Growth inhibitory activity of gutta-percha points containing root canal medications on common endodontic bacterial pathogens as determined by an optimized quantitative in vitro assay.

Gutta-percha points containing calcium hydroxide, zinc oxide (ZnO), a mixture of ZnO and chlorhexidine (ZnO/CHX), iodine-polyvinylpyrrolidone (ZnO/J-PVP), or a mixture of CHX and J-PVP and ZnO (ZnO/CHX/J-PVP) were tested for their ability to inhibit growth of pure cultures of bacterial species commonly involved in endodontic infections (Peptostreptococcus micros, Streptococcus intermedius, Enterococcus faecalis, and Porphyromonas gingivalis). To quantitate growth inhibition, an in vitro assay was established that controlled for important parameters of root canal infection. Approximately 10(7) bacteria per assay were suspended in diluted human serum and co-incubated with the gutta-percha points in an anaerobic atmosphere for up to 2 wk. Aliquots used for determination of colony counts were taken on days 0, 1, 2, 4, 7, and 14 of incubation. As judged by colony-forming unit reduction kinetics and final counts, calcium hydroxide had better growth inhibitory activity than ZnO/CHX, ZnO/J-PVP, and ZnO alone for all bacteria tested except Peptostreptococcus micros. The combination of CHX and J-PVP with ZnO did not render results different from those of ZnO/CHX or ZnO/J-PVP. The results of this study support the introduction of standardized assays for testing antibacterial properties of root canal medications under conditions that more closely resemble those encountered in endodontal infections.