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PubMedDate not supplied

The machining of cobalt-chromium alloy in partial denture construction.

PURPOSE: To investigate the performance of different rotary instruments when machining cobalt-chromium alloy. MATERIALS AND METHODS: One tungsten carbide bur, 1 diamond bur, and 2 aluminum oxide abrasive points (pink stones) of different diameter were used to machine cobalt-chromium alloy under standardized conditions. The rate of metal removal was determined and the resulting surfaces and bur wear were investigated using scanning electron microscopy and energy dispersive analysis. RESULTS: Although the larger diameter pink stone was shown to be the most efficient instrument, the tungsten carbide bur produced the smoothest surface. CONCLUSION: Because of its low cost and high cutting efficiency the pink stone is well suited for laboratory use. The tungsten carbide bur is the preferred instrument for clinical use.

Aluminum Oxide↗
PubMed1999

A mechanism of oxygen free radical production in the Dahl hypertensive rat.

OBJECTIVE: To determine if oxygen free radicals derived from xanthine oxidase are involved in the development of salt-induced hypertension. Enhanced production of oxygen free radicals may play a role in hypertension by affecting vascular smooth muscle contraction and provide a mechanism for lesion formation. METHODS: Dahl salt-sensitive (Dahl-S) and salt-resistant (Dahl-R) rats were fed either a low-salt, high-salt or high-salt + tungsten diet for 4 wk. In vivo production of superoxide (O2-) was detected by the reduction of a tetranitroblue tetrazolium (TNBT) dye in the rat mesentery, while plasma hydrogen peroxide (H2O2) production levels were determined using a modified electrochemical electrode technique. RESULTS: The tungsten diet lowered the blood pressure of Dahl-S rats compared to high-salt-treated Dahl-S rats, but had no effect on blood pressure in Dahl-R rats. Light absorption of formazan deposits revealed that tungsten-treated Dahl-S rats had reduced TNBT staining along the endothelium of arterioles and venules compared to hypertensive, high-salt-treated Dahl-S rats. In addition, tungsten-treated Dahl-S rats had a lower plasma H2O2 concentration compared to hypertensive, high-salt-treated Dahl-S rats. CONCLUSIONS: These findings indicate that xanthine oxidase-derived oxygen free radicals are involved in the pathogenesis of salt-induced hypertension.

Animals↗
PubMedDate not supplied

The effects of tooth preparation on pressure measured in the pulp chamber: a laboratory study.

PURPOSE: The purpose of this study was to determine pressure changes in the pulp space during tooth preparation with either diamond or tungsten carbide burs in a high-speed dental handpiece in the laboratory. MATERIALS AND METHODS: Twenty premolar teeth were collected and randomly assigned to two groups: group 1 received preparation with diamond burs and group 2 with tungsten carbide burs. The teeth were mounted on a pressure transducer and the pulp chambers were filled with saline. A 0.1-mm thickness of tooth tissue was removed from the proximal surface of each tooth, alternating dry and wet cutting, until the pulp chamber was exposed. Pressure and temperature changes were recorded during tooth preparation. RESULTS: At 0 to 1 mm of remaining dentin depth dry cutting with diamond and tungsten carbide burs generated a mean positive pulpal pressure of 12 kPa and 6 kPa, respectively. Wet cutting under the same conditions produced 0.6 kPa and 0.15 kPa, respectively. The difference between wet and dry cutting was highly significant (P < 0.001). Diamond burs produced significantly higher pressure increases than carbide burs at all levels for both wet and dry techniques (P < 0.05). When cutting farther than 2 mm from the pulp, tooth preparation created a mean 0.09-kPa pressure increase, which was not influenced by either coolant use or bur type. The temperature change was minimal during wet cutting and only minor temperature increases were recorded during dry cutting. CONCLUSION: From this laboratory study it is concluded that significant pressure changes occur in the pulp chamber during tooth preparation of extracted teeth when the remaining dentin thickness is less than 2 mm.

Body Temperature↗
PubMed2000

Pharmacokinetics of sodium tungstate in rat and dog: a population approach.

Sodium tungstate has been found to correct hyperglycemia in insulin- and noninsulin-dependent models of diabetes when administered in drinking fluid with a low degree of toxicity; thus, it provides a potential treatment for diabetes. In the present report, pharmacokinetic studies with sodium tungstate were carried out in the Sprague-Dawley rat and beagle dog. This drug was administered either i.v. (8.97 mg/kg in rat; 25 and 50 mg/kg in dog) or orally in the form of solution (35.9 and 107.7 mg/kg in rat; 25 and 50 mg/kg in dog). Tungsten was quantified using an inductively coupled plasma method. Pharmacokinetic parameters were estimated using a population approach. Sodium tungstate followed first order kinetics, and plasma concentration-versus-time data were adequately described by a two-compartment model. In rat, bioavailability was high (92%), whereas it was lower in dog (approximately 65%). The total volume of distribution expressed by unit of body weight was much higher when the animal was smaller (0.46 l/kg in rat versus 0.23 l/kg in dog). The total body clearance normalized by weight, 0.19 l/h/kg in rat versus 0.043 l/h/kg in dog, changed as for the volume of distribution. The elimination half-life was two times higher in dog (approximately 4 h) than in rat (approximately 1.7 h). In the range of 35.9 to 107.7 mg/kg after oral administration in rat and 25 to 50 mg/kg after oral and i.v. administration in dog, tungsten plasma concentrations increased in proportion to dose.

Administration, Oral↗
PubMed2000

Changes in F-actin organization induced by hard metal particle exposure in rat pulmonary epithelial cells using laser scanning confocal microscopy.

Chronic inhalation of hard metal (WC-Co) particles causes alveolitis and the eventual development of pulmonary fibrosis. The initial inflammatory response includes a change in the alveolar epithelial cell-capillary barrier, which has been shown to be regulated by the state of assembly and organization of the actin cytoskeletal network. The objective of this study was to evaluate the effect WC-Co particles have on F-actin organization of lung epithelial cells in an in vitro culture system. Rat lung epithelial (L2) cells were exposed to 5, 25, and 100 microg/mL of WC-Co particles, as well as the individual components (Co and WC) of the hard metal mixture particles for 24 h. The effect on F-actin organization was visualized by laser scanning confocal microscopy (LSCM) following Bodipy-Phallacidin staining. Minimal changes in the F-actin microfilaments of L2 cells were observed by LSCM after exposure to WC and WC-Co at 5 and 25 microg/mL, while at 100 microg/mL, there was a noticeable disruption in the uniform distribution of L2 cell F-actin microfilaments. After exposure to Co, a dose-dependent change in the F-actin organization of the L2 cells was observed. Little change in F-actin assembly was observed after treatment with 5 microg/mL of Co (the concentration equivalent to the 5% amount of Co commonly present in 100 microg/mL of the WC-Co sample mixture). However, at 100 microg/mL of Co, the microfilaments aggregated into homogeneous masses within the cells, and a significant loss in the organization of L2 F-actin was observed. These dramatic alterations in F-actin organization seen after exposure to the higher doses of Co were attributed to an increase in L2 cell injury as measured by lactate dehydrogenase and trypan blue exclusion. We conclude the pulmonary response evoked in the lung by inhalation of high levels of WC-Co particles is unlikely due to alterations in the F-actin microfilaments of lung-epithelial cells.

Actin Cytoskeleton↗
PubMed2000

Hard metal lung disease--the first case in Singapore.

INTRODUCTION: We report the first case of hard metal lung disease in Singapore and the occupational investigative work and control measures that were undertaken. CLINICAL PICTURE: A 38-year-old machinist in the tool manufacturing industry presented with exertional dyspnoea and cough. Chest X-ray revealed bilateral reticulonodular infiltrates with honeycombing. High resolution computed tomography scan of the thorax confirmed the presence of interstitial fibrosis. Open biopsy of the lung showed features of pneumoconiosis. Particle induced X-ray emission (PIXE) analysis, a relatively new elemental analysis technique, performed on the lung biopsy specimen confirmed the presence of tungsten and titanium; and he was diagnosed to have hard metal lung disease. Microbiologic, serologic and histologic investigations excluded an infective cause. Serial pulmonary function tests on follow-up showed no progression. He presented with haemoptysis 10 months later and was diagnosed to have tuberculosis on the basis of positive sputum and bronchoalveolar lavage cultures for Mycobacterium tuberculosis complex. TREATMENT: Preventive measures and permanent transfer to non-cobalt work were instituted. OUTCOME: The interstitial fibrosis appears to have stabilised. CONCLUSION: The diagnosis of hard metal lung disease must be considered in a worker exposed to cobalt presenting with interstitial fibrosis.

Adult↗
PubMedDate not supplied

Three-dimensional optical profilometry analysis of surface states obtained after finishing sequences for three composite resins.

The operating protocols used for finishing composite resins are numerous and affect the success of filling from a mechanical, biological, and aesthetic point of view. The study determined the most favorable finishing for each of the composites considered. The three-dimensional optical profilometry examination was used to obtain qualitative and quantitative measurements of three hybrid composites. Tungsten carbide burs left irregularities harder to eliminate than those caused by diamond burs. Sof-Lex disks and the Enhance System gave good results for the three materials. Charisma presented a good surface regardless of polishing method used. Finishing Z100 and Prisma TPH required a special operating protocol as specified by the manufacturers. This study demonstrated that the finishing procedure for composite materials must be strictly followed to obtain optimal results. Profilometry proved to be an excellent method to study the surface roughness of samples.

Analysis of Variance↗
PubMedDate not supplied

The effect of tooth preparation on microleakage behavior.

Many factors contribute to the microleakage of a restoration. One of the more important is the method of cavity preparation. This study compared the microleakage behavior of composite restorations placed in cavities prepared by different techniques. It also compared and correlated the microleakage data produced by an electrochemical vs a staining technique. Class V cavities were prepared in 48 premolars by four techniques: (1) tungsten carbide bur in a high-speed handpiece followed by acid etching; (2) air abrasion (27 microns Al2O3) followed by acid etching; (3) air abrasion (50 microns Al2O3) and (4) air abrasion (27 microns Al2O3), with n = 12 in each group. All teeth were restored with Prime and Bond 2.1 and Tetric Flow, then thermocycled between 5 degrees and 55 degrees C for 5000 cycles with a one minute dwell at each temperature. After thermocycling, a PVC-covered Cu wire was inserted apically into the pulp chamber of each tooth and sealed into position. Leakage was continuously followed by a conductimetric method for 75 days. The teeth then were immersed in 50% AgNO3 for two hours, rinsed in distilled water for 60 seconds, then placed in a rapid photographic developer solution for two hours, followed by rinsing and sectioning for microscopic examination. Electrochemical data were examined by ANOVA and Newman-Keuls multiple comparison tests, while Kruskal-Wallis and Rank Sum Difference tests were used on the staining evaluations. Spearman's rho test was used to correlate the two test techniques. Electrochemical data for cavities prepared with a bur or air abrasion followed by acid etching prior to restoration showed significantly less (p < or = 0.05) microleakage (mean leakage currents of 1.89 & 1.57 microA, respectively) than teeth prepared with air abrasion alone (mean leakage currents of 3.60 & 3.40 microA, respectively). Rank sum AgNO3 staining data (196 & 242 vs 371 & 368) supported these findings. The correlation between the electrochemical and staining data was significant (p < or = 0.05) for all four groups of test specimens.

Acid Etching, Dental↗
PubMed1999

New light curing options for composite resin restorations.

The concerned practitioner needs to understand the chemistry of the materials, the dynamics of polymerization, the stress factors created, and the specific light energy requirements needed to attain maximum results. If a practitioner chooses to use one of the nontraditional curing systems, he or she needs to consult with the manufacturer to determine the spectral output of the system, and contact the manufacturer of the composite to ensure that the material used will cure properly with the chosen light source. The manufacturers have customer service representatives who are usually very knowledgeable about their products. Current claims about new technological developments based on laboratory experiments and anecdotal information are promising. However, multicenter prospective clinical studies are still needed to validate safety and efficacy. Then clinicians can make informed decisions that will enable them to provide the highest quality dentistry for their patients. We will revisit this topic as more information becomes available.

Argon↗
PubMed2001

Effect of gamma-irradiation on H3 histone and DNA in solution.

Three methods, namely, absorbance of colour by reaction with Folin-Ciocalteau reagent, UV absorbance and fluorescence intensity measurements for detection of H3 histone in 0.15 M standard saline citrate (SSC) solution were compared. Maximum sensitivity was found with the Folin-Ciocalteau method. Effect of varying pH and of gamma- radiation on H3 histone and on interaction of H3 histone with DNA were studied. For this, solutions of H3 histone in SSC, in 0.9% NaCl, H3 histone + DNA in 0.9% NaCl were subjected to varying pH (1-10) and gamma- radiation (dose 10-50 Gy) and lambda(max) and Alambda(max) were monitored. From the molar ratios of histone and DNA in the complex, it was observed that at gamma -radiation dose of 50 Gy and pH 8.54, there was a depletion of 6-8 microg/ml of histone from the histone-DNA complex.

Animals↗
PubMedDate not supplied

[Turbidimetric method for quantitative determination of triton X-100 with silicotungstic acid].

The Formation of Triton X-100-silicotungstic acid complex was studied. Quantitative turbidimetric determination of the detergent based on this process was suggested. This method allows to determining the complex formation at any wavelength in the range from 350 (epsilon 350 = 15,600 cm-1 M-1) to 600 nm (epsilon 600 = = 9090 cm-1 M-1). The calibration curve for Triton X-100 recorded at 350 nm is linear in the concentration range of 0 to 30 micrograms/ml. A sigmoid calibration curve was observed at longer wavelengths. A linear fragment of the calibration curve recorded at 600 nm was found at a concentration of Triton X-100 of about 5 micrograms/ml. The complex nature of calibration curves can be explained by heterogeneity of the complex dispersion.

Calibration↗
PubMedDate not supplied

Surface texture of resin-modified glass ionomer cements: effects of finishing/polishing systems.

This study investigated the surface texture of two resin-modified glass ionomer cements (RMGICs) in the vertical and horizontal axis after treatment with different finishing/polishing systems. Class V preparations were made on the buccal and lingual/palatal surfaces of freshly extracted teeth. The cavities on each tooth were restored with Fuji II LC (GC) and Photac-Fil Quick (ESPE) according to manufacturers' instructions. Immediately after light-polymerization, gross finishing was done with 8-flute tungsten carbide burs. The teeth were then randomly divided into four groups and finished/polished with (a) Robot Carbides (RC); (b) Super-Snap system (SS); (c) OneGloss (OG) and (d) CompoSite Points (CS). The sample size for each material-finishing/polishing system combination was eight. The mean surface roughness (microm) in vertical (RaV) and horizontal (RaH) axis was measured using a profilometer. Data was subjected to ANOVA/Scheffe's tests and Independent Samples t-test at significance level 0.05. Mean RaV ranged from 0.59-1.31 and 0.83-1.52, while mean RaH ranged from 0.80-1.43 and 0.85-1.58 for Fuji II LC and Photac-Fil, respectively. Results of statistical analysis were as follows: Fuji II LC: RaV-RC, SS<OG & SS<CS; RaH-SS, CS<RC, OG; Photac-Fil: RaV- SS, CS<OG; RaH-SS<RC, OG & CS<RC (where < indicates significantly greater Ra values). Significant differences in RaV and RaH values were observed when Fuji II LC was finished with RC. The use of carbides (RC) and one-step rubber abrasive system (OG) for finishing/polishing of RMGICs is not recommended. Graded abrasive disk (SS) or two-step rubber abrasive (CS) systems should be used instead.

Analysis of Variance↗
PubMed2002

The effect of six polishing systems on the surface roughness of two packable resin-based composites.

PURPOSE: To evaluate the surface roughness of two packable composites after finishing and polishing with six different systems. MATERIALS AND METHODS: Solitaire and Alert composite samples were prepared and polished with Poli I and Poli II aluminum oxide pastes, Ultralap diamond paste, Enhance finishing points, Politip rubber polishers, fine and extra fine diamond burs, and 30-blade tungsten carbide burs according to the manufacturers' instructions. The polished surfaces were then evaluated with a profilometer and a scanning electron microscope. RESULTS: Solitaire composite resin presented the smoothest surfaces when polished with Poli I and II aluminum oxide pastes, Ultralap diamond paste, Politip finishing points and 30-blade tungsten carbide burs. The smoothest surfaces for Alert composite were evident with the 30-blade tungsten carbide burs.

Aluminum Oxide↗
PubMedDate not supplied

Effects of finishing/polishing techniques on microleakage of resin-modified glass ilonomer cement restorations.

This study investigated the effect of finishing/polishing techniques on the microleakage of resin-modified glass ionomer restorations. Class V preparations were made on the buccal and lingual/palatal surfaces of freshly extracted teeth. The cavities on each tooth were restored with Fuji II LC (FT [GC]) and Photac-Fil Quick (PF [3M-ESPE]) according to manufacturers' instructions. Immediately after light-polymerization, gross finishing was done with eight-fluted tungsten carbide burs. The teeth were then randomly divided into four groups and finishing/polishing was done with one of the following systems: (a) Robot Carbides (RC); (b) Super-Snap system (SS); (c) OneGloss (OG) and (d) CompoSite Polishers (CS). The sample size for each material-finishing/polishing system combination was eight. After finishing/polishing, the teeth were stored in distilled water at 37 degrees C for one week. The root apices were then sealed with acrylic and two coats of varnish was applied 1 mm beyond the restoration margins. The teeth were subsequently subjected to dye penetration testing (0.5% basic fuchsin), sectioned and scored. Data was analyzed using Kruskal-Wallis and Mann-Whitney U tests at a significance level of 0.05. Results of statistical analysis were as follows: Enamel margins: PF-OG<SS; FT-OG<RC; Dentin margins: PF-no significant difference; FT-OG & CS<RC. Regardless of the finishing/polishing technique, leakage at dentin margins was significantly greater than at enamel margins for FT. For PF, no significant difference in leakage scores was observed between dentin and enamel with the exception of finishing/polishing with OG. FT restorations had significantly less enamel and dentin leakage than PF restorations when treated with OG. The effect of finishing/polishing techniques on microleakage was both tissue and material dependent.

Acrylic Resins↗
PubMedDate not supplied

Surface geometry of three packable and one hybrid composite after finishing.

This study compared the effects of different finishing techniques on the surface of a traditional hybrid composite and three packable composites. Four composites were used in the study (Herculite XRV/Kerr, Definite/Degussa, SureFil/Dentsply and Solitaire/Heraeus-Kulzer). Fifty specimens were made of each material, sized 7 x 7 x 4 mm. Fifteen specimens of each material were subjected to the following finishing procedures: (1) a 30 microm diamond, (2) a 30 microm and a 20 microm diamond and (3) a 30 pm diamond followed by a tungsten carbide finishing bur. As a reference, five specimens of each material were treated by Sof-Lex discs (3M). For quantitative surface evaluation, laser-stylus profilometry was used. Roughness parameters included average roughness (Ra) and profile-length-ratio (LR). Statistical analysis was performed with one- and two-way Anova and Scheffé post-hoc tests. Qualitative surface evaluation in SEM was performed at a tension of 25kV. Significant effects were found with both the composites and the finishing methods with respect to surface roughness (p < 0.001 for Ra and LR). A 30 microm diamond caused the greatest roughness on all composites, with Ra ranging from 2.015-2.079 microm (p<0.001). After finishing using methods 2 and 3, the Solitaire surfaces were significantly smoother (p < 0.001 for LR). The lowest roughness values were achieved after using disks; again, the Solitaire specimens yielded the lowest Ra and LR values (p < 0.001 except for Sure-Fil). With scanning electron microscopy, surface areas with signs of destruction were found after using a 30 microm diamond on Definite specimens.

Analysis of Variance↗