Fracture frequency of all-ceramic crowns during dynamic loading in a chewing simulator using different loading and luting protocols

OBJECTIVE: The purpose of this laboratory study was to compare the frequency of failures (complete fractures or partial cracks) of molar crowns made of two different all-ceramic materials during dynamic loading in a chewing simulator, as well as the fracture load when subjected to static loading, in relation to different dynamic loading and luting protocols. METHODS: One hundred and forty-four molar crowns fabricated with IPS Empress or an experimental e.max Press material with high translucency (e.max Press Exp) were luted on CAD/CAM milled PMMA abutments (first lower molar, circular chamfer) either with Variolink or glass-ionomer cement (GIC). All crowns were loaded according to three different loading protocols (n=12 per group) and two force profiles (sinusoidal, rectangular) in a pneumatically driven chewing simulator with a steel stylus (? 8mm) and they underwent simultaneous thermocycling (5 degrees C/55 degrees C). After each phase the crowns were evaluated with regard to fractures or cracks. After dynamic testing, the crowns that did not fail were subjected to compression loading until complete fracture in a universal testing machine (UTM). As control groups, unloaded crowns were also subjected to a UTM. Survival statistics with log-rank tests were applied for the results of the dynamic loading, while ANOVA with post hoc Tukey B was used for the fracture load results and two-way ANOVA was carried out for logarithmically transformed data. Weibull statistics were calculated for pooled fracture load data of the dynamically loaded and control groups. RESULTS: In the 144 IPS Empress crowns, complete fractures were observed in 9 crowns and partial cracks in another 3 crowns. When the data was pooled, a statistically significant increase in fractures occurred when the sinusoidal force profile was applied compared to a rectangular force profile (log-rank, p<0.05). No fractures occurred in the e.max Press Exp crowns. The two-way ANOVA showed that the type of luting protocol used had the most significant effect on the fracture load of both materials. In conjunction with Empress, however, the luting material influenced the variability twice as much as in e.max Press Exp. There was no statistically significant difference in the fracture load of GIC-luted e.max Press Exp crowns and that of the Variolink luted Empress crowns. The force profile had a significant effect on the fracture load only of the Empress crowns but not of the e.max Press Exp crowns. Weibull statistics revealed a higher scattering of the data of dynamically loaded crowns compared to that of the control groups. CONCLUSIONS: For testing all-ceramic materials, dynamic loading is indispensable to draw valid conclusions on clinical performance of all-ceramic molar crowns. A sinusoidal profile is advisable, while a gradual increase of the force amplitude does not significantly affect the results.     

补益中药对老龄雄性大鼠下丘脑神经递质——甲状腺轴机能作用的研究

本文通过对3月龄、18月龄、24月龄雄性大鼠下丘脑去甲肾上腺素(NE)、多巴胺(DA)、5-羟色胺(5-HT)、5-羟吲哚乙酸(5-HIAA),和下丘脑垂体促甲状腺释放激素(TRH)、垂体、血甲状腺释放激素(TSH)、血甲状腺激素(T_3、T_4)的测定,研究了大鼠下丘脑神经递质与甲状腺轴机能的增龄性变化,并在此基础上探讨了补益中药对老龄大鼠下丘脑—垂体—甲状腺机能的作用。结果提示:老龄大鼠下丘脑机能的减退是甲状腺轴机能减退的重要原因;补益中药可能改善了老龄大鼠下丘脑的调控机能,进而延缓了甲状腺轴机能的老年性变化。     

An optimal dynamic output feedback controller for a flexible spacecraft

The design of a low-order dynamic output feedback controller for a flexible spacecraft is carried out using modified linear quadratic Gaussian (LQG) theory. The necessary conditions for optimization are given. The linear equations governing a flexible spacecraft with a central rigid body and two sun-tracking solar panels are presented. The parameters of the Solar Electric Propulsion Spacecraft (SEPS) are selected for analysis and simulation. The optimal gains for the dynamic controller are estimated using an iterative algorithm. The sequential procedure which assures convergence is selected. The initial gains which stabilize the system are chosen on the basis of the principle of a PD controller. A third-order controller for pitch, roll and yaw axes of the 18th-order system, which includes sensor and actuator dynamics, is designed. Numerical simulations carried out to ascertain the performance of the controller show the performance to be satisfactory.     

Reconstruction of plantar defects

Plantar defects are a challenge for the plastic surgeon; from 1984–1995 59 operations were performed in 57 patients. The radial forearm flap and the latissimus dorsi (LD) flaps were mainly used depending on the amount of tissue loss. Local flaps such as dorsalis pedis and instep flaps were used for smaller defects. The radial forearm flap is ideal in terms of thickness and stability for the sole but limited in its size. The LD flap is a safe procedure especially for severe injuries and osteitis, but has the disadvantage of being bulky and debulking procedures are frequently performed. For nerve reconstruction deep sensibility seems to be sufficient in order to obtain stable postoperative results. In this report the different operative methods are evaluated. Since 1991, the patients were monitored with static and dynamic foot pressure measurements and gait analysis to assess the postoperative result and prevent pressure ulcers, scar irritation and hyperkeratosis. Preoperative investigations may contribute to an optimal schedule for planning and stabilization of the operative regimen.     

Morphometric insights into nephrotic syndrome in children: Are we any wiser?

Summary: The present study was undertaken in the hope that conflicting opinions concerning interrelationships among minimal change disease (MCD), mesangial proliferative glomerulonephritis (MPG) and focal segmental glomeruloscierosis (FSGS) might be elucidated by morphometric methods performed by image analysis, as well as to study whether serum creatinine and changes in quantitatively analysed glomeruli could correlate with the interstitial fibrosis in these glomerulopathies. Fifteen renal biopsy specimens from children with MCD, 10 with primary MPG and 12 with FSGS for whom both light and electron microscopy as well as immunofluorescence microscopy and full clinical data were available, were examined quantitatively. As a control five biopsy and 10 autopsy specimens of the normal kidneys were used. Our quantitative study showed that in MCD, MPG and FSGS glomerular and interstitial values differed from normal. Morphometric differences between MPG and both MCD and FSGS groups were also shown. Although the mean values of total glomerular area and relative interstitial volume were increased in FSGS patients, in total glomerular cells per unit of glomerular area and mesangium (% of total glomerular area) were similar in both MCD and FSGS groups. In MPG strong positive correlations existed between interstitial volume and serum creatinine, interstitial volume and total glomerular cells per unit of glomerular area as well as between interstitial volume and glomerular mesangium (% of total glomerular area). In FSGS there was significant positive correlation between interstitial volume and serum creatinine. In the MCD group all correlations were weak and not significant. In conclusion, our morphometric studies suggest a close relationship between MCD and FSGS, and indicate that MPG is a separate morphologic entity in children.     

Mechanisms of proteinuria in nephrotic humans

The glomerular capillary wall imposes a remarkably efficient barrier to the passage of proteins the size of albumin and larger. The development of heavy proteinuria signifies impairment of the function of this barrier. Because endogenous proteins of graded size are heterogeneous with respect to their molecular charge and undergo extensive tubular reabsorption, they are not useful for quantifying the extent of barrier dysfunction. An alternative approach is to determine the fractional clearance of uncharged and non-reabsorbable polymers of graded size. When combined with a hydrodynamic theory of solute transport through a heteroporous membrane, the intrinsic properties of healthy and diseased glomerular capillary walls can be inferred. This approach reveals the nephrotic range proteinuria that attends minimal change nephropathy to be associated with impairment of both the size- and charge-selective properties of glomerular capillary walls.     

Detection of Human Heart Rate in Exercises State

作者介绍了一种动态心率检测电路，它能准确、可靠地检出在运动状态下的人体心率。电路采用两种检测技术，一种为双时值ＱＲＳ波检测法，另一种为光电脉搏检测法。     

An Accurate Prediction of the pH Change Due to Degradation: Correction for a “Produced” Secondary Buffering System

Esmolol hydrochloride degrades in aqueous solutions by the hydrolysis of a labile aliphatic carboxy-ester group. The products are methanol and ASL-8123. The resulting aliphatic carboxylic acid moiety (ASL-8123) has a pK of 4.80, which is within 1 pH unit of the pH of the formulation. ASL-8123 therefore acts as a secondary buffer and minimizes the change in pH due to degradation. Equations are presented to calculate the change in the pH when the primary degradation product acts as a secondary buffer. This information can be used in the development of a parenteral product to predict, a priori, the concentration of buffer necessary for optimal pH maintenance. This knowledge can reduce the number of formulation screens required to determine the necessary buffer capacity for optimal drug stability.