Hiroki Nikawa

Antifungal effect of zeolite-incorporated tissue conditioner against Candida albicans growth and/or acid production

A new antimicrobial material, Ag-zeolite (Zeomic), was combined with a commercial tissue conditioner (GC-Soft Liner (GC); 1-5%) and, through monitoring the pH of the growth medium, examined for effects on the in vitro growth and/or acid production of Candida albicans on protein-free and saliva-coated specimens. The effect of incorporation of this agent on the physical property of the lining material was also examined according to the ISO penetration test. Comparison studies were carried out using GC, Coe Comfort (CC) or undecylenate combined GC (1-5%) specimens. Although the pH changes in the media varied depending upon the materials on which the Candida was grown, reverse sigmoidal pH curves were observed with most samples. As compared with GC, the soft lining materials showed, to some extent, an inhibitory effect on the acid production and/or the growth of C. albicans. These inhibitory effects consisted of a delay in the onset of rapid pH decline, decreases in the rate of pH change and increases in minimum pH. In most cases, the inhibitory effects of test specimens were dose-dependent, and zeolite specimens showed a significantly higher antifungal effect, followed by CC and undecylenate-combined GC; GC showed the least antifungal effect. The inhibitory effects of these materials on fungal growth were decreased by the presence of a saliva-coat, particularly with zeolite specimens and CC. However, four of eight 5%-Zeomic specimens still exhibited perfect growth inhibition in the presence of the salivary pellicle. Furthermore, test specimens containing 2-5% Zeomic showed a significantly greater effect on the delay in rapid decline of pH, as compared with the other specimens examined. In addition, the significantly higher minimum pH was observed where the yeasts were grown on 4%- and 5%-Zeomic specimens. The physical properties of all the test specimens conformed with the ISO standard as examined by penetration test. These results taken together suggest that an antimicrobial zeolite-combined tissue conditioner would be a potential aid in denture plaque control.

The fungicidal effect of human lactoferrin on Candida albicans and Candida krusei

Five oral isolates each of Candida albicans and Candida krusei were studied for their sensitivity to the fungicidal effect of human lactoferrin. Significant inter- and intraspecies variations were observed and with most isolates the sensitivity of C. krusei to lactoferrin was greater than that of C. albicans. Fungicidal activity of lactoferrin was dose-dependent and observable only with the iron-free form of the molecule (apo-lactoferrin). Iron-saturated lactoferrin was ineffective against all isolates. Supernatant protein assays and scanning electron microscopy indicated cell surface alterations--leakage of proteins and formation of surface blebs--only in those Candida isolates that were sensitive to apo-lactoferrin. As lactoferrin is a common, non-immune, mucosal defence protein, its varying mode of action against C. albicans and C. krusei may be related to their different oral carriage rates.

Interactions between denture lining material, protein pellicles and Candida albicans

The interactions between pellicles derived from saliva, serum, mucin and lysozyme deposited on lining material (tissue conditioner) and Candida albicans were investigated by monitoring pH changes associated with protein-free and protein-coated lining material and by ultrastructural observations of yeast colonization. No significant differences in pH reduction between culture media in contact with the protein-free, control lining materials and those coated with saliva, serum or mucin were observed after 120 h of incubation. However, scanning electron microscopy revealed that much greater numbers of the yeasts colonized the saliva- or serum-coated lining material than the lysozyme-, mucin-coated or control material. Hyphal invasion was observed in saliva-coated lining material. These results suggested that denture pellicle derived from saliva and/or serum may potentiate candidal colonization of denture lining materials.

In vitro evaluation of Candida albicans adherence to soft denture-lining materials

The adherence of Candida albicans to seven commercial soft denture-lining materials was studied in vitro with BCA protein assay reagent. A good correlation was observed between the amount of protein in yeast cells and the number of yeasts (r = 0.993, p < 0.01), and it was revealed that the adherence of C. albicans to bare surfaces of these soft denture-lining materials correlated well with their relative hydrophobic properties (r = 0.905, p < 0.01); thus there was consistency with the thermodynamic theory. These results combined corroborated the accuracy of this method. To know the effect of pellicle on fungal adherence, the adherence of C. albicans to saliva-coated samples was examined. It was revealed that neither the amount of protein adsorbed by substrates nor the adherence of yeast to saliva-coated substrates correlated with the relative hydrophobic properties of these samples, suggesting that factors other than hydrophobic interaction play an important role in the adherence of C. albicans to pellicle-coated soft liners and tissue conditioners.

Effects of denture cleansers on direct soft denture lining materials

The deterioration of six commercial resilient denture lining materials immersed in seven groups of denture cleansers was investigated. Although the grades of deterioration of these soft liners were not related to the amount of peroxide content or the pH of denture cleansers, the effects of peroxide cleansers were, with few exceptions, more severe than those of the other types. For example, an enzyme cleanser caused severe changes of one soft liner. The grades of surface porosity were correlated well with the log of the gelation time of the tissue conditioners (except for one soft liner), in four kinds of peroxide cleansers. These results suggest that various components of denture cleansers and soft lining materials, particularly peroxides, in cleansers and gel formation components of soft liners play important roles in the deterioration of soft liners caused by cleansers.

In vitro cariogenic potential of Candida albicans.

The adherence and dissociation of Candida albicans, C. tropicalis, Streptococcus mutans and S. sanguis to six substrates including hydroxylapatite (HAP) which exhibit various hydrophobicity, was examined by the use of a bioluminescent adenosine triphosphate (ATP) assay. Dissolution of HAP by C. albicans or S. mutans was determined spectrophotometrically by the use of o‐cresolphthalein complexone. In the adherence of C. tropicalis, S. mutans and S. sanguis, the amount of adherent cells correlated with the hydrophobicity of the substrates. In contrast, the adherence of C. albicans to HAP was extraordinary high, although the adherence of the fungi also correlated with the hydrophobicity of the substrates, except for HAP. The yeasts attached to HAP was effectively removed by high concentration of either phosphate or calcium ions. The amount of calcium‐release from HAP caused by C. albicans and S. mutans was 113 μg ml−1 (final pH = 3.45), and 5.4 μg ml−1 (final pH 4.81), respectively and the maximum growth of C. albicans and S. mutans was 107 cfu ml−1 and 7.4 × 1012 cfu ml−1, respectively. The results, taken together, suggest that C. albicans adhere to HAP specifically through electrostatic interaction, and that, in a much smaller number (1.0/7.4 × 105), C. albicans possesses the ability to dissolve HAP to a greater extent (approximately 20‐fold) when compared with S. mutans.

Rheology of tissue conditioners

STATEMENT OF PROBLEM Tissue conditioners can be used to condition abused tissues, record functional impressions, make temporary relinings, and for other clinical applications, mainly because of their specific viscoelasticity. However, little information is available on the rheology of the materials, manipulation, and suitability for various clinical applications. PURPOSE This study evaluated the gelation times, the viscoelastic properties after gelation of tissue conditioners, and the influence of the powder/liquid (P/L) ratio. MATERIAL AND METHODS Ten tissue conditioners were used and gelation times were obtained with an oscillating rheometer. A series of stress relaxation tests were also conducted to evaluate the viscoelastic properties after gelation and the changes with the passage of time by means of Maxwell model analogies. RESULTS Significant differences were found in the gelation times and flow properties after gelation among the materials mixed with the P/L ratios recommended by the manufacturers. The flow properties tended to increase with time of storage. Large differences in the limits of the clinically acceptable P/L ratios and the adjustable limits of elasticity and viscosity by altering P/L ratios were found among the materials. CONCLUSIONS The results suggested that each material should be selected according to each clinical purpose because of the wide ranges of viscoelastic properties and changes in viscoelasticity with time among the materials. Furthermore, gelation times and the viscoelastic properties after gelation can be controlled to improve handling and suit various applications by altering the P/L ratios within the acceptable limits.

Effect of serum concentration on Candida biofilm formation on acrylic surfaces

The biofilm formation of the oral fungal pathogen Candida on denture acrylic strips coated with saliva, serum and, saliva–serum pellicle were examined in vitro using Candida albicans (four isolates), Candida glabrata (three isolates) and Candida tropicalis (three isolates). The degree of biofilm activity varied depending upon both the isolate and the pellicle. Significantly increased biofilm activity on the pellicle (particularly serum)‐coated strips was observed with three isolates of C. albicans and another of C. glabrata on protein‐coated acrylics, with increasing concentration of serum in the pellicle. Similar trends were observed with one isolate of C. albicans and C. glabrata, although the effects of pellicles were not significant. In contrast, with all three isolates of C. tropicalis and a single isolate of C. glabrata, although the biofilm activity on the protein‐free control strips was significantly higher than that of saliva‐coated strips, the increase in activity of pellicle‐admixed biofilm depended upon the serum concentration. Candidal biofilm formation on acrylic surfaces is essentially promoted with increasing concentration of serum in the pellicle. This suggests that inflammation in the oral environment would facilitate fungal colonization on denture acrylic.

Growth factor-defined culture medium for human mesenchymal stem cells.

Human bone marrow-derived mesenchymal stem cells (hMSCs) are potential cellular sources of therapeutic stem cells as they have the ability to proliferate and differentiate into a wide array of mesenchymal cell types such as osteoblasts, chondroblasts and adipocytes. hMSCs have been used clinically to treat patients with graft vs. host disease, osteogenesis imperfect, or alveolar cleft, suggesting that transplantation of hMSCs is comparatively safe as a stem cell-based therapy. However, conventional culture medium for hMSCs contains fetal bovine serum (FBS). In the present study, we developed a growth factor-defined, serum-free medium for culturing hMSCs. Under these conditions, TGF-beta1 promoted proliferation of hMSCs. The expanded hMSC population expressed the human pluripotency markers SSEA-3, -4, NANOG, OCT3/4 and SOX2. Furthermore, double positive cells for SSEA-3 and a mesenchymal cell marker, CD105, were detected in the population. The potential to differentiate into osteoblasts and adipocytes was confirmed. This work provides a useful tool to understand the basic biological properties of hMSCs in culture.

Binding of salivary or serum proteins to Candida albicans in vitro

This binding was investigated with a simplified method: whole saliva and mucin bound to C. albicans in significantly greater quantities than other proteins such as whole serum, albumin, lysozyme or fibrinogen; and the enzymatic treatment of C. albicans with chymotrypsin, papain or mannosidase decreased the amounts of these proteins bound. These results, taken together, suggest that salivary proteins or mucin may bind to the mannoprotein of C. albicans.