Correlation between degree of conversion, filler concentration and mechanical properties of posterior composite resins

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Abstract
The degree of conversion, filler concentration and mechanical properties of seven proprietary light-cured posterior composite resins were investigated. The degree of conversion of composites ranged from 43.5–73.8%. The weight fraction of filler that was obtained was in the range 66.4–85.2%. The volume fraction varied from 58.2–74.2%. The mean values of the observed compressive and diametral tensile strengths ranged from 242.3–324.7 MPa and from 39.8–62.6 MPa, respectively. The Knoop hardness numbers ranged from 41.8–81.9. Significant correlations were observed between the volume fraction of filler and the diametral tensile strength (r=0.89), and between the volume fraction of filler and the Knoop hardness number (r=0.89). No correlation was found between the degree of conversion and any of the mechanical properties of the composite resins tested. Because of the positive correlations between the volume fraction of filler and the diametral tensile strength, and between the volume fraction of filler and the Knoop hardness numbers, it is concluded that the filler concentration plays a prominent role in determining the properties of contemporary posterior composite resins.