to reinforce the denatured layer and increase the bonding performance of RMGI to laser-affected dentin, were investigated.<br> Methods: Flat dentin surfaces from freshly-extracted bovine teeth were prepared and irradiated with Er: YAG laser (Erwin Adverl) at low power (50 mJ/1 pps) or low power followed by medium power (150 mJ/1 pps). These lased dentin and non-lased dentin were conditioned with 20% polyacrylic acid+3% aluminum chloride solution (Al) or 10% citric acid+2% ferric chloride solution (Fe), followed by the placement of Fuji Lining Bond LC/Clearfil AP-X. The micro-tensile bond strengths (μTBSs) and fractomorphology were evaluated (Scheffé test, α=0.05), and cross-sectional observation of the interface was conducted under SEM.<br> Results: The μTBSs to non-lased dentin without any conditioning or with Al or Fe conditioning were approximately 12 or 24 MPa respectively, leading to significant conditioning effects on bond strength to non-lased dentin (p<0.05). The μTBSs to lased dentin without any conditioning were non-quantifiable. The Al or Fe conditioning of lased dentin showed 5～6 MPa or 10～13 MPa, respectively. Fe exhibited significant conditioning effects to lased dentin (p<0.05). Microcrack formation from dentin to RMGI, mixed failure in dentin and RMGI and adhesive failure occurred characteristically in the Fe group compared to the Al group. These findings demonstrated that Fe might reinforce the denatured layer and cause strain concentration both in the denatured layer and RMGI, leading to the increase of μTBSs.<br> Conclusion: The present findings revealed that the conditioning with 10% citric acid+2% ferric chloride solution might be very effective for improving the bonding performance of RMGI to Er: YAG lased dentin as a dentin bonding system.