Influence of dentin cavity surface finishing on micro-tensile bond strength of adhesives

The current trend toward minimal-invasive dentistry has introduced innovative techniques for cavity preparation. Chemical vapor deposition (CVD) and laser-irradiation technology have been employed as an alternative to the common use of regular burs in high-speed turbines. Objectives. The purpose of this study was to assess the influence of alternative techniques for cavity preparation on the bonding effectiveness of different adhesives to dentin, and to evaluate the morphological characteristics of dentin prepared with those techniques. Methods. One etch&rinse adhesive (OptiBond FL, Kerr) and three self-etch systems (Adper Prompt L-Pop, 3M ESPE; Clearfil SE Bond, Kuraray; Clearfil S3 Bond, Kuraray) were applied on dentin prepared with a regular bur in a turbine, with a CVD bur in a turbine, with a CVD tip in ultrasound and with an ErCr:YSGG laser. The micro-tensile bond strength (mu TBS) was determined after storage in water for 24 h at 37 degrees C, and morphological evaluation was performed by means of field -emission -gun scanning electron microscopy (Feg-SEM). Results. Feg-SEM evaluation revealed different morphological features on the dentin surface after the usage of both the conventional and alternative techniques for cavity preparation, more specifically regarding smear-layer thickness and surface roughness. CVD bur-cut, CVD ultra-sonoabraded and laser-irradiated dentin resulted in lower mu TBSs than conventionally bur-cut dentin, irrespective of the adhesive employed. Significance. The techniques, such as CVD diamond-bur cutting, CVD diamond ultra-sonoabrasion and laser-irradiation, used for cavity preparation may affect the bonding effectiveness of adhesives to dentin, irrespective of their acidity or approach. (C) 2007 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Influence of Er,Cr : YSGG laser treatment on the microtensile bond strength of adhesives to dentin

Purpose: In light of the concept of minimally invasive dentistry, erbium lasers have been considered as an alternative technique to the use of diamond burs for cavity preparation. The purpose of this study was to assess the bonding effectiveness of adhesives to Er,Cr:YSGG laser-irradiated dentin using irradiation settings specific for cavity preparation. Materials and Methods: Fifty-four midcoronal dentin surfaces, obtained from sound human molars, were irradiated with an Er,Cr:YSGG laser or prepared with a diamond bur using a high-speed turbine. One etch-and-rinse (Optibond FL/Kerr) and three self-etching adhesives (Adper Prompt L-Pop/3M ESPE, Clearfil SE Bond/Kuraray, and Clearfil S-3 Bond/Kuraray) were used to bond the composite to dentin. The microtensile bond strength (mu TBS) was determined after 24 h of storage in water at 37 degrees C. The Kruskal-Wallis test was used to determine pairwise statistical differences (p < 0.05). Prepared dentin surfaces, adhesive interfaces, and failure patterns were analyzed using a stereo microscope and Field-emission gun Scanning Electron Microscopy (Feg-SEM). Results: Significantly lower mu TBS was observed to laser-irradiated than to bur-cut dentin (p < 0.05), irrespective of the adhesive employed. Feg-SEM photomicrographs of lased dentin revealed an imbricate patterned substrate and the presence of microcracks at the dentin surface. Conclusion: Morphological alterations produced by Er,Cr:YSGG laser-irradiation adversely influence the bonding effectiveness of adhesives to dentin. Keywords: dentin, adhesion, adhesives, laser, ErCr:YSGG.

Absolute Thellier paleointensities from Ponta Grossa dikes (southern Brazil) and the early Cretaceous geomagnetic field strength

We report a detailed rock magnetic and Thellier paleointensity study from similar to 130.5 Ma Ponta Grossa Dike Swarms in Southern Brazil. Twenty-nine samples from seven cooling units were pre-selected for paleointensity experiments based on their low viscosity index, stable remanent magnetization and close to reversible continuous thermomagnetic curves. 19 samples characterized by negative pTRM tests, Arai concave- up curves or positive pTRM tests with NRM loss uncorrelated with TRM acquisition were rejected. High quality reliable paleointensity determinations are determined from detailed evaluation criteria, with 10 samples belonging to three dikes passing the tests. The site-mean paleointensity values obtained in this study range from 25.6 +/- 4.3 to 11.3 +/- 2.1 mu T and the corresponding VDM`s range from 5.7 +/- 0.9 to 2.5 +/- 0.5 (10(22) Am(2)). These data yield a VDM mean value of 4.1 +/- 1.6 x 10(22) Am(2). Significant variability of Earth`s magnetic field strength is observed for Ponta Grossa Dikes with the mean value being significantly lower as compared to the mean VDM obtained from the nearby Parana Magmatic Province. The paleointensities for the Ponta Grossa Dikes are in agreement with absolute paleointensities retrieved from the submarine basaltic glasses from 130 to 120 Ma. It seems that a relatively low field prevailed just before the Cretaceous Normal Superchron.

Callus induction and micropropagation improved by colchicine and phytoregulators in Kappaphycus alvarezii (Rhodophyta, Solieriaceae)

Tissue culture techniques were applied for micropropagation of the red alga Kappaphycus alvarezii in order to select the best strain and experimental system for in vitro culture. Five strains were tested: brown (BR), green (GR) and red (RD) tetrasporophytes, brown female gametophyte (BFG), and a strain originating from tetraspore germination (""Edison de Paula"", EP). The effects of three culture media were tested on callus formation, regeneration from explants and from callus in the three tetrasporophytic and EP strains: seawater enriched with half-strength of von Stosch`s (VS 50) and Guillard & Ryther`s (F/2 50) solutions, plus synthetic ASP 12-NTA medium, with or without gelling agent. Explants of the EP strain were treated with glycerol and the phytoregulators indole-3-acetic acid (IAA); 2,4-diclorophenoxyacetic acid (2,4-D); and benzylaminopurine (BA), alone or in combination. The effects of colchicine (0.01%) during 24, 48, 72 hours and 14 days were analyzed in the BFG and EP strains. The EP strain showed the highest percentage of explants forming callus and regeneration from explants in VS 50, indicating its high potential for micropropagation in comparison to the other strains. Regeneration from callus was very rare. Treatments with glycerol and IAA:BA (5:1 mg L(-1)) stimulated the regeneration from explants. Significant differences were observed in the percentages of regeneration of EP strain explants treated with colchicine for 14 days. Our results indicate that IAA and BA stimulated the regeneration process, and that colchicine produced explants with high potential for regeneration, being useful for improving the micropropagation of K. alvarezii.

Thermal Phase Behavior of DMPG Bilayers in Aqueous Dispersions as Revealed by (2)H- and (31)P-NMR

The synthetic lipid 1,2-dimyristoyl-sn-3-phosphoglycerol (DMPG), when dispersed in water/NaCl exhibits a complex phase behavior caused by its almost unlimited swelling in excess water. Using deuterium ((2)H)- and phosphorus ((31)P)-NMR we have studied the molecular properties of DMPG/water/NaCl dispersions as a function of lipid and NaCl concentration. We have measured the order profile of the hydrophobic part of the lipid bilayer with deuterated DMPG while the orientation of the phosphoglycerol headgroup was deduced from the (31)P NMR chemical shielding anisotropy. At temperatures > 30 degrees C we observe well-resolved (2)H- and (31)P NMR spectra not much different from other liquid crystalline bilayers. From the order profiles it is possible to deduce the average length of the flexible fatty acyl chain. Unusual spectra are obtained in the temperature interval of 20-25 degrees C, indicating one or several phase transitions. The most dramatic changes are seen at low lipid concentration and low ionic strength. Under these conditions and at 25 degrees C, the phosphoglycerol headgroup rotates into the hydrocarbon layer and the hydrocarbon chains show larger flexing motions than at higher temperatures. The orientation of the phosphoglycerol headgroup depends on the bilayer surface charge and correlates with the degree of dissociation of DMPG-Na(+). The larger the negative surface charge, the more the headgroup rotates toward the nonpolar region.

Bond Strength of Dental Adhesive Systems Irradiated with Ionizing Radiation

Purpose: The aim of the present paper was to determine the effect of different types of ionizing radiation on the bond strength of three different dentin adhesive systems. Materials and Methods: One hundred twenty specimens of 60 human teeth (protocol number: 032/2007) sectioned mesiodistally were divided into 3 groups according to the adhesives systems used: SB (Adper Single Bond Plus), CB (Clearfil SE Bond) and AP (Adper Prompt Self-Etch). The adhesives were applied on dentin and photo-activated using LED (Lec 1000, MMoptics, 1000 mW/cm(2)). Customized elastomer molds (0.5 mm thickness) with three orifices of 1.2 mm diameter were placed onto the bonding areas and filled with composite resin (Filtek Z-250), which was photo-activated for 20 s. Each group was subdivided into 4 Subgroups for application of the different types of ionizing radiation: ultraviolet radiation (UV), diagnostic x-ray radiation (DX), therapeutic x-ray radiation (TX) and without irradiation (control group, CG). Microshear tests were carried out (Instron, model 4411), and afterwards the modes of failure were evaluated by optical and scanning electron microscope and classified using 5 scores: adhesive failure, mixed failures with 3 significance levels, and cohesive failure. The results of the shear bond strength test were submitted to ANOVA with Tukey`s test and Dunnett`s test, and the data from the failure pattern evaluation were analyzed with the Mann Whitney test (p = 0.05). Results: No change in bond strength of CB and AP was observed after application of the different radiation types, only SB showed increase in bond strength after UV (p = 0.0267) irradiation. The UV also changed the failure patterns of SB (p = 0.0001). Conclusion: The radio-induced changes did not cause degradation of the restorations, which means that they can be exposed to these types of ionizing radiation without weakening the bond strength.

Measurement of shrinkage of composite resin by laser speckle contrast analysis

The aim of this study was to evaluate the shrinkage of a microhybrid dental composite resin photo-activated by one LED with different power densities by means of speckle technique. The dental composite resin Filtek (TM) Z-250 (3M/ESPE) at color A(2) was used for the samples preparation. Uncured composite was packed in a metallic mold and irradiated during 20 s from 100 to 1000 mW cm(-2). For the photo-activation of the samples, it was used a LED prototype (Light Emission Diode) with wavelength centered at 470 nm and adjustable power density until 1 W cm(-2). The speckle patterns obtained from the bottom composite surfaces were monitored using a CCD camera without lens. The speckle field is recorded in a digital picture and stored by CCD camera as the carrier of information on the displacement of the tested surface. The calculated values were obtained for each pair of adjacent patterns and the changes in speckle contrast as a function of time were obtained from six repeated measurements. The speckle contrasts obtained from the bottom surface with 100 mW cm(-1) were smaller than those than the other power densities. The higher power densities provided the higher shrinkage.

Optical and dielectric relaxor behaviour of Ba(Zr(0.25)Ti(0.75))O(3) ceramic explained by means of distorted clusters

In this work, Ba(Zr(0.25)Ti(0.75))O(3) ceramic was prepared by solid-state reaction. This material was characterized by x-ray diffraction and Fourier transform Raman spectroscopy. The temperature dependent dielectric properties were investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurements indicated a diffuse phase transition. The broadening of the dielectric permittivity in the frequency range as well as its shifting at higher temperatures indicated a relaxor-like behaviour for this material. The diffusivity and the relaxation strength were estimated using the modified Curie-Weiss law. The optical properties were analysed by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements at room temperature. The UV-vis spectrum indicated that the Ba(Zr(0.25)Ti(0.75))O(3) ceramic has an optical band gap of 2.98 eV. A blue PL emission was observed for this compound when excited with 350 nm wavelength. The polarity as well as the PL property of this material was attributed to the presence of polar [TiO(6)] distorted clusters into a globally cubic matrix.

Orthodontic brackets removal under shear and tensile bond strength resistance tests - a comparative test between light sources

We have investigated if a new LEDs system has enough efficient energy to promote efficient shear and tensile bonding strength resistance under standardized tests. LEDs 470 +/- 10 nm can be used to photocure composite during bracket fixation. Advantages considering resistance to tensile and shear bonding strength when these systems were used are necessary to justify their clinical use. Forty eight human extracted premolars teeth and two light sources were selected, one halogen lamp and a LEDs system. Brackets for premolar were bonded through composite resin. Samples were submitted to standardized tests. A comparison between used sources under shear bonding strength test, obtained similar results; however, tensile bonding test showed distinct results: a statistical difference at a level of 1% between exposure times (40 and 60 seconds) and even to an interaction between light source and exposure time. The best result was obtained with halogen lamp use by 60 seconds, even during re-bonding; however LEDs system can be used for bonding and re-bonding brackets if power density could be increased.

Protecting clean critical points by local disorder correlations

We show that a broad class of quantum critical points can be stable against locally correlated disorder even if they are unstable against uncorrelated disorder. Although this result seemingly contradicts the Harris criterion, it follows naturally from the absence of a random-mass term in the associated order parameter field theory. We illustrate the general concept with explicit calculations for quantum spin-chain models. Instead of the infinite-randomness physics induced by uncorrelated disorder, we find that weak locally correlated disorder is irrelevant. For larger disorder, we find a line of critical points with unusual properties such as an increase of the entanglement entropy with the disorder strength. We also propose experimental realizations in the context of quantum magnetism and cold-atom physics. Copyright (C) EPLA, 2011

The effects of anticalcification treatments and hydration on the molecular dynamics of bovine pericardium collagen as revealed by (13)C solid-state NMR

This article describes a solid-state NMR (SSNMR) investigation of the influence of hydration and chemical cross-linking on the molecular dynamics of the constituents of the bovine pericardium (BP) tissues and its relation to the mechanical properties of the tissue. Samples of natural phenetylamine-diepoxide (DE)- and glutaraldehyde (GL)-fixed BP were investigated by (13)C cross-polarization SSNMR to probe the dynamics of the collagen, and the results were correlated to the mechanical properties of the tissues, probed by dynamical mechanical analysis. For samples of natural BP, the NMR results show that the higher the hydration level the more pronounced the molecular dynamics of the collagen backbone and sidechains, decreasing the tissue`s elastic modulus. In contrast, in DE- and GL-treated samples, the collagen molecules are more rigid, and the hydration seems to be less effective in increasing the collagen molecular dynamics and reducing the mechanical strength of the samples. This is mostly attributed to the presence of cross-links between the collagen plates, which renders the collagen mobility less dependent on the water absorption in chemically treated samples. Copyright (C) 2010 John Wiley & Sons, Ltd.

Effect of light-curing units on push-out fiber post bond strength in root canal dentin

The purpose of this study was to evaluate the effectiveness of different light-curing units on the bond strength (push-out) of glass fiber posts in the different thirds of the root (cervical, middle and apical) with different adhesive luting resin systems (dual-cure total-etch; dual-cured and self-etch bonding system; and dual-cure self-adhesive cements), Disks of the samples (n = 144) were used, with approximately 1 mm of thickness of 48 bovine roots restored with glass fiber posts, that were luted with resin cements photo-activated by halogen LCU (QTH, Optilux 501) and blue LED (Ultraled), with power densities of 600 and 550 mW/cm(2), respectively. A universal testing machine (MTS 810 Material Test System) was used with a 1 mm diameter steel rod at cross-head speed of 0.5 mm/min until post extrusion, with load cell of 50 kg, for evaluation of the push-out strength in the different thirds of each sample. The push-out strength values in kgf were converted to MPa and analyzed through Analysis of Variance and Tukey`s test, at significance level of 5%. The results showed that there were no statistical differences between the QTH and LED LCUs. The self-adhesive resin cement had lower values of retention. The total-etch and self-adhesive system resin cements seem to be a possible alternative for glass fiber posts cementation into the radicular canal and the LED LCU can be applied as an alternative to halogen light on photo-activation of dual-cured resin cements.

Bond Strength and Etching Pattern of Adhesive Systems to Enamel: Effects of Conditioning Time and Enamel Preparation

Statement of the problem: The performance of self-etch systems on enamel is controversial and seems to be dependent on the application technique and the enamel preparation. Purpose of the Study: To examine the effects of conditioning time and enamel surface preparation on bond strength and etching pattern of adhesive systems to enamel. Materials and Methods: Ninety-six teeth were divided into 16 conditions (N = 6) in function of enamel preparation and conditioning time for bond strength test. The adhesive systems OptiBond FL (Kerr, Orange, CA, USA), OptiBond SOLO Plus (Kerr), Clearfil SE Bond (Kuraray, Osaka, Japan), and Adper Prompt L-Pop (3M ESPE, St. Paul, MN, USA) were applied on unground or ground enamel following the manufacturers` directions or doubling the conditioning time. Cylinders of Filtek Flow (0.5-mm height) were applied to each bonded enamel surface using a Tygon tube (0.7 mm in diameter; Saint-Gobain Corp., Aurora, OH, USA). After storage (24 h/37 degrees C), the specimens were subjected to shear force (0.5 mm/min). The data were treated by a three-way analysis of variance and Tukey`s test (alpha = 0.05). The failure modes of the debonded interfaces and the etching pattern of adhesives were observed using scanning electron microscopy. Results: Only the main factor ""adhesive"" was statistically significant (p < 0.001). The lowest bond strength value was observed for OptiBond FL. The most defined etching pattern was observed for 35% phosphoric acid and for Adper Prompt L-Pop. Mixed failures were observed for all adhesives, but OptiBond FL showed cohesive failures in resin predominantly. Conclusions: The increase in the conditioning time as well as the enamel pretreatment did not provide an increase in the resin-enamel bond strength values for the studied adhesives. CLINICAL SIGNIFICANCE The surface enamel preparation and the conditioning time do not affect the performance of self-etch systems to enamel. (J Esthet Restor Dent 20:322-336, 2008)

Thermal characterization of dental composites by TG/DTG and DSC

Dental composites can be improved by heat treatment, as a possible way to increase mechanical properties due to additional cure (post-cure). Direct dental composites are essentially similar to the indirect ones, supposing they have the same indication. Therefore, to establish a heat treatment protocol for direct composites, using as indirect (photoactivated by continuous and pulse-delay techniques), a characterization (TG/DTG and DSC) is necessary to determine parameters, such as mass loss by thermal decomposition, heat of reaction and glass transition temperature (T (g)). By the results of this study, a heat treatment could be carried out above 160 A degrees C (above T (g), and even higher than the endset exothermic event) and under 180 A degrees C (temperature of significant initial mass loss).

First study on the thermo-solvatochromism in aqueous 1-(1-butyl)-3-methylimidazolium tetrafluoroborate: A comparison between the solvation by an ionic liquid and by aqueous alcohols

The thermo-solvatochrornic behaviors of 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl) phenolate, RB; 2,6-dichloro-4-(2,4,6-triphenyloyridinium-1-yl) phenolate, WB; 2,6-dibromo-4-[(E)-2-(1-methylpyridinium-4-yl)ethenyl] phenolate, MePMBr(2); 2,6-dibromo-4-[(E)-2-(1-n-octylpyridinium-4-yl)ethenyl] phenolate, OcPMBr(2), have been investigated in binary mixtures of the ionic liquid, IL, 1-(1-butyl)-3-methylimidazolium tetrafluorborate, [BuMeIm][BF(4)], and water (W), in the temperature range from 10 to 60 degrees C. Plots of the empirical solvent polarities, ET (probe) in kcal mol(-1), versus the mole fraction of water in the binary mixture, chi(w) showed nonlinear, i.e., nonideal behavior. Solvation by these IL-W mixtures shows the following similarities to that by aqueous aliphatic alcohols: The same solvation model can be conveniently employed to treat the data obtained; it is based on the presence in the system-bulk medium and probe solvation shell of IL, W, and the ""complex"" solvent 1:1 IL-W. The origin of the nonideal solvation behavior appears to be the same, preferential solvation of the probe, in particular by the complex solvent. The strength of association of the IL-W complex, and the polarity of the IL are situated between the corresponding values of aqueous methanol and aqueous ethanol. Temperature increase causes a gradual desolvation of all probes employed. A difference between solvation by IL-W and aqueous alcohols is that probe-solvent hydrophobic interactions appear to play a minor role in case of the former mixture, probably because solvation is dominated by hydrogen-bonding and Coulombic interactions between the ions of the IL and the zwitterionic probes.