Calcium hydroxyapatite nanoparticles as a reinforcement filler in dental resin nanocomposite.

The current study focuses on the fabrication of calcium hydroxyapatite (Ca10(PO4)6(OH)2) (HA) in a nanorange having whiskers- and cubic-shaped uniform particle morphology. The synthesized HA particles hold a promising feature as reinforcement fillers in dental acrylic resin composite. They increase the efficacy of reinforcement by length and aspect ratio, uniformity, and monodispersity. Therefore, the acrylic resin was reinforced with the as-synthesized monodispersed HA filler particles (0.2-1 Wt%). The presence of filler particles in the composite had a noticeable effect on the tribological and mechanical properties of the dental material. The morphological effect of HA particles on these properties was also investigated, revealing that cubic-shaped particles showed better results than whiskers. The as-fabricated composite (0.4 Wt%) of the cubic-shaped filler particles showed maximum hardness and improved antiwear/antifriction properties. Particle loading played its part in determining the optimum condition, whereas particle size also influenced the reinforcement efficiency. The current study revealed that particle morphology, particle size, uniformity, etc., of HA fillers, greatly influenced the tribological and mechanical properties of the acrylic resin-based nanocomposite. Improvement in the tribological properties of HA particle-reinforced acrylic resin composites (HA-acrylic resin) followed the trend as AR < CmC < WC < CC.

Super-Toughened Fumed-Silica-Reinforced Thiol-Epoxy Composites Containing Epoxide-Terminated Polydimethylsiloxanes.

In response to the demand for high-performance materials, epoxy thermosetting and its composites are widely used in various industries. However, their poor toughness, resulting from the high crosslinking density of the epoxy network, must be improved to expand their application to the manufacturing of flexible products. In this study, ductile epoxy thermosetting was produced using thiol compounds with functionalities of 2 and 3 as curing agents. The mechanical properties of the epoxy were further enhanced by incorporating fumed silica into it. To increase the filler dispersion, epoxide-terminated polydimethylsiloxane was synthesized and used as a composite component. Thanks to the polysiloxane-silica interaction, the nanosilica was uniformly dispersed in the epoxy composites, and their mechanical properties improved with increasing fumed silica content up to 5 phr (parts per hundred parts of epoxy resin). The toughness and impact strength of the composite containing 5 phr nanosilica were 5.17 (±0.13) MJ/m3 and 69.8 (±1.3) KJ/m2, respectively.

Synthesis and Characterization of Novel Quaternary Ammonium Urethane-Dimethacrylate Monomers-A Pilot Study.

Six novel urethane-dimethacrylate analogues (QAUDMAs) were synthesized and characterized. They consisted of the 2,4,4,-trimethylhexamethylene diisocyanate (TMDI) core and two methacrylate-terminated wings containing quaternary ammonium groups substituted with alkyl chains of 8, 10, 12, 14, 16, or 18 carbon atoms. QAUDMAs, due to the presence of quaternary ammonium groups, may have possible antibacterial effects. Since they showed satisfactory physicochemical properties, they will be subjected to further research towards the development of dental composites with a capacity to reduce secondary caries. The synthesis of QAUDMAs included three stages: (i) transesterification of methyl methacrylate (MMA) with N-methyldiethanolamine (MDEA), (ii) N-alkylation of the tertiary amino group with alkyl bromide, and (iii) addition of TMDI to the intermediate achieved in the second stage. The formation of QAUDMAs was confirmed by 1H and 13C NMR. They were characterized for density (dm), viscosity (η), refractive index (RI), glass transition temperature (Tg), polymerization shrinkage (S), and degree of conversion (DC). QAUDMAs were yellow, viscous resins (the η values ranged from 1.28 × 103 to 1.39 × 104 Pa·s, at 50 °C). Their RI ranged from 1.50 to 1.52, Tg from -31 to -15 °C, DC from 53 to 78%, and S from 1.24 to 2.99%, which is appropriate for dental applications.

Mechanically Strong Polyurethane Composites Reinforced with Montmorillonite-Modified Sage Filler (Salvia officinalis L.).

Rigid polyurethane (PUR) foams reinforced with 1, 2, and 5 wt.% of salvia filler (SO filler) and montmorillonite-modified salvia filler (MMT-modified SO filler) were produced in the following study. The impact of 1, 2, and 5 wt.% of SO filler and MMT-modified SO filler on the morphological, chemical, and mechanical properties of PUR composites were examined. In both cases, the addition of 1 and 2 wt.% of SO fillers resulted in the synthesis of PUR composites with improved physicomechanical properties, while the addition of 5 wt.% of SO fillers resulted in the formation of PUR composites with a less uniform structure and, therefore, some deterioration in their physicomechanical performances. Moreover, the results showed that the modification of SO filler with MMT improved the interphase compatibility between filler surface and PUR matrix. Therefore, such reinforced PUR composites were characterized by a well-developed closed-cell structure and improved mechanical, thermal, and flame-retardant performances. For example, when compared with reference foam, the addition of 2 wt.% of MMT-modified SO filler resulted in the formation of PUR composites with greater mechanical properties (compressive strength, flexural strength) and improved dynamic-mechanical properties (storage modulus). The PUR composites were characterized by better thermal stability as well as improved flame retardancy-e.g., decreased peak rate of heat release (pHRR), reduced total smoke release (TSR), and increased limiting oxygen index (LOI).

Effect of silane modified microcrystalline cellulose on the curing kinetics, thermo-mechanical properties and thermal degradation of benzoxazine resin.

In the frame of developing sustainable, eco-friendly and high performance materials, microcrystalline cellulose modified through silane coupling agent (MCC Si) is used as a reinforcing agent of benzoxazine resin to manufacture composites at different loadings of 5, 10, 15, 20 wt%. The structural, morphological and crystallinity characterizations of the modified MCC were initially performed to scrutinize the changes and confirm the modification. Then, an investigation on the crosslinking process of the prepared composites was held through curing kinetic study employing isoconversional methods. The kinetic data revealed a decrease in the average values of activation energy and the pre-exponential factor, particularly for composite supplemented with 10% MCC Si, whereas all samples disclosed a tendency of an autocatalytic curing mechanism. Furthermore, the study of the dynamic mechanical properties and degradation features of the cured specimens, respectively, indicated a superior stiffness attributable to the good interaction between BA-a and MCC Si, and enhanced thermal stability for the composites compared to pristine resin.

Development of an antibacterial and anti-metalloproteinase dental adhesive for long-lasting resin composite restorations.

Despite all the advances in adhesive dentistry, dental bonds are still fragile due to degradation events that start during application of adhesive agents and the inherent hydrolysis of resin-dentin bonds. Here, we combined two outstanding processing methods (electrospinning and cryomilling) to obtain bioactive (antimicrobial and anti-metalloproteinase) fiber-based fillers containing a potent matrix metalloproteinase (MMP) inhibitor (doxycycline, DOX). Poly(ε)caprolactone solutions containing different DOX amounts (0, 5, 25, and 50 wt%) were processed via electrospinning, resulting in non-toxic submicron fibers with antimicrobial activity against Streptococcus mutans and Lactobacillus. The fibers were embedded in a resin blend, light-cured, and cryomilled for the preparation of fiber-containing fillers, which were investigated with antibacterial and in situ gelatin zymography analyzes. The fillers containing 0, 25, and 50 wt% DOX-releasing fibers were added to aliquots of a two-step, etch-and-rinse dental adhesive system. Mechanical strength, hardness, degree of conversion (DC), water sorption and solubility, bond strength to dentin, and nanoleakage analyses were performed to characterize the physico-mechanical, biological, and bonding properties of the modified adhesives. Statistical analyses (ANOVA; Kruskal-Wallis) were used when appropriate to analyze the data (α = 0.05). DOX-releasing fibers were successfully obtained, showing proper morphological architecture, cytocompatibility, drug release ability, slow degradation profile, and antibacterial activity. Reduced metalloproteinases (MMP-2 and MMP-9) activity was observed only for the DOX-containing fillers, which have also demonstrated antibacterial properties against tested bacteria. Adhesive resins modified with DOX-containing fillers demonstrated greater DC and similar mechanical properties as compared to the fiber-free adhesive (unfilled control). Concerning bonding performance to dentin, the experimental adhesives showed similar immediate bond strengths to the control. After 12 months of water storage, the fiber-modified adhesives (except the group consisting of 50 wt% DOX-loaded fillers) demonstrated stable bonds to dentin. Nanoleakage was similar among all groups investigated. DOX-releasing fibers showed promising application in developing novel dentin adhesives with potential therapeutic properties and MMP inhibition ability; antibacterial activity against relevant oral pathogens, without jeopardizing the physico-mechanical characteristics; and bonding performance of the adhesive.

Synthesis of chitosan-acrylic acid/multiwalled carbon nanotubes composite for theranostic 47Sc separation from neutron irradiated titanium target.

A simple and efficient separation method of carrier-free 47Sc from neutron irradiated titanium target using a novel chitosan-acrylic acid/multiwalled carbon nanotubes (CS-AA/MWCNTs) composite was established. The synthesis of the CS-AA/MWCNTs composite was achieved using gamma radiation-induced template polymerization. The grafting efficiency (GE%) of AA on CS onto the surface of f-MWCNTs reached a maximum of~84% under the optimized conditions (30 wt% CS, 1.0 wt% AA, 0.15 wt% f-MWCNTs, >0.2 wt% N,N'-Methylenebisacrylamide (NMBA), and irradiation dose ~25 kGy). Different analyses (FT-IR, SEM, TGA and DTA) were examined for confirming the structural morphology and mechanical properties of the new synthesized composite. Interestingly, the CS-AA/MWCNTs composite depicted a selective adsorption of Sc(III) rather than Ti(IV) ions at pH 5 with adsorption efficiency of ~93.93%. The ionic exchange separation of no-carrier-added (NCA)47Sc(III) from irradiated TiO2 target on CS-AA/MWCNTs composite packed column efficiently eluted 47Sc(III) by 91 ± 0.8% using 1 M HCl solution. The quality control tests (radionuclidic, radiochemical, and chemical purities) for the eluted 47Sc(III) clarified its high purity and validity for cancer theranostics.

Efeito de diferentes sistemas de polimento na rugosidade superficial e brilho de resina composta: análise clínica e laboratorial / Effect of different polishing systems on the surface roughness and gloss of resin composite: Clinical and in vitro analysis

Este trabalho foi composto por dois estudos: um in vitro e um clínico randomizado e duplo-cego. O objetivo deste estudo foi compreender o efeito de diferentes sistemas de polimento na rugosidade e brilho superficial da resina composta avaliados em diferentes períodos. Estudo Laboratorial: Cinquenta espécimes de resina composta (Amaris, VOCO) foram confeccionados e divididos em dois grupos variando o sistema de polimento utilizado SFE: Sof-Lex Espiral (3M ESPE) - dois passos e DMT: Dimanto (VOCO) - passo único. Análises de brilho espectral, brilho subjetivo e rugosidade superficial foram realizadas, imediatamente após o polimento, após seis meses e após um ano. O teste de Kolmogorov-Smirnov foi utilizado para verificar a normalidade dos dados. Para o brilho espectral foi utilizada análise de variância de medidas repetidas (ANOVA)(p<0,05) seguida do teste de Tukey (α = 0,05) que demonstraram que o grupo SFE apresentou maior brilho e ainda, ambos os grupos obtiveram valores de brilho menores após seis meses. Como os dados de brilho subjetivo e rugosidade superficial não apresentaram normalidade, foram aplicados os testes Mann-Whitney U e Frideman (α = 0,05). Para o brilho subjetivo, SFE apresentou maiores valores do que DMT quando avaliado após o polimento, porém, em seis e doze meses não houve diferença estatisticamente significante entre eles. Quanto a rugosidade superficial não houve diferenças significantes entre os dois sistemas de polimento nem quanto a fator tempo e nem na interação desses fatores. Estudo Clínico: Cinquenta facetas em resina composta (Amaris, VOCO) foram realizadas em pacientes e divididas em dois grupos, dependendo do sistema de polimento utilizado e avaliadas quanto a brilho subjetivo por pacientes e examinadores, quanto a rugosidade superficial em rugosímetro através de réplicas em resina epoxi e pelo paciente através da Escala Análoga Visual (EAV) e percepção pela língua comparando a um dente natural (controle), após o polimento e após seis meses. Os resultados foram submetidos à análise estatística para verificar a normalidade dos dados. Para a analise com EAV não foi encontrada diferença estatística. Para a percepção da textura da superfície, não houve diferença após o polimento, demonstrado pelos testes Exato de Fischer e Qui-Quadrado. Após seis meses o grupo DMT percebeu diferença de rugosidade, onde os pacientes consideraram o dente da faceta mais liso. Em relação a percepção de brilho pelo paciente, o teste Qui-quadrado demonstrou que não houve diferença entre os grupos. Quanto a avaliação pelo profissional, os testes de Mann-Whiteney e Wilcoxon demonstraram que para o grupo após o polimento, sistema DMT apresentou maiores valores de brilho do que SFE e ambos perderam brilho após seis meses. Quanto a rugosidade os testes de Mann-Whiteney e Wilcoxon demonstraram que o grupo DMT apresentou menores valores enquanto SFE apresentou maiores valores em seis meses. Os resultados da avaliação subjetiva realizada pelos profissionais foram bem próximos a dos pacientes, sendo uma alternativa para avaliação da satisfação do paciente com o tratamento recebido(AU)

This research was composed of two studies: an in vitro and a double-blind randomized clinical study. The aim of the research was to understand the effect of different polishing systems on the surface roughness and gloss of resin composite measured in different periods of time. In vitro study: Fifty specimens of composite resin (Amaris, VOCO) were made and divided into two groups according to the polishing system used SFE: Sof-Lex Spiral (3M ESPE) - two steps and DMT: Dimanto (VOCO) - single step. Spectral and subjective gloss and surface roughness analysis were performed at baseline (right after polishing), after six and twelve months. The Kolmogorov-Smirnov test was used to verify the normality of the data. For spectral gloss analysis repeatedmeasures (ANOVA) followed by Tukey´s test (α = 0.05) demonstrated that SFE presents higher values than DMT and both groups obtained higher values of gloss right after polishing than after six months. As the subjective data of gloss and roughness did not present normal distribution, Mann-Whitney and Friedman tests were applied for statistical analysis (α = 0.05). SFE group presented higher values of subjective gloss than DMT just right after polishing, however for other periods evaluated, there was no statistically significant difference. Regarding the surface roughness, there were no significant differences between the two groups evaluated, neither in terms of time, nor for the interaction time and polishing systems. Clinical Study: Fifty composite veneers (Amaris, VOCO) were made on patients and divided into two groups, according to the polishing systems used and assessed for subjective gloss obtained by patients and by examiners evaluation, surface roughness measured using a profilometer and veneer epoxi resin replicas and by patients with Visual Analogue Guide (VAG) and texture perception by the tongue comparing a natural tooth (control) right after polishing and after six months. The results were submitted to statistical analysis to verify the normal distribution of the data. For the surface roughness evaluated by the patients with the VAG no statistical differences were found. For the surface texture perception, patients were not able to identify differences right after the polishing as demonstrate by Fischer Exact and Chi-Square tests, however, after six months DMT group reported differences where natural teeth were consider rougher than the veneers. Regarding the perception of gloss by the patient, the Chi-Square test showed no difference between the groups. However, some patients of DMT group described the veneers glossier than the natural tooth. For the subjective gloss assessed by the professional, the Mann-Whitney and Wilcoxon tests demonstrated that DMT system showed higher values of gloss than SFE right after polishing and at six-month evaluation both groups demonstrated lower values of gloss. For roughness, the Mann-Whitney and Wilcoxon tests showed that the DMT group had lower values of surface roughness and SFE group showed an increase after six months evaluation. The results of the subjective assessment made by professionals were close to that made by patients and was an alternative to evaluate patient satisfaction with the treatment received(AU)

Effect of Long-Term Brushing on Deflection, Maximum Load, and Wear of Stainless Steel Wires and Conventional and Spot Bonded Fiber-Reinforced Composites.

Fiber-reinforced composite (FRC) retainers are an aesthetic alternative to conventional Stainless Steel splints. They are generally used with a full bonded technique, but some studies demonstrated that they could be managed with a spot bonding technique to significantly decrease their rigidity. In order to propose this FRC spot bonding technique for clinical use, the aim of this study was to evaluate mechanical properties and surface wear of fibers left uncovered. Tests were made by simulating tooth brushing, comparing FRC spot bonding technique splints with stainless steel and FRC traditional technique splints. Specimens were tested both at 0.1 mm of deflection and at maximum load, showing higher values of rigidity for the FRC full bonded technique. After tooth brushing, no significant reduction in values at 0.1 mm deflection was reported, while we found a similar reduction in these values for the Stainless Steel and FRC spot bonding technique at maximum load, and no significant variation for the FRC full bonded technique. SEM images after tooth brushing showed wear for FRC fibers left uncovered, while no relevant wear signs in metal and conventional FRC fibers were noticed. Results showed that FRC spot bonding technique has advantages in mechanical properties when compared to the FRC traditional full bonding technique, also after tooth brushing. However, the surface wear after tooth brushing in the FRC spot bonding technique is considerable and other tests must be performed before promoting this technique for routine clinical use.

Synthesis, characterization and application of Ag doped ZnO nanoparticles in a composite resin.

The biofilm accumulation over the composite resin restorations can contribute to the formation of secondary caries. In this way, antibacterial restorative composite resins are highly desired. Then, the purpose of this study was to modify a composite resins using Ag doped ZnO nanoparticles (NPs), evaluate the antibacterial and mechanical properties of the modified composite resin. The ZnO/AgNPs were synthesized by two different routes, polymeric precursor and coprecipitation methods, and characterized by thermal decomposition, X-ray diffraction, specific surface area by N2 desorption/desorption and scanning electron microscopy (SEM). Antibacterial activity of composite resin specimens (4 mm in height and 2 mm in diameter; n = 15) modified by ZnO/Ag nanoparticles was performed against 7-days Streptococcus mutans biofilm. Colony forming units (CFU/mL) were used to evaluate the bacterial activity. Additionally, the morphology and the bacteria adherence area were analyzed by SEM images. Cylindrical specimens (6 mm in height and 4 mm in diameter; n = 20) of the composite resin containing ZnO/Ag NPs were prepared to perform compressive strength in a universal mechanical test machine, and the surface of fractured specimens was analyzed by EDX element mapping to verify NPs homogeneity. The normal distribution was confirmed and the two-way analysis of variance (ANOVA) and Tukey's test for pair comparison were performed. The nanospheres of ZnO/Ag lead to a better biofilm inhibition, than nanoplates. No difference on compressive strength was found for the composite resin modified by ZnO/Ag nanoplates. Based on these results, this material could be a good option as a new restorative material.

Synthesis and application of triclosan methacrylate monomer in resin composites.

OBJECTIVES: To evaluate the antibacterial activity, bacterial viability, cytotoxicity, and mechanical/physical properties of a novel methacrylate triclosan-derivative monomer (TM) incorporated in dental resin composite. METHODS: TM was synthesized by esterification and, after characterization by FT-IR, was added to an experimental composite. Samples were divided into two groups according to TM presence, i.e., C1 (control) and C2 (C1 + 14.4% TM). Microbiological properties: Specimens (C1 and C2) were prepared and placed on bacterial suspensions of Streptococcus mutans. Antibacterial activity, MTT, and live/dead bacterial viability were used to test the resin composites. All assays were performed in triplicates. Mechanical properties: Specimens underwent compression (CS) and flexural strength (FS) tests conducted in an Instron universal testing machine at a crosshead speed of 0.5 mm/min. Physical properties: Specimens were assessed for Knoop hardness (KHN) and crosslink density (CD). Fourier transform infrared spectroscopy allowed the degree of conversion (DC) to be evaluated. Data were subjected to appropriate statistical tests according to data distribution and assay (p < 0.05). RESULTS: Microbiological properties: C2 showed the lowest biofilm accumulation and the highest membrane-compromised bacteria in the biofilm. Mechanical/physical properties: For CS, FS, KHN, and DC, there was no significant difference between groups C1 and C2; however, significant difference was observed for the CD assay. CONCLUSIONS: The triclosan methacrylate reduces bacterial adhesion of S. mutans and decreased the formation of bacterial biofilm without affecting important polymer properties. The triclosan methacrylate incorporated in resin composite could greatly reduce the live bacterial adhesion of S. mutans and decrease the formation of bacterial biofilm without affecting important polymer properties. CLINICAL SIGNIFICANCE: The resin composites containing triclosan methacrylate could greatly reduce the bacterial adhesion and biofilm formation. That might prevent the secondary caries round the margins of the restorations.

Synthesis of core-shell structured ZnO@m-SiO2 with excellent reinforcing effect and antimicrobial activity for dental resin composites.

OBJECTIVE: The aim of this study is to explore the reinforcing effect and the antimicrobial activity of the core-mesoporous shell structured ZnO@m-SiO2, which possesses the micromechanical resin matrix/filler interlocking in dental composites, and to investigate the effect of filler compositions on their physical-mechanical properties. METHODS: ZnO@m-SiO2 was synthesized by a simple self-assembly method and then characterized by electron microscopy, X-ray diffraction (XRD) and N2 adsorption/desorption measurements. Mechanical properties of dental composites reinforced with ZnO@m-SiO2 and nonporous SiO2 particles were measured with a universal mechanical testing machine. Fracture morphologies of these composites were observed by field-emission scanning electron microscopy (FE-SEM), and their antimicrobial activities were evaluated according to the ASTM E 2180-07 (2012) method. Resin composites containing unimodal silanized SiO2 were served as the control group. RESULTS: The impregnation of lower loading of ZnO@m-SiO2 (≤7wt%) into dental composites including silanized SiO2 substantially increased their mechanical properties. Among all composites, the optimal composite Z7S63 (ZnO@m-SiO2: silanized SiO2=7:63, wt/wt, total filler loading 70wt%) demonstrated the best flexural strength, flexural modulus and compression strength, which were increased by 121.2, 67.1 and 32.5%, respectively, in comparison with the control composite Z0S70. In addition, this optimal composite also exhibited superior antimicrobial activity (>99.9%) and acceptable degree of conversion, polymerization shrinkage and curing depth. SIGNIFICANCE: The incorporation of ZnO@m-SiO2 and silanized SiO2 as bimodal fillers led to the design and formulation of dental composites with excellent comprehensive performance, especially the improved mechanical properties and the superior antimicrobial activity.

Protein-repellent nanocomposite with rechargeable calcium and phosphate for long-term ion release.

OBJECTIVE: There has been no report on the effect of incorporating protein repellent 2-methacryloyloxyethyl phosphorylcholine (MPC) into a composite containing nanoparticles of amorphous calcium phosphate (NACP) on calcium (Ca) and phosphate (P) ion rechargeability. The objectives of this study were to develop a Ca and P ion-rechargeable and protein-repellent composite for the first time, and investigate the effects of MPC and NACP on mechanical properties, protein-repellency, anti-biofilm effects, and Ca and P ion recharge and re-release. METHODS: NACP were synthesized using a spray-drying technique. The resin contained ethoxylated bisphenol A dimethacrylate (EBPADMA) and pyromellitic glycerol dimethacrylate (PMGDM). Three NACP composites were made with 0 (control), 1.5%, and 3% of MPC. NACP (20%) and glass particles (50%) were also added into the resin. Protein adsorption was measured using a micro-bicinchoninic acid (BCA) method. A human saliva microcosm biofilm model was used to determine biofilm metabolic activity, lactic acid, and colony-forming units (CFU). Ca and P ion recharge and re-release were measured using a spectrophotometric method. RESULTS: Flexural strengths and moduli of CaP-rechargeable composites matched those of a commercial composite without CaP rechargeability (p>0.1). Adding 1.5% and 3% MPC reduced protein adsorption to 1/3 and 1/5, respectively, that of commercial composite (p<0.05). Adding 3% MPC suppressed biofilm metabolic activity and lactic acid production, and reduced biofilm CFU by nearly 2 logs. All three NACP composites had excellent ion rechargeability and higher levels of ion re-releases. One recharge yielded continuous ion release for 21 days. The release was maintained at the same level with increasing number of recharge cycles, indicating long-term ion release. Incorporation of MPC did not compromise the CaP ion rechargeability. SIGNIFICANCE: Incorporating 3% MPC into NACP nanocomposite greatly reduced protein adsorption, biofilm growth and lactic acid, decreasing biofilm CFU by nearly 2 logs, without compromising Ca and P recharge. This protein-repellent NACP-MPC rechargeable composite with long-term remineralization is promising for tooth restorations to inhibit secondary caries.

Effect of nano-bioceramics on monomer leaching and degree of conversion of resin-based composites.

The aim of this laboratory study was to evaluate the monomer leaching and degree of conversion (DC) from experimental bioactive resin composites (RBCs) and to do comparison with commercial bulkfill and packable resin composites. Experimental dimethacrylatebased resin composites were reinforced with silanated nano-hydroxyapatite (30 and 45 wt%). The ion leaching and DC of these resin composites were compared and contrasted with SDR™ and Filtek P60™ by using the high performance liquid chromatography (HPLC) and Fourier transform infrared spectroscopy (FTIR), respectively. A significant difference was found in elution of monomer between the resin composites. SDR™ showed significantly high monomer elution and structural changes compared to other resin composites. The DC of bioactive RBCs showed the highest conversion rate after polymerization. Resin composite with nano-hydroxyapatite with the presence of a bioactive component might provide biomimetic approach for the material. Moreover, a low concentration of nanohydroxyapatite nano-fillers have shown better properties than micro-fillers based resin composites.

Preparation and characterization of Bis-GMA-free dental composites with dimethacrylate monomer derived from 9,9-Bis[4-(2-hydroxyethoxy)phenyl]fluorene.

OBJECTIVE: Synthesize a new BPA-free monomer for use in methacrylate-based materials and evaluate critical properties of resin and composite materials based on the monomer. METHODS: Bis-EFMA was synthesized through reaction between 9,9-bis[4-(2-hydroxyethoxy)-phenyl]fluorene and 2-(methacryloyloxy)ethyl isocyanate. Experimental Bis-EFMA-based resin (Bis-EFMA/TEGDMA=50/50, wt./wt.) and composite were prepared. Critical properties were investigated according to standard or referenced methods Bis-GMA/TEGDMA (50/50, wt./wt.) resin system, Bis-GMA-based composite and 3M ESPE Filtek™ Z250 were used as controls. RESULTS: FT-IR and 1H NMR spectra confirmed the structure of Bis-EFMA monomer. Cured resin materials: Bis-EFMA-based and Bis-GMA-based resins had nearly the same degree of conversion (p>0.05); Bis-EFMA-based resin had significantly lower shrinkage, water sorption and solubility, and cytotoxicity than Bis-GMA-based resin (p<0.05); flexural properties of Bis-EFMA-based resin were all higher than those of Bis-GMA-based resin (p<0.05). Cured composite materials: There was no significant difference in conversion (p>0.05); Bis-EFMA-based composite had significantly lower shrinkage and solubility (p<0.05); water sorption of Bis-EFMA-based composite and Z250 were similar (p>0.05), but lower compared to Bis-GMA-based composite (p<0.05); Bis-EFMA-based composite had the deepest curing depth (p<0.05); Before water immersion, there was no significant difference in flexural strength between Bis-EFMA-based composite and each control composite (p>0.05), while FS became lower than that of Z250 (p<0.05), but higher than that of Bis-GMA-based composite (p<0.05) after water immersion; Flexural modulus of Bis-EFMA-based composite and Z250 were nearly the same (p>0.05), higher than that of Bis-GMA-based composite (p<0.05); Bis-EFMA-based composite showed less cytotoxicity than Bis-GMA-based composite and Z250 (p<0.05). SIGNIFICANCE: Bis-EFMA has potential as a substitute for Bis-GMA to prepare Bis-GMA-free dental composites.

BisGMA analogues as monomers and diluents for dental restorative composite materials.

Current commercially available dental composite materials have certain limitations for their use, including high monomer viscosity and high polymerization shrinkage, resulting in residual stresses and interfacial gaps. This study focused on the chemical modification of resin monomer bisphenol A-glycidyl methacrylate (bisGMA), so as to reduce the viscosity and polymerization shrinkage. In this design, the hydroxyl groups of bisGMA were transformed into ester groups with various alkyl chain length and branching. The modified monomers showed promising properties including reduced viscosity, reduced polymerization shrinkage, increased hydrophobicity, increased degree of double bond conversion, and improved mechanical properties of the resulting dental resin composites. The structure/property relationships of the new monomers were investigated, and optimal monomer structures were identified for dental composites with improved properties.

Preparation of a low viscosity urethane-based composite for improved dental restoratives.

Several new urethane-based dimethacrylates were synthesized, characterized and used to formulate the resin composites. Compressive strength (CS) was used as a screen tool to evaluate the mechanical property of the formed composites. Flexural strength, diametral tensile strength, water sorption, degree of conversion and shrinkage of the composites were also evaluated. The results show that most of the synthesized urethane-based dimethacrylates were solid, which are not suitable to dental filling restorations. However, it was found that liquid urethane-based dimethacrylates could be derivatized using asymmetrical methacrylate synthesis. Not only the newly synthesized urethane-based dimethacrylates showed lower viscosity values but also their constructed composites exhibited higher mechanical strengths. Without triethyleneglycol dimethacrylate (TEGDMA) addition, the new urethane-constructed composites showed significantly lower water sorption and shrinkage.

Controlled release of chlorhexidine from a HEMA-UDMA resin using a magnetic field.

OBJECTIVES: To functionalize novel chlorhexidine (CHX) particles with iron oxide (Fe3O4) nanoparticles and control their release kinetics in a dental resin using an external magnetic field. METHODS: Fe3O4 nanoparticles were synthesized and incorporated into spherical CHX particles and the powder was freeze dried. Resin disc specimens were produced using a UDMA-HEMA resin mixed with freeze dried spherical Fe3O4-CHX particles (5wt.%), which were placed into a Teflon mould (10mm diameter×1mm depth) and covered with a Mylar strip. A MACS magnet was left in contact for 0min (Group 1), 5min (Group 2) or 10min (Group 3) and the resin discs subsequently light cured (Bluedent LED pen, Bulgaria) for 60s per side. The resin discs were immersed in deionized water at various time points up to 650h. UV-Vis absorbance was used to determine the CHX content. CHX released for each time point was determined. The functionalized CHX particles and resin discs were characterized using TEM, TGA, EDX and SEM. RESULTS: Fe3O4 nanoparticles (20nm) incorporated into the spherical CHX particles led to a mean (SD) particle size reduction from 17.15 (1.99)µm to 10.39 (2.61)µm. The presence of Fe3O4 nanoparticles in the spherical CHX particles was confirmed with SEM, EDX, and TGA. SEM of Group 1 resin discs (no magnetic exposure) showed functionalized CHX spheres were homogeneously distributed within the resin discs. For resin discs which had magnetic exposure (5 or 10min) the particles started to cluster nearer the surface (Group 2: 43.7%, Group 3: 57.3%), to a depth of 94µm. UV-Vis absorbance revealed Group 1 resin discs had a cumulative CHX release of 4.4% compared to 5.9% for Group 2 and 7.4% for Group 3 resin discs, which had magnetic exposure (5, 10min). SIGNIFICANCE: Fe3O4 nanoparticle functionalized CHX spheres demonstrated a magnetic field responsive property. A magnetic field responsive release of CHX may be useful in clinical situations where the drug can be directed to give a tailored release at the site of infection.

Ion-releasing dental restorative composites containing functionalized brushite nanoparticles for improved mechanical strength.

OBJECTIVES: This study describes the synthesis of brushite nanoparticles (CaHPO4·2H2O) functionalized with triethylene glycol dimethacrylate (TEGDMA) and their application in dental restorative composites with remineralizing capabilities. METHODS: Nanoparticles were synthesized, with TEGDMA being added to one of the precursor solutions at three different molar ratios (0:1, 0.5:1 and 1:1, in relation to the ammonium phosphate precursor). Then, they were added (10 vol%) to a photocurable dimethacrylate matrix containing 50 vol% of reinforcing glass particles. The resulting composites were tested for degree of conversion, biaxial flexural strength and elastic modulus (after 24h and 28days in water), and ion release (over a 28-day period). Commercial composites (one microhybrid and one microfilled) were tested as controls. RESULTS: The final TEGDMA content in the functionalizing layer was modulated by the molar ratio added to the precursor solution. Functionalization reduced nanoparticle size, but did not reduce agglomeration. Improved mechanical properties were found for the composite containing nanoparticles with higher TEGDMA level in comparison to the composite containing non-functionalized nanoparticles or those with a low TEGDMA level. All brushite composites presented statistically significant reductions in strength after 28 days in water, but only the material with high-TEGDMA nanoparticles retained strength similar to the microhybrid commercial control. Overall, ion release was not affected by functionalization and presented steady levels for 28 days. SIGNIFICANCE: Though agglomeration was not reduced by functionalization, the improvement in the matrix-nanoparticle interface allowed for a stronger material, without compromising its remineralizing potential.

Synthesis and characterization of Ciprofloxacin-containing divinyl oligomers and assessment of their biodegradation in simulated salivary esterase.

OBJECTIVE: Two leading causes contributing to dental restoration replacement are the marginal breakdown at the composite/dentin interface and secondary caries mediated by bacteria. The objective of the present study was to synthesize oligomers which incorporated enhanced bio-stability but would also be able to generate antimicrobial function if they underwent degradation. METHODS: Stability was incorporated into the oligomers by generating structural features that would physically hinder the availability of hydrolytically sensitive groups in the oligomers. As a proof-of concept for the antibacterial feature, antimicrobial function was achieved by covalently incorporating Ciprofloxacin (CF) into the backbone of cross-linking divinyl oligomers (referred to as EDV and HLH-CFPEG). The hydrolytic stability of the oligomers was studied in simulated human salivary esterase and compared to the commercial monomer 2,2-bis[4(2-hydroxy-3-methacryloxypropoxy)-phenyl]propane (BisGMA). RESULTS: Both drug oligomers were found to be significantly more stable than BisGMA. Upon degradation, both drug oligomers released CF differentially in free form. Polymer synthesis from resin formulations containing 15wt% HLH-CFPEG showed a high degree of vinyl group conversion and gel content, and under hydrolytic conditions showed the release of CF during a 28-day monitoring study period. SIGNIFICANCE: HLH-CFPEG can be used in dental resin adhesive systems for local delivery of CF to the marginal interface. Minimizing the growth of Streptococcus mutans at the marginal site can improve longevity by reducing esterase activity derived specifically from S. mutans.