Denture plaque and adherence of Candida albicans to denture-base materials in vivo and in vitro.
The aim of this paper is to review our understanding of the mechanisms and clinical significance of adhesion of C. albicans to denture-base materials in relation to denture plaque and denture-related stomatitis. Earlier reports in the literature of a 65% prevalence level of denture-related stomatitis seem to be exaggerated. More recent studies indicate that denture-related stomatitis is considerably less common, particularly in normal healthy subjects. The etiology of the condition is discussed in this review, and although much of the literature supports the view that the condition is strongly associated with C. albicans, this is not always so. In some subjects, the cause appears to be related to a non-specific plaque. This review also considers the role of denture plaque in the pathogenesis of denture-related stomatitis, the sequential development of denture plaque, and its colonization by Candida organisms. Designing controlled in vivo studies is difficult, and as a consequence, many investigators have had to resort to in vitro studies. The majority of these studies have attempted to investigate the hydrophobicity of C. albicans, relating the surface free-energy of denture-base materials, particularly acrylic resin, to that of the organism. Surprisingly little work has been directed at surface roughness and how it affects retention of organisms. Further, no attention has been paid to the properties and character of the surface, other than average surface roughness, as it affects adhesion. A comparison of results from in vitro studies on the effect on adhesion of pre-coating the surfaces of denture-base materials with saliva has produced equivocal conclusions. This is largely due to little standardization of experimental protocols between studies, particularly in the collection and handling of the saliva used. In conclusion, the review strongly supports the suggestion that adherence of C. albicans to denture-base materials in vitro is related to the hydrophobicity of the organism. The clinical significance of the observation and the mechanisms for the development and maturation of denture plaque are yet to be understood. There is a clear need for further investigation of other factors that may moderate the adhesion of organisms and subsequent colonization of denture-base materials. (+info
Effects of thermal cycling on dynamic viscoelastic properties of four commercial resins for crown and bridge.
To elucidate the effects of thermal cycling on the viscoelastic properties of four commercial resins for crown and bridge, dynamic shear modulus (G'), mechanical loss tangent (tan delta), Knoop hardness, water sorption and appearance of specimen surfaces before and after thermal cycling test were determined. The changes of G' and tan delta for two materials were insignificant with increased repetitions of thermal cycling. Those of the other two materials were statistically significant: in particular, G' at temperatures above 60 degrees C was inclined to increase slightly and tan delta decreased considerably. While the Knoop hardness of the materials was a little decreased over a number of 75,000 thermal cycles, the water sorption almost attained an equilibrium in uptake after 14,000 thermal cycles. Furthermore, cracks on the specimen surface were observed after 37,500 to 75,000 thermal cycles. From these results, the deterioration of materials was observed as damage to the specimen surface. Moreover, it could be presumed that the materials would be further polymerized during the period of thermal cycling. (+info
Use of self-assembled monolayers of different wettabilities to study surface selection and primary adhesion processes of green algal (Enteromorpha) zoospores.
We investigated surface selection and adhesion of motile zoospores of a green, macrofouling alga (Enteromorpha) to self-assembled monolayers (SAMs) having a range of wettabilities. The SAMs were formed from alkyl thiols terminated with methyl (CH(3)) or hydroxyl (OH) groups or mixtures of CH(3)- and OH-terminated alkyl thiols and were characterized by measuring the advancing contact angles and by X-ray photoelectron spectroscopy. There was a positive correlation between the number of spores that attached to the SAMs and increasing contact angle (hydrophobicity). Moreover, the sizes of the spore groups (adjacent spores touching) were larger on the hydrophobic SAMs. Video microscopy of a patterned arrangement of SAMs showed that more zoospores were engaged in swimming and "searching" above the hydrophobic sectors than above the hydrophilic sectors, suggesting that the cells were able to "sense" that the hydrophobic surfaces were more favorable for settlement. The results are discussed in relation to the attachment of microorganisms to substrata having different wettabilities. (+info
Femoral prosthetic heads and their significance in polyethylene wear.
We used scanning electron microscopy to perform an ultrastructural analysis and two optical interferometric profilers to measure roughness on 40 prosthetic femoral heads. We expressed roughness as Ra (roughness average) value and Rsk (roughness skewness) value. Our results show that in order to obtain an ideal surface finish a low or not very high Ra value and a negative Rsk value are needed. The presence of depressions or holes (rather than scratches) with smooth (rather than sharp) edges seems to improve the lubrication and wettability properties. (+info
Intercalation compounds of layered materials for drug delivery use. II. Diclofenac sodium.
Intercalation compounds of ternary layered inorganic materials, synthetic mica (Na-TSM), with diclofenac sodium (DFS) and its drug release characteristics were investigated. Hygroscopic DFS was selected as a model drug to verify the anti-humidity and anti-oxidation of the intercalation compounds. Na-TSM powder was first mixed with the reduced-type phosphatidylcholine (H-PC) solution of chloroform or ethanol. DFS was then mixed with these solutions and heated at 37 degrees C to prepare the ternary Na-TSM/H-PC/DFS compound. A remarkable phenomenon was observed in the drug release study. The net amount of DFS from the DFS powder decreased apparently after 20 min arising from the decomposition of DFS in acidic medium. On the other hand, the net amount of the released DFS from the intercalation compound was invariant. Thermal analyses study indicated that DFS powder was hygroscopic and a significant endothermic peak was observed accompanied by a large weight loss due to the dehydration of adsorbed water from 40 to 90 degrees C. On the other hand, no significant dehydration reaction was observed in the intercalation compounds even in the sample stored under humid conditions. The present results indicated that the ternary intercalation compound was resistant to acid in addition to anti-humidity. (+info
Polymer properties on resins composed of UDMA and methacrylates with the carboxyl group.
The properties of dental matrix resins have been improved by synthesis of new monomers. However, except for improvements in water-resistance, monomers with better mechanical properties than Bis-GMA and UDMA could not being synthesized. Changing the point of emphasis, we tried to improve the mechanical properties controlling the matrix resin higher structure using noncovalent bonds. We prepared a matrix resin structured by UDMA, which is a high viscosity base monomer with imino groups, and by a low viscosity acidic monomer with carboxyl groups, which permits noncovalent bonds such as hydrogen bonds or electrostatic interaction with imino groups. The maximal mechanical strength for matrix resins structured by UDMA and an acidic monomer was obtained with a composition of imino groups and carboxyl groups at a ratio of 1:1. This mechanical strength value was higher than those obtained with UDMA resin or with a Bis-GMA/TEGDMA/UDMA resin with typical composition. The improvement in mechanical properties may be due to the complex based on noncovalent bonds, between the imino groups of UDMA and the carboxyl groups of the acidic monomers. (+info
Moisture-insensitive adhesives: reactivity with water and bond strength to wet and saliva-contaminated enamel.
The purpose of this study was to investigate the reactivity with water of a moisture-insensitive orthodontic primer (Transbond MIP), in conjunction with a no-mix orthodontic adhesive (Unite), and a moisture-insensitive adhesive (Smartbond), and to assess their bond strength to wet and saliva-contaminated enamel relative to the conventional application of the no-mix adhesive. The reactivity of the moisture-insensitive products with water was investigated by micro-multiple internal reflectance Fourier transform infrared spectroscopy (micro-MIR FTIR). Sixty premolars were divided into two groups of 30 teeth each and, on the buccal enamel surfaces, a standardized volume (0.1 ml) of water or fresh whole saliva was applied. Standard edgewise stainless steel brackets were then bonded to enamel surfaces as follows: (a) Unite, (b) Unite with the Transbond MIP, and (c) Smartbond. The brackets were debonded under shear force at a speed of 2 mm/min and the debonded enamel surfaces were subjected to fractographic analysis. The statistical analysis of the bond strength values was performed by two-way ANOVA with condition (water, saliva) and adhesive type serving as discriminating variables (n = 10, alpha = 0.05). The results of the fractographic analysis were evaluated by chi 2 test (alpha = 0.05). FTIR analysis showed that only Smartbond set in the presence of water. Application of water in Transbond MIP increased the extent of carboxyl ionization without inducing any setting reaction. Transbond MIP did not improve bond strength values when combined with the no-mix adhesive. Most adhesive-enamel condition combinations showed a trend to present lower bond strength in the presence of saliva; however, this was not confirmed statistically. Fractography of enamel and bracket base surfaces showed that Unite + Transbond MIP resulted in the most adhesive fractures (leaving no resin on enamel surface), whereas Smartbond presented the highest frequency of cohesive fractures (adhesive left on bracket and enamel surfaces). (+info
Radiation effects of carbon ions and gamma ray on UDMA based dental resin.
The radiation effects on the mechanical and physical properties of photo-polymerized UDMA resin without filler was investigated by various mechanical tests and spectroscopic measurements. The radiation sources were carbon ion (12C ion) and gamma ray (gamma-ray). With 640 Gy of 12C ion radiation, Vickers hardness increased by about 40%, the degree of abrasion decreased by 30%, and the flexural strength increased by 20%. With the same dose of gamma-ray radiation, only Vickers hardness increased by 19%. The spectra taken by the Fourier Transform Infrared Spectrometer (FT-IR), Raman spectroscopy, and Fluorescence spectrophotometer showed little change in the peak configuration and background intensities. The relative degree of conversion (DC) of carbon double bonds by radiation to the state of non-radiated samples were estimated by FT-IR. Spectroscopic results were indicative for the formation of cross-linking between carbon chains. Cross-linking of carbon molecules induced by radiation might be one of the reasons for the improved mechanical properties of UDMA resin. (+info