Screening of matrices and fibers for reinforced thermoplastics intended for dental applications.

Plastics reinforced with continuous fibers (FRC) are being developed for dental applications, such as prosthodontic frameworks and orthodontic retainers. Flexure properties, stress relaxation and hydrolytic stability of FRC based on six thermoplastic matrices, three types of fibers, and three fiber volume fractions were evaluated. Samples with clinically relevant dimensions were tested. Polycarbonate was the preferred matrix material. Polycarbonate reinforced with 42 volume percent glass fibers exhibited the highest combination of flexure modulus (17.9 +/- 2.6 GPa), flexure strength (426 +/- 40 MPa), reinforcing efficiency (0.79), and resistance to stress relaxation. No statistically significant difference was observed between E and S2 glass reinforced composites under the experimental conditions used. Kevlar reinforced materials exhibited a low flexure modulus and strength. The apparent flexure moduli of all composites decreased with span length in the range of clinical interest. Generally, the prevalent mode of failure for all FRC investigated was brittle failure under flexure loading. Relatively large sample-to-sample variation in both composition and properties indicated that improved fabrication methods will be needed in future studies. The combination of good flexure properties, formability, and translucency suggests that novel appliance designs for dentistry are feasible with FRC, but further studies of its properties and particularly the effects of fiber/matrix interfacial quality are needed.