Cytotoxicity of silica-glass fiber reinforced composites

Objectives: Silica-glass fiber reinforced polymers can be used for many kinds of dental applications. The fiber reinforcement enhances the mechanical properties of the polymers, and they have good esthetic attributes. There is good initial bonding of glass fibers to polymers via an interface made from silane coupling agents and sizing materials. The aim of this in vitro study was to determine the cytotoxicity before and after thermal cycling of two polymers reinforced with two differently sized silica-glass fibers. Cytotoxicity of the matrix polymers without fibers was also evaluated.

Methods: Two different resin mixtures (A and B) were prepared from poly(vinyl chloride-co-vinyl acetate) powder and poly(methyl methacrylate) (PMMA) dissolved in methyl methacrylate and mixed with different cross-linking agents. The resin A contained the cross-linking agents ethylene glycol dimethacrylate and 1,4-butanediol dimethacrylate, and resin B contained diethylene glycol dimethacrylate as a cross-linking agent. Woven silica-glass fibers were used for reinforcement. The silanized fibers were sized with either linear poly(butyl methacrylate)-sizing or cross-linked PMMA-sizing. Cytotoxicity was evaluated by filter diffusion test (ISO 7405:1997) of newly made and thermocycled test specimens. Extracts of newly made and thermocycled specimens were prepared according to ISO 10993-12 and tested by the MTT assay. The results from the experiments were statistically analyzed by one-way ANOVA and Tukey's test (ñ<0.05).

Results: The filter diffusion test disclosed no change in staining intensity at the cell-test sample contact area indicating non-cytotoxicity in all experimental groups. Cell viability assessed by MTT assay was more than 90 % in all experimental groups.

Conclusion: It can be concluded that correctly processed heat polymerized silica-glass fiber reinforced polymers induced no cytotoxicity and that thermo-cycling did not alter this property.