Antifungal Efficacy and Physical Properties of Poly(methylmethacrylate) Denture Base Material Reinforced with SiO2 Nanoparticles

Antifungal recombinant psoriasin of human origin effectively inhibits fungal growth on denture base

OBJECTIVE

To evaluate the efficacy of recombinant psoriasin as a novel treatment for oral candidiasis by eliminating Candida albicans growth on polymethyl methacrylate denture base.

MATERIALS AND METHODS

Recombinant psoriasin protein was expressed and purified from E. coli, and Candida growth was monitored in vitro with varying concentrations of psoriasin. Subsequently, denture-base polymethyl methacrylate was immersed in psoriasin's solution or voriconazole, and fungal growth on the acrylic base and in the medium was examined by scanning electron microscopy and optical density, respectively. Cellular viability of HeLa and human gingival fibroblast cells treated with psoriasin was measured by methylene blue assay.

RESULTS

The findings reveal an effective antifungal activity of psoriasin, completely inhibiting Candida albicans growth in RPMI at a protein concentration above 400 nM. Immersing the polymethyl methacrylate with 50 μM psoriasin completely eradicates fungal growth. Psoriasin has low cytotoxicity in HeLa cells at a concentration higher than 12 μM and no toxic effect on human gingival fibroblasts.

CONCLUSIONS

This study marks psoriasin as an effective alternative to conventional antifungal treatments for denture stomatitis and a safe alternative to chemical antifungals in dental medicine and beyond.

Mapping the research landscape of nanoparticles and their use in denture base resins: a bibliometric analysis

BACKGROUND

Nanoparticles are increasingly used in dentistry for various applications, including enhancing the mechanical properties of denture base resins. This study aimed to comprehensively review and analyze the research landscape of nanoparticles and their effect on the flexural strength of denture base resins to identify key research areas and trends and to highlight the importance of collaboration between authors and institutions.

METHODS

A Bibliometric Analysis was conducted using the Keywords "Nanoparticle*" AND "Denture*" OR "CAD/CAM." The literature search from the WOS database was restricted to the publication years 2011 to 2022.

RESULTS

Key findings encompass an increase in research publications but a decline in citations. Saudi Arabia, China, and Iraq led this research, with specific institutions excelling. Notable journals with high impact factors were identified. Authorship patterns show variations in citation impact. Additionally, keyword analysis revealed that current research trends offer insights into influential authors and their networks.

CONCLUSIONS

The analysis of nanoparticles and denture base resins reveals a dynamic and evolving landscape that emphasizes the importance of collaboration, staying current with research trends, and conducting high-quality research in this ever-evolving domain.

Nanoparticle-Modified 3D-Printed Denture Base Resins: Influence of Denture Cleansers on the Color Stability and Surface Roughness In Vitro

This study aimed to evaluate the influence of denture cleansers on the color, stability, and surface roughness of three-dimensional (3D)-printed denture base resins modified with zirconium dioxide nanoparticles (nano-ZrO2). A total of 440 specimens were fabricated using one heat-polymerized resin, and two 3D-printed resins (NextDent and ASIGA). According to the nano-ZrO2 content, the specimens for each resin were divided into five groups (0%, 0.5%wt, 1%wt, 3%wt, and 5%wt). Each concentration was divided into four subgroups (n = 10) based on the immersion solution (distilled water, sodium hypochlorite, Corega, and Fittydent) and immersion duration (360 and 720 days). The color changes (∆E00) and surface roughness (Ra, µm) of each specimen were measured at different time intervals (base line, 360 days, 720 days) using a spectrophotometer and a non-contact profilometer, respectively. The results were statistically analyzed using ANOVA and a post hoc Tukey's test (α = 0.05). Sodium hypochlorite showed the highest significant color change of all the denture base resins (p < 0.001). The average value of ΔE00 for sodium hypochlorite was significantly higher than the values for the other solutions (Fittydent, Corega, and water) (p < 0.001). Color stability was significantly affected by immersion time for all types of solutions except Corega (p < 0.001). All of the tested immersion solutions (distilled water, sodium hypochlorite, Corega, and Fittydent) showed a significant increase in the surface roughness of all the denture base resins (p < 0.05). Surface roughness was substantially increased by immersion time for all types of solution except Fittydent (p < 0.001). Denture cleansers can result in substantial color change and affect the surface roughness of unmodified and nanoparticle-modified denture base resins. Therefore, the selection of denture cleanser and appropriate types of material is critical for denture longevity.

In Vitro Evaluation of Candida albicans Adhesion and Related Surface Properties of CAD/CAM Denture Base Resins

OBJECTIVE

 The aim of this study was to evaluate the surface roughness, contact angle, and adhesion of Candida albicans to computer-aided designing/computer-aided manufacturing (CAD/CAM) and heat-polymerized (HP) denture base materials.

MATERIALS AND METHODS

 Specimens were allocated to six groups based on the composition of studied denture base materials, HP acrylic resin, milled resins (AvaDent and IvoCad), and 3D-printed resins (ASIGA, FormLabs, and NextDent). Ten specimens per group were used for each test (n = 10/test). Surface roughness and contact angles were analyzed using profilometer and goniometer, respectively. Adhesion of C. albicans was counted using colony-forming unit (CFU/mL). Means and standard deviations were calculated, and then one-way analysis of variance (ANOVA), followed by Tukey's post hoc test. Correlation of Candida adhesion and surface parameters was determined by using Pearson's correlation analysis.

RESULTS

 No statistically significant difference was noted in surface roughness between HP, milled, and 3D-printed denture base resins except NextDent, which showed significantly higher roughness in comparison to all other resins (p = 0.001). In terms of contact angle, milled resins had the lowest value, followed by HP, ASIGA, and FormLabs, whereas NextDent showed the highest contact angle (p = 0.001). C. albicans adhesion showed no significant difference between all denture base resins. A positive and significant correlation was found between C. albicans adhesion and contact angle (p = 0.003), while no correlation was reported between C. albicans adhesion and surface roughness (p = 0.523).

CONCLUSION

 Adhesion of C. albicans was similar in all tested specimens. Surface roughness showed no significant difference between all groups except NextDent, which had the highest value. Milled denture base resins had the lowest contact angle among all groups.

Nanotechnology-based fungal detection and treatment: current status and future perspective

Fungal infections impose a significant impact on global health and encompass major expenditures in medical treatments. Human mycoses, a fungal co-infection associated with SARS-CoV-2, is caused by opportunistic fungal pathogens and is often overlooked or misdiagnosed. Recently, there is increasing threat about spread of antimicrobial resistance in fungus, mostly in hospitals and other healthcare facilities. The diagnosis and treatment of fungal infections are associated with several issues, including tedious and non-selective detection methods, the growth of drug-resistant bacteria, severe side effects, and ineffective drug delivery. Thus, a rapid and sensitive diagnostic method and a high-efficacy and low-toxicity therapeutic approach are needed. Nanomedicine has emerged as a viable option for overcoming these limitations. Due to the unique physicochemical and optical properties of nanomaterials and newer biosensing techniques, nanodiagnostics play an important role in the accurate and prompt differentiation and detection of fungal diseases. Additionally, nano-based drug delivery techniques can increase drug permeability, reduce adverse effects, and extend systemic circulation time and drug half-life. This review paper is aimed at highlighting recent, promising, and unique trends in nanotechnology to design and develop diagnostics and treatment methods for fungal diseases.

Evaluating the Translucency, Surface Roughness, and Cytotoxicity of a PMMA Acrylic Denture Base Reinforced with Bioactive Glasses

The colonisation of the surface of removable acrylic dentures by various types of microorganisms can lead to the development of various diseases. Therefore, the creation of a bioactive material is highly desirable. This study aimed to develop a denture base material designed to release bioactive ions into the oral environment during use. Four types of bioactive glasses (BAG)-S53P4, Biomin F, 45S5, and Biomin C-were incorporated into the PMMA acrylic resin, with each type constituting 20 wt.% (10 wt.% non-silanised and 10% silanised) of the mixture, while PMMA acrylic resin served as the control group. The specimens were subsequently immersed in distilled water, and pH measurements of the aqueous solutions were taken every seven days for a total of 38 days. Additionally, surface roughness and translucency measurements were recorded both after preparation and following seven days of immersion in distilled water. The cytotoxicity of these materials on human fibroblast cells was evaluated after 24 and 48 h using Direct Contact and MTT assays. Ultimately, the elemental composition of the specimens was determined through energy-dispersive X-ray (EDX) spectroscopy. In general, the pH levels of water solutions containing BAG-containing acrylics gradually increased over the storage period, reaching peak values after 10 days. Notably, S53P4 glass exhibited the most significant increase, with pH levels rising from 5.5 to 7.54. Surface roughness exhibited minimal changes upon immersion in distilled water, while a slight decrease in material translucency was observed, except for Biomin C. However, significant differences in surface roughness and translucency were observed among some of the BAG-embedded specimens under both dry and wet conditions. The composition of elements declared by the glass manufacturer was confirmed by EDX analysis. Importantly, cytotoxicity analysis revealed that specimens containing BAGs, when released into the environment, did not adversely affect the growth of human gingival fibroblast cells after 48 h of exposure. This suggests that PMMA acrylics fabricated with BAGs have the potential to release ions into the environment and can be considered biocompatible materials. Further clinical trials are warranted to explore the practical applications of these materials as denture base materials.

The Impact of Adding Chitosan Nanoparticles on Biofilm Formation, Cytotoxicity, and Certain Physical and Mechanical Aspects of Directly Printed Orthodontic Clear Aligners

Aligner treatment is associated with bacterial colonization, leading to enamel demineralization. Chitosan nanoparticles have been demonstrated to have antibacterial properties. This in vitro study aims to determine the effect of adding chitosan nanoparticles to directly 3D-printed clear aligner resin with regard to antibiofilm activity, cytotoxicity, degree of conversion, accuracy, deflection force, and tensile strength. Different concentrations (2%, 3%, and 5% w/w) of chitosan nanoparticles were mixed with the clear resin, and the samples were then 3D printed. Additionally, the thermoforming technique for aligner manufacturing was utilized. The obtained specimens were evaluated for antibiofilm activity against Streptococcus mutans bacteria and cytotoxicity against L929 and 3T3 cell lines. Additionally, Fourier transform infrared spectroscopy via attenuated total reflection analysis was used to assess the degree of conversion. Geomagic Control X software was utilized to analyze the accuracy. In addition, the deflection force and tensile strength were evaluated. The results indicated a notable reduction in bacterial colonies when the resin was incorporated with 3 and 5% chitosan nanoparticles. No significant changes in the cytotoxicity or accuracy were detected. In conclusion, integrating biocompatible chitosan nanoparticles into the resin can add an antibiofilm element to an aligner without compromising the material's certain biological, mechanical, and physical qualities at specific concentrations.

Antibiofilm Activity of 3D-Printed Nanocomposite Resin: Impact of ZrO2 Nanoparticles

Poly(methyl methacrylate) (PMMA) is a commonly used material, as it is biocompatible and relatively cheap. However, its mechanical properties and weak antibiofilm activity are major concerns. With the development of new technology, 3D-printed resins are emerging as replacements for PMMA. Few studies have investigated the antibiofilm activity of 3D-printed resins. Therefore, this study aimed to investigate the antibiofilm activity and surface roughness of a 3D-printed denture base resin modified with different concentrations of zirconium dioxide nanoparticles (ZrO₂ NPs). A total of 60 resin disc specimens (15 × 2 mm) were fabricated and divided into six groups (n = 10). The groups comprised a heat-polymerized resin (PMMA) group, an unmodified 3D-printed resin (NextDent) group, and four 3D-printed resin groups that were modified with ZrO₂ NPs at various concentrations (0.5 wt%, 1 wt%, 3 wt%, and 5 wt%). All specimens were polished using a conventional method and then placed in a thermocycler machine for 5000 cycles. Surface roughness (Ra, µm) was measured using a non-contact profilometer. The adhesion of Candida albicans (C. albicans) was measured using a fungal adhesion assay that consisted of a colony forming unit assay and a cell proliferation assay. The data were analyzed using Shapiro-Wilk and Kruskal-Wallis tests. A Mann-Whitney U test was used for pairwise comparison, and p-values of less than 0.05 were considered statistically significant. The lowest Ra value (0.88 ± 0.087 µm) was recorded for the PMMA group. In comparison to the PMMA group, the 3% ZrO₂ NPs 3D-printed group showed a significant increase in Ra (p < 0.025). For the 3D-printed resins, significant differences were found between the groups with 0% vs. 3% ZrO₂ NPs and 3% vs. 5% ZrO₂ NPs (p < 0.025). The highest Ra value (0.96 ± 0.06 µm) was recorded for the 3% ZrO₂ NPs group, and the lowest Ra values (0.91 ± 0.03 µm) were recorded for the 0.5% and 5% ZrO₂ NPs groups. In terms of antifungal activity, the cell proliferation assay showed a significant decrease in the C. albicans count for the 0.5% ZrO₂ NPs group when compared with PMMA and all other groups of 3D-printed resins. The group with the lowest concentration of ZrO₂ NPs (0.5%) showed the lowest level of C. albicans adhesion of all the tested groups and showed the lowest Candida count (0.29 ± 0.03). The addition of ZrO₂ NPs in low concentrations did not affect the surface roughness of the 3D-printed resins. These 3D-printed resins with low concentrations of nanocomposites could be used as possible materials for the prevention and treatment of denture stomatitis, due to their antibiofilm activities.

Prospects on Tuning Bioactive and Antimicrobial Denture Base Resin Materials: A Narrative Review

Denture base resin (DBR) materials are used in dentistry in constructing removable dentures and implant-supported prostheses. A plethora of evidence has demonstrated that DBR materials are associated with a high risk of denture stomatitis, a clinical complication where the soft oral tissues underneath the resin-based material are inflamed. The prevalence of denture stomatitis among denture wearers is high worldwide. Plaque accumulation and the infiltration of oral microbes into DBRs are among the main risk factors for denture stomatitis. The attachment of fungal species, mainly Candida albicans, to DBRs can irritate the underneath soft tissues, leading to the onset of the disease. As a result, several attempts were achieved to functionalize antimicrobial compounds and particles into DBRs to prevent microbial attachment. This review article explored the advanced approaches in designing bioactive and antimicrobial DBR materials. It was reported that using monomer mixtures, quaternary ammonium compounds (QACs), and organic and inorganic particles can suppress the growth of denture stomatitis-related pathogens. This paper also highlighted the importance of characterizing bioactive DBRs to be mechanically and physically sustainable. Future directions may implement a clinical translational model to attempt these materials inside the oral cavity.

3D-Printable Denture Base Resin Containing SiO2 Nanoparticles: An In Vitro Analysis of Mechanical and Surface Properties

PURPOSE

To evaluate the flexural strength (FS), impact strength (IS), surface roughness (Ra), and hardness of 3D-printed resin incorporating silicon dioxide nanoparticles (SNPs).

MATERIALS AND METHODS

A total of 320 acrylic specimens were fabricated with different dimensions according to test specifications and divided into a control group of heat denture base resin, and 3 test groups (80/test (n = 10) of unmodified, 0.25 wt%, and 0.5 wt% SNPs modified 3D-printed resin. 10,000 thermal cycles were performed to half of the fabricated specimens. FS, IS (Charpy impact), Ra, and hardness were evaluated and the collected data was analyzed with ANOVA followed by Tukey's post hoc test (α = 0.05).

RESULTS

Incorporating SNPs into 3D-printed resin significantly increased the FS, IS (at 0.5%) and hardness compared to unmodified 3D-printed resin (p < 0.001). However, the FS of pure 3D-printed and 3D/SNP-0.50% resin and IS of all 3D-printed resin groups were significantly lower than the control group (p < 0.0001). Hardness of 3D/SNP-0.25% and 3D/SNP-0.50% was significantly higher than control and unmodified 3D-printed resin (p < 0.0001), with insignificant differences between them. The Ra of all 3D-printed resin groups were significantly higher than control group (p < 0.001), while insignificant difference was found between 3D-printed groups. Thermal cycling significantly reduced FS and hardness for all tested groups, while for IS the reduction was significant only in the control and 3D/SNP-0.50% groups. Thermal cycling significantly increased Ra of the control group and unmodified 3D-printed resin (p < 0.001).

CONCLUSION

The addition of SNPs to 3D-printed denture base resin improved its mechanical properties while Ra was not significantly altered. Thermal cycling adversely affected tested properties, except IS of unmodified 3D-printed resin and 3D/SNP-0.25%, and Ra of modified 3D-printed resin.

Influence of ZrO2 Nanoparticle Addition on the Optical Properties of Denture Base Materials Fabricated Using Additive Technologies

This study investigated the translucency of 3D-printed denture base resins modified with zirconium dioxide nanoparticles (ZrO₂NPs) under thermal cycling. A total of 110 specimens were fabricated and divided into 3 groups according to the materials, i.e., heat-polymerized resin, and 3D-printed resins (NextDent, and ASIGA). The 3D-printed resins were modified with 0, 0.5, 1, 3, and 5 wt.% of ZrO₂NPs. All the specimens were subjected to 5000 thermal cycles. The translucency was measured using a spectrophotometer. The results showed that the heat-polymerized resin had considerably higher translucency than the 3D-printed resins. Compared to the unmodified group, the translucency decreased significantly after adding 5% ZrO₂NPs to NextDent and 3% ZrO₂NPs to ASIGA resins. The highest translucency was achieved for NextDent by adding 0.5% ZrO₂NPs and for ASIGA without any ZrO₂NPs. It was found that the average concentration level in ASIGA was significantly higher than that in NextDent. These findings revealed that 3D-printed resins have lower translucency than heat-polymerized acrylic resin, and adding ZrO₂NPs at low concentrations did not affect the translucency of the 3D-printed resins. Therefore, in terms of translucency, 3D-printed nanocomposite denture base resins could be considered for clinical applications when ZrO₂NPs are added at low concentrations.

Assessment of Zinc-Bound Phosphate-Based Glass-Coated Denture-Relining Material with Antifungal Efficacy for Inhibiting Denture Stomatitis

This study investigated the surface properties, biocompatibility, and antifungal activity against Candida albicans of a denture-relining material coated with zinc-bound phosphate-based glass. First, zinc-bound phosphate-based glass was fabricated. A polymerized denture-relining disk was coated with zinc-bound phosphate-based glass (2%, 4%, and 6%). The surface properties of the control and experimental groups were measured, including the wettability, microhardness, color difference, and gloss. The biocompatibility was evaluated using the MTT assay according to ISO 10993-5. The antifungal activity was investigated by counting the number of colony-forming units of Candida albicans. The results were analyzed using a one-way ANOVA and Tukey's test (p = 0.05). The results of this study indicate that, despite the antimicrobial effect of zinc-bound phosphate-based glass, a coated denture-relining material does not degrade the surface properties and biocompatibility. Therefore, this novel material is considered promising for use as a dental material with antimicrobial properties that can potentially prevent denture stomatitis.

Effects of incorporation of nanoparticles into dental acrylic resins on antimicrobial and physico-mechanical properties: A meta-analysis of in vitro studies

Background

A meta-analysis study was conducted to determine whether the incorporation of nanoparticles into the dental acrylic resins influence the physico-mechanical properties and whether there are the appropriate nanoparticles exhibiting excellent antimicrobial activity against cariogenic bacteria along with acceptable physico-mechanical properties.

Methods

We systematically searched the various databases up to December 2021. The review was performed based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and the Consolidated Standards of Reporting Trials (CONSORT) guidelines. A meta-analysis of physico-mechanical properties was performed by a random-effects model at a 95% confidence interval and the antimicrobial effects were analyzed descriptively.

Results

27 studies were included for the final analysis. There was no statistically significant difference in flexural strength (0.553, [95% confidence interval (CI) 0.501-0.604]), microhardness (0.509, [95% CI 0.278-0.736]), surface roughness (0.753, [95% CI 0.315-0.953]), impact strength (0.90, [95% CI 0.188-0.997]), and elastic modulus (0.848, [95% CI 0.514-0.967]), with nanoparticles addition compared with the control group. Forest plots were not generated for the thermal conductivity, tensile strength, and translucency because of the lack of comparison. Although the articles showed high heterogeneity without the high risk of bias, the finding showed the nanoparticles at low concentrations into dental acrylic resins could improve the antimicrobial activities without adverse effects on their physico-mechanical properties.

Conclusion

Adding the low concentration of nanoparticles such as 0.5% Ag, ≤0.25% TiO₂, and ≤0.25% SiO₂ as the most abundant antimicrobial nanoparticles do not influence their physico-mechanical properties and can be effective in the elimination of cariogenic pathogens.

Evaluation and comparison of flexural strength, surface roughness and porosity percentage of denture base resins incorporated with Thymoquinone and silver nano-antimicrobial agents-an in vitro study

Aim

To evaluate and compare the flexural strength, surface roughness and porosity percentage of acrylic denture base material modified with two antimicrobial agents, Thymoquinone (TQ) and Silver nanoparticles (AgNP).

Materials and methods

A total of 90 specimens were fabricated and divided into groups A, B and C with 30 specimens each. Of the 30 specimens, 10 specimens measuring 65mmx 10mmx 2.5 mm were used to study the flexural strength, 10 specimens measuring 10 mm × 20 mm × 3 mm to study surface roughness and 10 specimens measuring 10 mm × 20 mm × 3 mm to study porosity percentage. Group A specimens were made of unmodified denture base resin, group B and C were modified with 2.5% AgNP and 1% TQ respectively. The specimens were processed in the conventional manner. A universal testing machine was used to measure flexural strength and a profilometer was used to measure surface roughness. Porosity percentage was evaluated with help of a desiccator. The data obtained was subjected to statistical analyses using One-way ANOVA and the Tukey-post hoc test, with statistical significance at p ≤ 0.05.

Results

Addition of 2.5% AgNP and 1% TQ to acrylic denture base resin significantly reduced flexural strength and increased the porosity percentage (p < 0.01) but within clinically acceptable limits. No significant difference was found in the surface roughness between the various groups tested.

Conclusions

Heat cured acrylic denture base resins modified with 2.5% AgNPs,1% TQ exhibited clinically acceptable flexural strength and surface properties and could be incorporated into the denture base material as an antimicrobial agent.

3D-Printed Nanocomposite Denture-Base Resins: Effect of ZrO2 Nanoparticles on the Mechanical and Surface Properties In Vitro

Due to the low mechanical performances of 3D-printed denture base resins, ZrO2 nanoparticles (ZrO2NPs) were incorporated into different 3D-printed resins and their effects on the flexure strength, elastic modulus, impact strength, hardness, and surface roughness were evaluated. A total of 286 specimens were fabricated in dimensions per respective test and divided according to materials into three groups: heat-polymerized as a control group and two 3D-printed resins (NextDent and ASIGA) which were modified with 0.5 wt.%, 1 wt.%, 3 wt.%, and 5 wt.% ZrO2NPs. The flexure strength and elastic modulus, impact strength, hardness, and surface roughness (µm) were measured using the three-point bending test, Charpy’s impact test, Vickers hardness test, and a profilometer, respectively. The data were analyzed by ANOVA and Tukey’s post hoc test (α = 0.05). The results showed that, in comparison to heat-polymerized resin, the unmodified 3D-printed resins showed a significant decrease in all tested properties (p < 0.001) except surface roughness (p = 0.11). In between 3D-printed resins, the addition of ZrO2NPs to 3D-printed resins showed a significant increase in flexure strength, impact strength, and hardness (p < 0.05) while showing no significant differences in surface roughness and elastic modulus (p > 0.05). Our study demonstrated that the unmodified 3D-printed resins showed inferior mechanical behavior when compared with heat-polymerized acrylic resin while the addition of ZrO2NPs improved the properties of 3D-printed resins. Therefore, the introduced 3D-printable nanocomposite denture-base resins are suitable for clinical use.

Comparative Effect of Incorporation of ZrO2, TiO2, and SiO2 Nanoparticles on the Strength and Surface Properties of PMMA Denture Base Material: An In Vitro Study

Objective

This study aimed to investigate the effects of nanoparticles (zirconium dioxide (ZrO₂), titanium dioxide (TiO₂), and silicon dioxide (SiO₂)) on the flexural strength, impact strength, hardness, and wear resistance of the acrylic resin denture base material.

Materials and Methods

Acrylic resin specimens were fabricated in dimensions according to American Dental Association (ADA) specifications per test. Specimens were divided according to nanofiller into four groups; unmodified as control, ZrO₂ (Z), TiO₂, (T), and SiO₂ (S) groups. Each one was subdivided into two subgroups according to nanoparticle concentrations; 3% and 7% (Z3, Z7, T3, T7, S3, and S7). A 3-point bending test, Charpy impact test, and Vickers hardness test were used for flexural strength, impact strength, and hardness measurements, respectively. Wear resistance was measured by the differences in surface roughness of tested specimens before and after the wear test. A scanning electron microscope was used to assess nanoparticle specifications and distributions and for fracture surfaces analysis. ANOVA, Bonferroni's post hoc test, and the Kruskal–Wallis test were applied for data analysis (α = 0.05).

Results

Regarding the flexural and impact strength, there was a statistically remarkable increase for all tested groups compared with the control group, except for the T7 and S7 groups (P value <0.001, effect size = 0.893) and (P value <0.001, effect size = 0.759), respectively. There was a statistically significant improvement in the hardness of all tested groups compared with the control group (P value <0.001, effect size = 0.67) except T3 and S3. Regarding wear, a statistically significant enhancement was noticed in the wear resistance of all tested groups (P value <0.001, effect size = 0.685), except for the T7 and S7 groups.

Conclusion

The flexural strength, impact strength, and wear resistance improved with both concentrations of ZrO₂ and low TiO₂ and SiO₂ concentrations. The hardness increased with both concentrations of ZrO₂ and high TiO₂ and SiO₂ concentrations.

Hydrophobicity of denture base resins: A systematic review and meta-analysis

Objectives:

The aim of this article is to review the factors that attract Candida albicans to denture base resin (DBR) and to verify the influence of different surface treatments, chemical modification, or structural reinforcements on the properties of DBR.

Materials and Methods:

Searches were carried out in PubMed, Scopus, WOS, Google Scholar, EMBASE, and J-stage databases. The search included articles between 1999 and 2020. This study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. The keywords used during the search were “Candida albicans,” “Denture base,” “PMMA,” “Acrylic resin,” “Surface properties,” “hydrophobicity/hydrophilicity,” “contact angle,” and “surface free energy.” English full-text articles involving in-vitro studies with different acrylic resin modifications were included, whereas abstracts, dissertations, reviews, and articles in languages other than English were excluded. A meta-analysis was performed where appropriate.

Results:

Out of the 287 articles, 21 articles conformed to inclusion criteria. Sixteen articles were subjected to meta-analysis using random-effects model at 95% confidence interval. Results showed that DBR coatings/plasma coatings were effective methods to modify surface properties with estimated contact angle (CA) of 59.37° [95% confidence interval (CI): 53.69, 65.04]/55.87° (95% CI: 50.68, 61.06) and surface roughness (R_a) of 0.55 µm (95% CI: 0.52, 0.58)/0.549 µm (95% CI: 0.5, 0.59), respectively. Antifungal particle incorporation into poly(methylmethacrylate) DBR also produced similar effects with an estimated R_a of 0.16 µm (95% CI: 0.134, 0.187).

Conclusion:

The three properties responsible for C. albicans adhesion to DBR were R_a, CA, and surface free energy in terms of hydrophobicity. Therefore, the correlations between the hydrophobicity of DBR and C. albicans adhesion should be considered during future investigations for Candida-related denture stomatitis.

Antifungal Activities and Some Surface Characteristics of Denture Soft Liners Containing Silicon Dioxide Nanoparticles

Objective

This study aimed at determining the influence of adding silicon dioxide nanoparticles (nano-SiO₂) to soft relining materials on C. albicans adhesion, surface roughness, and contact angle.

Materials and Methods

Eighty heat-polymerized acrylic resin disks were constructed and relined by using auto-polymerized acrylic soft liners (COE-SOFT, GC Co., Tokyo, Japan). The specimens were categorized into two groups according to the tests conducted. Group A was composed of 40 specimens for evaluating antifungal activity, and Group B was composed of 40 specimens for testing surface roughness and contact angle. Each group was subcategorized into four subgroups (n = 10) according to the concentration of nano-SiO₂ added to the soft-liner powder: control, 0.25%, 0.5%, and 1.0% by weight. The colony forming unit (CFU) was used to assess C. albicans count. A profilometer was used to measure the surface roughness values (Ra; μm). The sessile drop method was used to evaluate the contact angle (^o) by using a goniometer. Analysis of variance and Tukey's post hoc tests (α = 0.05) were used for the data analysis.

Results

In comparison with the unmodified group, the 0.25% and the 0.5% nano-SiO₂ groups exhibited significantly lower C. albicans counts (P < 0.001), surface roughness (P < 0.001), and contact angles (P < 0.001). The exception was the 1% group, which exhibited higher C. albicans count, surface roughness, and contact angles than lower-concentration nano-SiO₂ groups; however, these values in the 1% group were still less than their respective values in the control group.

Conclusion

The addition of 0.25% and 0.5% nano-SiO₂ to an auto-polymerized acrylic soft liner decreased C. albicans adhesion, surface roughness, and contact angle.

Effect of Low Nanodiamond Concentrations and Polymerization Techniques on Physical Properties and Antifungal Activities of Denture Base Resin

Background: Denture base resin has some drawbacks. This study investigated the impact of nanodiamonds (ND) and autoclave polymerization on the surface characteristics, translucency, and Candida albicans adherence in polymethyl methacrylate (PMMA) denture base resin after thermocycling. Methods: Heat-polymerized PMMA discs (15 × 2 mm) with a total sample size n = 160 were studied. Specimens were categorized into two main groups (N = 80): conventional water-bath-polymerized PMMA (CP/PMMA) and autoclave-polymerized PMMA (AP/PMMA). Each group was subdivided according to the ND concentration into four groups (n = 20): unmodified PMMA as a control, and 0.1%, 0.25%, and 0.5% ND–PMMA. Scanning electron microscopy (SEM) was used to inspect the morphology of the ND and the ND–PMMA mixtures before heat polymerization. The specimens were exposed to thermal cycling (5000 cycles at 5 and 55 °C), then surface roughness was measured with a non-contact optical interferometric profilometer, contact angle with an automated goniometer, and translucency using a spectrophotometer. Colony-forming units (CFU) were used to determine the adherence of Candida albicans cells to the specimens. ANOVA and Tukey post hoc tests for pairwise comparison were utilized for the statistical analysis (α = 0.05). Results: Surface roughness was significantly reduced with ND addition to CP/PMMA (p ˂ 0.001), while the reduction was not statistically significant in AP/PMMA (p = 0.831). The addition of ND significantly reduced the contact angle, translucency, and Candida albicans count of CP/PMMA and AP/PMMA (p ˂ 0.001). The incorporation of ND in conjunction with autoclave polymerization of PMMA showed significant reduction in all tested properties (surface roughness, contact angle and Candida albicans adherence) except translucency (p = 0.726). Conclusions: ND addition to PMMA and autoclave polymerization improved the surface properties with respect to antifungal activities, while the translucency was adversely affected.

Effects of SiO2 Incorporation on the Flexural Properties of a Denture Base Resin: An In Vitro Study

Objective  The aim of this study was to evaluate the effects of the addition of low-silicon dioxide nanoparticles (nano-SiO ₂ ) on the flexural strength and elastic modulus of polymethyl methacrylate (PMMA) denture base material.

Materials and Methods  A total of 50 rectangular acrylic specimens (65 × 10 × 2.5 mm ³ ) were fabricated from heat-polymerized acrylic resin. In accordance with the amount of nano-SiO ₂ , specimens were divided into the following five groups ( n = 10 per group): a control group with no added SiO ₂ , and four test groups modified with 0.05, 0.25, 0.5, and 1.0 wt% nano-SiO ₂ of acrylic powder. Flexural strength and elastic modulus were measured by using a 3-point bending test with a universal testing machine. A scanning electron microscope was used for fracture surface analyses. Data analyses were conducted through analysis of variance and Tukey’s post hoc test (α = 0.05).

Results  Compared with the control group, flexural strength and modulus of elasticity tended to significantly increase ( p ˂ 0.001) with the incorporation of nano-SiO ₂ . In between the reinforced groups, the flexural strength significantly decreased ( p ˂ 0.001) as the concentrations increased from 0.25 to 1.0%, with the 1.0% group showing the lowest value. Furthermore, the elastic modulus significantly increased ( p ˂ 0.001) at 0.05% followed by 1.0%, 0.25%, 0.5%, and least in control group.

Conclusion  A low nano-SiO ₂ addition increased the flexural strength and elastic modulus of a PMMA denture base resin.

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.