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The purpose of this study was to evaluate the effect of remaining dentin thickness (RDT) on the bond strength of current adhesive systems. Third molars were randomly allocated among four groups depending on the adhesive system used: Clearfil SE Bond ONE (SE1), G-Bond PLUS (GB), BeautiBond (BB), and Clearfil Mega Bond (MB). Bonded specimens were stored in water at 37°C for 24 h. Teeth were then sectioned perpendicular to the adhesive interface to produce beams. After measuring RDT of each beam, microtensile bond strength test was carried out using a universal testing machine at a crosshead speed of 1 mm/min. All data were analyzed by linear regression analysis. Bond strengths of one-step self-etch materials used in this study increased with an increase in RDT. In contrast, that of two-step self-etch adhesive system was not affected by RDT.

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...

The purpose of this study was to evaluate the µTBS (microtensile bond strength) of currently available self-etching adhesives with an experimental self-etch adhesive in normal and caries-affected dentin, using a portable hardness measuring device, in order to standardize dentin Knoop hardness. Normal (ND) and caries-affected dentin (CAD) were obtained from twenty human molars with class II natural caries. The following adhesive systems were tested: Mega Bond (MB), a 2-step self-etching adhesive; MTB-200 (MTB), an experimental 1-step self-etching adhesive (1-SEA), and two commercially available one-step self-etching systems, G-Bond Plus (GB) and Adper Easy Bond (EB). MB-ND achieved the highest µTBS (p<0.05). The mean µTBS was statistically lower in CAD than in ND for all adhesives tested (p<0.05), and the 2-step self-etch adhesive achieved better overall performance than the 1-step self-etch adhesives.

Fluorine (F) and strontium (Sr) are key elements in the de-and remineralization of teeth. To quantitatively analyze the distribution of F and Sr, micro-particle-induced gamma/X-ray emission (PIGE/PIXE) technique was used. The cavities were prepared and filled with the fluoride-and Sr-containing restorative materials (FSCMs) in extracted human molars. The single-section enamel specimens were prepared by slicing from the buccal to lingual surface including the FSCMs. After 5 weeks of automatic pH cycling, the demineralization was calculated by integrated mineral loss (ΔIML) from transverse-microradiography. The distributions of F and Sr were analyzed by the PIGE/PIXE technique. The micro-PIGE/PIXE technique indicated a fluorine uptake difference between the enamel surface and enamel cavity wall. ΔIML of FSCMs were significantly lower than intact enamel. The micro-PIGE/PIXE technique enables measurement of F and Sr uptake from FSCMs into enamel, which would be beneficial for research on caries development and prevention.

Root caries is an increasingly problem in aging societies with severe implications for the general health and wellbeing of large numbers of people. Strengthening type-I collagen, a major organic component of human dentin, has proved effective in preventing root caries. This study sought to determine whether exposure to riboflavin followed by UVA irradiation (RF/UVA) could promote additional collagen crosslinking, and thus improve the acid and enzymatic resistance of human dentin under simulated oral environments. If so, it could offer potential for treatment of the intractable problem of root caries. The greatest flexural strengths were found in dentin exposed to a 0.1% riboflavin solution for 1 minute followed by 1,600 mW/cm2 UVA irradiation for 10 minutes. Mineral loss and lesion depth were significantly lower in the RF/UVA group than in the control group. The microstructures of dentinal tubules and collagen networks after RF/UVA treatment retained their original forms after acidic and enzymatic degradation. In conclusion, RF/UVA treatment may be a new method for preventing root caries with promising prospects for clinical application.

The accuracy and efficiency of the lattice Boltzmann method (LBM) and the finite difference method (FDM) are numerically investigated. In the FDM for incompressible viscous flows, it is usually needed to solve a Poisson equation for the pressure by iteration or relaxation technique, while in the LBM, such special treatment is not required. Two-dimensional problems of incompressible viscous flows and thermal fluid flows are computed by using the LBM and FDM. In the problem of flows through a porous structure, the present results indicate that the LBM is more efficient than the FDM, because there is no need to relax the pressure fields in the LBM at relatively high Reynolds numbers. Therefore, it is found that the LBM is useful for the investigation of transport phenomena in complex geometries such as porous structures.

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