INTRODUCTIONAlthough many intrinsic and extrinsic factors are involved in the etiology and pathogenesis of dental caries, pH in the oral cavity is known to be one of the main factors. In particular, fluctuations in dental plaque pH after carbohydrate consumption exacerbate caries occurrence and severity. As shown by Stephan 1） , the pH value following sucrose intake drops rapidly to its minimum level （which is below pH 5.0） , and then over a period of 30 minutes to several hours, the pH value slowly returns to its original value （which is above pH 7.0） . As a result, pH in the oral cavity is subjected to successive fluctuations between pH below 5 and then above 7 with each carbohydrate intake. Such a pH fluctuation occurs because metabolism of fermentable substrates by the plaque flora leads to acid production 2）; following which, acid dilution and/or neutralization occurs according to the flow rate of saliva and its buffering capacity 3） . It should also be highlighted that these pH fluctuations play a key role in de-and remineralization of teeth. This is because enamel dissolution rate is reduced when pH value is increased 4）, and when pH is sustained above 5.5 both hydroxyapatite（HAP）and fluorapatite（FAP）are synthesized. Moreover, when pH is between 4.5 and 5.5, HAP is dissolved, but FAP synthesis is still in progress if fluoride exists 5） . Caries formation is a dynamic process that involves alternating periods of de-and remineralization of the teeth with pH changes. When the rate of remineralization exceeds the rate of ion transport out of the tooth surface, the surface layer can be retained with the continuous renewal. However, if demineralization is the predominant process over a defined period, or that the rate of demineralization exceeds the rate of remineralization, the net result will be a gradational loss of tooth minerals leading to irreversible cavity formation. Thus, the outbreak occurrence and progression of a caries lesion are associated with an imbalance between de-and remineralization. In various researches 6-9） , protocols have been designed to investigate caries progression using a pH cycle in which the teeth were immersed alternately and periodically into two different pH solutions. Those studies indicated that the rate of demineralization process was highly dependent on the low pH and ion concentration of such ions as Ca 2＋ , PO 4 3-, and F -of demineralization solutions 10,11） . Among the ions mentioned above, fluoride is known to have anticariogenic effect. As such, there are many studies concerning fluoride release from fluoride-containing materials 12-15） . However, most of the studies performed did not indicate the influence of demineralizationremineralization imbalance on the teeth in human oral conditions, as shown in Stephan's curve under changing pH. Therefore, in the clinical setting, a direct correlation between pH changes simulating oral cavity conditions and caries formation is still a matter of discussion.For the purpose of observing caries occurrence The aim of this...

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To the end of developing a convenient research tool to calculate the mineralization status of teeth in detail, a new program was developed using Visual Basic for Applications combined with Microsoft Excel 2004. To demonstrate the usefulness of this program, it was used to analyze tooth enamel mineralization after acid exposure. Transverse microradiography images (TMR) of specimens were digitalized with a charge-coupled device camera with a microscope (CCD camera) and a digital film scanner (FS). Subsequently, the mineral content profile of each specimen after de-and remineralization studies were calculated using the Angmar's formula. The newly developed program was applied to calculating the mineral loss (ΔZ), lesion depth (Ld), surface zone depth (SZd), and lesion body depth (LBd) of tooth specimens. In addition, the outer surface zone (OSZ), inner lesion body (ILB), and sandwich area (SA) between OSZ and ILB -which together constituted ΔZ -were calculated by the newly developed program. Data obtained with the newly developed program were in good agreement for both CCD camera and FS, indicating that the program was reliable for tooth enamel mineralization research studies.

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Objectives The aim of this study was to investigate whether the newly developed artificial dental plaque (A‐DP) is useful as an educational tool for denture care of dental hygienist that compared it with conventional artificial dental plaque from the viewpoint of practical skills. Material and methods The 125 dental hygienist school students and 26 dental hygienists who had clinical experience were subjected a practical training of denture plaque control using the conventional denture plaque (C‐DP) and the A‐DP. The questionnaires based on the semantic differential method were used to survey whether the A‐DP is similar to the real denture plaque (R‐DP). Factor analysis by rotation of promax was carried out. Results In the results of the factor analysis, the two factors could be detected in students and three factors in dental hygienists. The total score of each denture plaque was calculated for each factor, and correlation coefficient was examined. There was significant correlation between the A‐DP and the R‐DP at the first factors, both students and dental hygienists. C‐DP was not similar to R‐DP in all factors. Conclusions These results suggested that A‐DP resembles R‐DP better than C‐DP. It was concluded that the A‐DP was similar to the R‐DP and could be a potent educational tool for practical denture care.