Micro-shear bond strength of different composites and glass-ionomers used to reinforce root dentin

Purpose: Comparison of microshear bonding strength of reinforcing root dentin materials (microhybrid composite, nanocomposite, conventional glass ionomer, nano-glass ionomer). Materials methods: A total of 20 roots of similar-sized undamaged one rooted lower premolars were used, 40 root halves were embedded in the acrylic block and were randomly divided into four equal groups (10 each) according to the reinforcing materials. Group I: microhybrid composite, group II: nano-composite, group III: conventional glass ionomer was used and group IV: light cured nano-ionomer was used. Teeth were sliced and loaded to a testing machine. A shearing load with tensile mode of force was applied via materials. The mode of failure was observed under stereomicroscope. The results were statistically analyzed using one way ANOVA and t-test. Results: Nano-composite group recorded the highest µ-shear bond strength mean value (23.52±3.997 MPa) followed by µ-Hybrid composite group (16.88 ±3.356 MPa) then nano glass-ionomer group (8.77 ± 1.341 MPa) while conventional glass-ionomer group showed the lowest µ-shear bond strength mean value (4.062 ± 0.9623 MPa). The difference was statistically significant between all groups (P 0.05). The failure modes indicated that high bond strength showed cohesive or mixed modes, while low bond strength groups tended to exhibit adhesive, cohesive or mixed modes. Conclusion: Nano-composite recorded the highest microshear bond strength close to that required to resist the polymerization contraction stress.