Inhibitory Effects of Nitrite on Acid Production in Dental Plaque in Children.

PURPOSE: To assess the inhibitory effects of nitrite on plaque acidogenicity and its relationship with caries experience. MATERIALS AND METHODS: Plaque (2 µl) was collected from 76 children (age 5.8 ± 2.6 years, dmft 2.9 ± 3.5, DMTF 0.6 ± 1.4) and mixed with nitrite solution (final concentration = 0.63 mM) or distilled water (control). The initial pH (pH-0) of each sample was measured using a portable pH meter. The samples were incubated for 10 min, then their pH (pH-1) was measured again. Next, glucose (final concentration = 0.67%) was added to the samples, which were then incubated for a further 10 min before their pH was assessed for a third time (pH-2). RESULTS: The pH-0, pH-1, and pH-2 values of the control samples were 7.25 ± 0.16, 6.07 ± 0.44, and 5.11 ± 0.48, respectively, and those of the nitrite-treated samples were 7.26 ± 0.16, 6.37 ± 0.45, and 5.34 ± 0.48, respectively. The pH-1 and pH-2 values of the nitrite-treated samples were higher than those of the control samples (p < 0.005). Greater plaque acid production was associated with stronger inhibition of plaque acid production by nitrite (p < 0.005). No relationship was detected between the inhibition by nitrite and caries experience. CONCLUSIONS: Nitrite inhibited both endogenous and exogenous plaque acid production. Nitrite inhibited acid production more markedly in plaque that exhibited greater acid production, suggesting that nitrite might be effective at preventing caries, as it contributes to pH homeostasis in plaque by countering excess acidification.

pH Response and Tooth Surface Solubility at the Tooth/Bacteria Interface.

Evaluating the physiochemical processes at the tooth surface/bacteria interface is important for elucidating the etiology of dental caries. This study aimed to compare the mineral solubility and protein degradation of coronal enamel (CE) and root dentin (RD), and investigate the involvement of dissolved components in bacteria-induced pH changes using a model of tooth/bacteria interface. An experimental apparatus forming a well was made of polymethyl methacrylate, and a bovine tooth (CE or RD) specimen was fixed at the bottom of the well. A miniature pH electrode was placed on the tooth, and Streptococcus mutans NCTC 10449 cells, grown in 0.5% glucose-containing complex medium, were packed into the well. The pH at the tooth/S. mutans interface was monitored continuously for 120 min after the addition of 0.5% glucose at 37°C. S. mutans cells were recovered from the wells, and the amounts of lactate and calcium were measured using a portable lactate meter and a fluorescent dye, respectively. Proteolytic activity was also evaluated fluorometrically. The pH of the RD/S. mutans interface was significantly higher than that of the CE/S. mutans interface (30 min: 6.37 ± 0.12 vs. 6.18 ± 0.11, 60 min: 6.08 ± 0.14 vs. 5.66 ± 0.27, 90 min: 5.49 ± 0.24 vs. 5.14 ± 0.22, p < 0.05). Greater amounts of calcium were dissolved from RD (3.19 ± 0.74 µg/mL) than from CE (1.84 ± 0.68 µg/mL; p < 0.05), while similar amounts of lactate were produced. Proteolytic activity was not detected at any of the interfaces. These results indicate that RD is more soluble to bacteria-induced acidification than CE. This method can contribute to the evaluation and development of caries-preventive materials.

Effect of fluoride-releasing restorative materials on bacteria-induced pH fall at the bacteria-material interface: an in vitro model study.

OBJECTIVES: Inhibition of bacterial acid production by dental restorative materials is one of the strategies for secondary caries prevention. This study aimed to evaluate the effect of fluoride-releasing restorative materials on bacteria-induced pH fall at the bacteria-material interface. METHODS: Four fluoride-releasing restorative materials, glass-ionomer cement (GIC), resin-modified glass-ionomer cement (RMGIC), resin composite (RC) and flowable resin composite (FRC) were used. Each specimen was immersed in potassium phosphate buffer at pH 7.0 for 10min and 4 weeks, and in potassium acetate buffer at pH 5.5 for 4 weeks. An experimental apparatus was made of polymethyl methacrylate and had a well with restorative materials or polymethyl methacrylate (control) at the bottom. The well was packed with cells of Streptococcus mutans, and the pH at the interface between cells and materials was monitored using a miniature pH electrode after the addition of 1% glucose for 90min, and the fluoride released into the well was quantified using a fluoride ion electrode. RESULTS: The pH of GIC (4.98-5.18), RMGIC (4.77-4.99), RC (4.62-4.75) and FRC (4.54-4.84) at 90min were higher than that of control (4.31-4.49). The fluoride amounts released from GIC were the highest, followed by RMGIC, RC and FRC, irrespective of immersion conditions. Saliva coating on materials had no significant effect. CONCLUSIONS: The fluoride-releasing restorative materials inhibited pH fall at the bacteria-material interface. The degree of inhibition of pH fall seemed to correspond to the amount of fluoride detected, suggesting that the inhibition was due to the fluoride released from these materials. CLINICAL SIGNIFICANCE: A little amount of fluoride actually released from the fluoride-releasing materials may have caries preventive potential for oral bacteria.

Chairside evaluation of pH-lowering activity and lactic acid production of dental plaque: correlation with caries experience and incidence in preschool children.

OBJECTIVES: Because caries activity may be related to dental plaque acidogenicity, a method was developed for chairside evaluation of pH-lowering activity and lactic acid production by dental plaque. Moreover, this study examined the association of these 2 factors with caries experience on oral examination and with caries activity by following caries incidence for 4 years in a group of preschool children. METHOD AND MATERIALS: A dental plaque sample (2.4 microL) was collected from sound buccal surfaces of maxillary primary second molars using a spoon excavator and placed onto the sensor area of a portable pH meter. Sucrose (30 microL, 228 mmol) was mixed with the plaque sample, and pH changes were monitored for 10 minutes. After pH determination, lactic acid concentration in the plaque-sucrose mixture was measured using a portable lactate meter. RESULTS: Caries experience of subjects correlated with minimum pH (at 10 minutes after sucrose addition) ( r = -0.53, P < .001) and lactic acid production ( r = 0.38, P < .001). In addition, increments of both primary tooth caries (Delta dft) and permanent tooth caries (Delta DFT) for 4 years correlated with minimum pH ( r = -0.47, P < .005 and r = -0.38, P < .05, respectively). Setting cutoff values of pH and lactic acid concentration at 5.0 and 7.0 mmol/L for DELTA dft allows screening for caries-susceptible subjects (sensitivity = 0.950 and 0.800, specificity = 0.391 and 0.783, respectively). CONCLUSION: Plaque in caries-susceptible preschool children displays greater pH-lowering activity and lactic acid production. This method can be applied as a chairside screening test for caries activity and susceptibility for preschool children in dental clinics.