Dental composite biodeterioration in the presence of oral Streptococci and extracellular metabolic products.

OBJECTIVE: Secondary caries is a primary cause of early restoration failure. While primary dental caries has been extensively researched, our knowledge about the impact of secondary caries on dental restorations is relatively limited. In this study, we examined how different clinically relevant microbially-influenced environments impact the degradation of nano-filled (FIL) and micro-hybrid (AEL) dental composites. METHODS: Material strength of two commercial dental composites was measured following incubation in aqueous media containing: i) cariogenic (Streptococcus mutans) and non-cariogenic bacteria (Streptococcus sanguinis) grown on sucrose or glucose, ii) abiotic mixtures of artificial saliva and sucrose and glucose fermentation products (volatile fatty acids and ethanol) in proportions known to be produced by these microorganisms, and iii) abiotic mixtures of artificial saliva and esterase, a common oral extracellular enzyme. RESULTS: Nano-filled FIL composite strength decreased in all three types of incubations, while micro-hybrid AEL composite strength only decreased significantly in biotic incubations. The strength of both composites was statistically significantly decreased in all biotic incubations containing both cariogenic and non-cariogenic bacteria beyond that induced by either abiotic mixtures of fermentation products or esterase alone. Finally, there were no statistically significant differences in composite strength decrease among the tested biotic conditions. CONCLUSIONS: The results show that conditions created during the growth of both cariogenic and non-cariogenic oral Streptococci substantially reduce commercial composite strength, and this effect warrants further study to identify the mechanism(s). CLINICAL SIGNIFICANCE: Dental biofilms of oral Streptococci bacteria significantly affect the mechanical strength of dental restorations.

Production of hybrid AgNPs - TEMPO-mediated oxidation cellulose composite from jackfruit peduncle agro-waste and its thermal management application in electronic devices.

The urgent need for eco-friendly and cost-effective cellulose paper substrates in thermal management for biomedical electronic devices has driven the exploration of agro-waste materials. In this study, jackfruit peduncle waste was utilized as a precursor to produce a hybrid of AgNPs-tempo-mediated oxidation cellulose strands (AgNPs-TOCS) through acid hydrolysis, TEMPO oxidation, and an in-situ generation process. The resulting hybrid AgNPs-TOCS composite exhibited a cylindrical cellulose structure with a diameter of 27.3 µm, on which spherical AgNPs with a diameter of 16.3 nm were embedded. This hybrid AgNPs-TOCS displayed an impressive inhibition zone diameter against E. coli bacteria (15.2 nm) and exhibited excellent thermal stability up to 269 °C. Furthermore, the AgNPs-TOCS composite paper substrate was fabricated using non-solvent techniques, and its mechanical, thermal, and electrical properties were investigated. This composite paper substrate exhibits good tensile strength (65 ± 2 MPa), in-plane thermal conductivity (5.8 ± 0.2 W/(m·K)), and electrical resistivity (0.0575 KΩ·m). These findings strongly suggest that this type of composite paper substrate holds promise for applications in thermal management within the field of biomedical electronics.

Biodegradation of Urethane Dimethacrylate-based materials (CAD/CAM resin-ceramic composites) and its effect on the adhesion and proliferation of Streptococcus mutans.

OBJECTIVE: To investigate whether urethane dimethacrylate (UDMA) -based dental restorative materials biodegrade in the presence of Streptococcus mutans (S. mutans) and whether the monomers affect the adhesion and proliferation of S. mutans in turn. METHODS: Cholesterol esterase and pseudocholinesterase-like activities in S. mutans were detected using p-nitrophenyl substrate. Two UDMA-based CAD/CAM resin-ceramic composites, Lava Ultimate (LU) and Vita Enamic (VE), and a light-cured UDMA resin block were co-cultured with S. mutans for 14 days. Their surfaces were characterized by scanning electron microscopy and laser microscopy, and the byproducts of biodegradation were examined by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS). Then, the antimicrobial components (silver nanoparticles with quaternary ammonium salts) were added to the UDMA resin block to detect whether the biodegradation was restrained. Finally, the effect of UDMA on biofilm formation and virulence expression of S. mutans was assessed. RESULTS: Following a 14-day immersion, the LU and UDMA resin blocks' surface roughness increased. The LU and VE groups had no UDMA or its byproducts discovered, according to the UPLC-MS/MS data, whereas the light-cured UDMA block group had UDMA, urethane methacrylate (UMA), and urethane detected. The addition of antimicrobial agents showed a significant reduction in the release of UDMA. Biofilm staining experiments showed that UDMA promoted the growth of S. mutans biofilm and quantitative real-time polymerase chain reaction results indicated that 50 µg/mL UDMA significantly increase the expression of gtfB, comC, comD, comE, and gbpB genes within the biofilm. CONCLUSIONS: UDMA in the light-cured resin can be biodegraded to produce UMA and urethane under the influence of S. mutans. The formation of early biofilm can be promoted and the expression of cariogenic genes can be up-regulated by UDMA. CLINICAL SIGNIFICANCE: This study focuses for the first time on whether UDMA-based materials can undergo biodegradation and verifies from a genetic perspective that UDMA can promote the formation of S. mutans biofilms, providing a reference for the rational use of UDMA-based materials in clinical practice.

Inorganic Compounds as Remineralizing Fillers in Dental Restorative Materials: Narrative Review.

Secondary caries is one of the leading causes of resin-based dental restoration failure. It is initiated at the interface of an existing restoration and the restored tooth surface. It is mainly caused by an imbalance between two processes of mineral loss (demineralization) and mineral gain (remineralization). A plethora of evidence has explored incorporating several bioactive compounds into resin-based materials to prevent bacterial biofilm attachment and the onset of the disease. In this review, the most recent advances in the design of remineralizing compounds and their functionalization to different resin-based materials' formulations were overviewed. Inorganic compounds, such as nano-sized amorphous calcium phosphate (NACP), calcium fluoride (CaF2), bioactive glass (BAG), hydroxyapatite (HA), fluorapatite (FA), and boron nitride (BN), displayed promising results concerning remineralization, and direct and indirect impact on biofilm growth. The effects of these compounds varied based on these compounds' structure, the incorporated amount or percentage, and the intended clinical application. The remineralizing effects were presented as direct effects, such as an increase in the mineral content of the dental tissue, or indirect effects, such as an increase in the pH around the material. In some of the reported investigations, inorganic remineralizing compounds were combined with other bioactive agents, such as quaternary ammonium compounds (QACs), to maximize the remineralization outcomes and the antibacterial action against the cariogenic biofilms. The reviewed literature was mainly based on laboratory studies, highlighting the need to shift more toward testing the performance of these remineralizing compounds in clinical settings.

Surface properties and Streptococcus mutans biofilm adhesion of ion-releasing resin-based composite materials.

OBJECTIVE: To evaluate the adhesion of Streptococcus mutans (S. mutans) and related surface properties of ion-releasing resin-based composite (RBC) restorative materials. METHODS: Two ion-releasing RBCs, Activa (ACT) and Cention-N (CN), were compared to a conventional RBC (Z350) and a resin-modified glass ionomer cement (Fuji-II-LC). Ten disk-shaped specimens were fabricated for each material (n = 40). After standardized surface polishing procedure, the surface properties of the specimens were evaluated using surface roughness measurements by a profilometer and hydrophobicity using water contact angle measurements. To assess bacterial adhesion, the number of S. mutans bacteria was calculated from colony-forming units (CFU). Confocal laser scanning microscope analysis was done for qualitative & quantitative assessment. The data were analyzed using One-way ANOVA followed by Tukey's post-hoc test to compare the mean values of surface roughness, water contact angle and CFU values. To compare the mean dead cell percentage Kruskal-Wallis rank test and Conover test were used. A p-value of ≤ 0.05 was used to report the statistical significance. RESULTS: Z350 and ACT had the smoothest surfaces, followed by CN, and the roughest surface was seen in FUJI-II-LC. The lowest water contact angles were seen in CN, and Z350, and the highest were in ACT. S. mutans counts were the highest in ACT and the lowest in Z350 and CN. CN and Fuji-II-LC registered the highest percentage of dead bacterial cells, while the lowest were in ACT. SIGNIFICANCE: Surface properties did not significantly influence bacterial adhesion. More S. mutans bacteria accumulated on ACT than on the nanofilled composite and on CN. CN had antibacterial effects against Streptococcus mutans biofilms.

Comparative evaluation of osteogenic cell growth on titanium surface and titanium coated with boron nitride surface: An in vitro study.

Context: To promote better biological response and osseointegration continuous research is going on to modify the titanium (Ti) implant surface for successful implant treatment modality. Aims: This study aims to evaluate the osteogenic cell growth upon the uncoated Ti discs and boron nitride (BN) coated Ti to assess osseointegration and clinical success of dental implants. Settings and Design: This is an descriptive experimental study which includes coating of uncoated titanium alloy suraface with boron nitride in the form of hexagonal boron nitride sheets. Than comparative evaluation of osteogenic cell growth upon both coated and uncoated titanium surfaces was done using specific cell growth determinants. Materials and Methods: In this descriptive experimental study, both BN-coated and uncoated Ti discs were assessed for osteogenic cell growth using 3-(4, 5-dimethyl thiazolyl-2)-2, 5-diphenyltetrazolium bromide assay, 4',6-diamidino-2-phenylindole, is a fluorescent stain assay, and cell adhesion assay. Statistical Analysis Used: As this study is a descriptive experimental analysis between two variables only so there is no need of statistical analysis or p-value. Results: Overall good cell adhesion, cell differentiation, and cell proliferation occurred in the BN-coated Ti discs as compared to uncoated Ti discs. Conclusions: To promote osseointegration of dental implants, surface coating with BN proved to be an effective approach toward better osseointegration and long-duration success of dental implants as a single unit or implant-supported prosthesis BN which is a biocompatible graphene material with advantages in chemical and thermal stability. BN promoted better osteogenic cell adhesion, differentiation, and proliferation. Hence, it can be used as a new promising Ti implant surface-coating material.

In vitro investigation of the impact of contemporary restorative materials on cariogenic bacteria counts and gene expression.

OBJECTIVES: The aim of this study was to compare the antibacterial effect of different fluoride-containing and bioactive restorative materials, and their effect on the expression of specific biofilm-associated genes and therefore the caries process. MATERIALS AND METHODS: The restorative materials utilized in this study included: 1. Filtek Z250, 2. Fuji II LC, 3. Beautifil II, 4. ACTIVA, and 5. Biodentine. For each material, disc-shaped specimens were prepared. The inhibitory effects against Streptococcus mutans, Lactobacillus acidophilus, and Leptotrichia shahii were tested. After incubation for 24 h and 1 week, colony-forming units (CFUs) were enumerated. From the plates dedicated for biomass quantification and RNA purification, the target glucosyltransferase B (gtfB) and glucan-binding protein B (gbpB) genes were chosen for S. mutans. For L. acidophilus, a gene involved in exopolysaccharide synthesis (epsB) was chosen. RESULTS: Except for Filtek Z250, all four materials showed statistically significant inhibitory effects on the biofilms of all three species. When biofilms were grown in the presence of the same four materials, the expression of S. mutans gtfB and gbpB genes, was significantly reduced. For L. acidophilus, the decrease in the expression of gtfB gene in the presence of ACTIVA was the highest change seen. The epsB gene expression also decreased. Compared to fluoride-releasing materials, bioactive materials had more inhibitory effect against L. acidophilus, both at 24 h and 1 week. CONCLUSIONS: Both fluoride releasing and bioactive materials exhibited a significant inhibitory effect on the biofilm growth. The expression of the targeted biofilm-associated genes was downregulated by both material groups. CLINICAL SIGNIFICANCE: The findings from this study give insight into the antibacterial effect of fluoride-containing and bioactive materials which would help to reduce the chances for secondary caries and therefore increase the lifetime of dental restorations placed for patients.

The evaluation of prepared microstructure pattern by carbon-dioxide laser on zirconia-based ceramics for dental implant application: an in vitro study.

3 mol% yttria-stabilized zirconia ceramics have been gaining attention as promising restorative materials that are extensively used in dental implant applications. However, implant failure due to bacterial infection and its bioinert surface slow osseointegration in vivo, which are significant issues in clinical applications. In this work, surface modification was achieved using a continuous wave carbon dioxide laser at a wavelength of 10.6 µm in an air atmosphere. Changes in the surface characteristics were evaluated using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and 2D roughness and hardness tests. The bioactivity of the laser-treated samples was studied by examining their behavior when immersed in the SBF solution. The formation of the hydroxyapatite phase on the laser-treated sample was much more uniform than that of its untreated counterparts. The antibacterial properties of surface-treated zirconia ceramics against Streptococcus mutans and Escherichia coli bacteria were rigorously examined. These results indicate that the laser-induced nanoscale grooves significantly improved antibacterial activity by creating hydrophobic surfaces. The cellular response was evaluated for 7 days on microtextures on the zirconia surfaces and an untreated sample with MC3T3-E1 pre-osteoblast cell line cultured under basal conditions. Surface topography was revealed to improve the cellular response with increased metabolic activity compared to the untreated sample and showed modulation of cell morphology for the entire time. These results suggest that laser modification can be an appropriate non-contact method for designing nanoscale microtextures to improve the biological response and antibacterial behavior of zirconia ceramics in restorative dentistry.

Stabilization of Apatite Coatings on PPENK Surfaces by Mechanical Interlocking to Promote Bioactivity and Osseointegration In Vivo.

Apatite coatings with high stability can effectively improve the surface bioactivity and osteogenic activity of implant materials. In clinical practice, the ability of apatite coatings to bond with the substrate is critical to the effect of implants. Here, we propose a strategy to construct a three-dimensional (3D) nanoporous structure on the surface of a poly(phthalazinone ether nitrile ketone) (PPENK) substrate and introduce a polydopamine (PDA) coating with grafted phosphonate groups to enhance the overall deposition of a bone-like apatite coating in the 3D nanoporous structure during mineralization. This method leads to a mechanical interlocking between the apatite coating and the substrate, which increases the stability of the apatite coating. The apatite coating confers a better bioactive surface to PPENK and also promotes osteogenic differentiation and adhesion of MC3T3-E1 osteoblasts in vitro. The samples are then implanted into rat femurs to characterize in vivo osseointegration. Micro-CT data and histological staining of tissue sections reveal that PPENK with a stable apatite coating induces less fibrous capsule formation and no inflammatory response and promotes osteogenic differentiation and bone-bonding strength. This enhances the long-term use of PPENK implant materials and shows great potential for clinical application as orthopedic implants.

N-Acetyl Cysteine-Mediated Improvements in Dental Restorative Material Biocompatibility.

The fibroblast-rich gingival tissue is usually in contact with or adjacent to cytotoxic polymer-based dental restoration materials. The objective of this study was to determine whether the antioxidant amino acid, N-acetyl cysteine (NAC), reduces the toxicity of dental restorative materials. Human oral fibroblasts were cultured with bis-acrylic, flowable composite, bulk-fill composite, self-curing acrylic, and titanium alloy test specimens. Cellular behavior and function were analyzed on and around the materials. Impregnation of the bulk-fill composite and self-curing acrylic with NAC reduced their toxicity, improving the attachment, growth, and function of human oral fibroblasts on and around the materials. These mitigating effects were NAC dose dependent. However, NAC impregnation of the bis-acrylic and flowable composite was ineffective, with no cells attaching to nor around the materials. Although supplementing the culture medium with NAC also effectively improved fibroblast behaviors, direct impregnation of materials with NAC was more effective than supplementing the cultures. NAC-mediated improvements in fibroblast behavior were associated with reduced production of reactive oxygen species and oxidized glutathione together with increased glutathione reserves, indicating that NAC effectively directly scavenged ROS from materials and reinforced the cellular antioxidant defense system. These results establish a proof of concept of NAC-mediated improvements in biocompatibility in the selected dental restorative materials.

Impact of curcumin loading on the physicochemical, mechanical and antimicrobial properties of a methacrylate-based experimental dental resin.

Oral biofilms are directly linked to one of the most common chronic human diseases, dental caries. Resin-based dental materials have significant potential to replace amalgam, however they lack sufficient antimicrobial power. This innovative study investigates a curcumin-loaded dental resin which can be utilized in an antimicrobial photodynamic therapy (aPDT) approach. The study evaluated the effects of curcumin loading on resin physicochemical, mechanical, and adhesive properties, as well as the antimicrobial response associated with blue light activation. Preliminary tests involving degree of conversion (DC) and sample integrity determined the optimal loading of curcumin to be restricted to 0.05 and 0.10 wt%. These optimal loadings were tested for flexural strength (FS), water sorption (WS) and solubility (SL), shear bond strength to dentin (SBS), and viability of Streptococcus mutans under 14.6 J/cm2 blue light or dark conditions, in 6 h and 24 h biofilms. The results demonstrated that 0.10 wt% curcumin had minimal impact on either FS or SBS, but detectably increased WS and SL. A 2 log10 (CFU/mL) reduction in S. mutans after light application in both 6 h and 24 h biofilms were corroborated by CLSM imaging and highlighted the significant potential of this novel aPDT approach with resin-based dental materials.

Dental restorative materials containing quaternary ammonium compounds have sustained antibacterial action.

BACKGROUND: This narrative review addresses dental restorative materials with sustained antibacterial action, especially those containing quaternary ammonium compounds. Secondary caries occurs around restorations, causing further loss of mineral and breakdown of the restoration. Lesions adjacent to restorations account for more than 40% of needed restorations. Restorative materials with antibacterial properties will potentially solve this problem. TYPES OF STUDIES REVIEWED: Several groups are researching composite restorative materials that incorporate antibacterial agents. These agents are mostly exhausted over time. Newer studies involve materials that incorporate antibacterial microparticles that remain active and do not leach out. RESULTS: One such antibacterial agent, quaternary ammonium coupled with inorganic silica into minute particles (QASi), has been studied in the laboratory and in humans. QASi particles incorporated into dental materials retain their antibacterial action over time without leaching or loss of activity. A clinical in situ study in humans using dental composite containing QASi resulted in highly significantly less demineralization in the adjacent enamel than the control composite material. CONCLUSIONS AND PRACTICAL IMPLICATIONS: Dental restorative materials that contain QASi have sustained antibacterial properties, have mechanical properties comparable to those of presently marketed materials, and have been cleared by the US Food and Drug Administration. Clinical studies have shown that composites incorporating QASi have the potential to markedly reduce the occurrence of caries around restorations. Because caries around restorations is a major problem, restorative materials with sustained antibacterial properties will have an important effect in reducing secondary caries around restorations.

Anti-inflammatory properties of S53P4 bioactive glass implant material.

OBJECTIVES: To assess whether the dissolution products of S53P4 bioactive glass (BG) affect cellular response of macrophages and clinically relevant peri­implant cell populations to dental implant particles in vitro. Cells chosen were human gingival fibroblasts (HGFs), osteoblasts and bone marrow derived stromal cells (HBMSCs). METHODS: Melt-derived S53P4 bioactive glass were prepared. HGFs, Saos-2 human osteoblastic cell line, HBMSCs and macrophages, derived from THP-1 human monocytic cell line, were cultured in the presence of particles from commercially pure titanium (Ti-CP4), grade 5 titanium alloy (Ti-6Al-4V), titanium-zirconium alloy (Ti-15Zr) or zirconia (Zr) (with respective diameters of 34.1 ± 3.8, 33.3 ± 4.4, 97.8 ± 8.2 and 71.3 ± 6.1 µm) with or without S53P4 dissolution products (conditioned media contained 327.30 ± 2.01 ppm Ca, 51.34 ± 0.41 ppm P and 61.48 ± 1.17 ppm Si, pH 8.01 ± 0.21). Inflammatory and macrophage polarisation markers including TNF-ɑ, IL-1, IL-6 and CD206 were quantified using enzyme-linked immunosorbent assay (ELISA). RESULTS: The presence of Ti-6Al-4V implant particles significantly induced the expression of pro-inflammatory markers in all tested cell types. S53P4 BG dissolution products regressed the particle induced up-regulation of pro-inflammatory markers and, appeared to suppress M1 macrophage polarisation. CONCLUSIONS: Implant particles, Ti-6Al-4V in particular, resulted in significant inflammatory responses from cells. S53P4 BG may possess anti-inflammatory properties and potentially mediate macrophage polarisation behaviour. CLINICAL SIGNIFICANCE: The findings highlight that the use and benefits of BG is a promising field of study. Authors believe more collective efforts are required to fully understand the reliability, efficiency and exact mechanisms of action of BG in the search for new generation of treatment modalities in dentistry.

Effects of Surface Prereacted Glass on Saliva-Derived Polymicrobial Biofilms in an Active Attachment Biofilm Model.

Bioactive restorative materials are being developed to either influence the de/remineralization balance of the dental hard tissues locally or to release components that interact with the oral microbiota. Surface prereacted glass (S-PRG, Shofu, Japan) is a material that may influence both processes. S-PRG releases fluoride, which can interact with the de/remineralization process, and a range of other compounds that may influence the oral microbiota. In the current study, several experiments were performed to investigate the potential of S-PRG to influence both the growth and lactic acid production of saliva-derived polymicrobial biofilms. Biofilm formation was studied using the Amsterdam Active Attachment model. An eluate of the S-PRG particles was tested by adding it to the growth medium or by exposing the biofilms to it for 1 h. The effect of S-PRG particles was tested by adding the particles to the growth medium. The current experiments showed that the presence of S-PRG eluate in the medium influenced biofilm growth and lactic acid production even at low concentrations. The composition of the biofilms changed in the presence of S-PRG eluate, even at concentrations of S-PRG eluate at which biofilm viability was not affected. Treatment of developing biofilms with S-PRG eluate did neither show an effect on biofilm viability nor on lactic acid production. The addition of S-PRG particles to the growth medium resulted in both a lower biofilm viability and lower lactic acid production, indicating that the release of ions from the particles was fast enough to influence biofilm formation. From the current experiments, it can be concluded that S-PRG has the potential to influence biofilm growth, but the presence of the released ions during biofilm formation is required to show an effect.

In-vitro models of biocompatibility testing for restorative dental materials: From 2D cultures to organs on-a-chip.

Dental caries is a biofilm-mediated, diet-modulated, multifactorial and dynamic disease that affects more than 90% of adults in Western countries. The current treatment for decayed tissue is based on using materials to replace the lost enamel or dentin. More than 500 million dental restorations are placed annually worldwide, and materials used for these purposes either directly or indirectly interact with dentin and pulp tissues. The development and understanding of the effects of restorative dental materials are based on different in-vitro and in-vivo tests, which have been evolving with time. In this review, we first discuss the characteristics of the tooth and the dentin-pulp interface that are unique for materials testing. Subsequently, we discuss frequently used in-vitro tests to evaluate the biocompatibility of dental materials commonly used for restorative procedures. Finally, we present our perspective on the future directions for biological research on dental materials using tissue engineering and organs on-a-chip approaches. STATEMENT OF SIGNIFICANCE: Dental caries is still the most prevalent infectious disease globally, requiring more than 500 million restorations to be placed every year. Regrettably, the failure rates of such restorations are still high. Those rates are partially based on the fact that current platforms to test dental materials are somewhat inaccurate in reproducing critical components of the complex oral microenvironment. Thus, there is a collective effort to develop new materials while evolving the platforms to test them. In this context, the present review critically discusses in-vitro models used to evaluate the biocompatibility of restorative dental materials and brings a perspective on future directions for tissue-engineered and organs-on-a-chip platforms for testing new dental materials.

Occlusion effects of bioactive glass and hydroxyapatite on dentinal tubules: a systematic review.

OBJECTIVE: Bioactive glass and hydroxyapatite are biocompatible materials used as an adjunct to various dental materials. The present study aimed to evaluate the occlusion effects of bioactive glasses and hydroxyapatite on dental tubules. MATERIALS AND METHODS: We searched the PubMed/Medline, Embase, and Web of Science databases for the relevant records. The methodological quality of the studies was assessed by an accepted quality assessment tool. RESULTS: From the electronic databases, 372 articles were retrieved. After evaluating the records, 35 in vitro studies were included. The studies revealed a low risk of bias. The primary outcomes from bioactive glass studies demonstrated the potential efficacy of both bioactive glass and hydroxyapatite in dentin tubule occlusion compared to the control. CONCLUSION: The current systematic review showed that bioactive glass and hydroxyapatite could effectively occlude the dentinal tubules. Thus, desensitizing agents containing bioactive glass and hydroxyapatite can be used to manage dentin hypersensitivity (DH). However, long-term follow-up clinical trials are required in the future before definitive recommendations can be made. CLINICAL RELEVANCE: This work achieved a satisfactorily systematic review for assessing desensitizing agents containing bioactive glass and hydroxyapatite in dentine hypersensitivity treatments recommended for clinical practice and research.

Physical-chemical and microbiological performances of graphene-doped PMMA for CAD/CAM applications before and after accelerated aging protocols.

OBJECTIVES: Innovative, nanotechnologies-featuring dental materials for CAD/CAM applications are becoming available. However, the interaction with the oral environment poses critical challenges to their longevity. The present study evaluated specific physical-chemical properties and antimicrobial potential of a CAD/CAM graphene-doped resin before and after accelerated aging protocols. METHODS: Graphene nanofibers (GNF)-doped (<50 ppm) PMMA (GPMMA) and control PMMA CAD/CAM discs were used. Specimens underwent aging procedures of their bulk (thermo- and load-cycling) and surface (24 h-immersion in absolute ethanol), then they were tested for flexural strength, ultimate tensile strength, sorption/solubility, and methyl-methacrylate elution. Surface characterization included x-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, surface roughness, microhardness, and scanning electron microscopy (SEM). Adherence of Streptococcus mutans and Candida albicans, and biofilm formation (continuous-flow bioreactor) by the same strains and an artificial oral microcosm were investigated. RESULTS: GNF-doping improved the physical-chemical bulk properties of the PMMA resin. Surface aging reduced microhardness and increased the roughness of both test and control materials. Surfaces displayed signs of swelling and degradation at SEM. Microbiological data of non-aged surfaces showed that GNF-doping significantly reduced biofilm formation by all tested strains despite having no impact on microbial adherence. After aging, microbial adherence was higher on GPMMA surfaces, while biofilm formation was not promoted. SIGNIFICANCE: GNF-doping improved the material's performance and influenced its antimicrobial potential. This strategy seems a valuable option to overcome the effects of surface degradation induced by aging on the antimicrobial potential of PMMA resin.

Effects of resin materials dedicated for additive manufacturing of temporary dental restorations on human gingival keratinocytes.

OBJECTIVE: This study investigated the effect of eluates of conventional and 3D-printed resin materials for manufacturing temporary dental restorations on gingival keratinocytes. METHODS: Three-dimensional (3D)-printed resin materials: 3Delta temp (Deltamed), NextDent MFH (Nextdent), Freeprint temp (Detax), GC temp (GC), were compared to Grandio disc (Voco) and Luxatemp (DMG). Human gingival keratinocytes (IHGKs) were exposed to eluates of the materials and XTT assays were performed at 24 h, 48 h, 72 h, or 144 h. For quantification of the proinflammatory response, the protein amount of IL-6 and 8 was determined in the supernatants using ELISA. One-way ANOVA with post hoc analysis was used to compare differences in cell viability and IL-6 and IL-8 levels between groups. RESULTS: At 24 h, and more remarkably at 48 h, a significant decrease in cell viability occurred for the 3D-printed materials compared to the untreated IHGKs, but also compared to Grandio disc and Luxatemp. Except for the expression of IL-8 in presence of the eluate of Grandio disc at 24 and 48 h, all tested materials caused attenuation of IL-6 and 8 from IHGKs for any observation period. CONCLUSIONS: The materials for additive manufacturing affect cell proliferation differently than the subtractive manufactured material Grandio disc and the conventional material Luxatemp. CLINICAL SIGNIFICANCE: In comparison to conventional and subtractive manufactured restorations, 3D printed temporary restorations might induce more negative effects on the gingival and probably also on pulpal health since viability and the proinflammatory response of oral keratinocytes are more intensively affected by these materials.

Novel rechargeable nanostructured calcium phosphate crown cement with long-term ion release and antibacterial activity to suppress saliva microcosm biofilms.

OBJECTIVE: Resin cements with remineralizing and antibacterial properties are favorable for inhibition of caries. The objectives of this study were: (1) to investigate the capability of the novel dimethylaminohexadecyl-methacrylate (DMAHDM) and nano-sized amorphous calcium phosphate (NACP) containing cement to reduce saliva microcosm biofilm, and (2) to investigate the long-term ion release, recharge, and re-release of DMAHDM-NACP cement. METHODS: Pyromellitic glycerol dimethacrylate (PMGDM) and ethoxylated bisphenol-A-dimethacrylate (EBPADMA) were used to make PEHB monomer. Five cements were fabricated: (1) PEHB+0%NACP+0%DMAHDM (experimental control); (2) PEHB+25%NACP+0%DMAHDM, (3) PEHB+25%NACP+0%DMAHDM; (4) PEHB+25%NACP+3%DMAHDM; (5) PEHB+25%NACP+5%DMAHDM. RelyX luting cement was used as commercial control. Colony-forming units (CFU), lactic acid production, metabolic activities, and minimum inhibitory concentration (MIC) were performed. Long-term Calcium (Ca) and phosphate (P) ion release, recharge, and re-release were assessed. RESULTS: Compared to experimental and commercial controls, the NACP-DMAHDM cement significantly reduced CFU biofilm by 2-3 orders of magnitude, metabolic activities from 0.24±0.06 A540/cm2 to 0.03±0.01 A540/cm2, and lactic acid production from 27.7 ± 2.5 mmol/L to 5.4 ± 2.1 mmol/L (n = 6) (p<0.05). The DMAHDM showed an MIC value of 0.03 mg/L. However, when the DMAHDM was combined with PMGDM monomer, the MIC was greater than DMAHDM alone. The ion concentrations for the experimental groups significantly increased over time (1-84 days), indicating continuous ion release (n = 3) (p<0.05). Increasing the DMAHDM mass fraction from 0% to 5% and 3% to 5% significantly enhanced ion recharge and re-release at the third cycle (p<0.05). CONCLUSIONS: Incorporating DMAHDM and NACP into resin-based crown cement provides strong antibacterial action against saliva microcosm biofilm and presents a high level of Ca and P ion recharge abilities, exhibiting long-term Ca and P ion release and remineralization potential. CLINICAL SIGNIFICANCE: Resin based cement containing NACP and DMAHDM were developed with remineralizing and potent antibacterial effects. This cement formulation showed ion release and remineralization potential and are promising formulations to inhibit the incidence of recurrent caries and could promote remineralization and be sustainable for the long term.

Raffinose Inhibits Streptococcus mutans Biofilm Formation by Targeting Glucosyltransferase.

Streptococcus mutans is a representative biofilm-forming bacterium that causes dental caries through glucosyltransferase (GTF) activity. Glucans are synthesized from sucrose by GTFs and provide binding sites for S. mutans to adhere tightly to the tooth enamel. Therefore, if a novel compound that interferes with GTF function is developed, biofilm formation control in S. mutans would be possible. We discovered that raffinose, an oligosaccharide from natural products, strongly inhibited biofilm formation, GTF-related gene expression, and glucan production. Furthermore, biofilm inhibition on saliva-coated hydroxyapatite discs through the reduction of bacterial adhesion indicated the applicability of raffinose in oral health. These effects of raffinose appear to be due to its ability to modulate GTF activity in S. mutans. Hence, raffinose may be considered an antibiofilm agent for use as a substance for oral supplies and dental materials to prevent dental caries. IMPORTANCE Dental caries is the most prevalent infectious disease and is expensive to manage. Dental biofilms can be eliminated via mechanical treatment or inhibited using antibiotics. However, bacteria that are not entirely removed or are resistant to antibiotics can still form biofilms. In this study, we found that raffinose inhibited biofilm formation by S. mutans, a causative agent of dental caries, possibly through binding to GtfC. Our findings support the notion that biofilm inhibition by raffinose can be exerted by interference with GTF function, compensating for the shortcomings of existing commercialized antibiofilm methods. Furthermore, raffinose is an ingredient derived from natural products and can be safely utilized in humans; it has no smell and tastes sweet. Therefore, raffinose, which can control S. mutans biofilm formation, has been suggested as a substance for oral supplies and dental materials to prevent dental caries.