Tetsuo Ichikawa

Fracture mechanisms of retrieved titanium screw thread in dental implant

Titanium and its alloy are increasingly attracting attention for use as biomaterials. However, delayed fracture of titanium dental implants has been reported, and factors affecting the acceleration of corrosion and fatigue have to be determined. The fractured surface of a retrieved titanium screw and metallurgical structures of a dental implant system were analyzed. The outer surface of the retrieved screw had a structure different from that of the as-received screw. It was confirmed that a shear crack initiated at the root of the thread and propagated into the inner section of the screw. Gas chromatography revealed that the retrieved screw had absorbed a higher amount of hydrogen than the as-received sample. The grain structure of a titanium screw, immersed in a solution known to induce hydrogen absorption, showed features similar to those of the retrieved screw. It was concluded that titanium in a biological environment absorbs hydrogen and this may be the reason for delayed fracture of a titanium implant.

Characteristics of thermoluminescence bands of intact leaves and isolated chloroplasts in relation to the watersplitting activity in photosynthesis

Plant materials (intact leaves, chloroplasts or subchloroplast particles) pre-illuminated at a low temperature (e.g. -60 degrees C) were rapidly cooled to -196 degrees C and then the luminescence emitted from the sample on raising the temperature was measured as a function of temperature, by means of a sensitive photo-electron counting technique. Mature spinach leaves showed five luminescence bands at different temperatures which were denoted as ZV, A, B1, B2 and C bands. The A, B1, B2 and C bands appeared at constant temperatures, -10, +25, +40 and +55 degrees C, respectively, being independent of the illumination temperature, but the ZV band appeared at a variable temperature slightly higher than the illumination temperature. The B1 and B2 bands were absent in the thermoluminescence profiles of samples devoid of the oxygen-evolving activity, such as heat-treated spinach leaves, wheat leaves greened under intermittent illumination and photosystem-II particles prepared with Triton X-100. It was deduced that these luminescence bands arise from the energy stored by the electron flow in photosystem II to evolve oxygen, and other bands were ascribed to charge-separation in some other sites not related to the oxygen evolving system.

Second derivative spectrophotometry as an effective tool for examining phenylalanine residues in proteins.

The second derivative absorption spectra of N-acetyl ethyl esters of phenylalanine, tyrosine and tryptophan, as models of the aromatic amino acid residues in proteins, were measured. The second derivative spectra of tyrosine and tryptophan were found to have no influence on the spectrum of phenylalanine over the range of 245 to 270 nm, where characteristic absorbance bands of phenylalanine were observed. Thus the second derivative spectrum is a good tool for examining the optical properties of phenylalanine residues in proteins.

Effect of substrate surface hydrophobicity on the adherence of yeast and hyphal Candida

A biofilm composed of various microorganisms including Candida is found on denture surfaces and is likely to be involved in the etiology of denture‐induced stomatitis. The purpose of this study was to examine the role of hydrophobic interactions in candidal adherence to acrylic surfaces, particularly that of the hyphal form of Candida albicans. Candida clinical isolates were used. Acrylic plates coated with carrageenan and hydrocolloid (Hitachi chemical, Tokyo, Japan) were used as a hydrophilic substratum. A microbial suspension was placed on each acrylic plate and incubated. All plates were washed in phosphate‐buffered saline containing CaCl2 and MgCl2 [PBS (+)] and cells still adhering to the acrylic surface were collected by 0.25% trypsin treatment. Cell‐surface hydrophobicity was estimated using a modification of the technique used to measure adherence to hydrocarbons. When the acrylic plates were coated with hydrophilic materials, the adherence of hydrophobic clinical isolates of Candida and the hydrophobic hyphal C. albicans decreased, whereas the adherence of non‐hydrophobic Candida was not affected or increased. We suggest that hydrophilic coating of denture surfaces could be a potent method for reduction of the adherence of relatively hydrophobic fungal cells, particularly hyphal C. albicans, which causes denture stomatitis and related infections.

Estimation of state and amount of phenylalanine residues in proteins by second derivative spectrophotometry.

The second derivative absorption spectra of serum albumin, insulin, ribonuclease and lysozyme were measured under various conditions to determine the state and amount of their phenylalanine residues. The second derivative spectra of these proteins were very similar to that of phenylalanine in the region between 245 and 270 nm where tryptophan and tyrosine residues caused no appreciable interference. Denaturation of proteins with urea or guanidine hydrochloride caused decrease in the intensity of the second derivative spectra, but scarcely affected the positions of peaks and troughs. The amounts of phenylalanine residues in proteins calculated from a second derivative spectra of denatured proteins coincided well with those reported in the literature. The states of the phenylalanine residues in the proteins could be deduced from the change in optical intensity on denaturation.

Biofilm formation of Candida albicans on implant overdenture materials and its removal

OBJECTIVES The purposes of this study were to clarify the surface characteristics of various implant overdenture materials and the capabilities of Candida albicans adherence and biofilm formation on these surfaces, and to investigate the role of salivary mucin in biofilm formation. METHODS Seven commonly used implant and restorative materials were assessed. The surface roughness averages of all materials were limited to 0.07-0.10 μm. Contact angles and salivary mucin absorption were measured. After 90-min initial adhesion and 2-day biofilm formation, the amounts of C. albicans were determined by counting colony-forming units and the morphological characteristics were observed by scanning electron microscopy (SEM). The effects of saliva coating and the influences of material surface property on initial adhesion, biofilm formation and its removability were analysed by univariate two-way analysis of variance and multiple linear regression analysis. RESULTS Surface contact angle of materials, the index of hydrophobicity, was found to be correlated positively with initial adhesion and biofilm formation of C. albicans. A negative correlation between mucin absorption and removability of Candida biofilm indicates that mucin plays an important role in biofilm formation and its rigidity. SEM observation also revealed fewer Candida cells on saliva-coated Ti than on saliva-coated hydroxyapatite or acrylic resin. CONCLUSIONS The materials with different hydrophobic property and compositions display diverse manners of salivary mucin absorption, initial adhesion and biofilm formation. The hydrophobic materials encourage enhanced initial adhesion, subsequently resulting in the active biofilm formation. Mucin has decisive effects on Candida immobilization and biofilm development on the materials. CLINICAL SIGNIFICANCE Surface hydrophilic property and composition of materials and salivary proteins, especially mucin, affect the process of Candida biofilm formation and influence the amount and rigidity of formed biofilm. The present data may be applied as a reference for selecting materials in implant overdenture treatment from a microbiological point of view.

Enhanced germicidal effects of pulsed UV‐LED irradiation on biofilms

Aims:  The major objective of the study was to evaluate the enhanced germicidal effects of low‐frequency pulsed ultraviolet A (UVA)‐light‐emitting diode (LED) on biofilms.

Development of thermoluminescence bands during greening of wheat leaves under continuous and intermittent illumination.

Abstract— Mature wheat leaves excited by 1‐min illumination at a low temperature of ‐60° C showed five thermoluminescence bands at ‐45, ‐10, +25, +40 and +55° C (denoted as Zu, A, B1 B2 and C bands, respectively). The development of these bands during greening of etiolated wheat leaves under continuous and intermittent illumination was investigated, and the following results were obtained. (1) Etiolated leaves showed only the C band. When these leaves were greened under continuous light, the B1 and B2 bands appeared at 3 h and the Zu band appeared at 10 h. The B1 and B2 bands were intensified during prolonged greening under continuous illumination to be the strong bands observed for mature leaves. The A band and the group of B1 and B2 bands were alternative: Similar experiments by excitation of thermoluminescence at ‐20° C showed the development of the A band instead of these B1 and B1 bands. (2) When the etiolated leaves were greened under intermittent illumination (1‐ms light + 5‐min dark), the Zu band first appeared after 5 h of illumination (60 flashes) and was gradually intensified during further illumination with 340 flashes but, interestingly, neither the B1 nor the B2 band appeared even after 24–28 h of illumination with 280–340 flashes. (3) On exposure of such leaves greened under intermittent illumination to continuous light, the B1 and B2 bands were rapidly developed. The appearance of these bands was accompanied by the generation of the Hill activity (DCIP photoreduction with water as electron donor). (4) These results were discussed in relation to the previous study on photoactivation of the latent water‐splitting system accumulated in the leaves greened under intermittent illumination. It was deduced that the structure responsible for the A band or the group of B1 and B2 bands is involved in the evolution of oxygen in chloroplasts, and probably involves cations of the Mn2+ catalyst generated by the action of light.

The effect of simvastatin-loaded polymeric microspheres in a critical size bone defect in the rabbit calvaria

The present study describes the development of a microsphere capsule based on polylactide-co-glycolide (PLGA) loaded with simvastatin that was subsequently incorporated into synthetic bone cement. The osteogenic effect of simvastatin-loaded bone cement was in a critical sized defect in vivo to test the hypothesis the biologic response would be different depending on the dosage of simvastatin applied to bone cement. Our results showed that simvastatin loaded PLGA microspheres can be successfully obtained through O/W emulsion/solvent evaporation method with appropriate morphologic characteristics and high encapsulation efficiency for incorporation in bone cements. The biodegradable characteristic of the microspheres successfully presented a slow release and the duration of the release lasted for more than 1 month. The in vivo experiment revealed that the microspheres containing simvastatin significantly enhanced bone formation in the rabbit calvaria critical size defect.

The enhancement effect of three sugar alcohols on the fungicidal effect of benzethonium chloride toward Candida albicans

OBJECTIVE The purpose of this study was to evaluate if the sugar alcohols erythritol, xylitol and sorbitol enhance the fungicidal effect of benzethonium chloride (BTC) toward in vitro candidal biofilms. METHODS An in vitroCandida albicans biofilm was formed on a plastic coverslip coated with type I collagen. The enhancement of the fungicidal effect was evaluated using microbial assay after treating the biofilm with the test solutions (sugar alcohols: erythritol, xylitol, and sorbitol, each containing BTC solution). RESULTS No fungicidal effect was observed with sugar alcohols without BTC. The fungicidal effect of erythritol-containing BTC increased with the erythritol concentration. Further, the level of enhancement of erythritol was the highest in three sugar alcohols. CONCLUSION Sugar alcohols, especially erythritol, enhanced the fungicidal effect of BTC toward in vitro candidal biofilms.