Effect of Resin-Modified Glass-Ionomer Cement Containing Doxycycline against Streptococcus Mutans

Objectives: To evaluate in vitro inhibitory effects of a resin-modified glass-ionomer cement (RMGIC) associated or not with different concentrations of doxycycline hyclate on the growth of Streptococcus mutans (SM). Methods: Two microbiological tests were performed to access the antibacterial activity of RMGIC, broth and agar diffusion test. For broth test, specimens of the RMGIC Fuji Lining LC (GC America) containing or not doxycycline hyclate (dox) at 1.5, 3.0 and 4.5% concentrations were prepared using sterilized metal molds (4mm diameter; 2mm depth) following the manufacturer's instructions and stored at 37°C for 1h and 100% humidity. SM was inoculated at 1.0 x 10⁷ CFU/mL to BHI broth in 24-wells plates containing each specimen (n=6) and incubated at 37°C. After 8 and 24hs, a aliquot of the bacterial suspension was collected, spread on BHI agar plates after serial ten-fold dilution and incubated at 37°C for 48 hrs in anaerobic jars to posterior colony-forming units (CFU) counting. For agar diffusion test, base layers containing 15mL of BHI agar and 300 microlitres of SM inoculum were prepared in Petri dishes. Six wells (5mm diameter) were made in each plate and completely filled with RMGIC or RMGIC+dox. Plates were incubated at 37°C for 24 h, and then zones of bacterial growth inhibition around the wells were measured using a digital caliper. The statistical analyses were conducted using Wilcoxon and Mann-Whitney tests (p<0.05). Results: There was a significant log₁₀ SM counts reduction for RMGIC +dox at 3% and 4.5% comparing to the control group without dox. In agar plates, all the tested groups showed significant inhibitory effect against SM compared to the control, with larger inhibition zones for the higher concentration groups. Conclusion: This investigation demonstrated that doxycycline improved considerably the inhibitory effects of Fuji Lining LC against Streptococcus mutans. Supported by FAPESP 08/00359-0 and 08/02606-5.