Material properties and fractography of an Indirect Dental Resin Composite.
Janet B. Quinn, George D. Quinn
Objectives: Determination of material and fractographic properties of a dental indirect resin composite material. Methods: A resin composite (Paradigm, 3M-ESPE, MN) was characterized by strength, static elastic modulus, Knoop hardness, fracture toughness and edge toughness. Fractographic analyses of the broken bar surfaces was accomplished with a combination of optical and SEM techniques, and included determination of the type and size of the failure origins, and fracture mirror and branching constants. Results: The flexure test mean strength + standard deviation was 145 MPA 17 MPa, and edge toughness, Te, was 171 N/mm 12 N/mm. Knoop hardness was load dependent, with a plateau at 0.99 GPa .02 GPa. Mirrors in the bar specimens were measured with difficulty, resulting in a mirror constant of approximately 2.6 MPa m1/2. Fracture in the bar specimens initiated at equiaxed material flaws that had different filler concentrations that sometimes were accompanied by partial microcracks. Using the measured flaw sizes, which ranged from 35 m to 100 m in size, and estimates of the stress intensity shape factors, fracture toughness was determined to be 1.1 MPa m1/2 0.2 MPa m1/2. Significance: Coupling the flexure tests with fractographic examination enabled identification of the intrinsic strength limiting features The same techniques could be useful in determining if clinical restorations of similar materials fail from the same causes. The existence of a strong load-dependence of the Knoop hardness of the resin composite is not generally mentioned in the literature, and is important for material comparisons and wear evaluation studies. Finally, the edge toughness test was found promising as a quantitative measure of resistance to edge chipping, an important failure mode in this class of materials.