Rheology DENTAL MATERIALS

Rheology
Rheology is the study of flow of matter. In dentistry, study of rheology is necessary because many dental materials are liquids at some stage of their use, e.g. molten alloy and freshly mixed impression materials and cements. Other materials appear to be solids but flow over a period of time.
VISCOSITY
It is the resistance offered by a liquid when placed in motion, e.g. honey has greater viscosity than water. It is measured in poise (p) or centipoise (cp).

CREEP
It is the increase in strain in a material under constant stress. It is time dependent plastic deformation or change of shape that occurs when a metal is subjected to a constant load near its melting point. The term flow has been used rather than creep to describe rheology of amorphous materials such as waxes.
Application:
Dental amalgam has components with melting points that are slightly above room temperature and the creep produced can be very destructive to the restoration; e.g. glass tube fractures under a sudden blow but bends gradually if leaned against a wall.
THIXOTROPIC
These materials exhibit a different viscosity after it is deformed, e.g. zinc oxide eugenol cements show reduced viscosity after vigorous mixing.