In vitro characterization of two laboratory-processed resin composites

Purpose. To compare various characteristics of two new-generation laboratory-processed resin composites (BelleGlass HP/SDS-Kerr and Sinfony/3M-ESPE). The properties evaluated were degree of C=C conversion, microhardness, roughness, biaxial flexural strength and polymerization shrinkage-strain. Materials and methods. All specimens were subjected to a first and a second polymerization cycle according to the manufacturers' instructions. The degree of C=C conversion (DC) was recorded on rectangular (3 X 2 X 0.5 mm(3)) specimens (n = 3) by FT-IR micromultiple internal reflectance spectroscopy immediately after each of the two polymerization cycles. Twenty cylindrical specimens (10 X 2 mm 2) of each material were prepared for surface microhardness (n = 10, VHN, 200 g load, 20 s) and surface roughness (n = 10, Ra) measurements. The biaxial flexural strength and stiffness were determined on disk-shaped (n = 8, 15 X 0.7 mm(2)) specimens loaded to fracture at 1 mm/min crosshead speed. The polymerization shrinkage-strain was calculated with the bonded-disk method. All values were statistically analyzed by Student's unpaired t-test (p < 0.05). Results. The second polymerization cycle significantly increased the degree of C=C conversion for both materials (p < 0.05). BelleGlass HP exhibited significantly higher degree of C=C conversion, surface microhardness, surface roughness, biaxial flexural strength and stiffness values compared to Sinfony (p < 0.05). Significance. Several differences exist between the materials although both products are recommended for the same clinical applications. (C) 2003 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.