Effects of Nitrate and Nitrite on Plaque pH Decrease and Nitrite-Producing and -Degrading Activities of Plaque in vitro.

INTRODUCTION: The purpose of this study was to investigate the effects of nitrate and nitrite on the pH-lowering activity of human plaque, the nitrite-producing and -degrading activities of human plaque, and their correlation. METHODS: Nitrate and nitrite were added to human plaque suspensions collected from the buccal aspect of maxillary molars of patients visiting a general dental clinic, and changes in pH were measured with and without glucose addition. Nitrite-producing and -degrading activities were evaluated by adding nitrate and nitrite to the plaque suspension and measuring the increase and decrease in nitrite with Griess reagent, respectively. RESULTS: The addition of nitrate inhibited both endogenous and glucose-induced plaque pH-lowering. The addition of glucose enhanced the production of nitrite from nitrate by about 3.3-fold. The addition of nitrite also inhibited endogenous plaque pH-lowering, but the addition of glucose promoted nitrite degradation by only about 1.1-fold. Nitrite-producing activity was positively correlated with age, but not with nitrite-degrading activity. CONCLUSION: This study revealed that nitrite was produced from nitrate and inhibited the pH-lowering activity of human plaque, which may contribute to caries control. Both nitrite-producing and -degrading activities occurred in human plaque, but no correlation was found between them. Furthermore, nitrite production was enhanced by glucose metabolism, which may function as a self-regulatory mechanism (resilience) to prevent excessive acidification by glucose metabolism.

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.

Actual state of the diurnal masseteric electromyogram: Differences between awareness and non-awareness of awake bruxism.

PURPOSE: This study aimed to elucidate the relationship between diurnal masseter muscle activity and awareness of diurnal awake bruxism (d-AB) by conducting a comparative analysis of electromyographic (EMG) data from individuals with and without awareness of diurnal awake bruxism (d-AB), utilizing EMG data gathered from multiple subjects. METHODS: Unilateral masseter electromyography (EMG) recordings were performed during the daytime using an ultraminiature wearable EMG device. A total of 119 participants (59 with awareness of diurnal tooth clenching [d-TC] and 60 without awareness of d-TC) were included. Waveforms longer than 0.25 s with the two amplitude conditions, exceeding twice the baseline and >5% of maximum voluntary clenching, were extracted. In addition, the number of bursts and episodes (groups of bursts), burst duration, and burst peak amplitude were calculated for each participant. RESULTS: There were no significant differences in the EMG parameters between the groups with and without awareness of d-TC. Additionally, the frequency distribution of the number of EMG waveforms exhibited wide ranges and substantial overlap between the two groups. CONCLUSIONS: The variability in the number of bursts and episodes, burst peak amplitude, and burst duration among subjects suggests the need for an objective classification of d-AB severity based on EMG values. The absence of significant differences and large overlap in frequency distributions between the groups with and without awareness of d-TC indicate difficulty in predicting muscle activity solely based on awareness of d-AB.

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.