Interactions between thermal cycled resilient denture lining materials, salivary and serum pellicles and Candida albicans in vitro. Part I. Effects on fungal growth

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.

Effect of Silver-Emitting Filler on Antimicrobial and Mechanical Properties of Soft Denture Lining Material

Colonization of silicone-based soft lining materials by pathogenic yeast-type fungi is a common problem associated with the use of dentures. In this study, silver sodium hydrogen zirconium phosphate (SSHZP) was introduced into polydimethylsiloxane-based material as an antimicrobial filler at concentrations of 0.25, 0.5, 1, 2, 4, 6, 8, 10, 12, and 14% (w/w). The in vitro antimicrobial efficacy was investigated. Candida albicans was used as a characteristic representative of pathogenic oral microflora. Staphylococcus aureus and Escherichia coli were used as the typical Gram-positive and Gram-negative bacterial strains, respectively. The effect of filler addition on the Shore A hardness, tensile strength, tensile bond strength, sorption, and solubility was investigated. An increase in the filler concentration resulted in an increase in hardness, sorption, and solubility, and for the highest concentration, a decrease in bond strength. The favorable combination of antimicrobial efficacy with other properties was achieved at filler concentrations ranging from 2% to 10%. These composites exhibited mechanical properties similar to the material without the antimicrobial filler and enhanced in vitro antimicrobial efficiency.

Surface characteristics and microbial adherence ability of modified polymethylmethacrylate by fluoridated glass fillers

BACKGROUND

The current study objectives were to evaluate the influence of fluoridated glass fillers loading on the surface roughness, wettability, and adherence of candida and bacteria with and without saliva presence to a polymethylmethacrylate (PMMA) denture base material surface.

METHODS

Four concentrations of fluoridated glass fillers were added to PMMA: 1%, 2.5%, 5% and 10% by weight pre-polymerization and 0% was the control. Discs of each concentration were fabricated (n = 5 for each variable). Surface roughness (Ra ) was measured using atomic force microscopy (AFM). Wettability was assessed by measuring the contact angle of a sessile drop of water. Specimens were incubated with Candida albicans, or Streptococcus mutans with and without saliva coating. Adherence was presented as a percentage of the colonized surface area, counted using an optical microscope at x100 magnification.

RESULTS

The 10% group showed significantly greater roughness than the control and 1% groups; however, no significant differences in contact angle values were detected. The microbial adhesion was inversely proportional to the fluoridated glass fillers concentration where 10% concentration significantly decreased candidal and bacterial adhesion compared to others. Saliva coating significantly decreased microbial adhesion.

CONCLUSIONS

It was concluded that fluoridated glass fillers could decrease microbial adhesion to acrylic denture base without adversely affecting surface properties.

Long-Term Soft Denture Lining Materials

Long-term soft denture lining (LTSDL) materials are used to alleviate the trauma associated with wearing complete dentures. Despite their established clinical efficacy, the use of LTSDLs has been limited due to the unfavorable effects of the oral environment on some of their mechanical and performance characteristics. The unresolved issue of LTSDL colonization by Candida albicans is particularly problematic. Silicone-based LTSDL (SLTSDL) materials, which are characterized by more stable hardness, sorption and solubility than acrylic-based LTSDLs (ALTSDLs), are currently the most commonly used LTSDLs. However, SLTSDLs are more prone to debonding from the denture base. Moreover, due to their limitations, the available methods for determining bond strength do not fully reflect the actual stability of these materials under clinical conditions. SLTSDL materials exhibit favorable viscoelastic properties compared with ALTSDLs. Furthermore, all of the lining materials exhibit an aging solution-specific tendency toward discoloration, and the available cleansers are not fully effective and can alter the mechanical properties of LTSDLs. Future studies are needed to improve the microbiological resistance of LTSDLs, as well as some of their performance characteristics.

Candida albicans biofilms and MMA surface treatment influence the adhesion of soft denture liners to PMMA resin

The effect of Candida albicans biofilms and methyl methacrylate (MMA) pretreatment on the bond strength between soft denture liners and polymethyl methacrylate (PMMA) resin was analyzed. Specimens were prepared and randomly divided with respect to PMMA pretreatment, soft liner type (silicone-based or PMMA-based), and presence or absence of a C. albicans biofilm. Samples were composed of a soft denture liner bonded between two PMMA bars. Specimens (n = 10) were incubated to produce a C. albicans biofilm or stored in sterile PBS for 12 days. The tensile bond strength test was performed and failure type was determined using a stereomicroscope. Surface roughness (SR) and scanning electron microscopy (SEM) analysis were performed on denture liners (n = 8). Highest bond strength was observed in samples containing a silicone-based soft liner and stored in PBS, regardless of pretreatment (p < 0.01). Silicone-based specimens mostly underwent adhesive failures, while samples containing PMMA-based liners predominantly underwent cohesive failures. The silicone-based specimens SR decreased after 12 days of biofilm accumulation or PBS storage, while the SR of PMMA-based soft liners increased (p < 0.01). The PMMA-based soft liners surfaces presented sharp valleys and depressions, while silicone-based specimens surfaces exhibited more gentle features. In vitro exposure to C. albicans biofilms reduced the adhesion of denture liners to PMMA resin, and MMA pretreatment is recommended during relining procedures.

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®.

Candida colonisation and the efficacy of chlorhexidine gluconate on soft silicone-lined dentures of diabetic and non-diabetic patients

OBJECTIVES

The aim of this study was to evaluate Candida colonisation in the dentures with silicone soft liner in diabetic and non-diabetic patients and to assess the antifungal efficacy of chlorhexidine gluconate on Candida colonies.

MATERIALS AND METHODS

Thirty patients with resorbed ridges, fifteen each in the diabetic and non-diabetic group, were selected. The mandibular denture of each patient was lined with heat-polymerised silicone resilient liner. Patients were instructed to clean the dentures with soap water and brush. Samples from the fitting surface of mandibular dentures were collected at 15, 21 and 30 days. Subsequently, samples were collected at 15, 21 and 30 days, after cleaning the dentures with a detergent solution of 4% chlorhexidine gluconate, and incubated for the evaluation of Candida growth. These data were subjected to statistical analysis by Mann-Whitney U-test.

RESULTS

Normal oral flora in diabetics and non-diabetics showed no difference (p > 0.05). The density of colonies increased after 21 and 30 days in diabetic patients (p < 0.05). Number of Candida colonies significantly reduced in both the groups after 21 and 30 days of cleaning the dentures with 4% chlorhexidine gluconate (p < 0.05).

CONCLUSION

Dentures with silicone resilient liner exhibit increased Candida growth in diabetic patients. Four per cent chlorhexidine gluconate solution effectively disinfects these dentures.

In vitro adhesion of Candida glabrata to denture base acrylic resin modified by glow-discharge plasma treatment

This study evaluated the potential of plasma treatments to modify the surface chemistry and hydrophobicity of a denture base acrylic resin to reduce the Candida glabrata adhesion. Specimens (n = 54) with smooth surfaces were made and divided into three groups (n = 18): control - non-treated; experimental groups - submitted to plasma treatment (Ar/50 W; AAt/130 W). The effects of these treatments on chemical composition and surface topography of the acrylic resin were evaluated. Surface free energy measurements (SFE) were performed after the treatments and after 48 h of immersion in water. For each group, half (n = 9) of the specimens were preconditionated with saliva before the adhesion assay. The number of adhered C. glabrata was evaluated by cell counting after crystal violet staining. The Ar/50 W and AAt/130 W treatments altered the chemistry composition, hydrophobicity and topography of acrylic surface. The Ar/50 W group showed significantly lower C. glabrata adherence than the control group, in the absence of saliva. After preconditioning with saliva, C. glabrata adherence in experimental and control groups did not differ significantly. There were significant changes in the SFE after immersion in water. The results demonstrated that Ar/50 W treated surfaces have potential for reducing C. glabrata adhesion to denture base resins and deserve further investigation, especially to tailor the parameters to prolong the increased wettability.

Antifungal activity of denture soft lining material modified by silver nanoparticles-a pilot study

Soft liner materials in oral cavity environments are easily colonized both by fungi and dental plaque. These factors are the cause of mucosal infections. The microorganism that most frequently colonizes soft liner materials is Candida albicans. Colonization occurs on the surface of materials and within materials. A solution to this problem might involve modification of soft liner materials with silver nanoparticles (AgNPs). In this article, we present results showing the antifungal efficacy of silicone soft lining materials modified with AgNPs. The modification process was conducted by dissolving both material components (base and catalyst) in a colloidal solution of AgNPs and evaporating the solvent. Composites with various AgNP concentrations (10, 20, 40, 80, 120 and 200 ppm) were examined. The in vitro antifungal efficacy (AFE) of composite samples was 16.3% to 52.5%.

In vitro colonization of an experimental silicone by Candida albicans

Denture soft-lining materials are exposed to the oral cavity for long periods and are in continuous contact with saliva, subject to inhibition of liquid molecules, and susceptible to colonization by microorganisms. The opportunist yeast Candida albicans is of particular concern in this context, being associated with denture plaque and denture-related stomatitis. In this study, penetration of C. albicans into an experimental silicone elastomer soft-lining material was investigated under batch and continuous culture conditions. A model "denture plaque" microcosm was also used. Increasing the filler concentration within the elastomer decreased penetration under both batch and continuous culture conditions. In continuous culture, C. albicans penetration was significantly greater in pure culture than in the presence of bacteria after 72-h incubation (p < 0.05).

Biofilm formation of Candida albicans on the surface of a soft denture-lining material

BACKGROUND

Soft denture lining-materials are more susceptible to microbial adhesion than hard denture base acrylic resin. Poor oral hygiene and Candida albicans infection are common among elderly denture wearers as these patients usually have difficulty in keeping them clean.

PURPOSE

To evaluate the influence of the oral hygiene methods on the formation of a biofilm over a soft denture-lining material.

MATERIAL AND METHODS

Twenty volunteers were randomly separated into two groups: G1 and G2. Ten volunteers performed daily hygiene of the prostheses with a soft toothbrush and toothpaste. The G2 performed a treatment identical to G1 but also immersed the prostheses in sodium hypochlorite 0.5% for 20 min, once a week. Quantification of the mean score values of biofilm formation at different times were statistically analysed using analysis of variance and Tukey's test (alpha = 0.05).

RESULTS

G1 (0.65 +/- 0.52) showed the lowest mean score values of biofilm formation. There was statistical difference between G1 and G2. The highest mean score values were found at 6 weeks (1.3 +/- 1.08) and were statistically different from other times.

CONCLUSION

The oral hygiene methods had a significant effect in the formation of the biofilm over a soft denture-lining material.

Influence of acrylic resin polymerization methods and saliva on the adherence of four Candida species

STATEMENT OF PROBLEM

There is limited information on the role of polymerization methods and saliva on the adherence of pathogenic Candida species, with the exception of the adherence of Candida albicans to acrylic resins and the relation of this to surface roughness and surface free energy, which appear to play a major role in the initial phases of microorganism adhesion.

PURPOSE

This study evaluated the influence of polymerization methods and human whole saliva on the adherence of Candida species to acrylic resin surfaces.

MATERIAL AND METHODS

Acrylic resin specimens (n=256) measuring 2.5 x 1.2 x 0.2 cm were heat (Classico) or microwave (OndaCryl) polymerized and evaluated for surface roughness using a profilometer, and for surface free energy by measuring the contact angle of a sessile drop of water. For the adherence assay, specimens of each acrylic resin were divided by lottery into 8 groups, according to whether they were exposed to human saliva or not (control), and to 1 of the 4 following suspensions: C albicans, Candida tropicalis, Candida dubliniensis, or Candida glabrata (1 to 5 x 10(6) cells/mL). Adhered yeasts were counted using an optical microscope at x400 magnification. Data were analyzed by 3-way ANOVA and the Tukey honestly significant difference test (alpha=.05).

RESULTS

No statistical difference was found for roughness (P=.156), whereas higher surface free-energy values were found for the heat-polymerized acrylic resin (P=.0013). The overall adherence of Candida species was significantly decreased by human saliva (P<.001).

CONCLUSION

Within the limitations of this study, saliva was capable of reducing the adherence of Candida species, whereas roughness and free energy did not influence the adherence rates.

CLINICAL IMPLICATIONS

As growth on surfaces is a natural part of the Candida lifestyle, its colonization in denture users may be expected. The presence of human whole saliva, however, decreased the overall yeast adherence to the acrylic resin surface, whereas surface roughness and free energy did not interfere with the adherence of Candida species.

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.

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.

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.