Flexural strength and hardness of direct and indirect composites

Abstract

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.

The impact of in vitro aging on the mechanical and optical properties of indirect veneering composite resins

“…The composition of these indirect, veneering composite resin systems is similar to that of the direct composite resins, but they differ in additional polymerization. 12 The mechanical and physical properties of veneering composite resins are based on their chemical composition: resin matrix, 13,14 filler particle type, 14 filler size, 15 filler percentage, 15,16 and filler-matrix bonding (silane coupling agent). 16,17 Temperature, 17,18 environmental conditions, 19 and light intensity of 18931-rev2-figs edits 3 the polymerization unit are all important factors.…”

“…27,37 These new composite resins have an approximately 66% volume percentage of inorganic ceramic fillers, which results in improved mechanical properties with a flexural strength of between 120 and 160 MPa and an elastic modulus of 8.5-12 GPa. 12 Most veneering composite resins are applied with a post-curing process through heat and photo-polymerization, which results in superior flexural strength to veneering ceramic, minimal polymerization shrinkage, and a wear rate comparable to tooth enamel. 38,39 So far, chipping of veneering composite resin has not been reported in short-term clinical studies.…”

Effects of layering technique on the shade of resin overlays and the microhardness of dual cure resin cement

“…However, some studies reported that the flexural strength and surface hardness of direct resin composite materials were superior to those of indirect resin composites. 19,20 Therefore, direct resin composite systems were used for resin overlay fabrication with either a dentin layer or dentin and enamel layers and compared with indirect resin composite systems with dentin, enamel, and translucent layers. Because the incorporation of highly translucent enamel and translucent layers is reported to affect the final color of the resin overlays, 7 the color of the resin overlays was measured and compared with a shade A3 resin denture tooth.…”

Consequences of the Additional Polymerization on Knoop Microhardness of Direct Composite Resin

“…It leads to higher mobility of free monomers and greater flexibility of polymeric chain which possibilities new reaction between active radical. It promotes a major number of cross ligations of organic matrix making a composite with greater stability and hardness leading to higher strength (Bagis & Rueggeberg The new composites have improved a technology of loading and show modification in organic matrix and higher degree of polymerization which improves its mechanical and physic characteristics (Bagis & Rueggeberg;Borba et al, 2009;Ferracane).…”