The Effect of the Pre-Conditioning Step on the Shear Bond Strength of Nano-Filled Resin-Modified Glass-Ionomer to Dentin

OBJECTIVES: The purpose of this study was to evaluate the effect of the pre-conditioning step using different dentin conditioners on the shear bond strength (SBS) of the nano-filled resin-modified glass ionomer (RMGI) to dentin. METHODS: Twenty-four human molars were used in this study. Subsequent to teeth sectioning in the mesio-distal direction and creation of the smear layer, the teeth were divided into six groups with and without the pre-conditioning step. Dentin surfaces were restored with RMGI cylinders and the specimens were stored in distilled water at 37ºC for 24 hours. SBS test were performed using a Universal Testing Machine at a crosshead speed of 0.5 mm/minute. Statistical analysis was performed using One-Way ANOVA followed by Duncan’s Multiple Range Test. RMGI/dentin interface was evaluated using SEM operated at 12 Kv at 2000X magnification. RESULTS: 35% phosphoric acid and EDTA yielded significantly higher SBS (12.0±1.8 and 11.9±4.4 MPa, respectively), compared to all tested groups. In addition, 25% polyacrylic acid (8.6±3.1 MPa) reported significantly higher SBS than the nano-filled RMGI when applied according to manufacturer instructions (5.5±2.2 MPa). When nano-filled RMGI was applied without its nano-primer, or directly over 25% polyacrylic acid conditioned dentin exhibited 100% pre-test failure, and their SBS were expressed as 0.0±0.0 MPa. SEM revealed that the nano-primer was unable to decalcify and hybridize the dentin surface. CONCLUSIONS: Based on the results of the current study, the pre-conditioning step effectively improves the SBS of nano-filled RMGI to dentin. The self-adhesiveness of nano-filled RMGI was not proved in this study.