Camphorquinone Research Articles

Copper Complexes in Radical Photoinitiating Systems: Applications to Free Radical and Cationic Polymerization upon Visible LEDs

Three copper complexes (E1, G1, and G2) with different ligands in combination with an iodonium salt (and optionally another additive) were used to generate radicals upon soft visible light exposure (e.g., polychromatic visible light from a halogen lamp, laser diodes at 405 and 457 nm, LEDs at 405 and 455 nm). This approach can be worthwhile and versatile to initiate free radical photopolymerization, ring-opening cationic photopolymerization, and the synthesis of interpenetrating polymer networks. The photochemical mechanisms for the production of initiating radicals are studied using cyclic voltammetry, electron spin resonance spin trapping, steady state photolysis, and laser flash photolysis techniques. The photoinitiation ability of the copper complexes based photoinitiating systems are evaluated using real-time Fourier transform infrared spectroscopy. G1 and G2 are better than the well-known camphorquinone (CQ)-based systems (i.e., TMPTA conversion = 18%, 35%, 48%, and 39% with CQ/iodonium salt, CQ/ami...

Degree of conversion and monomer elution of CQ/amine and TPO adhesives

ObjectiveTo evaluate the effect of photo-initiator on the degree of conversion (DC) and elution of Bis-GMA and HEMA for 8 one-step adhesive formulations. MethodsWe used Scotchbond Universal (‘SBU-CQ/amine_4.0’, 3M ESPE), containing about 2wt% camphorquinone (CQ) and 2wt% ethyl-4-dimethylamino benzoate (EDMAB), an experimental ‘SBU-TPO_2.1’ version, containing 2.1wt% diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and 6 experimental LUB adhesives (Kuraray Noritake), namely ‘LUB-CQ/amine_0.7’, ‘LUB-CQ/amine_1.4’, ‘LUB-CQ/amine_4.0’, ‘LUB-TPO_0.35’, ‘LUB-TPO_0.7’ and ‘LUB-TPO_2.0’, respectively containing 0.35wt% CQ and 0.35wt% EDMAB, 0.7wt% CQ and 0.7wt% EDMAB, 2.0wt% CQ and 2.0wt% EDMAB, 0.35wt% TPO, 0.7wt% TPO, and 2.0wt% TPO. DC was measured using micro-Raman spectroscopy. Additional specimens were immersed in ethanol for 24h to determine the elution of Bis-GMA and HEMA using HPLC. ResultsDC of the respective SBU and LUB adhesives was alike at high photo-initiator concentration. At low concentration, TPO was significantly more efficient than CQ/amine (LUB adhesives only). A statistically significant positive photo-initiator concentration effect on DC was noted for both CQ/amine and TPO (LUB adhesives only). A statistically significant inverse photo-initiator concentration effect on HEMA elution was noted for both the CQ/amine- and TPO-containing LUB adhesives. A significantly strong correlation was found between DC and Bis-GMA elution (R2=0.744, p=0.026), and between DC and HEMA elution (R2=0.913, p=0.002) for the LUB adhesives. SignificanceThe photo-initiator kind and concentration affect DC and the Bis-GMA/HEMA elution. TPO can be used as an alternative photo-initiator for CQ/amine.

Properties of a new dental photocurable resin based on the expanding monomer and three-component photoinitiator system

The purpose of this study was to use a three-component photoinitiation system comprising 1wt% CQ (camphorquinone), 2wt% DMAEMA (2-(dimethylamino) ethyl meth acrylate) and 2wt% Ph2I+PF6− (diphenyliodonium hexafluorophosphate) to initiate the copolymerization of the matrix resins which combine bisphenol-S-bis (3-methacrylate-2-hydroxy propyl) ether (BisS-GMA) with the expanding monomer unsaturated spiro orthoesters 2-methylene-1,4,6-trispiro[4,4] nonane (MTOSN), for minimizing the volumetric shrinkage that generally occurs during polymerization. It was hypothesized that MTOSN would expand volumetrically during polymerization under the three-component photoinitiator system and further reductions in volumetric shrinkage would be obtained. The performance study which consists of degree of conversion and condition of the ring-opening reactions of MTOSN, volumetric shrinkage and mechanical properties including tensile bond strength, compressive strength and Vicker’s hardness were carried out respectively by Fourier transfer infrared, the dilatometer and the universal testing machine. The results supported that the dental composites based on the expanding monomer and three-component photoinitiator system engendered a greater decrease of volumetric shrinkage and better mechanical properties.

Carboxylated camphorquinone as visible-light photoinitiator for biomedical application: Synthesis, characterization, and application

Camphorquinone (CQ) is by far the most widely used visible-light photoinitiator in biomedical applications. Despite the fact that CQ is well established and has a good clinical acceptance, photoinitiating systems based on CQ have some drawbacks in particular poor water solubility and low photoreactivity. Here the synthesis and testing of a new camphorquinone derivative are described. Carboxylated-camphorquinone (CQCOOH) was synthesized using ketopinic acid as the starting material. The chemical structure of CQCOOH was verified by 1H-NMR, 1H–13C-COSY-NMR, FT-IR, mass spectroscopy, and UV–visible spectrophotometry. CQCOOH was used with an amine coinitiator and diphenyliodonium chloride (DPIC) accelerator as a visible light induced photoinitiating system for the preparation of hydrogels. CQCOOH exhibits a significantly higher photoreactivity compared to CQ with the same amine-DPIC system. Already after 5s exposure time, the polymer crosslinked with the CQCOOH-amine-DPIC system to form a hydrogel. Furthermore, higher crosslink density and better mechanical properties are observed compared to those hydrogels prepared with the CQ-amine-DPIC system. Experiments measuring the activity or integrity of cells (MTT and LDH assay, respectively) were performed to investigate the compatibility of the photoinitiating system components with human gingival fibroblast (HGF). According to these experiments neither CQCOOH, l-arginine nor N-phenylglycine as amine coinitiators have toxic effects even in high concentrations. In contrast, HGF cell viability is considerably decreased at DPIC-concentrations higher than 0.25%.

Characterization of a Low Shrinkage Dental Composite Containing Bismethylene Spiroorthocarbonate Expanding Monomer

In this study, a novel dental composite based on the unsaturated bismethylene spiroorthocarbonate expanding monomer 3,9-dimethylene-1,3,5,7-tetraoxa-spiro[5,5]undecane (BMSOC) and bisphenol-S-bis(3-meth acrylate-2-hydroxypropyl)ether (BisS-GMA) was prepared. CQ (camphorquinone) of 1 wt % and DMAEMA (2-(dimethylamino)ethyl methacrylate) of 2 wt % were used in a photoinitiation system to initiate the copolymerization of the matrix resins. Distilled water contact angle measurements were performed for the wettability measurement. Degree of conversion, volumetric shrinkage, contraction stress and compressive strength were measured using Fourier Transformation Infrared-FTIR spectroscopy, the AccuVol and a universal testing machine, respectively. Within the limitations of this study, it can be concluded that the resin composites modified by bismethylene spiroorthocarbonate and BisS-GMA showed a low volumetric shrinkage at 1.25% and a higher contact angle. The lower contraction stress, higher degree of conversion and compressive strength of the novel dental composites were also observed.

Perylene derivatives as photoinitiators in blue light sensitive cationic or radical curable films and panchromatic thiol-ene polymerizable films

The perylene derivatives (PTCTE, BPTI and DPPDI) combined with an iodonium salt or an amine (and optionally an additive) are used as photoinitiating systems to initiate the cationic polymerization (CP) of epoxides, the free radical polymerization (FRP) of acrylates, or the thiol-ene polymerization (TEP) of a Trithiol/divinylether mixture under different irradiation sources i.e. very soft halogen lamp or laser diodes at 473nm or 457nm (blue light). Upon a blue light exposure, the PTCTE based systems are very efficient for CP and FRP and better than the camphorquinone (CQ) based reference systems. Interestingly, the combination of PTCTE with previously studied green light and red light sensitive perylene derivatives and an iodonium salt ensures the manufacture of a panchromatic thiol-ene polymerizable film (400–650nm) usable under various household LED bulbs irradiations (i.e. blue, green, yellow or red lights). The photochemical mechanisms are studied by steady state photolysis, fluorescence, cyclic voltammetry, laser flash photolysis and electron spin resonance spin-trapping techniques.

Oxidative stress is responsible for genotoxicity of camphorquinone in primary human gingival fibroblasts

The photoinitiator camphorquinone (CQ), used in dental restorative materials, was found to be cytotoxic in cell cultures. Previously, we have shown that CQ induces alkali labile sites and DNA strand breaks in human gingival fibroblasts (HGF) associated with an increase of intracellular reactive oxygen species (ROS). Therefore, the objective of our study was to evaluate if DNA damage in HGF cells is caused by the generation of ROS. HGF cells were treated with different concentrations (0.5-2.5 mM) of CQ. The cell viability was assessed using propidium iodide (PI) assay. Oxidative DNA damage was evaluated by an enzyme-modified comet assay using human 8-hydroxyguanine DNA-glycosylase 1 (hOGG1), which converts oxidized 7,8-dihydro-8-oxoguanine (8-oxoguanine) into DNA strand breaks and functions as a marker for oxidative modified DNA. The results showed that CQ induced DNA damage in HGF cells without cytotoxic effects for the chosen treatment time. CQ treatment led to the generation of 8-oxoguanine in DNA, which can be shown by a significant increase in tail moment after CQ treatment by the enzyme-modified comet assay. It may be concluded that DNA damage due to CQ is caused by oxidative stress in gingival fibroblasts. A more detailed insight into genotoxic mechanisms in oral cells can be of great importance for a better understanding of the biocompatibility of CQ.

The effects of dentin bonding agent formulas on their polymerization quality, and together with tooth tissues on their microleakage and shear bond strength: an explorative 3-step experiment.

PURPOSEBonding agents (BA) are the crucial weak link of composite restorations. Since the commercial materials' compositions are not disclosed, studies to formulize the optimum ratios of different components are of value. The aim of this study was to find a proper formula of BAs.MATERIALS AND METHODSThis explorative experimental in vitro study was composed of 4 different sets of extensive experiments. A commercial BA and 7 experimental formulas were compared in terms of degree of conversion (5 experimental formulas), shear bond strength, mode of failure, and microleakage (3 experimental formulas). Statistical analyses were performed (α=.05). The DC of selected formula was tested one year later.RESULTSThe two-way ANOVA indicated a significant difference between the shear bond strength (SBS) of two tissues (dentin vs. enamel, P=.0001) in a way that dentinal bonds were weaker. However, there was no difference between the four materials (P=.283). The adhesive mode of failure was predominant in all groups. No differences between the microleakage of the four materials at occlusal (P=.788) or gingival (P=.508) sites were detected (Kruskal-Wallis). The Mann-Whitney U test showed a significant difference between the microleakage of all materials (3 experimental formulas and a commercial material) together at the occlusal site versus the gingival site (P=.041).CONCLUSIONA formula with 62% bisphenol A-glycidyl methacrylate (Bis-GMA), 37% hydroxy ethyl methacrylate (HEMA), 0.3% camphorquinone (CQ), and 0.7% dimethyl-para-toluidine (DMPT) seems a proper formula for mass production. The microleakage and SBS might be respectively higher and lower on dentin compared to enamel.

Solvent Effect on Photoinitiator Reactivity in the Polymerization of 2-Hydroxyethyl Methacrylate

Efficacy of photoinitiators such as riboflavin (RF), camphorquinone (CQ), and safranin T (ST) and triethanolamine as a coinitiator has been compared in carrying out the polymerization of 2-hydroxyethyl methacrylate (HEMA) in aqueous and organic solvents. HEMA solutions were polymerized in the presence of RF, CQ, and ST using a low intensity visible radiation source. HEMA was assayed by a UV spectrophotometric method during the initial stages of the reactions (i.e.,~5% change). A comparison of the efficacy of photoinitiators in causing HEMA polymerization showed that RF is more efficient than CQ and ST. The rate of polymerization is directly related to solvent dielectric constant and inversely related to the solvent viscosity. RF is the most efficient photoinitiator in the polymerization of HEMA and the highest rate of reaction occurs in aqueous solutions. A general scheme for the polymerization of HEMA in the presence of photoinitiators is presented.

Polymerization kinetics of phosphonic acids and esters using an iodonium initiator

ABSTRACTPhosphonic acids are known to be useful monomers in dental restorative materials because of their good potential to provide enhanced adhesion to hydroxyapatite and their high hydrolytic stability. In this study, the photopolymerization of phosphonic acid‐based monomer via the camphorquinone (CQ)/ethyl‐4‐(dimethylaminobenzoate) (EDAB) photoredox system is compared with a ternary system composed of iodonium hexafluorophosphate and CQ/EDAB. Photocalorimetry shows that the ternary system does not provide a significant acceleration of the polymerization with either acrylamide or methacrylate phosphonic acids. The complexation of the iodonium by the phosphonic moiety of the acidic monomers leads to a lowered iodonium reactivity and reduced polarizability of the medium and as a consequence limits the rate enhancement effect normally observed by phosphonic acids on the polymerization rate. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5046–5055

Effect of radical amplified photopolymerization (RAP) in resin-based composites

The objective of this study was to evaluate the effect of irradiation time and specimens thickness on the polymerization kinetic and variation in micro-mechanical properties of two commercial resin-based composites (RBCs) based on radical amplified photopolymerization (RAP) technology™, and to compare them with four camphorquinone (CQ)/amine-based RBCs. The materials were analysed by assessing the polymerization kinetic and the degree of cure (DC) at 0.1 mm and 2 mm depth during 5 minutes after photoinitiation, after curing for 10 s, 20 s and 40 s (Elipar Freelight2). The variation in micro-mechanical properties (Vickers hardness (HV), indentation modulus (E), and depth of cure (DOC)) was assessed in 100 μm steps on 6-mm-high specimens irradiated as above and stored in the water for 24 h at 37 °C. The results were statistically compared using one-way ANOVA with Tukey HSD post hoc test (α = 0.05) and a general linear model. The parameter material exerted the strongest effect on DC (partial eta-squared η p (2) = 0.83), followed by irradiation time (η p (2) = 0.27), and depth (η p (2) = 0.09). The polymerization kinetic, well described by an exponential sum function, showed in all materials a faster decrease in carbon-carbon double bonds at 0.1 mm than at 2 mm depth. The materials based on RAP achieved the highest DC values and a faster polymerization at both depths. The irradiation time exerted the strongest effect on the mechanical properties (DOC, η p (2) = 0.96; HV, η p (2) = 0.89; E, η p (2) = 0.86), followed by depth (HV, η p (2) = 0.63; E, η p (2) = 0.54) and material (HV, η p (2) = 0.40; E, η p (2) = 0.67). At the most favorable curing conditions (40 s, surface), the mechanical properties of the analyzed materials varied between 11.38 (0.80) GPa in Estelite® Sigma Quick and 20.80 (1.42) GPa in Estelite® Posterior for E, and between 74.33 (3.56) N/mm(2) in Tetric EvoCeram® and 120.71 (6.24) N/mm(2) in Estelite® Posterior for HV. RAP-initiated material demonstrated a higher increase in DOC with prolonged irradiation time than the analyzed CQ/amine based materials. An irradiation time of 20 s is also recommended for RAP-initiated RBCs.

Dynamic mechanical thermal analysis of composite resins with CQ and PPD as photo-initiators photoactivated by QTH and LED units

ObjectivesThe aim of this study was to evaluate the thermal and mechanical properties of the composite resins containing the photo-initiators camphorquinone (CQ) and/or phenyl-propanodione (PPD) when photoactivated with halogen lamp (XL2500/3M-ESPE), monowave (UltraBlueIS/DMC) and polywave (UltraLume5/Ultradent) LED units. Materials and methodsA blend of BisGMA, UDMA, BisEMA and TEGDMA was prepared with the same wt% of photo-initiators CQ and/or PPD and 65wt% of silaneted filler particles. Compression strength (CS), diametral tensile strength (DTS) and diametral modulus (DM) were tested. Thermogravimetric analysis (TGA) was made and the lost residual monomer were verified. Dynamic mechanical thermal analysis (DMTA) was used for to analyze the glass transition temperature (Tg) and the storage modulus in 37°C. Degree of conversion (DC) was accomplished in the same samples of DMA using middle-infrared spectroscopy (mid-IR). ResultsCQ, CQ/PPD and PPD obtained the same results for all mechanical properties (CS, DTS and DM), lost residual monomer and storage modulus in 37°C, regardless LCU used. The results of Tg showed that the combination PPD-UltraLume5 produced the highest values. DC showed that the combination CQ-UltraLume5 resulted in the highest values and PPD-XL2500 in the lowest DC values. ConclusionThe study shows that PPD is not only effective photosensitizers, but also photocrosslinking agents for dental composite resins with a similar efficiency to CQ.

Photo-polymerization efficiency of self-etch dental adhesives composed of camphorquinone or trimethylbenzoyl-diphenyl-phosphine oxide

Unique design of self-etch adhesive monomers combines acidic functional group and double bond into a single molecule, which presents complexity as using the environmentally-sensitive photoinitiators in such a system. The objective of this study was to evaluate the kinetics of polymerization for self-etch adhesives cured with two different photoinitiators camphorquinone (CQ) and trimethylbenzoyl-diphenyl-phosphine oxide (TPO). Model self-etch adhesives contained bis[2-(methacryloyloxy)ethyl] phosphate (2MP) and 2-hydroxyethyl methacrylate (HEMA) (mass ratio of 2MP:HEMA=1:1). Different contents of water from 0wt% to 60wt%, or NaOH from 0.2wt% to 2wt% were incorporated to the system. The adhesives were cured using quartz–tungsten–halogen (QTH) or light-emitting diode (LED) light curing units. The degree of conversion (DC) and polymerization rate (PR) of the model self-etch adhesives were determined using ATR/FT-IR with a time-based spectrum analysis. TPO generally outperformed CQ/4E to initiate the self-etch adhesives when using the QTH curing unit. In addition, the DC of the TPO-initiated adhesives displayed increasing trend with water content, in contrast to a decreasing trend for the CQ/4E-initiated system. Furthermore, polymerization of the TPO-initiated system was independent of pH of the self-etch adhesives, whereas the DC and PR of the CQ/4E-initiated system were strongly influenced by the pH. As the LED curing unit was used, polymerization of both TPO and CQ/4E-initiated adhesives was greatly depressed. However, the DC and PR of the CQ/4E initiated adhesives could be improved by increasing pH of the system. In summary, the TPO-initiated system exhibits superior polymerization performance to the CQ/4E system as well as water-favorable and pH-independent features as using QTH curing unit.

1,3-Diethyl-2-thiobarbituric acid as an alternative coinitiator for acidic photopolymerizable dental materials

The ethyl-4-dimethylaminobenzoate (EDAB) is widely used as a coinitiator of the camphorquinone (CQ), but in acidic circumstances it might present some instability, reducing the polymerization efficiency of the material. Considering this, new coinitiators are being evaluated. Hence, this study evaluated the kinetic of polymerization (KP), the degree of conversion (DC), and the rate of polymerization (RP ) of experimental resin adhesives containing 1,3-diethyl-2-thiobarbituric acid (TBA) as a coinitiator of the CQ. The experimental monomeric blend was prepared with bisphenol A glycidyl dimethacrylate, 2-hydroxyethyl methacrylate, and acidic monomers. CQ was added at 1 mol % as photoinitiator. Six groups were formulated: four containing concentrations of 0.1, 0.5, 1, and 2 mol % of TBA, one without coinitiator, and the last one containing 1 mol % of EDAB (control group). The KP and the RP were performed using real-time Fourier Transform infrared spectroscopy. The group without coinitiator has not formed a polymer, whereas the addition of TBA resulted in the conversion of monomers in polymer. The DC of the adhesives was as higher as the increase in the TBA content. The group with 2 mol % of TBA presented improved DC and reactivity (RP ) than the other groups and the control one. Hence, the TBA has performed as a coinitiator of the CQ for the radical polymerization of methacrylate resin adhesives and it has improved the DC and the reactivity of the materials. Thus, it is a potential coinitiator for the photopolymerization of dental materials.

Quantification of elutable substances from methacrylate based sealers and their cytotoxicity effect on with human gingival fibroblasts

ObjectivesPrevious studies have shown that resin composites may cause persistent inflammation of oral or pulpal tissues as well as cell death through eluted substances. The aim of this study was to investigate the leaching of ingredients from commercial dental fissure sealers as well as their cytotoxic effects on human gingival fibroblast (HGF). MethodsThe sealers tested were: Helioseal® F, Helioseal® Refill, Fissurit® F, Grandio® Seal, Ultraseal XT® plus and Delton® FS. Ten discs of each sealer were respectively immersed in methanol or water and incubated at 37°C. The eluates were analysed by gas chromatography/mass spectrometry at day 1, 3 and 7. In the XTT-test, eight discs of each fissure sealer were immersed into medium. The eluates of the respective sealer were mixed and used undiluted and diluted with medium. HGF were incubated with the dilutions at 37°C for 24h. Then XTT-salt was added and the XTT-formazan formation was quantified. ResultsIn eluates from polymerized sealers, comonomers (triethylene glycol dimethacrylate (TEGDMA)) and additives were found (e.g. camphorquinone (CQ), butylated hydroxytoluene, triphenylstibane). 7 d after the beginning of the experiments the highest amount of TEGDMA was found in the aqueous eluate from Grandio® Seal (9944.31 (2250.56)μmol/l). The most cytotoxic eluate found in the XTT-test was from Fissurit® F (EC50 value at 27.13 (7.04)%; (mean(SD)). SignificanceBecause of the use of sealers in preventative dental medicine it should be taken into account that substances like TEGDMA or CQ, that are often causing allergic reactions, are elutable. Before using the sealers patients should be asked for allergic reactions to these substances.

Scanning Microradiography: Measurement of X-ray Attenuation Coefficient of Fissure Sealants Containing Tin Methacryloxytri-n-butyltin (SnM) as Radio-opaquer

Objective: Radio-opacity is a fundamental requirement for fissure sealants in order to be clearly visible radiographicallyand may be well differentiated from caries. Many attempts have been made to make resin based fissure sealants radio-opaque. Researchers achieved radio-opacity of the sealants by blending heavy metals as fillers into the polymeric matrix. Keeping the demerits of using heavy metals in view, a novel fissure sealant was developed by chemically incorporating Tin (Sn) in monomer of methacrylate. This study has been done to assess under scanning micro-radiography (SMR), the radiopacity of the indigenously prepared fissure sealants containing increasing amount of SnM until the consistency of the mix remains workable and clinically useful. Design: Experimental study. Place of study: Biophysical Lab Queen Mary University of London, United Kingdom. Methodology: An organo-tin compound – Methacryloxytri-n-butyltin (SnM) and Ethylene Glycol Dimethacrylate (EGDMA) in varying quantities were mixed to prepare fissure sealant indigenously. Camphorquinone (CQ) and N, N-Dimethyl-P-Toluidine (DMPT) were added to above mixture. The prepared sealants were polymerized in cuvettes and mounted on Scanning microradiography machine. The machine was run for 100 seconds repeatedly for 60 runs. Obtained results were processed and calculated in Microsoft Excel software. Results: It was observed that increasing the weight of Tin (Sn) content in a sealant increases the radio-opacity of the sealant but SnM more than 9.5 gm renders the material unworkable. Conclusion: This study will not only help in enhancing the radio-opacity of fissure sealants but also the radio-opacity of other clinical composite materials maybe enhanced by this method.

Visible light polymerization of epoxy monomers using an iodonium salt with camphorquinone/ethyl-4-dimethyl aminobenzoate

A visible light initiator system for the photoinduced cationic polymerization of epoxy monomers is reported. The system consists of camphorquinone (CQ) in combination with ethyl-4-dimethyl aminobenzoate (EDMAB) and a diaryliodonium salt (Ph2ISbF6.) The three-component system efficiently photoinitiates the polymerization of monomers containing an epoxycyclohexane group, 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexane carboxylate (UVR) and 1,3-bis(3,4-epoxycyclohexyl-2-ethyl),1,1,3,3-tetramethyldisiloxane (SIB), under irradiation with blue light (λ = 467 nm). Very rapid photopolymerization resulted from irradiation of SIB containing Ph2ISbF6 in combination with CQ and better results were obtained in the presence of EDMAB. On the other hand, no polymerization was detected after irradiation of UVR photoactivated with Ph2ISbF6 and CQ. However, this monomer polymerized readily and to high conversion when EDMAB was present. Moreover, almost complete conversion of UVR occurs in the absence of external heating. The polymer resulting from UVR displayed higher values of compressive and flexural properties than the polymer prepared from SIB. This is explained in terms of a higher density of crosslinking points in UVR which is accompanied by a lower content of non-reacted monomer; this has a plasticizing effect on the hardened material. © 2013 Society of Chemical Industry

Sal de iodônio aumenta a resistência coesiva de uma resina adesiva experimental na presença de solvente

This study evaluated the effect of organic solvent concentration on the tensile strength for an experimental adhesive resin containing a ternary photoinitiator system. A monomer blend based on the Bis-GMA, TEGDMA and HEMA was used as a model dental adhesive resin. Two photoinitiation systems were used: a binary system camphorquinone (CQ) and ethyl 4-dimethylamine benzoate (EDAB)] and a ternary system CQ, EDAB and diphenyliodonium hexafluorphosphate (DPIHFP)]. Varied ethanol concentrations were added to the resins, viz. 0, 5, 10, 20, 30, 40 wt%. The ultimate tensile strength test was used to investigate the influence of the solvent amount on the resistance of resins. Furthermore, the use of iodonium salt in photoinitiation system increased the cohesive strength when compared with the binary system. Regardless of solvent concentration, the cohesive strength of polymers containing diphenyliodonium was higher than for the binary photoinitiator system.

Measurement of Solubility and Water Sorption of Dental Nanocomposites Light Cured by Argon Laser

Different parameters used for photoactivation process and also composition provide changes in the properties of dental composites. In the present work the effect of different power density of argon laser and filler loading on solubility (SL) and water sorption (WS) of light-cure dental nanocomposites was studied. The resin of nanocomposites was prepared by mixing bisphenol A glycol dimethacrylate (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) with a mass ratio of 65/35. 20 wt.% and 25 wt.% of nanosilica fillers with a primary particle size of 10 nm were added to the resin. Camphorquinone (CQ) and DMAEMA were added as photoinitiator system. The nanocomposites were cured by applying the laser beam at the wavelength of 472 nm and power densities of 260 and 340 mW/cm(2) for 40 sec. Solubility and water sorption were then measured according to ISO 4049, which in our case, the maximums were 2.2% and 4.3% at 260 mW/cm(2) and 20% filler, respectively. The minimum solubility (1.2%) and water sorption (3.8%) were achieved for the composite containing 25% filler cured at 340 mW/cm(2). The results confirmed that higher power density and filler loading decreased solubility of unreacted monomers and water sorption and improved physico-mechanical properties of nanocomposites.

Color stability, conversion, water sorption and solubility of dental composites formulated with different photoinitiator systems

ObjectivesThe aim of this study was to formulate materials with high color stability and reduced degradation by using photoinitiator systems derived from phosphine oxides alternative to the traditional camphorquinone (CQ)/amine system. MethodsMaterials were formulated with the monomers BisGMA and TEGDMA as organic matrix. The photoinitiators tested were CQ+amine (EDMAB), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), BAPO+EDMAB, diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO) and TPO+EDMAB. A 60% mass of silanated glass filler particles was added. Degree of CC conversion was evaluated by Fourier-transformed infrared spectroscopy 10min after photopolymerization. The color properties were evaluated by a digital spectrophotometer, applying the CIELab parameters, either before photoactivation, immediately after photoactivation, 24h after dry storage, and one month after water immersion. Water sorption and solubility were assessed by mass gain or loss after storage in water for 30 days. Data were analyzed using ANOVA and Tukey's test (5%). ResultsDegree of conversion did not differ statistically among all the tested formulations. Regarding color, only groups with TPO presented satisfactory color stability after one month of water storage (ΔE<3.3). Water sorption and water stability did not differ among the groups. ConclusionsDegree of conversion, water sorption and water solubility did not differ among all the tested groups. The TPO-based groups were the only materials with satisfactory color stability after one month of water storage. Clinical significanceThe use of a photoinitiator system containing TPO might improve the color stability of resin composites compared with the traditional CQ/amine system while attaining similar physico-chemical properties for the composite.