Evaluation of antibacterial activity of three dentin primers using an in vitro tooth model

This study compared the antibacterial activities of three dentin primers and investigated a newly designed experimental system using a bovine tooth model method for evaluating antibacterial activity by comparing this method with a conventional disk diffusion method. The antibacterial activities of SA primer in Clearfil Liner Bond, LB primer in Clearfil Liner Bond II, and ED primer in Panavia 21 were evaluated using the conventional disk diffusion method. The 50 microliters aliquot of each primer was applied to three sterilized paper disks, then placed onto Tryptic Soy agar plates already inoculated with Streptococcus mutans. After anaerobic incubation for 48 hours, the diffusion of antibacterial components was determined using the inhibition zone produced around the paper disk. The diameter of the inhibition zones was measured and the average calculated. Standardized cavities (diameter 5.0 mm, depth 3.0 mm) were prepared on the labial surfaces of bovine teeth and inoculated with S mutans (10(6) CFU/microliter) following sterilization by 60Co gamma rays (50 KGy). The teeth were divided into four groups: SA primer, LB primer, ED primer, and a control group. Except for the control teeth, the cavity preparations were treated with the respective dentin primers, and then firmly sealed with a temporary sealing material. The teeth were placed in bottles containing melted Tryptic Soy agar. Five ml of Tryptic Soy broth was then added to the surface of the hardened Tryptic Soy agar. After 1 week's incubation of the teeth in the bottles at 37 degrees C, the number of bacteria remaining in each cavity was counted, except for eight specimens, which were used for SEM observation. The ED primer showed the widest inhibition zone in the disk diffusion test, which was significantly different from the other primers. Using the bovine tooth model, all dentin primers showed antibacterial activity, with significant differences found among the four groups. The results indicated that ED primer had the strongest antibacterial effect among the three primers.