Bioactive Base Cement: In-vivo Effect of Etching on Bacterial Survival

Objectives: After caries treatment, some bacteria still might be left within caries-affected dentin. This research focused on the effect of etching prior to application of an experimental resin-based calcium phosphate cement, on bacterial survival within caries-affected teeth. Methods: Twenty-eight cavities in carious teeth, indicated for extraction, were selected. Caries removal was standardized using a polymer instrument. Dentin was etched (N=13) or not-etched (N=15) prior to application of the base. After caries removal the clinical characteristics of cavity walls were assessed and dentin biopsies were taken with a #4 round bur, both at baseline prior to etching and three months later after extraction and removal of restoration. The total DNA and RNA from these paired dentin biopsies was extracted and quantified by quantitative PCR and quantitative RT-PCR respectively with bacterial universal 16S rRNA primers. The number of bacterial cells within the dentin biopsies was calculated based on a standard curve with known cell numbers. Statistical analysis was performed using SAS repeated measurement procedure. Results: No statistically significant differences were found in bacterial DNA and RNA between groups with and without etching either at baseline (p=0.109 for DNA, p= 0.593 for RNA) or at 3-month (p=0.702 for DNA, p=0.618 for RNA). A statistically significant decrease in RNA quantity was shown in the dentin biopsies taken after three months compared to baseline (p=0.010), while no significant differences were found in DNA amount (p=0.179), indicating a decline in number of viable cells. Conclusions: Etching does not provide an additional effect on the survival of residual bacteria in caries-affected dentin. Three months after treatment the number of viable cells was significantly reduced. This could be due to the natural starvation process of bacteria left within caries-affected dentin or the bactericidal effect of this experimental resin-based cement. In part supported by Ivoclar/Vivadent, NIH-DE016499 and NIH-DE013298.