Posts Tagged ‘dental research’

Optimal Solvent Ratio for Adhesive Systems

Wednesday, June 1st, 2011
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Hybridization morphology and dentin bond stability of self-etch primers with different ethanol/water ratios

Silvia T. Fontes, Giana S. Lima, Fabrício A. Ogliari, Evandro Piva and Rafael R. Moraes

Odontology, DOI: 10.1007/s10266-011-0030-5

Abstract


This study evaluated the influence of ethanol/water ratios on the bond strength to dentin of experimental two-step, self-etch adhesive systems. Self-etch primers were prepared with constant 40 mass % of solvents. The ethanol/water ratios tested were 7:1 (P1), 3:1 (P2), and 1:1 (P3); primers with only ethanol (PE) or water (PW) as solvent were also tested. The bond strength to the dentin was investigated through a microtensile bond strength test. Resin–dentin beam-shaped specimens were obtained and tested after 24 h, 6 months, and 1 year of storage in water at 37°C. The hybridization morphology was analyzed using SEM. For bond strength at 24 h, PE = P1, P1 = P2, and P2, P3 and PW > PE. After 6 months, PE = P1 < P2, P3 and PW. After 1 year, no significant differences among the materials were detected. No significant differences among the periods were detected for PE. For P1, 24 h > 6 months = 1 year. For P2, P3 and PW, 24 h = 6 months > 1 year. For PE and P1, adhesive failures were predominant at 24 h, mixed or adhesive failures after 6 months, and premature debonding was predominant after 1 year. For P2, mixed failures were predominant at 24 h and 6 months, and premature debonding after 1 year. For P3 and PW, mixed failures were predominant at all storage periods. The SEM analysis revealed no clear differences in the hybridization patterns yielded by the water-based primers; PE showed formation of irregular resin tags.
Odontology 123 Page 6. Acknowledgments This study was partially supported by grant #04/ 1374.1 from the FAPERGS, Brazil. The authors also thank Esstech, Inc. for donating the reagents used in the present investigation


LINK:  http://www.springerlink.com/content/84hl1518hl85023w/

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Reduced Shrinkage Stress with Optimized BisGMA/TEGDMA Ratios

Thursday, May 5th, 2011
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BisGMA/TEGDMA ratio and filler content effects on shrinkage stress

Flávia Gonçalve, Caio L.N. Azevedo, Jack L. Ferracane,Roberto R. Braga
Dental Materials, Volume 27, Issue 6, Pages 520-526 (June 2011)

Abstract

Objective

To investigate the contributions of BisGMA:TEGDMA and filler content on polymerization stress, along with the influence of variables associated with stress development, namely, degree of conversion, reaction rate, shrinkage, elastic modulus and loss tangent for a series of experimental dental composites.

Methods

Twenty formulations with BisGMA:TEGDMA ratios of 3:7, 4:6, 5:5, 6:4 and 7:3 and barium glass filler levels of 40, 50, 60 or 70wt% were studied. Polymerization stress was determined in a tensilometer, inserting the composite between acrylic rods fixed to clamps of a universal test machine and dividing the maximum load recorded by the rods cross-sectional area. Conversion and reaction rate were determined by infra-red spectroscopy. Shrinkage was measured by mercury dilatometer. Modulus was obtained by three-point bending. Loss tangent was determined by dynamic nanoindentation. Regression analyses were performed to estimate the effect of organic and inorganic contents on each studied variable, while a stepwise forward regression identified significant variables for polymerization stress.

Results

All variables showed dependence on inorganic concentration and monomeric content. The resin matrix showed a stronger influence on polymerization stress, conversion and reaction rate, whereas filler fraction showed a stronger influence on shrinkage, modulus and loss tangent. Shrinkage and conversion were significantly related to polymerization stress.

Significance

Both the inorganic filler concentration and monomeric content affect polymerization stress, but the stronger influence of the resin matrix suggests that it may be possible to reduce stress by modifying resin composition without sacrificing filler content. The main challenge is to develop formulations with low shrinkage without sacrificing degree of conversion.

LINK:  http://www.demajournal.com/article/S0109-5641%2811%2900020-0/abstract


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BisGMA – UDMA Composite with Nanosilica Fibers

Tuesday, March 29th, 2011
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Synthesis of Nanosilica Fillers for Experimental Dental Nanocomposites and Their Characterisations
Tuan Noraihan Azila Tuan Rahim1, Dasmawati Mohamad1*, Abdul Rashid Ismail1 and Hazizan Md Akil2

1School of Dental Sciences, Universiti Sains Malaysia,
2School of Material and Mineral Resources Engineering, Universiti Sains Malaysia

MATERIALS:

Tetraethyorthosilicate (TEOS), absolute ethanol, ammonia,  γ-methacryloxypropyl-trimethoxysilane (γ-MPS), acetic acid (CH3COOH), bisphenol A glycidyl methacrylate (BisGMA, Esstech), diurethane dimethacrylate (UDMA), triethylene glycol dimethacrylate (TEGDMA), camphorquinone (CQ), (2-dimethylaminoethyl) methacrylate (DMAEMA) and distilled water were used in this work. The chemicals were employed without any further purification.

ABSTRACT:

The aim of this study was to synthesise nanosilica fillers for use in the fabrication of experimental dental nanocomposites and to evaluate their properties,  including surface and mechanical properties. Monodispersed, spherical silica nanoparticles were synthesised via a sol-gel process, and a size range of 10–20 nm was obtained. Surface treatment of the nanosilica was carried out with the silane coupling agent γ-methacryloxypropyltrimethoxysilane (MPS) to reduce agglomeration of nanosilica. Experimental dental nanocomposites with two different filler contents, 30 and 35 wt%, were fabricated and polymerised with a light curing unit for 40 s. The surface morphology, surface roughness, flexural strength and elastic modulus were evaluated and compared. A nanocomposite with 35% filler content showed higher filler compaction, lower surface roughness and higher elastic modulus than a nanocomposite filled with 30% filler. However, the nanocomposite filled with 30% filler content showed higher flexural strength. Based on the results obtained, the synthesised nanosilica is a promising material for the fabrication of dental nanocomposites for tooth-filling applications.



LINK:  http://web.usm.my/jps/22-1-11/22.1.6.pdf


Journal of Physical Science, Vol. 22(1), 93–105, 2011
© Penerbit Universiti Sains Malaysia, 2011

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BISGMA & TEGDMA Form Polymer Matrix of Montmorillonite Nanocomposites

Monday, March 7th, 2011
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Preparation and characterization of light-cured methacrylate/montmorillonite nanocomposites

Veronica Mucci, Javier Perez, Claudia I Vallo


ABSTRACT

Polymer/clay nanocomposites were prepared from dimethacrylate monomers, commonly used in dental restorative resins, and an organically modified silicate (montmorillonite). The photopolymerization process was hardly affected by the presence of the silicate filler, and thus 2 mm thick samples containing 3 wt% clay were extensively cured. Transmission electron microscopy revealed that the montmorillonite platelets were either intercalated or exfoliated. Nevertheless, for all formulations, intermediate-sized aggregates of about 1 µm were present and their fraction increased as the amount of filler increased. The presence of the clay was found to have no major effect on the flexural modulus and compressive yield strength of the nanocomposites. Moreover, the water uptake of nanocomposites containing 3 wt% clay was about 10–15% higher than that of unfilled monomers. Modification of the clay surface with alternative organic cations is certainly necessary in order to achieve an optimal dispersion of the clay in the polymer matrix.

The methacrylate monomers used for the preparation of the nanocomposites were 2,2-bis[4-(2-methacryloxyethoxy)phenyl]pro-pane  (BisEMA; from Esstech, Essington, PA), triethylene glycoldimethacrylate and 1,6-bis(meth-acrylyloxy-


Article first published online: 14 OCT 2010.  DOI: 10.1002/pi.2935.  Copyright © 2010 Society of Chemical Industry

LINK:  http://onlinelibrary.wiley.com/doi/10.1002/pi.2935/full


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Properties of UDMA and Bis-GMA based Composites

Monday, February 28th, 2011
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Hydrogen bonding interactions in methacrylate monomers and polymers

Marianela T. Lemon, Melissa S. Jones, Jeffrey W. Stansbury
Department of Craniofacial Biology, University of Colorado School of Dentistry, Aurora, Colorado 80045

ABSTRACT

It is well appreciated that hydrogen bonding affects a variety of monomer and polymer properties. This study focused on Bis-GMA and urethane dimethacrylate (UDMA) to help elucidate how the strength and nature of
specific noncovalent interactions involved with these different functional dimethacrylate structures are expressed in the monomers and polymers. Hydrogen bonding interactions in monomers and comonomer mixtures as well as in appropriate model compounds were examined by FT-IR under ambient conditions, at elevated temperatures and in dilution studies. The investigation of hydrogen bonding extended to monomer viscosity, photopolymerization reaction kinetics, and polymer mechanical properties.

CONCLUSION

The strength of hydrogen bonding was shown not only to be greater for Bis-GMA compared with UDMA, but there is also greater contribution from intermolecular interactions that enhance the hydrogen bonding effects. While UDMA-based polymers reach significantly higher levels of conversion compared with Bis-GMA materials, the stronger hydrogen bonding reinforcement associated with Bis-GMA appears to provide for comparable mechanical strength properties. Depending on the hydrogen bond donor functionality of a monomer as well as its neighboring functional groups, overall monomer structure and comonomers used, hydrogen bonding can favorably affect polymerization reactivity and mechanical properties, even in materials that form highly crosslinked polymeric networks.


Wiley Periodicals, Inc. J Biomed Mater Res 83A: 734–746,2007

Link:  http://onlinelibrary.wiley.com/doi/10.1002/jbm.a.31448/abstract



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4-META Improves Adhesion in Bonding Systems

Monday, January 17th, 2011
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Effect of etchant variation on wet and dry dentin bonding primed with 4-META/acetone

N. Nakabayashi, K. Hiranuma

In the paper referenced, a 4-META based adhesive proves effective in improving monomer impregnation of demineralized dentin resulting in improved adhesion.

Abstract

Objective: To collect data that explains the advantage, if any, of wet bonding versus dry bonding to dentin, and to more clearly understand the mechanism of wet bonding.

Methods: Bovine dentin samples were prepared with #600-grit paper and were divided into four groups of six each. The first six specimens were etched with 10% citric acid and 3% ferric chloride for 10s then rinsed and blot-dried (Gr. 1: 10-3:W). The second six were etched with 10% citric acid and 3% ferric chloride then rinsed and air-dried (Gr. 2: 10-3:D). The third six were etched with 10% citric acid for 10s, rinsed and blot-dried (Gr. 3: 10-0:W). The fourth group of six samples was etched, rinsed and air-dried (Gr. 4: 10-0:D). All groups were primed with 5% 4-methacryloyloxyethyl trimellitate anhydride (4-META) in acetone for 60s and an acrylic rod was bonded to the samples using a 4-META/methyl methacrylate (MMA)-tri-n-butyl borane (TBB) resin. The samples were fashioned into dumbbell-shaped specimens and stressed in tension until bond failure, to determine tensile bond strengths. Fractured surfaces were examined by scanning electron microscopy.

 

Significance: Effective dentin bonding depended upon the etchants employed. 10-0 etching and air-drying caused the demineralized dentin to collapse in which case wet bonding became necessary to obtain good TBS data. The specimens demineralized with 10-3 did not collapse, even when air-dried; consequently both wet and dry bonding proved effective for obtaining high tensile bond strength data.

LINK:  http://www.demajournal.com/article/S0109-5641%2800%2900017-8/abstract


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4-META History and Applications

Tuesday, October 19th, 2010
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4-META use in dentistry:  A literature review

Jeffrey Chai Chang, DDS, MS, Thomas L. Hurst, DDS, MS, Deborah A. Hart, DMD, and Allan W. Estey, DDSd.  University of Texas Dental Branch, and V.A. Medical Center, Houston, Texas

(J Prosthet Dent 2002;87:216-24.)

ABSTRACT:
4-META (4-methacryloyloxyethy trimellitate anhydride) adhesive resins have been reported in the dental literature for more than 20 years. While the majority of available bonding agents available have gone through changes from the first generation to the fifth, 4-META products have had basically the same ingredients since inception. They consistently produce excellent results, are easy to use, and are not technique-sensitive. Some new adhesive products may have higher bond strengths, but the optimum strength for adhesive materials has not been determined clinically.  For ease of use and consistency of results, 4-META adhesive resins appear to be a good choice.

LINK: http://www.prosdent.org/article/S0022-3913%2802%2961035-2/abstract


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Effect of Varying Filler Content in BisGMA:TEGDMA Composites

Friday, September 10th, 2010
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Contraction stress related to composite inorganic content

F. Gonçalvesa, Y. Kawanob, R.R. Bragaa

Dental Materials Volume 26, Issue 7, Pages 704-709 (July 2010).

Objectives: The role of inorganic content on physical properties of resin composites is well known. However, its influence on polymerization stress development has not been established. The aim of this investigation was to evaluate the influence of inorganic fraction on polymerization stress and its determinants, namely, volumetric shrinkage, elastic modulus and degree of conversion.

Methods: Eight experimental composites containing 1:1 BisGMA (bisphenylglycidyl dimethacrylate):TEGDMA (triethylene glycol dimethacrylate) (in mol) and barium glass at increasing concentrations from 25 to 60vol.% (5% increments) were tested. Stress was determined in a universal test machine using acrylic as bonding substrate. Nominal polymerization stress was obtained diving the maximum load by the cross-surface area. Shrinkage was measured using a water picnometer. Elastic modulus was obtained by three-point flexural test. Degree of conversion was determined by FT-Raman spectroscopy.

Results: Polymerization stress and shrinkage showed inverse relationships with filler content (R2=0.965 and R2=0.966, respectively). Elastic modulus presented a direct correlation with inorganic content (R2=0.984). Degree of conversion did not vary significantly. Polymerization stress showed a strong direct correlation with shrinkage (R2=0.982) and inverse with elastic modulus (R2=0.966).

Significance: High inorganic contents were associated with low polymerization stress values, which can be explained by the reduced volumetric shrinkage presented by heavily filled composites.

Link:  http://www.demajournal.com/article/PIIS0109564110000801/fulltext


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An Overview of Esstech, Inc.

Tuesday, August 10th, 2010
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Alternative Photoinitiator Assists in Camphorquinone Cure

Tuesday, July 27th, 2010
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Degree of conversion and color stability of the light curing resin with new photoinitiator systems

Dong-Hoon Shin, H. Ralph Rawls

Dental Materials, August 2009 (Vol. 25, Issue 8, Pages 1030-1038)

Objectives: This study investigated p-octyloxy-phenyl-phenyl iodonium hexafluoroantimonate (OPPI) as a photoinitiator, in combination with camphorquinone/amine photoinitiation systems, for use with di(meth)acrylate-based composite resins. The investigation determined if the inclusion of OPPI improved degree and rate of conversion, initial color and color stability of a representative composite resin dental material.

Methods: Camphorquinone (CQ) and OPPI were combined in various proportions with the amine co-initiator 2-dimethylaminoethyl methacrylate (DMAEMA) and used at two levels in which CQ+OPPI+DMAEMA=1wt.% or 3wt.% to photoinitiate a BisGMA/BisEMA/TEGDMA (37.5:37.5:25wt.%) monomer blend. Monomer mixture (GTE) was made by mixing 37.5wt.% BISGMA (lot # 568-21-07, ESSTECH, Essington, PA), 37.5wt.% BISEMA (lot # 474-32-02, ESSTECH), and 25wt.% TEGDMA (lot # 597-23-02, ESSTECH). A total of eight groups (four groups for each level of total photoinitiator, 1% and 3%) were tested according to the following proportion of components in the photoinitiator system: Each monomer was polymerized using a quartz-halogen curing unit (Demetron 400, Demetron Research Corp., Danbury, CT) with an intensity of 400mW/cm2 for 5s, 20s, 40s, 60s, 300s and their conversion levels (DC) were determined at each exposure time using a Fourier transform infrared spectrophotometer (FTIR). To examine color stability, experimental composite resins were made by mixing 3.2% silanated barium glass (78wt.%, average filler size; 1μm) with each monomer system, except both CQ only group and 1% CO group, which were found to cure insufficiently to be able to prepare useful specimens. Disk-shaped samples (10mm in diameter and 1.5mm in thickness) were made and stored under the conditions of dry or saline solution at room temperature (25°C) or 60°C water bath. Each CIELAB scale was determined with a colorimeter (CHROMA METER CR-400) at the time of baseline (day after curing), 1 week, 2 weeks, and 4 weeks later.

Results: The high level (3%) photoinitiated groups exhibited greater DC than the low level (1%) groups. In the 3% group, the COA group showed the fastest and the highest DC, while in the 1% group the CA and COA groups showed the greatest DC. In the color stability test, both CA groups were darker and more yellow than the CO and COA groups. Color was more stable in composite resins containing OPPI than those containing only the CQ and amine components. The least color change (greatest color stability) was found using 25°C saline solution aging, and the most change (least color stability) occurred using 60°C dry air aging.

Significance: This study suggests that OPPI can be used to replace the amine in a given CQ/amine photoinitiator system to accelerate cure rate, increase conversion, reduce initial color and increase color stability.

Link: http://www.demajournal.com/article/S0109-5641%2809%2900139-0/abstract


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