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In this study, microstructures of dental composites were observed using high resolution scanning transmission electron microscopy (HR STEM). Samples for these observations were prepared by focused ion beam system. Two kinds of dental composites were investigated: (1) polymer-ceramic composite containing nano-sized ceramic fillers and (2) ceramic-polymer composite based on the nano-structured yttrium stabilized zirconia. The first composite is a popular material for dental fillings whereas the second is used for the fabrication of fixed partial dentures. The results are discussed in terms of the evaluation of fabrication process of the composites. [ABSTRACT FROM AUTHOR]

Abstract: Objective: The purpose of this study was to examine the fracture toughness (K IC) of three direct dental composites and one indirect dental composite subject to cyclic loading. Methods: The composites were a micro-filled (Micronew, Bisco INC., Schaumburg, IL, USA), a hybrid (Renew, Bisco INC.), a nano-filled composite (Filtek Supreme Plus, 3M ESPE, St. Paul, MN, USA) and an indirect dental composite (BelleGlass HP, SDS-Kerr, Orange, CA, USA). Rectangular bar specimens (3mm×3mm×25mm) were fabricated, notched, aged (5 months) and cyclic loaded in four different environments, air, water, artificial saliva, and a 50/50 by volume mixture of ethanol and water. Specimens were cyclic loaded for 1, 1000, 10,000, and 100,000 cycles. Results: A 3-way ANOVA (non-aged and aged group, four aging media, four loading cycles) showed a significant difference between non-aged and aged, aging media, and loading cycles. For the control groups as the number of cycles increased, there were no significant differences on the number of cycles completed and fracture toughness, except for Micronew, which showed an increased specimen failure rate and decreased fracture toughness. In the aged groups, cyclic loading in water and artificial saliva did not have a significant effect on BelleGlass HP, Filtek Supreme Plus and Renew for fracture toughness and the number of cycles completed, However for Renew in the 50/50 mixture at 100,000 cycles, Filtek Supreme Plus in air and the 50/50 mixture, and Micronew, there was an increased specimen failure rate and a decreased fracture toughness during cyclic fatigue loading as the number of cycles increased. Significance: BelleGlass HP displayed the best overall resistance to cyclic loading, followed by Renew and Filtek Supreme Plus, and Micronew. [Copyright &y& Elsevier]

Abstract: Objective: The aim of this investigation was to determine the effect of an experimental liquid rubber (LR) toughening agent on fracture toughness, crosslink density and Barcol hardness of polymerized mixtures of 50/50wt% Bis-GMA and TEGDMA. Methods: An experimental LR, was added to a solution of Bis-GMA and TEGDMA containing 1wt% dimethylamino ethyl methacrylate and 0.5wt% camphoroquinone at concentrations 0–10%. The composites were polymerized by exposure to a visible light curing unit for 60s. Fracture toughness was determined according to ASTM. 399. Crosslink density was evaluated using a swell test in ethanol. Results: Mean fracture toughness values ranged from 0.39MPam1/2 for samples containing 6% to 1.24MPam1/2 for samples containing 8% LR. Fracture toughness of samples containing 2%, 4%, and 8% LR were significantly higher than controls. The highest degree of cross-linkage was obtained in controls and lowest for samples containing 2% LR. Barcol Hardness values ranged from 36.7 for the control and 4% LR composition to 31.2 for samples containing 10% LR. Significance: Addition of 2, 4 and 8% LR increases the fracture toughness of Bis-GMA/TEGDMA composites. Addition of LR shows promise as a method of improving the fracture toughness of Bis-GMA based dental composites. [Copyright &y& Elsevier]

The aim of the study was to evaluate the effects of beverages like coffee, tea, coke and distilled water on hybrid and nano-filled composites cured by LED light and halogen light. Specimens were fabricated in Dow Dental College and tested for color change at Textile Lab, PCSIR labs complex, Karachi. A total of 80 composite specimens were fabricated. Forty composite specimens were fabricated from Filtek Z350. Twenty out of these forty specimens were cured with LED curing unit and twenty by halogen curing unit. Forty composite specimens fabricated from Esthet-X. Twenty were cured by LED curing unit and twenty by halogen curing unit. Specimens were fabricated using acrylic mold of 10mm diameter and 2mm thickness. All 4 groups were tested for baseline color change ΔE. Five specimens of each group of twenty were immersed in distilled water (control), tea, coffee and coke®. Color change ΔE values were recorded at 15 and 30 days. Statistical analysis was done by Three-Way, Repeated measure ANOVA. Post Hoc analysis was done by Dunnet's test. At 15 days, all immersion media except control caused significant color change ΔE At 30 days, all immersion media including control caused significant color change ΔE Type of composite and curing units caused no significant color change ΔE. All composites may get discolored overtime due to different beverages. Different beverages cause different degree of staining. This can limit overall esthetic lifespan of composite restorations. [ABSTRACT FROM AUTHOR]

This work was aimed at the study of some physical properties of two current light-cured dental resin composites, Rok (hybrid) and Ice (nanohydrid). As filler they both contain strontium aluminosilicate particles, however, with different size distribution, 40 nm–2.5 μm for Rok and 10 nm–1 μm for Ice. The resin matrix of Rok consists of UDMA, that of Ice of UDMA, Bis-EMA and TEGDMA. Degree of conversion was determined by FT-IR analysis. The flexural strength and modulus were measured using a three-point bending set-up according to the ISO-4049 specification. Sorption, solubility and volumetric change were measured after storage of composites in water or ethanol/water (75 vol%) for 1 day, 7 or 30 days. Thermogravimetric analysis was performed in air and nitrogen atmosphere from 30 to 700°C. Surface roughness and morphology of the composites was studied by atomic force microscopy (AFM). The degree of conversion was found to be 56.9% for Rok and 61.0% for Ice. The flexural strength of Rok does not significantly differ from that of Ice, while the flexural modulus of Rok is higher than that of Ice. The flexural strengths of Rok and Ice did not show any significant change after immersion in water or ethanol solution for 30 days. The flexural modulus of Rok and Ice did not show any significant change either after immersion in water for 30 days, while it decreased significantly, even after 1 day immersion, in ethanol solution. Ice sorbed a higher amount of water and ethanol solution than Rok and showed a higher volume increase. Thermogravimetric analysis showed that Rok contains about 80 wt% inorganic filler and Ice about 75 wt%. [ABSTRACT FROM AUTHOR]

New urethane dimethacrylate oligomers functionalized with carboxylic acid groups (CAd-1-÷4) were synthesized and evaluated as co-monomers in dental resin composites. Photopolymerization of these oligomers containing polyethylene oxide spacer was monitored by FT-IR spectroscopy comparatively with the low molecular monomer (CAd-M), as well as by fluorescence technique. The polymerization shrinkage for several mixtures including the urethane oligomers and BisGMA/ TEGDMA system was determined and, for some cured specimens, the equilibrium water uptake, water sorption and contact angle were measured to establish their behaviour into a wet environment. The compatibility between the organic and inorganic phase was investigated by SEM analysis in fractured surfaces indicating the formation of compact homogeneous materials. Aspects of the crack propagation behaviour of some composites subjected to Vickers indentation were examined by polarizing optical microscopy (POM) and atomic force microscopy (AFM), a visible crack being visible only in AFM image. Mechanical properties (compressive and diametral tensile strengths), determined for several resins composites, sustains the formation of materials with a hardness comparable to those frequently encountered in dental practice. [ABSTRACT FROM AUTHOR]

The aim of the study was to investigate the temperature rise of a nanocomposite and a conventional hybrid dental composite during photopolymerization when cured with halogen curing lamp (QHT) and light-emitting diode (LED). Temperature rise during photopolymerization of two commercially available composites (Filtek Supreme® and TetricCeram®) were measured using a K-type thermocouple and a digital thermometer. Different curing modes were utilized to cure the composites: a high-intensity QHT unit (Optilux 501) in two different modes (standard and ramp), a low-intensity QHT unit (Coltolux 50), and an LED unit (Ultralume-2). Total temperature rise, polymerization reaction exotherm, and irradiation-induced temperature rise of the composites were determined. Degree of conversion of the specimens was measured using FTIR spectroscopy. The results revealed that the Filtek Supreme® nanocomposite showed lower temperature rise and degree of conversion in comparison with the hybrid composite ( p < 0.05). It was also found that the LED curing unit induced considerable total and irradiation temperature rise without any improvement in the degree of conversion. Ramp curing mode showed lower temperature rise and delayed gel point and was found to be more effective than QHT standard mode and LED units. Although it is claimed that the LED curing units exhibit lower temperature rise during the photopolymerization, the present study showed that the curing units have no advantage over the conventional QHT units regarding the temperature rise and degree of polymerization conversion. [ABSTRACT FROM AUTHOR]

Commercial light-cured dental composites were used in this study. Two laboratorial composites, Resilab (Wilcos/Brazil), Epricord (Kuraray/Japan) were compared under cured and uncured conditions. Thermal analysis, infrared spectroscopy and scanning electron microscopy were used to evaluate the dental composites. The mass change and heat flow signals (TG–DSC) were recorded simultaneously by using STA 409 PC Luxx (NETZSCH), in the 25–800 °C temperature range at a heating rate of 10 °C/min under nitrogen atmosphere (70 mL/min). Employing thermo-microbalance TG 209 C F1 Iris (NETZSCH) coupled to the BRUKER Optics FTIR TENSOR, the samples were analyzed by combined thermogravimetric and spectroscopic methods (TG–FTIR). The initial sample mass was about ~12 mg, the data collection have been done in the 35–800 °C temperature range at a heating rate of 20 K/min in nitrogen atmosphere (flow rate: 40 mL/min). Finally, superficial topographic was analyzed by scanning electron microscopy (SEM). Dental composite evaluation suggests a high thermal stability and inorganic content in RES D sample. Degrees of conversion (DC) values were almost the same and there was no direct relationship between DC and amount of particles and size. Similar compositions were found in all samples. [ABSTRACT FROM AUTHOR]

Abstract: Besides the complexity of the contact between teeth, the mouth is also a very specific service environment. Dental restorative materials, and teeth, are subjected to very specific service conditions, wide-ranging temperatures, contact loading, loading rates, sliding conditions and pH variation. Several studies have established that an exposure of resin composites to aqueous environments lowers their mechanical properties. Due to changes in the structure of these materials, softening of the resin matrix and/or bond failure in the outer layer of the filler and in the filler–matrix interface region reduce the mechanical and tribological performance. During the day, the mouth presents different values of pH, and thus it is important to determine the effect of pH on the composites’ tribological behaviour. The main objective of this study is the determination of the nature of the dependency between the tribological behaviour of commercial composites and the influence of values of pH and aging time. Seven commercial resin composites, condensable and suitable for posterior restoration, have been characterized. Each material composite was aged during a period of 3, 6 and 22 months at a temperature of 37°C, and considering three values of pH: 3, 7 and 9. The tribological behaviour was evaluated in a reciprocating contact against glass spheres. At the end of the tests, the wear was assessed on the composite and also on the counterface. The removal mechanisms enclosed in the wear process are discussed, taking into account the systematic SEM observations to evaluate the failure modes. [Copyright &y& Elsevier]

Abstract: Objective: The intent of the project was to evaluate the fatigue behavior of particle and fiber filled dental composites that are fabricated either directly or indirectly using a notched specimen with respect to the number of cycles until failure. Methods: The materials were five dental composites, three normally cured in the oral cavity (Restolux, Renew and Filtek Supreme), direct processing, and two laboratory produced (BelleGlass, and Tescera), indirect processing. The specimens were 3mm×3mm×25mm bars with a 0.75 or 1.0mm notch in the mid-span of the bars, polished with 320 grit SiC paper and aged for 6 months in air, distilled water, artificial saliva, and a 50/50 mixture of ethanol and distilled water. Testing was performed with a stress mean range of 5–49MPa, the maximum number of cycles was 100,000, and the number of cycles to failure was recorded. Results: For the specimens that failed, BelleGlass, Restolux, and Tescera were able to withstand a higher cyclic loaded stress than Renew and Filtek. The 50/50 by volume mixture of water and ethanol resulted in the lowest resistance to fatigue for all materials. Conclusions: Of the dental composite materials investigated, the indirect processed and those with large particle fillers (higher weight percent filler) had better cyclic fatigue resistance than micro- and nano-particle fillers (lower weight percent filler). [Copyright &y& Elsevier]

Abstract: Objective: To compare the build-up of internal stresses in four different dental composites (Venus, Tetric Ceram, Ceram X mono and Filtek Supreme) during the curing reaction, based on the results of a former paper on polymerization kinetics, and to characterize the developing mechanical behavior for different modes of activation using experimental methods and simulation tools. Methods: A four-parameter viscoelastic model combined with a curing model and a kinetic model was developed to simulate the mechanical behavior in three dimensions using the finite element software ABAQUS. In order to study the influence of slow polymerization behavior on the mechanical properties, the length of the activation period was doubled at half intensity of the curing light. Results: Using a model which describes the complex interplay of stiffness, flowability, curing speed and activation intensity during the curing process gives deeper insight into the spatial and temporal build-up of stresses. An advantageous reaction kinetic or a lower stiffness can compensate for the effect of a higher polymerization shrinkage on the resulting peak stress. The evolution of stress is not directly proportional to the level of shrinkage of the composites. Significance: A material model which includes the developing mechanical characteristics of a curing dental composite can be used to develop and optimize dental materials and to assess the effect of different treatment strategies (i.e. mode of photo-polymerization, filling geometries, interfacial strength). [Copyright &y& Elsevier]

Abstract: Objectives: Recently, we found that dental bonding substances tested alone or in combination with composites are far more cytotoxic than composite materials alone. These data are in line with several cytotoxicity reports but contradict in vivo studies showing the beneficial effects of bonding materials. The aims of the present study were to develop a preparation method for composite specimens modelling conditions in the oral cavity and to analyse the influence of bonding substances on the cytotoxicity of six different composite materials. Methods: Cylindrical composite specimens were prepared in polyethylene blocks containing 5mm diameter cylindrical holes (cylinder height 2mm), covered with a polyethylene foil and light cured from one end for 40s. In a second series of experiments, composite specimens were combined with bonding materials. Bonding was applied onto the polyethylene foil in one or two layers and light cured according to the manufacturers’ instructions. Subsequently, polyethylene moulds were placed on top of the bonding materials and composites prepared as described above. After unilateral light curing from the top of the cylindrical holes, visual confirmation of adherence at the base was obtained. Specimens were added to the cultures immediately after production or after preincubation for 7 days under cell culture conditions. Specimens were incubated with L-929 fibroblasts for 72h and cell numbers determined by flow cytometry. To evaluate the degree of conversion (DC) of bonding materials cured with and without air inhibition a third series of experiments was performed. FTIR spectroscopic measurements were made on thin-films of dentin-bonding agents, cured under both an-aerobic and aerobic conditions, to determine degree of conversion. Results: Cytotoxicities of all six tested composites were significantly different (p <0.0001) and diminished after 7 days of preincubation (p <0.0001). Bonding substances had no statistically significant influence on the cytotoxicity of composite materials (p =0.159). A highly significant statistical reduction in the degree of conversion for each resin cured under air inhibition conditions was documented (p <0.01). Significance: Our study demonstrates that cell culture toxicity data are highly model dependent and that internationally standardized test protocols for toxicity screening of dental materials in line with the existing standards are clearly needed to obtain comparable results. [Copyright &y& Elsevier]

Abstract: Objectives: The purpose of this study was to image the sites of fracture initiation and slow crack propagation in a fiber reinforced composite, using the optical coherence tomography (OCT) technique. Methods: Bar specimens (2mm×3mm×25mm) of fiber reinforced composite were mechanically and thermally cycled to emulate oral conditions. The interior of these samples was analyzed prior to and after loading, using OCT. The device used was a home-built Fourier domain OCT setup working at 800nm with 6μm spatial resolution. Results: Intact specimens after load cycling were analyzed. It was clearly seen that OCT images provide an insight into crack propagation, which is not seen by the naked eye. Significance: By using OCT the possibility of analyzing the fracture propagation quantitatively, and in depth, was added, opening up possibilities to quantitative studies. [Copyright &y& Elsevier]

Abstract: Objectives: Methods to prepare dental composites with a periodic filler arrangement were developed following a strategy of colloidal crystallization. The aims of this study were to determine the influence of suspension medium, silane treatment and amine additive on colloidal particle redispersion and subsequent ordering, and to evaluate the effect of filler ordering on mechanical properties of composites. Methods: Dry monodisperse silica particles (spherical, ∼500-nm diameter) were redispersed in selected solvents and monomers (e.g. triethyleneglycol dimethacrylate, TEGDMA) to form sediments or dispersions with ordered particle arrangements. Ordering was evaluated by microscopy and mechanical properties of the composites were measured using compression tests (n =6). Results: A face-centered cubic packed structure could form in both the sediment from silica dispersions in polar solvents and stable dispersions in TEGDMA. Dimethylaminoethyl methacrylate (DMAEMA) was found to disrupt an ordered structure when non-silanized silica particles were used. Silanization with 3-methacryloxypropyl trimethoxysilane (MPS) promoted filler ordering. Standard compression tests on composites containing 60wt% silica in TEGDMA with or without DMAEMA indicated that DMAEMA had a clearly significant effect (p <0.05) on failure strain, compressive strength, and toughness, and a marginally significant effect on modulus (p =0.12). Significance: Significant increases in compressive strength (16%), failure strain (71%), and toughness (135%) were observed for composites with ordered filler compared to non-ordered composites. [Copyright &y& Elsevier]

Abstract: Objectives: The work was motivated by the necessity to evaluate the emission changes of dental composites, as the emission under UV light is one of the important optical parameters of the hard tooth tissue. Methods: Fulfill extra, Artemis and Durafill VS materials in A3.5 shade were tested. Coffee, tea, red wine and distilled water (blank) were used as staining drinks. The samples were soaked for 7 days. Total luminescence matrices were collected with an interval of 1nm in emission and 10nm in excitation, in the front-face geometry. Results: The exposure of dental composites to staining drinks caused a reduction in luminescence intensity by up to 40%, the magnitude of the reduction depending on the drink and on the composite material. In the special case of the intrinsically weak fluorescent Durafill VS, the exposure to coffee apparently caused an increase in luminescence intensity due to coffee components adsorbed on the sample surface. Significance: It is important to improve the emission stability of dental composites. The presently proposed methods are effective in evaluating the emission of dental composites. Emission needs to be tested in addition to color, as the two parameters are uncorrelated. [Copyright &y& Elsevier]

Abstract: Objective: The fundamental optical characteristics of dental polymers as a function of curing time are exiguously reported in the literature. In this work the refractive index and the extinction coefficient of bisphenol-A-glycidyldimethacrylate–triethyleneglycoldimethacrylate (BisGMA/TEGDMA)-based polymers of different volume fractions have been studied as a function of the curing time. A comparison between the measured index of refraction and theoretical calculation based on molar refraction is made. Also the temporal behavior of both the refractive index and extinction coefficient is compared. Methods: Index of refraction: BisGMA/TEGDMA monomer samples were cured with a commercial light-curing unit by using camphorquinone and DMAEMA as the photoinitiator system. Curing times of 0, 40, 60, 300, 900 and 1800s were used. The refractive indices were determined with a refractometer at 470nm wavelength, where the peak absorption of the camphorquinone photoinitiator is located. Extinction coefficient: BisGMA/TEGDMA samples having different lengths were cured and the relative attenuation of light at 470nm was measured as a function of the curing time (0, 40, 60, 300, 900, 1800s). Results: The results show that in general the index of refraction increases during the photopolymerization process in a time frame from 0 to 40s and then approaches a steady-state value, which depends on the original composition of the admixture. The detailed refractive index change depends on the volume fractions of the constituent substances. The extinction coefficient decreases in a time frame from 60 to 900s and reaches a steady-state value thereafter. Significance: Knowledge of the fundamental optical characteristics of commonly used dental polymers is essential in the development of advanced light-initiated curing methods. [Copyright &y& Elsevier]

Abstract: Objectives: The aim of this study is to compare the wear resistance and hardness of two dental nanohybrid composites and to evaluate the influence of artificial saliva storage on those properties. Methods: Specimens were made from two commercial nanohybrid dental composites (Esthet-X®-Dentsply and Filtek Supreme®-3M). Abrasion tests were carried out in a ball-cratering machine (three body abrasion) and microscopic analysis of the wear surfaces was made using optical and scanning electron microscopy; hardness was quantified by Vickers hardness test. Those tests were repeated on specimens stored in artificial saliva. Results: Results show that the wear rate of the studied materials is within 10−7 mm3/Nmm range, one of the composites presenting wear rate twice as large as the other. After storage in artificial saliva, the wear resistance increases for both materials. Microhardness of the composites is around 52 and 64HV, Esthet-X® presents higher hardness values than Filtek Supreme®. After storage in artificial saliva, the microhardness of both materials decreases. Data were analyzed using ANOVA test, p ≤0.05. Conclusions: Artificial saliva storage increases the materials’ wear resistance, suggesting that in both materials bulk post-cure takes place and saliva absorption occurs only on the surface of the composites. This effect was confirmed by comparing the Vickers hardness before and after artificial saliva treatment and FTIR analyses. Surface microhardness of the composites decreases after storage in artificial saliva whereas bulk microhardness of the materials increases. [Copyright &y& Elsevier]

Abstract: Objective: The volume and thermal behavior of dental composites during the curing reaction was analyzed for different modes of initiation using a combination of experiments and models for polymerization kinetics. Methods: The volume behavior of four dental composites (Venus, Tetric Ceram, Ceram X mono and Filtek Supreme) was studied with buoyancy measurements during the initiation and dark phase of the curing process. The volume and temperature development of the composites were described for different intensities of the photo-initiation with a mathematical model based on the “mixed termination model” for the polymerization reaction. Results: A good agreement between volumetric data and the model function was achieved. A non-linear regression of the experimental data with the model yields results for the adjustable parameters describing the kinetics of the polymerization reaction which are typical for comparable polymerization reactions. Using kinetic models of the polymerization reaction for analyzing the volume behavior of radically crosslinking curing dental composites, thermal and polymerization-specific components of the overall shrinkage of the composites can be distinguished and compared for different materials. Significance: With the developed methodology, a more detailed insight into the curing process can be achieved which can contribute to the understanding of the build-up of internal stresses in dental fillings. These stresses can negatively affect the marginal integrity of the filling, which is a relevant precondition of long-term chemical, biological and mechanical stability. [Copyright &y& Elsevier]

The intent of this article is to review the numerous factors that affect the mechanical properties of particle- or fiber-filler-containing indirect dental resin composite materials. The focus will be on the effects of degradation due to aging in different media, mainly water and water and ethanol, cyclic loading, and mixed-mode loading on flexure strength and fracture toughness. Several selected papers will be examined in detail with respect to mixed and cyclic loading, and 3D tomography with multi-axial compression specimens. The main cause of failure, for most dental resin composites, is the breakdown of the resin matrix and/or the interface between the filler and the resin matrix. In clinical studies, it appears that failure in the first 5 years is a restoration issue (technique or material selection); after that time period, failure most often results from secondary decay. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Evaluate the effects of core structure and storage conditions on the mechanical properties of acid-resin modified composites and a control material by three point bending and conversion measurements 15min and 24h after curing. Methods: The monomers pyromellitic dimethacrylate (PMDM), biphenyldicarboxylic-acid dimethacrylate (BPDM), (isopropylidene-diphenoxy)bis(phthalic-acid) dimethacrylate (IPDM), oxydiphthalic-acid dimethacrylate (ODPDM), and Bis-GMA were mixed with triethyleneglycol dimethacrylate (TEGDMA) in a 40/60 molar ratio, and photo-activated. Composite bars (Barium-oxide-glass/resin=3/1 mass ratio, (2mm×2mm×25mm), n =5) were light-cured for 1min per side. Flexural strength (FS), elastic modulus (E), and work-of-fracture (WoF) were determined in three-point bending after 15min (stored dry); and after 24h under dry and wet storage conditions at 37°C. Corresponding degrees of conversion (DC) were evaluated by Fourier transform infrared spectroscopy. Data was statistically analyzed (2-way analysis of variance, ANOVA, Holm–Sidak, p <0.05). Results: Post-curing significantly increased FS, E and DC in nearly all cases. WoF did not change, or even decreased with time. For all properties ANOVA found significant differences and interactions of time and material. Wet storage reduced the moduli and the other properties measured with the exception of FS and WoF of ODPDM; DC only decreased in BPDM and IPDM composites. Significance: Differences in core structure resulted in significantly different physical properties of the composites studied with two phenyl rings connected by one ether linkage as in ODPDM having superior FS, WoF and DC especially after 24h under wet conditions. As expected, post-curing significantly contributed to the final mechanical properties of the composites, while wet storage generally reduced the mechanical properties. [Copyright &y& Elsevier]

Abstract: Objectives: The objective of this study was to investigate the use of ormocers, which were synthesized from amine or amide dimethacrylate trialkoxysilanes. Ormocers showed improved biocompatibility in dimethacrylate-diluent-free composite restoratives. Selected mechanical properties, such as flexural strength and flexural modulus of experimental composites containing ormocers were investigated. In addition, the influence of methacrylate-substituted ZrO2 clusters and SiO2 organosols on the mechanical properties of composites was studied. Methods: The flexural strength and flexural modulus of elasticity were determined according to ISO 4049: 2000. For this purpose, test specimens (2mm×2mm×25mm) of the composites investigated were prepared in stainless steel moulds and light-cured (150mW/cm2, 2×180s). The flexural strength and flexural modulus of elasticity were measured after the samples had been stored in water for 24h at 37°C. Results: While visible light-cured dimethacrylate-diluent-free composite restoratives based on the investigated ormocers showed a similar flexural strength and flexural modulus of elasticity compared to composites that contain only dimethacrylates, their double bond conversion was considerable lower. The simultaneous addition of methacrylate-substituted ZrO2 clusters and SiO2 organosols to the ormocer composite improved the mechanical properties of the composites. Significance: Ormocers of amine or amide dimethacrylate trialkoxysilanes enabled the preparation of dimethacrylate-diluent-free composite restoratives. Based on the lower cytotoxicity of the ormocers, the prepared restorative composites should show improved biocompatibility. With the addition of nanoparticles, such as methacrylate-substituted ZrO2 clusters or SiO2 organosols, the mechanical properties of composites can be improved. [Copyright &y& Elsevier]

Abstract: Objectives: The use of resin-based dental restorative materials is rapidly increasing, concurrently the biocompatibility of the materials is under investigation. Attention has been placed on studies addressing the cytotoxic, genotoxic and estrogenic potential of these materials. Therefore, the degree of exposure to eluted compounds from the dental materials is of high interest. The aim of this study was to assess the amounts of 2-hydroxyethyl methacrylate (HEMA) and triethyleneglycol dimethacrylate (TEGDMA), released from two composites, eluting into human saliva. To improve the method of quantification, three tailor-made internal standards were synthesized. Methods: Specimens made from two composites (Tetric EvoCeram and Filtek Z250) were polymerized and immersed in human saliva for 24h. Eluted TEGDMA and HEMA were identified and quantified. The quantitative analyses were performed by use of combined gas chromatography–mass spectrometry (GC/MS) with tailor-made internal standards synthesized by dissolving HEMA or TEGDMA in methanol and reducing the double bond of the methacrylate group by hydrogenation with 1H2 and 2H2 (D2) gas. Results: HEMA was released from both materials, whereas TEGDMA eluted from Filtek Z250 only. Full scan GC–MS analysis of each tailor-made internal standard demonstrated one peak only, which was well separated from the corresponding analyte''s peak and with no traces of HEMA or TEGDMA. Significance: The quantification method seems well suited for in vivo analysis, and the three standards synthesized represent an improved tool for quantification of the eluted monomers. The synthesis may be applied to other methacrylate monomers to produce tailor-made standards for quantification. [Copyright &y& Elsevier]

Abstract: Objectives: The first objective of this work is the study by DMTA of viscoelastic properties (E′, E″, tan δ, T g) of two current dental resin composites Tetric EvoCeram (nanohybrid) and Heliomolar (microfilled) in dry condition and in water for up to 30 days. The second objective is to determine the sorption characteristics of these composites in water and ethanol/water solution 75vol.%. Methods: For DMTA the bar-shaped specimens divided into five groups of three samples each. The first group consisted of dry samples measured 1h after curing. The second and third group consisted of samples, which had been heated in air at 80±1°C for 1 day or had been stored in distilled water at 80±1°C for 1 day. The fourth and fifth group consisted of samples, which had been stored in distilled water at 37±1°C for periods 1 and 7 days correspondingly. Also specimen discs (15mm in diameter and 1mm in thickness) were immersed in water or a 75vol.% ethanol/water solution at 37±1°C. At fixed time intervals they were removed, blotted dry to remove excess liquid, weighted and returned to the liquid. This process continued for 30 days. Results: The viscoelastic properties (E′, E″, tan δ, T g) of the two composites treated under different conditions were recorded and compared. Also the mass uptake, diffusion coefficient, solubility and volumetric changes for immersion of composites in water and ethanol/water solution 75vol.% at 37±1°C were determined. Significance: Tetric EvoCeram a nanohybrid composite with similar about resin matrix with Heliomolar which is a microfilled showed better dynamic thermomechanical properties and sorption characteristics than Heliomolar. [Copyright &y& Elsevier]

Purpose: This study assessed the effect of 6 months of aging in water on surface roughness and surface/subsurface hardness of two microhybrid resin composites. Materials and Methods: Filtek Z250 and Charisma were tested. Cylindrical specimens were obtained and stored in distilled water for 24 hours or 6 months, at 37°C. For Knoop hardness evaluation, the specimens were transversely wet-flattened, and indentations were made on surface and subsurface layers. Data were submitted to three-way ANOVA and Tukey's test (α≤ 0.05). Surface roughness baseline measurements were made at 24 hours and repeated after 6 months of storage. Data were submitted to repeated measures ANOVA and Tukey's test (α≤ 0.05). Results: Surface hardness (KHN, kg/mm2) means (± standard deviation) ranged from 55 ± 1 to 49 ± 4 for Z250 and from 50 ± 2 to 41 ± 3 for Charisma, at 24 hours and 6 months, respectively. Subsurface means ranged from 58 ± 2 to 61 ± 3 for Z250 and from 50 ± 1 to 54 ± 2 for Charisma, at 24 hours and 6 months. For both composites, the aged specimens presented significantly softer surfaces ( p < 0.01). For the subsurface hardness, alteration after storage was detected only for Charisma, which presented a significant rise in hardness ( p < 0.01). Z250 presented significantly harder surface and subsurface layers in comparison with Charisma. Surface roughness (Ra, μm) means ranged from 0.07 ± 0.00 to 0.07 ± 0.01 for Z250 and from 0.06 ± 0.01 to 0.07 ± 0.01 for Charisma, at 24 hours and 6 months, respectively. For both composites, no significant roughness alteration was detected during the study ( p= 0.386). Conclusions: The 6-month period of storage in water presented a significant softening effect on the surfaces of the composites, although no significant deleterious alteration was detected for the subsurface hardness. In addition, the storage period had no significant effect on the surface roughness of the materials. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: The purpose of this study was to measure the development of contraction stress of three composite resin restorative materials during photo-polymerization: a micro-hybrid composite (Filtek Z250, 3M ESPE, St. Paul, MN, USA); a nano-filled composite (Filtek Supreme, 3M ESPE, St. Paul, MN, USA); and a low-shrinkage composite (Ælite LS, Bisco Inc., Schaumburg, IL, USA). Methods: Curing shrinkage stress was measured using a stress-analyzer. Composites were polymerized with a halogen-curing unit (VIP, Bisco Inc., Schaumburg, IL, USA) for 40s. The contraction force (N) generated during polymerization was continuously recorded for 150s after photo-initiation. Contraction stress (MPa) was calculated at 20, 40, 60 and 150s. Data were statistically analyzed. Results: The low-shrinkage composite Ælite LS exhibited the lowest stress values compared to other materials (p <0.05). Statistical analysis did not show significant differences between Filtek Z250 and Filtek Supreme. Significance: The low-shrinkage composite showed lower contraction stress than micro-hybrid and nano-filled composite. Ideally, non-shrinking resins would represent the ultimate solution to overcome polymerization contraction and stress-related problems. [Copyright &y& Elsevier]

Abstract: HPLC method was developed for determination of bisphenol A diglycidyl methacrylate (bis-GMA), bisphenol A diglycidyl acrylate (bis-GA), bisphenol A dimethacrylate (bis-DMA), glycidylmethacrylate (GMA) and triethylenglycol dimethacrylate (TEGDMA). Separation was carried out on a reversed phase Omnisphere 5 C18 column with a gradient mobile phase of CH3CN/H2O. UV detection was set at 205 nm and 275 nm parallel. The limits of quantification were found. The method has been applied for quantification of unreacted monomers trapped in polymer network of fillings. [Copyright &y& Elsevier]

Abstract: Objectives: We formulate a new model for the shrinkage strain developed during photo polymerization in dental composites. The model is based on the diffusion type fractional order equation, since it has been proved that polymerization reaction is diffusion controlled (Atai M, Watts DC. A new kinetic model for the photo polymerization shrinkage-strain of dental composites and resin-monomers. Dent Mater 2006;22:785–91). Our model strongly confirms the observation by Atai and Watts (see reference details above) and their experimental results. The shrinkage strain is modeled by a nonlinear differential equation in (see reference details above) and that equation must be solved numerically. In our approach, we use the linear fractional order differential equation to describe the strain rate due to photo polymerization. This equation is solved exactly. Results: As shrinkage is a consequence of the polymerization reaction and polymerization reaction is diffusion controlled, we postulate that shrinkage strain rate is described by a diffusion type equation. We find explicit form of solution to this equation and determine the strain in the resin monomers. Also by using equations of linear viscoelasticity, we determine stresses in the polymer due to the shrinkage. The time evolution of stresses implies that the maximal stresses are developed at the very beginning of the polymerization process. Significance: The stress in a dental composite that is light treated has the largest value short time after the treatment starts. The strain settles at the constant value in the time of about 100s (for the cases treated in Atai and Watts). From the model developed here, the shrinkage strain of dental composites and resin monomers is analytically determined. The maximal value of stresses is important, since this value must be smaller than the adhesive bond strength at cavo-restoration interface. The maximum stress determined here depends on the diffusivity coefficient. Since diffusivity coefficient increases as polymerization proceeds, it follows that the periods of light treatments should be shorter at the beginning of the treatment and longer at the end of the treatment, with dark interval between the initial low intensity and following high intensity curing. This is because at the end of polymerization the stress relaxation cannot take place. [Copyright &y& Elsevier]

Abstract: Objectives: The standardization protocols for biomaterial cytotoxicity testing require fine tuning for oral biomaterials to obtain international comparability as the basis for risk assessment. The principal aims were specifically to evaluate the effect of (i) relative interface area (ratio of specimen surface to cell layer surface) and (ii) volume of cell culture medium on cytotoxicity as a potential modification of ISO 10993-5. Methods: ISO 10993-5 was followed with an interface area of 12.5%, as recommended, using primary human gingival fibroblasts and L-929 mouse fibroblasts. In another series of experiments (using L-929 cells) the interface area was varied between 12.5% and 0.71%. For each relative interface area, three conditions for affecting the cure of the resin composite were investigated by using three mould materials: white, transparent and black moulds. In addition, the volume of cell culture medium was varied. Composite specimens (Herculite XRV) were added to the cultures immediately after production or preincubation for 1, 2, 7 days or 6 weeks under cell culture conditions. Specimens were incubated with fibroblasts for 72h and cell numbers determined by flow cytometry. Glass specimens resembling composite specimens in diameter and height were used as negative controls. Results: Cytotoxicity results with primary gingival fibroblasts were comparable to results with the cell line L-929. An effect from the color/material of the specimen moulds was found. Different ratios of specimen sizes to cell culture parameters (cell layer surface, volume of cell culture medium) produced different results. Three out of four differently designed specimens showed the same behavior in cell culture. Significance: Cytotoxicity tests should be further standardized in line with existing standards with regard to specimen production protocols to ensure results are internationally comparable to validate these tests as tools for risk assessment. [Copyright &y& Elsevier]

Abstract: Objectives: To evaluate the dependence of the toxicity of various dental composites on the use of high- and low-power light curing units (LCUs). Methods: The composites Filtek Z 250, Durafill VS, Solitaire 2 and Grandio were polymerized using different light densities from three LCUs, namely Heliolux II, Swiss Master Light (SML) and a prototype LED. The toxicity of polymerized samples was tested by exposing them to the cell culture medium up to 28 days. The extracts of the composites were collected daily and used for incubation in human gingival fibroblasts cultures. Results: Slow, low-intensity curing using the LED or the Heliolux II showed similar characteristics for all four composites, regarding the cell viability rate of human gingival fibroblasts. After 1 day of storage suboptimal results could be observed for the SML/Durafill and optimal results for SML/Grandio combination (approximately 100% cell viability). In addition, the composite Solitaire the SML yielded significantly better results than the other LCUs (cell viability, p ≤0.001: SML 60.5%, Heliolux 44.5%, LED 44.2%). Furthermore, the combination of the SML with Z 250 composite showed, after the first day and up to day 28, statistically significantly higher cell viability rates than the combination with the LED or Heliolux II. Significance: This study shows that the combination of a high power LCU with some composites positively influences the HGF cell viability effected by the investigated composite extracts. Moreover, there is further indication that a reduction of composite toxicity is possible if the curing mode is adapted to the used composite. [Copyright &y& Elsevier]

The purpose of this study was to investigate the compressive fatigue behavior of five dental composites. Cylindrical specimens of 8 mm length and 4 mm diameter were made according to manufacturers' recommendations and stored for two weeks in distilled water at 37°C. Compressive fracture strength was measured, and subsequently fatigue tests at 10 Hz frequency were carried out in distilled water. Compressive fatigue strength was thereby obtained using the staircase method for 105 cycles (n=17) under sinusoidal loading. Acquired data for compressive fracture strength were analyzed using ANOVA and Weibull statistics. Among the dental composites examined, Filtek® Z250 exhibited the highest fatigue strength. This seemed to be due to the superior matrix properties coupled with a specific filler type at the highest weight%/volume% ratio. In addition, fracture mechanisms of the composites were examined. [ABSTRACT FROM AUTHOR]

Abstract: Materials and methods: A wear method was developed that mainly simulates attrition wear using a commercially available chewing simulator (Willytec, Germany). In this test, a standardized stylus made of pressable ceramic (Empress) hits flat specimens 120,000 times with a 5kg weight, a descent speed of 60mm/s and a lateral movement of 0.7mm with a speed of 40mm/s under constant exchange of water at different temperatures (325×5°C/55°C). The volume loss was measured on plaster replicas with the Laserscan 3D (Willytec) and the Match 3D software. Twenty-four experimental and commercial composites (n =8) were tested with a volumetric wear range of between 5.5 and 147×10−2 mm3. On standardized specimens made of the same composites, the Vickers hardness (H), elastic modulus (E) and fracture toughness (K 1c) were measured. The mean particle size (d) and volume content () of the inorganic filler were evaluated. Furthermore, a differentiation was made between the main filler with the largest mean size (d 1, ) and the total filler content (). Results: The best linear regression curve fit with an adjusted R 2 of 0.908 was found for Conclusions: The good mathematical fit of the formula may be an indication that the wear method is based on physical properties and that it provides a highly reproducible standard. [Copyright &y& Elsevier]

Abstract: Objectives: The objective of this study was to investigate the use of three new bis-(acrylamide)s as cross-linker in resin-based composite restoratives. Selected mechanical properties such as flexural strength and flexural modulus of model composites containing bis-(acrylamide)s were investigated and compared to the properties of composites that are based on only conventional dimethacrylates. In addition, the hydrolytic stability of composites containing an acidic monomer was examined. Methods: The flexural strength and flexural modulus of elasticity were determined according to ISO 4049:2000. For this purpose, test specimens (2mm×2mm×25mm) of the composites investigated were prepared in stainless steel moulds and light-cured (150mW/cm2, 2× 180s). The flexural strength and flexural modulus were measured after the samples had been stored in dry conditions or in water for 24h at 37°C as well as after they had been stored in water for 7 days at 37°C, and in certain cases, after they had been boiled for 24h in water. Results: Visible light cured mixtures of dimethacrylates with bis-(acrylamide)s and composites based on these mixtures show a similar reactivity, flexural strength and flexural modulus of elasticity compared to materials that contain only dimethacrylate. The composites did not show any deterioration of the mechanical properties after water storage. Only when strongly acidic monomers were added to the composites containing dimethacrylates or bis-(acrylamide)s did the flexural strength and flexural modulus of the samples decrease after they were stored in water. Significance: Bis-(acrylamide)s were similarly reactive than dimethacrylates and therefore can be used as diluents to substitute dimethacrylate diluents in composites. Although the bis-(acrylamide)s are entirely soluble in water, non-ionic materials based on bis-(acrylamide)s did not strongly change their mechanical properties during storage in water. [Copyright &y& Elsevier]

With the emergence of commercial grafted caged silica (Polyhedral Oligomeric Silesquioxanes, POSS) having a three-dimensional (3D) morphology with peripheral functionality, new opportunities have been created for formulating dental adhesives and composites with enhanced mechanical and physical properties. The objective of the present study was to investigate the properties obtained by incorporating grafted caged silica into acrylate based dental composite and adhesive systems. Two commercial POSS materials (methacrylated and octaphenyl grafted) were added to dental restorative-glass-filled pre-polymers, based on BisGMA (bis-phenol A-glycidyldimethacrylate), HEMA (2-hydroxyethylmethacrylate) and TEGDMA (tetraethylglycidylmethacrylate). The nanostructured organic/inorganic hybrid compounds exhibited enhanced mechanical and thermal properties in cases where the POSS added was in concentrations up to 2 wt%. Beyond this threshold concentration, properties decreased due to agglomeration. In the case of the acrylated POSS, the Tg increased by 5°C, the composite compressive strength by 7%, and the bond shear strength by 36% and the shrinkage was reduced by 28% compared with neat dental composites and adhesives. Furthermore, in the case of octaphenyl grafted POSS, the compressive strength was reduced by 20%, the adhesive shear bond strength decreased by 49% and the shrinkage was reduced by 67%. It was concluded that the type of the grafted functional group of the caged silica was the dominant factor in nano-tailoring of improved dental composites and adhesives. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: The aims of this study were to formulate a novel fluoride-releasing dental composite and to evaluate its mechanical properties, fluoride release and recharge capabilities, water sorption and solubility. Methods: A fluoride-releasing dimethacrylate monomer containing a ternary zirconium fluoride chelate was synthesized. Three experimental fluoride-releasing composites were fabricated with different monomer formulas (wt.%)—(1) Control A: 40 BisGMA/40 TEDMA/20 UEDMA; (2) Experimental: 20 F-releasing monomer/20 BisGMA/40 TEDMA/20 UEDMA; (3) Control B: the same formula as Control A except that it contained 10wt.% (of total monomer) tetrabutylammonium fluoride (TBAF), which had a fluoride content equivalent to Experimental. All three materials had the same filler content: 55wt.% silanized fluoroaluminosilicate particles (0.8μm) and 10wt.% silanized fumed silica (14nm). All materials contained 0.17wt.% camphorquinone (CQ) as a photoinitiator and 0.69wt.% ethyl-4-dimethylaminobenzoate (4EDMAB) as an accelerator. The materials were tested for fluoride release (for 184 days), fluoride recharge, compressive and flexure strength, water sorption and solubility. The data were analyzed using ANOVA and Tukey-HSD tests, and Kruskal–Wallis test. Results: The experimental composite had significantly higher fluoride release and fluoride recharge capabilities than both Control composites. It had significantly better physical and mechanical properties than Control B. Significance: The combined use of the fluoride-releasing dimethacrylate monomer and fluoride-releasing filler can provide sustained high fluoride release and recharge as well as acceptable mechanical and physical properties. Simply adding organic fluoride salt in the monomer yields composites with poor mechanical and physical properties. [Copyright &y& Elsevier]

Abstract: Objectives: The aim of the study was to develop a new kinetic model for the shrinkage-strain rates of dental resin composites. The effect of filler content on the shrinkage-strain kinetics and degree of conversion of dental composites was also investigated. Methods: A resin matrix containing 65wt.% Bis-GMA and 35wt.% TEGDMA was prepared. 0.5wt.% camphorquinone and 0.5wt.% dimethyl aminoethyl methacrylate were dissolved in the resin as photo-initiator system. Silanized glass fillers were added in different percentages to the resin-monomers. The shrinkage-strain of the specimens photopolymerized at circa 550mW/cm2 was measured using the bonded-disc technique at 23, 37 and 45°C for the matrix monomers and 23°C for the composites. Initial shrinkage-strain rates were obtained by numerical differentiation of shrinkage-strain data with respect to time. Degree-of-conversion of the composites containing different filler contents was measured using FTIR spectroscopy. Results: A new kinetic model was developed for the shrinkage-strain rate using the autocatalytic model of Kamal [Kamal MR, Sourour S. Kinetic and thermal characterization of thermoset cure. Polym Eng Sci 1973;13(1):59–64], which is used to describe the reaction kinetics of thermoset resins. The model predictions were in good agreement with the experimental data. The results also showed a linear correlation between the shrinkage-strain (and shrinkage-strain rate) and filler-volume fraction. The filler fraction did not affect the degree-of-conversion of the composites. Significance: The rate of polymerization, determined via the shrinkage, being invariant with filler-fraction, suggests that only a relatively high filler-surface area, as may be obtained with nano-fillers, will affect the network-forming kinetics of the resin matrix. [Copyright &y& Elsevier]

Light-cured dental composites, which are evaluated by means of the determination of the depth of cure, compression stress, diametrical tensile stress, absorption and solubility in water were studied. The composites formulation were prepared with Bis-GMA/DMTEEG/SIPERNAT D 10 (SD); Bis-GMA/DMTEEG/FK310 (F) y Bis-GMA/MPS/FK310 (M) systems. With the first two systems the authors intend to study the behavior of SIPERNAT D 10 (hydrophobic filler) and FK310 (hydrophilic filler). In the third system, it changes the diluter monomer, making the hydrophilic filler react directly with silane, to improve the mentioned properties. The prepared composites with the system SD and F were the best properties, fulfilling most of them, with the values reported in the corresponding norm. The M composites present small values of depth of cure, and mechanical properties and high properties of absorption and solubility in water. [ABSTRACT FROM AUTHOR]

Hybridized zirconium amorphous calcium phosphate (ACP)-filled methacrylate composites make good calcium and phosphate releasing materials for anti-demineralizing/remineralizing applications with low mechanical demands. The objective of this study was to assess the effect of the particle size of the filler on the mechanical properties of these composites. Photo-curable resins were formulated from ethoxylated bisphenol A dimethacrylate, triethylene glycol dimethacrylate, 2-hydroxyethyl methacrylate and methacryloxyethyl phthalate. Camphorquinone and ethyl 4-N,N-dimethylaminobenzoate were utilized as components of the photoinitiator system. After 2 h of mechanical milling in isopropanol, an approximate 64% reduction in the median particle diameter was observed (27.48 μm vs. 9.98 μm) for unmilled and milled wet ACP, respectively. Dry ACP showed a 43% reduction in particle size from pre- to post-milling. As well as dry composites, those that had been immersed in aqueous media were evaluated for their Young's Modulus, water sorption, biaxial tensile, three-point flexural and diametral tensile strength. Mechanical milling the filler increased the volume of fine particles in the composite specimens, resulting in a more homogeneous intra-composite distribution of ACP and a reduction in voids. Since less water diffused into the milled composites upon aqueous exposure, a marked improvement in biaxial flexure strength and a moderate improvement in flexural strength over composites with unmilled ACP was observed. This improvement in the mechanical stability of milled Zr-ACP composites may help extend their dental applicability. [ABSTRACT FROM AUTHOR]

Summary: Objectives: The purpose of this study was to investigate the effect of ceramic fillers (containing leucite crystals) and their porosity on the mechanical properties of a new experimental dental composite in order to compare with the properties of composites containing conventional glass fillers. Methods: In this study, experimental composites were prepared by mixing the silane-treated fillers with monomers. Experimental composites were divided into four groups according to their filler type, amount and porosity. The monomers were composed of 70% Bis-GMA and 30% TEGDMA by weight for all groups. Glass and leucite-containing-ceramic were prepared as different filler types. In order to make fillers porous, leucite-containing-ceramic fillers were treated with HF acid. Camphorquinone and DMAEMA were used as photo initiator system. Post-curing was done for all groups before mechanical testing. Degree of Conversion of composites was measured using FTIR spectroscopy. The diametral tensile strength (DTS), flexural strength and flexural modulus were measured and compared among the groups. Results: The results showed that the stronger and more porous filler has a positive effect on flexural strength. Porosity of filler increased flexural strength significantly. No significant difference was found in DTS tests among the groups. Flexural modulus was affected and increased by using ceramic fillers. The type of the filler affected the DC of the composite and DC increased by post-curing. Significance: Flexural strength is one of the most important properties of restorative dental materials. Higher flexural strength can be achieved by stronger and more porous fillers. Investigation into the effect of filler on dental material properties would be beneficial in the development of restorative dental material. [Copyright &y& Elsevier]

Porous fillers can be used to obtain micromechanical interlocking between the filler particles and polymer matrix. Micromechanical interlocking in dental composites can overcome the traditional problem of hydrolysis associated with silane coupling. Such an interlocking could also enhance the overall performance of dental composites. In the current study, mesoporous silica was used as fillers to obtain experimental composites. Light curable dental resin (BisGMA/TEGDMA) was used as polymer matrix. The mechanical (compressive) and aging properties of these experimental composites were investigated. The results demonstrated that mesoporous fillers improved the mechanical and aging properties of experimental dental composites. [ABSTRACT FROM AUTHOR]

Summary: Objectives: The objective of this manuscript is to outline the factors associated with hygroscopic and hydrolytic effects in dental polymer networks, and to review the literature generated over the past thirty years or more in this area. Methods: Information was gathered from nearly 90 published articles or abstracts appearing in the dental and polymer literature. Studies were predominantly identified through a search of the PubMED database. Results: Studies were included that provided direct evidence for the uptake of solvent by a polymer network and its subsequent physical or chemical effect, or the loss of molecular species into solvents. An attempt was made to select articles that spanned the timeframe from approximately 1970 to today to ensure that most of the classic literature as well as the latest information was included. Conclusions: Dental polymer networks have been shown to be susceptible to hygroscopic and hydrolytic effects to varying extents dependent upon their chemistry and structure. The importance of these effects on the clinical performance of polymer restoratives is largely unknown, though numerous investigators have alluded to the potential for reduced service lives. Significance: While the physical and mechanical properties of these materials may be significantly altered by the effects of solvent uptake and component elution, what may constitute the greatest concern is the short-term release of unreacted components and the long-term elution of degradation products in the oral cavity, both of which should be strongly considered during restorative material development. [Copyright &y& Elsevier]

The aims of this study were, first, to measure shrinkage induced by different methods of pulse-delay light curing and, second, to verify their influence on the marginal adaptation of class V restorations in enamel and dentin. Eight groups, comprising seven groups ( n = 6) with different pulse-delay parameters and a control group, were compared for dynamic linear displacement and force by using a fine hybrid composite. Based on these results, the pulse-delay curing procedure with the lowest shrinkage force was chosen and tested against the control group with respect to marginal adaptation in class V restorations ( n = 8) before and after simultaneous thermal and mechanical loading. Statistically significant differences between groups were found for both shrinkage properties tested, with one pulse-delay group giving the lowest overall shrinkage values. However, the percentages of ‘continuous margin’ of this group, and of the control before and after loading, were not significantly different in dentin, whereas a significantly lower percentage of ‘continuous margin’ was detected in the pulse-delay group in enamel after loading. [ABSTRACT FROM AUTHOR]

Summary: Objectives: Frictional forces play a major role in the oral wear process of dental resin-based composites (RBCs) and it would be of interest to consider how the energy from friction is dissipated at the material surface. Consequently, the micromechanical wear properties of conventional methacrylate compared with novel oxirane RBCs were assessed. Method: The frictional coefficient (μ), volume loss and Vickers hardness number (VHN) of oxirane (EXL596 and H1) and methacrylate RBCs (Z100 and Filtek™ Z250) were evaluated. Archard''s wear equation was implemented to obtain the wear coefficient (K) and expressed as a ‘fraction of friction’ (K/μ) to indicate the dissipation of frictional energy that resulted in wear. Scanning electron microscopy (SEM) was used to qualitatively asses the wear facets of each RBC following 50000-cycles. Results: The mean frictional coefficients observed between the oxirane and methacrylate RBCs were not significantly different (P>0.05). However, the volume loss of EXL596 and H1 (5.9±0.4 and 4.7±0.3×10−2 mm3) was significantly increased compared with Z100 and Filtek™ Z250 (1.7±0.2 and 2.3±0.3×10−2 mm3). The VHN of EXL596 and H1 was either significantly greater (P=0.021) or similar (P=0.089) to Filtek™ Z250, respectively. An increase in K/μ was reported for EXL596 and H1 (34.7±4.1 and 22.8±2.4×10−4) compared with Z100 and Filtek™ Z250 (8.50±0.7×10−4 and 8.62±1.0×10−4) (P<0.05). SEM images of the oxirane RBCs exhibited increased surface fatigue and delamination of the surface layers compared with the methacrylate RBC specimens following 50,000-cycles. Conclusion: The significant decrease in wear resistance of the oxirane compared with methacrylate RBCs was unexpected since frictional coefficients and/or surface hardness were statistically similar. The decreased wear resistance of EXL596 and H1 compared with Z100 and Filtek™ Z250 was further explained by the increase in K/μ from wear theory and the associated increase in surface fatigue identified from SEM. The simplistic testing procedure combined with SEM utilized in the current investigation provided a greater insight into the wear mechanism by considering the effect of frictional energy at the specimen surface which may benefit the development of improved wear resistance for experimental RBC materials. [Copyright &y& Elsevier]

Summary: Objectives: The depth-sensing micro-indentation testing was recently introduced for the characterization of dental composites. One of the critical issues raised was the possible influence of surface finish on material properties. The aim of this study was to investigate the effects of surface finish on the indentation modulus and micro-hardness of resin-based dental composite materials. Methods: The materials used included minifill (Z100, 3M ESPE), microfill (A110, 3M ESPE) and poly-acid modified (F2000, 3M ESPE) composites. The specimens were polished successively using SiC grinding papers of different grit size and diamond suspensions to achieve varying surface roughness. The arithmetic mean of the roughness (R a) was measured using profilometry. In the depth-sensing micro-indentation test, specimens (n=7) were indented to 10N with Vickers indenter and the load-displacement (P–h) data was obtained using a universal testing system. The indentation modulus (E in) and hardness (H) were then computed using the developed analytical solutions. Data was analyzed using ANOVA/post-hoc Scheffe''s test at significance level 0.05. Results: The polished specimens had surface roughness ranging from 0.02 to 0.81μm. The roughness of F2000 was significantly higher than A110 and Z100. The E in and H for Z100 ranged from 14.02 to 14.83GPa and 1.18 to 1.27GPa, respectively. E in for F2000 and A110 ranged from 12.25 to 13.82GPa and 5.26 to 5.52GPa and hardness ranged from 0.89 to 0.98GPa and 0.52 to 0.55GPa, respectively. Significance: The indentation modulus and hardness of dental composite restoratives were independent of the surface finish provided indenter penetration is sufficiently deep (h max/R a>30). [Copyright &y& Elsevier]

Summary: Objectives: 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. Methods: Two hundred rectangular specimens of five veneering composites were electron beam irradiated with 25, 100 and 200kGy using an electron accelerator of 10MeV. Fracture toughness, work of fracture, Vickers hardness, color changes and three-medium wear were measured and compared with non-irradiated specimens. Results: Visible color changes (ΔE>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. Significance: Electron beam irradiation can significantly change the mechanical properties of dental composites. However, color changes can limit the use of irradiation for dentistry. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to investigate the shrinkage strain rate of different monomers, which are commonly used in dental composites and the effect of monomer functionality and molecular mass on the rate. Bis-GMA, TEGDMA, UDMA, MMA, HEMA, HPMA and different ratios of Bis-GMA/TEGDMA were mixed with Camphorquinone and Dimethyl aminoethyle methacrylate as initiator system. The shrinkage strain of the samples photopolymerised at Ca. 550mW/cm2 and 23°C was measured using the bonded-disk technique of Watts and Cash (Meas. Sci. Technol. 2 (1991) 788–794), and initial shrinkage-strain rates were obtained by numerical differentiation. Shrinkage-strain rates rose rapidly to a maximum, and then fell rapidly upon vitrification. Strain and initial strain rate were dependent upon monomer functionality, molecular mass and viscosity. Strain rates were correlated with Bis-GMA in Bis-GMA/TEGDMA mixtures up to 75–80w/w%, due to the higher molecular mass of Bis-GMA affecting termination reactions, and then decreased due to its higher viscosity affecting propagation reactions. Monofunctional monomers exhibited lower rates. UDMA, a difunctional monomer of medium viscosity, showed the highest shrinkage strain rate (). Shrinkage strain rate, related to polymerization rate, is an important factor affecting the biomechanics and marginal integrity of composites cured in dental cavities. This study shows how this is related to monomer molecular structure and viscosity. The results are significant for the production, optimization and clinical application of dental composite restoratives. [Copyright &y& Elsevier]

Summary: Objective: It was hypothesized that by standardizing variables such as light sources, filler types and filler surface treatment, it should be possible to use Beer–Lambert''s law to predict light absorption in visible light-cured dental composites. Methods: Mixture of 50wt% bisGMA and 50wt% TEGDMA to which a photo-initiator (0.35wt% champhorquinone) and a co-initiator (0.7wt% of dimethylaminoethylmethacrylate) was prepared. Three different filler types (HBB, SBB and KU) were added to that mixture in eight different volume percentage. Filler particles were either silane surface treated or not. Specimens were made with thicknesses of 1–5mm. Total number of 1200 specimens were made for this study. Light transmission was obtained for halogen source and laser lights, which made the number of observations 2400. The absorbance values of the different materials were analyzed in Matlab with respect to the differences in filler fraction and sample thickness. Results: The obtained results revealed that of the two light sources, more light was absorbed by the composite when the laser light was used. Among different filler types, the HBB filler absorbed most light and the KU filler the least. There were significant differences (p&#60;0.05) in light absorption between all three filler types. Significance: By comparing the modeled surfaces generated by Matlab for different materials it was possible to determine how different variables such as filler type, filler surface treatment and light source affect light attenuation. The characteristic of incident light affected the light absorbance, meaning that not only the composite''s composition needs to be considered in light absorption studies of dental composites. [Copyright &y& Elsevier]

Abstract: Resin composites were first introduced as anterior restorative materials, but are more and more used in posterior teeth, as amalgam replacements. Nowadays the so-called ‘condensable’ composites are frequently used in posterior teeth. These materials are subjected to high values of contact and mastigatory loads, loading rates and sliding distances. In such contact conditions, wear is the major failure mode of dental composites. Wear of dental composites includes such diverse phenomena as adhesion, abrasion and fatigue. These mechanisms may operate either alone or in combination. Most of the performed studies involve commercial composite materials and focus on the effect of curing time, and their reflection on the abrasive wear behavior. The wear compatibility of both materials in contact should be one of the concerns of the wear studies. However, the majority of studies do not consider the wear produced on the antagonist material. The present study aims to the understanding of the behavior of commercial composites under reciprocating contact. For the tests, a glass ball was used as opponent. At the end of each test, the wear volume was calculated on both contact materials: the composite and the glass counterface. The removal mechanisms involved in the wear process were discussed taking into account SEM observations of the contact surfaces. [Copyright &y& Elsevier]

Summary: Objectives: The objectives were to investigate the structure and selected physical properties of products resulting from the photopolymerization of a binary mixture containing an aliphatic dioxirane, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (ECHM-ECHC) and a potential expanding monomer, 3,9-bis(oxiranylcyclohexylmethyl)-1,5,7,11-tetraoxaspiro[5.5]undecane (BOCHM-TOSU). Methods: Reaction mixtures were irradiated with a dental curing lamp at room temperature. Some reactions were quenched prior to gel point. Oligomeric products were separated from unreacted monomers by column chromatography, and analyzed by NMR. Physical properties of polymeric solids were measured using accepted standard methods. Protonation energies for monomers were calculated using semi-empirical quantum mechanical methods. Results: Types of oligomers found included poly(ether)s and poly(carbonate)s. Quantum mechanical calculations indicated preferential attack at the more nucleophilic oxaspirocyclic ring sites. For cured solid polymer samples, the elastic modulus was 2.39±0.24GPa and the fracture toughness was 0.73±0.10MPam1/2. These values were similar to those measured for a cured conventional BISGMA/TEGDMA matrix resin. Significance: The room-temperature photopolymerization of an aliphatic dioxirane and a potential expanding monomer demonstrates the possibility of making cross-linked copolymer resins with improved polymerization shrinkage characteristics for use in dental composites. [Copyright &y& Elsevier]