Adherence of Candida albicans to glow-discharge modified acrylic denture base polymers

An important aetiologic factor in the pathogenesis of denture-induced stomatitis, is the presence of numerous yeasts, usually Candida albicans, on the fitting surfaces of dentures. In the present study, effect of glow-discharge plasma, a technique applied to increase surface wettability of acrylic resins, on candidial adherence was evaluated. The durability of glow-discharge modification with saliva coating was also evaluated. Samples including control and experimental groups were prepared by using heat compression mould technique. To create a hydrophobicity gradient, experimental groups were exposed to a radiofrequency glow discharge in an O2 atmosphere under different discharge powers. To characterize the wetting properties, an expression of surface hydrophobicity, contact angle measurements were performed by the sessile drop method. The organism used was C. albicans (ATTC10321). Acrylic samples were coated with unstimulated whole saliva collected from a healthy man. The fungal suspension was poured on saliva-inoculated samples and incubated at 37 degrees for 2 h. The samples were then fixed with glutaraldehyde and Gram stained. Adhered candidial cells were examined by light microscope. Diffuse Reflectance FTIR (DRIFT) and scanning electron-microscope examinations were also performed to evaluate the surface composition and roughness of the test groups. Glow-discharge plasma was found to be an effective means of increasing surface wettability even with salivary pellicle. Amounts of candida cells adhered were significantly higher in all the plasma treated surfaces than the unmodified control group (P < 0.001). It was concluded that improving the surface wettability of acrylic resins by glow-discharge plasma in O2 atmosphere increased the adherence of the C. albicans.     

Characterization of acquired denture pellicle from healthy and stomatitis patients.

Little information is available about the acquired pellicle layer that is formed on denture surfaces or its role in regulating microbial colonization of the prosthetic surface. Because denture-induced stomatitis is associated with increased numbers of Candida albicans and other microorganisms on the denture surface, the acquired denture pellicle (ADP) may play a role in modulating this colonization. This study examined and compared ADP from healthy patients and patients with stomatitis by chemical and immunochemical methods. The ADP was found to be composed of a selectively adsorbed layer containing salivary amylase, high molecular weight mucin (MG1), lysozyme, albumin, and sIgA. Salivary cystatins, proline-rich proteins, and low molecular weight mucin (MG2) were not detected. ADP amino acid composition was distinct from any of the ductal salivas, but had many similarities with enamel pellicle. Immunoblots of ADP from patients with stomatitis identified additional serum components, degradation products, and C. albicans cell components that were not detected in ADP from healthy patients. Quantification of these molecules in ADP could lead to a diagnostic test for oral mucosal disease underlying a denture base. Identification of specific molecules in denture pellicle that promote adhesion of C. albicans may elucidate a mechanism of fungal cell colonization on the denture surface. Future studies that chemically modify the denture acrylic resin surface to immobilize antimicrobial proteins may be a means of decreasing pathogenic plaque development.     

Modification of glass fibers to improve reinforcement: a plasma polymerization technique.

OBJECTIVES: This study evaluates the effect of plasma treated E-glass fiber to improve the mechanical properties of acrylic resin denture base material, polymethylmethacrlyate (PMMA). Plasma surface treatment of fibers is used as reinforcement in composite materials to modify the chemical and physical properties of their surfaces with tailored fiber-matrix bonding strength. METHODS: Three different types of monomer 2-hydroxyethyl methacrylate (HEMA), triethyleneglycoldimethylether (TEGDME) and ethylenediamine (EDA) were used in the plasma polymerization modification of glass fibers. A radiofrequency generator was used to sustain plasma in a glass vacuum chamber. Glass fibers were modified at the same glow-discharge power of 25 W and exposure time of 30 min for each monomer. Fibers were incorporated into the acrylic with 1% (w/w) loading except control group. Specimens were prepared using a standard mold of 3 cmx0.5 cmx0.8 cm in dimension with eight specimens in each group. Samples were subjected to a flexural strength test set up at a crosshead speed of 5mm/min. Scanning electron microscopy (SEM) was used to examine the microstructure and X-ray photoelectron spectroscopy (XPS) was used for chemical analysis of the surface. RESULTS: Data were analyzed by means of ANOVA and Duncan's tests. Test results revealed that fiber reinforcement had a significant effect on the flexural strength of the specimens (p<0.05). Among the fiber reinforced groups, plasma treatment with EDA monomer resulted in the most significant increase in flexural strength values (p<0.05). XPS results have shown an increasing number of nitrogenous compounds in EDA treated fibers. The chemical structure of the surface, especially with the increase in nitrogenous compounds could give an idea for the amine film deposition and SEM figures showed an increase in surface roughness. SIGNIFICANCE: The results showed that plasma treatment with EDA monomer was an effective alternative method of increasing the flexural strength of PMMA based denture base polymers through fiber reinforcement.     

Effect of surface treatments on the bond strength between composite resin and acrylic resin denture teeth

PURPOSE: This investigation studied the effects of 3 surface treatments on the shear bond strength of a light-activated composite resin bonded to acrylic resin denture teeth. MATERIALS AND METHODS: The occlusal surfaces of 30 acrylic resin denture teeth were ground flat with up to 400-grit silicon carbide paper. Three different surface treatments were evaluated: (1) the flat ground surfaces were primed with methyl methacrylate (MMA) monomer for 180 seconds; (2) light-cured adhesive resin was applied and light polymerized according to the manufacturer's instructions; and (3) treatment 1 followed by treatment 2. The composite resin was packed on the prepared surfaces using a split mold. The interface between tooth and composite was loaded at a cross-head speed of 0.5 mm/min until failure. RESULTS: Analysis of variance indicated significant differences between the surface treatments. Results of mean comparisons using Tukey's test showed that significantly higher shear bond strengths were developed by bonding composite resin to the surfaces that were previously treated with MMA and then with the bonding agent when compared to the other treatments. CONCLUSION: Combined surface treatment of MMA monomer followed by application of light-cured adhesive resin provided the highest shear bond strength between composite resin and acrylic resin denture teeth.     

Evaluation of the level of residual monomer in acrylic denture base materials having different polymerization properties

The aim of this study was to evaluate the level of residual monomer in acrylic denture base materials having different polymerization properties. The investigation included a conventional-type acrylic cured under heat and pressure, as well as a pour-type resin polymerized by an injection-moulding technique at room temperature and under pressure. It was found that the residual monomer content ranged from 0.22-0.54% in pour-type resin, and from 0.23-0.52% in routinely used resins when the specimens were analysed by high performance liquid chromatography. These findings revealed that there were no significant differences between the two types of acrylic in terms of their residual monomer content.     

Comparative bond strengths of plastic teeth to microwave-curing, heat-curing and 4-META containing denture base resins

Bond strength of hardened plastic teeth or acrylic resin teeth to microwave-curing, conventional heat-curing and 4-META-containing denture base resins were comparatively investigated in this study. Effects of grinding and monomer coating of the tooth ridge lap were also studied. Bond strength of plastic denture teeth to microwave-curing denture base resin was slightly higher than the other two resins. With all denture base resins used, an increased bond strength was obtained with hardened plastic teeth by treatment of tooth ridge lap but not with acrylic resin teeth. However, scattering of the bond strength was reduced by treatment of tooth ridge lap in acrylic resin teeth specimens. With hardened plastic teeth specimens, fracture in the base resin was increased by monomer coating. With acrylic resin teeth specimens, no specific fracture patterns were demonstrated by treatment of tooth ridge lap. Fracture occurred mostly in the acrylic resin teeth. These results suggest that bond strength of both denture teeth to microwave-curing or 4-META-containing denture base resin was increased or solidified by grinding or monomer coating of tooth ridge lap.     

Experimental salivary pellicles on the surface of orthodontic materials.

The purpose of this study was to define the composition of salivary pellicles that form on the surfaces of orthodontic materials and to further investigate whether qualitative differences exist between the composition of adsorbed salivary pellicles that form on 3 different orthodontic materials: stainless steel bracket metal, elastomeric ligature ring, and bracket bonding resin. Experimental pellicles were formed by incubating these materials in fresh human parotid or submandibular-sublingual saliva for 2 hours. Pellicles were extracted with sodium dodecyl sulfate buffer and lyophilized. They were then subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting to identify the adsorbed salivary components. Remarkable differences in the profiles of pellicle components were found, dependent on the type of orthodontic materials. The pellicle components on the bracket metal were almost the same as those found on the elastomeric ligature ring. Salivary protein adsorption patterns to bonding resin showed different features. Distinct differences were also found between the surface-binding affinities of the same salivary proteins from different glandular salivas. These results may be explained on the basis that binding sites for specific proteins on the surfaces of the materials are covered by molecules of submandibular-sublingual saliva, probably mucins. The results of this study provide valuable information concerning initial bacterial adhesion to the surfaces of orthodontic materials, as well as information that could be used in the development of orthodontic materials with enhanced surface properties.     

Measurement of adsorption of salivary proteins onto soft denture lining materials.

STATEMENT OF PROBLEM: The adhesion of Candida albicans to soft liners is a major causative factor in denture stomatitis. It has been suggested that salivary proteins play an important role in this candidal adhesion. PURPOSE: This study measured the adsorption of salivary proteins on soft liners. MATERIAL AND METHODS: Five commercial materials and 1 experimental material were immersed in saliva, albumin solution, or milk. Proteins adsorbed on the material surfaces were measured by ATR/FT-IR spectroscopy. RESULTS: The amount of proteins adsorbed to the 6 materials varied considerably. Protein adsorption was significantly lower in the experimental fluoropolymer and polyphosphazene, and higher in acrylic resin and silicone. CONCLUSION: Different soft liners promote adsorption of varying amounts of protein.     

Failure load of acrylic resin denture teeth bonded to high impact acrylic resins

Statement of problem. Techniques for bonding denture teeth to an acrylic resin denture base remain empirical, with little consensus from the literature, among clinicians, or among dental laboratories. Purpose. This study evaluated the failure load of acrylic resin teeth bonded to 2 high impact acrylic resins. Methods and material. The ridge lap portion on 120 identical denture teeth were modified with 3 variables: (1) placing a diatoric, (2) using monomer to prewet the denture tooth, and (3) breaking the glaze. Variables were combined to form 6 groups of 10 teeth each, and processed with Lucitone 199 (Lucitone) or SR-Ivocap (Ivocap) acrylic resin. Data analysis included the use of a heterogeneous variance linear regression model. Results. Mean (± SD) failure load ranged between 10.25 ± 1.48 Kg to 28.43 ± 11.05 Kg for the 6 Ivocap groups and 16.63 ± 5.87 Kg to 28.05 ± 5.35 Kg for the Lucitone groups. For Lucitone 199 acrylic resin, the highest failure loads resulted when the ridge lap was left with an intact glaze and did not have a diatoric, with no significant influence from the use of monomer. For Ivocap resin, the highest failure loads resulted when the ridge lap had a diatoric but did not have monomer placed, with no significant influence from glaze. Conclusion. Failure load of bonding highly cross-linked denture teeth to SR-Ivocap or Lucitone 199 acrylic resin was significantly influenced by modifications to the ridge lap before processing. (J Prosthet Dent 1998;80:666-71.)     

A Study on Effect of Surface Treatments on the Shear Bond Strength between Composite Resin and Acrylic Resin Denture Teeth

Visible light-cured composite resins have become popular in prosthetic dentistry for the replacement of fractured/debonded denture teeth, making composite denture teeth on partial denture metal frameworks, esthetic modification of denture teeth to harmonize with the characteristics of adjacent natural teeth, remodelling of worn occlusal surfaces of posterior denture teeth etc. However, the researches published on the bond strength between VLC composite resins and acrylic resin denture teeth is very limited. The purpose of this study is to investigate the effect of five different methods of surface treatments on acrylic resin teeth on the shear bond strength between light activated composite resin and acrylic resin denture teeth. Ninety cylindrical sticks of acrylic resin with denture teeth mounted atop were prepared. Various treatments were done upon the acrylic resin teeth surfaces. The samples were divided into six groups, containing 15 samples each. Over all the treated and untreated surfaces of all groups, light-cured composite resin was applied. The shear strengths were measured in a Universal Testing Machine using a knife-edge shear test. Data were analyzed using one way analysis of variance (ANOVA) and mean values were compared by the F test. Application of bonding agent with prior treatment of methyl methacrylate on the acrylic resin denture teeth resulted in maximum bond strength with composite resin.     

Time-related wettability characteristic of acrylic resin surfaces treated by glow discharge

STATEMENT OF PROBLEM: Adhesion and cohesion have important roles in denture retention, and attempts have been made to improve the wettability of the acrylic resin material by surface treatments. PURPOSE: This study examined the initial and subsequent wettability of an acrylic resin denture base material treated under air or argon plasma atmosphere before and after exposure to air or distilled water. MATERIAL AND METHODS: Acrylic resin specimens were treated with plasma under air or argon atmosphere and were either exposed to air or distilled water for up to 60 days. Wettability characteristics of the acrylic resin specimens were determined by contact-angle measurements after 2 hours and after 60 days. Surface composition of the specimens also was analyzed with x-ray photoelectron spectroscopic (XPS) measurements. RESULTS: Statistically significant difference was found between control and each of the plasma treatment groups (P <.05). Although the storage condition and storage period caused statistically significant difference on contact angle values (P <.05), atmosphere type did not have any effect on the results (P >.05). XPS spectra of the plasma-treated specimens differed from control specimens only in the O1s region with a narrower and more intense peak that could be assigned to -COH groups. During 60 days of exposure, the O/C atomic ratios decreased within the first 2 weeks but settled to 0.40 and 0. 32 up to 60 days compared with 0.26 for untreated control specimens. CONCLUSION: Glow discharge plasma altered the surfaces of the acrylic resin and increased thc wettability as shown both by XPS and contact-angle measurements, and plasma treatment seemed to offer a durable (at least up to 60 days) wettability.     

An investigation of the variables which may affect the bond between plastic teeth and denture base resin

OBJECTIVES: The failure of the bond between acrylic resin denture base material and resin teeth remains a significant problem. This study evaluated the tensile bond strength of specimens produced by commonly employed tooth preparation and processing methods as used in dental laboratories. METHODS: Twenty-two experimental groups, each consisting of 36 specimens, were investigated by subjecting the tooth-resin bond to tensile loading. The groups were allocated to one of five experimental sets to investigate: (a) effect of resin dough time, (b) effect of tooth surface condition, (c) effect of processing variables, (d) effect of monomer cementing, and (e) effect of acrylic resin cement. The results were analysed statistically using a one factor ANOVA and a Student t test. RESULTS: A significantly stronger bond was obtained when the resin was packed late in the dough stage, and a superior bond, in all cases, when high-impact resin was used. Tooth surface modification by grinding or grooving made no significant difference when compared with unmodified surfaces. Wax-contaminated surfaces produced highly significant weaker bonds. Time of introduction and duration of water-bath processing had no significant effect on bond strength. Monomer cementing of the tooth surface, especially with high-impact monomer. significantly improved the bond strength. The application of resin cements was found to produce the most significant increase in denture tooth bond strength. CONCLUSIONS: The important steps in obtaining a consistently high value denture tooth bond are thorough dewaxing of the tooth surface followed by the application of a suitable resin cement.     

Adsorption of whole saliva onto hydrophilic and hydrophobic solid surfaces: influence of concentration, ionic strength and pH.

The influence of the concentration of salivary proteinaceous material from solutions of whole saliva on the kinetics of in vitro pellicle formation were studied together with the effects of ionic strength, pH and certain substrate characteristics. The pellicle formation was monitored by an automated Rudolph ellipsometer, equipped with a He-Ne laser (wavelength 632.8 nm). The substrates compared in the study were hydrophilic negatively charged silica surfaces and hydrophobic methylated silica surfaces. The results show that the adsorption of salivary proteins is a very rapid process on both types of surfaces. Part of the formed biofilm, however, desorbed upon rinsing, indicating that the proteinaceous material was adsorbed with varying binding strengths. Larger adsorbed amounts were recorded on hydrophobic than on hydrophilic surfaces. Increase of ionic strength caused larger amounts to be adsorbed on both types of surfaces but change of pH did not affect the adsorption on either of the studied surfaces. Ellipsometry was found to be a suitable technique to monitor the adsorption of salivary proteins at solid/liquid interfaces.     

Adsorption of whole saliva onto hydrophilic and hydrophobic solid surfaces: influence of concentration, ionic strength and pH

The influence of the concentration of salivary proteinaceous material from solutions of whole saliva on the kinetics of in vitro pellicle formation were studied together with the effects of ionic strength, pH and certain substrate characteristics. The pellicle formation was monitored by an automated Rudolph ellipsometer, equipped with a He-Ne laser (wavelength 632.8 nm). The substrates compared in the study were hydrophilic negatively charged silica surfaces and hydrophobic methylated silica surfaces. The results show that the adsorption of salivary proteins is a very rapid process on both types of surfaces. Part of the formed biofilm, however, desorbed upon rinsing, indicating that the proteinaceous material was adsorbed with varying binding strengths. Larger adsorbed amounts were recorded on hydrophobic than on hydrophilic surfaces. Increase of ionic strength caused larger amounts to be adsorbed on both types of surfaces but change of pH did not affect the adsorption on either of the studied surfaces. Ellipsometry was found to be a suitable technique to monitor the adsorption of salivary proteins at solid/liquid interfaces.     

Comparative bond strengths of autopolymerising denture resin and light cured composite resin to denture teeth

AIM: To investigate the shear bond strengths between light cured composite and autopolymerised acrylic resin bonded to acrylic resin denture teeth. METHODS: Surface treatments were used for the denture teeth included wetting with methylmethacrylate (MMA) monomer, composite bonding agent and acid etching. The samples were divided into seven groups. Two groups of specimens were immersed in distilled water for 30 days to hydrate the teeth. Five other groups of embedded denture teeth were stored in air at room temperature for 30 days. RESULTS: Analysis of variance indicated statistically significant differences between groups (P < 0.001). CONCLUSION: The greatest bond strengths to denture teeth were in acrylic resins polymerised with pressure and wetted with monomer. The bond strengths of hydrated and unhydrated samples gave similar results both with acrylic resins and composites.     

树脂基托表面低温等离子体处理研究

目的评估等离子体用以处理树脂表面减小接触角提高材料润湿性的作用.方法将树脂材料制成10mm×10mm×2mm的试件,置入等离子体处理装置中,先氩气处理10min再氧气处理10min,并对标本进行接触角测量和扫描电镜观察.结果经等离子体处理后,树脂材料接触角明显下降,其表面细微结构无明显变化.结论低温等离子体表面处理技术可用于提高树脂材料表面润湿性.     

Effect of Tea, Coffee and Turmeric Solutions on the Colour of Denture Base Acrylic Resin: An In Vitro Study

Discoloration of acrylic resin denture base when it comes in contact with various food materials and beverages in the oral cavity may cause aesthetic concern to a denture wearer. The objective of this study was to evaluate the effect of tea, coffee and turmeric solutions on the colour of different brands of heat cure acrylic resin denture base materials commonly used in India. Spectrophotometer was used to evaluate the colour change. A significant difference was found when change in colour was statistically analysed.     

The effectiveness of seven denture cleansers on tea stain removal from PMMA acrylic resin

PURPOSE: In this study, seven denture cleansers were evaluated for their mode of action of tea stain removal from Perspex acrylic resin material. MATERIALS AND METHODS: Perspex acrylic resin specimens were stained using a combination of chlorhexidine and tea solution. The specimens were also treated with saliva to form an initial pellicle layer and facilitate the uptake of the stain. The capacity for stain removal was determined by measuring the optical density of the treated specimens by using a spectrophotometer. These were then exposed, for 5 minutes, to seven denture cleansers to demonstrate the percentage stain-removal ability of each cleanser. The same procedure was applied for roughened Perspex acrylic resin specimens. Water was used as a control in the two parts of the experiment. RESULTS: The products containing alkaline hypochlorite had the highest ability for removing stain from the acrylic resin material together with a bleaching effect. The results varied when the same denture cleansers were used on the roughened Perspex surface, and this was attributed to the presence of irregularities and porosities on the blocks. CONCLUSION: Denture cleansing agents containing hypochlorite and Boots Denture Cleaning Powder (constituents not stated by the manufacturer) exhibited the ability to remove stain from the denture base materials most effectively. Irregularities and porosities present on the denture surface played a major role in reducing the activity of denture cleaning agents and hence increased stain and plaque retention.     

Shear bond strengths for composite and autopolymerized acrylic resins bonded to acrylic resin denture teeth

Statement of problem. Composite has been used to modify acrylic resin denture teeth. Purpose. This in vitro investigation examined the shear bond strengths between composite and autopolymerized acrylic resin bonded to acrylic resin denture teeth. Material and methods. The surface treatments used for the denture teeth included wetting with methyl methacrylate (MMA), vinylethyl methacrylate monomer (VEMA), unfilled liquid resin, composite bonding agent, and composite color modifier. Nonhydrated and hydrated denture tooth groups were included. A commercial composite was bonded to the denture teeth. The control group consisted of autopolymerized PMMA resin bonded to the acrylic resin denture teeth, and another group consisted of polyvinylethyl methacrylate bonded to acrylic resin denture teeth. The samples were thermocycled and tested in shear. Results. Acrylic resin denture teeth prewetted with MMA and treated with unfilled resin or a bonding agent had bond strength values comparable to the control group. VEMA was not as effective in promoting the bond. Composite color modifier did not produce a significantly weaker bond between the acrylic resin teeth and added composite. No prewetting of the teeth with MMA resulted in the lowest bond strength. Mean shear bond strengths for corresponding hydrated and non-hydrated groups were not significantly different. Conclusion. Bond strength of composite-to-acrylic resin denture teeth was comparable to the bond strength of autopolymerized acrylic resin.     

Compositional analysis of human acquired enamel pellicle by mass spectrometry

Relatively little is known about the formation of the acquired enamel pellicle other than that it involves the selective adsorption of specific proteins from oral fluids. Previous studies on the identification of pellicle components have relied largely on immunological or enzymatic detection and have been hampered by the fact that only minute quantities of pellicle can be removed from tooth surfaces. The present work describes an improved method of harvesting pellicle that combines mechanical and chemical removal; this approach was used to investigate systematically the desorption of in vitro pellicle components with different solutions. Eleven major in vitro pellicle proteins were identified by using a combination of electrophoretic separation and matrix-assisted laser desorption/ionization-reflectron time-of-flight mass spectrometry. A similar analysis of in vivo-formed pellicle revealed the presence of intact statherin, lysozyme, albumin and amylase. Further analysis of in vivo pellicle by liquid chromatography-electrospray ionization mass spectrometry suggested the presence of numerous low molecular-weight fragments of precursor proteins. The protein composition of in vitro whole-salivary pellicle adsorbed to hydroxyapatite and that of in vivo enamel pellicle differed for proline, the result of a reduction in the content of acidic proline-rich proteins in the in vivo samples. Unique features of the oral environment such as enzymatic activities or mineral surface properties may account for these differences between in vivo and in vitro pellicle formation.