Photoactivation Time Research Articles

Influence of Different Exposure Times Required to Stabilize Hardness Values of Composite Resin Restorations

The purpose of this study was to evaluate if Knoop hardness values (KHN) for top and bottom surfaces of resin composite materials can reach a plateau within a clinically acceptable photoactivation time. Four light-curing units (LCUs) were evaluated in this study (n=5): QTH (Optilux501: 550 mW/cm2) and LEDs (FreeLight2: 1100 mW/cm2; UltraLume5: 900 mW/cm2; and Radii: 750 mW/cm2). Composite resin discs (4 mm x 2 mm) of Heliomolar (Ivoclar/Vivadent) and Herculite XRV (Kerr) were tested using five photoactivation times (20, 40, 60, 80, and 100 seconds). KHN were obtained for each test specimen and comparisons between LCUs, depths, and photoactivation times were analyzed using two-way analysis of variance (ANOVA) and polynomial regression analysis. Data for Heliomolar discs using linear regression found a relationship between the independent variables KHN and time with the Optilux501 at the top and bottom surfaces (r2=0.68/ r2=0.66). Radii presented a linear regression at the top surface (r2=0.75) and a quadratic regression at the bottom (r2=0.94). A quadratic regression was also detected for UltraLume5 and FreeLight2 at both top (r2=0.84/ r2=0.94) and bottom surfaces (r2=0.97/ r2=0.90), respectively, reaching a plateau at 80 seconds in all cases. For Herculite XRV, a quadratic regression was observed for all LCUs at the top and bottom surfaces and 80 seconds irradiation time was needed to reach a plateau in KHN. There is a specific, but not clinically acceptable, photoactivation time that KHN at both top and bottom surfaces can reach a plateau and is dependent on LCUs and the resin-composite tested. The LCUs and the resin-composite formulation affected the exposure time required to stabilize hardness values. The overall performance of LED LCUs was better than the QTH LCU regardless of the material evaluated.

Onium salt reduces the inhibitory polymerization effect from an organic solvent in a model dental adhesive resin

This study evaluated the effect of organic solvent concentration on the polymerization kinetics for a model dental 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, which was polymerized using a binary system [camphorquinone (CQ) and ethyl 4-dimethylamine benzoate (EDAB)] and a ternary system [CQ, EDAB, and diphenyliodonium hexafluorphosphate (DPIHFP)]. Additionally, these blends had 0, 10, 20, 30, and 40 wt % ethanol added. Real-time Fourier transform infrared spectroscopy was used to investigate the polymerization reaction over photoactivation time. Data were plotted, and Hill's three-parameter nonlinear regression was performed for curve fitting. The addition of a solvent to the monomer blends decreased the polymerization kinetics, directly affecting the rate of polymerization, delaying vitrification, and attenuating the Trommsdorf effect. The introduction of DPIHFP displayed a strong increase in reaction kinetics, reducing the solvent inhibition effect. After 10 s of photoactivation, the binary system obtained in 0, 10, 20, 30, and 40% of ethanol, a degree of conversion of 44.6, 26.3, 13.4, 1.15, and 0.0%, respectively, whereas when a ternary system was used, the values were 54.6, 40.5, 27.4, 14.5, and 3.4%. An improvement was observed in the polymerization kinetics of a model dental adhesive resin when using a ternary photoinitiation system, making the material less sensitive to the residual presence of a solvent before photoactivation.

Onium salt improves the polymerization kinetics in an experimental dental adhesive resin

The aim of this study was to evaluate the influence of an onium salt in the polymerization kinetics of a dental adhesive model resin. A monomer mixture, based on Bis-GMA, TEGDMA and HEMA, was used as a model dental adhesive resin, which was polymerized using camphorquinone (CQ) as a photo-initiator in addition to either binary or ternary photo-initiator systems. The binary systems were formulated with different concentrations of diphenyliodonium hexafluorphosphate or ethyl 4-dimethylaminobenzoate in relation to the monomer and 1mol% of CQ. The ternary system was a blend of 1mol% of CQ, 2mol% of ethyl 4-dimethylamino benzoate and 0.25, 0.5, 1, 2 or 4mol% of onium salt. Real time Fourier Transform infrared spectroscopy was used to investigate the polymerization reaction over the photo-activation time. When CQ was used as photo-initiator, a slow polymerization reaction was observed and a lower monomer conversion. The addition of a second component (onium salt or amine) increases the polymerization rate and conversion independent on the co-initiator concentration. Ternary photo-initiator system showed an improvement on the polymerization rate of the dental adhesive model resin leading to high conversion in short photo-activation time. Also, a mechanism for initiating polymerization using an amine or onium salt as a co-initiator component is proposed.

Influence of chain extender length of aromatic dimethacrylates on polymer network development

Objective To investigate the role of chain extender size from Bis-EMA monomers on the polymerization profiles and properties of the crosslinked polymers. Additionally, the influence of Bis-GMA was also evaluated. Methods The polymer network from homopolymers Bis-EMA4, Bis-EMA10 and Bis-EMA30 was characterized, as well as copolymers formed among these monomers and Bis-GMA. The degree of conversion from neat and blended monomers as a function of photo-activation time was evaluated by FTIR. Rate of polymerization, network parameter and cross-link density from materials were demonstrated. Water sorption and solubility were determined according to ISO 4049 specification and the data obtained were analyzed by two-way ANOVA/Tukey's test ( α = 0.05). Flexural strength and Young's modulus from polymerized monomers/co-monomers were measured after 24 h water storage at 37 °C and the results were analyzed by one-way ANOVA/Tukey's test ( α = 0.05). Results Monomers with larger ethylene oxide units presented the highest values regarding the degree of conversion and cross-link density. The effect of the chain extender length was also observed in water sorption and solubility polymer characteristics, with Bis-EMA4 being the most hydrophobic polymer. Bis-EMA10 and Bis-EMA30 homopolymers were not able to be tested with the three point bending test due to their great flexibility. The addition of Bis-GMA produced stronger and more rigid Bis-EMA polymers ( p < 0.05). Significance Aromatic dimethacrylates with different chain extender lengths can be a useful alternative in controlling the properties of a dental material, adjusting those to specific applications.

Optical study of the photoactivation time of a sol–gel titania suspension in ethanol

The photoactivation time of sol–gel nanostructured titania, in an ethanol suspension, was studied by optical methods in the UV–Vis region. Titania activation was induced using a Hg lamp and the process was analyzed using light transmittance. The Hg lamp light beam was transmitted through the sample and collected with a spectrophotometer as a function of time. The titania powder was thermally treated to observe the effect in the photoactivation. When the photoactivation of the titania suspension occurs, the transmittance falls and afterwards, a constant value is reached. It was found that the activation time depends on the crystalline structure and the crystallite size.

Photochromism and two-photon luminescence of Ag-TiO_2 granular composite films activated by near infrared ps/fs pulses

We reported photochromism and largely enhanced visible two-photon luminescence (TPL) of Ag-TiO(2) granular composite films by using ps/fs laser at the wavelength of 800 nm. Three types of photochromism spectra were observed when the Ag atom fraction are less than, comparable to and larger than the percolation threshold. The strong surface-plasmon-resonance enhanced visible TPL emissions near Ag(2)O transition band from the photoactivated Ag-TiO(2) samples were also observed. Furthermore, we found that the TPL intensity saturatedly increased while the absorbance at 800 nm exponentially decreased with the same rate as the increasing of photoactivation time, which means that both photochromism and TPL of Ag-TiO(2) composite films are originated from the photo-oxidation of Ag to Ag(+). These observations exhibit the multifunctional features of Ag nanoparticle materials.

Intermediates in Assembly by Photoactivation after Thermally Accelerated Disassembly of the Manganese Complex of Photosynthetic Water Oxidation

The Mn4Ca complex bound to photosystem II (PSII) is the active site of photosynthetic water oxidation. Its assembly involves binding and light-driven oxidation of manganese, a process denoted as photoactivation. The disassembly of the Mn complex is a thermally activated process involving distinct intermediates. Starting from intermediate states of the disassembly, which was initiated by a temperature jump to 47 degrees C, we photoactivated PSII membrane particles and monitored the activity recovery by O2 polarography and delayed chlorophyll fluorescence measurements. Oxidation state and structural features of the formed intermediates of the Mn complex were assayed by X-ray absorption spectroscopy at the Mn K-edge. The photoactivation time courses, which exhibit a lag phase characteristic of intermediate formation only when starting with the apo-PSII, suggest that within approximately 5 min of photoactivation of apo-PSII, a binuclear Mn complex is formed. It is proposed that a MnIII2(di-mu-oxo) complex is a key intermediate both in the disassembly and in the assembly reaction paths.

Development of photochemical method for meniscal repair: A preliminary study

Visible light combined with naphthalimides has previously been shown to catalyze formation of physical bonds in avascular meniscal tissue. The first objective was to modify the existing in vitro testing method (i.e., adhesion testing using lap-jointed slices) to gain more sensitivity in detecting relative bonding strengths among candidate bonding agents. A repeated measures experimental design (RMED) was used to account for variability in properties among bovine menisci and was achieved by testing all treatments/controls on slices from each meniscus. Additionally, to make the method more clinically relevant in modeling a bucket-handle tear, the bovine meniscal slices were cut with collagen fibers parallel to the test slice's length. Peak stress was greater for the complete treatment group (light plus naphthalimide) than for the control or incomplete treatment groups (light only or napthalimide only). The second objective was to perform concentration and photoactivation time dose-response studies. In the concentration dose-response study, peak stress was greater for all treatments when compared with the control but not different among treatment groups; however, there was a trend of increased bonding strength with increased concentration. In the photoactivation time dose-response study, peak stress was greater for all treatments when compared with the control and greater for the 3-min treatment vs. the 6- and 9-min treatments. Peak stress was not different between the longer treatments. The RMED provided increased reproducibility and statistical sensitivity for detecting differences among treatments and will be used to test candidate bonding agents prior to in vivo testing.

New technology for deep light distribution in tissue for phototherapy.

Photodynamic therapy is one of several techniques developed for phototherapy for solid cancers and hematologic malignancies. Photodynamic therapy is a treatment that utilizes a molecular energy exchange between visible light and a photosensitive drug, which results in the production of 1O2, a highly reactive cytocidal oxygen species. The effect is limited to the region where light and drug are combined so that malignant tissue is destroyed and the usual side effects associated with standard cancer therapies are avoided. The light component of photodynamic therapy is customarily generated via dye-pumped or diode lasers. The cost and the complexity of lasers have seriously limited the clinical use of photodynamic therapy for malignancies. A new device technology, based on light-emitting diodes, has been developed (Light Sciences Corporation, Issaquah, WA) that allows light production inside the target tissue. This new technology will expand the current range of indications that are treatable with photodynamic therapy to include moderate- and large-volume refractorytumors. Conventional photodynamic therapy utilizes the delivery of intense light for seconds or minutes. The new approach differs from conventional photodynamic therapy in that it combines a novel interstitial light delivery system with prolonged photoactivation of photosensitive drugs. Prolonging photoactivation time in order to deliver a higher light dose results in an amplification effect, whereby the repeated activation of each photosensitive drug molecule leads to the generation of many thousands of 1O2 molecules. The production of overwhelming numbers of these powerful oxidants in individual cells and the vascular supply of tumors leads to irreversible damage and death of the targeted lesions. Results of preclinical studies have indicated a significant correlation between increased duration of photoactivation and increased volume and depth of photodynamic therapy-induced necrosis. The new developments will enable photodynamic therapy to be used effectively against refractory bulky disease as frontline therapy or in combination with chemotherapy, radiation therapy, or biologics. Perhaps most promising, many patients with advanced refractory disease may now be relieved of symptoms or may return to the treatable population.

The in vitro cytotoxicity of eluates from dentin bonding resins and their effect on tyrosine phosphorylation of L929 cells

Objectives: The aim of this study was to examine the relationship between the monomers eluted from dentin-bonding systems and their cytotoxicities, and to investigate the biochemical effect of the monomers on tyrosine phosphorylation, especially relating to the cell growth activity, of L929 cells in vitro. Methods: The primers, uncured or cured adhesives (3M and Kuraray) were tested to determine the cytotoxicity of confluent L929 cells cultured by Eagle's MEM medium supplemented with 10% FCS. The area of cells affected by the eluted monomers were evaluated with an image analyzer and the concentrations of monomers eluted into the medium were measured with high performance liquid chromatography (HPLC) after 24 h incubation. The protein composition of the stimulated cells was compared by sodium dodecyl sulfate–polyacrylamide gel electrophoresis and tyrosine phosphorylation was detected by Western blot. Results: The primer and uncured adhesives revealed variable cytotoxicities. 2-hydroxyethyl-methacrylate (HEMA) was the major component eluted from uncured primers and adhesives. Small amounts of triethylene glycol dimethacrylate (TEGDMA) were also detected from the uncured adhesives. The cytotoxicities of the adhesives decreased as photo activation time increased. The amount of monomers eluted from the cured adhesives was almost undetectable and did not reach a sufficient concentration to suppress cell viability or cell growth. The cytotoxicities of the primers and adhesives correlated well with the amounts of either HEMA or TEGDMA eluted. Moreover, a high concentration of HEMA (4 mg/ml medium) affected intracellular tyrosine phosphorylation, which is related to cellular activities. Significance: Although the monomers present in dentin bonding resins are cytotoxic to L929 cells, the amount from cured bonding resin is very small and does not provide a cytotoxic dose. This data does however suggest that clinical exposure to the uncured primers and adhesives of dentin bonding resins should be minimized.