| Background & Objective Caries is a kind of the most common disease among human beings. WHO has already taken it, together with cancer and cardiovascular diseases, as the major diseases that should be paid more attention to prevent and cure. Many researchers have studied the relationship between the dental plaque and dental caries from different points because it is suggested as the indispensable microenvironment of caries. At present, people think that acidic fermentation products produced by dental plaque microorganisms in the presence of sugar or carbohydrate are responsible for dissolving tooth substances and producing dental caries. So to control the acidic production of dental plaque has become one of the most effective anticaries methods. Therefore, plaque pH changes generally serve as a reliable indicator for detecting the acidogenicity of the plaque or individual's susceptibility to dental caries. Xylitol as a low-calorie sugar substitute has been used comprehensivly in many kinds of food. And people find that long-term habitual consumption of xylitol appears to can reduce the caries. But the exactly anticariogenic property of the xylitol hasn't been clarified yet. In our study, by using ion selective microelectrode to detect the metabolism of xylitol in dental plaque to prove the noncaries property of xylitol. And then we will study the inhibitory effect of xylitol on the growth and acid production of streptococcus mutans under anaerobic condition to confirm xylitol's anticariogenic property. And we also test the effect of xylitol-containing gum and a combination of Zncl2 and xylitol solution on the glycometabolism of dental plaque to provide some guidances for clinical application. Methods 1. Ten healthy young volunteers with no periodontal disease and new caries activity were selected. All the volunteers were refrained from oral hygiene for 48 h to allow for sufficient plaque formation. Plaque pH measurements were carried out on nine occasions (0, the 5th, the 10th, the 15th, the 20th, the 30th, the 40th, the 50th and the 60th min) after 2 min rinsing with 20 ml of a 10% sucrose,10% glucose,10% maltose,10% fructose and 10% xylitol respectively by inserting the microelectrode into the interproximal space between the second premolar and the first molar in the maxillary right quadrant. This experiment was performed to compare the differences between xylitol and the other sugars on the cariogenicity. 2. To study the inhibitory effect of xylitol on the growth and acid production of streptococcus mutans we incubated streptococcus mutans in 3% sucrose culture medium,2% xylitol culture medium and 3% sucrose-2% xylitol culture medium under anaerobic conditions. And then we measured the changes of OD600 and pH of the mediums by spectro photometer and compound glass pH electrode. 3. Ten young volunteers ages of 20~23 years were selected and the criteria was the same to experiment one. All the volunteers were refrained from oral hygiene for 48 h to allow for sufficient plaque formation. The pH change was measured by inserting a Beetrode pH microelectrode into the interproximal space between the second premolar and the first molar in all the four quadrants within 50 min (on nine occasions : 0, the 5th, the 10th, the 15th, the 20th, the 25th, the 30th, the 40th and the 50th min) after 10% sucrose rinsing followed by chewing sugar-containing gum and sugar-free gum 20 min. The volunteers were asked to stop chewing gum when the pH changes were being tested. This experiment was performed to evaluate the superiority of chewing sugar-free gum after sucrose challenge on the recovery of dental plaque pH in situ. 4. Ten young volunteers ages of 20~23 years were selected and the criteria was the same to experiment one. The pH changes were determined by inserting a Beetrode pH microelectrode into the interproximal space between the second premolar and the first molar in all the four quadrants within 1 h ( on ten occasions: 0, the 5th, the 10th, the 15th, the 20th, the 25th, the 30th, the 40th, the 50th and the 60th min ) after sucrose rinsing following Zncl2 solution and Zncl2 plus xylitol solution 30,60,120 min respectively. This experiment aimed to compare the anticaries mechanism of xylitol and zinc from dental plaque metabolism. Results 1. Plaque pH decreased immediately after sucrose,glucose,maltose and fructose challenge, and then rise slowly, which showed a typical Stephan response. There were nosignificant differences between sucrose,glucose and maltose in all the pH change parameters. But the pH change of fructose was less than the three groups (P<0.05). While the pH after xylitol challenge had no differences contrast to the rest pH of plaque (P>0.05) and significant differences of the pH in each time point and the pH change parameters had been observed between xylitol and the other four groups (P<0.001). 2. During the incubation of streptococcus mutans in vitro culture, we found that the growth of streptococcus mutans was inhibited significantly in the xylitol medium. The OD600 of xylitol medium was significantly lower than the other two mediums. While the growth of streptococcus mutans was inhibited in some degree of xylitol-sucrose medium, which OD600 was lower than sucrose medium (P<0.001). And the glycolysis was also inhibited significantly in xylitol medium, which pH was too high than the other mediums. Moreover, the pH of xylitol-sucrose medium was higher than the sucrose medium (P<0.001). 3. Chewing gum 20 min at the 5th min after sucrose rinse (the lowest pH) could raise pH significantly. Sugar-free gum can raise pH to 7.30 which higher than the pre-rinsing period (P<0.001). While sugar-containing gum had little effect on pH recovering at the first 5 min chewing period, which had no difference between the baseline Stephan curve (P>0.05). 4. All the plaque pH decreased and then rised slowly after sucrose challenge following Zncl2 solution 30,60,120 min respectively. But the pH decreased less in the 30 min group and the 60 min group, which was significantly higher than the baseline Stephan curve and last 25 min after sucrose challenge (P<0.001). While there was no difference between the 120 min group and the baseline Stephan curve in each time point (P>0.05). On the other hand, all the plaque pH decreased less after sucrose challenge following Zncl2 plus xylitol solution 30,60,120 min respectively. The pH in each time point of the 30 min group was significantly higher than the baseline Stephan curve and the same to pH after sucrose challenge 40 min in the 60 min group (P<0.001). Moreover, the lowest pH of the 120 min group after sucrose challenge was also higher than the baseline Stephan curve and lasted to 20 min after sucrose challenge.Conclusions 1. The plaque pH don't have any changes after xylitol challenge. That means xylitol is a non-cariogenicity sugar substitute which can't provide the necessity nutrition to streptococcus mutans. 2. Xylitol can inhibit the growth and acid production of streptococcus mutans effectively. And xylitol can also influence the utilization of sucrose of streptococcus mutans, which displays the quality of xylitol as the most promising sweetener for preventing caries risk. 3. Chewing sugar-free gum after sucrose rinsing can neutralize acid production produced by baicteria in dental plaque and raise plaque pH significantly more effectively. While chewing sugar-containing gum has little effect on pH at the first 5 min chewing period. So we suggest that people chew sugar-containing gum at least 10 min so that we can get the best anticaries effect from chewing gum. 4. Zncl2 solution can inhibit plaque acidogenicity for up to 60 min and the strength of the effect of Zncl2 will decrease with the interval time lasting. While the combination of Zncl2 and xylitol solution can inhibit plaque acidogenicity for up to120 min. At the same zinc concentration, the combination of Zncl2 and xylitol solution is significantly more effective at inhibiting acid production than Zncl2 solution alone and the working time also last significantly. |
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