Chapter 8 TERMS Flashcards
(28 cards)
define accelerator
A compound that speeds up the reaction; also refers to the catalyst in the reaction of impression materials.
define addition reaction
A polymerization reaction in which each polymer chain grows to a maximal length in sequence.
define base paste
The component that forms the main three-dimensional structure of a final impression.
define cast
A dimensionally accurate reproduction of a part of the oral cavity or extraoral facial structures that is produced in a durable hard material.
define catalyst paste
A component of a polymerization reaction that decreases the energy required for the reaction and usually does not become part of the final product; however, the term catalyst has been used for the structural component of dental materials that initiates the polymerization reaction.
define colloid
A solid, liquid, or gaseous substance made up of large molecules or masses of smaller molecules that remain in suspension in a surrounding continuous medium of different matter.
define condenstation reaction
A polymerization process in which bifunctional or multifunctional mono- mers react to form first dimers first, then trimers, and eventually long-chain polymers; the reactions may or may not yield by-products; the preferred term is step-growth polymerization. All condensa- tion impression materials yield by-products.
define crosslinking
The process of joining polymer chains to form a three-dimensional network structure.
define elastomer
Any of various polymers having the elastic properties of natural rubber.
define fusion temperature
The temperature below which a definite reduction in plasticity occurs during cooling of an impression compound.
define gel
A network of fibrils forming a weak, slightly elastic brush-heap structure of hydrocolloid; also the solid network structure of a cross-linked polymer.
define gelation
The process of transforming a hydrocolloid from a sol to a gel.
define imbibition
The displacement of one fluid by another immiscible fluid in a hydrocolloid. In the context
of impression materials, it is the uptake by agar or alginate when immersed in water.
define inelastic
Incapable of sustaining significant elastic deformation without fracturing under stress.
define initiator
The component that starts a polymerization reaction; types include photoinitiators, chemi- cal initiators, and heat initiators.
define micelle
An aggregate of surfactant molecules or ions in solution.
define model
A positive full-scale replica of teeth, soft tissues, and restored structures used as a diagnostic aid for the construction of orthodontic and prosthetic appliances; a facsimile used for display purposes.
define polymerization
A chemical reaction that transforms small molecules into large polymer chains.
define pseudoplasticity
The tendency of a material to become less viscous as the shear rate increases and
to recover viscosity immediately upon the elimination of shear stress.
define rheology
Pertaining to the science that describes the fluid or flow characteristic of materials.
define set
The state of being sufficiently rigid or elastic to permit removal from the mouth without plastic deformation.
define setting time
The time from the start of mixing to the point where the material loses its flow poten- tial or plasticity.
define shear thinning
The tendency for viscosity to decrease as the shearing rate increases (see pseudo- plasticity and thixotropy).
define static mixing
A technique of transforming two fluid (or paste-like) materials into a homogeneous mixture without mechanical stirring; it requires a device that forces two streams of material into a mixer cylinder, such that as the streams move through the mixer, while the stationary elements in the mixer continuously blend the materials.
