Masakazu Kurachi

Effects of adding silver nanoparticles on the toughening of dental porcelain

STATEMENT OF PROBLEM Dental porcelains currently used for ceramic restorations are brittle, and it is sometimes necessary to replace fractured or chipped restorations. Porcelain is fragile and exhibits elastic deformation rather than plastic deformation, leading to fracture or chipping of restorations. PURPOSE The purpose of this study was to investigate the toughening of porcelain through the addition of silver nanoparticles. MATERIAL AND METHODS Noritake Super (NS) Porcelain AAA modified with the addition of silver nanoparticles was used. The concentration of silver in the solution was adjusted to 100, 200, 500, and 1000 ppm (Ag100, Ag200, Ag500, and Ag1000). The Vickers hardness (Hv) and median crack length extending from the corner of each indent were measured. The fracture toughness (KIC) was calculated by the indentation method. Optical reflectance spectra were recorded by using a spectrometer in the wavelength range of 200 to 700 nm. X-ray diffraction spectroscopy, color measurement, Fourier transform infrared spectroscopy, and electron probe microanalysis were also performed. The observed values of Hv, 2a, E, and KIC were compared and evaluated with a 1-way ANOVA, followed by the Bonferroni method (α=.05). RESULTS The addition of silver nanoparticles significantly increased the Hv of all specimens with the exception of Ag100. The median crack length was significantly smaller in Ag500 (104.5 μm, SD: 11.9) and Ag1000 (100.0 µm, SD: 5.5). Significantly higher toughness values were observed for Ag500 (1.54 MPa·m(1/2), SD: 0.05) and Ag1000 (1.51 MPa·m(1/2), SD: 0.08) than for the control (1.36 MPa·m(1/2), SD: 0.03). In terms of color difference, Ag500 (5.08, SD:1.32) and Ag1000 (5.47, SD:1.05) had values significantly greater than ΔE*=2.69. CONCLUSIONS The addition of silver nanoparticles significantly increased the fracture toughness and Vickers hardness of the NS porcelain. A residual compressive stress was generated due to the ion exchange reaction and differential thermal expansion of the silver metal nanoparticles. However, the addition of Ag500 and Ag1000 nanoparticles led to a color change.

Wettability and Durability of Si-O Coatings on Zirconia Substrate by RF-Magnetron Plasma Sputtering

The wettability and durability of Si-O coatings prepared on zirconia substrate using radiofrequency magnetron sputtering (rf-sputtering) was studied. XRD analysis revealed no phase transformation of zirconia before/after rf-sputtering process. XPS spectroscopy showed that as-deposited films with a SiO2 configuration was formed. EDX analysis indicated that the Si/Zr ratio was high and when magnetron rf-sputtering was performed using a plasma gas Ar+5% O2, which may be the optimum condition of rf-sputtering to form a sustainable hydrophilic layer on zirconia substrate. The wear testing using pin on disc wear apparatus was performed. The wettability and durability of Si-O coatings fabricated by magnetron radiofrequency magnetron sputtering (rf-sputtering) on zirconia substrate was studied. A plasma gas Ar+5% O2 may be the optimum condition of rf-sputtering to form a sustainable hydrophilic layer on zirconia substrate

Promotion of Nickel (Ni) Allergy by Anamnestic Sensitization with a Bacterial Component, Lipopolysaccharide (LPS), in Mice

Background/Objective: Lipopolysaccharides (LPS) promote allergic responses to nickel (Ni) both in the sensitization and elicitation steps. In this study, we examine the effect of pre-sensitization to LPS on the occurrence of Ni allergy using a mouse model. Method: A 100 mg of LPS was injected into C57BL/6J mice intraperitoneally (ip). Three weeks later, the mice were subsequently injected with 0.3 μ moles of nickel dichloride (NiCl2) and 100 μg of CpG-DNA, which acted as an adjuvant. The mice were repeatedly immunized with the 0.3 μg of nickel sulfate (NiSO4), along with 300 μl of the adjuvant, Inject Alum (Pierce, USA). Then we examined the producing capabilities of T helper type 1 (Th1) and 2 (Th2) cytokines (interferon-gamma- (IFN)-γ and interleukin (IL)-10, respectively) from anti CD3 antibody-stimulated spleen cells. Results: Pre-treatment with LPS, followed by repeated challenges with Ni2+ and adjuvants significantly enhanced the IFN-γ-producing capability of spleen cells (n=5, p<0.01); however, that could not enhance the capability of spleen cells by a single challenge with Ni2+ and adjuvants (n=5). In contrast, without LPS treatment, single or even repeated challenges by Ni2+ could not enhance the IFN-γ-producing capability. On the other hand, the IL-10-producing capability of spleen cells was not enhanced even by LPS and repeated challenges with Ni2+ and adjuvants. Conclusion: The solitary pre-sensitization to LPS is essential for the onset of Ni allergy by shifting the Th1/Th2 immune balance toward a Th1 dominant.

Correlation between Chewing Path and Muscle Activity in Chewing Movement. Premature Contact.

This study was performed to determine whether or not malocclusion decreases the interdependent relationship between the chewing path and muscle activity. For experimental premature contact attached to the lower 1st molar on the habitual chewing side, two thicknesses (50 μm and 100μm) of metal foil were used. Chewing movements using a stick of gum were recorded simultaneously as the path and electromyograms. The parameters for the path were the amount of anterior-posterior and right-left movements at 1 mm, 7 mm and lowest point vertically below the intercuspation in the opening-closing path and the maximum amount of mouth opening per stroke, and those for electromyograms were the interval of EMG bursts and the integrated in the central portion of the bilateral masseter muscles and the anterior portion of the bilateral temporal muscles. The presence or absence of premature contact, and changes in the relationship between the chewing path and muscle activity according to the thickness of interference were analyzed in terms of the first canonical correlation coefficient in canonical correlation analysis. Premature contact could be a factor that decreases the first canonical correlation coefficient, but no differences were observed between the two thicknesses.

An Evalution of Relationship between Chewing Cycle and Mastication Muscle Activities.

The present study was to determine the fluctuation patterns in the path and activity of masticatory muscle during chewing masticatory movements in three groups of subjects having different degrees of persistent lateralized mastication (expressed as a lateralized mastication index): group I (mild), group II (intermediate), group III (severe).With regard to the standard deviation of each parameter, N-HM mastication showed a greater variance than HM mastication in all three groups.The difference between the sides of mastication was the smallest in group I and the largest in group II.Furthermore, the number of subjects showing such a relationship was the smallest for most parameters in group I and the largest in group III. Subsequently, the interdependent relationship of the course and masticatory activity was examined by the first canonical correlation coefficient of canonical correlation analysis. In HM mastication, all three groups showed practically equal correlation coefficients of 0.87-0.88.In addition, the subjects in group I showed little or no difference between the two chewing sides, while groups II and III showed a decrease in correlation in N-HM mastication.

The Influence of Continuous Mastication with Non-habitual Chewing Side on Masticatory Movements.

The present study was designed to analyze the influence of the continuous mastication with the nonhabitual chewing side on mastication movements.1. The daily increase in the ratio of one side biased chewing on the nonhabitual chewing side was either rapid or gradual.2. On the habitual chewing side, there were no daily characteristic fluctuations in the 2 variables of area, but other parameters tended to increase. On the other hand, on the nonhabitual chewing side, all parameters tended to decrease daily.3. As a result of a canonical correlation analysis made between the number of chewing strokes and all parameters on the habitual and the nonhabitual sides, the first canonical correlation coefficient was larger on the nonhabitual side than on the habitual side.

Tolerance of Left-right Deviations on the Arrangement of the Upper Middle Artificial Teeth

The present study investigated the tolerance of left-right deviations in the arrangement of the upper middle artificial teeth relative to the median line of the face. For this purpose, the alignment of the maxillary incisor relative to the median line of the face was used as a point of reference.The model photos used for this investigation were prepared by combining 5 photos of both the face and the rows of teeth. In a stimulation series, the center of the row of teeth was displaced either to the left or to the right, and magnitude of this displacement was evaluated by groups of dentists, patients and students, who examined these photos. The results were classified into 5 reaction categories. According to magnitude adaptation level and estimation method, the left-right deviation tolerance was determined by psychological judgement.The results revealed that the lowest average tolerance of measuring 2.586mm was reported by the group of dentists, followed by values of 3.704mm and 4.204mm, which were reported by patients and students, respectively.

1/f Fluctuation on Appearance in Tapping Rhythms.

The present study was made not only to spectro-analyze the fluctuation of the tapping rhythm in subjects with normal masticatory function and to examine its overlapping with 1/f fluctuation as vital responsibility, but also to observe the influence of an experimental object intervened on the occlusal surface.As a result, normal subjects showed 1/f spectrum at each subjects proper rhythm, but not 1/f at a metronome-loading rhythm. In case of an object intervened at proper rhythm, the thickness of the object (100, 400μm) was suggested to make change in spectrum.

Estimate of the Original Gingival Color in Reflection Spectrum Data of Redness Gingiva by Multiple Regression Analysis.

This study was made to examine if original gingival color of an individual patient in healthy condition can be presumed from the observed data on the color of his gingiva having presented pericoronal gingival redness. The subjects were 50 males (aged 23-31) whose gingivae have been identified as clinically healthy. X, y, V, Bl and f values were determined from raw data obtained by the color measurement of 4 gingival spots near the cervical regions of maxillary central and lateral incisors. Multiple regression analysis was made with x, y and V values of the healthy papillary gingiva as objective variable and with each element of the observed data (twenty-dimensional observed value vector) upon the manifestation of gingival redness, which has bi-graded according to the degree of redness (slight redness, redness), as explanatory variable.As a result, the analysis of a bi-graded observed data series according to the degree of gingival redness was confirmed to make it possible to presume the original gingival color of the papillary part in healthy condition, suggesting the usefulness for its clinical application.