Invitro Antifungal Evaluation of Denture Soft Liner Incorporated with Tea Tree Oil: A New Therapeutic Approach Towards Denture Stomatitis

Zinc-modified phosphate-based glass micro-filler improves Candida albicans resistance of auto-polymerized acrylic resin without altering mechanical performance

Colonization of auto-polymerized acrylic resin by pathogenic Candida albicans is a common problem for denture users. In this study, zinc-modified phosphate-based glass was introduced into an auto-polymerized acrylic resin at concentrations of 3, 5, and 7 wt.%. The mechanical or physical properties (flexural strength, elastic modulus, microhardness, and contact angle), surface morphology of the resultant materials, and the antimicrobial effect on C. albicans were investigated. There were no statistical differences in the mechanical properties between the control and the zinc-modified phosphate-based glass samples (p > 0.05); however, the number of C. albicans colony-forming units was significantly lower in the control group (p < 0.05). Scanning electron microscopy revealed that C. albicans tended not to adhere to the zinc-modified-phosphate-based glass samples. Thus, the zinc-modified materials retained the advantageous mechanical properties of unaltered acrylic resins, while simultaneously exhibiting a strong antimicrobial effect in vitro.

Individual and Synergistic Effects of Tea Tree Oil and Neem Extract on Candida albicans Adhesion to Denture Soft Liner

Background

Inflammation is present in denture stomatitis. Denture stomatitis's etiology is complex, but there is evidence that it is brought on by Candida albicans growing in biofilms on its surface.

Objective

This study aimed to examine and assess the effectiveness of several herbal products, such as tea tree oil and neem extracts, on Candida albicans adhesion to denture soft liners.

Method

Each wall of the tissue culture plate was filled with 30 acrylic blocks lined with soft liners, followed by the addition of 0.1 ml of the standardized Candida albicans suspension, which was then left to incubate for 48 hours. Each specimen was placed in a disinfectant solution for 10 minutes. A colony was counted after 0.1ml of the solution was plated on a sabouraud dextrose agar (SDA) plate and cultured for 72 hours. Data were compared using a one-way analysis of variance (ANOVA) test.

Results

The mean colony forming units (CFU) per ml for combined tea tree oil and neem extract was least (0.40), followed by tea tree oil (2.30), followed by neem extract (30.33). The treated blocks were effective in reducing the growth of Candida albicans.

Conclusion

Combining tea tree oil and neem extract significantly reduced the growth of Candida albicans, suggesting a new form of intraoral effective antifungal treatment.

The Influence of Decontamination Procedures on the Surface of Two Polymeric Liners Used in Prosthodontics

Polymeric liners are materials commonly used in prosthodontics to reshape denture surfaces contacting the soft tissues of the oral cavity. The aim of the study was to determine the impact of different cleaning methods on two polymeric materials used in prosthodontics as non-adhesive permanent liners. The material for the research consisted of samples made from Mollosil Plus (Detax, Ettlingen, Germany)-direct polysiloxan liner; and Plastitanium (Pressing Dental, San Marino, Republic of San Marino)-an injection-molded liner. A total of 198 samples were made, 99 of each assessed material. They were exposed to different cleaning methods-a toothbrush, a toothbrush and soap, a toothbrush and toothpaste (BlendaMed, Procter&Gamble, Cincinnati, OH, USA), a toothpaste and denture cleaning paste (Protefix Hygiene Denture Paste, Queisser Pharma, Germany), denture cleansing tablets (Protefix Hygiene Cleaning Tablets, Queisse Pharma, Germany), and a disinfecting spray (Aftermat, Port Jefferson Station, New York City, NY, USA)-for 1 min, 5 min, 10 min, and 15 min. The image acquisition was performed with scanning electron microscopy and samples were analyzed for the homogeneity of their surfaces-the presence of holes, grooves, precipitate, and small and large separating pieces of the material marking departures from this homogeneity. For each type of damage, one point was given. Continuous data from two groups were compared with Mann-Whitney U testing. Due to a small sample size and distribution of variables other than normal, to compare more than two groups, Kruskal-Wallis testing with post hoc analysis (Dunn test with Bonferroni correction) was used. Categorical data were compared with the chi-square test and the Fisher's exact test. The Mollosil Plus material should be decontaminated with the use of a toothbrush or toothbrush with soap, while Plastitanium material should be disinfected. Plastitanium samples are more susceptible to damage during the decontamination procedures than Mollosil Plus.

Antifungal Activity of Denture Base Resin Containing Nanozirconia: In Vitro Assessment of Candida albicans Biofilm

Objective

To evaluate the antimicrobial effects of different concentrations of zirconium dioxide nanoparticles (nano-ZrO₂) reinforcement of poly(methyl) methacrylate (PMMA) on surface roughness and C. albicans biofilm.

Methods

20 heat-polymerized acrylic resin discs were conventionally made and divided into 4 groups (n = 5) according to nano-ZrO₂ concentration: control (0% filler) and 3 experimental groups (2.5% (Z2.5), 5.0% (Z5.0), and 7.5% (Z7.5)). An optical profilometer was used for surface roughness evaluation, followed by Candida adherence assay. Specimens were sterilized, then immersed in cultured yeast (C. albicans), and incubated at 37°C for 48 hours. After that, discs were rinsed before extracting the clustered pellets of Candida. The attached C. albicans was counted using the direct method after spreading on agar media and incubating for 48 hours. Statistical analysis was performed using one-way ANOVA and Tukey's post hoc test at α = 0.05.

Results

Surface roughness was significantly increased with all modified groups compared with control (P < 0.01), which showed the lowest roughness value (0.027 ± 0.004 μm). There was no significant difference in the roughness value among reinforced groups (2.5, 5.0, and 7.5%) (P > 0.05), with Z7.5 showing the highest roughness value (0.042 ± 0.004 μm). Candida count was reduced as the nano-ZrO₂ increased but not significantly (P=0.15).

Conclusions

The addition of different concentrations of nano-ZrO₂ particles to PMMA increased the surface roughness compared with control; in contrast, insignificant reduction of C. albicans biofilm was detected.

Evaluation of Antimicrobial and Antibiofilm Activities of Copper Oxide Nanoparticles within Soft Denture Liners against Oral Pathogens

OBJECTIVES

Soft denture liners provide a favorable environment for adhesion and colonization of microorganisms. This in vitro study aimed to examine the efficacy of different concentrations of copper oxide nanoparticles (CuO NPs) incorporation into soft denture liner on the biofilm formation of the microbial species.

METHODS

Field Emission Scanning Electron Microscopy (FESEM) images from NPs were recorded. Antifungal susceptibility testing of CuO NPs against five standard strains of Candida albicans (CBS 10261, 1905, 1912, 1949, 2730), Streptococcus mutans (ATCC35668), Streptococcus sobrinus (ATCC27607), and Streptococcus salivarius (ATCC9222) was performed by the broth microdilution method with the Clinical and Laboratory Standards Institute reference method. The biofilm inhibition percentages of CuO NPs on the soft denture liners were determined by XTT assay.

RESULTS

The characterization of CuO NPs by scanning electron microscope (SEM) analyses confirmed the synthesis of NPs with appropriate structure and size with a mean diameter of 18.3 ± 9.1 nm. The CuO NPs successfully inhibited the growth of the tested standard strains of C. albicans and Streptococcus spp. at concentrations ranging from 64 to 128 µg mL-1. Indeed, incorporation of CuO NPs at a concentration of 500 µg mL-1 into the soft denture liners exhibited a significant activity (75%) in inhibition of C. albicans. biofilm formation in a dose-dependent manner. The biofilm formation of C. albicans in the presence of CuO NPs was lower than Streptococcus spp. in comparison with the control group (p < 0.05).

CONCLUSION

Incorporation of CuO NPs significantly decreased the colonization and plaque formation of the oral pathogens, especially C. albicans accumulation. These NPs may be useful as a promising agent for the antimicrobial management of soft denture liner materials.

Antibiofilm and Protein-Repellent Polymethylmethacrylate Denture Base Acrylic Resin for Treatment of Denture Stomatitis

Candida albicans (C. albicans) biofilm is a common etiological factor in denture stomatitis. The purpose of this study was to investigate the effects of incorporating 2-methacryloyloxyethyl phosphorylcholine (MPC) as a protein repellent into a new high-impact denture acrylic (HIPA) resin on the surface roughness, solution pH, and C. albicans biofilm adhesion to the denture base. The new acrylic denture resin base was formulated by mixing MPC into HIPA resin at mass fractions of 1.5%, 3%, and 4.5%. Surface roughness was measured using a Mitutoyo surface roughness tester. C. albicans biofilm growth and viability were assessed via colony forming unit counts. The pH of the biofilm growth medium was measured using a digital pH meter. Adding MPC to the HIPA resin at percentages of 1.5% and 3% increased the roughness values significantly (p < 0.05), while adding 4.5% MPC resulted in no difference in roughness values to that of the control group (p > 0.05). All experimental groups demonstrated neutral pH values (pH ≅ 7) and were not significantly different from each other (p > 0.05). Incorporating 2-methacryloyloxyethyl phosphorylcholine at 4.5% resulted in a significant (≅1 log) colony-forming unit reduction compared with the control group with 0% MPC (p < 0.05). A fungal-retarding denture acrylic resin was developed through the incorporation of MPC for its protein-repelling properties. This newly developed denture acrylic material has the potential to prevent oral microbial infections, such as denture stomatitis.

Therapeutic Role of Nystatin Added to Tissue Conditioners for Treating Denture-Induced Stomatitis: A Systematic Review

Denture-induced stomatitis (DIS) represents a pathological condition caused by ill-fitting dentures trauma, manifested as inflammation of the palatal tissue beneath the denture. The fungal infections are the principal contributory factors to DIS. Although the aetiology of DIS is multifactorial, the Candida albicans fungal infection remains the main cause. The objective of the present systematic review was to evaluate the latest literature on the addition of nystatin into the tissue conditioners (TCs) in the management of DIS. To search the published literature about “the addition of nystatin in TCs for treating DIS”, electronic databases (PubMed (National library of medicine) and Cochrane Library (Wiley)) were searched (from 1975 until December 2020) using different keywords. Various studies described the effectiveness and efficacy of incorporating nystatin into several TCs. The present systematic review reported that the addition of nystatin is beneficial, with slight or no consequences on both the mechanical and physical features of TCs. Adding nystatin to various TCs for treating DIS can be suggested.

The effects of adding fluorescent carbon nanoparticles on various mechanical properties of denture liners

The aim of this in vitro study was to evaluate the effects of incorporating fluorescent carbon nanoparticles (FCNs) on the hardness, tear, and tensile bond strength of an acrylic-based tissue conditioner and a silicone-based soft denture liner. FCNs added to an acrylic-based tissue conditioner (Viscogel, Dentsply; Group V) and a silicone-based soft denture liner (Ufigel P, Voco; Group U) were divided into subgroups according to the concentrations (Group 0: no water, Group 1: with only water, Group 2: 0.5% FCNs, Group 3: 1% FCNs and Group 4: 10% FCNs) (n=10/per group). Shore A hardness, tear, and tensile bond strength tests were performed. Significant decreases occurred in Groups U2, U3, and U4 compared to the control groups (Groups U0 and U1) in the tear and tensile bond strength test parameters (p<0.025). However, in both types of the tested materials, there were no statistically significant differences among the shore A hardness test results (p>0.025).

Guanidine derivative inhibits C. albicans biofilm growth on denture liner without promote loss of materials' resistance

To reduce the burden of denture stomatitis and oral candidiasis, an aqueous solution containing polyhexamethylene guanidine hydrochloride (PHMGH) was investigated as an antifungal disinfectant against the leading cause of these oral conditions, Candida albicans. The solutions formulated with concentrations ranging from 0.125 to 0.50 wt% enabled increasing disinfection at the initial 5min-contact with 72h-mature candida biofilms formed on denture liner specimens. After 10 min-contact, the solution at lower concentration has reached total fungal elimination. The results also indicated that the denture liners preserved their mechanical property after the maximum contact time with the solution at the highest tested concentration. The PHMGH aqueous solutions at 0.125 wt% could be applied to promote interim denture liner disinfection without promoting the loss of materials' mechanical property.

Antifungal activity and Shore A hardness of a tissue conditioner incorporated with terpinen-4-ol and cinnamaldehyde

PURPOSE

This study investigated the anti-Candida activity and the Shore A hardness of a tissue conditioner (Softone™) modified by incorporation of terpinen-4-ol and cinnamaldehyde.

MATERIAL AND METHODS

Agar diffusion, microdilution, and mechanism of action methods were performed to determine to evaluate the antifungal activity of phytoconstituents. Then, phytoconstituents in varying concentrations were incorporated into the tissue conditioner. The anti-Candida effect of the modified conditioner was evaluated through agar punch well and biofilm formation methods. Shore A hardness of the experimental liners was evaluated after baseline, 24 h, 48 h, 4 days, and 7 days immersion on artificial saliva.

RESULTS

The phytoconstituents incorporated into Softone showed completely inhibited fungal growth in concentrations of 20-40% and did not present significant antifungal activity until their concentrations where higher than 5%. There were differences between non-modified Softone and M5, M10, C10, and T10% (p < 0.05). The groups containing 10-40% of cinnamaldehyde incorporated into Softone were able to completely inhibit the biofilm. Concentrations below 40% of terpinen-4-ol showed unsatisfactory biofilm inhibition. The T40% and C40% groups presented the lowest Shore A hardness values. Hardness values from groups T40% at 7 days (p = 0.476); C40% at 4 days (p = 0.058); and T20% (p = 0.058), C20% (p = 0.205), T30% (p = 0.154), and C30% (p = 0.874) after 48 h did not differ from the control group.

CONCLUSIONS

Cinnamaldehyde incorporated into Softone inhibited Candida biofilm formation at concentrations of 10-40%, being more effective than terpinen-4-ol modification despite of halo inhibition observed by both products.

CLINICAL RELEVANCE

All modifications showed a very similar pattern of hardness being useful for clinical practice.

Lactoferrin, chitosan and Melaleuca alternifolia-natural products that show promise in candidiasis treatment

The evolution of microorganisms resistant to many medicines has become a major challenge for the scientific community around the world. Motivated by the gravity of such a situation, the World Health Organization released a report in 2014 with the aim of providing updated information on this critical scenario. Among the most worrying microorganisms, species from the genus Candida have exhibited a high rate of resistance to antifungal drugs. Therefore, the objective of this review is to show that the use of natural products (extracts or isolated biomolecules), along with conventional antifungal therapy, can be a very promising strategy to overcome microbial multiresistance. Some promising alternatives are essential oils of Melaleuca alternifolia (mainly composed of terpinen-4-ol, a type of monoterpene), lactoferrin (a peptide isolated from milk) and chitosan (a copolymer from chitin). Such products have great potential to increase antifungal therapy efficacy, mitigate side effects and provide a wide range of action in antifungal therapy.

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.

Functional denture soft liner with antimicrobial and antibiofilm properties

Background/purpose

Denture soft liners, especially used for elders who have poor disinfection habits, provide a favourable environment for accumulation and colonization of microorganisms. This in vitro study is aimed to investigate the effectiveness of natural carvacrol incorporation into soft lining material on the inhibition of oral pathogens.

Materials and methods

Antimicrobial susceptibility of carvacrol was primarily determined by disc diffusion method. Soft lining material was prepared as recommended by the manufacturer and 10 μL carvacrol was added aseptically to the soft liner discs. Inhibition zones for the control discs without carvacrol (C) and carvacrol-incorporated discs (CL) were determined by disc diffusion method. The biofilm inhibition percentages of carvacrol on soft liner was determined by MTT assay and also observed by Scanning Electron Microscopy (SEM).

Results

Carvacrol displayed great antimicrobial activity for yeast, Gram-negative and Gram-positive strains. The highest inhibition zone of carvacrol (41.33 ± 1.53 mm) was measured for Bacillus subtilis strain which is followed by Candida albicans and Streptococcus sanguis (34.00 ± 1.73 mm and 32.33 ± 0.58 mm, respectively). The inhibition zones were also similar for soft liner discs with carvacrol, with the highest inhibition zones against B. subtilis, Streptococcus mutans and C. albicans (43.67 ± 0.58 mm, 40.33 ± 0.58 mm and 38.33 ± 1.15 mm, respectively). Incorporation of carvacrol into the soft liner decreased (98.03 ± 0.2%) of the biofilm formation for C. albicans.

Conclusion

Carvacrol-incorporation obviously decreased the colonization and plaque formation of oral pathogens, especially C. albicans accumulation. Carvacrol may be useful as a promising agent for antibacterial and antifungal management for denture soft lining materials.

Influence of ozone and paracetic acid disinfection on adhesion of resilient liners to acrylic resin

PURPOSE

The aim of this study was to evaluate the effect of paracetic acid (PAA) and ozone disinfection on the tensile bond strength (TBS) of silicone-based resilient liners to acrylic resins.

MATERIALS AND METHODS

One hundred and twenty dumbbell shaped heat-polymerized acrylic resins were prepared. From the mid segment of the specimens, 3 mm of acrylic were grinded off and separated parts were reattached by resilient liners. The specimens were divided into 2 control (control1, control7) and 4 test groups of PAA and ozone disinfection (PAA1, PAA7, ozone1 and ozone7; n=10). While control groups were immersed in distilled water for 10 min (control1) and 7 days (control7), test groups were subjected to PAA (16 g/L) or ozone rich water (4 mg/L) for 1 cycle (10 min for PAA and 60 min for ozone) per day for 7 days prior to tensile tests. Measurements of the TBS were analyzed using 3-way ANOVA and Tukey's HSD test.

RESULTS

Adhesive strength of Mollosil decreased significantly by application of ozone disinfection. PAA disinfection had no negative effect on the TBS values of Mollosil and Molloplast B to acrylic resin. Single application of ozone disinfection did not have any negative effect on TBS values of Molloplast B, but prolonged exposure to ozone decreased its adhesive strength.

CONCLUSION

The adhesion of resilient liners to acrylic was not adversely affected by PAA disinfection. Immersion in ozonated water significantly decreased TBS of Mollosil. Prolonged exposure to ozone negatively affects adhesion of Molloplast B to denture base materials.