To determine flexural strength and modulus after water storage and thermal cycling of carbon–graphite fiber-reinforced (CGFR) polymers based on poly(methyl methacrylate) and a copolymer matrix, and to examine adhesion between fiber and matrix by scanning electron microscopy (SEM).

Solvent cleaned carbon–graphite (CG) braided tubes of fibers were treated with a sizing resin. The resin mixture of the matrix was reinforced with 24, 36, 47 and 58 wt% (20, 29, 38 and 47 vol.%) CG-fibers. After heat polymerization the specimens were kept for 90 days in water and thereafter hydrothermally cycled (12,000 cycles, 5/55 °C). Mechanical properties were evaluated by three-point bend testing. After thermal cycling, the adhesion between fibers and matrix was evaluated by SEM.

Hydrothermal cycling did not decrease flexural strength of the CGFR polymers with 24 and 36 wt% fiber loadings; flexural strength values after thermocycling were 244.8 (±32.33) MPa for 24 wt% and 441.3 (±68.96) MPa for 36 wt%. Flexural strength values after thermal cycling were not further increased after increasing the fiber load to 47 (459.2 (±45.32) MPa) and 58 wt% (310.4 (±52.79) MPa).

SEM revealed good adhesion between fibers and matrix for all fiber loadings examined.

The combination of the fiber treatment and resin matrix described resulted in good adhesion between CG-fibers and matrix. The flexural values for fiber loadings up to 36 wt% appear promising for prosthodontic applications such as implant-retained prostheses.