Harnessing D-amino acids for peptide motif designs

In examining the use of d -amino acids in designing specific peptide folding motifs, the tetrapeptide Boc-d -Glu-Ala-Gly-Lys-NHMe 1 and its analog 2 featuring l -Glu were synthesized for a comparison of their solution conformations by NMR spectroscopy. The temperature coefficients of amide proton resonances, NOE data, side-chain CH₂ anisotropies and salt titration results suggest a weak type _II reverse-turn conformation for peptide 2 , and a tandem type II ’ turn-3₁₀-helix conformation of appreciable conformational stability for peptide 1 in apolar solvents. The latter is of potential interest as the N-terminal helix cap that could support the design of longer 3₁₀ helices. Possible origins of appreciable difference in the conformational stabilities of the diastereomers are discussed.     

Cantilever and Implant Biomechanics: A Review of the Literature, Part 1

In Part 1 of this two-part literature review, the biomechanics of cantilever fixed partial dentures are reviewed. Theoretical constructs of implant biomechanics with special emphasis on implant-supported cantilevers are also discussed. Finally, an overview of the literature regarding occlusal forces generated by patients with implant-supported prostheses is presented.     

正常国人跖骨应力骨折的实验研究

本文将人体双足简化为一承受体重的悬臂梁结构,将跖骨简化为受悬臂弯曲的杆件;取正常国人新鲜尸体跖骨16个,在2H型悬臂疲劳试验机上进行实验。实验确定了跖骨发生应力骨折的极限范围,即在0.906kg/mm~2应力作用下,循环次数为5.6×10~5次。文章还对疲劳断口进行了生物力学分析。     

CONFORMATION OF DISULFIDE BRIDGES IN PEPTIDES WITH PEPSIN PARTIAL SEQUENCES

On the basis of Raman spectra investigation of two model heterodetic cyclic peptides, containing partial sequences of pepsin fragments 45–50 and 206–210 of the chain, it was concluded that the disulfide bridge conformation in pepsin is determined not only by the size and conformation of the peptide loops created by disulfide bridges, but also by the peptide fragments located outside these loops.     

Flexure-FET biosensor to break the fundamental sensitivity limits of nanobiosensors using nonlinear electromechanical coupling

In this article, we propose a Flexure-FET (flexure sensitive field effect transistor) ultrasensitive biosensor that utilizes the nonlinear electromechanical coupling to overcome the fundamental sensitivity limits of classical electrical or mechanical nanoscale biosensors. The stiffness of the suspended gate of Flexure-FET changes with the capture of the target biomolecules, and the corresponding change in the gate shape or deflection is reflected in the drain current of FET. The Flexure-FET is configured to operate such that the gate is biased near pull-in instability, and the FET-channel is biased in the subthreshold regime. In this coupled nonlinear operating mode, the sensitivity (S) of Flexure-FET with respect to the captured molecule density (N(s)) is shown to be exponentially higher than that of any other electrical or mechanical biosensor. In other words, while S(Flexure) ~ e(γ1 [square root]Ns-γ2Ns), classical electrical or mechanical biosensors are limited to S(classical) ~ γ(3)N(S) or γ(4) ln(N(S)), where γ(i) are sensor-specific constants. In addition, the proposed sensor can detect both charged and charge-neutral biomolecules, without requiring a reference electrode or any sophisticated instrumentation, making it a potential candidate for various low-cost, point-of-care applications.     

上切牙区双端悬臂梁种植固定桥的应力分析

目的：通过分析双端悬臂梁种植义齿修复上颌切牙区牙列缺损的种植体在不同加载条件下的周围骨应力分布及位移量,进而探讨临床修复的可行性。方法：应用CT断层扫描技术对上颌骨及上颌牙列的大致轮廓进行三维重建,后于上中切牙区植入种植体,完成牙冠修复并建立模型。通过三维有限元技术模拟载荷,比较不同加载条件下种植体的周围骨组织应力分布及位移量。结果：经统计学分析,种植体-骨界面的皮质骨唇侧、舌侧、近中、远中、根尖部五个部位应力值的差异有统计学意义（P〈0.001）,五个部位的位移量的差异也有统计学意义（P〈0.001）。模型在各种加载条件下的应力分布及位移量的特征大致相同,且变化趋势相似,种植体颈部及周围骨皮质为应力集中区。在各种不同的加载条件中,30°加载角度时种植体周围骨应力分布更为科学。结论：在适当的负重条件下,双端悬臂梁种植义齿是临床修复切牙区缺失可供选择的一种设计方案。     

Corrosion investigation of two materials for implant supraconstructions coupled to a titanium implant

Abstract – The corrosion of two materials for implant supraconstructions, a carbon fiber/PMMA composite and a silver-palladium alloy, was investigated in vitro, the materials being galvanically coupled to a titanium implant. Corrosion current and pH of the electrolyte were monitored, and corrosion products were identified by powder X-ray diffraction. The carbon composite and the silver-palladium per se did not corrode, whereas a silver-palladium specimen brazed with the recommended brazing alloy corroded unmistakably, yielding copper-containing corrosion products. The action of local corrosion cells around the brazed joint is considered, and it is concluded that the two materials seem well suited for implant supraconstructions, provided that brazing the silver-palladium can be avoided. Considering the clinical relevance of the experimental model used, it is concluded that the model is likely to predict a lower corrosion susceptibility than the one found in vivo.     

Implant-supported fixed cantilever prostheses in partially edentulous arches. A seven-year prospective study

The purpose of the following study was to evaluate the medium- to long-term prognosis of implant-supported cantilever fixed prostheses, and to establish to what degree this is influenced by factors such as length, type of cantilever (mesial or distal), and opposite dentition versus cantilever prostheses. This study was performed on a sample of 38 partially edentulous patients treated between January 1994 and March 2001 with 49 partial cantilever fixed prostheses supported by 100 implants. Marginal bone resorption (MBL) has been studied and used as a reference parameter to define therapeutic success. The MBL measurement was made possible by transposing X-ray images of patients selected on a PC and then using a software program. Statistical analysis was carried out for possible correlation between peri-implant bone resorption and the parameters considered in this study: length and type (mesial or distal) of cantilever and opposite dentition to cantilever prostheses. Seven years after loading cantilever prostheses, the overall cumulative implant survival rate (OCSR) was 97%, and the prostheses success rate is 98%. Mesial cantilever prostheses registered a lower success rate (97.1%) than distal cantilever prostheses (100%). Furthermore, a better prognosis was not observed when the opposite dentition of the prostheses comprised natural teeth, or fixed prostheses on natural teeth, when compared with the cases in which opposite teeth were implant-supported fixed prostheses. The authors concluded that medium-term prognosis of implant-supported cantilever fixed prostheses and traditional implant-supported fixed prostheses was comparable. However, a thorough pre-treatment analysis of risk factors regarding implant-supported prosthesis survival is important.     

Dual-arch impressions

All dual-arch impression techniques utilize special stock impression trays of various designs. These trays are made of flexible plastic with fabric or mesh material placed across the occlusal surfaces of the teeth connecting their buccal and lingual flanges. The presence of this material will result in errors by (1) not allowing complete intercuspation during impression-taking; (2) producing incorrect recording of centric occlusion; and (3) because of the elastic memory of the tray/fabric, creating distortion of the elastic impression material. An impression technique is presented which provides a simple and effective method of obtaining dual-arch impressions for single restorations, post and cores, and small bridges. This technique obivates the need for impression trays thus eliminating the errors outlined.