The mechanical properties of acrylic resins exhibits frequently the fracture of acrylic bases of dental prosthesis. Therefore, studies on reinforcements for dental acrylic resins have been encouraged. Objectives: This study aim to determine the effect of the pre-polymerization of reinforcements on the final flexural strength (FFS) and elastic modulus (E) of fiber reinforced composites (FRC). Methods: 72 specimens were dived into 12 groups (n=6), formed by self-cured and heat-cured acrylic resin (control) and associating these with: a pre-impregnated glass fiber, Fibrex-Lab^®, a composite resin, Z-250 3M^® or a non-impregnated glass fiber, Fibrante^® (NP). Each pre-impregnated reinforcement was pre-polymerized (CRB and PFB) or post-polymerized (CRA and PFA), before or after included into the acrylic resin. Tests and specimens followed the ISO/FDIS 1567:1998 specification. Results: The table summarizes the respective results and standard deviations in Mpa.

	Self		Heat
	FFS	E	FFS	E
Control	89,8(6,2)	2,5(0,2)	99,4(5,7)	3,7(0,2)
CRB	101,5(6,7)	3,5(0,4)	96,1(11,2)	4,0(0,3)
CRA	83,3(3,0)	2,7(0,1)	104,8(9,0)	3,9(0,3)
PFB	197,8(13,5)	6,6(0,7)	180,7(9,0)	6,3(0,3)
PFA	138,6(20,8)	3,9(0,7)	159,4(13,0)	4,9(0,5)
NP	114,4(13,5)	4,8(0,6)	150,3(20,9)	3,6(0,5)

Statistical analysis (Anova and Tukey test, p<0,05) revealed that PFB, PFA and NP increased FFS for both acrylic resins. PFA increased E to heat- and self-cured resins and FFS only for the self-cured group. Also is showed that CRB was effective on both acrylic resins types with respect to E, nevertheless was not significant to FFS. Conclusions: It was concluded that pre-polymerized reinforcements and pre-impregnated fibers had a positive effect on the final flexural strength and elastic modulus of FRC.  

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