Real-time PCR analysis of gtfB , gtfD and aguD gene expression by S. mutans treated with the test agents. A) Biofilms 49-h old; B) 97-h old. The mRNA level of each gene in each sample was normalized to that of 16S rRNA. These values were then compared to those from vehicle-treated biofilms (V) (corresponding to an arbitrary value of 1) to determine the change (n-fold) in gene expression. Data are expressed as means ± standard deviations of triplicates from at least three separate experiments; values marked with an asterisk are significantly different from that for the vehicle-treated biofilms (p < 0.05, ANOVA, comparison for all pairs using Tukey test).