Light-cured Dental Composites Research Articles

Effect of the Silanization of Aerosil OX50 in the Properties of Light-Cured Dental Composites

In this study, the surface of aerosil OX50 was treated with γ-methacryloxypropyltrimethoxysilane in order to evaluate its effect on light-cured dental composites. Four composites were prepared with Bis-GMA/tetraethylene glycol dimethacrylate/γ-methacryloxypropyltrimethoxysilane, Bis-GMA/tetraethylene glycol dimethacrylate, and a 45% treated or untreated aerosil OX50, using the camphorquinone/N,N-dimethylaminoethyl methacrylate pair as initiator. Evidence of filler silanization was provided by FTIR as a low-intensity absorption at 1707 cm−1 (carbonyl functional group) while thermogravimetric analysis showed a mass loss of approximately 2% associated with the decomposition of γ-methacryloxypropyltrimethoxysilane. The experimental composites studied meet the requirements of the ISO 4049:2019 standard for depth of cure, water sorption, and solubility. The composites are shown to be thermally stable and presented a degree of conversion higher than 70%, being higher than that reported for many commercial composites. Based on the observed properties, the best formulations were those in which the silane is incorporated into the matrix and the filler was previously treated.

Light-curing dental resin-based composites: How it works and how you can make it work

AimClinicians may become quite familiar with the rapid transformation of composite pastes to rigid solids, as a routine phenomenon in operative dentistry. But they may still lack scientific understanding of how and why this happens. Efforts to learn scientifically about the interaction between light beams and resin-composites can significantly promote effective clinical placement of restorations. Neglect of such study can result in practical procedures of light-curing that are inadequate or even seriously defective.MethodThis review addresses the underlying science and technology to elucidate how light curing works, for dental resin-based composites, including—but not limited to—bulk fill types. This involves questions concerning: (a) the particle-wave understanding of light; (b) how photons can penetrate sufficiently deeply into bulk fill composites; (c) the necessary technology of LED light-curing units (LCUs); (d) the criteria for absorption of photons by photo initiators to initiate free-radical addition polymerisation.ConclusionsThe implications for clinical practice are surveyed. These include design variables and selection criteria for LED-LCUs and guidelines on their use. This is to guide practitioners towards safe and effective light-curing procedures so that they can achieve optimal result for their patients.

Miscibility and Optimization of the Liquid Rubber Content in the Resins of Light-Cured Dental Composites

Fracture toughness is one of the main factors influencing the durability of light-cured composites used for dental restorations and fillings. One of the methods of increasing the fracture toughness is the modification of the matrix with liquid acrylonitrile-free liquid rubber. This study aimed to assess the miscibility of acrylonitrile-free liquid rubber with a blend of resins and their stability over time, and to determine the optimal amount of liquid rubber (LR) in the blend due to mechanical properties. Two blends of dimethacrylate resins were used: resin "F" composed of BisGMA (60 wt.%), TEGDMA (20 wt.%), BisEMA (10 wt.%) and UDMA (10 wt.%), and "C" resin containing BisGMA (40 wt.%), TEGDMA (40 wt.%), BisEMA (10 wt.%) and UDMA (10 wt.%). The modifier Hypro® 2000X168LC VTB liquid rubber was used in at 1%, 2%, 3%, 4%, 5%, 10%, 15% and 20% by weight in the resin blend. The miscibility was assessed by microscopy. The fracture toughness, flexural strength and Young's modulus were determined in the bending test. The results showed that the solubility of the liquid rubber depends on the ratio of BisGMA/TEGDMA in the resins. In resins with 40 wt.% TEGDMA, the LR solubility was as high as 5%, while resins with 20 wt.% TEGDMA, the liquid rubber did not dissolve. The LR-resin mixtures showed good time stability, and no changes in the size or morphology of the rubber domains were found after 24 h of mixing. The maximum fracture toughness (2.46 MPa m1/2) was obtained for 5 wt.% LR in resin F and for 15 wt.% LR in resin C (2.53 MPa m1/2). The modification with liquid rubber resulted in an exponential reduction in both flexural strength and Young's modulus. The analysis of the results of the mechanical tests allowed us to determine the optimal amount of LR for both resins. For resin F it was 5.4 wt.%, and for resin C it was 8.3 wt.%. It can be stated that the optimal amount of liquid rubber increases with its solubility in the resin.

EVALUATION OF STRENGTH PARAMETERS OF POLYMER COMPOSITES USED FOR DENTAL RESTORATION BY THE METHOD OF ACOUSTIC EMISSION

The aim of the study is to create a technique and perform mechanical tests to determine the strength parameters of dental composites from the standpoint of linear fracture mechanics, and using the phenomenon of acoustic emission to determine the origin and development of destruction of light-curing dental composites under quasi-static local compression load. The following hybrid dental composites of domestic and foreign manufacturers were selected for comparison: Latelux (Latus, Ukraine), TETRIC N-CERAM (Ivoclar Vivadent, Liechtenstein), CHARISMA CLASSIC (Kulzer, Germany). 10 disc samples of 13 mm diameter and 5 mm thick of each material were made by using a specially designed mould for study purposes. Packaging and moulding of the material into the mould was performed in laboratory conditions at an air temperature of 18 – 21°C. Before testing, the samples were kept for 24 hours at a temperature of 37°C in saline solution. The samples were loaded on the SVR-5 machine using a ball indenter. During the experiments, acoustic emission data were simultaneously recorded using the SKOP-8 measuring system. In the post-processing stage, the dependencies of the load change during the experiment, the distribution of the amplitudes of the registered AE signals and their sum over time were recorded. The fracture load, indenter displacement, and the features of composite fracture were determined from the obtained dependencies based on the analysis of AE generation under the load. Analysis of the parameters of the AE signals showed that during the destruction of the Tetric N-Ceram composite the signals had the largest amplitude and energy, and of Latelux had the smallest ones.

Polymerization kinetics of experimental resin composites functionalized with conventional (45S5) and a customized low-sodium fluoride-containing bioactive glass

This study aimed to investigate polymerization kinetics and curing light transmittance of two series of experimental dental resin composites filled with 0–40 wt% of either 45S5 bioactive glass (BG) or a customized low-Na F-containing BG. Polymerization kinetics in 0.1-mm and 2-mm thick layers were investigated through real-time degree of conversion measurements using a Fourier transform infrared (FTIR) spectrometer. FTIR spectra were continuously collected at a rate of 2 s−1 during light-curing (1340 mW/cm2). Light transmittance through 2-mm thick composite specimens was measured using a UV–Vis spectrometer at a rate of 20 s−1. Unlike BG 45S5, which led to a dose-dependent reduction in the rate and extent of polymerization, the customized low-Na F-containing BG showed a negligible influence on polymerization. The reduction in light transmittance of experimental composites due to the addition of the low-Na F-containing BG did not translate into impaired polymerization kinetics. Additionally, the comparison of polymerization kinetics between 0.1-mm and 2-mm thick layers revealed that polymerization inhibition identified for BG 45S5 was not mediated by an impaired light transmittance, indicating a direct effect of BG 45S5 on polymerization reaction. A customized low-Na F-containing BG showed favourable behaviour for being used as a functional filler in light-curing dental resin composites.

Changes in color and contrast ratio of resin composites after curing and storage in water

PurposeTo verify the color change and contrast ratio of resin composites after curing and after 30 days of storage in water. MethodsDentin A2 shades of different light-cured dental resin composites (Vittra APS, FGM, Brazil; Z350 XT, 3M ESPE, EUA; Tetric N-Ceram, Ivoclar Vivadent, Liechtenstein, and Charisma Diamond, Heraeus Kulzer, Germany) were tested. Ten rounded specimens (8 mm × 2 mm) were prepared for each material. Reflectance for all samples was obtained using a spectrophotometer (Minolta CM 3700d, Konica Minolta, Japan) before curing, immediately after curing, and after 30 days of storage in water. The color change (ΔE*lab) and contrast ratio (CR) data were analyzed using a one-way analysis of variance with Tukey's and paired t-tests (α = 1%). ResultsFor all materials tested, significant color changes were noticeable after curing and after 30 days in water (p < 0.01). Significant changes in the CR values before curing, after curing, and 30 days of storage in water were observed in the resin composites investigated (p < 0.01) except for Z350 (p > 0.01). ConclusionThe CR values and color changes after curing and 30 days of storage in water varied depending on the material tested. This study corroborates the clinical practice of curing a small amount of unpolymerized resin composite on the tooth surface to select the desired shade before undertaking esthetic restorative procedures.

Water Sorption and Solubility of Light-Cured Dental Composites Prepared from Two Different Types of Matrix Monomers

Two groups of resins reinforced by different ratios of nano-hydroxyapatite were used to produce the novel dental composite, with the main purpose of measuring the water sorption (WS) and solubility (SO) of the prepared nanocomposites. Ten experimental specimens were prepared in disk-shaped with and without filler materials, in two groups, each group was classified according to filler contents (0, 1, 2, 3, and 4) wt. % of nano-hydroxyapatite. Each specimen was stored for 7 days in water, proceeding to measure the mass of each specimen. After drying process, the specimen masses were determined. Then WS and SO were calculated from these determinations. The results showed that values of water sorption after 1 week for group A composite and group B composite ranged (9.66 to 13.07 mg/mm3) and (5.11 to 8.52) mg/mm3, respectively, while solubility was (2.97 to 3.25) mg/mm3 for group A and (1.83 to 2.26 mg/mm3)for the composites specimens of group B, respectively. For composite with different filler contents the results showed a high filler contents of 4% for each group with high value of water sorption (WS) and solubility (SO). It could be concluded that the percentage of sorption and solubility of composite based on acrylic and amide were significantly lower than that based on acrylate.

First-principles study on Sr-doped hydroxyapatite as a biocompatible filler for photo-cured dental composites

The first-principles calculations based on density functional theory with generalized gradient approximation were carried out to investigate the fundamental features of hydroxyapatite, the primary constituent of human bone and tooth, for use in light-curable dental composites. Moreover, the influence of strontium incorporation into hydroxyapatite on structural, electronic and optical properties of hydroxyapatite was comprehensively studied while we believe this substitution can promote radiopacity and remineralization ability of apatite. After geometry optimization, the computed structural parameters are found to yield a satisfactory agreement with the reported experimental results indicating the accuracy of the calculations. The elastic characteristics demonstrate that both hexagonal apatites possess higher Young’s modulus and Poisson’s ratio compared silica glass which is known as traditional filler used in dental composites. The analysis of the electronic density of states reveals that some variation in macroscopic mechanical properties can arise from difference between d state energy of calcium and strontium elements. Moreover, the origins of optical features affecting the curing depth of composite have been discussed in terms of the dielectric function and refractive index. The weak energy loss in the range of 3–3.5 eV demonstrates that these biocompatible fillers can provide an increased curing depth when are used in a UV-LED cured restorative dental materials.

Contemporary aesthetic restorative dental composite materials

Purpose: This is a review paper that gives an insight into the most popular group ofaesthetic dental materials - dental composite materials. This article describes the historicalbackground, the main features of this group of materials, the cathegorization of the materialsin relation to clinical applications and the polymerization proces.Design/methodology/approach: This review is based on the contemporary scientificliterature most relevant to the topic. The literature search has been made in Elsevier -Science Direct.Findings: Light-curing dental composites exhibit some resemblance to the constructionof the hard tissues of the tooth. They also consist of two basic components. These are:an organic matrix and an inorganic filler. The third component, which is regularly added, isso-called binding agent. According to the composition of the materials they make a goodchoice for aesthetic restoration in natural dentition.Practical implications: In the clinical observations there are many complications resultingfrom inadequate polymerization of composite materials. This may be the result of poorquality of curing lights of a very low intensity, too long distance between the tip of the lampand the surface of the material or improper exposure timeOriginality/value: Dental composite materials are the only group of dental materialsin which these features are combined together, ensuring naturally looking final effect ofthe restoration. Easy handling of the dental composite materials together with effectivepolymerization process with portable light units make these materials a good choice forclinical use.

Study Of Ceramic-Polymer Composites Reliability Based On The Bending Strength Test

Abstract In this paper the reliability assessment of structural reliability of the selected light-cured dental composites based on the biaxial flexural strength test results has been presented. A two-parameter Weibull distribution was applied as a reliability model in order to estimate probability of strength maintenance in the analysed population. Weibull distribution parameters were interpreted as a characteristic material strength (scale parameter) and structural reliability parameter in terms of ability to maintain strength by each of specimen from the general population (shape parameter). 20 composite specimens underwent strength tests, including 2 “flow” type composites and 2 standard composites (with typical filler content). “Flow” type composites were characterized with lower characteristic strength and higher structural reliability comparing to other studied composites.

Effect of 457 nm diode-pumped solid state laser on the polymerization composite resins: microhardness, cross-link density, and polymerization shrinkage.

The purpose of the present study was to test the usefulness of 457 nm diode-pumped solid state (DPSS) laser as a light source to cure composite resins. Five different composite resins were light cured using three different light-curing units (LCUs): a DPSS 457 nm laser (LAS), a light-emitting diode (LED), and quartz-tungsten-halogen (QTH) units. The light intensity of LAS was 560 mW/cm(2), whereas LED and QTH LCUs was ∼900 mW/cm(2). The degree of polymerization was tested by evaluating microhardness, cross-link density, and polymerization shrinkage. Before water immersion, the microhardness of laser-treated specimens ranged from 40.8 to 84.7 HV and from 31.7 to 79.0 HV on the top and bottom surfaces, respectively, and these values were 3.3-23.2% and 2.9-31.1% lower than the highest microhardness obtained using LED or QTH LCUs. Also, laser-treated specimens had lower top and bottom microhardnesses than the other LCUs treated specimens by 2.4-19.4% and 1.4-27.8%, respectively. After ethanol immersion for 24 h, the microhardness of laser-treated specimens ranged from 20.3 to 63.2 HV on top and bottom surfaces, but from 24.9 to 71.5 HV when specimens were cured using the other LCUs. Polymerization shrinkage was 9.8-14.7 μm for laser-treated specimens, and these were significantly similar or lower (10.2-16.0 μm) than those obtained using the other LCUs. The results may suggest that the 457 nm DPSS laser can be used as a light source for light-curing dental resin composites.

Multiaxial Strength and Stress Forming Behavior of Four Light-Curable Dental Composites

The resulting internal stress situation in curing dental composites is still oversimplified due to analytical inaccessibility of local information of state and loading. Similar applies to the strength behavior of cured dental composites. Using recent progress of a finite-element-based curing model, we developed and attempted to benchmark dental composites based on their mechanical behavior and tendency to form internal stress. Additionally, in order to understand the influence of restoration techniques on the mechanical loading, curing simulations were necessary. Three-point flexural strength, compressive strength and diametral tensile strength and the necessary curing parameters were studied for four state-of-the-art dental composites (Tetric EvoCeram, Venus Diamond, EsthetX, Filtek Supreme XT). The investigated composites fracture can be analyzed by the Drucker Prager failure criteria for each composite. The lowest resulting curing stresses were found for Tetric EvoCeram because of its low volumetric shrinkage and a high ratio of initiation phase to dark phase conversion. Venus Diamond showed the best overall mechanical properties because it can withstand tensile as well as compressive stress. In order to draw conclusions on comparisons between several composites, flexural strength tests, volume shrinkage measurements, cavity classifications and general preparation recommendations may still be a suitable way for the simplification of the immense complexity in curing and restoration. Nevertheless, finite-element-based simulations are necessary to include fundamental effects such as stress relaxation by flow and multiaxial strength of the composite.

Dielectric analysis of depth dependent curing behavior of dental resin composites

ObjectivesThe aim of this study is to investigate depth dependent changes of polymerization process and kinetics of visible light-curing (VLC) dental composites in real-time. The measured quantity – “ion viscosity” determined by dielectric analysis (DEA) – provides the depth dependent reaction rate which is correlated to the light intensity available in the corresponding depths derived from light transmission measurements. MethodsThe ion viscosity curves of two composites (VOCO Arabesk Top and Grandio) were determined during irradiation of 40s with a light-curing unit (LCU) in specimen depths of 0.5/0.75/1.0/1.25/1.5/1.75 and 2.0mm using a dielectric cure analyzer (NETZSCH DEA 231 with Mini IDEX sensors). The thickness dependent light transmission was measured by irradiation composite specimens of various thicknesses on top of a radiometer setup. ResultsThe shape of the ion viscosity curves depends strongly on the specimen thickness above the sensor. All curves exhibit a range of linear time dependency of the ion viscosity after a certain initiation time. The determined initiation times, the slopes of the linear part of the curves, and the ion viscosities at the end of the irradiation differ significantly with depth within the specimen. The slopes of the ion viscosity curves as well as the light intensity values decrease with depth and fit to the Lambert–Beer law. The corresponding attenuation coefficients are determined for Arabesk Top OA2 to 1.39mm−1 and 1.48mm−1, respectively, and for Grandio OA2 with 1.17 and 1.39mm−1, respectively. For thicknesses exceeding 1.5mm a change in polymerization behavior is observed as the ion viscosity increases subsequent to the linear range indicating some kind of reaction acceleration. SignificanceThe two VLC composites and different specimen thicknesses discriminate significantly in their ion viscosity evolution allowing for a precise characterization of the curing process even with respect to the polymerization mechanism.

Polymerization stress of dental resin composite continues to develop 12 hours after irradiation.

This study assessed the development of stress from polymerization of light-cured dental resin composites for 24 hours after irradiation. Initial cracks were made near the edge of a cylindrical hole in glass, and crack lengths were measured. Revolution Formula 2, Kalore and Venus Diamond were polymerized in the hole. Crack lengths were measured at several intervals after irradiation up to 24 hours. Stresses at the composite-glass interface were calculated using the crack lengths. Elastic moduli of the composites were measured at the same time intervals. Interfacial stress and elastic modulus were significantly related to material and time. Stress continued to increase up to 12 hours after irradiation. Significantly lower stresses were measured in Kalore and Venus Diamond than Revolution Formula 2 throughout 24 hours. Stress at 24 hours was two times greater than the stress at 30 minutes. The increase in elastic modulus from 30 minutes to 24 hours ranged from 8 to 24%, which was less than the increase in stress over the same time period. Interfacial stress and elastic modulus of the composites demonstrated the average increases of 155% and 14%, respectively, from 30 minutes to 24 hours after irradiation. Since the elastic modulus is a measure of stiffness and resistance to load, clinicians might consider advising their patients to avoid heavy occlusal function until the elastic modulus has reached a plateau, which would be 60 minutes for Venus Diamond, 12 hours for Kalore, and 24 hours for Revolution Formula 2.

Influence of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; as Filler Loading on the Fracture Toughness of Light-Cured Dental Resin Composites

The purpose of the present study was to evaluate the effect of filler loading on the fracture toughness of light-cured dental resin composites (DRCs). The monomer Bis-GMA and TEGDMA (75/25 wt/wt) were mixed with treated micro-sized aluminum oxide (Al2O3) particles ranging from 40-60 wt% as filler. The composite samples were cured with LED for 80s. The bulk density (g/cm3) and apparent porosity (%) of the samples were determined according to the ASTM standard. The fracture toughness (KIC) values of the composites were determined using a single edge notched specimen in the three-point bending test. There was a significant difference in KIC of the composites with different loading of Al2O3 particles (p &lt; 0.05). The highest amount of filler (60 wt%) reduced the KIC value to 1.5 MPa.m1/2. As a conclusion, the Al2O3 particles used as filler loading does have an effect on the mechanical properties of DRCs.

Effect of alumina particles loading on the mechanical properties of light-cured dental resin composites

The purpose of this study is to evaluate the effect of alumina (Al2O3) loading on the mechanical properties of dental resin composites (DRCs). The DRCs were prepared based on Al2O3 particles and bisphenol A-glycidyl methacrylate (Bis-GMA) was used as the base monomer. The silane-treated Al2O3 particles were mixed with the resin matrix in proportions of 40, 50, and 60wt%, respectively. Resin matrix without filler was used as the control sample. The Vickers hardness (HV) and flexural modulus (FM) of the DRCs mixed with Al2O3 particles were found to be superior compared to the control sample; the values increased from 14.4 to 23.5kg/mm2 and 1.5 to 5.7GPa, respectively. However, the flexural strength (FS) values of DRCs were slightly decreased as the filler loading increased i.e. from 84.5 to 74.2MPa. The results also revealed statistically significant increases in the HV and FM. On the other hand, FS values showed significant decrease when filler loading was increased (P<0.05).

Relation between in-vitro wear and nanomechanical properties of commercial light-cured dental composites coated with surface sealants

This work investigates the correlation between the in-vitro wear resistance and the nanomechanical properties of dental sealants commercially available. Mechanical properties, namely hardness (H) and elastic modulus (E), were assessed by nanoindentation technique. The coated samples presented lower H and E values than the Z250 composite resin substrate. Such measurements were used to calculate H/E ratios. Wear tests were carried out in water by using a pin-on-plate apparatus. Scars formed on the samples were qualitatively examined by optical microscopy, while their wear depths were measured by contact profilometry. Based on the findings, an empirical correlation between the wear depths and H/E was obtained. A high H/E ratio was associated to surfaces with enhanced wear resistance. For the tribological conditions here employed, the H/E ratio could be, therefore, considered a useful parameter for ranking the in-vitro wear of dental sealants.

Terahertz time-domain spectroscopy for monitoring the curing of dental composites

We apply terahertz (THz) time-domain spectroscopy for monitoring the curing process of three different light-curing dental composites. Exact knowledge of the sample thickness is required for a precise determination of the THz dielectric parameters, as the materials exhibit shrinkage when they are cured. We find very small but significant changes of the THz refractive index and absorption coefficient during stepwise light exposure. The changes in the refractive index are correlated with changes in the density of the materials. Furthermore, the refractive index and the sample thickness are found to give the most reliable result for monitoring the curing process of the dental composites.

Light Curable Dental Composites – Kinetics by Plasma and Halogen Lamps

A series of commercial dental composites curable by visible light have been investigated and compared in terms of their photoreactivity thanks to the photocalorimetry technique by using two different types of lamps, a conventional lamp (halogen lamp) from ESPE and a plasma lamp, Apollo 98E manufactured by DMDS. In terms of kinetics, dental composites cure in just a few seconds with plasma lamp compared to 20-40 s with halogen lamp allowing dentists to save time. Recent investigations on new composite systems having low contraction show that they are less photoreactive compared to former systems. Досліджено ряд торгівельних стоматологічних композитів, затверджуваних видимим світлом. За допомогою фотокалориметричного методу аналізу, з використанням двох різних типів ламп: звичайних (галогенових) та плазмових типу Аполлон 98E проведено порівняння фотореактивності таких композитів. Визначено, що час затвердження композитів за допомогою плазмової лампи становить декілька секунд, у порівнянні з 20–40 с у випадку затвердження галогенними лампами. Показано, що нові композити менш фотореакційноздатні у порівнянні з попередніми системами.

Synthesis and properties of liquid crystalline urethane methacrylates for dental composite applications

Three novel liquid crystalline methacrylates have been synthesized and characterized to be tested as comonomers in light-curing dental resin-based composites. The selected formulations consist of an alkylammonium or cholesteryl urethane methacrylate and 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropyl)phenyl]propane (BisGMA) or a BisGMA derivate modified with urethane methacrylate groups, further diluted with triethyleneglycol dimethacrylate (TEGDMA) and reinforced with 70% filler (zirconium silicate nanopowder, silanized filler). This study addresses the relationships between the LC monomer structure, photopolymerization rates (by differential scanning photo calorimetry), and specific properties of the dental resin composites (volumetric shrinkage, water sorption, water solubility, and hydrophobicity). The investigation of LC properties by differential scanning calorimetry and polarizing microscopy indicated that the LC mesophase is stable to room temperature (cationic monomers) or at 40 °C (cholesteryl methacrylate). It was found that the polymerization rate for LC urethane methacrylates used in combination with BisGMA/TEGDMA (0.122–0.136 s−1) is higher than that of the mesogenic monomers alone (0.085–0.107 s−1). The structures of the urethane monomers and, consequently, the viscosity of the comonomer mixture influence both the rate and the degree of conversion (44.8–67.5 %) of the photopolymerization process. Polymerization shrinkage measured by pycnometry showed lower values for LC monomers (3.25–3.43 vol %) comparatively with the monomer mixture (5.19–6.65 vol %). Preliminarily, the effect of ammonium groups from two resin composites incorporating alkylammonium structures (4.5 wt %) was tested on Streptococcus mutans, and distinct zone of inhibition was observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011