Carbon-graphite fiber-reinforced polymers for implant suprastructures

Abstract: Carbon-graphite fiber-reinforced polymers (CGFR) can be used as the core material for implant-retained prostheses as an alternative to metal frameworks. The purpose was to formulate and develop carbon-graphite fiber-reinforced polymers intended for implant suprastructures and to determine physicochemical, mechanical properties and possible cytotoxic effects. The adhesion strength between CGFR polymer to a titanium surface or CGFR polymer to opaquer layer/denture base polymer were evaluated. The resin mixtures, based on methyl methacrylate (MMA), poly(methyl methacrylate) and poly(vinyl chloride-co-vinyl acetate), were produced with two different cross-linking agent systems: 1,4-butanediol dimethacrylate and ethylene glycol dimethacrylate or diethylene glycol dimethacrylate. The matrix resins were reinforced with tubes of braided CG fibers, cleaned and treated with a size, with fiber loadings 24-58 wt%. Water uptake and water sorption/solubility was determined and dilatometric analysis was performed. Mechanical properties, adhesion, residual monomer and cytotoxicity were evaluated. Basic requirements regarding water sorption, water solubility, water uptake, residual MMA monomer, coefficient of linear thermal expansion were met and were similar for the two resin matrices. However, flexural properties and fracture toughness were higher for the matrix resin containing the cross linker diethylene glycol dimethacrylate, making it a more suitable resin binder. Flexural properties increased with fiber loadings up to and including 47 wt% (38 vol%) when tested in dry and wet condition. The combination of the described fiber surface treatment, the sizing resin and the developed resin matrix contributed to good adhesion between the carbongraphite fibers and the polymer matrix. Hydrothermal cycling did not decrease flexural strength of the CGFR polymers with 24 and 36 wt% fiber loadings, when compared to dry and water stored specimens. However, more porosity was observed with higher fiber loadings; flexural strength decreased after thermal cycling for fiber loadings of 47 wt% and 58 wt% in relation to composites tested in dry and wet condition. There was no evidence of cytotoxicity for the CGFR polymer and residual monomer content was within the international standard limits. Good adhesion with a cohesive fracture type was achieved between the layers of the silicatized titanium/CGFR polymer/ opaquer/denture base polymers. The combination of these materials in an implant-retained supraconstruction is promising for in vivo evaluation.