The purpose of this study was to evaluate the extent of bacterial reduction with nickel-titanium rotary instrumentation and 1.25% NaOCl irrigation. Also, the additional antibacterial effect of calcium hydroxide for >1 wk was tested. Forty-two subjects with radiographic and clinical signs of chronic apical periodontitis were recruited. The canals were sampled before treatment, during and after instrumentation, and after treatment with calcium hydroxide and the samples incubated anaerobically for 7 days at 37 degrees C. The bacteria from each sample were quantified and the log10 values were used for calculations and comparisons. The initial sample confirmed infection of the canals. There was a significantly greater pattern of reduction of bacteria when NaOCl was used as an irrigant, compared with sterile saline (p< 0.05). After instrumentation with NaOCl irrigation, 61.9% of canals were rendered bacteria-free. The placement of calcium hydroxide for at least 1 wk rendered 92.5% of the canals bacteria free. This was a significant reduction, compared with NaOCl irrigation alone (p = 0.0001). The results of this study indicate that NaOCl irrigation with rotary instrumentation is an important step in the reduction of canal bacteria during endodontic treatment. However this method could not consistently render canals bacteria-free. The addition of calcium hydroxide intracanal medication should be used to more predictably attain this goal.

The results of this study suggest that the molecular size of the penetrating agent may not be the relevant parameter when attempting to determine an appropriate test for the sealability of root canal fillings.

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