An antimicrobial agent, cetylpyridinium chloride (CPC), was added to a commercially available light cured composite resin, and the antimicrobial and physical properties of the modified composite were evaluated. CPC was added at concentration of 2.5, 5.0 and 10.0 wt%. Discs were incubated with Streptococcus mutans for 48 hours. An agar disc diffusion assay was used to measure zones of bacterial growth inhibition for a period of 196 days. Discs were soaked in distilled water for a period of 180 days. The amount of CPC released from the modified discs into the water was measured and recorded on days 7, 15, 30, 60, and 180 using a spectrophotometer. Diametral tensile strength of the modified composite discs was measured with a universal testing machine, and the effect of water aging on diametral tensile strength was also evaluated by soaking CPC-composite discs in distilled water at 37°C for a period of 178 days. Results showed an increase in the measured zone of bacterial growth inhibition as CPC content increased. All CPC-composite samples maintained their antimicrobial activity up to 196 days. No zone of growth inhibition was measured around the control samples. The CPC release was observed through the end of 180-day period; but the largest amount of release was recorded in the first week (day 7). There was no significant difference (P .05) in diametral tensile strength between 2.5% CPC-composite group and the original product; whereas, there were significant differences among the 5.0 and 10.0% CPC-composite groups and the control. Water aging demonstrated no significant effect on diametral tensile strength except for test group containing 10.0% CPC. In conclusion, the incorporation of 2.5% CPC on composite material imparted antimicrobial activity to the original composite without altering its physical properties.
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