Rheological thermal properties

What is rheology?

The study of how materials flow or deform

What is viscosity?

Liquids resistance to flow

What is high viscosity? With example

Resists flowing - high viscosity glass ionmer cement

What is low viscosity with example

Flows easily - flowable composite

Is thixotropy a change in viscosity?

Yes, due to applied force over time

What is a thixotrophic material?

Material that becomes more fluid when a constant force is applied

Example of thixotrophic materials?

Plaster of Paris - resin cements

What is creep?

Increase in deformation over time under constant stress

What is static creep? And example

When there is constant, steady stress - wax pattern distorting under its own weight

What is dynamic creep?

When there is fluctuating or repeated stress - amalgam restoration deforming under chewing forces

What can dynamic creep in amalgam contribute?

Marginal breakdown and ditching

What is shear stress? Example

Force per unit area applied parallel to a surface - spatulating cement

Difference between creep and flow?

Creep: deformation increases over time under constant stress

Flow: continuous, irreversible deformation under applied shear strength over time

What is high thermal conductivity? Examples?

Heat passes through easily such as metals

What is low thermal conductivity and examples

Heat passes through less easily - enamel and dentin

Amalgam has high conductivity, what should be done?

Insulating cement base placed under such as zinc oxide- engenol and glass ionomer cement

What is thermal diffusivity?

How quickly does the temperature change spread?

Order of thermal expansion measurement

Hard tooth structure: smallest

Metals: intermediate

Polymers: largest

What does an exothermic reaction do? Examples

Release heat - acrylic resins and zinc phosphate cement