Mechanical Properties Of Dental Composites Research Articles

Influence of fibre reinforcement on selected mechanical properties of dental composites.

For splinting or designing adhesive bridges, reconstructive composite structures with increased mechanical properties owing to embedded reinforcement fibres are used. The aim of this article was to determine the influence of glass and aramid fibres on the mechanical strength of composites reinforced with these fibres. Two polymer-ceramic microhybrid materials: Boston and Herculite were tested. Three types of reinforcement fibres were used: aramid (Podwiązka) with a single layer weave, a single layer weave glass fibre (FSO) and triple layer weave glass fibre (FSO evo). Tests were conducted in accordance with the requirements of ISO 4049:2009. The following material types were chosen for research: Boston, Boston + Podwiązka, Herculite, Herculite + Podwiązka, Herculite + FSO and Herculite + FSO evo. The scope of research included: flexural strength B, bending modulus of elasticity εB and work to failure of the reinforced composite Wfb. Additionally, microscopic observations of fracture occurring in samples were made. In comparison: the Herculite (97.7 MPa) type with the Herculite + FSO evo (177.5 MPa) type was characterized by the highest strength. Fibre reinforcement resulted in decreasing the elasticity modulus: Herculite + reinforcement (6.86 GPa; 6.33 GPa; 6.11 GPa) in comparison with the Herculite (9.84 GPa) and respectively Boston + reinforcement (10.08 GPa) as compared with the Boston (11.81 GPa). Using glass fibres increases flexural strength of the test composites. Using aramid fibres does not change their strength. The elasticity modulus of the reinforced reconstructive structures decreases after application of either type of fibres. However, their resistance to the crack initiation increases.

EFFECT OF AGING ON THE FLEXURAL STRENGTH AND FRACTURE TOUGHNESS OF A FIBER REINFORCED COMPOSITE RESIN VERSUS TWO NANOHYBRID COMPOSITE RESINS

INTRODUCTION: It is known that posterior composite restorations have high failure rates and high frequency of replacement as shown by studies. This may be attributed to the inability of conventional fillers to withstand the forces of mastication in the posterior region. New methods of reinforcement such as glass fibers are being used to increase the mechanical properties of dental composites. OBJECTIVES: was to compare the effect of aging in distilled water at 37°C for 1 day, 3 months and 6 months on the flexural strength and fracture toughness of a fiber reinforced composite (EverX posterior, GC, Europe), a nano-hybrid ceramic filled composite (IPS Empress Direct, Ivoclar Vivadent, Lieschtenstein) and a nano-hybrid zirconia filled composite (Z250 XT, 3M ESPE, USA). MATERIALS AND METHODS: For each test, twenty-one specimens were fabricated from each of the three composites and were then subdivided into three subgroups of seven specimens each according to the aging period in distilled water. After each aging period, the specimens were fractured in a Universal testing machine and the results were analyzed using ANOVA and post hoc test (Fisher's LSD) at p < 0.05 significance level. Following each test, the fractured surfaces of the 6 months aged specimens were examined using SEM. RESULTS: The flexural strength and fracture toughness of the fiber-reinforced composite was the highest with a statistical significance in the three aging periods followed by the nano-hybrid zirconia filled composite and the least was the nano-hybrid ceramic filled composite.SEM imaging findings were consistent with the results. CONCLUSIONS: The fiber-reinforced composite had the highest flexural strength and fracture toughness after each of the three aging periods Although aging in water decreased the mechanical properties of the fiber-reinforced composite, it still remained higher than the two nanohybrid composites which ensures its ability to withstand forces of mastication in the posterior region.

Fluoridated hydroxyapatite nanorods as novel fillers for improving mechanical properties of dental composite: Synthesis and application

Abstract Fluoridated hydroxyapatite (FHA) in nanorod morphology and hexagonal cross section were synthesised via hydrothermal process using Apricot Tree Gum (ATG) as a surfactant. The synthesised FHA nanorods were then used as reinforcement in bisphenol A-glycol dimethacrylate (Bis-GMA) as base monomer of composite matrix. The FHA nanorods with different ratios were incorporated in the matrix to examine fluoride ion release and pH changes in the Simulated Body Fluid (SBF) and their mechanical properties. The resin without FHA reinforcement was used as the control sample. The Diametral Tensile Strength (DTS), Flexural Strength (FS), and Flexural Modulus (FM) of the reinforced composite were found to be higher compared to the control sample; the values increased from 34.8 to 45.4 MPa, 76.5 to 99.4 MPa, and 1.7 to 2.5 GPa, respectively. Moreover, findings revealed that the pH is reduced by releasing the fluoride ions into the SBF which can be effective for preventing secondary caries. The most optimum mechanical properties were achieved with 0.2 wt% of FHA reinforcement. The FHA nanocomposite meets the minimum standard requirements for dental applications and compared to other dental composites has advantage of preventing formation of secondary caries due to release of fluoride.

Characterization of mesoporous silica nanoparticle composites at low filler content

Porous fillers are considered as an effective way to improve the mechanical properties of dental composites through the interlocking with organic matrix. In this paper, mesoporous silica (mobil crystalline materials-41) of different particle sizes was synthesized, modified, and added in bisphenol-A glycidyl dimethacrylate/triethylene glycol dimethacrylate resins to obtain composites at different loading levels. The influence of mesoporous filler concentration, particle size, and surface modification on the mechanical properties (flexural strength, flexural modulus, and Vickers microhardness) of composites has been investigated in detail. Compared to nonporous silica, mesoporous silica significantly improved composites’ mechanical properties. Flexural strength and flexural modulus are increased by 44.5% and 33.4%, respectively, when filler mass fraction reaches 15 wt%. Samples filled with silane-modified mesoporous silica show a higher flexural strength with the particle size decreasing from around 470 to 35 nm. The results implied potential applications for dental composites filled with porous fillers.

Numerical evaluation of bulk material properties of dental composites using two-phase finite element models

ObjectivesThe aim of this study was to numerically evaluate the effects of filler contents and resin properties on the material properties of dental composites utilizing realistic 3D micromechanical finite element models. Methods3D micromechanical finite element models of dental composites containing irregular fillers with non-uniform sizes were created based on a large-scale, surrogate mixture fabricated from irregularly shaped stones and casting resin. The surrogate mixture was first scanned with a micro-CT scanner, and the images reassembled to produce a 3D finite element model. Different filler fractions were achieved by adjusting the matrix volume while keeping the fillers unchanged. Polymerization shrinkage, Young's modulus, Poisson's ratio and viscosity of the model composites were predicted using the finite element models, and their dependence on the filler fraction and material properties of the resin matrix were considered. Comparison of the numerical predictions with available experimental data and analytical models from the literature was performed. ResultsIncreased filler fraction resulted in lower material shrinkage, higher Young's modulus, lower Poisson's ratio and higher viscosity in the composite. Predicted shrinkage and Young's modulus agreed well with the experimental data and analytical predictions. The McGee–McCullough model best fit the shrinkage and Young's modulus predicted by the finite element method. However, a new parameter, used as the exponent of the filler fraction, had to be introduced to the McGee–McCullough model to better match the predicted viscosity and Poisson's ratio with those from the finite element analysis. SignificanceRealistic micro-structural finite element models were successfully applied to study the effects of filler fraction and matrix properties on a wide range of mechanical properties of dental composites with irregular fillers. The results can be used to direct the design of such materials to achieve the desired mechanical properties.

Synthesis of dental resins using diatomite and nano-sized SiO2 and TiO2

The mechanical properties of dental composites were improved by porous diatomite and nano-sized silica (OX-50) used as co-fillers. The resin composites, filled with silanized OX-50 and silanized diatomite (40:60wt/wt), presented the best flexural strength (133.1MPa), elastic modulus (9.5GPa) and Vickers microhardness (104.0HV). Besides these, TiO2 nanoparticles were introduced to tune the dental resin composites colours which were valued by the CIE-Lab system. The colour parameters (L⁎, a⁎, b⁎) showed that the colour changes of resin composites could be perceived obviously, when 300–400nm TiO2 particles were introduced as fillers. The resin composite, filled with 0.5wt% TiO2, exhibited both clear discolouration (ΔE⁎=3.22) and high mechanical strength. Using scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX), the titanium elemental mapping results indicated that the TiO2 particles were distributed evenly in the prepared dental composites.

Nano-porous thermally sintered nano silica as novel fillers for dental composites

Objectives The study evaluates properties of an experimental dental composite consisting of a porous thermally sintered nano-silica as filler. The properties are compared with those of an experimental composite containing micro fillers and a commercially available nano-composite, Filtek Supreme ® Translucent. Different models are used to predict the elastic modulus and strength of the composites. Methods Nano-silica with primary particles of 12 nm was thermally sintered to form nanoporous filer particles. The experimental composites were prepared by incorporating 70 wt.% of the fillers into a mixture of Bis-GMA and TEGDMA as matrix phase. Having added photoinitiator system the composites were inserted into the test molds and light-cured. The microfiller containing composites were also prepared using micron size glass fillers. Degree of conversion (DC%) of the composites was measured using FTIR spectroscopy. Diametral tensile strength (DTS), flexural strength, flexural modulus and fracture toughness were measured. SEM was utilized to study the cross section of the fractured specimens. The surface topography of the specimens was investigated using atomic force microscopy (AFM). The specific surface area of the sintered nano silica was measured using BET method. The data were analyzed and compared by ANOVA and Tukey HSD tests (significance level = 0.05). Results The results showed improvements in flexural modulus and fracture toughness of the composites containing sintered filler. AFM revealed a lower surface roughness for sintered silica containing composites. No significant difference was observed between DTS, DC%, and flexural strength of the sintered nanofiller composite and the Filtek Supreme ®. The results also showed that the modulus of the composite with sintered filler was higher than the model prediction. Significance The thermally sintered nano-porous silica fillers significantly enhanced the mechanical properties of dental composites introducing a new approach to develop materials with improved properties.

BisGMA/TEGDMA dental composite containing high aspect-ratio hydroxyapatite nanofibers

Objectives The objectives of this study are to investigate the properties of high aspect-ratio hydroxyapatite (HAP) nanofibers and the reinforcing effect of such fibers on bisphenol A glycidyl methacrylate (BisGMA)/triethylene glycol dimethacrylate (TEGDMA) dental resins (without silica microparticle filler) and dental composites (with silica microparticle filler) with various mass fractions (loading rates). Methods HAP nanofibers were synthesized using a wet-chemical method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermal gravimetric analysis (TGA). Biaxial flexural strength (BFS) of the HAP nanofibers reinforced dental resins without any microsized filler and dental composites with silica microparticle filler was tested and analysis of variance (ANOVA) was used for the statistically analysis of acquired data. The morphology of fracture surface of tested dental composite samples was examined by SEM. Results The HAP nanofibers with aspect-ratios of 600 to 800 can be successfully fabricated with a simple wet-chemical method in aqueous solution. Impregnation of small mass fractions of the HAP nanofibers (5 wt% or 10 wt%) into the BisGMA/TEGDMA dental resins or impregnation of small mass fractions of the HAP nanofibers (2 wt% or 3 wt%) into the dental composites can substantially improve the biaxial flexural strength of the resulting dental resins and composites. A percolation threshold of HAP nanofibers, beyond which more nanofibers will no longer further increase the mechanical properties of dental composites containing HAP nanofibers, was observed for the dental composites with or without silica microparticle filler. Our mechanical testing and fractographic analysis indicated that the relatively good dispersion of HAP nanofibers at low mass fraction is the key reason for the significantly improved biaxial flexural strength, while higher mass fraction of HAP nanofibers tends to lead to bundles that cannot effectively reinforce the dental resins or composites and may even serve as defects and thus degrade the resulting dental resin and composite mechanical properties. Significance The incorporation of small mass fraction of HAP nanofibers with good dispersion can improve the mechanical property of dental resins and dental composites.

Synthesis of a novel spiro orthocarbonate containing bisphenol-a unit and its application to the dental composites

Dental restorative composites containing spiro orthocarbonates (SOCs) have been studied extensively to minimize the volumetric shrinkage that occurs during polymerization. Previous reports suggested that dental composites with low volumetric shrinkage could be obtained by mixing SOC with conventional resins. However, its inclusion had adverse effects on the mechanical properties of dental composites. A novel SOC (2,2-bis-4,4′-(7-phenyl-1,4,6,9-tetraoxaspiro[4.4]nona-2-ylmethoxyphenyl)propane), SOC-N, was synthesized to overcome these adverse effects resulting from the previously developed SOCs. The mechanical strength and volumetric shrinkage of the dental composites composed of 70 wt% inorganic fillers and resin matrices containing SOC-N, 2,2-bis-[4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane (Bis-GMA), and triethylene glycol dimethacrylate (TEGDMA) were explored. When compared to a control resin-containing composite (Bis-GMA/TEGDMA=70/30), the volumetric shrinkage of the composite containing new resin matrix, obtained through the addition of SOC-N to the Bis-GMA/TEGDMA=70/30 mixture, was reduced gradually by increasing the SOC-N content. Furthermore, the latter sample showed better mechanical strength than the former when the resin matrix contained 30 wt% SOC-N.

Electron beam irradiation of dental composites

Electron beam irradiation can be used to influence the mechanical properties of polymers. It was the aim of this study to investigate whether dental composites can benefit from irradiation in order to achieve increased fracture toughness, work of fracture, hardness or less wear. Two hundred rectangular specimens of five veneering composites were electron beam irradiated with 25, 100 and 200 kGy using an electron accelerator of 10 MeV. Fracture toughness, work of fracture, Vickers hardness, color changes and three-medium wear were measured and compared with non-irradiated specimens. Visible color changes (DeltaE>3) were observed with all composites and with all dose rates. Fracture toughness, work of fracture, Vickers hardness and resistance against wear increased significantly with few exceptions. Composites with a simple curing process needed higher dose rates while systems with a more complex curing procedure should be irradiated with lower dose rates. Electron beam irradiation can significantly change the mechanical properties of dental composites. However, color changes can limit the use of irradiation for dentistry.

In situ evaluation of the polymerization kinetics and corresponding evolution of the mechanical properties of dental composites

Polymer composites have been used in dental applications for more than 25 years. Although their properties and behavior have been systematically improved, they still are not able to produce dental restorations chemically, dimensionally and mechanically stable for long periods of time. Low degrees of monomer conversion and poor processing control are some of the main features responsible for the materials instability. In this work, the monomer conversion of dental composites during visible light irradiation was in situ monitored by infrared spectroscopy. The relationship between degree of conversion and mechanical properties was obtained by evaluating the microhardness of composites with different degrees of conversion. The relationship obtained was then used to identify the evolution of the mechanical properties during photopolymerization.

Flexural creep deformation and recovery in dental composites

Objectives: Three different popular composite resin systems for dental restorative applications are microfilled, minifilled and midifilled types in which deformation under stress and recovery after stress removal may be strongly influenced by filler parameters and resin formulation. The purpose of this in vitro study was to evaluate these differences in selected composite resins. Materials: Three composites, Clearfil (midifill), Charisma (minifill) and Durafill (microfill), were evaluated. Elastic, viscoelastic and viscous deformation of the composites under a constant stress and the subsequent recovery on removal of stress were measured. Dynamical mechanical properties of these materials were also characterized. Results: The mean values (and SD) of elastic, viscoelastic and viscous components of overall deformation (mm), respectively, under a constant stress of 45(5) KPa were as follows: Clearfil, 0.17(0.03), 0.06(0.02), 0.03(0.05); Charisma, 0.34(0.1), 0.09(0.04), 0.14(0.03); Durafill, 0.68(0.06), 0.14(0.03), 0.23(0.03) The results show that there are significant differences ( P<0.0001) between the different composite resins in the elastic, viscoelastic and viscous segments of deformation. The microfilled system deformed significantly more than the minifilled, and the minifilled system more than the midifilled. Storage modulus values evaluated by dynamic mechanical analysis were also significantly different ( P<0.0001). The observed differences were readily explained by the differences in the type and volume fraction of the filler content in the composites. Conclusions: Differences in time dependent deformation and recovery as well as dynamic mechanical properties of dental composites were strongly influenced by filler parameter differences. The clinical performance of restorations may be strongly influenced by the observed differences.

Evaluation of chemical and mechanical properties of dental composites

Composite materials were aged in distilled, deionized water and a solution by volume of 50% distilled, deionized water and 50% ethanol for three mon at 37°C. Also investigated was the effect of aging dental glass filler powder in distilled, deionized water for one, three, six, and ten mon at 2°C, 37°C, and 72°C. Atomic absorption analysis was performed on the aqueous media in which the samples were aged in order to determine the extent of leaching of silicon and strontium. From the leaching rates at various aging temperatures, the activation energies for silicon (10.3–16.4 j/mol) and strontium (57.0–58.4 j/mol) were determined. Aging in the 50% distilled, deionized water and 50% ethanol solution greatly increased the leaching rate of both silicon and strontium, as compared to aging in distilled, deionized water. Glass powder leached far more than the composite materials, due to an increase in exposed surface area, as well as a lack of chemical bonding to a resin matrix or a linked glass network. Temperature greatly increased the leaching rate of both silicon and strontium. Only after ten mon did strontium leach substantially more than silicon. For the dental composites investigated after 3 mon aging, Mode I fracture toughness decreased 57–68% in ethanol and 37–43% in water, and mode II fracture toughness decreased 41–49% in ethanol and 6–11% in water. © 1999 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 48: 540–545, 1999

Evaluation of chemical and mechanical properties of dental composites.

Composite materials were aged in distilled, deionized water and a solution by volume of 50% distilled, deionized water and 50% ethanol for three mon at 37 degrees C. Also investigated was the effect of aging dental glass filler powder in distilled, deionized water for one, three, six, and ten mon at 2 degrees C, 37 degrees C, and 72 degrees C. Atomic absorption analysis was performed on the aqueous media in which the samples were aged in order to determine the extent of leaching of silicon and strontium. From the leaching rates at various aging temperatures, the activation energies for silicon (10.3-16.4 j/mol) and strontium (57.0-58.4 j/mol) were determined. Aging in the 50% distilled, deionized water and 50% ethanol solution greatly increased the leaching rate of both silicon and strontium, as compared to aging in distilled, deionized water. Glass powder leached far more than the composite materials, due to an increase in exposed surface area, as well as a lack of chemical bonding to a resin matrix or a linked glass network. Temperature greatly increased the leaching rate of both silicon and strontium. Only after ten mon did strontium leach substantially more than silicon. For the dental composites investigated after 3 mon aging, Mode I fracture toughness decreased 57-68% in ethanol and 37-43% in water, and mode II fracture toughness decreased 41-49% in ethanol and 6-11% in water.

Post-cure heat treatments for composites: properties and fractography

Two commercial and four experimental composites were subjected to post-cure heat treatments of 10 min and 3 h duration immediately after light-curing. Fracture toughness, flexural modulus, microhardness and degree of conversion (FTIR) were evaluated 24 h later. The results showed that post-cure heat treatments at 120°C of short or long duration can be used to produce significant improvements in the degree of cure and the mechanical properties of dental composites used as inlays. A 10 min heat treatment was as effective as a 3 h treatment in enhancing properties and degree of cure. In addition, a 3 h heat treatment carried out 7 days after the initial light-curing was capable of improving properties and cure to almost the same extent as the immediate heat treatments. The improvement in properties, in conjunction with the fractography, indicate a toughening of the filled resin matrix and possibly an improved filler/matrix adhesion in the microfills. The changes appear to be predominantly the result of an increase in degree of cure.

Water sorption and mechanical properties of dental composites

The physical properties of four commercial dental composites were investigated through differential scanning calorimetry, water sorption and desorption measurements and flexural mechanical properties tests. The differential scanning calorimetry curves of samples as prepared and after different times of ageing in water indicated that the small residual monomer reactivity, present in the as prepared samples, disappeared after immersion in water, which probably acts as a plasticizer and facilitates a further cross-linking reaction of the material and the residual monomer desorption. Consistently, water causes the embrittlement of the material, as detected from the flexural mechanical properties. Water sorption and desorption kinetics were measured at different temperatures, the water diffusion coefficients were calculated and the activation energies of the diffusion process were determined. The SEM analysis of the fracture surfaces and the decrease of the water uptake on the temperature indicated the existence of a good filler/matrix adhesion.

Correlation between strength of bonding to enamel and mechanical properties of dental composites.

The strength of bonding of dental composites to enamel was measured in shear. The compressive strength, proportional limit, elastic modulus, and tensile strength of the composites were measured for correlation with the bond strength. Conventional and microfilled composites with a range of filler concentrations were studied. The densities of the composites and their fillers and the concentrations of the fillers were determined. The mechanical properties that were most highly correlated with bond strength to enamel were proportional limit and elastic modulus. Tensile strength and filler concentration had lower correlation coefficients, and compressive strength was not correlated with bond strength. Using unfilled resins as bonding agents between the composites and enamel resulted in increased bond strength with half of the composites.