Surface modification and microstructure of single-walled carbon nanotubes for dental resin-based composites

Flexural Strength of an Indirect Composite Modified with Single-Wall Carbon Nanotubes

OBJECTIVES

 The low resistance to fracture has limited the use of indirect composite resins for dental restorations, particularly in regions that are exposed to strong occlusal forces. To overcome this issue, different types of reinforcement for composites have been proposed, one of which is carbon nanotubes (CNTs). The aim of this study was to evaluate the flexural resistance of one commercial indirect composite resin (Sinfony, 3M/ESPE) after incorporation of single-wall carbon nanotubes (SWCNTs; Sigma-Aldrich, Inc., St. Louis, Missouri, United States) with or without the silanization form.

MATERIALS AND METHODS

 Specimens of composite resin were fabricated in a Teflon mold. The composite resin was prepared according to the manufacturer's instructions (n = 10 for each group), with SWCNTs in three concentrations.

STATISTICAL ANALYSIS

 The SWCNTs and SWCNT/SiO2-ATES specimens were evaluated by transmission electron microscopy, and a flexural test was conducted according to the ISO 4049/2009. Flexural strength data in MPa were submitted to one-way ANOVA following Tukey (p < 0.05).

RESULTS

 The SWCNTs did not improve the flexural strength of indirect composite resin when compared with the control, independent of the concentration added (p > 0.05). However, when SWCNTs and SWCNTs/SiO2-ATES were compared, the SWCNTs/SiO2-ATES showed higher values than the three concentrations of SWCNTs (p < 0.05).

CONCLUSION

 The silanization process improves the SWCNTs strength proprieties, but the modification of chemical bonding between SWCNT and SWCNT/SiO2-ATES modified resins, in different concentrations, did not improve the composite resin flexural strength.

Nanotechnology for Dentistry: Prospects and Applications

In the XXI century, application of nanostructures in oral medicine has become common. In oral medicine, using nanostructures for the treatment of dental caries constitutes a great challenge. There are extensive studies on the implementation of nanomaterials to dental composites in order to improve their properties, e.g., their adhesive strength. Moreover, nanostructures are helpful in dental implant applications as well as in maxillofacial surgery for accelerated healing, promoting osseointegration, and others. Dental personal care products are an important part of oral medicine where nanomaterials are increasingly used, e.g., toothpaste for hypersensitivity. Nowadays, nanoparticles such as macrocycles are used in different formulations for early cancer diagnosis in the oral area. Cancer of the oral cavity-human squamous carcinoma-is the sixth leading cause of death. Detection in the early stage offers the best chance at total cure. Along with diagnosis, macrocycles are used for photodynamic mechanism-based treatments, which possess many advantages, such as protecting healthy tissues and producing good cosmetic results. Application of nanostructures in medicine carries potential risks, like long-term influence of toxicity on body, which need to be studied further. The introduction and development of nanotechnologies and nanomaterials are no longer part of a hypothetical future, but an increasingly important element of today's medicine.

Long-Chain Modification of the Tips and Inner Walls of MWCNTs and Their Nanocomposite Reverse Osmosis Membranes

Multi-walled carbon nanotubes (MWCNTs) were modified on the tips and inner walls by 12-chloro-12-oxododecanedioic acid-methyl ester groups and then added to the polyamide composite membranes to prepare MWCNT-CH₂OCOC₁₂H₂₃O₂ membranes for desalination. The characterization results of transmission electron microscopy, Fourier transform, infrared transform, and thermogravimetric analysis showed that the 12-chloro-12-oxododecanedioic acid-methyl ester group was successfully grafted to the entrances and inner walls of the MWCNTs. The performance of the MWCNTs' composite membranes was evaluated by scanning electron microscopy, contact angle, and filtration test. The modified membrane morphology is more uniform, and there is no structural damage. The grafting of carbon nanotubes with methyl 12-chloro-12-oxydodecyldicarboxylate could improve the hydrophilicity of the membrane. Under identical conditions, the water flux of MWCNT-CH₂OCOC₁₂H₂₃O₂ membranes was higher than that of the pristine carbon nanotube's membrane, and the desalination rate was also slightly improved.

Effect of Nanostructures on the Properties of Glass Ionomer Dental Restoratives/Cements: A Comprehensive Narrative Review

Overall perspective of nanotechnology and reinforcement of dental biomaterials by nanoparticles has been reported in the literature. However, the literature regarding the reinforcement of dental biomaterials after incorporating various nanostructures is sparse. The present review addresses current developments of glass ionomer cements (GICs) after incorporating various metallic, polymeric, inorganic and carbon-based nanostructures. In addition, types, applications, and implications of various nanostructures incorporated in GICs are discussed. Most of the attempts by researchers are based on the laboratory-based studies; hence, it warrants long-term clinical trials to aid the development of suitable materials for the load bearing posterior dentition. Nevertheless, a few meaningful conclusions are drawn from this substantial piece of work; they are as follows: (1) most of the nanostructures are likely to enhance the mechanical strength of GICs; (2) certain nanostructures improve the antibacterial activity of GICs against the cariogenic bacteria; (3) clinical translation of these promising outcomes are completely missing, and (4) the nanostructured modified GICs could perform better than their conventional counterparts in the load bearing posterior dentition.

The Development of Filler Morphology in Dental Resin Composites: A Review

Dental resin composites (DRCs) with diverse fillers added are widely-used restorative materials to repair tooth defects. The addition of fillers brings an improvement in the mechanical properties of DRCs. In the past decade, diverse fillers have emerged. However, the change of emerging fillers mainly focuses on the chemical composition, while the morphologic characteristics changes are often ignored. The fillers with new morphologies not only have the advantages of traditional fillers (particles, fibrous filler, etc.), but also endow some additional functional characteristics (stronger bonding ability to resin matrix, polymerization resistance, and wear resistance, drug release control ability, etc.). Moreover, some new morphologies are closely related to the improvement of traditional fillers, porous filler vs. glass particles, core-sheath fibrous vs. fibrous, etc. Some other new morphology fillers are combinations of traditional fillers, UHA vs. HA particles and fibrous, tetrapod-like whisker vs. whisker and fibrous filler, mesoporous silica vs. porous and silica particles. In this review, we give an overall description and a preliminary summary of the fillers, as well as our perspectives on the future direction of the development of novel fillers for next-generation DRCs.

Functional fillers for dental resin composites

Dental resin composites (DRCs) are popular materials to repair caries. Although various types of DRCs with different characteristics have been developed, restoration failures still exist. Bulk fracture and secondary caries have been considered as main causes for the failure of composites restoration. To address these problems, various fillers with specific functions have been introduced and studied. Some fillers with specific morphologies such as whisker, fiber, and nanotube, have been used to increase the mechanical properties of DRCs, and other fillers releasing ions such as Ag⁺, Ca²⁺, and F^-, have been used to inhibit the secondary caries. These functional fillers are helpful to improve the performances and lifespan of DRCs. In this article, we firstly introduce the composition and development of DRCs, then review and discuss the functional fillers classified according to their roles in the DRCs, finally give a summary on the current research and predict the trend of future development.

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.

Nanomaterials in Dentistry: State of the Art and Future Challenges

Nanomaterials are commonly considered as those materials in which the shape and molecular composition at a nanometer scale can be controlled. Subsequently, they present extraordinary properties that are being useful for the development of new and improved applications in many fields, including medicine. In dentistry, several research efforts are being conducted, especially during the last decade, for the improvement of the properties of materials used in dentistry. The objective of the present article is to offer the audience a complete and comprehensive review of the main applications that have been developed in dentistry, by the use of these materials, during the last two decades. It was shown how these materials are improving the treatments in mainly all the important areas of dentistry, such as endodontics, periodontics, implants, tissue engineering and restorative dentistry. The scope of the present review is, subsequently, to revise the main applications regarding nano-shaped materials in dentistry, including nanorods, nanofibers, nanotubes, nanospheres/nanoparticles, and zeolites and other orders porous materials. The results of the bibliographic analysis show that the most explored nanomaterials in dentistry are graphene and carbon nanotubes, and their derivatives. A detailed analysis and a comparative study of their applications show that, although they are quite similar, graphene-based materials seem to be more promising for most of the applications of interest in dentistry. The bibliographic study also demonstrated the potential of zeolite-based materials, although the low number of studies on their applications shows that they have not been totally explored, as well as other porous nanomaterials that have found important applications in medicine, such as metal organic frameworks, have not been explored. Subsequently, it is expected that the research effort will concentrate on graphene and zeolite-based materials in the coming years. Thus, the present review paper presents a detailed bibliographic study, with more than 200 references, in order to briefly describe the main achievements that have been described in dentistry using nanomaterials, compare and analyze them in a critical way, with the aim of predicting the future challenges.

Chlorhexidine-modified nanotubes and their effects on the polymerization and bonding performance of a dental adhesive

OBJECTIVES

The purpose of this study was to synthesize chlorhexidine (CHX)-encapsulated aluminosilicate clay nanotubes (Halloysite®, HNTs) and to incorporate them into the primer/adhesive components of an etch-and-rinse adhesive system (SBMP; Scotchbond Multipurpose, 3M ESPE) and to test their effects on degree of conversion, viscosity, immediate and long-term bonding to dentin.

METHODS

CHX-modified HNTs were synthesized using 10% or 20% CHX solutions. The primer and the adhesive components of SBMP were incorporated with 15wt.% of the CHX-encapsulated HNTs. Degree of conversion (DC) and viscosity analyses were performed to characterize the modified primers/adhesives. For bond strength testing, acid-etched dentin was treated with one of the following: SBMP (control); 0.2%CHX solution before SBMP; CHX-modified primers+SBMP adhesive; SBMP primer+CHX-modified adhesives; and SBMP primer+CHX-free HNT-modified adhesive. The microtensile bond strength test was performed after immediate (24h) and long-term (6 months) of water storage. Data were analyzed using ANOVA and Tukey (α=5%) and the Weibull analysis.

RESULTS

DC was greater for the CHX-free HNT-modified adhesive, whereas the other experimental adhesives showed similar DC as compared with the control. Primers were less viscous than the adhesives, without significant differences within the respective materials. At 24h, all groups showed similar bonding performance and structural reliability; whereas at the 6-month period, groups treated with the 0.2%CHX solution prior bonding or with the CHX-modified primers resulted in greater bond strength than the control and superior reliability.

SIGNIFICANCE

The modification of a primer or adhesive with CHX-encapsulated HNTs was an advantageous approach that did not impair the polymerization, viscosity and bonding performance of the materials, showing a promising long-term effect on resin-dentin bonds.

Boron Nitride Nanotubes as Filler for Resin-Based Dental Sealants

The aim of this study was to evaluate the influence of boron-nitride nanotubes (BNNTs) on the properties of resin-based light-curing dental sealants (RBSs) when incorporated at different concentration. RBSs were formulated using methacrylate monomers (90 wt.% TEGDMA, 10 wt.% Bis-GMA). BNNTs were added to the resin blend at 0.1 wt.% and 0.2 wt.%. A Control group without filler was also designed. Degree of conversion, ultimate tensile strength, contact angle, surface free energy, surface roughness and color of the RBSs were evaluated for the tested materials. Their cytotoxicity and mineral deposition ability (Bioactivity) were also assessed. A suitable degree of conversion, no effect in mechanical properties and no cytotoxic effect was observed for the experimental materials. Moreover, the surface free energy and the surface roughness decreased with the addition of BNNTs. While the color analysis showed no difference between specimens containing BNNTs and the control group. Mineral deposition occurred in all specimens containing BNNTs after 7d. In conclusion, the incorporation of BNNTs may provide bioactivity to resin-based dental sealants and reduce their surface free energy.

Antibacterial quaternary ammonium compounds in dental materials: A systematic review

OBJECTIVE

Quaternary ammonium compounds (QACs) represent one of the most effective classes of disinfectant agents in dental materials and resin nanocomposites. This reviews aims to give a wide overview on the research in the field of antibacterial QACs in dental materials and nanocomposites.

METHOD

An introduction to dental materials components as well as the microorganisms and methods of evaluation for the antimicrobial assays are presented. Then, the properties and synthesis route of QACs, as monomer and filler, are shown. Finally, antimicrobial monomers and fillers, specifically those contain quaternary ammonium salts (QASs), in dental materials are reviewed.

RESULTS

QACs have been used as monomer and micro/nanofiller in restorative dentistry. They possess one or more methacrylate functional groups to participate in polymerization reactions. QACs with multiple methacrylate groups can also be used as crosslinking agents. Furthermore, QACs with chain length from ∼12 to 16 have higher antimicrobial activity in cured dental resins. In general, increasing the chain length leads to a threshold value (critical point) and then it causes decrease in the antimicrobial activity.

SIGNIFICANCE

The current state of the art of dental materials and resin nanocomposites includes a wide variety of antimicrobial materials. Among them, QACs presents low cytotoxicity and excellent long-term antimicrobial activity without leaching out over time.

Effect of dentin surface modification using carbon nanotubes on dental bonding and antibacterial ability

This study developed carbon nanotube coatings for the dentin surface and investigated the bonding strength and the in vitro antibacterial properties of carbon nanotube-coated dentin. Single-walled carbon nanotubes and multi-walled carbon nanotubes were first modified and then characterized using Fourier-transform infrared spectroscopy, scanning electron microscope, and transmission electron microscopy. Second, dentin samples were coated using either single-walled carbon nanotubes or multi-walled carbon nanotubes and observed under a scanning electron microscope. Then, the shear bonding strength and antibacterial properties of the dentin samples were tested. The results showed that both modified single-walled carbon nanotubes and multi-walled carbon nanotubes formed a stable coating on the dentin surface without affecting the shear bonding strength. Moreover, the antibacterial properties of the single-walled carbon nanotube-coated samples was obviously superior to those of the multi-walled carbon nanotube-coated samples. Consequently, single-walled carbon nanotube coating may be an antibacterial agent for potential application in the dental bonding field.

A comparative study on the in vitro cytotoxic responses of two mammalian cell types to fullerenes, carbon nanotubes and iron oxide nanoparticles

The present study was designed to evaluate and compare the time- and dose-dependent cellular response of human periodontal ligament fibroblasts (hPDLFs), and mouse dermal fibroblasts (mDFs) to three different types of nanoparticles (NPs); fullerenes (C₆₀), single walled carbon nanotubes (SWCNTs) and iron (II,III) oxide (Fe₃O₄) nanoparticles via in vitro toxicity methods, and impedance based biosensor system. NPs were characterized according to their morphology, structure, surface area, particle size distribution and zeta potential by using transmission electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller, dynamic light scattering and zeta sizer analyses. The Mössbauer spectroscopy was used in order to magnetically characterize the Fe₃O₄ NPs. The hPDLFs and mDFs were exposed to different concentrations of the NPs (0.1, 1, 10, 50 and 100 μg/mL) for predetermined time intervals (6, 24 and 48 h) under controlled conditions. Subsequently, NP exposed cells were tested for viability, membrane leakage and generation of intracellular reactive oxygen species. Additional to in vitro cytotoxicity assays, the cellular responses to selected NPs were determined in real time using an impedance based biosensor system. Taken together, information obtained from all experiments suggests that toxicity of the selected NPs is cell type, concentration and time dependent.

Effect of random/aligned nylon-6/MWCNT fibers on dental resin composite reinforcement

The aims of this study were (1) to synthesize and characterize random and aligned nanocomposite fibers of multi-walled carbon nanotubes (MWCNT)/nylon-6 and (2) to determine their reinforcing effects on the flexural strength of a dental resin composite. Nylon-6 was dissolved in hexafluoropropanol (10 wt%), followed by the addition of MWCNT (hereafter referred to as nanotubes) at two distinct concentrations (i.e., 0.5 or 1.5 wt%). Neat nylon-6 fibers (without nanotubes) were also prepared. The solutions were electrospun using parameters under low- (120 rpm) or high-speed (6000 rpm) mandrel rotation to collect random and aligned fibers, respectively. The processed fiber mats were characterized by scanning (SEM) and transmission (TEM) electron microscopies, as well as by uni-axial tensile testing. To determine the reinforcing effects on the flexural strength of a dental resin composite, bar-shaped (20×2×2 mm(3)) resin composite specimens were prepared by first placing one increment of the composite, followed by one strip of the mat, and one last increment of composite. Non-reinforced composite specimens were used as the control. The specimens were then evaluated using flexural strength testing. SEM was done on the fractured surfaces. The data were analyzed using ANOVA and the Tukey׳s test (α=5%). Nanotubes were successfully incorporated into the nylon-6 fibers. Aligned and random fibers were obtained using high- and low-speed electrospinning, respectively, where the former were significantly (p<0.001) stronger than the latter, regardless of the nanotubes׳ presence. Indeed, the dental resin composite tested was significantly reinforced when combined with nylon-6 fibrous mats composed of aligned fibers (with or without nanotubes) or random fibers incorporated with nanotubes at 0.5 wt%.

Avaliação da dureza superficial de cimentos de ionômero de vidro reforçados por nanotubos de carbono

Introdução Os cimentos de ionômero de vidro (CIV) são materiais com baixa resistência à tração e ao cisalhamento, mostrando-se, portanto, contraindicados para áreas sujeitas às grandes cargas oclusais. Objetivo Avaliar o efeito da incorporação de nanotubos de carbono em CIV por meio de dureza superficial Knoop. Material e método Foram confeccionados 48 espécimes, divididos em quatro grupos, de acordo com o tipo de CIV (n=12) – convencional ou de alta viscosidade, incorporados ou não de nanotubos de carbono (NC) a 2%: (A) Vidrion R; (B) Vidrion R + NC 2%; (C) Vitro Molar, e (D) Vitro Molar + NC 2%. Os espécimes foram preparados utilizando-se seringa Centrix, para inserção do material em moldes plásticos, e armazenados em água deionizada por 24 horas. Após polimento, realizou-se o teste de dureza superficial com penetrador do tipo Knoop. Foram realizadas cinco endentações em cada espécime, distanciadas entre si em 100 µm. Resultado Os valores médios de dureza foram 58,96 ± 8,29 (A), 34,81 ± 5,78 (B), 60,84 ± 4,91 (C) e 41,97 ± 5,45 (D). O teste ANOVA detectou diferenças estatisticamente significantes para os dois parâmetros estudados, tipo de material (p=0,016) e inclusão de NC (p<0,0001). Pelo teste de Tukey, observou-se que os grupos A e C foram estatisticamente semelhantes (p>0,05), enquanto os grupos B e D apresentaram diferenças significativas (p<0,05). Ao comparar o fator incorporação ou não de NC, observou-se diferença significativa entre os grupos A e B, e entre os grupos C e D (p<0,05). Conclusão A incorporação de nanotubos de carbono influenciou negativamente os valores de dureza superficial para os dois tipos de CIV utilizados.

Review of nanomaterials in dentistry: interactions with the oral microenvironment, clinical applications, hazards, and benefits

Interest in the use of engineered nanomaterials (ENMs) as either nanomedicines or dental materials/devices in clinical dentistry is growing. This review aims to detail the ultrafine structure, chemical composition, and reactivity of dental tissues in the context of interactions with ENMs, including the saliva, pellicle layer, and oral biofilm; then describes the applications of ENMs in dentistry in context with beneficial clinical outcomes versus potential risks. The flow rate and quality of saliva are likely to influence the behavior of ENMs in the oral cavity, but how the protein corona formed on the ENMs will alter bioavailability, or interact with the structure and proteins of the pellicle layer, as well as microbes in the biofilm, remains unclear. The tooth enamel is a dense crystalline structure that is likely to act as a barrier to ENM penetration, but underlying dentinal tubules are not. Consequently, ENMs may be used to strengthen dentine or regenerate pulp tissue. ENMs have dental applications as antibacterials for infection control, as nanofillers to improve the mechanical and bioactive properties of restoration materials, and as novel coatings on dental implants. Dentifrices and some related personal care products are already available for oral health applications. Overall, the clinical benefits generally outweigh the hazards of using ENMs in the oral cavity, and the latter should not prevent the responsible innovation of nanotechnology in dentistry. However, the clinical safety regulations for dental materials have not been specifically updated for ENMs, and some guidance on occupational health for practitioners is also needed. Knowledge gaps for future research include the formation of protein corona in the oral cavity, ENM diffusion through clinically relevant biofilms, and mechanistic investigations on how ENMs strengthen the tooth structure.

Resin composites reinforced by nanoscaled fibers or tubes for dental regeneration

It has been stated clearly that nanofillers could make an enhancement on the mechanical performances of dental composites. In order to address current shortage of traditional dental composites, fillers in forms of nanofibers or nanotubes are broadly regarded as ideal candidates to greatly increase mechanical performances of dental composites with low content of fillers. In this review, the efforts using nanofibers and nanotubes to reinforce mechanical performances of dental composites, including polymeric nanofibers, metallic nanofibers or nanotubes, and inorganic nanofibers or nanotubes, as well as their researches related, are demonstrated in sequence. The first purpose of current paper was to confirm the enhancement of nanofibers or nanotubes' reinforcement on the mechanical performances of dental restorative composite. The second purpose was to make a general description about the reinforcement mechanism of nanofibers and nanotubes, especially, the impact of formation of interphase boundary interaction and nanofibers themselves on the advanced mechanical behaviors of the dental composites. By means of the formation of interface interaction and poststretching nanofibers, reinforced effect of dental composites by sorts of nanofibers/nanotubes has been successfully obtained.

Novel dental composites reinforced with zirconia-silica ceramic nanofibers

OBJECTIVE

To fabricate and characterize dental composites reinforced with various amounts of zirconia-silica (ZS) or zirconia-yttria-silica (ZYS) ceramic nanofibers.

METHODS

Control composites (70 wt% glass particle filler, no nanofibers) and experimental composites (2.5, 5.0, and 7.5 wt% ZS or ZYS nanofibers replacing glass particle filler) were prepared by blending 29 wt% dental resin monomers, 70 wt% filler, and 1.0 wt% initiator, and polymerized by either heat or dental curing light. Flexural strength (FS), flexural modulus (FM), energy at break (EAB), and fracture toughness (FT) were tested after the specimens were stored in 37°C deionized water for 24h, 3 months, or 6 months. Degree of conversion (DC) of monomers in composites was measured using Fourier transformed near-infrared (FT-NIR) spectroscopy. Fractured surfaces were observed by field-emission scanning electron microscope (FE-SEM). The data were analyzed using ANOVA with Tukey's Honestly Significant Differences test used for post hoc analysis.

RESULTS

Reinforcement of dental composites with ZS or ZYS nanofibers (2.5% or 5.0%) can significantly increase the FS, FM and EAB of dental composites over the control. Further increase the content of ZS nanofiber (7.5%), however, decreases these properties (although they are still higher than those of the control). Addition of nanofibers did not decrease the long-term mechanical properties of these composites. All ZS reinforced composites (containing 2.5%, 5.0% and 7.5% ZS nanofibers) exhibit significantly higher fracture toughness than the control. The DC of the composites decreases with ZS nanofiber content.

SIGNIFICANCE

Incorporation of ceramic nanofibers in dental composites can significantly improve their mechanical properties and fracture toughness and thus may extend their service life.

Human endothelial colony forming cells undergo vasculogenesis within biphasic calcium phosphate bone tissue engineering constructs

An important consideration in bone regeneration is the need for expedited neovascularization within the defect site. Formation of a vascular network is critical for cell viability and normal function leading to tissue regeneration, but spontaneous angiogenesis is too slow to yield sufficient vessel formation. In this pilot study, human umbilical cord blood (hUCB)-derived endothelial colony forming cells (ECFCs) were evaluated for in vivo vasculogenesis in the macropores of biphasic calcium phosphate (BCP)/bone morphogenetic protein-2 (BMP-2) bone tissue engineering constructs. Constructs were implanted on the abdominal wall of NOD/SCID mice for 4 weeks. This study demonstrated in vivo vasculogenesis by human ECFCs within the macropore space of BCP/BMP-2 constructs. The human ECFC-derived vessels anastomosed with the host vasculature and perfused vessels were visible in the very center of the 5mm diameter, 2.5mm tall scaffolds. Additionally, the vessels were evenly distributed throughout the construct. This study suggests that scaffolds containing ECFCs have significant potential for expedited neovascularization in bony defects.

Recent advances and developments in composite dental restorative materials

Composite dental restorations represent a unique class of biomaterials with severe restrictions on biocompatibility, curing behavior, esthetics, and ultimate material properties. These materials are presently limited by shrinkage and polymerization-induced shrinkage stress, limited toughness, the presence of unreacted monomer that remains following the polymerization, and several other factors. Fortunately, these materials have been the focus of a great deal of research in recent years with the goal of improving restoration performance by changing the initiation system, monomers, and fillers and their coupling agents, and by developing novel polymerization strategies. Here, we review the general characteristics of the polymerization reaction and recent approaches that have been taken to improve composite restorative performance.

Nanotechnology applications in medicine and dentistry

Nanotechnology, or nanoscience, refers to the research and development of an applied science at the atomic, molecular, or macromolecular levels (i.e. molecular engineering, manufacturing). The prefix "nano" is defined as a unit of measurement in which the characteristic dimension is one billionth of a unit. Although the nanoscale is small in size, its potential is vast. As nanotechnology expands in other fields, clinicians, scientists, and manufacturers are working to discover the uses and advances in biomedical sciences. Applications of nanotechnology in medical and dental fields have only approached the horizon with opportunities and possibilities for the future that can only be limited by our imagination. This paper provides an early glimpse of nanotechnology applications in medicine and dentistry to illustrate their potentially far-reaching impacts on clinical practice. It also narrates the safety issues concerning nanotechnology applications.

Reinforcement of resin based cement with titania nanotubes

OBJECTIVE

One of the limitations of resin cements and flowable dental composites is their poor mechanical properties such as low flexural strength and fracture resistance under body conditions. The present study was performed to enhance the mechanical properties of commercial acrylic cement (CMW1) by introducing novel nanostructured titania tubes (n-TiO(2) tubes) into the cement matrix, with the tubes acting as a reinforcing phase. The long term objective is to add these fillers as reinforcement to dental resin cements and flowable composites in combination with existing fillers.

METHODS

The surface of the n-TiO(2) tubes was modified using a bi-functional monomer, methacrylic acid. The n-TiO(2) tube content of the cement was varied from 0 to 2 wt.%. The following cement properties were investigated: maximum polymerization temperature (T(max)), dough time (t(dough)), setting time (t(set)), complex viscosity-versus-time, radiopacity, fracture toughness (K(IC)), flexural strength (FS), flexural modulus (FM) and in vitro biocompatibility.

RESULTS

Based on the determined mechanical properties, the optimized composition was found at 1 wt.% n-TiO(2) tubes, which provided a significant increase in K(IC) (73%), FS (42%) and FM (56%). However the rheology, radiopacity and biocompatibility were not different from the control (CMW1).

SIGNIFICANCE

Enhanced interaction and strong adhesion between the functionalized n-TiO(2) tubes and polymer matrix allows external mechanical stress to be more effectively transferred through the filler-matrix interface. This novel filler in conjunction with the existing ones can be used to reinforce orthopedic and dental cements as well as flowable dental composites without altering the rheology, radiopacity and biocompatibility.