Growth and/or acid production of Candida albicans on soft lining materials in vitro

Digital Design of a Universal Rat Intraoral Device for Therapeutic Evaluation of a Topical Formulation against Candida-Associated Denture Stomatitis

Candida-associated denture stomatitis (DS) is a persistent and chronic oral infection of the denture-bearing palatal mucosa. DS stems from the ability of the fungal opportunistic pathogen Candida albicans to adhere to denture material and invade palatal tissue. Although DS is the most prevalent form of oral candidiasis, there are currently no feasible therapeutic strategies for the prevention of this recurrent condition. We developed a peptide-based antimicrobial bioadhesive formulation specifically designed for oral topical formulation. In this study, we aimed to evaluate the applicability of the novel formulation for the prevention of C. albicans colonization on denture material and development of clinical disease. To that end, using the latest technological advances in dental digital design and three-dimensional (3D) printing, we fabricated an intraoral device for rats with universal fit. The device was successfully installed and used to develop clinical DS. Importantly, by taking a preventative therapeutic approach, we demonstrated the potential clinical utility of the novel formulation as a safe and feasible prophylactic agent against DS.

The Role of Biofilms and Material Surface Characteristics in Microbial Adhesion to Maxillary Obturator Materials: A Literature Review

BACKGROUND

Maxillofacial prosthetics includes restoration of maxillary defects resulting from resection of palate and nasosinus neoplasms with obturator prostheses which may be colonized by microorganisms and function as a reservoir of infection. Patients with neoplasms commonly also require radiotherapy that can result in changes in saliva quality and quantity and changes in the oral microbial flora. The altered flora, in individuals immunocompromised from cancer therapy, increases their risk of prosthesis-related infections.

OBJECTIVES

In this review article, we explore microbial biofilms, their main components, mechanisms of microbial adhesion, and stages of biofilm development. We also discuss the different materials that are used for manufacturing maxillary obturators, their characteristic features, and how these can affect microbial adhesion. Furthermore, we shed some light on the factors that affect microbial adhesion to the surface of maxillary obturators including tissue proteins, protein adsorption, and the acquired enamel pellicle.

CONCLUSIONS

The conclusions drawn from this literature review are that it is imperative to minimize the risk of local and systemic infections in immunocompromised patients with cancer having maxillary defects. It is also important to determine the role of saliva in microbial adhesion to obturator materials as well as develop materials that have a longer life span with surface characteristics that promote less microbial adhesion than current materials.

Role of Candida species from HIV infected children in enamel caries lesions: an in vitro study

Objectives

This study analyzed the capacity of Candida spp. from dental biofilm of HIV infected (HIV+) children to demineralize primary molar enamel in vitro by Transversal Microhardness (TMH), Polarized Light Microscopy (PLM) and the quantity of calcium ions (Ca²⁺) released from the enamel.

Material and Methods

Candida spp. samples were isolated from the supragingival biofilm of HIV+ children. A hundred and forty (140) enamel blocks were randomly assigned to six groups: biofilm formed by C. albicans (Group 1); mixed biofilm formed by C. albicans and C. tropicalis (Group 2); mixed biofilm formed by C. albicans and C. parapsilosis (Group 3); mixed biofilm formed by C. albicans, C. parapsilosis and C. glabrata (Group 4); biofilm formed by C. albicans ATCC (Group 5) and medium without Candida (Group 6). Enamel blocks from each group were removed on days 3, 5, 8 and 15 after biofilm formation to evaluate the TMH and images of enamel were analyzed by PLM. The quantity of Ca²⁺ released, from Groups 1 and 6, was determined using an Atomic Absorption Spectrophotometer. The SPSS program was used for statistical analysis and the significance level was 5%.

Results

TMH showed a gradual reduction in enamel hardness (p<0.05) from the 1^st to 15^th day, but mainly five days after biofilm formation in all groups. The PLM showed superficial lesions indicating an increase in porosity. C. albicans caused the release of Ca²⁺ into suspension during biofilm formation.

Conclusion

Candida species from dental biofilm of HIV+ children can cause demineralization of primary enamel in vitro.

Effect of denture cleansers on Candida albicans biofilm formation over resilient liners

PURPOSE

The purpose of this study was to analyze the effect of denture cleansers on Candida albicans biofilm formation over resilient liners and to evaluate compatibility between resilient liners and denture cleansers.

MATERIALS AND METHODS

Acrylic resin (Lucitone 199®) and 3 resilient liners (COE-SOFT™, GC RELINE™ and SOFRELINER TOUGH TOUGH®) were incubated in denture cleansers (Polident® and Cleadent®) for 8 hours a day and in unstimulated saliva for 16 hours a day (n=25/gp) for 60 days. Two-way and three-way repeated measures ANOVA were performed to compare the surface roughness (Ra), pH and C. albicans binding level by radioisotope (α=0.05). The statistical significance of the relation between Ra and adhesion was evaluated by correlation analysis.

RESULTS

THE DEGREE OF RA WAS SIGNIFICANTLY DECREASED IN THE FOLLOWING ORDER: COE-SOFT™, acrylic resin, GC RELINE™ and SOFRELINER TOUGH®. The immersion in denture cleansers significantly increased Ra of resilient liners, except for SOFRELINER TOUGH® in Cleadent®. No significant differences in pH curves were observed among groups immersed in distilled water and denture cleansers. The binding levels of C. albicans were significantly decreased in the following order: COE-SOFT™, GC RELINE™, SOFRELINER TOUGH®, and acrylic resin. The immersion in Cleadent® seemed to decrease C. albicans binding level on GC RELINE™ and SOFRELINER TOUGH®.

CONCLUSION

Based on the C. albicans binding levels results, it is not recommended to immerse COE-SOFT™ in denture cleansers, and GC RELINE™ and SOFRELINER TOUGH® should be immersed in Cleadent®.

Studies on the possible aetiological role of different Candida species in pathogenesis of dentine caries by monitoring the calcium release from tooth particles

An in vitro model has been developed for study of cariogenic potential of different Candida species. Slices were prepared from the root of extracted healthy teeth. These disks were covered with inert material, only the central hole, i.e. the root canal dentin surface remained uncovered. These preparates with free root dentin surfaces were incubated in Sabouraud medium in the presence of six-six Candida albicans, Candida glabrata, Candida tropicalis, Candida krusei, Candida inconspicua and Candida norvegensis strains. The calcium release was detected for 15 days. Two types of release could be distinguished. C. albicans deliberated calcium more aggressively (type "A" curve), while other Candidas were characterized by less expressed calcium releasing capacity (type "B" curve). Curves type "A" and "B" were divided into four steps in order to characterize more precisely the different dynamics of calcium release. Analyses of the different steps also suggested the more aggressive behaviour of C. albicans. Our results indicate that in addition to cariogenic role of different bacteria, fungi may also actively take part in the dentinal caries progress.

Surface roughness of acrylic and silicone-based soft liners: in vivo study in a rat model

PURPOSE

The aim of this in vivo animal study was to investigate changes in the surface roughness of soft liners over time.

MATERIALS AND METHODS

Forty adult Wistar rats (Rattus norvergicus albinus) were fitted with acrylic custom-made palatal plates relined by dynamic impressions and tested with the following soft liners: Dentuflex (DF), Trusoft (TS), Dentusoft (DS), and Ufi Gel P (UG). Half of the animals for each tested material had the plates fitted during the material reline procedure. Their surface roughness was read immediately (IRa group, n = 5). The other half used the palatal plates for 14 days before roughness readings were performed (FRa group, n = 5). The surface roughness (Ra) of the inner surface from the relined dentures was recorded using a Surftest SJ-401 with eight readings per specimen, and mean values were obtained. Data (μm) were analyzed by two-way ANOVA and Tukey's test (α = 0.05).

RESULTS

IRa means (2.92 ± 0.87 μm) and FRa means (3.35 ± 0.65 μm) were significantly different (p = 0.016). UG showed a lower (p = 0.01) Ra mean (2.1 ± 0.52 μm) than DF (3.94 ± 0.81 μm), TS (4.12 ± 0.64 μm), and DS (3.27 ± 0.64 μm).

CONCLUSIONS

Ufi Gel P showed the smoothest surface among the materials evaluated. The period of use resulted in changes in the surface roughness of the materials tested.

Evaluation of Candida albicans adherence on the surface of various maxillofacial silicone materials

OBJECTIVES

Fungal infection resulting from Candida adherence on material surface is one of the most important medical risks for maxillofacial prosthesis wearers. Despite wide usage, there is a sparse data evaluating C. albicans adherence on various commercial maxillofacial silicone materials that have different surface contact angles. The objective of this study was to investigate the relationship between surface contact angle and fungal adherence on widely used maxillofacial silicone materials.

MATERIALS AND METHODS

Three maxillofacial silicone materials titled VST-50, A-2006, and A-2186F were used for fabrication of disc-shaped specimens. Surface contact angle of specimens were measured by the goniometric method. Adhesion quantity of two different C. albicans strains was evaluated with a colorimetric method using XTT/Coenzyme Q0. The Kruskal-Wallis and Mann-Whitney U tests were used for statistical analysis of data.

RESULTS

The lowest surface contact angle values with the highest Candida adhesion quantity were measured on the specimens fabricated with A-2006 silicone material. Statistically significant differences were found among three maxillofacial silicone materials in terms of both surface contact angle values and adhesion quantity (P<0.01).

CONCLUSION

There is a close relationship between surface contact angle and quantity of Candida adherence. However, it should be noted that various factors arising from material properties may affect the complex nature of the Candida adhesion process.

Influence of surface characteristics on the adhesion of Candida albicans to various denture lining materials

OBJECTIVE

This study evaluated the influence of surface characteristics of various denture lining materials on the adherence of Candida albicans.

MATERIALS AND METHODS

Four different types of materials (tissue conditioners, acrylic and silicone soft liners and hard reline materials) were selected. Disk-shaped material specimens were prepared and their surface roughness values (R(a) ) measured using a profilometer. The contact angles of four reference liquids were measured on the material surfaces and surface energy parameters (total surface energy, acid and base components, degree of hydrophobicity/hydrophilicity) of the materials were calculated in accordance with acid-base theory. Specimens were incubated with C. albicans and adhering fungi quantified using the colony counting method. Data were statistically analyzed using a one-way ANOVA with Games-Howell post-hoc test (α = 0.05). Pearson correlation analysis was applied to detect correlations between surface characteristics and Candida adhesion.

RESULTS

Significant differences in the surface roughness of the materials were found (p < 0.001). The acrylic soft liners were more hydrophilic than the other materials. Overall, the acrylic soft liners and tissue conditioners showed significantly greater Candida adhesion than silicone soft liners and hard reline materials (p < 0.05). The Pearson correlation analysis indicated that the base component and degree of hydrophobicity/hydrophilicity of the materials (p = 0.005/0.008), rather than the total surface energy and the surface roughness (p = 0.093/0.057), affected C. albicans adherence in a statistically significant way.

CONCLUSIONS

The adhesion of C. albicans to denture lining materials can be accounted for in terms of interfacial acid-base interactions.

Rechargeable infection-responsive antifungal denture materials

Candida-associated denture stomatitis (CADS) is a significant clinical concern. We developed rechargeable infection-responsive antifungal denture materials for potentially managing the disease. Polymethacrylic acid (PMAA) was covalently bound onto diurethane dimethacrylate denture resins in the curing step. The PMAA resins bound cationic antifungal drugs such as miconazole and chlorhexidine digluconate (CG) through ionic interactions. The anticandidal activities of the drug-containing PMAA-resin discs were sustained for a prolonged period of time (weeks and months). Drug release was much faster at acidic conditions (pH 5) than at pH 7. Drugs bound to the denture materials could be "washed out" by treatment with EDTA, and the drug-depleted resins could be recharged with the same or a different class of anticandidal drugs. These results suggest clinical potential of the newly developed antifungal denture materials in the management of CADS and other infectious conditions.

In vitro evaluation of artificial ageing on surface properties and early Candida albicans adhesion to prosthetic resins

OBJECTIVE

The aim of this in vitro study was to examine potential changes and influences of prosthetic resin surface properties on Candida albicans adhesion after surface treatment or artificial ageing.

MATERIALS AND METHODS

Standardized specimens of a denture base resin and a veneering composite were prepared, polished, and randomly subjected to different surface roughness treatments or artificial ageing protocols (storage in ethanol or artificial saliva for 7/90 d, thermocycling). Surface roughness (Ra) and surface free energy were determined prior and after each treatment. Specimens were incubated with phosphate buffered saline or whole saliva for 2 h at 37 degrees C, and later with Candida albicans suspension (2.5 h, 37 degrees C). Adherent viable fungi were quantified using a bioluminescence assay.

RESULTS

Artifical ageing did not affect substratum surface roughness, yet slight increases in substratum surface free energy and significant increases in Candida albicans adhesion were observed. Saliva coating marginally influenced Candida albicans adherence to reference and surface treated specimens, yet more pronounced differences in Candida albicans adhesion between the various artificially aged specimens were found.

CONCLUSION

No correlation between substratum surface roughness or surface free energy and Candida albicans adhesion could be established.

[Colonization of Candida species and efficacy of miconazole gel in overdenture wearers]

PURPOSE

Preliminarily to examine the efficacy of miconazole gel at inhibiting colonization of Candida species in overdenture wearers.

METHODS

The subjects were 26 overdenture wearers. Miconazole gel was used with the following directions: group A was prescribed miconazole gel 1.5 g 4 times daily for 1 week, group B was prescribed miconazole gel 0.5 g 4 times daily for 1 week. As a screening test, Candida species were examined in denture plaque, dental plaque, and pharyngeal mucosa. The number of Candida species, total bacteria, and oral streptococci were counted before and after application of miconazole gel to Candida-positive subjects.

RESULTS

Candida species were detected in 18 of 26 subjects and high incidence was found around the abutments under the denture base. All Candida species were sensitive to miconazole gel. Miconazole gel was applied to 13 subjects. The number of Candida was reduced after 1-week use of miconazole gel with few side effects during the application.

CONCLUSION

It is suggested that miconazole gel will be an effective and safe method for oral care and denture plaque control in overdenture wearers.

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.

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 microg ml(-1) (final pH = 3.45), and 5.4 microg ml(-1) (final pH 4.81), respectively and the maximum growth of C. albicans and S. mutans was 10(7) cfu ml(-1) and 7.4 x 10(12) 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 x 10(5)), C. albicans possesses the ability to dissolve HAP to a greater extent (approximately 20-fold) when compared with S. mutans.

Biofilm formation of Candida albicans on the surfaces of deteriorated soft denture lining materials caused by denture cleansers in vitro

Candidal colonization and subsequent biofilm formation on denture materials are important in the development of pathogenesis, such as denture stomatitis. Routine use of denture cleansers is one of the most effective methods of denture plaque control, although the incompatibility of soft liners and denture cleansers cause damage to the materials. The present study, biofilm formation of Candida albicans on the surfaces of soft denture lining materials, immersed in denture cleansers for 180 days were studied. Seven commercially available soft denture lining materials, were artificially deteriorated by immersion into three commercially available denture cleansers for 180 days, and subsequent fungal growth and biofilm formation were studied by measuring pH of the media and by the use of adenosine triphosphate (ATP) analysis. Fungal biofilm formation on the deteriorated soft liners varied depending upon the combination of the soft liners and denture cleansers. Several combinations of soft liners with denture cleansers exhibited the significantly high colonization capacity as compared with each sample immersed in distilled water, used as individual controls. The relationship between the biofilm formation on the samples of each material and the surface roughness of the soft lining materials was analyzed. However, no significant correlation was observed. The results, taken together, suggested that fungal colonization could be predominantly regulated by the combination of lining material with denture cleansers. In clinical terms, our findings suggests that daily cleansing of soft lining materials with mismatched denture cleansers promoted the subsequent biofilm formation of fungi on the materials.

Changes in surface roughness and colour stability of soft denture lining materials caused by denture cleansers

Soft denture lining materials were immersed into solutions of denture cleansers for 8 h at room temperature, and immersed into distilled water for the remainder of the 24-h period at 37 degrees C. Surface roughness of the soft denture lining materials was measured by contact type surface roughness instrument. For the colour stability test, soft denture lining materials were immersed in the denture cleansers as described above for 180 days. Finally, the colour changes of each material were quantitatively measured by a photometrical instrument to obtain the colour differences between newly processed specimen and immersed specimens (P < 0.01). An autopolymerizing silicone material, Evatouch, exhibited severe changes in surface roughness by all denture cleanser, and the generic material GC Denture Relining showed the minimal changes. Severe colour changes were also observed with some liner and cleanser combinations (P < 0.01). Except for Evatouth, the four silicone soft liners were more stable in surface roughness and in colour change than the two acrylic soft liners. One autopolymerizing silicone (GC denture relining) and one heat curing silicone (Molloplast B) demonstrated the best stability.

Effect of tissue conditioners on the dynamic viscoelastic properties of a heat-polymerized denture base

STATEMENT OF PROBLEM

Little is known about the influence of tissue conditioners on physical property alteration of denture base resins.

PURPOSE

This study evaluated the influence of a variety of commercial tissue conditioners on alteration of viscoelastic properties of a heat-polymerized denture base acrylic resin.

MATERIAL AND METHODS

Four tissue conditioners and 1 heat-polymerized denture base acrylic resin were used. In one experiment, acrylic resin specimens (1.0-mm thick) were immersed in the liquid component of tissue conditioners for 36 hours. In another experiment, tissue conditioners were applied to acrylic resin specimens (0.5-mm and 1.0-mm thick) in a 2-mm layer; the specimens then were immersed in distilled water for 1 week. Control specimens for both groups had no lining and were immersed in distilled water for 36 hours and 1 week, respectively. Dynamic viscoelastic properties of the acrylic resin specimens were measured at 37 degrees C with an automatic viscoelastometer. Tensile storage modulus (E'), tensile loss modulus (E"), and loss tangent (tan delta) were determined at 1 Hz. These parameters were compared with analysis of variance and the Dunnett test at a predetermined significance level of.05. All statistical comparisons were made with reference to the control group and not to each other.

RESULTS

Only the liquid of Hydro-Cast significantly reduced E' and increased tan delta of the acrylic resin (P<.05). Acrylic resin specimens 0.5-mm thick and lined with tissue conditioners tended to have lower E' and higher tan delta than the control. However, only Hydro-Cast and SR-Ivoseal significantly decreased E', and only Hydro-Cast raised tan delta of the acrylic resin (P<.05). No significant difference was found among the E" values. The tissue conditioners did not affect E', E", or tan delta of acrylic resin specimens 1.0-mm thick.

CONCLUSION

Within the limitations of this study, some tissue conditioners significantly plasticized the denture base acrylic resin 0.5-mm thick. However, when the acrylic resin was 1.0-mm thick, no plasticization by the tissue conditioners was noted.

Impact of components of denture acrylic resin on gingival cell growth and sensitivity to Candida albicans adhesion

The effects of four liquid components of denture acrylic resin on host cell activity and fungal adhesion were investigated in this study. The low concentration (1 micromol l(-1)) of the liquid components caused no change in the activities and morphologies of the gingival fibroblast cells, compared with control and dimethylsulphoxide-exposed cells. However, when the cells were exposed to high concentrations (1 mmol l(-1)) of benzqyl peroxide, morphological change was observed, implying that the exposure of the cells to high concentrations of the liquid components of denture acrylic causes the loss of adhesion proteins from the cells. Thus the amount of Candida adhesion to human gingival cells was analysed, and the adherence of fungi to the cell was significantly reduced when the cells were pre-exposed to methyl methacrylate, hydroquinone and benzoyl peroxide at a concentration of 1 micromol l(-1) (P < 0.01), which did not affect either the cell viability or the cell morphology. These results, taken together, suggested that the renewal of dentures could be a possible therapeutic and/or preventive aid for oral candidosis in denture-wearing patients.

Effects of triclosan on the cytotoxicity and fungal growth on a soft denture liner

STATEMENT OF PROBLEM

Contamination of removable prostheses with microorganisms, particularly Candida albicans, is a common clinical problem. Microban, a broad-spectrum antimicrobial containing triclosan, recently has been proposed to inhibit microbial growth.

PURPOSE

This study aimed to determine whether the addition of Microban to PermaSoft denture liner prevents the growth of C albicans and affects the cytotoxicity of the PermaSoft material.

MATERIAL AND METHODS

Experimental specimen disks (5 x 1 mm each) with and without incorporated Microban were fabricated aseptically (n = 6) against polyester film to produce a smooth surface. To assess the cytotoxic effect of Microban, the MTT assay was used. To determine the effect of Microban on the growth of C albicans, disks were placed in Transwell dishes, covered with Sabouraud's broth containing an ATCC strain of C albicans, and incubated at 37 degrees C for 24 hours. Wells containing fluorocarbon resin disks or broth alone served as controls. The disks were rinsed to remove unattached C albicans and then sonicated in sterile water to remove surface organisms. Serial dilutions of the water extracts were plated on Sabouraud's agar and returned to the incubator for 24 hours. Colonies were counted with a Brunswick Colony Counter. Growth of C albicans in the internal aspects of the specimens was determined in a manner as previously described, with the exception that the specimens were sonicated to remove surface organisms, minced, and sonicated once more before making serial dilutions. The results were compared with ANOVA and Tukey intervals (alpha=.05).

RESULTS

The number of colonies formed ranged from 17 to 31 x 10(5) (mean = 23 +/- 4 x 10(5)) and 14 to 69 x 10(5) (mean = 32 +/- 20 x 10(5)) for the PermaSoft with and without Microban groups, respectively. There was no statistically significant difference between PermaSoft with and without Microban.

CONCLUSION

The addition of Microban did not significantly alter the cytotoxicity of the PermaSoft denture lining material or reduce the adherence of viable C albicans to the surface of PermaSoft material after 24 hours.

Denture plaque--past and recent concerns

OBJECTIVE

This paper critically reviews the history of denture plaque and identifies some concerns with the presence of Candida in the mouth.

DATA SOURCES

This review covers literature sources related to Candida albicans and its relationship to denture plaque.

STUDY SELECTION

The articles selected for this review are from referred journals and describe C. albicans and its relationship to oral, gastrointestinal and pleuropulmonary infections. The relationship to caries, root caries and periodontal disease is also covered.

CONCLUSIONS

Denture plaque containing Candida could cause not only oral candidiasis, like oral thrush or denture-induced stomatitis, but also caries, root caries and periodontitis of abutment teeth. However, there is only limited experimental evidence or information available on the cariogenicity of Candida. The continuous swallowing or aspiration of micro-organisms from denture plaque exposes patients, particularly the immunocompromised host or medicated elderly, to the risks of unexpected infections. The term, 'denture plaque' has been used throughout the review. However, the term 'plaque on denture' should be used because the microbial flora and its pathogenicity of denture plaque resembles those of plaque formed on the tooth surface, so called dental plaque. In addition, the term 'denture related stomatitis' would be preferable to 'denture induced stomatitis', since the inflammation of (palatal) mucosa is not induced by the denture, but by wearing the denture or by plaque on the denture.

Evaluating the effect of soft lining materials on the growth of yeast

STATEMENT OF PROBLEM

Soft lining materials continue to have a place in clinical removable prosthodontics. However, there is an increased probability of yeast colonization on soft lining materials.

PURPOSE

This study (1) assessed a method of evaluating the effect of long-term soft lining materials on the growth of yeast and (2) investigated the effect five soft lining materials had on the growth of three species of yeast.

MATERIAL AND METHODS

Coe Supersoft, Novus, and three experimental soft lining materials were investigated together with Candida albicans, Candida tropicalis, and Issatchenkia orientalis (formerly Candida krusei) yeasts. Strips of soft lining material incubated on blood agar plates were examined for inhibition of the growth of yeast. Soft lining materials soaked in sterile trypticase soya broth or water were inoculated with yeast and incubated. The change in colony forming units per milliliter from the initial load of yeast at 3 days was measured. Statistical analysis was performed with an independent paired Student t test.

RESULTS

Inhibition of yeast growth occurred for two soft lining materials. Despite the presence of sufficient viable organisms, differences between the initial load of yeast and the 3-day results were mostly small, both for the test and control groups, suggesting that the material does not support the growth of the tested yeast during this period.

CONCLUSIONS

The often described increased prevalence of yeast associated with soft lining materials in the oral environment is likely related to readily available nutrients in the mouth and the difficulty in maintaining and cleaning these materials.

The effect of saliva or serum on Streptococcus mutans and Candida albicans colonization of hydroxylapatite beads

OBJECTIVE

Several recent reports imply the possibility of cariogenicity of denture plaque containing Candida albicans. Hence the purpose of this study was to investigate the effects of salivary and serum pellicles on C. albicans and Streptococcus mutans colonization on hydroxylapatite beads.

METHODS

The colonization of three isolates of C. albicans and two isolates of S. mutans was examined by the use of a bioluminescent adenosine triphosphate (ATP) assay based on the firefly luciferase-luciferin system.

RESULTS

In the preliminary study, a good correlation was observed between the cell number and ATP amount of each isolate tested, and the results yielded a level of significance (P < 0.001; Student's t-test), confirming the validity of this method. When the relative ATP content of the 48 h colonization of both isolates of S. mutans were compared, a saliva pellicle was significantly more effective in promoting bacterial colonization than either uncoated or serum pellicle (ANOVA; P < 0.01). In contrast, in the case of colonization of C. albicans isolates, a serum pellicle was significantly more effective in promoting the colonization of C. albicans GDH 18 and GDH 19, than both uncoated specimens and saliva pellicle (ANOVA; P < 0.01). Similar trends were observed with C. albicans GDH 16, though significant differences were not observed (ANOVA; P > 0.05).

CONCLUSION

The results suggest that the mechanism involved in fungal colonization on hydroxylapatite (HAP) should be different from that of mutans streptococci.

Effect of components of resilient denture-lining materials on the growth, acid production and colonization of Candida albicans

Variation in the components of soft lining materials, i.e. the size of polymer particles, the ethyl alcohol content of the liquids and the type of plasticizer, were investigated with respect to their effects on the growth and colonization of Candida albicans. Inhibitory effects on fungal growth and/or acid production were found to vary depending upon the components of soft lining materials. In particular, two plasticizers, benzyl benzoate (BB) and benzyl salicylate (BS), significantly decreased the growth rate, whereas the size of polymer particle had little effect on fungal growth. Ethyl alcohol content of liquid significantly affected the fungal growth and/or acid production depending upon the plasticizer used. For instance, in the case of BS, the antifungal effect was related to ethyl alcohol contents, whereas a reverse effect was observed with benzyl n-butyl phthalate (BBP). Further examination using scanning electron microscopy revealed that Candida blastospores colonized lining materials in the following two ways depending on the plasticizers used. On the BS and dibutyl phthalate (DBP) specimen, the blastospore of this yeast associated loosely, whereas, in the case of BB, BBP and butyl phthalyl butyl glycorate (BPBG), fungal blastospore tightly and invasively colonized onto the specimens. These results clearly demonstrated a relationship between components of soft lining materials and fungal growth and colonization.