Beith et.al tested the effect of the IPN on S.mutans. This in vitro study evaluated the antibacterial effect of alkylated polyethylenimine nanoparticles incorporated into 3 kinds of composite resins. The IPN were mixed in a low concentration of 1% w/w and cured by light polymerization. The cured samples were tested for antibacterial and mechanical properties. The addition of 1% w/w of nanoparticles did not affect significantly the flexural modulus and the flexural strength of the materials. The results indicate the IPN immobilized in resin based materials have a strong antibacterial activity on cariogenic bacteria upon contact.