Adhesion of biofilm, surface characteristics, and mechanical properties of antimicrobial denture base resin

The Effect of Manufacturing Factors on the Material Properties and Adhesion of C. albicans and S. mutans on Additive Denture Base Material

(1) Understanding the effects of manufacturing factors on microbial adhesion is essential for optimizing additive denture base materials and improving their clinical performance. This study evaluated how polymerization time, layer thickness, extended cleaning, and storage conditions influence C. albicans and S. mutans adhesion on a denture base material. (2) Specimens (n = 15/group, d = 8 mm, h = 2 mm) were additively fabricated or poured (reference). Digital light processing was performed with varying polymerization times, layer thicknesses, extended cleaning, and storage. Microbial adhesion was assessed using a luminescence assay. Surface properties were characterized by roughness (Sa/Sz), hardness, and surface free energy (SFE). Statistics: The Shapiro-Wilk test, ANOVA, Bonferroni post hoc test, and Pearson correlation (α = 0.05) were utilized. (3) Polymerization time, layer thickness, cleaning, and storage conditions significantly influenced C. albicans and S. mutans adhesion. Increased layer thickness reduced C. albicans adhesion but promoted S. mutans colonization, emphasizing the role of SFE. Extended polymerization and optimized cleaning reduced microbial adhesion, highlighting the need for tailored processing to enhance microbial resistance and material integrity. (4) Manufacturing factors influenced microbial adhesion, with additive materials reducing the abundance of C. albicans but increasing the abundance of S. mutans, underscoring the importance of material adjustments and extended polymerization to enhance microbial resistance.

Investigation of the mechanical properties of lavender-reinforced heat-activated polymethyl methacrylate denture base resin

STATEMENT OF PROBLEM

The antimicrobial efficacy of lavender has been well evidenced. However, investigations into its impact on the mechanical properties of denture resins are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the flexural strength, impact strength, surface characteristics, roughness, elastic modulus, and yield strength of lavender-reinforced, heat-activated polymethyl methacrylate denture base resin.

MATERIAL AND METHODS

A total of 200 specimens were categorized into 5 groups based on 0, 0.5, 1.0, 1.5, and 2.0 wt% of dry lavender extract incorporated into heat-activated polymethyl methacrylate denture base resin powder. Unmodified resin served as the control group. Flexural strength, elastic moduli, and yield strength were determined with a universal testing machine, impact strength with an Izod impact tester, surface characteristics with scanning electron microscopy, and roughness with a profilometer. The data were statistically analyzed with 1-way ANOVA followed by Tukey post hoc tests for pairwise comparison within the groups (α=.05).

RESULTS

Compared with the control group, all the mechanical properties significantly improved with the addition of lavender (P<.001). The highest flexural, yield, and impact strengths and elastic modulus values were in the 2% group. Elevated surface roughness in 0.5, 1.0 and 1.5 wt% and a decline in roughness at 2 wt% were noted when compared with the control group.

CONCLUSIONS

The addition of lavender enhanced the flexural strength, yield strength, impact strength, elastic moduli, and decreased surface roughness when added at 2 wt%.

Denture microbiome shift and changes of salivary inflammatory markers following insertion of 3D printed removable partial PMMA denture: a pilot study

BACKGROUND

The aim of this study was to investigate the microbiome shift of denture biofilm formation, the incidence of Candida and changes of salivary inflammatory markers following insertion of 3-dimensional printed PMMA denture.

METHODS

This was a pilot study of 6 patients provided with 3D printed (test group) or conventionally heat-cured (control group) removable partial acrylic dentures followed up for 6 weeks. 3 denture swabs were collected at week 1, 3 and 6; and saliva samples were collected at baseline, week 1, 3 and 6 following denture insertion. Microbial DNA was isolated, and the 16S rRNA gene was amplified and sequenced to assess the denture microbiota. The presence of Candida was determined using PCR assay. The levels of salivary biomarkers lactoferrin (LTF) and histatin (HTN) were determined using ELISA.

RESULTS

Denture microbiome of both groups exhibited similar microbial compositions at weeks 1, 3 and 6. However, the percentage of Streptococcus in the test group was significantly lower at week 1 (p < 0.05). Greater bacterial diversity was detected in the test group (p < 0.05; pairwise Wilcoxon) after 6 weeks. The presence of Candida was only detected in one sample of the 3D printed denture (test group) after 6 weeks. The level of LTF biomarkers increased in both groups after 6 weeks, however, the level of HTN increased only in the control group.

CONCLUSIONS

Denture microbiome of both groups demonstrated similar microbial compositions. After 6 weeks, 3D printed denture demonstrated higher diversity with delayed microbiome shift compared to conventional heat cure dentures. 3D printed denture may be a viable alternative to conventional denture and it has a potential to delay microbial dysbiosis.

CLINICAL RELEVANCE

Among wearers, 3D printed denture can potentially reduce the risk of denture stomatitis. A greater diversity may delay or slow the transition of denture microbiome to dysbiosis.

Antimicrobial gel with silver vanadate and silver nanoparticles: antifungal and physicochemical evaluation

Aim: To develop a β-AgVO3 gel and evaluate its physicochemical stability and antifungal activity against Candida albicans.Materials & methods: The gel was prepared from the minimum inhibitory concentration (MIC) of β-AgVO3. The physicochemical stability was evaluated by centrifugation, accelerated stability (AS), storage (St), pH, syringability, viscosity and spreadability tests and antifungal activity by the agar diffusion.Results: The MIC was 62.5 μg/ml. After centrifugation, AS and St gels showed physicochemical stability. Lower viscosity and higher spreadability were observed for the higher β-AgVO3 concentration and the minimum force for extrusion was similar for all groups. Antifungal effect was observed only for the β-AgVO3 gel with 20xMIC.Conclusion: The β-AgVO3 gel showed physicochemical stability and antifungal activity.

Impact of adding zirconium oxide nanoparticles to the 3D printable acrylic resin base material for implant-retained overdentures: A clinical comparative parallel study

STATEMENT OF PROBLEM

Three-dimensionally (3D) printed acrylic resin base materials have been adopted in prosthetic dentistry. However, their mechanical and biological properties require improvement.

PURPOSE

The purpose of this clinical study was to evaluate the effect of adding zirconium oxide nanoparticles to a 3D printable acrylic resin base material for a 2-implant-retained complete mandibular overdenture in terms of peri-implant tissue health, surface roughness, and biofilm formation.

MATERIAL AND METHODS

Twenty edentulous patients were enrolled in this clinical parallel study. All patients received maxillary complete dentures opposing a 2-implant-retained mandibular overdenture. The participants were randomly divided into 2 equal groups according to the mandibular overdenture base material, nonmodified 3D printable acrylic resin (control group) or 3D printable acrylic resin base material modified with 3.0 wt% zirconium oxide nanoparticles (study group). Peri-implant tissue health and surface roughness were measured immediately at the insertion of the mandibular overdenture (T0), after 3 months (T1), and after 6 months (T2). Microbiological assessment of the denture base was done after 1 week, 1 month, 3 months, and 6 months of overdenture use. The data were analyzed using a statistical software program. The Wilcoxon signed-rank test, paired t test, and Fisher exact test were used to compare distributed data. The Mann Whitney U test and repeated measures ANOVA test were used to compare distributed data at different times (α=.05).

RESULTS

The gingival index (GI), plaque index (PI), probing depth (PD), and surface roughness values at the baseline, 3 months, and 6 months were statistically higher with the nonmodified compared with the modified group (P=.001). Regarding the microbiological analysis, the nonmodified group also had a statistically higher mean bacterial and Candida albicans count than the modified group (P<.05). No significant increase in the bacteria was found in the nonmodified group with time (P=.252), but, for the modified group, a statistically significant decrease in bacteria count was found with time (P<.001).

CONCLUSIONS

Adding zirconium oxide nanoparticles to a 3D printable acrylic resin base material was found to be promising. This addition improved the peri-implant tissue health and decreased surface roughness and biofilm formation.

Silver vanadate nanomaterial incorporated into heat-cured resin and coating in printed resin - Antimicrobial activity in two multi-species biofilms and wettability

OBJECTIVES

To incorporate the nanostructured silver vanadate decorated with silver nanoparticles (AgVO3) into denture base materials: heat-cured (HC) and 3D printed (3DP) resins, at concentrations of 2.5 %, 5 %, and 10 %; and to evaluate the antimicrobial activity in two multi-species biofilm: (1) Candida albicans, Candida glabrata, and Streptococcus mutans, (2) Candida albicans, Pseudomonas aeruginosa, and Staphylococcus aureus, and the wettability.

METHODS

The AgVO3 was added to the HC powder, and printed samples were coated with 3DP with AgVO3 incorporated. After biofilm formation, the antimicrobial activity was evaluated by colony forming units per milliliter (CFU/mL), metabolic activity, and epifluorescence microscopy. Wettability was assessed by the contact angles with water and artificial saliva.

RESULTS

In biofilm (1), HC-5 % and HC-10 % showed activity against S. mutans, HC-10 % against C. glabrata, and HC-10 % and 3DP-10 % had higher CFU/mL of C. albicans. 3DP-5 % had lower metabolic activity than the 3DP control. In biofilm (2), HC-10 % reduced S. aureus and P. aeruginosa, and HC-5 %, 3DP-2.5 %, and 3DP-5 % reduced S. aureus. 3DP incorporated with AgVO3, HC-5 %, and HC-10 % reduced biofilm (2) metabolic activity. 3DP-5 % and 3DP-10 % increased wettability with water and saliva.

CONCLUSION

HC-10 % was effective against C. glabrata, S. mutans, P. aeruginosa, and S. aureus, and HC-5 % reduced S. mutans and S. aureus. For 3DP, 2.5 % and 5 % reduced S. aureus. The incorporation of AgVO3 into both resins reduced the metabolic activity of biofilms but had no effect on C. albicans. The wettability of the 3DP with water and saliva increased with the addition of AgVO3.

CLINICAL SIGNIFICANCE

The incorporation of silver vanadate into the denture base materials provides antimicrobial efficacy and can prevent the aggravation of oral and systemic diseases. The incorporation of nanomaterials into printed resins is challenging and the coating is an alternative to obtain the inner denture base with antimicrobial effect.

Mechanical and microbiological properties of orthodontic resin modified with nanostructured silver vanadate decorated with silver nanoparticles (βAgVO3)

OBJECTIVE

To investigate the impact of incorporating the antimicrobial nanomaterial β-AgVO3 into orthodontic resin, focusing on degree of conversion, surface characteristics, microhardness, adhesion properties, and antimicrobial activity.

METHODS

The 3 M Transbond XT resin underwent modification, resulting in three groups (Control, 2.5% addition, 5% addition) with 20 specimens each. Fourier transform infrared spectroscopy assessed monomer conversion. Laser confocal microscopy examined surface roughness, and microhardness was evaluated using Knoop protocols. Shear strength was measured before and after artificial aging on 36 premolar teeth. Microbiological analysis against S. mutans and S. sanguinis was conducted using the agar diffusion method.

RESULTS

Degree of conversion remained unaffected by time (P = 0.797), concentration (P = 0.438), or their interaction (P = 0.187). The 5% group exhibited the lowest surface roughness, differing significantly from the control group (P = 0.045). Microhardness showed no significant differences between concentrations (P = 0.740). Shear strength was highest in the control group (P < 0.001). No significant differences were observed in the samples with or without thermocycling (P = 0.759). Microbial analysis revealed concentration-dependent variations, with the 5% group exhibiting the largest inhibition halo (P < 0.001).

CONCLUSIONS

Incorporating β-AgVO3 at 2.5% and 5% concentrations led to significant differences in surface roughness, adhesion, and antimicrobial activity. Overall, resin modification positively impacted degree of conversion, surface characteristics, microhardness, and antimicrobial activity. Further research is warranted to determine clinically optimal concentrations that maximize antimicrobial benefits while minimizing adverse effects on adhesion properties.

CLINICAL SIGNIFICANCE

Incorporating β-AgVO3 into orthodontic resin could improve patient quality of life by prolonging intervention durability and reducing the impact of cariogenic microorganisms. The study's findings also hold promise for the industry, paving the way for the development of new materials with antimicrobial properties for potential applications in the health sector.

Correlation between fluoride release, surface hardness and diametral tensile strength of restorative glass ionomer cements

Background

The aim of this study was to determine if there is a correlation between fluoride release, surface hardness, and diametral tensile strength of restorative glass ionomer cements (GICs).

Material and Methods

Conventional (Riva Self Cure) and resin-modified (Riva Light Cure) GICs were used. Thirty-four samples (ø 6 x 3 mm) were prepared for each cement. The kinetics of fluoride release (n=4) was evaluated over 28 days using a fluoride-selective electrode (ISE 4010-C00). The analysis of surface hardness (n=10) was performed using a microhardness tester (Shimadzu HMV-2000, Japan) with a Knoop indenter and a load of 25 gf for 30 seconds. The diametral tensile strength test (n=10) was conducted on a universal testing machine at a speed of 0.75 mm/min. Fluoride release data were analyzed by two-way repeated measures ANOVA and Bonferroni post hoc test, while independent t-test was used for other analyses (α=0.05).

Results

Overall, the groups showed higher fluoride release until day 7 and a progressive decrease until day 28. On day 1 and day 21, Riva Self Cure showed a higher level of release than Riva Light Cure (p=0.026). Riva Light Cure showed higher diametral tensile strength (p<0.0001) and surface hardness (p=0.034) than Riva Self Cure. A negative correlation was found, indicating that higher fluoride release is associated with lower surface hardness and diametral tensile strength.

Conclusion

Fluoride release and mechanical performance are related properties of GICs, and these properties exhibit different values depending on the type of material. Resin-modified GIC release less fluoride but exhibit better mechanical performance compared to conventional GIC. Key words:Diametral Tensile Strength, Fluoride, Glass Ionomer Cement, Surface Hardness.

Strategies for Preventing and Treating Oral Mucosal Infections Associated with Removable Dentures: A Scoping Review

Oral infections occur due to contact between biofilm rich in Candida albicans formed on the inner surface of complete dentures and the mucosa. This study investigated historical advances in the prevention and treatment of oral mucosal infection and identified gaps in the literature. Bibliographic research was conducted, looking at PubMed, Embase, Web of Science, and Scopus, where 935 articles were found. After removing duplicates and excluding articles by reading the title and abstract, 131 articles were selected for full reading and 104 articles were included. Another 38 articles were added from the gray literature. This review followed the PRISMA-ScR guidelines. The historical period described ranges from 1969 to 2023, in which, during the 21st century, in vitro and in vivo studies became more common and, from 2010 to 2023, the number of randomized controlled trials increased. Among the various approaches tested are the incorporation of antimicrobial products into prosthetic materials, the improvement of oral and denture hygiene protocols, the development of synthetic and natural products for the chemical control of microorganisms, and intervention with local or systemic antimicrobial agents. Studies report good results with brushing combined with sodium hypochlorite, and new disinfectant solutions and products incorporated into prosthetic materials are promising.

Adhesion of Candida Albicans to digital versus conventional acrylic resins: a systematic review and meta-analysis

BACKGROUND

The present systematic review and meta-analysis investigated the available evidence about the adherence of Candida Albicans to the digitally-fabricated acrylic resins (both milled and 3D-printed) compared to the conventional heat-polymerized acrylic resins.

METHODS

This study followed the guidelines of the Preferred Reporting Items for Systematic Review and Meta-analyses (PRISMA). A comprehensive search of online databases/search tools (Web of Science, Scopus, PubMed, Ovid, and Google Scholar) was conducted for all relevant studies published up until May 29, 2023. Only in-vitro studies comparing the adherence of Candida albicans to the digital and conventional acrylic resins were included. The quantitative analyses were performed using RevMan v5.3 software.

RESULTS

Fourteen studies were included, 11 of which were meta-analyzed based on Colony Forming Unit (CFU) and Optical Density (OD) outcome measures. The pooled data revealed significantly lower candida colonization on the milled digitally-fabricated compared to the heat-polymerized conventionally-fabricated acrylic resin materials (MD = - 0.36; 95%CI = - 0.69, - 0.03; P = 0.03 and MD = - 0.04; 95%CI = - 0.06, - 0.01; P = 0.0008; as measured by CFU and OD respectively). However, no differences were found in the adhesion of Candida albicans between the 3D-printed digitally-fabricated compared to the heat-polymerized conventionally-fabricated acrylic resin materials (CFU: P = 0.11, and OD: P = 0.20).

CONCLUSION

The available evidence suggests that candida is less likely to adhere to the milled digitally-fabricated acrylic resins compared to the conventional ones.

Antimicrobial activity of essential oils against biofilms formed in dental acrylic resin: a systematic review of in vitro studies

This study aimed to answer the question formulated according to the PICO strategy: 'Which essential oils show antimicrobial activity against biofilms formed on dental acrylic resin?' composed by population (dental acrylic resin), intervention (application of essential oils), comparison (denture cleansers, antifungal drugs, chlorhexidine, and oral mouthwashes), and outcome (antibiofilm activity). In vitro experimental studies evaluating the activity of EOs on biofilm formed on acrylic resin were included. PRISMA guidelines were followed, and the search was performed in the PubMed, Science Direct, Embase, and Lilacs databases and in the gray literature using Google Scholar and ProQuest in December 2023. A manual search of the reference lists of the included primary studies was performed. Of the 1467 articles identified, 37 were selected for full-text reading and 12 were included. Twelve EOs were evaluated, of which 11 showed activity against Candida spp., 3 against Staphylococcus aureus, and 1 against Pseudomonas aeruginosa. The EOs of Cymbopogon citratus, Cinnamomum zeylanicum, and Cymbopogon nardus showed higher action than chlorhexidine, C. nardus higher than Listerine, C. citratus higher than nystatin, and Melaleuca alternifolia higher than fluconazole and nystatin. However, chlorhexidine was more effective than Lippia sidoides and Salvia officinalis, sodium hypochlorite was more effective than L. sidoides, nystatin was more effective than Zingiber officinale, Amphotericin B more effective than Eucalyptus globulus and M. alternifolia. In conclusion, the EOs of C. zeylanicum, C. citratus, C. nardus, and M. alternifolia showed antimicrobial activity to reduce biofilm on dental acrylic resin.

Efficacy of an impression disinfectant solution after repeated use: An in vitro study

Statement of problem

There are very few studies using Benzalkonium Chloride (BAC) as an active disinfection agent for immersion techniques and there are no studies investigating the efficacy of repeated use of a disinfectant solution.

Purpose

This study evaluated an impression disinfectant by testing bacterial contamination of disinfectant batches used in a clinical setting after repeated use.

Materials and methods

Liquid samples were collected from impression disinfectant solutions used to disinfect dental impressions taken at a university dental clinic. The experimental samples (500 ml from 1 L of solution) were collected from teaching and professional clinics and the in-house commercial processing laboratory and stored at room temperature each day of clinic operation over five weeks. To determine to what extent the disinfectant efficacy of the active product decreased over time, the following tests were carried out: a. Inoculation b. Gram staining technique c. Matrix Assisted Laser Desorption/Ionization Mass spectrometry (MALDI- MS). Microbial growth was monitored and photographed. A culture revival was made from colonies grown on sheep blood agar, to isolate pure colonies incubated for 24 h at 37 °C. Each morphologically distinct type of colony was gram stained and MALDI spectrometry analysis was performed using the VITEK MS (BioMerieux Inc.).

Results

Evidence of growth of bacteria was detected in teaching clinics' samples, and no growth from the professional clinic or the commercial laboratory.

Conclusions

The study demonstrated that impression disinfectanat solution tested is effective against common oral bacteria, despite some rare species such as Bacillus circulans, Bacillus horneckiae, Bacillus altitudinis/pumilus and Bacillus cereus showing evidence of survival in solutions used for disinfection of impressions. However, in a high use teaching clinic environment its efficacy deteriorated. Though a second level disinfection protocol in the commercial laboratory-maintained impression disinfection.

Microbiological evaluation of conjunctival anopthalmic flora after using digital 3D-printed ocular prosthesis compared to conventional one: a randomized clinical trial

BACKGROUND

This study aims to assess the influence of using 3D-printed acrylic resin versus conventional Poly-methyl methacrylate (PMMA) for fabricating ocular prostheses on the biofilm and microbial flora of anophthalmic socket.

METHODS

A randomized controlled trial was designed as a parallel group study. Participants were allocated randomly into two groups: the control group, which received conventionally fabricated ocular prostheses (CG, n = 11), and the test group, which received digitally 3D-printed ocular prostheses (DG, n = 11). Microbiological analysis was conducted before prosthesis insertion and three months after using the ocular prosthesis. Swab samples were inoculated on blood agar, MacConkey's agar, and Sabouraud's dextrose agar (SDA) for isolating Gram-positive, Gram-negative, and fungal organisms, respectively. Subsequently, the plates were incubated at 37 degrees Celsius for 48 h. Additionally, a validated questionnaire was used for subjective clinical evaluation, including parameters such as comfort level, socket discharge, lacrimation, and frequency of lubrication for each ocular prosthesis patient in both groups.

RESULTS

Test group (DG, n = 11) exhibited a positive, though statistically insignificant, difference (p > 0.001) in microbial growth when compared to the control group (CG, n = 11). A statistically significant difference was observed in comfort levels between the two groups, with more comfort level within group II (test group) patients. While parameters such as discharge amount, discharge location, lacrimation and lubrication frequency displayed statistically insignificant differences between the two groups, all parameters showed improved results after three months of prosthesis use.

CONCLUSIONS

The choice of ocular prosthesis fabrication technique did not yield a statistically significant difference in anophthalmic flora. However, the 3D-printed acrylic resin, as an artificial eye material, displayed potential advantages in reducing the colonization of opportunistic pathogens. All subjective clinical evaluation parameters exhibited enhanced outcomes after three months of prosthesis use, emphasizing the need for an adaptation period during which patients complains are alleviated. In comparison with PMMA, 3D-printed acrylic resin showcased a certain degree of anti-colonization ability against pathogenic bacteria, along with a significant level of patient comfort, suggesting its potential as a promising material for ocular prostheses.

TRIAL REGISTRATION

This parallel double-blinded RCT has been registered at ClinicalTrials.gov with identification number: NCT05584865, 18/10/2022.

Different Polymers for the Base of Removable Dentures? Part I: A Narrative Review of Mechanical and Physical Properties

Even before considering their introduction into the mouth, the choice of materials for the optimization of the prosthesis depends on specific parameters such as their biocompatibility, solidity, resistance, and longevity. In the first part of this two-part review, we approach the various mechanical characteristics that affect this choice, which are closely related to the manufacturing process. Among the materials currently available, it is mainly polymers that are suitable for this use in this field. Historically, the most widely used polymer has been polymethyl methacrylate (PMMA), but more recently, polyamides (nylon) and polyether ether ketone (PEEK) have provided interesting advantages. The incorporation of certain molecules into these polymers will lead to modifications aimed at improving the mechanical properties of the prosthetic bases. In the second part of the review, the safety aspects of prostheses in the oral ecosystem (fragility of the undercuts of soft/hard tissues, neutral pH of saliva, and stability of the microbiota) are addressed. The microbial colonization of the prosthesis, in relation to the composition of the material used and its surface conditions (roughness, hydrophilicity), is of primary importance. Whatever the material and manufacturing process chosen, the coating or finishes dependent on the surface condition remain essential (polishing, non-stick coating) for limiting microbial colonization. The objective of this narrative review is to compile an inventory of the mechanical and physical properties as well as the clinical conditions likely to guide the choice between polymers for the base of removable prostheses.