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.

Influence of different light sources and photo-activation methods on degree of conversion and polymerization shrinkage of a nanocomposite resin

The purpose of this study was to evaluate the influence of different light sources and photo-activation methods on degree of conversion (DC%) and polymerization shrinkage (PS) of a nanocomposite resin (Filtek (TM) Supreme XT, 3M/ESPE). Two light-curing units (LCUs), one halogen-lamp (QTH) and one light-emitting-diode (LED), and two different photo-activation methods (continuous and gradual) were investigated in this study. The specimens were divided in four groups: group 1-power density (PD) of 570 mW/cm(2) for 20 s (QTH); group 2-PD 0 at 570 mW/cm(2) for 10 s + 10 s at 570 mW/cm(2) (QTH); group 3-PD 860 mW/cm(2) for 20 s (LED), and group 4-PD 125 mW/cm(2) for 10 s + 10 s at 860 mW/cm(2) (LED). A testing machine EMIC with rectangular steel bases (6 x 1 x 2 mm) was used to record the polymerization shrinkage forces (MPa) for a period that started with the photo-activation and ended after two minutes of measurement. For each group, ten repetitions (n = 40) were performed. For DC% measurements, five specimens (n = 20) for each group were made in a metallic mold (2 mm thickness and 4 mm diameter, ISO 4049) and them pulverized, pressed with bromide potassium (KBr) and analyzed with FT-IR spectroscopy. The data of PS were analyzed by Analysis of Variance (ANOVA) with Welch`s correction and Tamhane`s test. The PS means (MPa) were: 0.60 (G1); 0.47 (G2); 0.52 (G3) and 0.45 (G4), showing significant differences between two photo-activation methods, regardless of the light source used. The continuous method provided the highest values for PS. The data of DC% were analyzed by Analysis of Variance (ANOVA) and shows significant differences for QTH LCUs, regardless of the photo-activation method used. The QTH provided the lowest values for DC%. The gradual method provides lower polymerization contraction, either with halogen lamp or LED. Degree of conversion (%) for continuous or gradual photo-activation method was influenced by the LCUs. Thus, the presented results suggest that gradual method photo-activation with LED LCU would suffice to ensure adequate degree of conversion and minimum polymerization shrinkage.

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.

Influence of Er:YAG laser on surface treatment of aged composite resin to repair restoration

The purpose of this study was to investigate the effect of Er:YAG laser on surface treatment to the bond strength of repaired composite resin after aged. Sixty specimens (n = 10) were made with composite resin (Z250, 3M) and thermocycled with 500 cycles, oscillating between 5 to 55A degrees C. The specimens were randomly separated in six groups which suffered the following superficial treatments: no treatment (GI, control), wearing with diamond bur (GII), sandblasted with aluminum oxide with 27.5 A mu m particles (GIII) for 10 s, 200 mJ Er:YAG laser (GIV), 300 mJ Er:YAG laser (GV), and 400 mJ Er:YAG laser (GVI), with the last 3 groups under a 10 Hz frequency for 10 s. Restoration repair was done using the same composite. The shear test was done into the Universal testing machine MTS-810. Analyzing the results through ANOVA and Tukey test, no significant differences were found (p-value is 0.5120). Average values analysis showed that superficial treatment with aluminum oxide presented the highest resistance to shear repair interface (8.91MPa) while 400 mJ Er:YAG laser presented the lowest (6.76 MPa). Fracture types analysis revealed that 90% suffered cohesive fractures to GIII. The Er:YAG laser used as superficial treatment of the aged composite resin before the repair showed similar results when used diamond bur and sandblasting with aluminum oxide particles.

Influence of pre-heat treatment and different light-curing units on Vickers hardness of a microhybrid composite resin

The aim of this study was to evaluate the hardness of a dental composite resin submitted to temperature changes before photo-activation with two light-curing unite (LCUs). Five samples (4 mm in diameter and 2 mm in thickness) for each group were made with pre-cure temperatures of 37, 54, and 60A degrees C. The samples were photo-activated with a conventional quartz-tungsten-halogen (QTH) and blue LED LCUs during 40 s. The hardness Vickers test (VHN) was performed on the top and bottom surfaces of the samples. According to the interaction between light-curing unit and different pre-heating temperatures of composite resin, only the light-curing unit provided influences on the mean values of initial Vickers hardness. The light-curing unit based on blue LED showed hardness mean values more homogeneous between the top and bottom surfaces. The hardness mean values were not statistically significant difference for the pre-cure temperature used. According to these results, the pre-heating of the composite resin provide no influence on Vickers hardness mean values, however the blue LED showed a cure more homogeneous than QTH LCU.

Comparative Histopathological Analysis of Human Pulps after Class I Cavity Preparation with a High-Speed Air-Turbine Handpiece or Er:YAG Laser

The purpose of this study was to comparatively evaluate the response of human pulps after cavity preparation with different devices. Deep class I cavities were prepared in sound mandibular premolars using either a high-speed air-turbine handpiece (Group 1) or an Er: YAG laser (Group 2). Following total acid etching and the application of an adhesive system, all cavities were restored with composite resin. Fifteen days after the clinical procedure, the teeth were extracted and processed for analysis under optical microscopy. In Group 1 in which the average for the remaining dentin thickness (RDT) between the cavity floor and the coronal pulp was 909.5 mu m, a discrete inflammatory response occurred in only one specimen with an RDT of 214 mu m. However, tissue disorganization occurred in most specimens. In Group 2 (average RDT = 935.2 mu m), the discrete inflammatory pulp response was observed in only one specimen (average RDT = 413 mu m). It may be concluded that the high-speed air-turbine handpiece caused greater structural alterations in the pulp, although without inducing inflammatory processes.

Femtosecond laser ablation on dental hard tissues-Analysis of ablated profile near an interface using local effective intensity

This study evaluated the process of ablation produced by a Ti:Sapphire femtosecond laser under different average powers taking place at the enamel/dentin interface. Based on the geometry of ablated microcavities the effective intensity for ablation was obtained. This study shows the validity for the local effective intensity analysis and allows a quantification of the variation in the ablation geometry taking place at the interface of two naturally different materials. It shows that the variation of the diameter of the ablated region as a function of the cavity depth comes essentially from a mechanism of effective intensity attenuation, as a result of a series of complex effects. Additionally, our data are sufficient to predict that a discontinuity on the ablation profile will occur on the interface between two biological media: enamel-dentin, showing a suddenly jump on the ablated cavity dimensions.

Changes in the temperature of a dental light-cured composite resin by different light-curing units

The purpose of this study was to evaluate the temperature increase during the polymerization process through the use of three different light-curing units with different irradiation times. One argon laser (Innova, Coherent), one halogen (Optilight 501, Demetron), and one blue LED (LEC 1000, MM Optics) LCU with 500 mW/cm(2) during 5, 10, 20, 30, 40, 50, and 60 s of irradiation times were used in this study. The composite resin used was a microhybrid Filtek Z-250 (3M/ESPE) at color A(2). The samples were made in a metallic mold 2 mm in thickness and 4 mm in diameter and previously light-cured during 40 s. A thermocouple (Model 120-202 EAJ, Fenwal Electronic, Milford, MA, USA) was introduced in the composite resin to measure the temperature increase during the curing process. The highest temperature increase was recorded with a Curing Light 2500 halogen LCU (5 and 31 degrees C after 5 and 60 s, respectively), while the lowest temperature increase was recorded for the Innova LCU based on an argon laser (2 and 11 degrees C after 5 and 60 s, respectively). The temperature recorded for LCU based on a blue LED was 3 and 22 degrees C after 5 and 60 s, respectively. There was a quantifiable amount of heat generated during the visible light curing of a composite resin. The amount of heat generated was influenced by the characteristics of the light-curing units used and the irradiation times.

Influence of light guide tip used in the photo-activation on degree of conversion and hardness of one nanofilled dental composite

The aim of this study was to evaluate the degree of conversion and hardness of a dental composite resin Filtek (TM) Z-350 (3M ESPE, Dental Products St. Paul, MN) photo-activated for 20 s of irradiation time with two different light guide tips, metal and polymer, coupled on blue LED Ultraled LCU (Dabi Atlante, SP, Brazil). With the metal light tip, power density was of 352 and with the polymer was of 456 mW/cm(2), respectively. Five samples (4 mm in diameter and 2mm in thickness-ISO 4049), were made for each Group evaluated. The measurements for DC (%) were made in a Nexus-470 FT-IR, Thermo Nicolet, E.U.A. Spectroscopy (FTIR). Spectra for both uncured and cured samples were analyzed using an accessory of reflectance diffuse. The measurements were recorded in absorbance operating under the following conditions: 32 scans, 4 cm(-1) resolution, 300-4000 cm(-1) wavelength. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1637 cm(-1)) against internal standard before and after curing of the sample: aromatic C-C (peak at 1610 cm(-1)). The Vickers hardness measurements (top and bottom surfaces) were performed in a universal testing machine (Buehler MMT-3 digital microhardness tester Lake Bluff, Illinois USA). A 50 gf load was used and the indenter with a dwell time of 30 s. The data were submitted to the test t Student at significance level of 5%. The mean values of degree of conversion for the polymer and metal light guide tip no were statistically different (p = 0.8389). The hardness mean values were no statistically significant different among the light guide tips (p = 0.6244), however, there was difference between top and bottom surfaces (p < 0.001). The results show that so much the polymer light tip as the metal light tip can be used for the photo-activation, probably for the low quality of the light guide tip metal.

Dentin hypersensitivity clinical study comparing LILT and LEDT keeping the same irradiation parameters

Dentin hypersensitivity is a common condition associated with high dental pain. A new LED-based (light emitting diode) light source has been used as an experimental tool in some studies. Purpose: The main objective was to compare these two light sources emitting in the same spectral band (red from 625 to 660 nm) to promote pain relief. Material and methods: A total of 6 sessions were accomplished, being three irradiation sessions and three follow-up sessions. This single-blind study compared a control group (Placebo) and two other groups with different equipments: low laser intensity treatment (LILT) and a light emitting diode system treatment (LEDT). Results: The results showed that there is no statistical difference between LILT and LEDT groups, however, both were better than control group (p=0.01) in terms of treatment efficiency; there is no difference between the second and the third sessions for both treatment, it means that the third session was not necessary; finally, the improvement at the end of the entire research (follow up care of 30 days) was very expressive in comparison to pre-treatment situation for all teeth (p=0.01). Conclusion: LILT and LEDT were equally effective to treat dentine hypersensitivity, a 3rd treatment session was not necessary/two sessions are enough.

Role of Halogen Bonds in Thyroid Hormone Receptor Selectivity: Pharmacophore-Based 3D-QSSR Studies

Most physiological effects of thyroid hormones are mediated by the two thyroid hormone receptor subtypes, TR alpha and TR beta. Several pharmacological effects mediated by TR beta might be beneficial in important medical conditions such as obesity, hypercholesterolemia and diabetes, and selective TR beta activation may elicit these effects while maintaining an acceptable safety profile, To understand the molecular determinants of affinity and subtype selectivity of TR ligands, we have successfully employed a ligand- and structure-guided pharmacophore-based approach to obtain the molecular alignment of a large series of thyromimetics. Statistically reliable three-dimensional quantitative structure-activity relationship (3D-QSAR) and three-dimensional quantitative structure-selectivity relationship (3D-QSSR) models were obtained using the comparative molecular field analysis (CoMFA) method, and the visual analyses of the contour maps drew attention to a number of possible opportunities for the development of analogs with improved affinity and selectivity. Furthermore, the 3D-QSSR analysis allowed the identification of a novel and previously unmentioned halogen bond, bringing new insights to the mechanism of activity and selectivity of thyromimetics.

Structural effects and hydrogen bonds on N,N `-di(methoxycarbonylsulfenyl)urea, [CH(3)OC(O)SNH](2)CO, studied by experimental and theoretical methods

Pure N,N`-di(methoxycarbonylsulfenyl)urea, [CH(3)OC(O)SNH](2)CO, is quantitatively prepared by the hydrolysis reaction of CH(3)OC(O)SNCO and characterized by (1)H NMR, GC-MS and FTIR spectroscopy techniques. Structural and conformational properties are analyzed using a combined approach with data obtained from X-ray diffraction, vibrational spectra and theoretical calculation methods. The IR and Raman spectra for normal and deuterated species are reported. The crystal structure of [CH(3)OC(O)SNH](2)CO was determined by X-ray diffraction methods. The substance crystallizes in the orthorhombic P2(1)2(1)2 space group with a = 9.524(2), b = 12.003(1), c = 4.481 (1) angstrom, and Z = 2 moieties in the unit cell. The molecule is sited on a twofold crystallographic axis (C(2)) parallel to c and shows the anti-anti conformation (S-N single bonds antiperiplanar with respect to the opposite C-N single bonds in sulfenyl-urea-sic group). Neighboring molecules are arranged in a chain motif that extends along the C(2)-axis and is held by bifurcated NH center dot center dot center dot O center dot center dot center dot HN intermolecular bonds. A local planar symmetry is observed in the crystal for the central -SN(H)C(O)N(H)S- skeleton. Experimental and calculated data allow to trace this structural feature to the occurrence of N-H center dot center dot center dot O=C hydrogen bonding interactions. Calculated vibrational and structural properties are in good agreement with the experimentally determined features. (C) 2008 Elsevier B.V. All rights reserved.

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)

Ca(2+)-mediated thiolysis of peptide-resin linkage as an option for preparing protected peptide thioesters

A mild new procedure for preparing protected peptide thioesters, based oil Ca(2+)-assisted thiolysis of peptide-Kaiser oxime resin (KOR) linkage, is described. Ac-Ile-Ser(Bzl)-Asp(OcHx)-SR (Ac: acetyl; Bzl: benzyl; cHx: cyclohexyl), model peptide, was readily released from the resin by incubating the peptide-KOR at 60 degrees C in mixtures of DMF with n-butanethiol [R = (CH(2))(3)CH(3)] or ethyl 3-mercaptopropionate [R = (CH(2))(2)COOCHCH(3)] containing Ca(CH(3)COO)(2). After serine and aspartic acid side-chain deprotection under acid conditions, Ac-Ile-Ser-Asp-S(CH(2))(2)COOCH(2)CH(3) was successfully obtained with good quality and high yield. This type of C-terminal modified peptide may act as an excellent acyl donor in peptide segment condensation by the thioester method, native chemical ligation and enzymatic methods. (c) 2008 Elsevier Ltd. All rights reserved.

Heterodinuclear Fe(III)Zn(II)-Bioinspired Complex Supported on 3-Aminopropyl Silica. Efficient Hydrolysis of Phosphate Diester Bonds

Presented herein is the synthesis and characterization of a new Fe(III)Zn(II) complex containing a Fe(III)-bound phenolate with a carbonyl functional group, which was anchored to 3-aminopropylfunctionalized silica as the solid support. The catalytic efficiency of the immobilized catalyst in the hydrolysis of 2,4-bis (dinitrophenyl) phosphate is comparable to the homogeneous reaction, and the supported catalyst can be reused for subsequent diester hydrolysis reactions.