Objectives: The antibacterial activitiy of different dentin bonding agents was compared and the effect of dentin on the antibacterial activity was evaluated.

Methods: The antibacterial effects of Prime & Bond NT, Prime & Bond NT without fluoride, Gluma Comfort Bond, ABF, Xeno CF II, HEMA, TEGDMA and 0.2 % chlorhexidine (positive control) were tested against Streptococcus mutans, Streptococcus sobrinus, and Lactobacillus acidophilus using the standard agar diffusion method. Additionally, bovine dentin disks (200µm and 500µm thickness) were placed between the bacteria and the test substances. From dentin bonding agents the non-polymerized components, as well as the polymerized system were tested. After incubation for 24 h (S. mutans and S. sobrinus) or 48 h (L. acidophilus) at 37°C with 5 %CO₂ the diameters of the inhibition zones were measured.

Results: Without dentin, ABF Primer showed growth inhibition for all bacterial strains used. Xeno CF II inhibited the growth of S. mutans and S. sobrinus, while Prime & Bond NT had an inhibitory effect on S. sobrinus only. ABF Bonding inhibited colony formation of L. acidophilus. Prime & Bond NT without fluoride, HEMA and TEGDMA did not have any antibacterial effects in this test system. Dentin disks of 500µm thickness reduced the inhibitory effect of chlorhexidine to 23-54 % compared to direct application. ABF Primer (non-polymerized) produced inhibition zones against all tester strains regardless of dentin disks interposed or not. Xeno CF II did not produce any inhibition zones when applied on 200µm thick dentin. After polymerization, the ABF system did not inhibit bacterial growth, if it was separated from the bacteria by a dentin disk of only 200 µm.

Conclusions: Dentin reduces significantly the antibacterial activity of chlorhexidine and of dentin bonding agents and the effect of the latter may be considered to be limited to the superficial dentin after curing.