Evaluation of dental restorative composites containing polyhedral oligomeric silsesquioxane methacrylate.

OBJECTIVES: The aim of this study was to explore novel polymeric dental restorative composites, in which polyhedral oligomeric silsesquioxane methacrylate monomer (POSS-MA) was used to partially (or completely) replace the commonly used base monomer 2,2'-bis-[4-(methacryloxypropoxy)-phenyl]-propane (Bis-GMA). METHODS: The composites were cured (hardened) by photo-initiated free radical polymerization. Mechanical properties (i.e. flexural strength, Young's modulus and diametral tensile strength) of the composites were tested by a universal mechanical testing machine; photopolymerization induced volumetric shrinkage was measured using a mercury dilatometer; and near infrared (NIR) technique was used to study the degree of methacrylate double bond conversion and photopolymerization rate. RESULTS: Small percentage POSS-MA substitution of Bis-GMA (i.e. mass fraction of 10% or less) in the resin system improved the mechanical properties of the composites; while large amount substitution led to less desirable mechanical properties, lower methacrylate double bond conversion, and slower photopolymerization rate. Statistical examinations showed the maximum flexural strength of the composites occurred when 10% (mass fraction) of Bis-GMA was replaced by POSS-MA, while the highest modulus occurred when the mass fraction of POSS-MA was 2%. SIGNIFICANCE: Polymeric dental restorative composites with improved mechanical properties may be designed by judicious choice of monomer (POSS-MA, Bis-GMA and TEGDMA) compositions.     

螺环原酸酯对牙科基体树脂的改性研究

目的：用螺环原酸酯膨胀单体对牙科BisS-GMA基体树脂进行改性的研究。方法：分别以BisS-GMA和Bis-GMA作树脂基质,TEGDMA为稀释单体,加入和不加入螺环原酸酯膨胀单体,配制四种基体树脂。以CQ/DMAEMA为光引发体系,光固化后测定并比较其体积收缩率、聚合转化率、粘接拉伸强度和固化时间。结果：含膨胀单体的BisS-GMA基体树脂的体积收缩率较低,聚合转化率和粘接拉伸强度较高,且固化时间合适。结论：螺环原酸酯膨胀单体的开环聚合反应能使BisS-GMA基体树脂的体积收缩率显著降低,并能提高其聚合转化率和粘接拉伸强度。     

Investigations of step-growth thiol-ene polymerizations for novel dental restoratives

OBJECTIVES: The goal of this work was to investigate the feasibility of formulating novel dental restorative materials that utilize a step-growth thiol-ene photopolymerization. Particularly, we are aiming to significantly reduce the polymerization shrinkage and shrinkage stress while retaining adequate physical properties as compared to current dimethacrylatre-based systems. METHODS: The thiol-ene system is composed of a 4:3 molar mixture of triallyl-1,3,5-triazine-2,4,6-trione (TATATO) and pentaerythritol tetramercaptopropionate (PETMP). The simultaneous measurement of shrinkage stress and functional group conversion was performed. Solvent extraction of unreacted monomers and dynamic mechanical analysis on the polymer networks that were formed were also studied. Flexural strength was measured for both filled and unfilled PETMP/TATATO and Bis-GMA/TEGDMA systems. RESULTS: Photopolymerization of PETMP/TATATO occurs at a much higher rate, with the maximum polymerization rate six times faster, than Bis-GMA/TEGDMA cured under the identical conditions. The results from the simultaneous measurement of shrinkage stress and conversion showed that the onset of shrinkage stress coincides with the delayed gel point conversion, which is predicted to be 41% for the 3:4 stoichiometric PETMP/TATATO resin composition. The maximum shrinkage stress developed for PETMP/TATATO was about 0.4 MPa, which was only approximately 14% of the maximum shrinkage stress of the Bis-GMA/TEGDMA system. Adequate flexural strength and flexural modulus values were obtained for both filled and unfilled PETMP/TATATO systems. SIGNIFICANCE: The dramatically reduced shrinkage stress, increased polymerization rate, significance increased functional group conversion, and decreased leachable species are all benefits for the use-of thiol-ene systems as potential dental restorative materials.     

Dimethacrylate based on cycloaliphatic epoxide for dental composite.

OBJECTIVES: The aim of this study was to investigate the kinetics and mechanical properties of dimethacrylate monomer based on cycloaliphatic epoxide for dental restorative composite. METHODS: Dimethacrylate based on cycloaliphatic epoxide (EPCDMA) was copolymeirzed with TEGDMA by varying the curing conditions: monomer composition and light intensity. A real-time near FTIR technique was employed to monitor the double bond conversion and the rate of polymerization. Dynamic mechanical analysis was performed on a dynamic mechanical analyzer, and volume shrinkage of the cured samples was determined by pycnometric method. RESULTS: The results of kinetics showed that, two peaks of maximum rate of polymerization (Rpmax) occurred when the amount of TEGDMA was more than 30wt%. Increasing the amount of TEGDMA, the final double bond conversion and polymerization shrinkage both increased, while the glass transition temperature (Tg) decreased. All EPCDMA/TEGDMA mixtures had slightly higher storage modulus at body temperature (37 degrees C). When compared with Bis-GMA/TEGDMA (70/30), the EPCDMA/TEGDMA (70/30) system assumed similar reactivity and volume shrinkage but higher Tg. SIGNIFICANCE: EPCDMA had comparable mechanical properties to those of Bis-GMA.     

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.     

Physicochemical properties of dental resins formulated with amine-free photoinitiation systems

ObjectiveTo assess the mechanical properties of two different dimethacrylate resin blends containing the photosensitizer camphorquinone (CQ) alone or in combination with one or more synergists including an amine and/or an iodonium.MethodsTwo co-monomer resin blends were formulated using Bis-GMA/TEGDMA and UDMA/TEGDMA, both at 1:1 mass ratio. Each resin blend was divided into four groups, comprising the following four photoinitiation systems: (1) CQ + 2-(dimethylamino)ethyl methacrylate (DMAEMA); (2) CQ + DMAEMA + bis(4-methyl phenyl)iodonium hexafluorophosphate (BPI); (3) CQ; and (4) CQ + BPI. Materials were evaluated for polymerisation kinetics, water sorption, solubility, flexural strength and modulus.ResultsBisGMA/TEGDMA with CQ showed minimal and insignificant degree of conversion and was not tested for water sorption/solubility and mechanical properties. The ternary system (i.e., CQ + DMAEMA + BPI), promoted the highest degree of conversion for each monomer blend. The resins containing amine had higher mechanical properties than the amine free. However, the UDMA amine free resins exhibited greater flexural strength and modulus than the corresponding amine free BisGMA resins. BisGMA/TEGDMA containing CQ + DMAEMA or CQ + BPI had significantly higher water sorption and solubility than the other groups.SignificanceResins containing amine presented better properties than the amine-free systems. The addition of iodonium salt (BPI) improved the degree of conversion of the resins, even without an amine co-initiator. The amine-free initiator system (CQ + BPI) was more effective when used with UDMA versus BisGMA based-resins respectively.     

Influence of polymerization initiator for base monomer on microwave curing of composite resin inlays

Microwave polymerization was used to make composite resin inlays and the effect examined of the concentration of polymerization initiator for the base monomer. The monomers used were 2,2-bis [4-(3-methacriloxy-2-hydroxypropoxy) phenyl] propane (Bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA). Bis-GMA and TEGDMA were mixed in a ratio of 6:4 by weight and were separated into five groups. To each group was added benzoyl peroxide (BPO) in the ratios of 0.1, 0.3, 0.5, 0.7 and 0.9 wt% as the polymerization initiator. These were used as the base monomers. The results showed that the degree of conversion of the cured sample increased with increasing concentration of BPO from 0.1 to 0.5 wt%, however there was no significant difference at 0.5, 0.7 and 0.9 wt% (P> 0.01). Compression strength, diametral tensile strength and the Knoop hardness showed a similar tendency as the degree of conversion. No significant difference was recorded in the Knoop hardness between the top and the bottom surfaces (P> 0.01), which suggested a uniform polymerization in the cured sample. Thus, microwave polymerization would be an efficacious method for making resin inlays with the addition of BPO to the base monomer (Bis-GMA:TEGDMA, 6:4). The maximum conversion was found at a concentration of 0.5 wt%.     

The effect of resin matrix composition on the polymerization shrinkage and rheological properties of experimental dental composites.

OBJECTIVES: This study was undertaken to evaluate the effect of the resin matrix composition of experimental composites on their polymerization shrinkage and rheological properties. METHODS: Six experimental composites consisting of varying ratios of Bis-GMA, TEGDMA, and UDMA were made. All composites had the same amount of filler (barium-aluminum-silicate glass, 76.5 wt.%) and initiator concentrations (camphorquinone, 1.7 wt.%). To investigate the effects of different resin matrices on the polymerization shrinkage, a newly developed measurement method was used. Using a rotational rheometer, a dynamic oscillatory shear test was undertaken to evaluate the rheological properties, including the storage shear modulus (G'), loss shear modulus (G'), loss tangent (tandelta), phase angle (delta), and complex viscosity (eta*) of the experimental composites as a function of frequency (0.1-10Hz). RESULTS: The polymerization shrinkage and complex viscosity of the experimental composites ranged from 2.61 to 3.88 vol.% and from 3.8 to 181.4Pas, respectively. The experimental composite composed of 17.5% Bis-GMA and 4.4% TEGDMA showed the lowest shrinkage and highest viscosity. The composite composed of 8.7% Bis-GMA and 13.1% TEGDMA showed the highest shrinkage and lowest viscosity. With increasing TEGDMA content, the polymerization shrinkage increased but the viscosity decreased. The substitution of UDMA for TEGDMA reduced the shrinkage level but increased viscosity. There was an inverse relationship between the polymerization shrinkage and complex viscosity. All experimental composites exhibited pseudoplasticity. SIGNIFICANCE: Within the limitations of this study, resin matrix composition significantly affected the volumetric shrinkage and rheological properties of the experimental composites.     

Synthesis and characterization of acetyloxypropylene dimethacrylate as a new dental monomer

Objective

In this study acetyloxypropylene dimethacrylate was synthesized and proposed as an alternative monomer for triethyleneglycol dimethacrylate (TEGDMA) in dental mixtures.

Methods

The monomer was prepared by the reaction of glycerol dimethacrylate with acetic anhydride. The exchange reaction was carried out in the presence of catalytic amounts of sulfuric acid. After purification the monomer was mixed with 2,2-dimethoxy-2-phenyloacetophenone and photo-irradiated. Unfilled homopolymer was evaluated for photopolymerization conversion and volumetric curing shrinkage. Water sorption, water solubility, flexural strength and hardness were measured. Also, dynamic mechanical studies were performed. For comparison TEGDMA was homopolymerized and its properties were evaluated.

Results

The proposed dimethacrylate has viscosity comparable to TEGDMA, lower curing shrinkage and lower degree of double bond conversion. After homopolymerization, its water sorption is much lower than that of homopolymerized TEGDMA. Concerning the mechanical properties, the homopolymerized acetyloxypropylene dimethacrylate has higher modulus and hardness than analogically cured TEGDMA.

Significance

New dimethacrylate is a promising photocurable dental diluent owing to its low viscosity, good mechanical and water uptake properties.     

Volume contraction in photocured dental resins: the shrinkage-conversion relationship revisited.

Polymerization shrinkage and degree of conversion (DC) of resin composites are closely related manifestations of the same process. Ideal dental composite would show an optimal degree of conversion and minimal polymerization shrinkage. These seem to be antagonistic goals, as increased monomer conversion invariably leads to high polymerization shrinkage values. OBJECTIVES: This paper aims at accurately determining the polymerization volume contraction of experimental neat resins and to link it to the number of actual vinyl double bonds converted in single ones instead of, as generally done, to the degree of conversion. METHODS: Different mixtures of Bis-GMA/TEGDMA (traditionally used monomers) were analyzed. Contraction of the polymers was determined by pycnometry and the use of a density column. DC was determined by the use of Raman spectrometry. RESULTS: An univocal relationship has been found between the volume contraction and the actual number of vinyl double bonds converted into single ones. A contraction value of 20.39 cm3/mole (of converted C=C) was deduced from 27 measurements. SIGNIFICANCE: This relationship helps in finding solutions to the polymerization shrinkage problem. A reduction of the polymerization shrinkage due to the chemical reaction may obviously be expected from the addition of molecules allowing a decrease in the number of double bonds converted per unit volume of resin matrix, while maintaining the degree of conversion (of Bis-GMA and TEGDMA) and thus the mechanical properties. Further research will be directed at this objective.     

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.     

Evaluation of methylene lactone monomers in dental resins.

alpha-Methylene-gamma-butyrolactone (MBL), which can be described as the cyclic analog of methyl methacrylate, exhibits greater reactivity in free radical polymerizations than conventional methacrylate monomers. Unfilled resin formulations composed of Bis-GMA/MBL or Bis-GMA/TEGDMA/MBL were light-cured. The effect of the more reactive methylene lactone monomer on mechanical properties and the degree of conversion of the polymers was examined. The infrared absorption bands for the carbon-carbon double bonds of MBL and the methacrylate monomers are well resolved and allow the conversion of each component to be calculated individually. The incorporation of a small amount of MBL (5 w/o) to Bis-GMA significantly increased the conversion; however, additional MBL (10 to 30 w/o) did not further increase the Bis-GMA conversion level. This appears to indicate an incompatibility between MBL and the bulky Bis-GMA monomer. Addition of 10 w/o MBL to Bis-GMA/TEGDMA (7:3) resulted in a cured resin with 71% methacrylate and 75% overall conversion efficiencies compared with the 57% conversion of the control formulation. The diametral tensile and the transverse strengths were approximately 10% greater for the MBL resin compared with the Bis-GMA/TEGDMA control; however, these differences were not statistically significant. The synthesis and polymerization of several substituted methylene lactones was also studied.     

Characterization of urethane-dimethacrylate derivatives as alternative monomers for the restorative composite matrix

ObjectiveThe aim was accomplished by a comparative analysis of the physicochemical properties of urethane-dimethacrylate (UDMA) monomers and their homopolymers with regard to the properties of basic dimethacrylates used presently in dentistry. The homologous series of UDMA were obtained from four oligoethylene glycols monomethacrylates (HEMA, DEGMMA, TEGMMA and TTEGMMA) and six diisocyanates (HMDI, TMDI, IPDI, CHMDI, TDI and MDI).MethodsPhotopolymerization was light-initiated with the camphorquinone/tertiary amine system. Monomers were tested for viscosity and density. Flexural strength, flexural modulus, hardness, water sorption and polymerization shrinkage of the polymers were studied. The glass transition temperature and the degree of conversion were also discussed.ResultsHEMA/IPDI appeared to be the most promising alternative monomer. The monomer exhibited a lower viscosity and achieved higher degree of conversion, the polymer had lower water sorption as well as higher modulus, glass temperature and hardness than Bis-GMA. The polymer of DEGMMA/CHMDI exhibited lower polymerization shrinkage, lower water sorption and higher hardness, however it exhibited lower modulus when compared to HEMA/TMDI. The remaining monomers obtained from HEMA were solids. Monomers with longer TEGMMA and TTEGMMA units polymerized to rubbery networks with high water sorption. The viscosity of all studied UDMA monomers was too high to be used as reactive diluents.SignificanceThe systematic, comparative analysis of the homologous UDMA monomers and corresponding homopolymers along with their physico-mechanical properties are essential for optimizing the design process of new components desirable in dental formulations. Some of the studied UDMA monomers may be simple and effective alternative dimethacrylate comonomers.     

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.     

Structure–property relationships in dimethacrylate networks based on Bis-GMA,UDMA and TEGDMA

ObjectivesIn this work the influence of structural heterogeneity of poly(dimethacrylate)s on mechanical properties was investigated. Rigid aromatic dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA) and flexible aliphatic urethane dimethacrylate (UDMA) have been chosen for room-temperature homopolymerizations and copolymerizations induced by a camphorquinone/N,N-dimethylaminoethyl methacrylate photoinitiating system.MethodsThe following mechanical properties of poly(dimethacrylate)s were investigated: flexural modulus, flexural strength, impact strength and hardness. Atomic force microscopy (AFM) and X-ray powder diffraction (XRPD) were used to describe the morphology of polymer networks.ResultsAFM observations showed that the heterogeneity of networks is spatially organized due to the formation of microgels and their agglomeration. Observed agglomerates are unidirectionally oriented, parallel to the direction of polymerization shrinkage. Of all the investigated mechanical properties of poly(dimethacrylate)s, the impact resistance appeared to be the least. The origin of this brittleness could be the presence of heterogeneities which were quantitatively characterized by means of XRPD. The impact resistance was shown to be related to the size of network heterogeneities which is probably influenced by intermolecular interactions, such as hydrogen bonding.SignificanceDifferences in monomer structure resulted in significantly different morphology and physical properties of the polymer networks which had been studied. The size and shape of heterogeneities affected the final mechanical properties of the polymers, especially impact resistance. In addition, the combined application of XRPD and AFM techniques can be a successful tool in the analysis of the dimethacrylate network morphology, and finally, in investigations on methacrylate-based dental materials.     

Durability of commercial composite resin. Chronological change in transverse strength and transverse elastic modulus of composite resin immersed in MeOH

The durability of visible light-cured composite resin was examined. Five kinds of commercial redox type composite resin and 7 kinds of visible light-cured composite resin were used and their base monomers were analyzed by HPLC. After the set products were immersed in MeOH, transverse strength and transverse elastic modulus were measured. Furthermore, the MeOH sorption, solubility in MeOH and main soluble component were examined. The main component of the base monomer in all 5 kinds of redox type was Bis-GMA. Seven kinds of visible light-cured composite resin consisted of 4 kinds of Bis-GMA (including BMPEPP) and 3 kinds of UDMA. Both cases of redox type and visible light-cured type of composite resin, when they were immersed in MeOH, transverse strength and transverse elastic modulus decreased. In the case of redox type (Clearfil posterior new bond), the decrease of transverse strength and transverse elastic modulus was small, that is, its base monomer was Bis-GMA, and large quantities of hybrid type filler were mixed. In the case of redox type, transverse strength and transverse elastic modulus showed a tendency to decrease with the increase of MeOH sorption. Solubility of 12 kinds of these composite resins was 0.25-4.78% and its main component in Pyrofil light bond A was BMPEPP, the residual were coincident with the main component of base monomer.     

The effect of light intensity on double bond conversion and flexural strength of a model, unfilled dental resin.

OBJECTIVE: Two visible light sources (tungsten-quartz-halogen and xenon-arc plasma) with vastly different intensities (200 and 1800 mW/cm(2)) but similar spectral outputs, were used to examine the effects of light intensity on conversion and flexural strength of a model dental resin formulation (75/25wt% bis-GMA/TEGDMA). METHODS: The exact same polymer samples were used to correlate double bond conversion (measured with near-IR spectroscopy) to flexural strength, both immediately after light exposure and after storage. RESULTS: In general, polymers which were irradiated with the high light intensity source exhibited greater double bond conversion. However, increasing the light intensity also increased the maximum temperature reached during polymerization. Therefore, the greater double bond conversion was caused by a combination of both photo and thermal effects. Regardless of the light intensity, a single linear relationship existed between conversion and final flexural strength (measured 4 days after cure) over the conversion range analyzed (50-80%). However, deviations from linearity were noted in several samples that were tested immediately after exposure. SIGNIFICANCE: These findings illustrate that light intensity does not affect the final flexural strength of a dental resin as long as the final conversions are similar.     

Monomer permeability of disposable dental gloves

STATEMENT OF PROBLEM: Studies have suggested that monomers may be able to permeate dental gloves. PURPOSE: This study examined the permeability of disposable dental gloves to 6 kinds of dental monomers. MATERIAL AND METHODS: The permeability of 6 kinds of dental monomers (methyl methacrylate [MMA], 2-hydroxyethyl methacrylate [HEMA], triethyleneglycol methacrylate [TEGDMA], ethyleneglycol dimethacrylate [EGDMA], urethane dimethacrylate [UDMA], and Bis-glycidyl methacrylate [Bis-GMA]) through 5 kinds of dental gloves (latex, powder-free latex, coated latex, polychloroprene, and polyvinyl chloride) was examined for up to 180 minutes at 37 degrees C. The fingers of unused gloves without pin holes were cut and used in the experiments. Five specimens per test group were examined. One type of monomer was poured into each finger and dipped in ethanol. The ethanol for extraction was measured by a spectrophotometer at a wavelength of 210 nm, and the results were analyzed by analysis of variance and the Kruskal-Wallis test (P<.05). RESULTS: Four of the monomers tested (MMA, HEMA, TEGDMA, and EGDMA) permeated the gloves tested, whereas 2 (UDMA and Bis-GMA) did not (P>.01). The amount of monomers permeating the latex in 10 minutes was 0.8 +/- 0.6, 0.6 +/- 0.6, 0.07 +/- 0.1, 0.07 +/- 0.1, 0.1 +/- 0.1 and 0.06 +/- 0.1 microL/mL for MMA, HEMA, EGDMA, TEGDMA, UDMA, and Bis-GMA, respectively. The amount of permeated monomer was then increased in relation to the examination time, and in MMA and HEMA, permeation occurred rapidly during the initial 60 minutes at 3 times the 10-minute values, then continued gradually and linearly. The polyvinyl chloride glove showed the greatest monomer permeability. Two-way analysis of variance showed significant correlations between MMA, HEMA, EGDMA or TEGDMA and UDMA or Bis-GMA (P<.01). Statistical significance was shown between polyvinyl chloride and latex, powder-free latex, coated latex or polychloroprene (P<.01). However, there was no significant relation between any kind of dental monomer and any kind of dental glove. CONCLUSION: Within the limitations of this study, 4 of the monomers tested permeated all of the gloves tested.     

Synthesis, characterization and evaluation of urethane derivatives of Bis-GMA.

OBJECTIVES: The aims of the study were to synthesize derivatives of Bis-GMA having pendant n-alkyl urethane substituents and to characterize and evaluate their physicochemical properties. METHODS: Stoichiometric amounts of Bis-GMA and n-alkyl isocyanates were reacted in dichloromethane with dibutyltin dilaurate as a catalyst. Volumetric shrinkage, water uptake, degree of vinyl conversion, refractive index and viscosity of resulting urethane monomers and those of Bis-GMA were measured. The flexural strengths of their corresponding homopolymers and that of Bis-GMA were also measured. RESULTS: These types of urethane derivatives of Bis-GMA exhibited lower viscosities and were more hydrophobic than Bis-GMA. Generally, the viscosity of these experimental monomers decreased with increasing chain length of the alkyl urethane substituent. Photopolymerization of the new monomers gave high degrees of vinyl conversion compared to Bis-GMA. The experimental monomers also yielded polymers with lower polymerization shrinkages at equivalent degrees of vinyl conversion, than Bis-GMA. The refractive indices of these urethane derivatives were similar to Bis-GMA, but the flexural strengths of their polymers were lower than that of the Bis-GMA homopolymer, decreasing with increasing chain length of the alkyl urethane substituent. SIGNIFICANCE: Because of their excellent overall properties, these new derivatives of Bis-GMA have potential as dental monomers that can improve many properties of resin based dental materials that utilize methacrylate monomer systems.     

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.