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The purpose of this study was to undertake a microscopic analysis of the structure of Concise® and Addent XV® with reference to matrix and fillers. The material consisted of 60 30-100 μm thick ground sections of teeth in which Class 5 Addent XV or Concise fillings had been inserted. The sections were studied by polarized and UV light (fluorescence) microscopy and contact microradiography. The structure of Concise differed greatly from that of Addent XV. Whereas the fillers of Concise displayed a strong birefringence, those of Addent XV were weakly birefringent. On the other hand, differentiation between fillers and matrix was difficult with Concise but easy with Addent XV. In Addent XV there was an indication of compression zones of the matrix bordering the fillers and accidental airspaces. A 20-300 μm wide rim of matrix at the borders of the fillings showed stronger birefringence than the bulk of the matrix. This birefringence remained unchanged during imbibition of the sections in the air (n = 1.0) and watery media (n = 1.33-1.62) series, but was altered by inhibition in alcohol. New type Addent XV available since January 1973 appeared structurally equal to Concise. [ABSTRACT FROM AUTHOR]

Electron micrographs of the various molecular forms of acetyleholinesterase (as previously characterized) are presented. The "globular" forms G and G' appear as tetramers, and dimers, respectively, whereas the "native" forms, A, C, and D show a structure "en grappe" where a cluster of globules (respectively 4, 6 to 8, and at least 10) is associated with a semi-rigid "tail". The globules seem identical in all forms and probably represent the sub-units of the enzyme (Mw 60 000-80000). The structures are 50 nm long in their greatest, dimension; the tail is 2- 3 nm thick and its visible part is longest in A and shortest in D; presumably part of it is masked by the head. These results explain our previous physico-chemical observations which had led us to propose that the native forms were asymmetric in structure. We discuss a possible model of the subunit structure for the "native" forms: A, C and D are proposed to consist of identical tails associated with respectively one, two, and three tetramers. This hypothesis provides a rationale for the occurrence of three well-defined "native" acetylcholinesterases, as well as for the derived "globular'' forms, the dimer and the tetramer. We further propose that the interactions inside the structures are not equivalent for the two kinds of subunits: for example, one of them might be linked directly to the tail, the other only through thc tetramer interactions. [ABSTRACT FROM AUTHOR]

Presents a study conducted on electron micrographs of shale fabric, showing in detail clay-flake orientation in shales possessing various degrees of fissility. Classification of samples having various degrees of fissility; Characteristics of illitic black shales of Pennsylvania; Factors that contribute to the formation of shale fabric.

Application of the potentiostatic polarization technique to the metallographic etching of set dental amalgam is described. Etching studies of amalgam prepared from a lathecut, a spherical, and a silver-copper dispersed-phase amalgam alloy are reported. The γ2 phase in set dental amalgam can be characterized by this electrochemical technique. [ABSTRACT FROM AUTHOR]

The microstructures of Ag3Sn and dental amalgam were analyzed to determine the nature of the variation of the tensile strength of dental amalgam containing mercury. Dental amalgam followed the laws of strengthening which have been developed to describe the tensile strengths of other alloy systems with variable phase percentages. [ABSTRACT FROM AUTHOR]

Polished, unetched amalgam surfaces were studied metallographically with a scanning electron microscope (SEM). By use of different modes of SEM operation, micrographs were obtained from variations in the electric properties of the respective phases present. This technique minimizes artifact formation that may result from conventional electric or chemical etching techniques. [ABSTRACT FROM AUTHOR]

This article discusses the results of a research study conducted to determine the microstructure and setting reactions of spherical-particle dental amalgams. Metallographic and X-ray diffraction methods were used to examine these behaviors in amalgams composed of a silver and tin compound (Ag3Sn).

This article discusses the results of a research study conducted to determine the microstructure of a dental amalgam using a metallographic polishing technique to identify and separate the phases of the structure. The researchers also recommend using an iodine etch on the dental amalgam to better display its phases.