Influence of resin matrix on the rheology,translucency, and curing potential of experimental flowable composites for bulk-fill applications

ObjectiveTo propose monomer formulations that show an optimal degree of conversion as a function of depth for bulk-fill applications.MethodsFour resin blends were formulated with methacrylate-based monomers: BisGMA + TEGDMA (control); BisEMA + BisGMA + TEGDMA (BisEMA-based); UDMA + BisGMA + TEGDMA (UDMA-based) and BisEMA + UDMA + BisGMA + TEGDMA (BisEMA + UDMA-based). For each material, a photoinitiating system and silanized filler particles were added. The rheological analyses were performed with a rotational rheometer using the cone/plate geometry. CIELab coordinates were assessed over black and white backgrounds using a bench spectrophotometer (SP60, X-Rite) to calculate the translucency parameter (TP) for samples with 0.5, 4, and 6 mm thickness. The degree of CC conversion (DC) was determined by infrared spectroscopy (FTIR/ATR) at 0.05 mm (top), 4, and 6 mm depths (bottom), and the bottom-to-top ratio was considered. A broad spectrum–based LED was used for light activation. Analysis of variance and Tukey’s test (95%) were performed on the results.ResultsThe materials tested showed pseudoplastic and thixotropic behavior and a predominance of viscous effects over elastics. The control resin yielded the lowest viscosity for the entire shear rate investigated, followed by the BisEMA-based, BisEMA + UDMA-based, and UDMA-based group, which had the highest viscosity. The UDMA-based material showed the lowest TP as a function of thickness. Both the materials’ formulations and depths significantly influenced the DC. The UDMA-based group promoted the highest DC ??on the top (71 ± 1%) and 4 mm depth (68 ± 1%) but exhibited lower bottom-to-top DC ratio. The BisEMA + UDMA-based material promoted the highest bottom-to-top DC ratio at 4 mm (99%) and 6 mm (97%).SignificanceThe resin matrix interferes in the rheological behavior, translucency parameter, and polymerization capacity as a function of depth. The material formulated with the addition of UDMA and BisEMA demonstrated the highest curing potential as a function of depth and can be useful for bulk-fill applications.     

Influence of successive light-activation on degree of conversion and knoop hardness of the first layered composite increment

Abstract

Purpose: To evaluate the influence of light-activation of second, third and fourth increments on degree of conversion (DC) and microhardness (KHN) of the top (T) and bottom (B) surface of the first increment. Materials and methods. Forty samples (n = 5) were prepared. In groups 1–4, after each increment light-activation (multiple irradiation), T and B of the first increment were measured in DC and KHN. In groups 5–8, only the first increment was made (single irradiation) and measurements of DC and KHN were taken at 15 min intervals. The light-activation modes were (XL) 500 mW/cm² × 38 s (G1/G5); (S) 1000 mW/cm² × 19 s (G2/G6), (HP) 1400 mW/cm² × 14 s (G3/G7); (PE) 3200 mW/cm² × 6 s (G4/G8). Data for DC and KHN were analyzed separately by using PROC MIXED for repeated measures and Tukey-Kramer test (α = 0.05). Results. For KHN, B showed lower values than T. PE resulted in lower values of KHN in B surface. For single and multiple irradiations, T and B of first measurement showed the lowest KHN and the fourth measurement showed the highest, with significant difference between them. For single irradiation, first and second increments presented similar KHN, different from the third and fourth increment, which did not differ between them. For multiple irradiations, the second light-activation resulted in KHN similar to first, third and fourth increments. For DC, except QTH, T presented higher DC than B. Conclusion. The light-activation of successive increments was not able to influence the KHN and DC of the first increment.     

Material properties and bioactivity of a resin infiltrant functionalized with polyhedral oligomeric silsesquioxanes

ObjectivesTo investigate the effect of methacrylate polyhedral oligomeric silsesquioxanes (POSS-8) on various material properties and mineral precipitation potential of a resin infiltrant.MethodsA TEGDMA-based resin infiltrant was mixed with 0.5, 1, 3, 5 or 10 wt% POSS-8 or left unchanged (control). Degree of conversion (DC), water sorption (WS), viscosity, elastic modulus (E-modulus), flexural strength (FS), Knoop microhardness (KHN) and softening ratio (SR) were assessed. Growth of calcium phosphate (Ca/P) precipitates infiltrant-treated bovine enamel and dentin specimens immersed in artificial saliva or artificial dentinal fluid, respectively, for 28 days was analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. For viscosity assessment, pure TEGDMA filled with 0–10 wt% POSS-8 was used. Statistical analyses were performed using ANOVA and Tukey's post-hoc tests (p < 0.05).ResultsPOSS-8 did not change the flexural strength, water sorption and softening ratio. The apparent degree of conversion was increased at lower concentrations only while E-modulus remained constant in almost all groups. The particles led to a slight decrease of KHN at concentrations below 3%. The effect on viscosity is comparable to the reinforcement effect. Ca/P precipitates formed on dentin specimens treated with POSS-8-filled infiltrant after 4 weeks of immersion, but were not detected on the control infiltrant. The mineral precipitation on enamel was not improved by POSS-8.SignificancePOSS-8 particles did not worsen the material properties of the resin infiltrant, while the Ca/P precipitation on dentin was stimulated.     

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 chlorhexidine on the degree of conversion and E-modulus of experimental adhesive blends

ObjectivesThis study examined the effect of chlorhexidine (CHX) content on degree of conversion (DC) and E-modulus of experimental adhesive blends. The hypothesis tested was that increasing concentrations of CHX result in decreased DC and E-modulus in relation to adhesive hydrophilicity.MethodsExperimental adhesive blends with increasing hydrophilicity R2 (70% bisGMA, 28.75% TEGDMA); R3 (70% BisGMA, 28.75% HEMA); R4 (40% BisGMA, 30% TCDM, 28.75% TEGDMA); R5 (40% BisGMA, 30% BisMP, 28.75% HEMA) and different CHX concentrations (1 and 5%) were analyzed. 5% CHX could not be dissolved in R2. A differential scanning calorimeter was used to measure the DC of resin blends. Photopolymerized disks of the experimental comonomer mixtures (n = 10/gp) were used to measure the E-modulus of each specimen using a biaxial flexure test. Data were analyzed with two-way ANOVA (resin type and CHX concentration) and Tukey's post hoc test.ResultsThe addition of 1% CHX did not significantly alter the DC of R2 and R3. Significant decrease in R3 DC values was observed when 5% CHX was added. CHX significantly increased the DC of R4 and R5. 1% CHX reduced the E-modulus of all resins (p < 0.05) except for R2, in which the E-modulus was significantly increased (p < 0.05). 5% CHX significantly reduced the E-modulus of resins R3 to R5 (p < 0.05).SignificanceIn conclusion, increasing concentrations of CHX dissolved in resin blends had little adverse effect on DC but decreased the E-modulus 27–48% compared to controls. Solvation of CHX in ethanol prior to incorporation of CHX into R2 may permit higher CHX concentrations without lower polymer stiffness.     

Influence of BisGMA, TEGDMA, and BisEMA contents on viscosity, conversion, and flexural strength of experimental resins and composites

Different monomer structures lead to different physical and mechanical properties for both the monomers and the polymers. The objective of this study was to determine the influence of the bisphenylglycidyl dimethacrylate (BisGMA) concentration (33, 50 or 66 mol%) and the co-monomer content [triethylene glycol dimethacrylate (TEGDMA), ethoxylated bisphenol-A dimethacrylate (BisEMA), or both in equal parts] on viscosity (η), degree of conversion (DC), and flexural strength (FS). η was measured using a viscometer, DC was obtained by Fourier transfer Raman (FT-Raman) spectroscopy, and FS was determined by three-point bending. At 50 and 66% BisGMA, increases in η were observed following the partial and total substitution of TEGDMA by BisEMA. For 33% BisGMA, η increased significantly only when no TEGDMA was present. The DC was influenced by BisGMA content and co-monomer type. Mixtures containing 66% BisGMA showed a lower DC compared with mixtures containing other concentrations of BisGMA. The BisEMA mixtures had a lower DC compared with the TEGDMA mixtures. The FS was influenced by co-monomer content only. BisEMA mixtures presented a statistically lower FS, followed by TEGDMA + BisEMA mixtures, and then by TEGDMA mixtures. Partial or total replacement of TEGDMA by BisEMA increased η, which was associated with the observed decreases in DC and FS. Although the BisGMA content influenced the DC, it did not affect the FS results.     

Can phenyl-propanedione influence Knoop hardness, rate of polymerization and bond strength of resin composite restorations?

Objectives

The aim of this study was to evaluate the degree of conversion (DC), rate of polymerization (R_p^max), Knoop hardness (KHN) and bond strength between tooth/restoration of composite resins containing different photo-initiators photo-activated by different light-curing units (LCUs).

Materials and methods

A mixture of BisGMA, UDMA, BisEMA and TEGDMA was prepared along with the following photo-initiators: camphorquinone (CQ), phenyl-propanedione (PPD) or the association (CQ/PPD) and 65 wt% of silanated filler particles. The LCUs included a halogen lamp XL 2500 and two LEDs: UltraBlueIS and UltraLume5. The conversion profiles during photo-polymerization were investigated using middle-infrared spectroscopy (mid-IR). Bond strength was evaluated using push-out test in ninety teeth with prepared cavities. Before the push-out test, Knoop hardness (KH) was verified in the top and at the base of the restorations.

Results

PPD obtained lower R_p^max values, regardless of the LCU used. It also provided a greater bond strength than CQ when the LEDs LCUs were used. The degree of conversion after 40 s of irradiation was the same for all composite resins, except PPD photo-activated for XL 2500, which showed lower DC values than CQ and CQ/PPD. In the top and at the base of the restorations, PPD showed the lowest KH values when photo-activated with XL 2500. XL 2500 produced higher KH values than UltraBlueIS when used with CQ or CQ/PPD photo-initiators.

Conclusion

Because it increased the bond strength without compromising the properties of composite resins when photo-activated by an LED, PPD can be used as an alternative photo-initiator.     

Cytotoxicity and estrogenicity in simulated dental wastewater after grinding of resin-based materials

ObjectiveThis study evaluated the cytotoxic and estrogenic effects of dust and eluates released into simulated wastewater after grinding of dental resin-based materials.MethodsFour materials were used: ceram.x® universal, Filtek™ Supreme XTE, Lava™ Ultimate and Core-X™ flow. From each composite material, samples (5 × 2 mm, n = 50) were prepared according to the manufacturers’ instructions. Lava™ Ultimate was used as blocks. All samples were ground to dust with a diamond bur (106 μm) and suspended in distilled water at 60 mg/mL. After storage for 72 h, the suspensions were separated into a soluble (eluate) and a particulate (dust) fraction. Eluates and dusts were evaluated for inhibition of Vibrio fischeri bioluminescence and cytotoxicity on human A549 lung cells (WST-1-Assay). The estrogenic activity was assessed by YES-Assay using Saccharomyces cerevisiae. Additionally, dental monomers (BisGMA, BisEMA, UDMA, TEGDMA, HEMA) and Bisphenol A were investigated.ResultsAll eluates showed inhibition of V. fischeri bioluminescence at concentrations above 1.1 mg/mL (p < 0.05). The activity of the eluates of ceram.x® universal and Filtek™ Supreme XTE was significantly higher than Lava™ Ultimate and Core-X™ flow (p < 0.05). In the WST-1-Assay, all materials induced cytotoxic effects at concentrations of 0.1 mg/mL (p < 0.05), while no significant differences were detected among them. The tested materials revealed no estrogenic activity. All dental monomers and Bisphenol A showed concentration dependent cytotoxic effects (p < 0.05), whereas only Bisphenol A induced an estrogenic effect (p < 0.01).SignificanceDust and eluates of resin-based dental materials released into wastewater exert bactericidal and cytotoxic effects in vitro. However, they reveal no estrogenic effect.     

Long-term elution of monomers from resin-based dental composites

Objective

To bridge the gap between the current alarming literature on resin-based dental materials and the limited clinical observations, more precise knowledge on the actual quantity of released compounds should be acquired. The objective of this study was to quantify the long-term elution of various compounds from resin-based dental composites during one year.

Effect of different photo-initiators and light curing units on degree of conversion of composites

The aim of this study was to evaluate: (i) the absorption of photo-initiators and emission spectra of light curing units (LCUs); and (ii) the degree of conversion (DC) of experimental composites formulated with different photo-initiators when activated by different LCUs. Blends of BisGMA, UDMA, BisEMA and TEGDMA with camphorquinone (CQ) and/ or 1-phenyl-1,2-propanedione (PPD) were prepared. Dimethylaminoethyl methacrylate (DMAEMA) was used as co-initiator. Each mixture was loaded with 65 wt% of silanated filler particles. One quartz-tungsten-halogen - QTH (XL 2500, 3M/ESPE) and two lightemitting diode (LED) LCUs (UltraBlue IS, DMC and UltraLume LED 5, Ultradent) were used for activation procedures. Irradiance (mW/cm2) was calculated by the ratio of the output power by the area of the tip, and spectral distribution with a spectrometer (USB 2000). The absorption curve of each photo-initiator was determined using a spectrophotometer (Varian Cary 5G). DC was assessed by Fourier transformed infrared spectroscopy. Data were submitted to two-way ANOVA and Tukey's test (5%). No significant difference was found for DC values when using LED LCUs regardless of the photo-initiator type. However, PPD showed significantly lower DC values than composites with CQ when irradiated with QTH. PPD produced DC values similar to those of CQ, but it was dependent on the LCU type.     

Determination of the optimal photoinitiator concentration in dental composites based on essential material properties

ObjectivesThe aim of this study was to determine the concentrations of the photosensitizer (camphoroquinone, CQ) and coinitiator (ethyl-4-dimethylaminobenzoate, EDMAB) that resulted in maximum conversion but generated minimum contraction stress in experimental composites.MethodsExperimental composites were prepared with an identical resin formulation [TEGDMA:UDMA:bis-GMA of 30.25:33.65:33.65]. Five groups of resin were prepared at varied CQ concentrations (0.1, 0.2, 0.4, 0.8 and 1.6 wt% of the resin). Five subgroups of resin were prepared at each level of CQ concentration, by adding EDMAB at 0.05, 0.1, 0.2, 0.4 and 0.8 wt% of the resin, resulting in 25 experimental resins. Finally, strontium glass (～3 μm) and silica (0.04 μm) were added at 71.5 and 12.6 wt% of the composite, respectively. Samples (n = 3) were then evaluated for Knoop hardness (KHN), degree of conversion (DC), depth of cure (DoC) and contraction stress (CS).ResultsThere was an optimal CQ and EDMAB concentration that resulted in maximum DC and KHN, beyond which increased concentration resulted in a decline in those properties. KHN testing identified two regions of maxima with best overlaps occurring at CQ:EDMAB ratio of 1.44:0.42 and 1.05:1.65 mol%. DC evaluation showed one region of maximum, the best overlap occurring at CQ:EDMAB ratio of 2.40:0.83 mol%. DoC was 4 mm. Overall, maximum CS was attained before the system reached the maximum possible conversion and hardness.Significance(1) Selection of optimal photoinitiator/amine concentration is critical to materials’ formulation, for excessive amounts can compromise materials’ properties. (2) There was no sufficient evidence to suggest that contraction stress can be reduced by lowering CQ/EDMAB concentration without compromising DC and KHN.     

Resin viscosity determines the condition for a valid exposure reciprocity law in dental composites

ObjectiveTo provide conditions for the validity of the exposure reciprocity law as it pertains to the photopolymerization of dimethacrylate-based dental composites.MethodsComposites made from different mass ratios of resin blends (Bis-GMA/TEGDMA and UDMA/TEGDMA) and silanized micro-sized glass fillers were used. All the composites used camphorquinone and ethyl 4-dimethylaminobenzoate as the photo initiator system. A cantilever beam-based instrument (NIST SRI 6005) coupled with NIR spectroscopy and a microprobe thermocouple was used to simultaneously measure the degree of conversion (DC), the polymerization stress (PS) due to the shrinkage, and the temperature change (TC) in real time during the photocuring process. The instrument has an integrated LED light curing unit providing irradiances ranging from 0.01 W/cm² to 4 W/cm² at a peak wavelength of 460 nm (blue light). Vickers hardness of the composites was also measured.ResultsFor every dental composite there exists a minimum radiant exposure required for an adequate polymerization (i.e., insignificant increase in polymerization with any further increase in the radiant exposure). This minimum predominantly depends on the resin viscosity of composite and can be predicted using an empirical equation established based on the test results. If the radiant exposure is above this minimum, the exposure reciprocity law is valid with respect to DC for high-fill composites (filler contents >50% by mass) while invalid for low-fill composites (that are clinically irrelevant).SignificanceThe study promotes better understanding on the applicability of the exposure reciprocity law for dental composites. It also provides a guidance for altering the radiant exposure, with the clinically available curing light unit, needed to adequately cure the dental composite in question.     

Vasodilatory effect of hydroxyethyl methacrylate and triethylene glycol dimethacrylate in rat aorta through calcium antagonistic action

Introduction

Resin-based dental materials contain various diluent monomers that can interfere with vascular function by causing vasodilation. In this study, we evaluated the vasoactive potential of hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA) and the possible mechanism of their vascular action on isolated rat aorta.

Methods

Responses of thoracic aorta rings were recorded isometrically by using force displacement transducers. After precontracting aorta rings with phenylephrine, relaxations to HEMA and TEGDMA were recorded in the absence and presence of nitric oxide synthase inhibitor N^ω-nitro-L-arginine methyl ester, cyclooxygenase inhibitor indomethacin, and K⁺ channel inhibitors tetraethylammonium, glibenclamide, and 4-aminopyridine. To investigate the Ca²⁺-channel antagonistic effect of HEMA and TEGDMA in different aorta rings, concentration-response curves to CaCl₂ were obtained in the absence and presence of the test monomers.

Results

Both HEMA and TEGDMA elicited concentration-dependent relaxations. The vasorelaxant effect of HEMA and TEGDMA was not mediated via endothelium-dependent nitric oxide and prostanoid-dependent mechanisms or by K⁺ efflux through K⁺ channels. Both monomers significantly inhibited the contractions induced by CaCl₂.

Conclusions

Our results showed that HEMA and TEGDMA induce vasodilation via Ca²⁺-antagonistic action, whereas nitric oxide and cyclooxgenase pathway and K⁺ channels were not responsible for this vasoactive effect.     

Cytotoxicity and anti-biofilm properties of novel hybrid-glass-based caries infiltrant

ObjectivesTo assess the cytotoxicity of an experimental hybrid-glass-based infiltrant and its effect on biofilm attachment, growth and metabolic activity, and to compare it to the resin-based infiltrant Icon.MethodsCytotoxicity of hybrid-glass-based material (EXP) and resin-based infiltrant Icon (Icon) was tested in direct contact tests on freshly cured (direct_mat) and on materials kept for 24 h in cell culture medium (direct_exmat), and extract test with materials 24-h extracts (extract). Cell viability of L929 mouse fibroblast cell line was measured with MTT assay, according to ISO10993–5:2009. Biofilm attachment (5 h), growth (24 h and 48 h) and lactic-acid production (24 h and 48 h) on glass-disk specimens coated with EXP or Icon, or uncoated (control), were assessed using a microcosm biofilm model and Amsterdam Active Attachment system. At indicated time points, biofilms were harvested, plated, and CFU counts were determined, while lactic-acid production was measured colorimetrically.ResultsCell viability reduction by EXP was below 30%-threshold in direct contact tests, while in extract test an increased cell viability was observed. Icon reduced cell viability substantially in all three tests. Significantly less bacteria attached to the surface of EXP after 5 h compared to Icon and control. Biofilm growth was significantly lower on EXP than on Icon and control after 24 h, but this difference was smaller and statistically insignificant after 48 h. There was no difference in lactic-acid production among groups.SignificanceNovel hybrid-glass-based infiltrant seems to have a better biocompatibility and accumulates on its surface less bacteria than resin-based infiltrant, which makes it an attractive resin-free alternative.     

Assessing the estrogenic activity of chemicals present in resin based dental composites and in leachates of commercially available composites using the ERα-CALUX bioassay

ObjectiveThe biocompatibility of resin based dental composites has not yet been fully characterized even though certain monomers used in these composites are synthesized from Bisphenol A (BPA), a well-known estrogenic endocrine disruptor. As a result, they show structural relationship to BPA and can contain it as an impurity. Therefore, the estrogenic activity of 9 monomers, 2 photoinitiators, one photostabilizer and leachates of 4 commercially available composites was determined.MethodsThe ERα-CALUX bioassay was used to determine both agonistic and antagonistic estrogenic activities of the pure compounds (BPA, BisDMA, BisGMA, BisEMA(3), BisEMA(6), BisEMA(10), TEGDMA, TCD-DI-HEA, BADGE, UDMA, HMBP, DMPA, CQ) and the leachates of cured composite disks. The leachates of 4 commercially available composites (Solitaire 2, Ceram.x Spectra ST, G-ænial Posterior and Filtek Supreme XTE) in water and 0.1 M NaOH (pH = 13, ‘worst-case scenario’) were tested for estrogenic activity (pooled leachates from 10 cured composite disks).ResultsAgonistic estrogenic activity was found for the monomer BisDMA, the photostabilizer HMBP and photoinitiator DMPA. All leachates from the 4 tested composites showed significant agonistic estrogenic activity higher than the DMSO control, and the highest activity (potency and efficacy) was found for Solitaire 2, followed by Ceram.x Spectra ST. Furthermore, antagonistic estrogenic activity was found in the leachates from G-ænial Posterior.SignificanceThese results show that significant estrogenic activity was found in all leachates of the cured composite disks, and that this estrogenicity is most likely due to a mixture effect of multiple estrogenic compounds (including BPA, HMBP and DMPA). This indicates that further research into the endocrine activity of all the compounds that are present in these composites (even at low quantities) and their possible mixture effect is warranted to guarantee their safe use.     

Genotoxicity and cytotoxicity of dental materials in human lymphocytes as assessed by the single cell microgel electrophoresis (comet) assay

OBJECTIVES: Resin monomers may be released from restorative dental materials and can diffuse into the tooth pulp or the gingiva, and can reach the saliva and the circulating blood. Whereas the cytotoxic potential of some components has been clearly documented, possible genotoxicity in human target cells demands further investigation. METHODS: The Comet assay was used to quantify DNA single strand breaks, alkali labile and incomplete excision repair sites in lymphocytes of 10 volunteers. The xenobiotics investigated were 2-hydroxyethylmethacrylate (HEMA), triethyleneglycoldimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), and bisphenol A-glycidyl methacrylate (Bis-GMA) with N-methyl-N'-nitro-N-nitrosoguanidine and dimethyl sulfoxide as controls. DNA migration was quantified using the tail moment according to Olive (OTM) and DNA migration was considered to be elevated at OTM levels above 2. Cytotoxicity was monitored using trypan blue. RESULTS: In the negative controls, OTM ranged between 1.0 and 1.2. With HEMA concentrations above 10(-6)M, TEGDMA 10(-3)M, Bis-GMA 10(-4)M, and UDMA above 10(-6)M relevant enhancements of DNA migration (OTM>2) were achieved. At higher concentrations of up to 2.5x10(-2) induced DNA migration was expressed by OTM of 3.3 for HEMA, 4.5 for TEGDMA, 7.4 for Bis-GMA, and 2.8 for UDMA. Relevant cytotoxic effects were also seen but vitality levels were at a critical range of 71% for Bis-GMA and 73% for TEGDMA, only. SIGNIFICANCE: In higher concentration levels, all tested substances induced significant but minor enhancement of DNA migration in the Comet assay as a possible sign for limited genotoxic effects. However, with the highest levels of DNA migration being combined with elevated cytotoxic effects, a low in vivo genotoxic strain appears to be posed by the resin components.     

Permeability of protective gloves to (di)methacrylates in resinous dental materials

Dentists may develop contact allergy induced by handling resinous dental materials, and vinyl and latex gloves may provide protection against the monomers of these materials only during the time it takes for a monomer to permeate the glove. The passage times and rates of penetration of four commonly used (di)methacrylates - HEMA, TEGDMA, BISGMA, and UEDMA - for 11 protective gloves were measured. The passage time for HEMA and TEGDMA through vinyl gloves was 1–3 min, and around 20 min for BISGMA and UEDMA. The rate of penetration of HEMA and TEGDMA in vinyl gloves was 0.5–4.5 μmol · min⁻¹· cm⁻². The passage time of HEMA and TEGDMA through most of the latex or the modified latex gloves was 5–8 min and the rate of penetration 0.5–3.1 μmol · min⁻¹· cm⁻². Latex or modified latex gloves provide a protection against BISGMA and UEDMA for 80 min or more with one exception (Elastyrene), which burst after about 50 min in contact with the resins. Of the tested gloves Ansell, Neutralon, Mediglove, and Biogel D provide protection against HEMA and TEGDMA for at least 5 min.     

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.     

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.