Optical effects of graphene addition on adhesives for orthodontic lingual retainers.

The objective of this study was to determine the effects on the colour of adding increasing concentrations of graphene to orthodontic fixed retainer adhesives and to evaluate changes in optical transmission during light curing and the resultant degree of conversion. Two different types of adhesives commonly used for fixed retainers were investigated: A packable composite (Transbond) and a flowable composite (Transbond Supreme). Graphene was added to the adhesives in three different concentrations (0.01, 0.05, and 0.1 wt%). Adhesives without graphene addition were set as control groups. A Minolta colourimeter was used to measure the colour and translucency parameters. Irradiance transmitted during curing was quantified using MARC Light Collector. Fourier-transform infrared spectroscopy was used to record degree of conversion. Data were statistically analysed with the Student's t-test and one-way ANOVA with Tukey's tests (α = 0.05). The findings showed that incorporating graphene darkened the adhesive colour significantly and reduced translucency. As the graphene concentration reached 0.1 wt%, samples became opaque; yet, no adverse effect on degree of conversion was observed. The addition of graphene reduces optical transmission of lingual retainer adhesives; the effect increases with graphene concentration.

Biofabrication, biochemical profiling, and in vitro applications of salivary gland decellularized matrices via magnetic bioassembly platforms.

Trending three-dimensional tissue engineering platforms developed via biofabrication and bioprinting of exocrine glands are on the rise due to a commitment to organogenesis principles. Nevertheless, a proper extracellular matrix (ECM) microarchitecture to harbor primary cells is yet to be established towards human salivary gland (SG) organogenesis. By using porcine submandibular gland (SMG) biopsies as a proof-of-concept to mimic the human SG, a new decellularized ECM bioassembly platform was developed herein with varying perfusions of sodium dodecyl sulfate (SDS) to limit denaturing events and ensure proper preservation of the native ECM biochemical niche. Porcine SMG biopsies were perfused with 0.01%, 0.1%, and 1% SDS and bio-assembled magnetically in porous polycarbonate track-etched (PCTE) membrane. Double-stranded DNA (dsDNA), cell removal efficiency, and ECM biochemical contents were analyzed. SDS at 0.1% and 1% efficiently removed dsDNA (< 50 ng/mg) and preserved key matrix components (sulfated glycosaminoglycans, collagens, elastin) and the microarchitecture of native SMG ECM. Bio-assembled SMG decellularized ECM (dECM) perfused with 0.1-1% SDS enhanced cell viability, proliferation, expansion confluency rates, and tethering of primary SMG cells during 7 culture days. Perfusion with 1% SDS promoted greater cell proliferation rates while 0.1% SDS supported higher acinar epithelial expression when compared to basement membrane extract and other substrates. Thus, this dECM magnetic bioassembly strategy was effective for decellularization while retaining the original ECM biochemical niche and promoting SMG cell proliferation, expansion, differentiation, and tethering. Altogether, these outcomes pave the way towards the recellularization of this novel SMG dECM in future in vitro and in vivo applications.

A critical analysis of research methods and biological experimental models to study pulp regeneration.

With advances in knowledge and treatment options, pulp regeneration is now a clear objective in clinical dental practice. For this purpose, many methodologies have been developed in attempts to address the putative questions raised both in research and in clinical practice. In the first part of this review, laboratory-based methods will be presented, analysing the advantages, disadvantages, and benefits of cell culture methodologies and ectopic/semiorthotopic animal studies. This will also demonstrate the need for alignment between two-dimensional and three-dimensional laboratory techniques to accomplish the range of objectives in terms of cell responses and tissue differentiation. The second part will cover observations relating to orthotopic animal studies, describing the current models used for this purpose and how they contribute to the translation of regenerative techniques to the clinic.

Streptococcus mutans forms xylitol-resistant biofilm on excess adhesive flash in novel ex-vivo orthodontic bracket model.

INTRODUCTION: During orthodontic bonding procedures, excess adhesive is invariably left on the tooth surface at the interface between the bracket and the enamel junction; it is called excess adhesive flash (EAF). We comparatively evaluated the biofilm formation of Streptococcus mutans on EAF produced by 2 adhesives and examined the therapeutic efficacy of xylitol on S mutans formed on EAF. METHODS: First, we investigated the biofilm formation of S mutans on 3 orthodontic bracket types: stainless steel preadjusted edgewise, ceramic preadjusted edgewise, and stainless steel self-ligating. Subsequently, tooth-colored Transbond XT (3M Unitek, Monrovia, Calif) and green Grengloo (Ormco, Glendora, Calif) adhesives were used for bonding ceramic brackets to extracted teeth. S mutans biofilms on EAF produced by the adhesives were studied using the crystal violet assay and scanning electron microscopy. Surface roughness and surface energy of the EAF were examined. The therapeutic efficacies of different concentrations of xylitol were tested on S mutans biofilms. RESULTS: Significantly higher biofilms were formed on the ceramic preadjusted edgewise brackets (P = 0.003). Transbond XT had significantly higher S mutans biofilms compared with Grengloo surfaces (P = 0.007). There was no significant difference in surface roughness between Transbond XT and Grengloo surfaces (P >0.05). Surface energy of Transbond XT had a considerably smaller contact angle than did Grengloo, suggesting that Transbond XT is a more hydrophilic material. Xylitol at low concentrations had no significant effect on the reduction of S mutans biofilms on orthodontic adhesives (P = 0.016). CONCLUSIONS: Transbond XT orthodontic adhesive resulted in more S mutans biofilm compared with Grengloo adhesive on ceramic brackets. Surface energy seemed to play a more important role than surface roughness for the formation of S mutans biofilm on EAF. Xylitol does not appear to have a therapeutic effect on mature S mutans biofilm.

Effects of chrondro-osseous regenerative compound associated with local treatments in the regeneration of bone defects around implants: an in vivo study.

OBJECTIVES: The objective of this study was to evaluate the use of a chondroitin sulfate and glycosaminoglycan-based chrondro-osseous regenerative compound (CORC) with different local treatments for bone regeneration in dehiscence defects. The hypothesis is that CORC can enhance bone regeneration with or without local treatment. MATERIALS AND METHODS: Twelve mongrel dogs received four implants each in the right femur. Bony defects (4-mm height × 4-mm width) were created and locally treated as follows: reabsorbable membrane (Mem), hidroxyapatite (HA), hydroxyapatite covered with membrane (HA+Mem), or left untreated (Con). Six dogs received one pill of the CORC daily. After 90 days, the implants were retrieved, and histological sections were obtained. The height of bone formation, new bone area (NBA), and bone to implant contact (BIC) within the threads were evaluated to assess the effects of the use of CORC to promote bone regeneration in the defects. Results were statistically analyzed using ANOVA and Tukey's test with 5% significance level. RESULTS: CORC was not capable to increase the height of bone formation, NBA, and BIC. When the local treatments were analyzed regardless of the use of CORC, HA+Mem and Ha presented higher BIC and height of bone formation. There was no difference for NBA among the local treatments. CONCLUSIONS: The hypothesis was rejected since the use of CORC has not increased any of the parameters evaluated. CLINICAL RELEVANCE: Dehiscence-like defects can compromise soft tissue support and result in loss of periodontal health and implants. Hydroxyapatite can induce bone regeneration in the defects created. CORC in the formulation used in this study did not promote further bone regeneration in dehiscence-like defects.

Structural reinforcement and sealing ability of temporary fillings in premolar with class II mod cavities.

AIM: To evaluate the capability to reinforce tooth structure and sealing ability of temporary filling materials in premolars with MOD cavities. The hypothesis is that temporary filling materials can concomitantly prevent microleakage and increase fracture resistance. MATERIALS AND METHODS: Premolars received root canal treatment and MOD cavities. Cavities were restored with non- eugenol cement (CIM), glass ionomer cement (GIC) or light curable composite (BIO). Higid and without restoration were controls. Materials for flexual strength and teeth were tested for microleakage and compressive strength. RESULTS: GIC and Higid presented similar compressive strength, higher than other groups. Bio and GIC presented similar flexural strength higher than BIO. CIM and BIO showed similar micro- leakage lower than GIC. CONCLUSION: The hypothesis was rejected as filling materials tested failed to prevent microleakage and to increase fracture resistance concomitantly. CLINICAL SIGNIFICANCE: GIC may be considered to restore weakened teeth subjected to occlusal loads. BIO and CIM are better choices to microleakage in teeth not subjected to mechanical stresses.

Physico-Mechanical Properties and Bonding Performance of Graphene-Added Orthodontic Adhesives.

This study aimed to assess the key physico-mechanical properties and bonding performance of orthodontic adhesives with graphene addition for bonding a fixed retainer. Transbond LR (3M) and Transbond LV (3M) with no graphene were set as the control groups. Graphene was added into LR and LV at concentrations of 0.01 wt%, 0.05 wt% and 0.1 wt%. The stickiness of the uncured samples (n = 5) and real-time degree of conversion (DC) of the samples (n = 3) were measured over a 24-h period using Fourier-transform infrared spectroscopy. The hardness and other mechanical parameters, including the Martens hardness (HM), indentation modulus (EIT), elastic index (ηIT) and creep (CIT), were measured (n = 5). To measure the shear bond strength (SBS), adhesive composites were applied using a mold to bond the retainer wire to the lingual surfaces of bovine incisors (n = 10). Fracture modes subsequent to the SBS test were examined under light microscopy. Statistical analysis was conducted using ANOVA and Tukey tests (α = 0.05). In the LR groups, the LR + 0.01 showed the highest SBS (12.6 ± 2.0 MPa) and HM (539.4 ± 17.9 N/mm2), while the LV + 0.05 (7.7 ± 1.1 MPa) had the highest SBS and the LV + 0.1 had the highest HM (312.4 ± 17.8 N/mm2) among the LV groups. The most frequent failure mode observed was adhesive fracture followed by mixed fracture. No statistical difference was found between the graphene-added groups and the control groups in terms of the EIT, ηIT and CIT, except that the CIT was significantly lower in the LR + 0.01 than in the control group. Graphene addition had no significant adverse effect on the stickiness and DC of both LR and LV.

What and where are the stem cells for Dentistry?

Disinfection of root canals followed by the replacement of the infected or inflamed pulp tissues by inert materials is the foundation for treating irreversible damaged dental pulps. The management of pathological conditions of the periodontium is mainly based solely upon infection control via the reestablishment of oral hygiene, scaling and root planing to control inflammation which stops progressive bone loss. As one may see, the clinical management of endodontic and periodontal diseases has not changed drastically despite the development of new materials, techniques and medicaments. Tissue engineering is a multi-disciplinary field focused on the development of materials, techniques and strategies to improve or replace damaged or lost biological functions and tissues. As the tissue engineering field progresses, "scaffolds", "suggest pathways" and "stem cells" abandoned their role as technical words exclusively used by scientists and slowly assume a part in the language of students, educators, clinicians and patients. However the unfamiliarity with some of the concepts can lead to misinterpretations of the current status and overexcitement about future applications of stem cells for dental-related tissue regeneration. This paper will present a panorama and the future challenges on the path to use of stem cells for endodontic and periodontal tissue regeneration.

Salivary gland regeneration: from salivary gland stem cells to three-dimensional bioprinting.

Hyposalivation and severe dry mouth syndrome are the most common complications in patients with head and neck cancer (HNC) after receiving radiation therapy. Conventional treatment for hyposalivation relies on the use of sialogogues such as pilocarpine; however, their efficacy is constrained by the limited number of remnant acinar cells after radiation. After radiotherapy, the salivary gland (SG) secretory parenchyma is largely destroyed, and due to the reduced stem cell niche, this gland has poor regenerative potential. To tackle this, researchers must be able to generate highly complex cellularized 3D constructs for clinical transplantation via technologies, including those that involve bioprinting of cells and biomaterials. A potential stem cell source with promising clinical outcomes to reserve dry mouth is adipose mesenchymal stem cells (AdMSC). MSC-like cells like human dental pulp stem cells (hDPSC) have been tested in novel magnetic bioprinting platforms using nanoparticles that can bind cell membranes by electrostatic interaction, as well as their paracrine signals arising from extracellular vesicles. Both magnetized cells and their secretome cues were found to increase epithelial and neuronal growth of in vitro and ex vivo irradiated SG models. Interestingly, these magnetic bioprinting platforms can be applied as a high-throughput drug screening system due to the consistency in structure and functions of their organoids. Recently, exogenous decellularized porcine ECM was added to this magnetic platform to stimulate an ideal environment for cell tethering, proliferation, and/or differentiation. The combination of these SG tissue biofabrication strategies will promptly allow for in vitro organoid formation and establishment of cellular senescent organoids for aging models, but challenges remain in terms of epithelial polarization and lumen formation for unidirectional fluid flow. Current magnetic bioprinting nanotechnologies can provide promising functional and aging features to in vitro craniofacial exocrine gland organoids, which can be utilized for novel drug discovery and/or clinical transplantation.

Graphene oxide increases PMMA's resistance to fatigue and strength degradation.

OBJECTIVES: to characterize the effects of graphene oxide (GO) on polymethyl methacrylate's (PMMA) reliability and lifetime. The hypothesis tested was that GO would increase both Weibull parameters and decreased strength degradation over time. METHODS: PMMA disks containing GO (0.01, 0.05, 0.1, or 0.5 wt%) were subjected to a biaxial flexural test to determine the Weibull parameters (m: modulus of Weibull; σ0: characteristic strength; n = 30 at 1 MPa/s) and slow crack growth (SCG) parameters (n: subcritical crack growth susceptibility coefficient, σf0: scaling parameter; n = 10 at 10-2, 10-1, 101, 100 and 102 MPa/s). Strength-probability-time (SPT) diagrams were plotted by merging SCG and Weibull parameters. RESULTS: There was no significant difference in the m value of all materials. However, 0.5 GO presented the lowest σ0, whereas all other groups were similar. The lowest n value obtained for all GO-modified PMMA groups (27.4 for 0.05 GO) was higher than the Control (15.6). The strength degradation predicted after 15 years for Control was 12%, followed by 0.01 GO (7%), 0.05 GO (9%), 0.1 GO (5%), and 0.5 GO (1%). SIGNIFICANCE: The hypothesis was partially accepted as GO increased PMMA's fatigue resistance and lifetime but did not significantly improve its Weibull parameters. GO added to PMMA did not significantly affect the initial strength and reliability but significantly increased PMMA's predicted lifetime. All the GO-containing groups presented higher resistance to fracture at all times analyzed compared with the Control, with the best overall results observed for 0.1 GO.

Specimen Shape and Elution Time Affect the Mineralization and Differentiation Potential of Dental Pulp Stem Cells to Biodentine.

The liquid extract method is commonly used to evaluate the cytotoxicity and bioactivity of materials. Although ISO has recommended guidelines for test methods, variations in elution period, and shape of samples can influence the biological outcomes. The aim of this study was to investigate the influence of material form and elution period of Biodentine on dental pulp stem cells (DPSCs)' proliferation and mineralization. Biodentine (0.2 g) discs or powder were immersed in culture media (10 mL) for 1, 3 or 7 days (D1, D3 and D7). The eluents were filtered and used to treat DPSC. The calcium release profile and pH were determined. Cell proliferation was evaluated by MTS for 3 days, and mineralization and differentiation were assessed by alizarin red S staining (Ca2+/ng of DNA) and qRT-PCR (MEPE, DSPP, DMP-1, RUNX2, COL-I and OCN) for 14 days. Statistical analysis was performed with a one or two-way ANOVA and post hoc Tukey's test (pH, calcium release and proliferation) or Mann-Whitney test (α = 0.05). pH and calcium ion release of powdered eluents were significantly higher than disc eluents. Powdered eluent promoted extensive cell death, while the disc form was cytocompatible. All disc eluents significantly increased the gene expression and mineralization after 14 days compared to the untreated control. D7 induced less mineralization and differentiation compared to D1 and D3. Thus, the materials' form and elution time are critical aspects to be considered when evaluating the bioactivity of materials, since this binomial can affect positively and negatively the biological outcomes.

Mesenchymal stromal cell exosomes enhance dental pulp cell functions and promote pulp-dentin regeneration.

Mesenchymal stromal/stem cell (MSC) therapies are currently being explored for dental pulp regeneration. As the therapeutic effects of MSCs in tissue repair are mediated mainly through the release of extracellular vesicles (EVs) including exosomes, we investigated here the cellular processes and molecular mechanisms modulated by MSC exosomes in dental pulp regeneration. Using dental pulp cell (DPC) cultures, we demonstrated that MSC exosomes could increase DPC migration, proliferation, and odontogenic differentiation. The enhancement of these cellular processes was mediated through exosomal CD73-mediated adenosine receptor activation of AKT and ERK signaling. Consistent with these observations, MSC exosomes increased the expression of dentin matrix proteins and promoted the formation of dentin-like tissue and bridge-like structures in a rat pulp defect model. These effects were comparable to that of mineral trioxide aggregate (MTA) treatment. MSC exosomes also yielded recellularized pulp-dentin tissues in the root canal of endodontically-treated human premolars, following subcutaneous implantation in the mouse dorsum. Together, our findings suggest that MSC exosomes could exert a multi-faceted effect on DPC functions including migration, proliferation and odontogenic differentiation to promote dental pulp regeneration. This study provides the basis for development of MSC exosomes as a cell-free MSC therapeutic alternative for pulp-dentin regeneration.

Regenerating the Dental Pulp-Scaffold Materials and Approaches.

Novel technologies and platforms have allowed significant breakthroughs in dental pulp tissue engineering. The development of injectable scaffolds that can be combined with stem cells, growth factors, or other bioactive compounds has enabled the regeneration of functional dental pulps able to secrete dentin in preclinical and clinical studies. Similarly, cell-homing technologies and scaffold-free strategies aim to modulate dental pulp self-regeneration mediated by resident stem cells and can evade some of the technical challenges related to cell-based tissue engineering strategies. This article will discuss emerging technologies and platforms for the clinical applications of dental pulp tissue engineering.

SMART: Silver diamine fluoride reduces microtensile bond strength of glass ionomer cement to sound and artificial caries-affected dentin.

Silver-modified atraumatic restorative technique (SMART) is an emerging restorative technique; however, the effect of silver diamine fluoride (SDF) application on the bond strength of glass ionomer cement (GIC) is unknown. This study aimed to determine if SDF application to sound and artificial caries-affected dentin (ACAD) immediately prior to GIC restoration affected microtensile bond strength (µTBS). Caries was induced on extracted molars using a pH-cycling protocol that was validated against natural caries (similar µTBS). Dentin surfaces were treated with 38% SDF, control groups with de-ionized water and immediately restored. Beam-shaped specimens were sectioned and subjected to tensile forces for µTBS determination. Two hundred and eighty-seven specimens from 40 teeth were tested. SDF application significantly (p<0.001) reduced µTBS in sound dentin (19.00±8.20 MPa vs. 14.60±6.68 MPa), while no difference was found in ACAD. No difference was found in failure mode among groups. For SMART, SDF application on sound dentin before immediate GIC restoration may decrease bond strength.

Characterization of silver diamine fluoride cytotoxicity using microfluidic tooth-on-a-chip and gingival equivalents.

OBJECTIVE: This study aims to characterize the cytotoxicity potential of silver diamine fluoride (SDF) on dental pulp stem cells (DPSC) and gingival equivalents. METHODS: DPSC cultured on 96-well plates was exposed directly to SDF (0.0001-0.01%) and cell viability (IC50) quantified. Effect of SDF on DPSC viability under flow (with dentin barrier) conditions was evaluated using a custom-designed microfluidic "tooth-on-a-chip". Permeability of dentin discs (0.5-1.5 mm thickness) was evaluated using lucifer yellow permeation assay. Dentin discs were treated with 38% SDF (up to 3 h), and cell viability (live/dead assay) of the DPSC cultured in the inlet (unexposed) and outlet (exposed) regions of the pulp channel was evaluated. To assess the mucosal corrosion potential, gingival equivalents were treated with 38% SDF for 3 or 60 min (OECD test guideline 431) and characterized by MTT assay and histomorphometric analysis. RESULTS: DPSC exposed directly to SDF showed a dose-dependent reduction in cell viability (IC50: 0.001%). Inlet channels (internal control) of the tooth-on-a-chip exposed to PBS and SDF-exposed dentin discs showed> 85% DPSC viability. In contrast, the outlet channels of SDF-exposed dentin discs showed a decreased viability of< 31% and 0% (1.5 and ≤1.0 mm thick dentin disc, respectively) (p < 0.01). The gingiva equivalents treated with SDF for 3 and 60 min demonstrated decreased epithelial integrity, loss of intercellular cohesion and corneal layer detachment with significant reduction in intact epithelial thickness (p < 0.05). SIGNIFICANCE: SDF penetrated the dentin (≤1 mm thick) inducing significant death of the pulp cells. SDF also disrupted gingival epithelial integrity resulting in mucosal corrosion.

RoBDEMAT: A risk of bias tool and guideline to support reporting of pre-clinical dental materials research and assessment of systematic reviews.

OBJECTIVES: To develop a risk of bias tool for pre-clinical dental materials research studies that aims to support reporting of future investigations and improve assessment in systematic reviews. METHODS: A four-stage process following EQUATOR network recommendations was followed, which included project launch, literature review, Delphi process and the tool finalization. With the support of the European Federation of Conservative Dentistry (EFCD) and the Dental Materials Group of the International Association for Dental Research (DMG-IADR), a total of 26 expert stakeholders were included in the development and Delphi vote of the initial proposal. The proposal was built using data gathered from the literature review stage. During this stage, recent systematic reviews featuring dental materials research, and risk of bias tools found in the literature were comprehensively scanned for bias sources. The experts thus reached a consensus for the items, domains and judgement related to the tool, allowing a detailed guide for each item and corresponding signalling questions. RESULTS: The tool features nine items in total, spread between 4 domains, pertaining to the following types of bias: bias related to planning and allocation (D1), specimen preparation (D2), outcome assessment (D3) and data treatment and outcome reporting (D4). RoBDEMAT, as presented, features signalling questions and a guide that can be used for RoB judgement. Its use as a checklist is preferred over a final summary score. CONCLUSION: RoBDEMAT is the first risk of bias tool for pre-clinical dental materials research, supported and developed by a broad group of expert stakeholders in the field, validating its future use. CLINICAL SIGNIFICANCE: This new tool will contribute the study field by improving the scientific quality and rigour of dental materials research studies and their systematic reviews. Such studies are the foundation and support of future clinical research and evidence-based decisions.

Regenerative endodontics in light of the stem cell paradigm.

Stem cells play a critical role in development and in tissue regeneration. The dental pulp contains a small sub-population of stem cells that are involved in the response of the pulp to caries progression. Specifically, stem cells replace odontoblasts that have undergone cell death as a consequence of the cariogenic challenge. Stem cells also secrete factors that have the potential to enhance pulp vascularisation and provide the oxygen and nutrients required for the dentinogenic response that is typically observed in teeth with deep caries. However, the same angiogenic factors that are required for dentine regeneration may ultimately contribute to the demise of the pulp by enhancing vascular permeability and interstitial pressure. Recent studies focused on the biology of dental pulp stem cells revealed that the multipotency and angiogenic capacity of these cells could be exploited therapeutically in dental pulp tissue engineering. Collectively, these findings suggest new treatment paradigms in the field of endodontics. The goal of this review is to discuss the potential impact of dental pulp stem cells to regenerative endodontics.

Effect of test environment and microstructure on the flexural strength of dental porcelains.

PURPOSE: The objective of this study was to verify the influence of test environment on the flexural strength of dental porcelains with distinct microstructures. MATERIAL AND METHODS: Disk-shaped specimens from three dental porcelains with distinct leucite content (VM: zero; CE: 12; NS: 22 vol%) were manufactured and tested for biaxial flexural strength in air and immersed in artificial saliva. The results were analyzed by means of two-way ANOVA and Tukey's test (α= 0.05). RESULTS: The flexural strength (MPa) obtained for ambient air and artificial saliva environments, respectively, were: 110.0 ± 16.0 and 81.5 ± 10.8 for VM; 51.9 ± 4.0 and 42.0 ± 4.7 for CE; 72.0 ± 11.5 and 63.6 ± 5.8 for NS. A numerical decrease in the mean flexural strength was observed for all groups when specimens were tested under artificial saliva; however, the difference was only statistically significant for VM. CONCLUSIONS: The results indicate that the effect of water immersion on the flexural strength of dental porcelains varies according to their leucite content, as only the material without leucite in its microstructure (VM) showed significant strength degradation when tested under water.

Graphene nanocoating provides superb long-lasting corrosion protection to titanium alloy.

OBJECTIVE: The presence of metallic species around failed implants raises concerns about the stability of titanium alloy (Ti-6Al-4V). Graphene nanocoating on titanium alloy (GN) has promising anti-corrosion properties, but its long-term protective potential and structural stability remains unknown. The objective was to determine GN's anti-corrosion potential and stability over time. METHODS: GN and uncoated titanium alloy (Control) were challenged with a highly acidic fluorinated corrosive medium (pH 2.0) for up to 240 days. The samples were periodically tested using potentiodynamic polarization curves, electrochemical impedance spectroscopy and inductively coupled plasma-atomic emission spectroscopy (elemental release). The integrity of samples was determined using Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and scanning electron microscopy. Statistical analyses were performed with one-sample t-test, paired t-test and one-way ANOVA with Tukey post-hoc test with a pre-set significance level of 5%. RESULTS: There was negligible corrosion and elemental loss on GN. After 240 days of corrosion challenge, the corrosion rate and roughness increased by two and twelve times for the Control whereas remained unchanged for GN. The nanocoating presented remarkably high structural integrity and coverage area (>98%) at all time points tested. SIGNIFICANCE: Graphene nanocoating protects titanium alloy from corrosion and dissolution over a long period while maintaining high structural integrity. This coating has promising potential for persistent protection of titanium and potentially other metallic alloys against corrosion.

Characterization, Antimicrobial Effects, and Cytocompatibility of a Root Canal Sealer Produced by Pozzolan Reaction between Calcium Hydroxide and Silica.

This study aimed to evaluate a newly developed pozzolan-based bioceramic sealer (PZBS) regarding setting time, radiopacity, antibacterial effect, and cytocompatibility. The PZBS was manufactured by mixing calcium hydroxide and silica. The pozzolan reaction was verified by identification of calcium silicate hydrate (C-S-H) using X-ray diffraction analysis. The initial setting time and radiopacity were measured using the ISO 6876/2012 protocol in comparison with other commercially available calcium silicate (CS) sealers. The antibacterial effect of PZBS on biofilms cultured in the bovine root canal was evaluated by measurement of colony-forming units and volume of biofilms in comparison with other calcium hydroxide pastes. The morphological features of the biofilms were observed by scanning electron microscopy (SEM). The cytocompatibility of PZBS was assessed by the viability of bone marrow-derived mesenchymal stem cells and scratch wound healing rate in comparison with other CS sealers. The morphology of the cells cultured on the tested sealers was observed by SEM. The detection of the CS peak confirmed the formation of C-S-H. The initial setting time of PZBS was around 11 h, which was twice as long as the other tested sealers. The radiopacity of PZBS was 4.3 mm/Al, which satisfied the ISO criteria. The antibacterial effect and cytocompatibility of PZBS were comparable to those of the commercially available intracanal medicaments and CS endodontic sealers, respectively. The PZBS has the potential to be used for root canal obturation, and is expected to exert a favorable antibacterial effect.