Objective To investigate the in vitro antimicrobial activity of nano- hydroxyapatite/polyamide 66 composites （nHA- PA66） as a pulp capping agent. Methods The micro- organisims used in this study included Streptococcous mutans（S.mutans）, Lactobacillus casei（L.casei） and Actinomyces viscosus（A.viscosus）, three standard bacterial strains predominant in deep carious lesions. Agar diffusion test was used to determine the diameter of bacterial inhibition zones of nHA- PA66 compared with hydroxyapatite paste, calcium hydroxide paste and nHA- PA66 mixed with iodoform paste. Results It showed that the polymerized films and fresh paste of nHA- PA66 had no antimicrobial activity to S.mutans and very little to L.casei and A.viscosus. The antimicrobial activity of nHA- PA66 mixed with iodoform paste obviously increased, but no significant difference compared with calcium hydroxide paste. There was no antimicrobial activity of hydroxyapatite paste to the three test bacterial strains. Conclusion These findings suggest nHAPA66 used as pulp capping agent alone almost has no antimicrobial effect to the three test bacteria, but the antimicrobial activity can be increased by combining with iodoform.
