Dual polymer networks: a new strategy in expanding the repertoire of hydrogels for biomedical applications.

Inspired by the double network hydrogel systems we report the formulation of dual networks, which expands the repertoire of this class of materials for potential biomedical applications. The tough dual network hydrogels were designed through sequential interpenetrating polymer formation, applying green chemistry and low-cost methods, devoid of any initiator-activator complexes that may pose risks in biomedical applications. The dual networks were synthesized in two steps, firstly the water soluble poly(vinyl alcohol) was subjected to cryogelation that formed the first network, which was then expanded by intrusion of a dilute solution of sodium alginate and complexed with a solution of calcium chloride under ambient conditions and further freeze-thawed. These hydrogels are flexible, ductile and porous with the ability to absorb and retain fluids as well as possess the versatility to easily incorporate biological molecules/drugs/antibiotics to be applied in tissue matrices or drug delivery systems. The dual network hydrogels can be tailored to have varying mechanical properties, shapes, size, thickness and particularly can be made physically porous if required, to suit the users intended application.

Combinatorial design of calcium meta phosphate poly(vinyl alcohol) bone-like biocomposites.

The incidence of degenerative diseases and the ageing population have added to the growing demand for bone grafts. Although autologous bone continues to be the gold standard, limited yield and potential morbidity of the donor site pose considerable challenges. Currently, clinically used synthetic grafts based on calcium phosphates are mechanically brittle and not compliant hence composite scaffolds are expected to be provide viable solutions. In this study we report composites of calcium meta phosphate-poly (vinyl alcohol) with tunable mechanical properties, low swelling and excellent biocompatibility. The elastomeric nature of the composites resist brittle fracture and the scaffolds can be easily shaped to the bone defect by the surgeon. Testing on bone plug shaped specimens of the scaffolds, exhibited superior mechanical properties compared to currently commercially available bone plugs with additional advantages being the ability to increase porosity without compromising properties in compression and degree of swelling, which make these composites promising synthetic alternatives for bone grafts and bone tissue engineering.

An in vitro assessment of gutta-percha coating of new carrier-based root canal fillings.

The first aim of this paper was to evaluate the push-out bond strength of the gutta-percha coating of Thermafil and GuttaCore and compare it with that of gutta-percha used to coat an experimental hydroxyapatite/polyethylene (HA/PE) obturator. The second aim was to assess the thickness of gutta-percha around the carriers of GuttaCore and HA/PE obturators using microcomputed tomography ( µ CT). Ten (size 30) 1 mm thick samples of each group (Thermafil, GuttaCore, and HA/PE) were prepared. An orthodontic wire with a diameter of 0.5 mm was attached to the plunger of an Instron machine in order to allow the push-out testing of the gutta-percha coating. Five samples of (GuttaCore and HA/PE) were scanned using µ CT. The data obtained were analysed with one-way analysis of variance and Tukey post hoc test. HA/PE obturators exhibited significantly higher push-out bond strength (P < 0.001) determined at 6.84 ± 0.96 than those of Guttacore around 3.75 ± 0.75 and Thermafil at 1.5 ± 0.63. GuttaCore demonstrated significantly higher bond strength than Thermafil (P < 0.001). µ CT imaging revealed that the thickness of gutta-percha around the experimental HA/PE carrier was homogeneously distributed. The bondability and thickness of gutta-percha coating around HA/PE carriers were superior to those of GuttaCore and Thermafil obturators.

Performance of novel enamel-conditioning calcium-phosphate pastes for orthodontic bonding: An in vitro study.

Background: This study aimed to develop remineralizing calcium-phosphate (CaP) etchant pastes for enamel conditioning before bracket bonding and evaluate the bonding performance, failure pattern, and enamel surface integrity post bracket debonding in comparison with the conventional phosphoric acid (PA) etchant gel. Material and Methods: Micro-sized monocalcium phosphate monohydrate and hydroxyapatite (micro- and nano-sized) powders were mixed with various phosphoric and nitric acid concentrations to develop eight acidic CaP pastes. Ninety extracted human premolars were randomly assigned into eight experimental and one control group (n=10). The developed pastes and control (commercial 37% PA-gel) were applied onto the enamel using the etch-and-rinse protocol before bonding metal brackets. Shear bond strength and adhesive remnant index (ARI) scores were evaluated after 24 hours water storage (24 h) and post 5000 thermocycling (TC). Field emission scanning electron microscopy (FE-SEM) was used to evaluate enamel damage after bracket debonding. Results: The developed CaP pastes, excepting MNA1 and MPA1, resulted in significantly lower SBS values and ARI scores than 37% PA gel. Etching with 37% PA yielded roughened, cracked enamel surfaces with excessive retention of adhesive residue. In contrast, enamel treatment with the experimental pastes exhibited smooth, unblemished surfaces, with obvious CaP re-precipitation induced by mHPA2 and nHPA2 pastes and to a lesser extent by MPA2 paste. Conclusions: Three newly developed CaP etchant pastes (MPA2, mHPA2, and nHPA2) can be promising alternative enamel conditioners that outperform conventional PA by generating adequate bracket bond strengths besides precipitating CaP crystals on the enamel. Moreover, these pastes maintained unblemished enamel surfaces with no or minimal adhesive residue after bracket removal. Key words:Enamel Conditioning, Calcium Phosphate, Bracket Bond Strength, Orthodontic Bonding, enamel damage.

A self-etch bonding system with potential to eliminate selective etching and resist proteolytic degradation.

OBJECTIVES: Bonded restorations using self-etch (SE) systems exhibit a limited lifespan due to their susceptibility to hydrolytic, enzymatic or fatigue degradation and poor performance on enamel. This study was conducted to develop and assess the performance of a two-step SE system using a functional monomer bis[2-(methacryloyloxy)ethyl]phosphate (BMEP) and demonstrate a strategy to enhance stability of bonded resin composite restorations to both enamel and dentine. METHODS: A two-step SE system was formulated with a primer containing BMEP, with an adhesive with or without BMEP, and compared to a commercial 10-MDP-containing system, ClearfilTM SE Bond 2 (CFSE). The systems were evaluated on enamel for surface roughness and microshear bond strength (µSBS) and on dentine for microtensile bond strength (µTBS), nanoleakage, MMP inhibition and cyclic flexural fatigue. RESULTS: Whilst all bonding systems resulted in statistically similar µSBS, BMEP-based primers yielded greater enamel surface roughness than the CFSE primer. The BMEP-free adhesives resulted in statistically similar or higher µTBS and lower nanoleakage compared to CFSE. In situ zymography revealed minimal to no MMP activity within the hybrid layer of BMEP-based systems. The BMEP-free adhesive exhibited flexural strength and fatigue resistance statistically similar to CFSE. CONCLUSIONS: Incorporation of BMEP in the primer led to satisfactory bond strengths with both enamel and dentine, potentially eliminating the need for selective enamel etching. Combined with an adhesive formulation that is solvent-free and hydrophobic, and confining the acidic functional monomer in the primer resulted in minimal interfacial leakage, and resistance to proteolytic degradation and the cyclic nature of chewing. CLINICAL SIGNIFICANCE: The SE bonding system containing BMEP combines the potent etching of phosphoric acid with the therapeutic function of the phosphate-based monomer in creating a homogenous hybrid layer with protection against endogenous proteolytic enzymes. This strategy may overcome current challenges that arise during selective enamel etching.

A multi-functional dentine bonding system combining a phosphate monomer with eugenyl methacrylate.

OBJECTIVE: The tooth-resin composite interface is frequently associated with failure because of microbial contamination, hydrolytic and collagenolytic degradation. Thus, designing a dentine bonding system (DBS) with an intrinsically antimicrobial polymerisable monomer is of significance especially if it can be used with self-etching primers enabling resistance to degradation of the interface. METHODS: Experimental adhesives were developed incorporating eugenyl methacrylate (EgMA) at concentrations of 0,10 or 20 wt%, designated as EgMA0, EgMA10 and EgMA20, respectively, for use as a two-step self-etch DBS with the functional monomer bis[2-(methacryloyloxy) ethyl] phosphate (BMEP) in the primer. The curing, thermal and wettability properties of the adhesives were determined, and hybrid layer formation was characterised by confocal laser scanning microscopy, microtensile bond strengths (µTBS) and nanoleakage by back-scattered SEM. In situ zymography was used to assess MMP inhibitory activity of the BMEP-EgMA DBS. RESULTS: EgMA in the adhesives lowered the polymerisation exotherm and resulted in higher Tg, without negatively affecting degree of conversion. Water sorption and solubility were significantly lower with higher concentrations of EgMA in the adhesive. The formation of a distinct hybrid layer was evident from confocal images with the different adhesives, whilst EgMA20 yielded the highest µTBS post water storage challenges and lowest nanoleakage after 6 months. The experimental DBS exhibited minimal to no MMP activity at 3 months. SIGNIFICANCE: The hydrophobic nature of EgMA and high cross-link density exerts considerable benefits in lowering water uptake and polymerisation exotherm. The application of EgMA, adhesives in conjunction with BMEP in a multi-functional self-etching DBS can resist MMP activity, hence, enhance longevity of the dentine-resin composite interface.

In-vitro adhesive and interfacial analysis of a phosphorylated resin polyalkenoate cement bonded to dental hard tissues.

OBJECTIVES: To assess the performance of a novel resin-modified glass-ionomer cement (pRMGIC) bonded to various tooth tissues after two-time intervals. METHODS: 192 sound human molars were randomly assigned to 3 groups (n = 64): sound enamel, demineralised enamel, sound dentine. Sixty-four teeth with natural carious lesions including caries-affected dentine (CAD) were selected. All substrates were prepared, conditioned and restored with pRMGIC (30% ethylene glycol methacrylate phosphate (EGMP, experimental), Fuji II LC (control), Fuji IX, and Filtek™ Supreme with Scotchbond ™ Universal Adhesive. Shear bond strength (SBS) was determined after 24 h and three months storage in SBF at 37 °C. The debonded surfaces were examined using stereomicroscopy and scanning electron microscopy (SEM). Multivariate Analysis of Variance (MANOVA), Bonferroni post hoc tests (alpha=0.05) and independent T-tests were used for multifactorial data analysis. RESULTS: The hydrophilicity and functionality of EGMP enhanced the bond strength of the pRMGIC to different substrates after 24 h and 3 months as compared to F2LC (p<0.05). Adhesive failures were found to decrease with pRMGIC and integration into exposed enamel prisms and dentine tubules was observed with SEM. Ageing enhanced bond strength of pRMGIC to all substrates but was statistically significantly only in sound dentine. The SBS of pRMGIC was higher with sound vs. demineralised enamel at both time periods (p<0.001), while it was higher to CAD initially and to sound dentine post-storage (p = 0.004). CONCLUSIONS: pRMGIC exhibited enhanced bonding performance to various tooth tissues with an ability to seal exposed enamel prisms and dentine tubules. CLINICAL SIGNIFICANCE: pRMGIC is a promising material exhibiting long-lasting bonded-tooth interfaces, for its use in minimally invasive reparative techniques.

A porous scaffold for bone tissue engineering/45S5 Bioglass derived porous scaffolds for co-culturing osteoblasts and endothelial cells.

One of the major factors in the therapeutic success of bone tissue engineered scaffolds is the ability of the construct to vascularise post implantation. One of the approaches for improving vascularisation within scaffolds has been to co-culture human umbilical vein endothelial cells (HUVECS) with human osteoblasts (HOBS), which may then promote vascularisation and facilitate tissue regeneration. However, in order to mimic a natural physiological niche it is vital that the scaffold is able to support and promote the proliferation of both cell types and thus become a viable tissue engineered construct. In this study we report the development of a porous bioactive glass-ceramic construct and examine the interaction with human umbilical vein endothelial cells (HUVEC's) and human osteoblast-like cell both in mono and co-culture. The study clearly demonstrated that the scaffolds were able to support both endothelial and human osteoblast cell proliferation both in mono and co-culture. A comparison of the proliferation response of HUVEC and HOB in mono-culture on the test scaffolds and the commercial porous hydroxyapatite was assessed over a 28 day period (4, 7, 14, 21 and 28 days), using alamar Blue assay. Proliferation of HOB cells seeded in the scaffolds was consistently shown to be above those observed on commercial HA scaffolds.

Evaluation of the effects of polishing systems on surface roughness and morphology of dental composite resin.

Objectives The aim of this in vitro study was to evaluate the effects of five different two-step diamond impregnated polishing systems (Sof-Lex Spiral, Venus Supra, Komet Spiral, CompoMaster and Shapeguard) on the surface roughness and morphology of a submicron hybrid composite resin material (Brilliant Everglow).Materials and methods Two-hundred composite resin discs were prepared with 180 SiC paper to produce a uniform baseline surface. The samples were randomly assigned to one of five groups and polishing was completed by one operator. The arithmetic mean surface roughness (Ra) was measured using contact profilometry and the surfaces were examined under an SEM.Results Statistical differences (p <0.05) were identified between the surface roughness remaining after use of the polishers. Diatech Shapeguard (0.22 µm, SD 0.08) and Komet Spiral (0.26 µm, SD 0.09) polishers yielded the lowest Ra values, while the CompoMaster polishing system led to the highest surface roughness values (0.55 µm, SD 0.19).Conclusions Within the limits of this in vitro study of the efficacy of diamond impregnated two-step polishing systems, Diatech Shapeguard and Komet Spiral polishing systems produced the lowest surface roughness values. These polishing systems yielded acceptable surface roughness values with regards to oral health and patient comfort.Clinical relevance Similarly designed polishing systems do not produce comparable surface roughness levels and clinicians should be aware of this when considering polishing protocols for composite restorations.

Resistance of bonded premolars to four artificial ageing models post enamel conditioning with a novel calcium-phosphate paste.

BACKGROUND: This in vitro study compares a novel calcium-phosphate etchant paste to conventional 37% phosphoric acid gel for bonding metal and ceramic brackets by evaluating the shear bond strength, remnant adhesive and enamel damage following water storage, acid challenge and fatigue loading. MATERIAL AND METHODS: Metal and ceramic brackets were bonded to 240 extracted human premolars using two enamel conditioning protocols: conventional 37% phosphoric acid (PA) gel (control), and an acidic calcium-phosphate (CaP) paste. The CaP paste was prepared from ß-tricalcium phosphate and monocalcium phosphate monohydrate powders mixed with 37% phosphoric acid solution, and the resulting phase was confirmed using FTIR. The bonded premolars were exposed to four artificial ageing models to examine the shear bond strength (SBS), adhesive remnant index (ARI score), with stereomicroscopic evaluation of enamel damage. RESULTS: Metal and ceramic control subgroups yielded significantly higher (p < 0.05) SBS (17.1-31.8 MPa) than the CaP subgroups (11.4-23.8 MPa) post all artificial ageing protocols, coupled with higher ARI scores and evidence of enamel damage. In contrast, the CaP subgroups survived all artificial ageing tests by maintaining adequate SBS for clinical performance, with the advantages of leaving unblemished enamel surface and bracket failures at the enamel-adhesive interface. CONCLUSIONS: Enamel conditioning with acidic CaP pastes attained adequate bond strengths with no or minimal adhesive residue and enamel damage, suggesting a suitable alternative to the conventional PA gel for orthodontic bonding. Key words:Enamel etching, calcium phosphate, bracket bond strength, adhesive residue, enamel damage.

In vitro bond strengths post thermal and fatigue load cycling of sapphire brackets bonded with self-etch primer and evaluation of enamel damage.

BACKGROUND: This in vitro study compares a self-etch primer (SEP) to an etch-and-rinse (EaR) for bonding sapphire brackets by evaluation of the enamel etch-pattern, shear bond strength, amount of remnant adhesive and enamel surface damage following thermal and fatigue cyclic loading. MATERIAL AND METHODS: Ceramic (sapphire) brackets were bonded to 80 extracted human premolars using two enamel etching protocols: conventional EaR using 37% phosphoric acid (PA) gel (control), and a SEP (Transbond Plus). Each group was subdivided into two subgroups (n=20 teeth) according to the time of bracket debonding: after 24 h water storage or following 5000 thermo-cycles plus 5000 cycles fatigue loading, to determine the shear bond strength (SBS), adhesive remnant index (ARI score), with scanning electron microscopy (SEM) evaluation of enamel condition. RESULTS: The control subgroups consistently exhibited significantly higher (p<0.05) SBS mean values (23.4-29.8 MPa) than the SEP subgroups (15.1-22.4 MPa) at both bracket debonding time points. However, the SEP subgroups yielded milder etch-patterns and attained SBS values above the minimum requirement range for clinical performance. In addition, the higher SBS of control subgroups was accompanied with higher ARI scores and enamel damage grades than SEP subgroups as confirmed by SEM. Thermocycling and fatigue significantly reduced the SBS of all subgroups, with a non-significant drop in the amount of adhesive residue or enamel damage. CONCLUSIONS: The use of SEP can be a suitable alternative to the conventional PA gel for sapphire bracket bonding as it maintains suitable bond strength and has the potential to produce both less remnant adhesive and enamel damage. Key words:Enamel etching, ceramic brackets, orthodontic bonding, adhesive remnants, enamel damage.

Antimicrobial Effectiveness of Calcium Silicate Sealers against a Nutrient-Stressed Multispecies Biofilm.

PURPOSE: This study compared the antimicrobial efficacy of calcium silicate sealers (BioRoot RCS and Total Fill BC) and conventional sealers (AH Plus and Tubli-seal) against planktonic bacteria and a nutrient-stressed multispecies biofilm. METHODS: Antimicrobial properties of freshly mixed sealers were investigated using the direct contact test (DCT) and a nutrient-stressed multispecies biofilm comprised of five endodontic strains. Antimicrobial activity was determined using quantitative viable counts and confocal laser scanning microscopy (CLSM) analysis with live/dead staining. The pH of the sealers was analysed over a period of 28 days in Hanks Balanced Salt Solution (HBSS). Analysis of variance (ANOVA) with Tukey tests and the Kruskal-Wallis test were used for data analysis with a significance of 5%. RESULTS: All endodontic sealers exhibited significant antimicrobial activity against planktonic bacteria (p < 0.05). BioRoot RCS caused a significant reduction in viable counts of the biofilms compared to AH Plus and the control (p < 0.05), while no significant difference could be observed compared to TotalFill BC and Tubli-seal (p > 0.05). CLSM analysis showed that BioRoot RCS and TotalFill BC exhibited significant biofilm inhibition compared to Tubli-seal, AH Plus and the control (p < 0.05). BioRoot RCS presented with the highest microbial killing, followed by TotalFill BC and Tubli-seal. Alkalizing activity was seen from the onset by BioRoot RCS, TotalFill BC and AH Plus. After 28 days, BioRoot RCS demonstrated the highest pH in HBSS (pH > 12). CONCLUSIONS: Calcium silicate sealers exhibited effective antimicrobial properties. This was demonstrated by superior biofilm inhibition capacity and microbial killing, with strong alkalizing activity compared to epoxy-based and zinc oxide-eugenol-based sealers.

Ex vivo investigations on bioinspired electrospun membranes as potential biomaterials for bone regeneration.

OBJECTIVES: To assess the surface characteristics and composition that may enhance osteoblasts viability on novel electrospun composite membranes (organic polymer/silicon dioxide nanoparticles). METHODS: Membranes are composed by a novel polymer blend, the mixture of two hydrophilic copolymers 2-hydroxyethylmethacrylate-co-methylmethacrylate and 2-hydroxyethylacrylate-co-methylacrylate, and they are doped with silicon dioxide nanoparticles. Then the membranes were functionalized with zinc or doxycycline. The membranes were morphologically characterized by atomic force and scanning electron microscopy (FESEM), and mechanically probed using a nanoindenter. Biomimetic calcium phosphate precipitation on polymeric tissues was assessed. Cell viability tests were performed using human osteosarcoma cells. Cells morphology was also studied by FESEM. Data were analyzed by ANOVA, Student-Newman-Keuls and Student t tests (p < 0.05). RESULTS: Silica doping of membranes enhanced bioactivity and increased mechanical properties. Membranes morphology and mechanical properties were similar to those of trabecular bone. Zinc and doxycycline doping did not exert changes but it increased novel membranes bioactivity. Membranes were found to permit osteoblasts proliferation. Silica-doping favored cells proliferation and spreading. As soon as 24 h after the seeding, cells in silica-doped membranes were firmly attached to experimental tissues trough filopodia, connected to each other. The cells produced collagen and minerals onto the surfaces. CONCLUSIONS: Silica nanoparticles enhanced surface properties and osteoblasts viability on electrospun membranes. CLINICAL SIGNIFICANCE: The ability of silica-doped matrices to promote precipitation of calcium phosphate, together with their mechanical properties, observed non-toxicity, stimulating effect on osteoblasts and its surface chemistry allowing covalent binding of proteins, offer a potential strategy for bone regeneration applications.

An integrated multifunctional hybrid cement (pRMGIC) for dental applications.

OBJECTIVE: Glass-ionomer and resin-modified glass-ionomer cements are versatile materials with the ability to form a direct bond with tooth tissues. The aim of this study was to formulate a novel class of dental bio-interactive restorative material (pRMGIC) based on resin-modified glass-ionomer cements via the inclusion of an organophosphorus monomer, ethylene glycol methacrylate phosphate, with a potential to improve the mechanical properties and also function as a reparative restorative material. METHODS: pRMGIC was formulated with modification of the resin phase by forming mixes of ethylene glycol methacrylate phosphate (EGMP; 0-40%wt) and 2-hydroxyethyl methacrylate monomer into the liquid phase of a RMGIC (Fuji II LC, GC Corp.). The physical properties of the cements were determined including setting characteristics, compressive strength and modulus (CS &CM), microhardness (MH) and biaxial flexural strength (BFS). Fluid uptake and fluoride release were assessed up to 60 days storage. Adhesion to sound dentine was measured using micro-tensile bond strength and surface integrity was analysed using SEM coupled with EDX. Statistical analysis was performed using ANOVA and Bonferroni post-hoc tests. RESULTS: The pRMGIC cements exhibited an increase in working time with increasing EGMP concentration however were within the limits of standard clinical requirements. Although the compressive strength of pRMGIC cements were comparable to control cements in the early stages of maturation, the higher EGMP-containing cements (EGMP30 and 40) exhibited significantly greater values (p < 0.05) after 4 weeks storage (141.0 ± 9 and 140.4 ± 8 MPa, respectively), in comparison to EGMP0 (128.8 ± 7 MPa). A dramatic two fold increase in biaxial flexural strength (p < 0.001) was observed for the pRMGIC's. Furthermore, the ability to decalcify tooth apatite resulted in enhanced interfacial adhesion due to chelation with calcium ions of tooth apatite. The inclusion of EGMP encouraged formation of reinforcing complexes within the RMGIC, thus improving physical properties, decreasing solubility and lower fluoride release. A dense microstructure was observed with increasing EGMP content. SIGNIFICANCE: A novel universal bio-interactive adhesive repair material will enable clinicians to offer more effective repair of the tooth-restoration complex, thus future treatments will benefit both patient and a severely constrained healthcare budget.

The synthesis of nano silver-graphene oxide system and its efficacy against endodontic biofilms using a novel tooth model.

OBJECTIVE: The deleterious caustic effects of sodium hypochlorite (NaOCl) as a root canal irrigant makes it imperative that alternative methods are developed for root canal disinfection. The purpose of this study was to examine the antimicrobial efficacy of silver nanoparticles (AgNPs) synthesized on an aqueous graphene oxide (GO) matrix (Ag-GO), with different irrigant delivery methods to enhance the disinfection regimen, using a novel ex vivo infected tooth model. METHODS: AgNPs were prepared by reducing AgNO3 with 0.01M NaBH4 in presence of GO. Elemental analysis was performed with scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) and scanning transmission electron microscopy (STEM) was used for size and morphology analysis of GO and Ag-GO. Nutrient stressed, multi-species biofilms were grown in prepared root canals of single-rooted teeth. The irrigants used were sterile saline, 1% and 2.5% NaOCl, 2% chlorhexidine gluconate (CHX), 17% EDTA and an aqueous suspension of 0.25% Ag-GO. The antimicrobial efficacy of the irrigants were performed with paper point sampling and measurement of microbial counts. The biofilm disruption in dentine tubule surfaces was analysed with confocal laser scanning microscopy (CLSM). The acquisition of total biovolume (µm3/µm2) and biofilm viability was performed using software BioImage_L. Two-way analysis of variance (ANOVA) with post hoc Tukey tests was used for data analysis with level of statistical significance set at P<0.05. RESULTS: SEM/EDS analysis confirmed impregnation of Ag within the GO matrix. TEM images showed polygonal GO sheets and spherical AgNPs of diameter 20-50nm, forming a network on the surface of GO sheets. The use of ultrasonic activation enhanced the efficacy of Ag-GO compared to 1% NaOCl, 2% CHX, 17% EDTA and sterile saline (P<0.05). The microbial killing efficacy of 2.5% NaOCl was superior compared to the experimental groups. The maximum biofilm disruption, in dentine tubule surfaces, was achieved by 2.5% NaOCl, however Ag-GO caused a significant reduction of total biovolumes compared to the rest of the experimental groups (P<0.05%). SIGNIFICANCE: The successful documentation of the microbial killing and biofilm disruption capacity of Ag-GO is a promising step forward to explore its unique properties in clinical applications and biomaterials in dentistry.

Semi-interpenetrating network composites reinforced with Kevlar fibers for dental post fabrication.

This study evaluates the reinforcement of semi-interpenetrating network composites of 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropyl)phenyl] propane (Bis-GMA)/ triethyleneglycol dimethacrylate (TEGDMA)/polymethyl methacrylate (PMMA) and 25% titanium dioxide (TiO2) nanofiller with surface treated Kevlar fibers for potential application as dental posts. The post material was subjected to thermo-cycling and flexural strength determined, characterised by dynamic mechanical analysis, water sorption, radiopacity and cytotoxicity tests. The results were compared with everStick®POST. Kevlar pre-treatment with acetic acid and silane coupling agent demonstrated a clear effect on the flexural strength of the composites with a significant increase compared to composites with fibers without surface treatment. The inclusion of TiO2 into the final formulation provided the desired radiopacity and improved both aesthetics and flexural strength, which exhibits a higher resistance on thermocycling. The ratios of fatigue limit to static flexural strength were about 0.73 for Kevlar and 0.58 for everStick®POST; MTT assay confirmed the absence of any toxic eluents, indicating its feasibility as new intracanal post material.

Eugenol functionalized poly(acrylic acid) derivatives in the formation of glass-ionomer cements.

Eugenol possesses analgesic and anti-inflammatory properties with the ability to relieve pain in irritated or diseased tooth pulp, thus, incorporating polymers with eugenol moieties in dental cements is attractive. An acrylic derivative of eugenyl methacrylate (EgMA) was copolymerized with acrylic acid (AA) using a radical initiator, to yield a water soluble copolymer of acrylic acid and eugenyl methacrylate {p(AA-co-EgMA)}, which was then applied in the formulation of glass-ionomer cements for potential application as dental cements. Three concentrations of the p(AA-co-EgMA) copolymer in water were studied by, 30wt%, 40wt% and 50wt%, and used with different powder:liquid ratios to formulate the glass-ionomer cements. The setting kinetics showed that both the concentration of the copolymer and the powder:liquid ratio influenced the working and setting times. Thus, selected formulations were used for further characterization of their mechanical properties, water uptake and fluoride release, to optimize the cement formulation. The experimental glass-ionomer cements exhibited physical and mechanical properties in compliance to ISO standard requirements with the benefit of the initial pH being greater than the commercial formulation used as the standard cement. Furthermore, the presence of the eugenyl moieties bound to the polymer matrix was advantageous with respect to moisture sensitivity and anti-bacterial properties.

Quantification by SIFT-MS of volatile compounds produced by the action of sodium hypochlorite on a model system of infected root canal content.

Root canal irrigation with sodium hypochlorite (NaOCl) is an indispensable part of the chemomechanical preparation of infected root canals in Endodontology. However, there is limited information on the emergence of toxic or hazardous volatile compounds (VOCs) from the interaction of NaOCl with the infected content of tooth biomaterials. The aim of this study was to assess the formation of VOCs and disinfection by-products (DBPs) following the interaction of NaOCl 2.5% v/v with a model system of different sources of natural organic matter (NOM) present in infected root canals, including dentine powder, planktonic multi-microbial suspensions (Propionibacterium acnes, Staphylococcus epidermidis, Actinomyces radicidentis, Streptococcus mitis and Enterococcus faecalis strain OMGS3202), bovine serum albumin 4%w/v and their combination. NaOCl was obtained from a stock solution with iodometric titration. Ultrapure water served as negative control. Samples were stirred at 37°C in aerobic and anaerobic conditions for 30min to approximate a clinically realistic time. Centrifugation was performed and the supernatants were collected and stored at -800 C until analysis. The reaction products were analysed in real time by selected ion flow tube mass spectrometry (SIFT-MS) in triplicates. SIFT-MS analysis showed that the released VOCs included chlorinated hydrocarbons, particularly chloroform, together with unexpected higher levels of some nitrogenous compounds, especially acetonitrile. No difference was observed between aerobic and anaerobic conditions. The chemical interaction of NaOCl with NOM resulted in the formation of toxic chlorinated VOCs and DBPs. SIFT-MS analysis proved to be an effective analytical method. The risks from the rise of toxic compounds require further consideration in dentistry.

Influence of the activator in an acrylic bone cement on an array of cement properties.

In all but one of the acrylic bone cement brands used in cemented arthroplasties, N,N-dimethyl-4-toluidine (DMPT) serves as the activator of the polymerization reaction. However, many concerns have been raised about this activator, all related to its toxicity. Thus, various workers have assessed a number of alternative activators, with two examples being N,N-dimethylamino-4-benzyl laurate (DMAL) and N,N-dimethylamino-4-benzyl oleate (DMAO). The results of limited characterization of cements that contain DMAL or DMAO have been reported in the literature. The present work is a comprehensive comparison of cements that contain one of these three activators, in which the values of a large array of their properties were determined. These properties range from the setting time and maximum exotherm temperature of the curing cement to the variation of the loss elastic modulus of the cured cement with frequency of the applied indenting force in dynamic nanoindentation tests. The present results, taken in conjunction with those presented in previous reports by the present authors and co-workers on other properties of these cements, indicate that both DMAL and DMPT are suitable alternatives to DMPT.

Synthesis of irregular graphene oxide tubes using green chemistry and their potential use as reinforcement materials for biomedical applications.

Micrometer length tubes of graphene oxide (GO) with irregular form were synthesised following facile and green metal complexation reactions. These materials were obtained by crosslinking of GO with calcium, zinc or strontium chlorides at three different temperatures (24, 34 and 55°C) using distilled water as solvent for the compounds and following a remarkably simple and low-cost synthetic method, which employs no hazardous substances and is conducted without consumption of thermal or sonic energy. These irregular continuous GO networks showed a very particular interconnected structure by Field Emission Scanning Electron Microscopy with Energy-Disperse X-Ray Spectroscopy for elemental analysis and High-resolution Transmission Electron Microscopy with Scanning Transmission Electron Microscope Dark Field Imaging, and were analysed by Raman Spectroscopy. To demonstrate the potential use of these 3D GO networks as reinforcement materials for biomedical applications, two composites of calcium alginate with irregular tubes of GO and with single GO nanosheets were prepared with the same amount of GO and divalent atoms and analysed. Thus, the dynamic-mechanical modulus of the composites synthesised with the 3D crosslinked GO networks showed a very significant mechanical improvement due to marked microstructural changes confirmed by confocal microscopy, differential scanning calorimetry and Fourier transform infrared spectroscopy.