Rheological material characterisation in dentistry

 RHEOLOGY

Rheology is the study of deformation and flow characteristic of matter.

Importance of Rheology in dentistry :

In dentistry we are subjected to manipulate material which flow or deform when subject to stress.

Classification of fluid based on rheology:

1. Newtonian
2. Pseudoplastic
3. Dilatant
4. plastic

1) Newtonin :

• Newtonian fluid have a constant viscosity they,have ideal fluid shear stress proportional to strain rate .
• For example- water and newly mixed zinc phosphate cement.

2) Pseudoplastic:

• Pseudoplastic fluid is a shear thinning fluid
• Viscosity decreases ,shear rate increases until it reaches constant value.
• For example: polycarboxylate cement ,elastomeric impression material.

3)Dilatant:

• Dilatant fluid is a shear thickening fluid
• Viscosity increases ,shear rate increases
• For example:traditional resin composite 

4) Plastic fluid:

• Plastic fluid until certain yield stress is applied ,attain constant viscosity.
• The application of yield stress to cause flow in material is known as bingham characteristic.
• Example ketchup bottle- ketchup is a thixotropic material ,when subjected to constant shear rate for a period of time the viscosity drops.

Factors affecting:

1) TEMPERATURE:

When temperature  increases , velocity decreases 

for example: ghee

2)Pressure

FLOW:

Term used in dentistry to describe rheology of atmospheric material such as wax.

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