| Background and ObjectiveCaries is a kind of the most common oral disease. It has been listed as one of the three diseases, which do great harm to the human health by WHO due to its high incident rate and widely involve area. Many researchers have studied the relationship between the dental plaque and dental caries from different point because it is suggested as the indispensable microenvironment of caries. Though the pathogenesis of caries has been recognized in some extent, the exact cariogenicity of the plaque hasn't be clarified yet. Acidic fermentation products produced by dental plaque microorganisms in the presence of sugar or carbohydrate are believed to be responsible for dissolving tooth substances and producing dental caries. Plaque pH changes generally serve as a reliable indicator for detecting the acidogenicity of the plaque, so it is important to determine the dynamic change of the plaque pH after sucrose challenge in studying the cariogenic potential of plaque or individual's susceptibility to dental caries. Ion selective microelectrode technology, a new method emerged recently years, has shown its special superiority in the stomatology research field. In our study, a kind of chemical modified IrO2 pH microelectrode will be fabricated and put into the use of plaque pH measurement in vivo. Then a systemic study of the dynamic change of the plaque pH after sucrose challenge and the effect of relative factors on this change pattern will be carried out in order to provide the experimental basis for the caries pathogenesis.Methods1. The chemical modified IrO2 microelectrodes were fabricated by electroplating the sensitive membrane of H+ -ion (iridium oxide) to the surface of platium wires. Then the pH responses of all the microelectrodes were determined and the one, which showed a rather stable electric voltage response of 55.8 mV/pH, was chosen for the following measurements performed in this study. It was further compared with the Beetrode pH microelectrode produced by WPI, USA.Thirty healthy volunteers with different caries history were selected based on the experimental design. They were divided into four groups according to the DMFS of each2. subject. The four groups are caries-free group (CF), caries-inactive group (CIA), caries-active sound sites group (CAS) and caries-active carious sites group (CAC) respectively (ten subjects were listed to both CAS and CAC groups). All subjects refrained from oral hygiene for 48h to allow for sufficient plaque formation. Plaque pH measurements were carried out prior to (resting pH) and on nine occasions (2, 5, 10, 15, 20, 30, 40, 50 and 60 min) after 2 min rinse with 20 mL of a 10% sucrose solution, by inserting the microelectrode into the interproximal space between the second premolar and first molar in the mandibular right quadrant. This experiment was performed to relate sucrose-induced pH response of dental plaque to the individual's susceptibility dental caries.3. Ten caries-free healthy volunteers consented to participate in this experiment. The same sites as mentioned above in both maxillary and mandibular were measured. Furthermore, the mixed saliva pH was determined on the saliva pool in the bottom of the mouth simultaneously. The sucrose-induced pH response of plaque and mixed saliva was assessed as described in step 2. 4. Forty healthy volunteers attended in this experiment. They were divided into four groups randomly. In each group, all the subjects were indicated to intake fluoride by one of the following pattern: A- brush their teeth with fluoridate toothpaste, twice everyday. B-brush their teeth with fluoridate toothpaste twice everyday and in the same time, rinse with 0.05% NaF solution once every evening. C-brush their teeth with fluoridate toothpaste twice everyday and in the same time, rinse with 0.2% NaF solution once every week. D-the same as group A, while in the experiment, the sucrose solution contained 0.2% NaF. After 2w, the same sucrose rinsing and measurements were carried our as described in step 2. In add...
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