dental

• Dental caries


  Appears to result from the action of multiple, interrelated factors

  
• A companion study dealt with the plaque-flora/caries relationship

  
• The plaque-pH/caries relationship is the subject of this study

  
• Both studies involve the same subjects, plaques, and tooth surfaces, so data on the examined factors have also been integrated

  
• In vivo plaque pH determinations


  1. Microelectrode

  2. Buccal sound (s) and "white-spot" (ws) caries surfaces

  3. Low-caries (no ws) and higher-caries subject group

  
• Evaluation of pH response to sugar


  1. Before and after

  2. Sugar rinse

  3. Local sugar application

  4. Sucking on a sugary lozenge

  
• pH profiles with sugar rinsing and normal or limited salivary flow conditions


  Progressively decreasing plaque pH values at various time points in the order of: low-caries subjects (s sites), higher-caries subjects (s sites), higher-caries subjects (s + ws sites), and higher-caries subjects (ws sites)

  
• Minimum pH values


  Showed the same trend as the pH profiles
• Analyses of all data indicated only a statistical difference for minimum values for s sites in low-caries subjects vs. ws sites in higher-caries subjects, and for s and ws sites in the higher-caries subjects
• Local sugar application and sucking on a sugary lozenge induced smaller pH drops than sugar rinsing
• Suboptimal sugar exposure caused a disappearance of the difference between the minimum pH values for s and ws sites observed with sugar rinsing in the higher-caries subjects

  
• Initial plaque pH values were similar regardless of subject or tooth caries status

  
• Initial plaque pH values were not correlated with the plaque levels of strongly iodophilic polysaccharide-storing bacteria

  
• Both studies indicate that increasing subject caries status is characterized by increasing plaque levels of highly-acid-tolerant, acidogenic bacteria and an increasing plaque-pH-lowering potential

  
• The studies support the dynamic relationship between plaque flora composition, plaque pH-lowering ability, and caries development

  
• y lozenge


  Tablet (Lifesaver, 1.7 grams of sugar) for 5 min with normal salivary access during a 30-minute test period

  
• Plaque pH measurements


  1. Time 0 min (initial pH) immediately prior to sugar rinsing, the local application of sugar solution, or the sucking of the tablet

  2. 5 min

  3. 10 min

  4. 15 min

  5. 20 min

  6. 30 min

  
• pH measurement procedure


  • Touch microelectrode connected with pH/ISP meter and glass reference electrode
  • Reference salt bridge established by each test subject dipping one finger into 3 mol/L KCl solution
• pH values used in unconverted form as well as after conversion to free H+ concentration (antilog)
• Data presented for groups of low-caries and higher-caries subjects or sound (s) and ws tooth-surface sites

  
• Mean pH value for each subject group at each time point calculated from the mean of the readings for each subject
• For converted pH values, the value for each plaque was first converted to free H+ concentration, then a mean of the antilogs was calculated for each group
• Plaque flora data from companion study, involving 3 groups of organisms: MS, total undifferentiated "low-pH" bacterial flora, and strongly iodophilic polysaccharide-storing organisms

  
• Bacteriological data from only one plaque sampling occasion per subject

  
• Initial plaque levels of strongly iodophilic polysaccharide-storing bacteria


  Initial plaque pH at time 0 min prior to sugar exposure

  
• Statistical analysis used two-tailed t test, ANOVA, and Spearman rank correlation test
• p value < 0.05 considered statistically significant
• ANOVA, p = 0.05) and particularly for converted values (t test, p < 0.01) under both conditions of salivary access

  
• For neither subjects (Table 4) nor tooth-surface sites (Table 5) were the lower pH values (both types) during normal salivary access statistically different from the values obtained during limited salivary access (t test)

  
• Comparison of the minimum, unconverted, and converted pH values for s sites in low-caries subjects (Table 4) with either the s or the ws sites in higher-caries subjects (Table 5) showed only a statistical difference between the s sites in low-caries subjects and ws sites during normal salivary access only (t test)

  
• The tests with topical sugar application and sucking of a sugary lozenge with the other nine or 10 higher-caries subjects showed generally higher minimum pH values for the s and ws sites compared to the sugar rinsing tests

  
• The initial pH values were closely comparable regardless of subject or tooth-site caries status (t test)

  
• Under conditions of normal salivary access, the correlation between lower pH values and higher plaque levels of the different types of bacteria was highly statistically significant. However, under conditions of limited salivary access, this correlation did not reach statistical significance for either of the bacterial groups

  
• No different initial pH values were observed for the different levels of strongly iodophilic polysaccharide-storing bacteria in either the low- or higher-caries subjects

  
• Plaque pH and microflora of dental plaque on sound and carious root surfaces were studied

  
• Restricted salivary access


  Imitation of the natural situation
• The plaque-pH-elevating effect of saliva has been documented in various studies

  
• In sugar-rinsing tests, saliva's effect was often only slightly discernible

  
• Continued exposure of plaque to salivary glucose after the rinse during conditions of normal but not of restricted salivary access


  Reason for the slight discernibility of saliva's effect

  
• Tests in which saliva was restricted after sugar exposure indicated that differences between the plaque pH values for s and ws sites, observed during normal salivary access, persisted during salivary restriction