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At least 649 records · Page 36Linked to original sources
PubMed2003

A pilot investigation of enamel reduction procedures.

OBJECTIVE: To test and describe the use of various combinations of mechanical and chemical techniques for enamel reduction to obtain a smooth surface. METHODS: Bovine teeth (2 surfaces on each of 32 teeth) were used. The teeth were mounted in blocks of dental plaster, which were then mounted in a vise. The mesiodistal enamel contact areas were reduced by various combinations of mechanical and chemical aids. The mesiodistal width of each tooth was measured with a digital caliper after initial reduction of the enamel surface and again after polishing. The teeth were subsequently prepared and mounted for scanning electron microscopy. RESULTS: All combinations yielded statistically significant enamel reduction (p < 0.05). The use of acid stripping in conjunction with mechanical procedures produced especially smooth enamel surfaces. CONCLUSIONS: Steps must be taken to ensure that a smooth enamel surface remains after enamel reduction and polishing. It is recommended that conventional enamel etchants be added to the polishing procedure. Enamel reduction can increase available space, but the quantity of enamel that can be removed without adverse consequences should be carefully evaluated.

Acid Etching, Dental↗
PubMed2002

[Spectrophotometric determination of vanadium(V) through the formation of a tungstovanadophosphate-TMBPS charge transfer complex].

A new spectrophotometric method was developed for the determination of vanadium(V). The method was based on the formation of tungstovanadophosphate-3,3',5,5'-tetramethylbenzidine-N-propanesulfonic (TMBPS) charge transfer complex. The spectrophotometric measurements were directly carried out at 450 nm and the apparent molar absorptivity was 2.74 x 10(4) L.mol-1cm-1. The linear range of the determination was 0.02-1 microgram.mL-1. The sensitivity was enhancement with a flotation-extraction preconcentration method and the apparent molar absorptivity was 3.10 x 10(5) L.mol-1cm-1.

Alkanesulfonic Acids↗
PubMed2000

[IR study on a series of tungsten clusters].

In this paper, the IR study on a series of tungsten clusters which contain a [W2S4]2+ or [W2MM'S4]4+ (M,M'=Cu,Ag) core is reported. According to the results of X-ray structural analysis and the IR spectra of the clusters, some characteristic IR absorptions of the clusters were assigned. The study of IR spectra of these clusters shows that the variation of structure can reflect on the IR spectra significantly.

Spectrophotometry, Infrared↗
PubMedDate not supplied

Comparison of two ultrasonic cleaning units for deterioration of cutting edges and debris removal on dental burs.

The effects of two ultrasonic cleaning units on surface deterioration and cleaning effectiveness of dental burs were compared in this study. The units tested were the Dextrex Model L 503B (Dextrex Chemical Industries, Inc., Bowling Green, KY) industrial ultrasonic unit and a conventional dental ultrasonic unit L & R T-21 B (L & R Manufacturing Co., Kearny, NJ). SEM photomicrographs of the burs were made before cleaning; and burs were processed for 10 min in each unit. Forty-eight new burs (24 #1/2A diamond and 24 #330 carbide) contaminated with human blood and 48 burs contaminated with tooth debris following cavity preparation were used to evaluate cleanliness. To assess deterioration, 48 new burs were evaluated for changes in the number of diamond chips or pits (carbide burs) and color changes following ultrasonic cleaning. Neither unit sufficiently cleaned the burs, as evidenced by remnants of remaining blood and debris on the burs. The loss of diamond chips was statistically significant for the burs processed in the Dextrex unit (P < 0.001) as well as for burs processed in the L & RT 21-B unit (P < 0.01). The mean number of pits was significant in carbide burs processed in both units as well (Dextrex unit: P < 0.01; L & RT-21 B unit: P < 0.001). No differences were noted in color changes for any of the burs in either unit. These data showed that the industrial-type unit was no more effective in cleaning dental burs than the conventional unit, though both units caused significant amounts of deterioration in the cutting surfaces.

Carbon↗
PubMed1992

Comparison of the Lowry and Coomassie Blue methods for the determination of protein concentration.

1. The Lowry and Coomassie Blue methods were compared for precision when applied to Schistosoma mansoni proteins, using bovine serum albumin (BSA) as standard. 2. The absorbance of five different concentrations was measured and the experiments were run in parallel to reduce bias in the comparison. Thus, for a given technique, all photometric data were obtained from reaction mixtures (BSA and test solutions) prepared and analyzed as simultaneously as possible. 3. To interpret the results, polynomial functions of different degrees--up to the third--were calculated to fit the absorbance values to the respective protein concentrations of BSA or worm protein present in the reaction mixtures, and the standard errors of all slopes were also calculated. 4. The protein concentration of worm extracts was calculated by two methods: 1) the ratio of the first-degree slopes of the polynomials applied to absorbance = f(x), with x being either mg BSA or ml worm extract, and 2) the utilization of the BSA function parameters to convert any worm absorbance value to protein concentration. 5. The results obtained with the slope ratio method were variable. However, the function method seemed to be reliable, especially when applied to Coomassie Blue data. When the results were derived from the BSA cubic function the concentration of soluble worm protein was calculated with a coefficient of variation of 1.20%.

Animals↗
PubMed1992

Multi-element follow up in biological specimens of hard metal pneumoconiosis.

The movement of Co and the other components of the hard metal in the body fluids, their solubility, their links to the cells and proteins of the body, and their clearance are largely unknown. The first aim of this work is to evaluate whether Neutron Activation Analysis (NAA), a new analytical technique based on the radiochemical separation of samples irradiated in a Nuclear Reactor, may be suitable for studying the movement of elements in tissues or body fluids of workers over time. We have investigated seven hard metal workers, all employed in the grinding process, with NAA studies (single study in two, follow-up in five) of 29 elements on lung tissue, BAL fluid, blood, urine, pubic hair, toenails and sperm. In three, the diagnosis of hard metal pneumoconiosis was easy; in the other four, due to evident bilateral hilar lymphadenopathy, it was difficult to distinguish between pneumoconiosis and sarcoidosis stage II, and the final diagnosis, after pulmonary biopsy, was hard metal pneumoconiosis in three, and sarcoidosis in one. In spite of high potential, NAA gives a number of unexpected results, with apparent controversies and no clear relationship in the evolution of levels of Co, W and Ta: there is no simple explanation for such apparent inconsistencies at present, so that the study of the movement of elements in body fluid sometimes appears disappointing with this technique. Other observations were noted from the data available: 1) the concentration of elements (Co, Ta, W) in lung tissue is far higher than in BAL fluid, but the factor is so variable that BAL fluid cannot be taken as representative of the concentration of elements in lung tissue. 2) High concentrations in tissues or body fluids are indicative for exposure, but not for disease. In the light of available data, there are no levels above which development of disease is inevitable. 3) When the problem is to distinguish between sarcoidosis and pneumoconiosis in exposed subjects, the concentration of elements is of no value, and the pulmonary biopsy is still necessary. However a NAA study may be helpful to confirm the presence of the offending agent, and to avoid pulmonary biopsy in cases where the occupational history is unclear.

Adult↗
PubMedDate not supplied

Finishing tooth-colored restorations in vitro: an index of surface alteration and finish-line destruction.

Many studies have evaluated the surface characteristics of finishing and polishing instruments on different restorative materials using two- and three-dimensional models based on mechanical and optical techniques. However, only limited data are available regarding the problem of marginal causing detectable surface alterations such as scratches or grooves may also cause marginal damage. This study aimed to correlate the smooth-surface polishing efficacy of different instruments with their potential for destructive effects on restoration margins and enamel finish lines. An index was created that will help to evaluate future polishing instruments and select suitable ones for different clinical situations. A planar inlay system with a 100 microm wide defined gap was simulated in vitro. Pre-fabricated ceramic (n = 40) and composite blocks (n = 40) were connected to bovine enamel without luting material. After standardized pre-polishing, mean surface roughness and marginal quality were assessed using a profilometer and scanning electron microscopy (SEM). Enamel and restorative surfaces were colored, and subsequently prepared using one of 10 different finishing and polishing instruments. Four specimens per instrument and material were evaluated, resulting in eight interfaces for each test group. Surface roughness (Ra) and marginal quality (expressed as the percentage fracture-free margin) were measured and compared statistically using unpaired t-tests and two-way ANOVA, respectively. The level of significance was set at 0.05 Eight-micrometer diamond burs and 40-fluted tungsten carbide finishers produced smoother surfaces and less finishing-line destructions than the other instruments under evaluation. The index values developed will prove helpful in evaluating and selecting appropriate instruments.

Analysis of Variance↗