Effects of silver diamine fluoride on mono-species cariogenic biofilms

Abstract

OBJECTIVES: This in vitro study investigated the effects of sodium diamine fluoride (SDF) on mono-species cariogenic bacterial biofilms on dentin caries-like lesions. METHODS: Caries-like lesions of size 2mmx2mm were created by demineralizing human dentin blocks prepared from extracted sound third molars (IRB-UW08-052). A total of 36 blocks were prepared and placed in the wells of 24-well plates. They were divided into three groups. Each group consisted of twelve dentin blocks and Streptococcus mutans (SM), Lactobacillus acidophilus (LA) and Actinomyces naeslundii (AN) were used for inoculation individually. Plates were incubated at 37 ºC in anaerobic chamber for 7 days to form bacterial biofilms on the caries-like lesions. In each group, half (six blocks) received a topical application of 0.001 ml distilled water (control) whereas the other six blocks received 0.001 ml 38% SDF (test). Biofilm morphology, microbial kinetics and viability were evaluated using scanning electron microscopy (SEM), colony forming units (CFU) and confocal laser scanning microscopy (CLSM). RESULTS: In the control blocks, SM formed confluent biofilms consisting of long-bead line chains on the caries-like lesions. AN also formed confluent biofilms which consisted of typical Y-shaped cells with branched networks. LA failed to form biofilms. Log CFU of SM group and AN group were 6.05±0.42 and 4.86±0.22 respectively. CLSM images of the SM and AN biofilms indicated that most of the bacteria were alive. In the SDF-treated dentine blocks, silver particles were observed scattered among bacterial aggregates. There were no live bacteria in the SDF-treated groups (CFU=0). CLSM images of the SM and AN biofilms showed dead bacteria. CONCLUSIONS: SDF imparts an antimicrobial effect on cariogenic bacteria viz. Streptococcus mutans, Lactobacillus acidophilus and Actinomyces naeslundii and inhibits these three cariogenic mono-species to form biofilms on caries-like dentin lesions.