Casting accuracy of experimental Ti-Cu alloys.
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The purpose of the present study was to investigate the casting accuracy and the dimensional change of experimental titanium-copper alloys (3.0 and 5.0 mass% Cu; hereafter, only "%" will be used) and to compare the findings with those of pure titanium. Castings were made using an argon-arc melting/pressure difference-casting unit. The fit of the metals cast in both full crown and MOD inlay dies was evaluated by measuring the distance between the shoulder margin and the cervical shoulder of the die. The changes in the inner diameter of castings were determined. In addition, surface roughness measurements inside the castings were carried out using a conventional profilometer, and thermal expansion measurements were made on cast cylindrical specimens using a differential dilatometer. There were no significant differences in dimensional change between pure titanium and the titanium-copper alloys. The fit of the titanium-copper alloys was inferior to pure titanium. The results of surface roughness measurements showed significance differences between the roughness of the pure titanium and titanium-copper alloys. (+info)
Disposition of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in bile duct-cannulated rats: stereoselective metabolism and tissue distribution.
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4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is a chiral compound, and the primary metabolite of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a major carcinogen in tobacco smoke. The goal of the present work was to study the pharmacokinetics and stereoselective metabolism and tissue retention of NNK and NNAL in the rat. Groups of rats were dosed with [5-(3)H]NNK (n = 3) or racemic [5-(3)H]NNAL (n = 3) at a target dose of 8.45 micromol/kg and were killed at selected time points for tissue collection. Separate groups of rats (n =5 per group) received the same dose of either NNK or NNAL and serial sampling of blood, bile and urine was carried out over 24 h. All samples were analyzed by C(18) reversed-phase HPLC with gradient elution and radioflow detection. A gas chromatograph-thermal energy analyzer (GC-TEA) was used to separate the (R)-/(S)-NNAL enantiomers. Racemic NNAL and NNK had large volumes of distribution (321 +/- 137 ml for NNK and 2772 +/- 1423 ml for NNAL) and similar total body clearances (12.8 +/- 2.0 ml/min for NNK and 8.6 +/- 2.6 ml/min for NNAL). The results indicated that the enantiomers of NNAL are stereoselectively metabolized and excreted. The glucuronide of (R)-NNAL, ((R)-NNAL-Gluc) was identified as the major metabolite in the bile after administration of either NNK or NNAL. (R)-NNAL was the major NNAL enantiomer in the bile or urine samples. At 24 h after racemic NNAL administration, NNAL comprised an average of 75.4% of total radioactivity in the lung with an (S)-/(R)-ratio of >20. The stereoselective localization of (S)-NNAL to lung tissue may contribute to the lung selectivity of NNK carcinogenesis. The present studies suggest a need to look beyond metabolic activation as the sole mechanism for lung carcinogenesis. (+info)
A resin veneer for enamel protection during orthodontic treatment.
(11/61)
The aims of this study were to test the tensile bond strength of a recently developed veneer. Sound premolar teeth (120) extracted for orthodontic purposes were divided into two experimental and two control groups. In one experimental group (V1) 4-META/MMA-TBB resin (4META) was used on the surface veneer prepared with micro particle filled resin (MFR) as an adhesive for bracketing and in the second group (V2) 4META was applied on the surface veneer with the trial resin. For the controls, in group R 4META was used on the enamel surface without veneer and in group G light-cured glass ionomer cement was applied. The 30 samples in each group were divided into three groups of 10 samples and thermal cycled (TC) at 3000, 10,000 or left uncycled. Tensile testing was carried out using an Instron machine. After tensile testing the bond failures in the experimental groups were recorded using a stereomicroscope. Statistical analysis was performed using ANOVA. In group V2 the resin veneer was able to maintain sufficient bond force to enamel during clinical use. The bond strength of group V1 was significantly higher than that of groups R (P < 0.05) and G (P < 0.01) at TC 0, but for both TC 3000 and 10,000, the bond strength of group V1 was lower than groups R and G, respectively. There were significant differences between groups V1 and R (P < 0.01) for TC 3000, and between groups V1 and R and G (P < 0.01) at TC 10,000. The bond strength of group V2 was almost equal to that of group R at TC 0. At TC 3000, group V2 showed significantly lower bond strength than group R (P < 0.05), but no significant difference was found compared with group G. At TC 10,000, there were no significant differences between groups V2, R or G. When comparing groups V1 and V2, the bond strength of group V1 was significantly higher than that of group V2 (P < 0.01) at TC 0, but the bond strength of group V1 was significantly lower than that of group V2 for both TC 3000 (P < 0.05) and TC 10,000 (P < 0.01). Comparison between groups R and G, showed that the bond strength of group R was significantly higher than that of group G for both TC 0 (P < 0.01) and TC 3000 (P < 0.01), but no significant difference was found for TC 10,000. In group V2, nine samples showed adhesive failure between the veneer surface and bracket adhesive before thermal cycling. There were significant differences between the MFR and both trial resin and glass ionomer cement (P < 0.01) when examining thermal expansion. No significant difference was found between the trial resin and glass ionomer cement. It is suggested that application of a resin veneer prior to bracket bonding is suitable for clinical application to protect the teeth and to prevent decalcification and caries. (+info)
Elucidation of solid-state complexation in ground mixtures of cholic acid and guest compounds.
(12/61)
The solid-state complexation between cholic acid (CA) and either methyl p-hydroxybenzoate (MPB) or ibuprofen (IBP) was investigated. Powder X-ray diffractometry, IR spectroscopy and thermal analysis suggested the complex formation between CA and MPB as well as between CA and IBP by co-grinding method. The stoichiometry of CA-MPB was 1 : 1 while that of CA-IBP was 2 : 1, reflecting the effect of guest size on complex formation. The guest compounds were assumed to be included in the channel of complexes formed by hydrogen bonds among CA molecules. (+info)
The effect of alkylpolyglycoside surfactants on the crystallization of spray-dried salbutamol sulphate: a GravimetricNear-Infrared Spectroscopy Study.
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This study monitored the effect of a series of structurally related surfactants on the crystallization of amorphous salbutamol sulphate. Amorphous salbutamol sulphate was prepared by spray drying from a solution in water and in the presence of various alkylpolyglycosides (APGs) at different concentrations. The particles were then analyzed using isothermal microcalorimetry and water vapor sorption (Dynamic Vapour Sorption, DVS) analysis combined with near-infrared spectroscopy (DVS-NIR). Both isothermal microcalorimetry and DVS-NIR were able to detect the transition from the amorphous to the crystalline state. The presence of APG surfactants modified the shape of the crystallization peak obtained using isothermal microcalorimetry. The gravimetric study combined with NIR revealed that while the crystallization was similar for the particles with or without surfactant, there was a great difference in the release of water from the newly formed crystal. In the presence of some of the surfactants tested, salbutamol sulphate released the water much faster than in the absence of surfactant. These results helped to explain the differences found in the isothermal microcalorimeter data. Differences were observed in the shapes of the NIR water peaks related to water due to the presence of the surfactant. In conclusion, the use of DVS combined with NIR has helped to analyze and understand the effect of APGs on the crystallization of amorphous salbutamol sulphate. (+info)
Physicochemical stability of cimetidine amorphous forms estimated by isothermal microcalorimetry.
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The effect of humidity on the physicochemical properties of amorphous forms of cimetidine was investigated using differential scanning calorimetry, isothermal microcalorimetry, and x-ray diffraction analysis. Amorphous forms were obtained by the melting (amorphous form M [AM]) and the cotton candy (amorphous form C [AC]) methods. Thermal behaviors of AM and AC with or without seed crystals were measured using an isothermal microcalorimeter under various conditions of relative humidity (RH) and temperature, respectively. The crystallization kinetics of amorphous solids was analyzed based on 10 kinds of solid-state reaction models. AM transformed into form A at 11% RH, 50 degrees C but transformed into a mixture of form A and monohydrate at 51% and 75% RH at 25 degrees C. The mean crystallization times (MCTs) of the heat flow curve of AM and AC at 11% RH, 50 degrees C were 47.82 and 32.00 hours, respectively, but at 11% RH, 25 degrees C both were more than 4320 hours. In contrast, AC transformed into form A under all storage conditions. The MCTs of AC at 51% and 75% RH were 29.61 and 11.81 hours, respectively; whereas the MCTs of AM were 46.79 and 15.52 hours, respectively. The crystallization of amorphous solids followed the three-dimensional growth of nuclei (Avrami equation) with an induction period (IP). The IP for AM at 11% RH, 50 degrees C was more than 2 times that for AC, but the difference in the crystal growth rate constant (CR) between AC and AM was within 10%. The IP for AM at 75% RH, 25 degrees C was reduced to only 10% of the IP at 51% RH with increasing humidity, but the CR did not change significantly. In contrast, the IP for AC was slightly reduced at 75% RH compared with 51% RH, but the CR was about 5 times greater. At 75% RH, 25 degrees C, the IP and CR of AM were about one-fourth the values of AC. This result suggests that the crystallization process consists of an initial stage during which the nuclei are formed and a final stage of growth. (+info)
Development of casting investment preventing blackening of noble metal alloys part 3. Effect of reducing agent addition on the strength and expansion of the investments.
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Different reducing agents (B, Al, Si and Ti) were individually added to two gypsum-bonded investments to prepare investments preventing surface blackening of some noble cast alloys. The effect of different additive contents on green-body and burnout compressive strength, setting and thermal expansion of the investments were evaluated. The strength and expansion of the investments were changed by the additives. The compressive strength of Al-, Si- and Ti-added investments decreased with the increase of additive contents. The burnout strength of B-added investments significantly increased while green-body strength remained unchanged. The setting expansion of the B-added investments increased while those of the Al-, Si- and Ti-added investments decreased with the increase of additive contents. The thermal expansion of the Si- and Ti-added investments decreased, and that of the Al- and B-added investments remained unchanged. Further study is necessary to evaluate the effects of these additives on the accuracy of dental castings. (+info)
Gypsum-bonded investment and dental precision casting (III) Composition of investment for the quick casting technique.
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A simultaneous differential thermal analysis and thermogravimetry method previously established was used to estimate the composition of gypsum-bonded investment marketed for the quick casting technique. Three commercial investments of this type were heated to 700 degrees C at 10 degrees C/min and the hemihydrate content was estimated by the mass decrease reached at 300 degrees C after subtracting the mass decrease at 100 degrees C as moisture content. The hemihydrate contents were between 25% and 30%, which appears to be the range also chosen for the conventional gypsum-bonded investment of cristobalite type over 70 years by the industry. However, the new type of investment contained both cristobalite and quartz. The small sample size is a disadvantage of the present method but this can be overcome by more frequent use of the method by investigators. (+info)