Improvements to light transmittance in light-cured composite resins by the utilisation of low refractive index dimethacrylates

In an effort to improve the light transmittance of light-cured composite resins while avoiding degradation of their physical properties, 4 dimethacrylates having low refractive indices and a bulky backbones such as alicyclic or fluorine-substituted bisphenol groups were synthesized. The depths of cure and physical properties of 6 experimental composite resins containing these new monomers were, then, examined and compared to those of 3 control composite resins containing UDMA, BisMEPP, or BisGMA. The depths of cure of the experimental group containing the synthesized monomers were greater than those of the control group with the exception of the composite containing UDMA. The depth of cure increased as the difference between the refractive indices of the matrix monomer and silica filler decreased. The physical properties of 2 composites in the experimental group were comparable to those of the control group. The matrix monomers of these 2 composites were a mixture of 4,8-dimethacryloxymethylene tricyclo [5.2.1.0] decane or 2,2-bis (4-methacryloxyethoxy phenyl) hexafluoropropane and TEGDMA in a molar ratio of 1/1.     

Mechanical properties of heat treated restorative resins for use in the inlay/onlay technique

Abstract – Inlay/onlay materials based on composite resins have recently been introduced. It was the aim of the present study to investigate the effect of post-curing temperature on selected mechanical properties. Four different composite resins were produced. The composite resins had identical filler content, but varied with respect to the content of the monomers BISGMA, TEGDMA, UEDMA, and HEMA. After Initial curing by light, the materials were post-cured at 37, 100, 125, 150, 175, or 200°C for 1 h. We then measured diametral tensile strength, flexural strength, and modulus of elasticity. These properties were found to vary with the composition of the material. Composites containing UEDMA or UEDMA/HEMA were stronger and stiffer than BISGMA/TEGDMA formulations. The optimum post-curing temperature was 150°C, but the increase in strength and stiffness was moderate, only about 9%.     

Mechanical properties of heat treated restorative resins for use in the inlay/onlay technique

Inlay/onlay materials based on composite resins have recently been introduced. It was the aim of the present study to investigate the effect of post-curing temperature on selected mechanical properties. Four different composite resins were produced. The composite resins had identical filler content, but varied with respect to the content of the monomers BISGMA, TEGDMA, UEDMA, and HEMA. After initial curing by light, the materials were post-cured at 37, 100, 125, 150, 175, or 200 degrees C for 1 h. We then measured diametral tensile strength, flexural strength, and modulus of elasticity. These properties were found to vary with the composition of the material. Composites containing UEDMA or UEDMA/HEMA were stronger and stiffer than BISGMA/TEGDMA formulations. The optimum post-curing temperature was 150 degrees C, but the increase in strength and stiffness was moderate, only about 9%.     

The application of fluorinated aromatic dimethacrylates and diacrylates to light-cured composite resins. 1. Improvement of transmittance of composite

To improve the transmittance of light-cured composite resins, the matching of the refractive indices of the matrix monomer and filler were examined. Eight fluorinated aromatic dimethacrylates and diacrylates with a low refractive index were synthesized. Three of these monomers had a poor solubility to TEGDMA. The depths of cure and the other physical properties of eight experimental composites prepared from one of five fluorinated monomers, TEGDMA and UDMA were determined compared with those of the control composites prepared from Bis-GMA or Bis-MEPP/ and TEGDMA in the same ratio. These composites contained 70 wt% of silanized silica filler. The depths of cure of the experimental composites except for one were significantly greater than those of the control composites. The mechanical properties of the experimental composites were comparable to those of the control composites with a few exceptions, but the difference in the mechanical properties between these exceptional composites and the control was small. The water sorption of the experimental composites was markedly lower than that of the composite containing Bis-GMA and comparable to that of the composite containing Bis-MEPP. These five fluorinated monomers are considered useful as the matrix monomer of light-cured composite resins.     

Physical properties of light-cured opaque resin. (1) Influence of monomer composition

Light-cured opaque resins with excellent physical properties were prepared using five types of monomer liquid and titanium dioxide as the powder. The five opaque resin monomer liquid had the following monomer compositions. Methyl methacrylate (MMA)/di(methacryloxyethyl) trimethylhexamethylene diurethane (UDMA) = 70/30 (M-U), MMA/neopenthylglycol dimethacrylate (NPG)/UDMA = 45/45/10 (M-N-U), UDMA/MMA = 70/30 (U-M), 2,2-bis (4-methacryloxypolyethoxy phenyl) propane (2.6 E)/2,2-bis [4-(3-methacryloxy-2-hydroxy propoxy) phenyl] propane (Bis-GMA)/triethyleneglycol dimethacrylate (3 G) = 60/35/5(2.6-B-3) and 3 G/UDMA = 70/30 (3-U) by weight. The bond strength, photo-curability and handling properties of the opaque resin were improved. Three MMA-based opaque resins showed nearly the same values in Knoop hardness number, diametral tensile strength and shear bond strength. The depth of cure increased with the decrease in MMA content of monomer composition, while the amount of residual monomer decreased. The 2.6-B-3 opaque resin had nearly the same properties in depth of cure and Knoop hardness number as the 3-U opaque resin. However, the 2.6-B-3 and 3-U opaque resins had a diametral tensile strength more than twice as high as that of the U-M opaque resin. The bond strength of three MMA-based opaque resins showed 0MPa after 5,000 thermocycles, while the 2.6-B-3 opaque resin, about 16 MPa, and the 3-U opaque resin, about 25 MPa. Therefore, the bond strength of the opaque resin was influenced by monomer composition. 3G-UDMA opaque resin showed excellent physical properties and may be clinically acceptable to bond fixed prosthodontic composite.     

Mechanical properties and curing depth of urethane tetramethacrylate-based composite resins

Mechanical properties and curing depth of light-cured composite resins based on five types of urethane tetramethacrylate (UTeMA; IP-4 M, XY-4 M, MC-4 M, HM-4 M and TM-4 M) were investigated, and compared them with those of UDMA-based composite resins. Composites based on UTeMA monomers containing an aromatic or cyclohexane ring in their chemical structure (IP-4 M, XY-4 M and MC-4 M) showed a relatively rigid properties than those based on aliphatic UTeMA (HM-4 M and TM-4 M). The composite resins based on XY-4 M monomer showed a curing depth and transmission coefficient superior to the other composite resins. UTeMA-based composites showed a significantly higher rigid properties than UDMA-based composites, while their rigidity did not improve the flexural strength.     

Polymer properties on resins composed of UDMA and methacrylates with the carboxyl group.

The properties of dental matrix resins have been improved by synthesis of new monomers. However, except for improvements in water-resistance, monomers with better mechanical properties than Bis-GMA and UDMA could not being synthesized. Changing the point of emphasis, we tried to improve the mechanical properties controlling the matrix resin higher structure using noncovalent bonds. We prepared a matrix resin structured by UDMA, which is a high viscosity base monomer with imino groups, and by a low viscosity acidic monomer with carboxyl groups, which permits noncovalent bonds such as hydrogen bonds or electrostatic interaction with imino groups. The maximal mechanical strength for matrix resins structured by UDMA and an acidic monomer was obtained with a composition of imino groups and carboxyl groups at a ratio of 1:1. This mechanical strength value was higher than those obtained with UDMA resin or with a Bis-GMA/TEGDMA/UDMA resin with typical composition. The improvement in mechanical properties may be due to the complex based on noncovalent bonds, between the imino groups of UDMA and the carboxyl groups of the acidic monomers.     

Development of new diacrylate monomers as substitutes for Bis-GMA and UDMA

ObjectiveBisphenol A-glycidyl methacrylate (Bis-GMA) and urethane dimethacrylate (UDMA) are widely used as the primary components of (meth)acrylic monomers. However, the use of Bis-GMA, which is a bisphenol A derivative, in dentistry is being questioned after bisphenol A was found to exhibit estrogenic activity. Although UDMA is being considered as a substitute for bis-GMA, the mechanical properties of cured resin composites containing UDMA are less than desirable. Therefore, in this study, we developed new alternative (meth)acrylic monomers to enhance the mechanical strength of cured composite resins.MethodsFive urethane acrylic monomers were synthesized in this study as (meth)acrylic monomer substituents to replace Bis-GMA and UDMA. The elastic modulus, strength, and breaking energy values of cured resins consisting of mixtures of the urethane acrylates and diluting monomers were determined using the three-point flexural test. The data obtained were analyzed using one-way ANOVA and the post-hoc Tukey HSD tests (p < 0.05). Viscosities of the urethane acrylic monomers were measured with a cone-plate viscometer. Refractive indices of the urethane acrylic monomers were determined with an Abbe refractometer.ResultsThe results of the three-point flexural tests revealed that the cured urethane acrylic monomer-based resin exhibited higher elastic modulus (up to 40%) and strength (up to 21%) compared to the cured UDMA-based resin. Viscosity and refractive index of the urethane acrylic monomers were between those of UDMA and Bis-GMA.SignificanceThe developed urethane diacrylates prepared from diisocyanates which have an aromatic or aliphatic ring, 1,3-bis(1-isocyanato-1-methylethyl)benzene (TMXDI), 1,3-bis(isocyanatomethyl)benzene (XDI), or norbornane diisocyanate (NBDI) are worth considering as alternative options of Bis-GMA and UDMA for restorative resin composites.     

Shear Bond Strength of Composite Veneers and Acrylic Veneer Bonded to Ni–Cr Alloy: A Laboratory Study

A growing number of composite materials are being used as an alternative for veneering cast restorations. The objective of this investigation was to evaluate and compare the shear bond strength of UDMA based composite, restorative composite, and heat cure acrylic when veneered to Ni–Cr alloy and to evaluate the type of bond failure. Three different veneering materials were used: heat cure acrylic, UDMA based composite and a restorative composite. 10 samples were fabricated, each with heat cure acrylic and restorative composite and 20 samples were fabricated with UDMA based composite; thus, the total number of samples amounted to 40. All the samples were subject to shear bond stress fracture tests and observed for the type of bond failure. The greatest mean shear bond strength was recorded in relation to the UDMA based composite material when thermal conducting paste was used during the curing (10.51 MPa). The mean bond strength values of UDMA based composite without thermal conducting paste (8.92 MPa), heat cured acrylic veneering material (4.24 MPa) and restorative composite material (5.03 MPa) were significantly different from each other (p > 0.05). Samples veneered with heat cure acrylic veneering material and restorative composite material showed adhesive failure. Samples prepared with UDMA based composite veneering composite showed cohesive or predominantly cohesive failure. UDMA based composite veneering material when used with heat protection paste exceeds the shear bond strength requirement as suggested by Matsumura et al. (>10 MPa). A statistically significant association between the test groups and the type of failure was observed.     

Curing potential of experimental resin composites filled with bioactive glass: A comparison between Bis-EMA and UDMA based resin systems

ObjectivesTo evaluate the degree of conversion, light transmittance, and depth of cure of two experimental light-curable bioactive glass (BG)-containing composite series based on different resin systems.MethodsExperimental composite series based on either Bis-EMA or UDMA resin were prepared. Each series contained 0, 5, 10, 20, and 40 wt% of BG 45S5. Reinforcing fillers were added up to a total filler load of 70 wt%. The degree of conversion was evaluated using Raman spectroscopy, while light transmittance was measured using visible light spectroscopy. The depth of cure was estimated from the degree of conversion data and using the ISO 4049 scraping test.ResultsReplacement of reinforcing fillers with BG can diminish the degree of conversion, light transmittance, and depth of cure. The effect of BG on the aforementioned properties was highly variable between the experimental series. While in the Bis-EMA series, the degree of conversion was significantly impaired by BG, all of the composites in the UDMA series attained clinically acceptable degree of conversion values. The reduction of the degree of conversion in the Bis-EMA series occurred independently of the changes in light transmittance. The UDMA series showed better light transmittance and consequently higher depth of cure than the Bis-EMA series. The depth of cure for all composites in the UDMA series was above 2 mm.SignificanceWhile the Bis-EMA series demonstrated clinically acceptable curing potential only for 0–10 wt% of BG loading, an excellent curing potential in the UDMA series was observed for a wide range (0–40 wt%) of BG loadings.     

The relationship between monomer composition and physical properties of light-cured opaque resin.

Light-cured opaque resins were prepared using four types of monomer liquids and titanium dioxide powder. This study investigated the relationship between the monomer composition and the physical properties of light-cured opaque resin. Depth of cure, KHN, residual monomer eluent, and bond strength between the opaque resin and cobalt-chromium alloy were measured. The physical properties of triethyleneglycol dimethacrylate (TEGDMA)-based compositions were superior to those of methyl methacrylate (MMA)-based compositions. Viscosity of the opaque resin's liquid monomer was enhanced by 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimeth ylhexane (UDMA). The TEGDMA-based light-cured opaque resins showed excellent physical properties and may be clinically acceptable in bonding prosthodontic composite to metal frameworks.     

The effect of comonomer composition, silane heating, and filler type on aqueous TEGDMA leachability in model resin composites

Experimental composites using either bisGMA/TEGDMA or UEDMA/ TEGDMA matrices, quartz or barium glass fillers, and 2 different filler silanization methods were evaluated regarding monomer leachability in distilled water. The leached amount was detected and quantified using gas chromatography. The results showed that twice as much TEGDMA is leached from a bisGMA/TEGDMA based composite than from an UEDMA/ TEGDMA based composite, when both contain 50 wt% TEGDMA. The hypothesis suggested that the higher degree of cure of UEDMA/TEGDMA based composites would be reflected in a lower monomer leaching value, and this hypothesis was supported by the findings. Whether such a correlation exists within groups of UEDMA/TEGDMA based matrices having different degrees of cure was not determined and needs to be investigated in future studies. Variables such as filler composition and silane treatment did not affect the leaching values of TEGDMA in water. That finding suggests that future studies should target differences in matrices, and that the need for considering effects of filler composition and silane treatment methods should not receive the same priority.     

Aging studies of light cured dimethacrylate-based dental resins and a resin composite in water or ethanol/water.

OBJECTIVE: To study the aging of neat resins, prepared from bis-GMA, UDMA, D(3)MA or a mixture of bis-GMA/UDMA/D(3)MA (65/20/15 w/w/w), in water or 75% (v/v) ethanol/water 37 degrees C. Also the study of aging of Heliomolar RO, which is a radiopaque, microfilled, light cured composite, the resin matrix of which is the copolymer of bis-GMA/UDMA/D(3)MA (65/20/15 w/w/w). METHODS: Samples of neat resins and Heliomolar RO prepared by light curing were immersed in water or 75% (v/v) ethanol/water 37 degrees C, for 1, 7 or 30 days. Then the flexural and tensile strength were determined. The fractured surface of samples after the flexural tests was observed by scanning electron microscopy. RESULTS: Bis-GMA and copolymer resin did not showed any significant change in mechanical properties after immersion in water or 75% (v/v) ethanol/water 37 degrees C, for 30 days. On the contrary UDMA, D(3)MA and the composite Heliomolar RO showed a significant decrease. SIGNIFICANCE: The results obtained showed that the effect of aging in water or ethanol/water solution on mechanical properties of a light cured dimethacrylate resin depends on the chemical structure of resin. In the case of resin composite this effect depends on the filler-matrix bond strength.     

Effect of monomer structure on the mechanical properties of light-cured composite resins

The effects of monomer structure on the mechanical properties of visible light-cured composite resins based on the seven types of aromatic dimethacrylates were investigated. The results of this study suggested that the mechanical properties of the composite resins were dependent upon the chemical structure of the dimethacrylate monomers employed. The composites based on dimethacrylates with hydroxy groups showed a relatively significant decrease in flexural strength, elastic modulus, and compressive proportional limit under wet conditions. The segmental mobility of dimethacrylate monomers considerably influenced the nature of cured composites. Bis-GMA-F-based composite showed superior mechanical properties to a conventional Bis-GMA-based material. The SEM observation of fractured surfaces revealed that failure mainly occurred through the resin matrix of the composite resins.     

Bending strength and depth of cure of light-cured composite resins irradiated using filters that simulate enamel

This study evaluates the light-attenuating effects of enamel on the properties of light-cured restorative resins using simple experimental filters. Three filters were designed to replicate the light transmittance characteristics of 0.5, 1.0 and 1.5 mm thick human enamel. The bending strength, depth of cure, and levels of residual monomer for 12 shades of three commercial light-cured composite resins were examined. These resins were cured either using direct irradiation from a light source or irradiation through one of the filters. For all materials, the bending strength and depth of cure of specimens irradiated through a filter were lower and the levels of residual monomer were higher than those found in specimens irradiated directly. The results indicate that the light-attenuating effect of enamel reduces the polymerization efficiency, resulting in poorer mechanical properties of light-cured composite resins.     

Physical properties of two new crown and bridge veneering resins

The degree of conversion and physical properties of two contemporary resin veneers based on light-cured microfilled composite formulations and employing proprietary curing systems were evaluated. Visio-gem (V) and Dentacolor (D) were polymerized using the appropriate curing systems. Polymer structure and degree of conversion were determined by Fourier transform infra-red (FTIR) techniques. Physical properties, including depth of cure, compressive and diametral tensile strengths, hardness, thermal expansion and colour stability were determined by standard test modalities. Both materials appear to have the properties of typical microfilled resins including low compressive yield strengths and high thermal expansion coefficients. The curing system for V produced an increased depth of cure compared to conventional light curing techniques and the D system, but no clinically significant increase in the physical properties.     

Cure behaviour of visible light-activated pattern materials

AIM: This study tested the hypothesis that the cure behaviour (depth of cure and polymerization contraction) of light-activated pattern materials was no worse than that of light-activated composite resins, allowing them to be handled in a similar fashion. METHODOLOGY: Depth of cure was measured by a penetrometer method. RESULTS: Cure depths were comparable to those of composite resins, ranging from 3.52 mm (Lumin-X paste) to 6.76 mm (Visioform) after visible light activation for 30 s. There were significant differences in the depth of cure of the three materials tested (P < 0.001). Polymerization contraction was assessed by a minimal load transducer method. Values ranged from 0.45% (Lumin-X paste) to 1.89% (Visioform), lower than that of composite resins. There were significant differences in the polymerization contraction values for each of the three materials (P < 0.001). CONCLUSIONS: It was concluded that light-activated pattern materials cure in a manner comparable to composite resins, and may be built up incrementally in a similar fashion.     

Effect of resin monomer composition on toothbrush wear resistance

The purpose of this study was to compare the toothbrush abrasion resistance of seven different experimental resins which were made by changing the composition of resin monomers. The experimental resins were made by mixing four kinds of dental resin monomers (Bis‐GMA, UDMA, TMPT and TEGDMA), camphorquinone (1 wt%), dimethylaminoethyl methacrylate (2 wt%) and 2,6‐di‐ tert ‐butyl‐ p ‐cresol (0·05 wt%). The resin specimens were stored in air for 2 weeks, and then put on a toothbrush abrasion testing machine. After 100 000 strokes, the wear loss of each specimen was determined by weight change during the wear test. TMPT‐TEGDMA resin showed the most wear resistance, while Bis‐GMA‐ and UDMA‐based resins showed increased wear resistance with an increased content of TEGDMA. Also, a inverse relationship between the microhardness number and the amount of wear of the respective resins was confirmed.     

Photobleaching of camphorquinone during polymerization of dimethacrylate-based resins

ObjectiveThe aim of this study was to compare the photobleaching rate of CQ in different dental resins.MethodsThe photodecomposition rate of CQ/amine system in bis-GMA/TEGDMA, bis-EMA and UDMA polymerizing monomers was evaluated at different light intensities. The photobleaching of the CQ was studied by monitoring the decrease in light absorption as a function of continuous irradiation time. The absorption changes were assessed by recording the transmitted light that passed through samples of monomers containing CQ/amine.ResultsComplete photobleaching of CQ was observed in all the monomer tested and the rate constant for the photobleaching was proportional to the radiation intensity. Hydrogen abstraction from amines by the excited CQ state via electron transfer and direct hydrogen abstraction from monomer structures were involved in the CQ photoreduction. CQ was photobleached in the absence of coinitiator in a dimethacrylate monomer containing a carbamate functional group (UDMA). This behavior was attributed to the presence of labile hydrogen atoms in the UDMA monomer. The CQ photobleaching rate constant in UDMA containing CQ/amine was similar to that in UDMA in the absence of amine. Moreover, the efficiency of CQ to photoinitiate the polymerization of UDMA in the absence of amine demonstrated that the radicals derived from the UDMA monomer via hydrogen abstraction are highly reactive toward double bonds.SignificanceCQ photoinitiates the polymerization of the UDMA monomer in the absence of amine and the efficiency of this process is comparable to that of traditional bis-GMA and bis-EMA monomers activated with CQ/amine.     

Time-dependent deformation of composite resins--compositional considerations

The compressive yield strength and creep of 21 dental composite resins were evaluated and correlated with filler volume percent and extent of cure in the resin. In general, yield and creep of composites were more dependent upon filler volume fraction than on extent of cure. However, the types of monomers and fillers used in the composite formulation appeared to play a major role in determining the compressive characteristics of the materials.