Sodium fluoride and silver diamine fluoride-coated tooth surfaces inhibit bacterial acid production at the bacteria/tooth interface

This study aimed to evaluate whether coating tooth surfaces with sodium fluoride (NaF) or silver diamine fluoride (SDF) inhibits bacteria-induced pH reductions at the bacteria/tooth interface. Specimens of coronal enamel (CE) or root dentin (RD) were prepared. The surfaces of the specimens were treated with 2% NaF or 38% SDF solution. Some specimens were aged for 1 week after being treated. A tooth specimen was fixed to the bottom of the well of the experimental apparatus. A miniature pH electrode was placed on the specimen and the well was filled with Streptococcus mutans (SM) cells. The pH was monitored after the addition of 0.5% glucose. SM cells were recovered from the wells, and the amounts of lactate, calcium, fluoride, and silver were measured. The fluoride-treated tooth specimens exhibited significantly higher pH values than the untreated controls, irrespective of the tooth substrate at 120 min (CE: NaF 4.62 ± 0.06 vs 4.34 ± 0.10 and SDF 5.23 ± 0.29 vs 4.44 ± 0.16, RD: NaF 5.10 ± 0.11 vs 4.54 ± 0.33 and SDF 6.65 ± 0.47 vs 4.64 ± 0.39). The SDF-coated RD specimens released the greatest amounts of fluoride (103.3 ± 48.1 nmol/well) and silver (70.4 ± 36.9 nmol/well), while they exhibited significantly lower lactate production and decalcification (calcium release) than the control samples (lactate: 4.0 ± 0.7 vs 7.4 ± 0.3 mmol/l, calcium: 2.2 ± 0.4 vs 3.7 ± 0.5 μg/ml). This antimicrobial effect was weakened by 1 week’s aging, while the acid resistance of the fluoride-treated surfaces seemed to increase with aging. Fluoride-treated tooth surfaces inhibit bacterial acid production at the bacteria/tooth interface. The SDF-coated RD had the strongest inhibitory effect. Coating RD with SDF could help to prevent root caries.