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.

Phosphoric acid/sodium hypochlorite mixture as dentin conditioner: a new approach.

PURPOSE: To investigate the effect of a phosphoric acid/sodium hypochlorite (NaOCl) mixture as a dentin conditioner on shear bond strength, the resin/dentin interface, as well as the surface area and tubular diameter of dentin. MATERIALS AND METHODS: Thirty human molars were prepared for shear bond strength testing. The teeth were randomly divided into five groups according to the method of dentin conditioning. In group I, dentin was conditioned with 37% phosphoric acid, in group II dentin was conditioned with 37% phosphoric acid followed by application of 5.25% NaOCl, and in groups III, IV, and V, dentin was conditioned with a phosphoric acid/NaOCl mixture for 15, 30, and 60 s, respectively. A resin-based restorative composite disk was bonded to the occlusal surface of each tooth and shear bond strength was measured in a universal testing machine. The resin/dentin interface was evaluated using a scanning electron microscope (SEM). The surface area and tubular diameter for different conditioning methods were assessed using atomic force microscopy (AFM). The data were submitted to one-way ANOVA at a significance level of 0.05 followed by the Tukey-Kramer Multiple comparisons test. RESULTS: Group III showed the highest shear bond strength value (36 MPa), which was significantly higher than groups I and II. SEM micrographs revealed hybrid layer formation for all groups except group II. AFM results showed that groups II and V have significantly higher surface areas and dentinal tubular diameters than other groups. CONCLUSION: The use of a phosphoric acid/NaOCl mixture as dentin conditioner improved the bond strength of an etch-and-rinse single-bottle adhesive to dentin.

Shear bond strength of glass-ionomer adhesive to dentin: effect of smear layer thickness and different dentin conditioners.

PURPOSE: To investigate the effect of two different smear layer thicknesses treated with different dentin conditioners on the bond strength of glass-ionomer adhesive to dentin. MATERIALS AND METHODS: Fifty human molars were used. Each tooth was sectioned in a mesiodistal direction into halves, using a low-speed diamond disk. The 100 halves were randomly divided into 10 equal groups. Groups I to V for the thick smear layer and groups VI to X for the thin smear layer. Eighty halves were used for shear bond strength testing, while the remaining 20 halves were used for SEM evaluation of the adhesive/dentin interface. After each dentin pretreatment, the glass-ionomer adhesive was applied over the conditioned dentin surfaces for all tested groups and restored with resin composite cylinders. Each half with its attached composite cylinder was subjected to shear load at crosshead speed of 0.5 mm/min until failure occurred. The dentin surfaces for SEM evaluation were treated as described for shear bond strength testing. The samples were examined using SEM operated at 30 kv, and the resin/dentin interface was examined at 1500X. RESULTS: Two-way ANOVA showed that there was no significant effect of the smear layer thickness on shear bond strength. There was a significant effect of the different conditioners used (p = 0.001). The interaction of the two independent variables (smear layer thickness and the dentin conditioners) showed no significant difference in the shear bond strength to dentin. The common feature in all evaluated specimen interfaces was the presence of a hybrid layer of different thicknesses with no visible resin tags. CONCLUSIONS: The shear bond strength of the glass-ionomer adhesive to dentin proved to be independent of the smear layer thickness. The use of dentin conditioner prior to the application of the glass-ionomer adhesive appeared to be an important step to improve its bond strength to dentin. Glass-ionomer adhesive failed to produce resin tags regardless of the type of dentin conditioner used.