The cfu represent a close estimate of viable bacteria penetrating into dentinal tubules at different layer depths. The numbers of cfu obtained from ï¿ ve consecutive dentinal layers are presented in Table 1 and Fig.1. In the positive control specimens, heavy bacterial infection was observed at the layer close to the lumen. This decreased from layer to layer up to the deepest layer tested (400-500 mm) which contained several 100 cfu. CH without additives significantly (P < 0.001) reduced the amount of viable bacteria in the ï¿ rst to fourth layers compared to the positive control group, but did not eliminate them completely. Application of low electric current to the group containing CH and copper completely eliminated bacterial survival in the dentinal tubules at least up to 500 mm from the root-canal lumen and in the second to ï¿ fth layers was statistically (P < 0.001) more effective than the experimental group and control. CH with IKI significantly (P < 0.001) reduced the amount of viable bacteria in all layers compared to the positive control group and was statistically (P < 0.001) more effective than CH without additives in the fourth and ï¿ fth layers. The negative control group showed no growth of bacteria, which indicate sterilization of the process and prevention of biased results.

Table 1. Logarithmic transformation of the number of colony forming units (cfu +1) at different dentine layer depths.


* One-way anova was performedonlog transformationof cfu for eachlayer. Horizontal lines connects data which does not show significant differences (Tukey's method).

Figure 1. Colony forming units (cfu) of bacteria in dentinal tubules facing the root-canal space following treatment with calciumhydroxide with no additives (CH), calciumhydroxide with IKI (CH þ IKI), and calciumhydroxide with electrophoretic activated copper (CH +CU + E). Each column represents the log transformation (cfu +1) obtained from nine dentinal specimens.