The effect of collagen removal on shear bond strength of four single bottle adhesive systems

Achieving adhesion between restorative materials and dentin as a wet and dynamic surface is an important topic in restorative and especially in conservative dentistry. Adhesion of new dentin bonding systems depends on the formation of hybrid layer and micromechanical retention. Nevertheless, an ideal adhesive system has not yet been introduced. Recent studies reveal an increase in bonding stability when the collagen is removed from demineralized dentin surfaces. This study investigates the effect of collagen removal on the shear bond strength of four single bottle dentin bonding systems regarding their structural differences. This experimental study was performed on 56 intact human premolar teeth. Smooth surfaces of dentin were prepared on buccal & lingual aspects of teeth, providing 112 dentin surfaces. The dentin surfaces were etched with 37% phosphoric acid for 15 seconds and then rinsed. The specimens were divided into 8 groups. Single bottle adhesive systems [Single Bond (3M), One-Step (Bisco), Prime & Bond NT (Dentsply), and Excite (Vivadent)] were then applied on the dentin surfaces of 4 groups using the wet bonding technique. In the other 4 groups, the demineralized dentin surfaces were treated with a 5.25% solution of sodium hypochlorite for one minute in order to remove the surface organic components. The adhesive systems mentioned before were applied to these 4 groups with the same wet bonding technique. A cylinder of Z100 (3M) dental composite with a 3 mm diameter and 2 mm height was placed on the adhesive covered dentin surface of all groups and light-cured (400 mW/cm2, 40 sec on each side). The specimens were kept in distilled water at room temperature for one week and then thermocycled for 3000 times (5-55 oc). Shear bond strength of specimens was measured using an Instron (1495) universal mechanical testing machine with cross-head speed of 0.5 mm/minute and chisel form shearing blade. Data were analyzed by Two Way ANOVA and Tukey HSD tests with p<0.05 as the limit of significance. The mean & standard deviation of shear bond strengths (in Mpa unit) of all groups were as follows: One-Step = 19.60 1.83 One-step +H = 19.72 2.01 Single Bond =21.44 3.94 Single Bond +H =18.26 2.85 Prime&Bond NT=26.51 5.02 Prime&Bond NT+H =26.98 5.70 Excite =29.78 3.85 Excite +H =19.07 9.94 Analysis of the results revealed that the use of 5.25% sodium hypochlorite for one minute on the surface of demineralized dentin significantly decreased the shear bond strength of Excite and Single Bond (P<0.05). For Prime & Bond NT and One-Step, shear bond strength increased with this treatment but was not statistically significant (P>0.05). Based on the results of this study, collagen removal from demineralized dentin surface caused a significant decrease in shear bond strength of alcohol & water/alcohol based bonding systems, while the bonding strength of the acetone based systems was not affected. Therefore, the effect of collagen removal on shear bond strength depends on the bonding system applied and its solvent type.