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The span length and cross-sectional design affect values of strength
Pasi Alander1, Lippo V J Lassila, Pekka K Vallittu
1Department of Prosthetic Dentistry and Biomaterials Research, Institute of Dentistry, University of Turku, Lemminkäisenkatu 2, 20520 Turku, Finland. pasi.alander@utu.fi
Objectives:
The aim of this study was to determine experimentally flexural strength and flexural modulus of fiber-reinforced composite (FRC) with different cross-sectional designs and diameters and tested with different span lengths.
Methods:
Continuous FRC test specimens (n = 6) were made with two different cross-sectional designs, namely circular and rectangular. The resin matrix of FRC was polymerized with a hand light-curing unit followed by a light-curing oven polymerization. Three-point flexural test for determination of ultimate flexural strength and flexural modulus of the dry test specimens was made with different span lengths for rectangular specimens and diameters for circular specimens. Thus, the span length/diameter ratio (L/D) was changed.
Results:
Flexural strength and flexural modulus of specimens with rectangular cross-section varied from 540 to 792 MPa and 9.8 to 20.3 GPa being the highest with the group of the 20 mm span length and the lowest with the group of the 10 mm span length. Flexural strength and flexural modulus of circular cross-section specimens varied from 847 to 1286 MPa and 19.9 to 36.6 GPa being the highest with 1.5 mm cross-section and the lowest with 2.8 mm cross-section.
Significance:
It was concluded, that by increasing the L/D ratio, the flexural strength and flexural modulus values in MPa increased and the maximum fracture load values in N decreased. Reporting the L/D ratio is essential for interpretation of flexural strength and flexural modulus values of small size test specimens.