Comparison of the fracture resistances of pulpless teeth restored with a cast post and core or carbon-fiber post with a composite core

Amphetamine and methamphetamine are commonly abused central nervous system stimulants. We describe a rapid new derivatization of amphetamine and methamphetamine using 2,2,2-trichloroethyl chloroformate for gas chromatography-mass spectrometric analysis. Amphetamine and methamphetamine, along with N-propyl amphetamine (internal standard), were extracted from urine using 1-chlorobutane. The derivatization with 2,2,2-trichloroethyl chloroformate can be achieved at room temperature in 10 minutes. The electron ionization mass spectrum of amphetamine 2,2,2-trichloroethyl carbamate showed two weak molecular ions at m/z 309 and 311, but showed diagnostic strong peaks at m/z 218, 220, and 222. In contrast, chemical ionization of the mass spectrum of amphetamine 2,2,2-trichloroethyl carbamate showed strong (M + 1) ions at m/z 310 and 312 and other strong diagnostic peaks at m/z 274 and 276. The major advantages of this derivative are the presence of a diagnostic cluster of peaks due to the isotopic effect of three chlorine atoms (isotopes 35 and 37) in the derivatized molecule and the relative ease of its preparation. We also observed strong molecular ions for derivatized methamphetamine in the chemical ionization mass spectrum, but the molecular ions were very weak in the electron ionization mass spectrum. We used the scan mode of mass spectrometry in all analyses. When using a urine standard containing 1,000 ng/mL of amphetamine (a 7.4-micromol/L concentration) and methamphetamine (a 6.7-micromol/L concentration), the within-run precisions were 4.8% for amphetamine and 3.6% for methamphetamine. The corresponding between-run precisions were 5.3% for amphetamine and 6.7% for methamphetamine. The assay was linear for amphetamine and methamphetamine concentrations of 250 to 5,000 ng/mL (amphetamine, 1.9-37.0 micromol/L; methamphetamine, 1.7-33.6 micromol/L). The detection limit was 100 ng/mL (amphetamine, 0.74 micromol/L; methamphetamine, 0.67 micromol/L) using the scan mode of electron ionization mass spectrometry. We observed good a correlation between the concentrations of amphetamine and methamphetamine in five urine specimens positive for amphetamines using the more conventional pentafluoropropionyl derivative and our new derivative using 2,2,2-trichloroethyl chloroformate.     

Evolution of post and core systems

In order to obtain a useful index that can predict the effectiveness of steroid therapy in IgA nephropathy, we investigated the relationship between steroid therapy and extracapillary change. We analysed 51 cases consisting of a group of 24 cases in which steroid was administered (initial dose: prednisolone 20-60 mg/day orally, or pulse therapy), and a group of 27 cases in which steroid was not administered. First of all, we compared these two groups in terms of a clinical improvement rate over 3, 12 and 60-month-periods after the therapy, respectively. It was found that steroid therapy led to a higher improvement rate (p < 0.01-0.05), indicating that steroid is effective for IgA nephropathy. Among the group undergoing steroid therapy, the frequency of cellular crescents (C) was significantly higher (p < 0.05-0.01) in the cases in whom steroid was effective and that of fibrous crescents or adhesion (F) was significantly lower (p < 0.05-0.01). We then assessed C/F in each case of the steroid-administered group, and studied its relationship with the improvement rate. As a result, the improvement rate was below 50% in the group of C/F < 0.25, over 50% of the group of 0.25 < or = C/F < 0.75, and 100% of the group of 0.75 < or = C/F. Accordingly, we concluded that C/F could be used a parameter for predicting the effectiveness of steroid therapy in IgA nephropathy and for determining indications for steroid therapy.     

Porcelain-fused-to-metal post and core: an esthetic alternative

Custom cast metal post and cores used to retain all-ceramic restorations are indicated in endodontically treated teeth when little clinical crown remains. The metal cores of these post and core restorations block light transmission and create a graying effect when used in support of all-ceramic restorations. This article describes a technique to minimize this effect using custom cast porcelain-fused-to-metal post and cores to achieve a more natural esthetic result.     

Comparison of the torsional forces at failure for seven endodontic post systems

Resistance to torsional forces is critical in restoration of endodontically treated teeth. Seven post designs (Flexi-Post, Flexi-Flange, Para-Post, AccessPost, World Post, Vlock, and Dentatus posts) were cemented in roots of natural teeth with zinc phosphate and Flexi-Flow cements, which resulted in 11 different groupings that were subjected to torsional forces in a clockwise direction. In addition, clockwise and counterclockwise torque was applied to the Flexi-Post and Flexi-Flange systems cemented with zinc phosphate and Flexi-Flow cements. A total of 150 samples were prepared, and groups for this study were: group 1, Flexi-Post/zinc phosphate clockwise and counterclockwise; group 2, Flexi-Post/Flexi-Flow clockwise and counterclockwise; group 3, Flexi-Flange/zinc phosphate clockwise and counterclockwise; group 4, Flexi-Flange/Flexi-Flow clockwise and counterclockwise; group 5, Para-Post/zinc phosphate clockwise; group 6, AccessPost/zinc phosphate clockwise; group 7, AccessPost/Flexi-Flow with grooved dentin clockwise; group 8, World Post/zinc phosphate clockwise; group 9, World Post/Flexi-Flow with grooved dentin clockwise; group 10, Vlock Post/zinc phosphate clockwise; and group 11, Dentatus post/zinc phosphate clockwise. Torsional forces for the groups ranged from 17 ounce-inches (Dentatus/zinc phosphate) to 81 ounce-inches (Flexi-Post/zinc phosphate). Flexi-Post and Flexi-Flange threaded posts exhibited statistically greater resistance to torsional forces. Analyses were computed with one-way and three-way analysis of variance followed by Duncan's multiple range test. Duncan's multiple range test indicated that Flexi-Post/zinc phosphate/clockwise was similar to Flexi-Post/Flexi-Flow/clockwise and that both had significantly higher torque levels than the other treatment conditions in the clockwise direction (p 0.0001). Dentatus/zinc phosphate/clockwise had significantly lower torque levels than the other treatment conditions (p 0.031).     

Terfenol-D/PMNT/Terfenol-D层状磁电复合材料的磁电效应分析

从压电效应和压磁效应本构方程出发,建立了层状磁电复合材料的1-3模型,结合材料机械运动学方程和电路状态方程,推导出层状磁电复合材料的磁-机-电等效电路,并全面分析磁电转换效应.既而提出新型层状磁电复合材料terfenol-D/PMNT/Terfeno1-D,以提出的1-3模型为例,对此材料的磁电响应进行数值计算,用Matlab仿真得出计算结果,从而得出该结构的层状磁电复合材料的磁电转换系数要高于市场上广泛使用的Terfenol-D/PZT/Terfenol-D复合材料的磁电转换系数,为新型磁电材料的制备提供理论依据.     

A fiber fracture model for metal matrix composite monotape consolidation

The consolidation of plasma sprayed monotapes is emerging as a promising route for producing metal and intermetallic matrix composites reinforced with continuous ceramic fibers. Significant fiber fracture has been reported to accompany the consolidation of some fiber/matrix systems, particularly those with creep resistant matrices. Groves et al. [Acta metall. mater.42, 2089 (1994)] determined the predominant mechanism to be bending at monotape surface asperities and showed a strong dependence of damage upon process conditions. Here, a previous model for the densification of monotapes [Elzey and Wadley, Acta metall. mater.41, 2297 (1993)] has been used with a stochastic model of the fiber failure process to predict the evolution of fiber fracture during either hot isostatic or vacuum hot pressing. Using surface profilometer measured roughness data for the monotapes and handbook values for the mechanical properties of different matrices and fibers, this new model is used to elucidate the damage dependence on process conditions, monotape surface roughness, and the mechanical properties both of the fiber and matrix. The model is used to investigate the “processibility” of several currently important matrix and fiber systems and to identify the factors governing this. An example is also given of its use for the simulation of a representative consolidation process cycle. This approach to the analysis of a complex, nonlinear, time-varying process has resulted in a clear understanding of the causal relationships between damage and the many process, material and geometric variables of the problem and identified new strategies for its elimination.     

钢纤维对摩擦材料性能的影响

树脂基复合材料性能优异,被大量用做汽车制动材料.以酚醛树脂为基体,钢纤维为增强纤维,添加填料,采用热压法制成刹车片,并进行摩擦试验.通过试验研究了酚醛树脂基复合材料中钢纤维不同添加量(质量分数)对复合材料冲击强度、摩擦性能的影响.结果表明:该配方类型中,在100～300℃温度范围内,材料冲击强度先增大后减小,钢纤维质量分数为24%时为转折点;材料的摩擦系数先增大后减小,钢纤维质量分数为26%时为转折点;磨损率随钢纤维添加量的增加而增大,钢纤维最佳添加量为24%～26%.     

Effects of oxidation on the fatigue crack growth resistance and the interfacial properties of a Ti-MMC laminate composite

Fatigue crack growth rates in a [0/90]_2s Ti-6Al-4V/SCS-6 cross-ply laminate, correlated with push-out tests, have been measured to assess the effects of varying test temperature, environment, load ratio (R), and initial stress intensity factor range (ΔK). The fatigue crack growth resistance is degraded in tests at 450 °C in air, but tests carried out at test temperatures of up to 450 °C under vacuum, both at R=0.1 and R=0.5, have shown crack arrest/catastrophic failure transitions (CA/CF), which are similar to those observed for specimens studied at room temperature and at 300 °C in air. Moreover, for such [0/90] composites, the critical role of intact 0 deg fibers bridging in the crack wake, in promoting fatigue crack growth resistance, has been confirmed. Sudden increases of fatigue crack growth rate can be attributed to individual fiber failure(s), which were detected by acoustic emission techniques. The effect of the experimental conditions (environment, test temperature, and duration) on the mechanical behavior (fatigue crack growth rate, push-out tests, and broken fibers pull-out lengths) of this laminate may be explained by the modification of the interfacial zone (decrease in the carbon layer thickness due to oxidation and formation of TiO₂).     

A guide to diagnosing and treating endodontic and periodontal lesions

178 439 cases of patients exposed to iodinated contrast media (ICM) corresponding to 137 147 to patients for excretory urography and 41 292 to cholangiography were studied. A direct interrogation making emphasis on personal antecedents of allergy to contrast media, iodinated products usage, nervous system and cardiovascular illnesses was made. Cutaneous test for iodinated contrast media was applied. If the result was positive no study with the ICM was made or it was made with special guidelines. 4302 positives and 1276 false negatives were found. 287 positive cases were premeditated and preventive medication was administered in cases of urticaria asthma/and angioedema with negative cutaneous test histories. There were no deaths registered.     

CPC芯材Mo70-Cu的熔渗法制备及加工性能

Mo70-Cu复合材料,由于致密度较低,常在后续轧制加工时出现严重的边裂。为了提高该复合材料的致密度和轧制性能,作者采用熔渗法制备Mo70-Cu复合材料,并对其样品进行冷轧实验,研究熔渗保温时间对密度和塑性的影响。实验结果表明,Mo70-Cu复合材料的密度及相应的加工性能均随保温时间的延长而提高,冷轧时的变形率达40％时,样品仍未出现宏观边裂现象,可以满足对CPC芯材的要求。     

Creep and rupture of an advanced fiber strengthened eutectic composite superalloy

Creep and rupture tests have been conducted on NiTaC-13, an advanced TaC fiber strengthened composite. A simple equation is developed to describe the creep behavior in argon for strains up to about 1 pct at temperatures between 871 and 1093°C. This equation may readily be incorporated in a nonlinear analysis of the deformation of a body subjected to nonsteady and nonuniform stresses and temperatures. The creep rates in air show a progressive increase relative to those in argon due to a loss in cross-section resulting from oxidation. The Larson-Miller parameter is shown to be unreliable for either correlation or extrapolation of rupture data. This is especially true for air tests. A modified parameter is, however, shown to give a good correlation with all the data. Although metallurgical instabilities are present, they have no clear effect on rupture strength and are not uniquely linked with the parametric representation. There is a systematic increase in ductility with increase in temperature and the generally high level of ductility is reflected in pronounced notch strengthening. Some load relaxation tests indicate that fiber failure occurs in excess of 1 pct composite strain. It is suggested, therefore, that 1 pct could be an appropriate design limiting strain for this class of material.     

Interfacial fatigue in a fiber reinforced metal matrix composite

An experimental investigation of interface fatigue in a fiber reinforced metal matrix composite has been conducted. For this purpose, the cyclic traction law (the relationship between the fiber stress and the pullout displacement) was measured using fiber pullout tests. On the first loading cycle, the traction law was found to be parabolic, in accord with predictions of a micromechanical model based on a constant interface sliding stress. Upon subsequent unloading and re-loading, the relationship changed, following trends which suggest that the sliding resistance degrades with cyclic sliding. Such effects have been confirmed through SEM examinations of the fiber coatings following fatigue testing. Furthermore, the degradation was found to be greatest near the plane of the matrix crack. The results are consistent with the notion that the degradation in sliding stress occurs most rapidly in regions where the relative sliding distance (fiber/matrix) is greatest. A phenomenological model incorporating such degradation is presented and compared with the experimental measurements.     

Investigation of the load sequence effects in fatigue of damaged composite laminate & characterization of fatigue damage

Carbon fiber reinforced composites are widely used today in various areas and specially in aerospace industry for structural applications. This investigation focuses on the effect of different load sequencing and impact damage on the fatigue behaviour of CFC laminates. The specimens made from plain CFC laminates and low energy impact damaged CFC laminates were subjected to a typical flight block loading sequence and the fatigue strength degradation was monitored through stiffness measurement using load displacement data obtained during block loading. Three different stress/strain levels were used in testing. All the tests were performed using a computer controlled 100 kN servo-hydraulic test machine in load mode at room temperature and in lab air atmosphere on undamaged and low energy impact damaged composite laminates. Fatigue tests were performed with a sinusoidal waveform at 3 Hz. It was observed that lower strain levels did not show any significant effect on the fatigue properties in both the type of loading i.e. low to high and in high to low block loading in case of both the undamaged and impact damaged CFC specimens. Significant.reduction in stiffness was seen at higher strain level i.e. 6500me in both the undamaged and impact damaged CFC specimens. The low energy impact damaged specimens showed early failure at higher strain levels compared to undamaged specimens. The specimens were observed to have delaminated in the high stress fatigue cycling. The observed stiffness reduction due to fatigue cycling and the presence of delamination provide a means of macroscopic identification of fatigue strength degradation in composite materials. The energy plots appear useful tool to assess the damage growth.     

Fracture strengths of three core restorative materials supported with or without a prefabricated split-shank post

BACKGROUND: Conventional anterior cervical discectomy with fusion is thought to require postoperative neck immobilization for the promotion of bony fusion. Rigid internal fixation with anterior cervical plates may decrease graft-related complications and provide immediate stability. This stability may obviate postoperative external immobilization. METHODS: This report reviews one surgeon's experience with the use of rigid internal fixation for two-level anterior cervical discectomy and fusion for radiculopathy to promote early mobilization without external bracing. It compares outcomes and costs with a similar population of patients treated with anterior cervical discectomy and fusion who did not undergo rigid internal fixation. We compared patients who underwent two-level allograft anterior cervical discectomy and fusion with or without rigid internal fixation between 1989 and 1994 performed by a single surgeon (FJP) to evaluate the cost advantages and outcome of each procedure. All patients had clinical evidence of cervical radiculopathy unresponsive to medical therapy with magnetic resonance imaging confirmation of the appropriate nerve root impingement. Thirty-nine patients underwent two-level Cloward allograft fusion using Synthes anterior cervical locking plates, 25 underwent identical fusion without plating. Follow-up was 6 months to 4 years (mean, 31 months). RESULTS: Twenty-three of 25 patients in the nonplated group and 36 of 39 patients in the plated group achieved excellent or good outcomes using the Odom criteria. There were six complications (two major and four minor) in each group. Patients who underwent plating returned to light activities (mean, 17 vs. 29 days), driving (28 vs. 57 days), and unrestricted work (66 vs. 136 days) sooner than non-plated patients (p < 0.05, paired t test). No patient with plates was given external immobilization. CONCLUSIONS: Two-level anterior cervical discectomy and fusion with anterior plating for radiculopathy is safe, effective, and seems to provide shorter convalescence compared with conventional anterior cervical discectomy and fusion. Patients returned to unrestricted work sooner, thus reducing short-term disability. Rigid internal fixation may provide cost advantages to patients and insurance disability providers. The authors conclude that the increased cost of treatment for rigid internal fixation is more than offset by the benefits of earlier mobilization.     

A structural study of oxidation in an Al2O3 fiber reinforced titanium aluminide composite

A composite of titanium aluminide, reinforced with ZrO₂ toughened Al₂O₃ fibers, has been produced by pressure casting. The stability of the microstructure during vacuum and air annealing was investigated by scanning and transmission electron microscopy (TEM). Processing resulted in partial dissolution of ZrO₂ of the fiber into the molten metal which solidified into a two phase lamellar α₂ + γ matrix. Vacuum annealing caused dissolution of Al₂O₃ fiber into the matrix, transformation of the matrix into γ and precipitation of ZrO₂ and Al₂Zr within γ. During air annealing diffusion of O through the fiber resulted in the formation of Al₂O₃ coated ZrO₂ nodules extending from the fiber surface into the matrix in some regions and in the other regions the growth of Al₂O₃ into the γ of the lamellar matrix. An A15 phase with the metal composition, Ti₃Al₂, was found between the external oxide scale and the metal matrix.     

准单向纤维排布环形炭/炭复合材料的组织与性能

以PAN基炭纤维无纬布为主体,与短切网胎纤维交互叠层制备准单向纤维排布环形炭预制体,然后采用等温化学气相渗透工艺,在丙烯与氮气分压比为1.2:1,系统压力为1.5 kPa的条件下进行增密,制备准单向纤维排布环形C/C复合材料,研究气相渗透温度对增密效率的影响,并对复合材料进行组织观察与导电导热性能测试。结果表明:在980℃温度下化学气相渗透效率最高,480 h后获得密度为1.84 g/cm~3、孔隙率为6.4%的准单向纤维排布C/C复合材料;准单向纤维排布环形C/C复合材料沿轴向方向具有高纤维取向,并且材料沿轴向具有较高的导电与导热性能,其电阻率为20.3μ?·m,热导率为72.8 W/(m·K)。热解炭组织为高织构粗糙层,热解炭生长良好,石墨化度为60.1%。