Comparative flow characteristics of selected dental materials with emphasis on thixotropic behavior.
Abstract Flow behavior of selected impression materials, dental cement liquids and fluoride gels were measured using a unique cup and bod viscometer. Programmable functions of the instrument allowed shear stress measurement during increasing and decreasing shear rates. Shear-dependent and time-dependent properties of plastic, pseudoplastic and thixotropic behavior were evaluated for these materials. The thixotropic index was also used to compare these materials. The impression materials tested showed pseudoplastic and thixotropic behavior, while the dental cements showed very little pseudoplastic or thixotropic behavior. The fluoride gels showed essentially plastic yield with minimal thixotropy.
Characterization of the Setting Process in Alginate Impression Materials
The functioning of an alginate impression material involves a change in its physical state from a viscous fluid to an elastic solid. (The paste obtained when water and the alginate powder are first mixed is a viscous fluid, since it flows irreversibly under the action of a force.) This change is effected by the reaction of calcium sulphate with the sodium or potassium alginate, thus forming a cross-linked molecular network.' The purpose of the present study has been to characterize the setting process in terms of easily measured physical parameters, and hence to make a rational study of the effect of those experimental variables that are of importance clinically.
A Text-Book of Qualitative Chemical Analysis
STUDENTS of chemistry usually begin their working lives with the study of qualitative analysis, carried out too often in crowded laboratories with inadequate equipment: it is the equivalent to “grubbing weeds from garden paths with broken dinner knives”. Such education is supposed to make “better men than you or I” doubtless because of its practical basis, but to-day we are sufficiently enlightened to wed practice with theory from the beginning and to realize that the more one understands what one is doing the greater the interest in the task becomes.A Text-Book of Qualitative Chemical AnalysisBy Dr. Arthur I. Vogel. Second edition. Pp. xi + 486. (London, New York and Toronto: Longmans, Green and Co., Ltd., 1941.) 10s. 6d.