Effects of cholesterol reduction on BP response to mental stress in patients with high cholesterol

Rotating instruments are becoming increasingly significant in the scaling and planing of the root surface. The objective of this in vitro study was to test various root-planing instruments on extracted teeth and then to compare the treated surfaces using scanning electron microscopy. Two manual instruments (scaler and curette) and five mechanically rotating instruments (Desmo-Clean; Perio-Set; Viking-Set; and 40-microns and 15-microns diamond finishers) were investigated. From a total of 42 teeth, six root surfaces were treated with each instrument. The results confirm the clear superiority of the manual instruments (especially the curette). The manual instruments permit good root planing with minimum ablation from the root surface and only a thin smear layer (a compound of grinding dust, dentinal fluid, and water). The best planing results by rotating instruments were achieved with the Desmo-Clean and the 15-microns diamond finisher, whose performance was almost equal to that of the manual instruments. The rotating instruments, however, were associated with higher ablation and a marked smear layer. Manual instruments remain the media of choice on easily accessible root surfaces; however, rotating instruments are of advantage in inaccessible areas (eg, furcations) because of their handling properties.     

Historical development of whiteners: clinical safety and efficacy

Trimming composite restorations includes gross removal of excess material, contouring, and finishing. Many surfaces such as the lingual surface of anterior teeth or the occlusal surfaces of posterior teeth require the use of rigid rotating instruments. The purpose of our study was to assess the suitability of eight finishing diamonds, five tungsten carbide finishing burs, and one ceramically coated finishing instrument for trimming a small-particle hybrid composite material. A total of 70 specimens of Herculite XRV were treated with the different finishing instruments under simulated practice conditions, and surface roughness was recorded quantitatively using an optical laser pick-up. The resulting surfaces were examined qualitatively with the help of scanning electron microscopy (SEM). Cutting efficiency of the diamonds and burs was evaluated at a constant pressure of 2.5 N using 42 additional specimens of Herculite XRV. Significant differences were calculated using one-way ANOVA and pairwise contrasts by Tukey's multiple range test. The results showed that finishing diamonds were characterized by high cutting efficiency and relatively rough corresponding composite surfaces, whereas tungsten carbide finishing burs led to smooth composite surfaces but had little cutting efficiency. For gross removal and contouring of composite restorations, a 15-40 microns finishing diamond is recommended followed by a tungsten carbide bur for finishing the restoration.     

Saccadic eye movement related scalp potentials--scalp distribution of presaccadic slow negative potential

This study compared the effects of various rotary instruments and polishing agents on tooth enamel. Topographical features of enamel were studied at consecutive stages of polishing with photoanalysis of scanning electron micrographs. The results indicate that enamel modified by diamond burs may be polished to produce the smoothest surface with white finishing stones, Ceramist finishing points, and flour of pumice.     

Scanning electron microscopic evaluation of different endodontic procedures on dentin morphology of human teeth

Four manual endodontic instruments, an ultrasonic and an endosonic system were studied with a view to evaluating the morphology of the smear layer and the amount of debris and pulpal residues in the apical third of human extracted straight teeth from 55- to 75-yr-old patients. The manual instruments were K files, Ergoflex files used with the step-back technique, Canal Master with its own technique, and Flex-R with the Roane technique. The ultrasonic system was Suprasson Piezo and the endosonic was Excalibur. Human extracted teeth with straight canals were used and examined under a scanning electron microscope. All manual instrumentations showed a homogeneous compact smear layer and no pulp residues. No statistical differences were observed among the four manual techniques. Ultrasonic technique showed the complete removal of the smear layer, leaving small amounts of pulp debris at the apical third, while the Excalibur showed an almost complete elimination of the smear layer, leaving a homogeneous layer of pulpal residues along the canal.     

金刚石工具胎体材料中碳化物形成元素的行为

研究了金刚石胎体材料中的碳化物形成元素(Cr,Ti,W)与石墨和金刚石之间的粘结行为。结果表明,碳化物形成元素与石墨或金刚石发生反应而形成碳化物层。通过碳化物层,胎体材料与金刚石之间产生冶金结合。Co基和Cu基胎体材料中加入Cr可提高胎体对金刚石的粘结强度,Cr对Co基胎体本身也有固溶强化作用。W对金刚石有一定粘结作用。     

Biosensor development

OBJECTIVES: This study compared the surface topography of roots resected with #57, Lindeman, and Multi-purpose burs. Further comparisons were made after refinements with either a multifluted carbide or an ultrafine diamond finishing bur. STUDY DESIGN: Three groups of single-rooted human teeth were resected with each resection bur, and resin replicas of the root ends were made. Root ends from each resection bur group were finished with either a multifluted carbide or an ultrafine diamond finishing bur, and the root ends were replicated. All replicas were evaluated at a magnification of x20 for smoothness and surface irregularities. Data analysis was done with the Wilcoxon signed rank test and the chi-square test at a significance level of p < 0.05. RESULTS: The Multi-purpose bur produced a smoother and more uniplanar surface than the #57 bur and caused less damage to the root than either the #57 or the Lindeman bur. The multifluted carbide finishing bur tended to improve the smoothness of the root end, while the ultrafine diamond tended to roughen the surface. CONCLUSIONS: The Multi-purpose bur produced the smoothest and most uniplanar resected root-end surface with the least root shattering. The multifluted carbide finishing bur produced a smoother surface than the ultrafine diamond bur.     

Wear resistance of polycrystalline diamond cutters for drill bits

In the present work, the wear resistance of GES 1313 polycrystalline diamond (PCD) cutters (produced by E6), which are cylindrical in form (diameter 13.44 mm, height 13 mm), in turning granite and abrasive wheels at different speeds is investigated. The optimal cutting speed is determined, and comparative data are obtained for the cutting of Mansurovsk granite and 64C (SiC) abrasive wheels, so as to develop recommendations regarding the test conditions for PCD cutters. The wear resistance is characterized in two ways: as the ratio of the loss of volume of the diamond layer to the volume of machined material removed (when it is a dimensionless number); or by the quantity of machined material removed with a fixed degree of cutter wear (when it is expressed in cm³ with respect to 1-mm wear of the rear surface). In cutting granite, the cutting speed varies from 80 to 320 m/min; in cutting abrasive wheels, the cutting speed is 500 m/min. To calculate the volume of the PCD cutters, 3D models of the worn sections are constructed by means of Kompas 3D software, and a calibration curve for determining the volume of material removed by wear at the rear surface of the PCD cutters is plotted. The cutting angle is–22°. The change in volume of the worn section of the PCD cutter with change in the cutting angle from–20 to–25° is less than the measuring precision of the wear area up to 0.8-mm blunting. Increase in speed from 80 to 160 m/min in cutting granite reduces the wear resistance of the PCD cutters by a factor of 12. The relative wear of the PCD cutters in cutting granite is (0.01–0.02) × 10–6, which is 20 times less than in cutting 64C abrasive wheels. The relative wear of the PCD cutters in cutting abrasive wheels does not depend on the blunting of the rear surface up to values of 1.4 mm. This method may be recommended for rapid determination of the wear resistance of PCD. The proposed method of calculating the worn volume of the PCD by means of Kompas 3D or other appropriate software may be used to assess the relative wear resistance of abrasives and cutting materials.     

Epitaxial overgrowth of apatite crystals on the thin-ribbon precursor at early stages of porcine enamel mineralization

The aim of the present work was to investigate changes in cross-sectional morphologies of enamel crystallites as a function of location in secretory porcine enamel. Enamel tissues were obtained from 5- to 6-month-old slaughtered piglets. For examination by electron microscopy, a portion of the secretory enamel was embedded in resin and ultrathin sections were prepared with a diamond knife. In parallel studies, compositional and structural changes of enamel mineral were assessed by chemical analysis and Fourier transform infrared (FTIR) spectroscopy. For this purpose, two consecutive layers of the outer secretory enamel, each approximately 30 microns thick, were separated from the labial side of permanent incisors. Using high-resolution electron microscopy, early events of enamel crystal growth were characterized as the epitaxial growth of small apatite units on the lateral surfaces of the initially precipitated thin ribbon. These apatite units had regular triangle or trapezoid cross-sections. After fusions of those isolated trapezoids on both lateral sides of the platy template, the resulting enamel crystallites had the well-documented flattened-hexagonal shapes in cross-sections. The initially precipitated thin plate was buried inside the overgrown apatite lamella and then retained as a central dark line. Similar morphological evidence for the epitaxial nucleation and overgrowth of carbonatoapatite on the platy template was obtained in vitro. Chemical and FTIR analyses of the enamel layer samples showed that the characteristics of the youngest enamel mineral were distinct from those of enamel crystals found in older secretory enamel.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tribotechnical characteristics of polymer composites reinforced with fibrous structures

Studies have been made on the effects of the nature, textile structure, and strength characteristics of fibrous reinforcement and on hybrid reinforcement, nature of the polymer matrix, and the addition of ultrafine diamond powder on the coefficient of friction and wear of a polymer composite containing a thermoreactive matrix. The tests were performed in air without lubricant with an insert-shaft pair scheme with counterbody composed of chromed cast iron and with a ceramic counterbody (boron carbide, silicon carbide and nitride) at sliding speeds of 5, 10, and 15 m/sec and pressure 0.5 MPa. Glass plastics show more wear than carbon plastics on reinforcements with woven or knitted structures. The carbon plastics have tribotechnical properties at the level of the best ones. The ultrafine diamond powder substantially reduced the wear. The best tribotechnical properties occurred with the friction pair carbon-glass plastic against silicon nitride.     

Tribotechnical characteristics of polymer composites reinforced with fibrous structures

Studies have been made on the effects of the nature, textile structure, and strength characteristics of fibrous reinforcement and on hybrid reinforcement, nature of the polymer matrix, and the addition of ultrafine diamond powder on the coefficient of friction and wear of a polymer composite containing a thermoreactive matrix. The tests were performed in air without lubricant with an insert-shaft pair scheme with counterbody composed of chromed cast iron and with a ceramic counterbody (boron carbide, silicon carbide and nitride) at sliding speeds of 5, 10, and 15 m/sec and pressure 0.5 MPa. Glass plastics show more wear than carbon plastics on reinforcements with woven or knitted structures. The carbon plastics have tribotechnical properties at the level of the best ones. The ultrafine diamond powder substantially reduced the wear. The best tribotechnical properties occurred with the friction pair carbon-glass plastic against silicon nitride.     

Structural transformations in titanium carbide during diamond grinding

Mechanically polished surfaces of sintered titanium carbide specimens are studied by scanning electron microscopy, Auger-electron spectroscopy, and electron diffractometry. It is shown that surface layer microplastic deformation occurs during polishing of specimens with diamond powder. This deformation leads to transformation of the FCC-lattice of titanium carbide into the structural polytype 6H. Georgian Technical University, Tbilisi. Republican Center for Structural Studies, Tbilisi. Translated from Poroshkovaya Metallurgiya, Nos. 5-6(407), pp. 91–97, May–June, 1999.     

Extracellular proteolysis alters tooth development in transgenic mice expressing urokinase-type plasminogen activator in the enamel organ

By catalyzing plasmin formation, the urokinase-type plasminogen activator (uPA) can generate widespread extracellular proteolysis and thereby play an important role in physiological and pathological processes. Dysregulated expression of uPA during organogenesis may be a cause of developmental defects. Targeted epithelial expression of a uPA-encoding transgene under the control of the keratin type-5 promoter resulted in enzyme production by the enamel epithelium, which does not normally express uPA, and altered tooth development. The incisors of transgenic mice were fragile, chalky-white and, by scanning electron microscopy, their labial surface appeared granular. This phenotype was attributed to a defect in enamel formation during incisor development, resulting from structural and functional alterations of the ameloblasts that differentiate from the labial enamel epithelium. Immunofluorescence revealed that disorganization of the ameloblast layer was associated with a loss of laminin-5, an extracellular matrix molecule mediating epithelial anchorage. Amelogenin, a key protein in enamel formation, was markedly decreased at the enamel-dentin junction in transgenics, presumably because of an apparent alteration in the polarity of its secretion. In addition, increased levels of active transforming growth factor-beta could be demonstrated in mandibles of transgenic mice. Since the alterations detected could be attributed to uPA catalytic activity, this model provides evidence as to how dysregulated proteolysis, involving uPA or other extracellular proteases, may have developmental consequences such as those leading to enamel defects.     

Some features of cutting tool wear in finish machining of low-porosity alloy powder metallurgy steels

Conclusions The presence in powder metallurgy steels being machined of voids even in an insignificant quantity has a significant influence on the amount and character of wear of the cutting tool. Even a decrease in residual porosity to 0.5% provides a significant increase in cutter life.In connection with the fact that the character of wear of sintered carbide cutters in machining of low alloy powder metallurgy is primarily adhesive, VK8 cutters, which have higher cyclic impact strengths, have the best life.As tool materials in machining of powder metallurgy steels at cutting speeds of more than 200 m/min it is desirable to use mineral ceramic materials.Translated from Poroshkovaya Metallurgiya, No. 2(254), pp. 74–79, February, 1984.     

Pathway and speed of calcium movement from blood to mineralizing enamel

We studied by autoradiography the distribution of 45Ca in the enamel organ of frozen rats 4.3, 6.1, 7.8, 10.6 and 13.7 sec after an i.v. injection. The intercellular junctions of the proximal side of the smooth-ended ameloblast (SA) and the distal side of the ruffle-ended ameloblast (RA) were closed to calcium. The junctions of the distal side of SA, the proximal side of RA, and both sides of the secretory stage ameloblasts were not. The time required for calcium to pass through the ameloblast layer was less than 1.8 sec in the secretory stage and SA region. The time in the RA region was 3.5-6.3 sec. In the transitional region from RA to SA, a band of strong radioactivity appeared from the papillary layer of RA region towards the enamel of the SA region. The radioactivity in the secretory stage enamel increased almost linearly with time. The diffusion speed of calcium in the enamel was more than 50 microns for 1.8 sec in the maturation stage and less than 15 microns for 9.4 sec in the secretory stage. These results indicate that in the secretory and SA regions calcium moves to the enamel surface through the intercellular spaces of ameloblasts and in the RA region via RA cells.     

Structural investigations of diamond composites prepared by the infiltration of the diamond compact near the line of thermodynamic equilibrium of graphite with diamond

The structural order of diamond polycrystalline composite materials obtained by the infiltration of the diamond compact by nickel-silicon alloys at pressures up to 5.0 GPa and temperatures reaching 1800 K is investigated. It is established that they consist of a diamond skeleton and intercrystallite metal-ceramic binder. The diamond skeleton is formed from diamond grains of the starting size with weak diamond-diamond bonds, while the intergrain space is filled by diamond fragments and an intermetallic binder. The formation of carbide layers from silicon carbide on the surface of diamond grains determines the strength properties of diamond composites in general.     

提高硬质合金拉丝模寿命的研究进展

如何提高使用寿命是硬质合金拉丝模研究的重要方向.而模芯材质、内孔涂层和内孔结构设计是影响硬质合金拉丝模寿命的重要因素.由于硬质合金拉丝模存在耐磨性较差、寿命较短的缺点,本文从基体材质优化、涂层处理、内孔结构优化三个方向,介绍了提高其寿命的研究进展.通过以下方法可以有效地提高硬质合金拉丝模的使用寿命:低钴超细晶硬质合金,...     

Recent advances of high-pressure generation in a multianvil apparatus using sintered diamond anvils

The tried and tested multianvil apparatus has been widely used for high-pressure and hightemperature experimental studies in Earth science. As a result, many important results have been obtained for a better understanding of the components, structure and evolution of the Earth. Due to the strength limitation of materials, the attainable multianvil pressure is generally limited to about 30 GPa (corresponding to about 900 km of the depth in the Earth) when tungsten carbide cubes are adopted as second-stage anvils.Compared with tungsten carbide, the sintered diamond is a much harder material. The sintered diamond cubes were introduced as second-stage anvils in a 6-8 type multianvil apparatus in the 1980s, which largely enhanced the capacity of pressure generation in a large volume press. With the development of material synthesis and processing techniques, a large sintered diamond cube (14 mm) is now available. Recently,maximum attainable pressures reaching higher than 90 GPa (corresponding to about 2700 km of the depth in the Earth) have been generated at room temperature by adopting 14-mm sintered diamond anvils. Using this technique, a few researches have been carried out by the quenched method or combined with synchrotron radiation in situ observation. In this paper we review the properties of sintered diamond and the evolution of pressure generation using sintered diamond anvils. As-yet unsolved problems and perspectives for uses in Earth Science are also discussed     

刀片可转位机卡式硬质合金齿圆锯片的设计开发

以锯片的实际锯切工况为背景,为满足高钢级工件的锯切要求,在现有硬质合金锯片的基础上,开发了刀片可转位机卡式硬质合金齿圆锯片。锯片的片体通过特殊加工工艺加工出带有斜面的齿座或者通过增加垫片的方式形成锯齿的部分角度,刀片设计成四面刃的结构,并且进行涂层处理,二者通过机卡的方式连接,可解决高等级钢的锯切困难的问题。     

Composition dependence of mechanical properties of diamond segments

This research is devoted to studying the mechanical characteristics of diamond-drilling-tool matrix. The infiltration method at a temperature of 1100–1150°C for 15 min in hydrogen medium was used for making model diamond-containing and diamond-free samples of 24 × 7 × 8 mm matrices of two types differing in content of nickel and fused tungsten carbide, namely WC-Co-Cu (1) and WC-Co-Cu-Ni + cast tungsten carbide (2). A8K160 (500/400 μm), AC50 (500/400 μm), and SDB1125 (30/40 mesh, i.e., 600/425 μm) diamonds were used as diamond-filling materials with a concentration of 9 vol % in the matrix. The bending strength, hardness, density, porosity, and abrasive resistance of drilling tool matrix samples are measured. It is found that WC-Co-Cu-Ni matrix samples have higher hardness and abrasive resistance when compared with WC-Co-Cu, which is explained by the occurrence of nickel and solid particles of tungsten carbide solids in them. The introduction of diamonds in the matrices results in a substantial increase in their hardness (by 8–10 HRC units), which distorts the hardness measured data of matrices in the diamond layer of drill crowns.