Coumarin-based iodonium hexafluoroantimonate as an alternative photoinitiator for experimental dental adhesives resin _ applied adhesion science _ full text


Developing of simplified dental adhesive systems has been one of the mayor progress of the dental adhesive technology over the last years. Marketing in the future Main research has been conducted in order to reduce clinical steps and therefore reducing the technical sensitivity and making the restorative procedure simpler and faster. Used book stores phoenix One-bottle adhesive systems using the total-etch technique or self-etching approach consists in complex formulations of different types of monomers (monofunctional, cross-linkers and acidic functional), solvents and initiation system that has caused some problems such as inhibition of polymerization [ 1– 3], reduced shelf-life [ 2], phase separation and potentially creating a more porous dentin/adhesive interface [ 4, 5]. Stock value history Therefore, these systems has been widely studied in order to improve their adhesive performance [ 6].

For the polymerization of dental adhesives, a binary photoinitiator system comprising camphorquinone (CQ) and amine is usually used [ 7, 8]. Jpy usd forecast The photoinitiator CQ is an α-dicarbonyl compound that becomes a reactive specie after light absorption at wavelength range between 400 and 500 nm [ 9]. Nonbinary definition CQ requires a co-initiator, typically a tertiary amine, as H-donor for effective radical generation that can start polymerization process [ 10, 11]. 1 sgd to 1 usd Such initiation system can causes yellowing of the dental material because CQ has an intense yellow coloration [ 12], moreover, amine can undergo yellowing due oxidation over time [ 13]. Binary definition computer Beside this, the combination of CQ and tertiary amine may present additional disadvantages. Binary code translator to text CQ, as being relatively hydrophobic, has difficulties in initializing the polymerization in the presence of solvents such as ethanol or water, and therefore showed a reduced degree of conversion, rate of polymerization and tensile strength of adhesive resins [ 3, 7, 14]; in addition, tertiary amine is chemically unstable in acidic material, because a reaction acid–base may occur between the acidic components and basic amines leads to the formation of undesirable quaternary ammonium salts, which reduces the longevity of adhesion to dentin over time [ 2, 8, 15].

To address these advantages, alternative initiation systems to CQ/EDAB have been investigated in the formulation of dental adhesive resins.

Euro pound conversion rate The coumarin-based iodonium hexafluoroantimonate (P3C-Sb) is a white colored photoinitiator used in the industry for cationic polymerization with a light absorption spectrum near blue light (λ max 347 nm), which makes it potentially useful for application in dental materials [ 16]. Eur usd exchange rate chart Previous studies showed that after exposure to a LED 405 nm wavelength, P3C-Sb acts as an excellent photoinitiator for concomitant cationic/radical photopolymerization of an epoxy/acrylate blend monomer [ 17].

Although P3C-Sb can be a promising alternative to the CQ/EDAB system, there is no evidence in the literature regarding the effectiveness of this alternative initiator in radical polymerization of methacrylate monomers used in dental materials. Usd cad exchange rate history Therefore, this study aimed to evaluate the performance of P3C-Sb as photoinitiator, used in combination with CQ/EDAB, in the radical polymerization of an experimental adhesive resin containing different amounts of solvent and acid monomers. Forex rates in pakistan today open market The null hypothesis is that P3C-Sb has a similar performance to CQ/EDAB system independent of solvent and acidic monomer concentration. Cnnmoney premarket futures Methods

To perform the monomer photoactivation, a light emitting diode polywave (Bluephase; Ivoclar Vivadent, Schaan, Liechtenstein), in continuous high power mode (1100 mW/cm 2) for 30 s was used. Convert usd to pound sterling The intensity of light irradiation was confirmed by a digital power meter (Ophir Optronics, Danvers, MA, USA) at standardized distance of 5 mm between the fiber tip and digital power meter Kinetics of polymerization evaluated by RT-FTIR spectroscopy

The degree of conversion and polymerization rate of the experimental adhesive resins were evaluated in real time using Fourier-transform infrared spectroscopy with a spectrometer (RT-FTIR, Shimadzu Prestige 21 spectrometer, Shimadzu, Japan) equipped with an attenuated total reflectance device composed of a horizontal diamond crystal with a 45° mirror angle (PIKE Technologies, Madison, WI, USA). Nzd usd analysis A support was coupled to the spectrometer, which was used to fix the light curing unit in place and standardized the distance at 5 mm in a parallel position between the fiber tip and the sample. Euro to aud forecast The IR Solution software package (Shimadzu, Columbia, MD, USA) was used in the monitoring scan mode using Happ–Genzel appodization in the range of 1500–1800/cm, a resolution of 4/cm and a mirror speed of 2.8 mm/s. Futures markets quotes With this configuration, one scan was acquired every 1 s during photoactivation.

Analysis was performed at a controlled room temperature of 23 °C (±2 °C) and 60% (±5%) relative humidity. Hkd to usd conversion In order to avoid light interference, the samples were stored in barrier packages that protect against ambient light and were only dispensed at the time of analysis. Eur usd history The sample (~3 μL) was directly dispensed to the diamond crystal and was immediately light cured for 30 s.The degree of conversion was calculated based on the intensity of the carbon–carbon double-bond stretching vibrations (peak height) at 1635/cm and using the symmetric ring stretching at 1610/cm from the polymerized and unpolymerized samples as an internal standard. Gbp to usd calculator Analyses were performed in triplicate (n = 3). Euro to usd history Data were plotted, curve fitting was applied using logistic non-linear regression, and polymerization rate (Rp (/s)) was calculated as the degree of conversion at time t subtracted from the degree of conversion at time /t. Mxn to usd converter Results

Traditional CQ/amine system used to the free-radical polymerization of dental adhesives presents some drawbacks and studies on alternative photoinitiator systems remains being necessary, especially when simplified adhesive techniques are used. Msn news page The present study characterized the polymerization kinetics of the P3C-Sb photoinitiator when used as part of a binary and ternary photopolymerization system. Usd to zambian kwacha The use of alternative initiator was proposed in an attempt to improve the polymerization reaction from model simplified dental adhesives both in the presence of solvent or acidic monomers. Usd to vnd chart The use of ternary photoinitiator systems formulated with CQ + EDAB + P3C-Sb improved the overall polymerization kinetics of model dental adhesive in the presence of solvents and showed similar degree of conversion to CQ + EDAB in the presence of acidic monomer. Exchange rate euro dollar today Thus the null hypothesis was partially rejected.

P3C-Sb was used in two different binary photoinitiation systems, one as a CQ coinitiator (P3C-Sb + CQ) and other as a photoinitiator in combination with a tertiary amine (P3C-Sb + EDAB). Dollar indian rupee exchange rate For both cases, low degree of conversion and polymerization rates values were achieved. Currency converter us dollars to pounds The conversion of methacrylate monomers is an important parameter to determine the final properties of the resin material. Binary code alphabet The presence of unpolymerized monomer can make the material more susceptible to hydrolytic degradation, leading to a poor durability [ 3, 7, 8]. Binary code converter In addition, higher polymerization rates decrease the time required for photo-activation during clinical application. Usd stock Lower degree of conversion and polymerization rates results of P3C-Sb + CQ photoinitiation system evidences the importance of a tertiary amine to start a polymerization reaction when CQ is used as photoinitiator. Usd cad exchange rate chart CQ is a type II photo-initiator that needs a second component for effective radical generation. Currency converter uk to us Tertiary amines are very effective in reacting with the excited CQ* species as an H-donor to generate free radicals that can start the polymerization process [ 10, 11].

In regards to P3C-Sb + EDAB system, an improvement in polymerization reaction when compared with P3C-Sb + CQ system could be observed, however, lower C=C conversion and polymerization rate than CQ + EDAB system were obtained. Usd to aud conversion calculator Coumarin-based iodonium hexafluoroantimonate (P3C-Sb) has the extinction coefficient at 365 nm on level of 75% of that at the peak maximum located at 345 nm [ 16], hence the absorptions levels at visible light wavelength to photolysis of phenyl radicals Ph • and cleavage of the C–I bond through blue light is possible. Equity finance jobs Previous studies showed that after exposure to an LED 405 nm wavelength, P3C-Sb appeared as an excellent photoinitiator for concomitant cationic/radical photopolymerization [ 17]. Binary tutorial The wavelength range absorption of the initiators in relation to the curing unit used could also have influenced adhesive resins efficiency. Improper fraction to a mixed number calculator In this study, even a polywave LED unit (Bluephase) that emits light in the wavelength range of 380–515 nm [ 9] was chosen to adequately activate the both photoinitiators used, absorption range of CQ (400–500 nm) [ 9], and P3C-Sb (270–390 nm) [ 16].

Although simplified adhesives have lower sensibility-technique, incomplete volatilization of the solvent can trigger a poor polymerization [ 19– 21]. Euro dollar exchange rate forecast The excess solvent residual during the in situ polymerization may compromise the mechanical properties of polymer and therefore, the quality of the bonding interface [ 7, 21]. Usd eur exchange rate Figures 2 and 3 demonstrates the effect of the solvent as a retarding agent for the polymerization reaction in photoinitiation binary systems. When does us futures market open Irrespective of ethanol concentration, CQ + EDAB showed a slower polymerization and the curve inflection point was obtained at a longer time. Euro to usd rate It can be theorized that, as the solvent amount increases, the photoinitiator and the density of double-bond terminations in the system, and as a result the reactivity, decreases, explaining the inhibition of the polymerization process [ 3]. What is binary system Also CQ, as being relatively hydrophobic, has difficulties in initializing the polymerization in the presence of solvents [ 3, 14]. Commodity futures meaning Despite this inhibition effect, similar final degree of conversion values was obtained. Dollar vs pound chart This phenomena occurs due that the polymerization reaction from monomer and solvent mixtures displays a larger mobility in the environment, which is favorable to a slower onset of gelation and vitrification [ 22].

Comparison between the rate of polymerization from binary and ternary photoinitiator systems polymerized in different acid monomer (GDMA-P) amounts ( a GDMA-P 0%; b GDMA-P 10%; c GDMA-P 20%; d GDMA-P 40%)

An alternative to enhance methacrylate polymerization is the use of ternary photoinitiator systems CQ + EDAB + P3C-Sb. Usd rmb The use of a ternary photoinitiator system, composed of a dye (CQ), an amine (EDAB), and an coumarin-based onium salt (P3C-Sb) resulted in a more effective initiation system than CQ + EDAB in the presence of solvent and showed similar degree of conversion to CQ + EDAB in the presence of acidic monomer. Usd price today The inhibition effect due the presence of solvent observed in binary systems, was lower for ternary systems. Stock super stock forum Moreover, some commercial solvent-based dental adhesives have water as co-solvent besides the dentin moisture, which potentially would be an additional challenge to evaporation and in situ polimerization. Gender labels Previously studies reported an improvement in polymer properties when an iodonium salt is used as part of the photoinitiation system [ 3, 26]. Euro pound exchange rate graph It has been suggested that onium salts acts as a catalyst, decreasing the activation energy of the photoinitiation and therefore, reducing the photoactivation times necessary to achieve optimal polymerization parameters [ 3]. Gender roles essay P3C-Sb presents a good solubility with the methacrylate monomers used in the formulation of model dental adhesives and its introduction in the photoinitiator system provided a significant increase in polymerization kinetics. Uss zumwalt Their addition as a photoinitiator and a polymerization reaction catalyst with an hydrophilic character could avoid the occurrence of phase separation and decrease polymerization inhibition by residual organic solvents. What are market futures Thus, materials that show a more stable initiation system in acidic media are expected. Stock symbol for oil futures A possible synergistic effect of solvent/acidic monomer in the presence of P3C-Sb should be added in further studies. Stock market future 2016 Although the results show that P3C-Sb yields improved polymerization reaction with increasing solvent content, it does not mean that residual solvent is not a concern. Peso to us dollar exchange rate today Since, even after long air-drying, a significant amount of residual solvent is kept in the monomer [ 25] and it may affect various other important aspects related to dental adhesion. Gender theories pdf In addition the effect of a higher degree of conversion on the mechanical properties of a polymer is directly related with bond strength. Futures market today Thus, the use of coumarin-based onium salt as a third component in the photoinitiation system appears to be an interesting alternative to improve the degree of conversion and performance of dental adhesive polymers. Canadian dollar to us exchange rate Such alternatives photoinitiators systems may represent new perspectives for development of dental materials; therefore, more studies should be conducted to investigate the behavior and applicability of this initiation system, regarding biological, optical and physic-mechanical properties. Decimal to binary encoder Conclusion

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