Effect of Shade, Increment Thickness and Light Curing Distance on Dentin Bond Strength, Degree of Conversion and Cytotoxic Behavior of Resin Composite Core Build-Up Material Thesis

Abstract

Dual-cured resin composites were introduced to combine both the advantages of light and chemical-cured composites and to ensure proper degree of conversion. This study was conducted to explore the effect of resin composite shade, light curing distance and increment thickness on the shear bond strength, degree of conversion and cytotoxic behavior of core build-up resin composite material. A total of 180 anterior bovine teeth were extracted from sacrificed bovine jaws. The labial surface of the cervical half was ground flat to remove enamel and expose an area of nearly 10mm diameter of dentin using 600 grit sand papers. The specimens were divided into 3 main groups 60 specimens each according to the shade of core material S1: BLUE, S2: DENTIN and S3: WHITE. Each group was divided into 3 sub-groups -20 specimens each- according to the thickness of the core material into T1: 2mm increment thickness, T2: 4mm increment thickness and T3: 2mm increment light cured and followed by another 2mm increment. Each sub-group was further subdivided into 2 divisions 10 specimens each according to the light curing distance of the curing unit from the specimen D1: zero distance (light guide of the curing unit is touching the surface of the specimen) and D2: 10mm distance. All the specimens will be subjected to shear bond strength testing using Universal Testing Machine. Representative samples of each experimental group n=5 were prepared and used for evaluation of the degree of conversion and cytotoxicity testing. Results of shear bond strength testing showed that resin composite shade and increment thickness had a significant effect on the shear bond S U M M A R Y & C O N C L U S I O N S 87 strength to bovine dentin (P=0.0001). On the other hand, light curing distance had no significant effect on the shear bond strength of resin composite on bovine dentin (p=0.056). Results of degree of conversion showed that Resin composite shade and increment thickness showed a statistical significant effect (p=0.0001) on degree of conversion of resin composite. Light curing distance showed a statistical significant effect (p=0.001) on the degree of conversion of resin composite. Results of cytotoxicity showed that resin composite core shade, increment thickness and the interaction among the three tested variables have a statistically significant effect (p=0.0001) on cytotoxic behavior of resin composite core material.