Micro Shear Dentin Bond Strength of Dual-Cure Composite Core Resins

Microtensile bond tests present alignment problems. Objective: To investigate microshear test procedures and evaluate the bond strength of composite core resins to dentin. Method: Recently extracted intact molar teeth were mounted by their roots with self-cure acrylic resin in square photometric cuvettes. The square shape allowed the bonded core buildup to be section by a fine diamond saw into microshear test specimens 1mm square. The composite core was bonded to an area formed by the saw at their height of contour perpendicular to the long axis of the tooth. After etching the area with 3M/ESPE etchant, rinsing for 10 seconds and forced air drying without desiccating, OptiBond Solo+(OBS+) was applied in two coats with forced air drying for 10 seconds between and after the last coat followed by 20 seconds of VLC(500mw/cm2,Optilux-Demetron model 401). BondLink was applied on the cured OBS+ and air dried before securing a tofflemeyer stainless steel band to shape the core. The composite was injected in the band with a syringe to a depth of 4mm and VLC occlusally for 40 sec. before the band removal and additional VLC from 4 sides after. Cores of Build-It(BI), CompCoreAF(CCAF-Stackable), FluorCore2(FC2)and LuxaCoreZ(LZ) were sectioned producing test specimens(n=8). The microshear specimens where glued in a custom shear jig with brass inserts to align and hold the specimens. The shear bar was milled to 0.2mm wide contact surface and was position at the core-dentin bond interface using black a light and magnification. Force was applied by an Instron at 0.5mm/min. Results: Mean shear bond strengths were BI=36.2+/-8.6MPa, CCAF=36.2+/-5.6MPa, FC2=34.1+/-5.3MPa and LZ=28.7+/-7.2MPa which were not significantly different by ANOVA(p<.05). Fracture analysis suggested that interface alignment, porosity in composite and support are critical. Conclusions: Improvement in alignment and support are needed and are being investigated.