The relationship between composition and properties of posterior resin composites

The effects of filler concentration and resinous components on the properties of highly filled composites were determined for prediction of the durability of the restorative resins. Resinous components of seven proprietary light-cured posterior resin composites were extracted by chloroform solvent and examined by the Fourier Transform Infrared (FTIR) method. Filler concentration was determined by the thermogravimetric method. Diametral tensile strength, Knoop hardness, and Barcol hardness tests for the composite, as well as extracted resinous matrix, were performed by standard experimental procedures. Toothbrush abrasion test of the resin composites was evaluated by a toothbrushing machine giving the equivalent of five years' toothbrushing and examined with a roughness meter. The degree of conversion of resin composites ranged from 43.5 to 73.8%. The volume fraction of filler varied from 58.2% to 74.2%. The ranges of diametral tensile strength and Knoop and Barcol hardness numbers obtained were 39.8 MPa to 60.0 MPa, 41.8 to 81.9, and 76.3 to 89.2, respectively. Significant correlations (p less than 0.01) were obtained between filler fraction and diametral tensile strength (r = 0.89, S.E. = 3.66) and between filler fraction and Knoop hardness number (r = 0.89, S.E. = 8.39). The increase in strength with increased filler concentration might be related to filler/matrix bonding.