Flexural strength and hardness of direct and indirect composites.

The objective of this study was to evaluate the flexural strength (sigma f) and hardness (H) of direct and indirect composites, testing the hypotheses that direct resin composites produce higher sigma f and H values than indirect composites and that these properties are positively related. Ten bar-shaped specimens (25 mm x 2 mm x 2 mm) were fabricated for each direct [D250 - Filtek Z250 (3M-Espe) and D350 - Filtek Z350 (3M-Espe)] and indirect [ISin - Sinfony (3M-Espe) and IVM - VitaVM LC (Vita Zahnfabrik)] materials, according to the manufacturer's instructions and ISO4049 specifications. The sigma f was tested in three-point bending using a universal testing machine (EMIC DL 2000) at a crosshead speed of 0.5 mm/min (ISO4049). Knoop hardness (H) was measured on the specimens' fragments resultant from the sigma f test and calculated as H = 14.2P/l(2), where P is the applied load (0.1 kg; dwell time = 15 s) and l is the longest diagonal of the diamond shaped indent (ASTM E384). The data were statistically analyzed using Anova and Tukey tests (alpha = 0.05). The mean sigma f and standard deviation values (MPa) and statistical grouping were: D250 - 135.4 +/- 17.6a; D350 - 123.7 +/- 11.1b; ISin - 98.4 +/- 6.4c; IVM - 73.1 +/- 4.9 d. The mean H and standard deviation values (kg/mm(2)) and statistical grouping were: D250 - 98.12 +/- 1.8a; D350 - 86.5 +/- 1.9b; ISin - 28.3 +/- 0.9 c; IVM - 30.8 +/- 1.0 c. The direct composite systems examined produce higher mean sigma f and H values than the indirect composites, and the mean values of these properties were positively correlated (r = 0.91), confirming the study hypotheses.