Shear bond strength of thermoviscous bulk-fill composite to sound dentin

Aim To evaluate the shear bond strength of Thermoviscous bulk-fill and Nano-hybrid composites to sound dentin surface after application of self-etch adhesive. Materials and methods Thirty freshly extracted sound human molars were used. The teeth roots were embedded in self-cure acrylic resin till the cervical line, The occlusal enamel was cut off to expose the sound dentin surface, The prepared specimens were randomly divided into three groups according to the type of composite (n=10 each): Futurabond DC adhesive (one-step self-etch adhesive) was applied in all groups using a disposable micro-brush and light cured for 10 s. The three groups were: G1, in which Grandio without preheating, was used, G2, in which Grandio with preheating, was used and G3, in which Viscalor-bulk, was used. Composite was applied to dentin using Teflon mold surrounded by metallic ring of 3 mm diameter and 4 mm height. All specimens were stored in artificial saliva at 37°C for one week. All specimens were subjected to thermocycling in water bath at 5°C and 55°C with a dwell time of 30 and 20 s transfer time for 500 thermal cycles which corresponds to 6 months of clinical service. The shear bond strength of specimens was measured using an instron machine at a cross head speed of 0.5 mm/min. The debonded surfaces were examined under a stereomicroscope at a magnification 50X to determine the mode of failure. All data were collected, tabulated, and statistically analyzed. Results Group 2 recorded a statistically significant highest shear bond strength values (16.19±3.81) Mpa among tested groups, followed by Group 1 recording (12.41±4.89) Mpa while the lowest shear bond strength values were found in Group 3 with mean values of (11.99±4.07) Mpa. One-way ANOVA test was used to compare the three tested groups at a level of significance P less than or equal to 0.05. A negative correlation between cohesive mode of failure and shear bond strength was recorded for the three tested groups. Clinical significance We safely recommend using nanohybrid composites than bulk fill ones particularly in stress bearing areas. Conclusion of the study Shear bond strength of Nano-hybrid composite better than Thermoviscous bulk-fill composite using self-etch adhesive to sound dentin surface.