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Dental Material
Dr. Omar S.M.J.Ali PhD Orthodontic
Yield strength
Ultimate tensile strength It is the maximum stress that a material can withstand before failure in tension. Ultimate compressive strength It is the maximum stress that a material can withstand before failure in compression.
Permanent deformation (Plastic Deformation )
Clinical Application
An elastic impression material deforms as it is removed from the mouth. However, due to its elastic nature it recovers its shape and little permanent deformation occurs.
Resilience
It is the amount of energy absorbed by a structure when it is stressed not to exceed its proportional limit. Resilience can be measured by calculating the area under the elastic portion (straight line portion)
Toughness
It is the energy required to fracture a material. It is also measured as the total area under the stress strain curve (elastic and plastic portions of stress strain curve). Toughness is not as easy to calculate as resilience.
Brittleness
Ductility
Hardness
Relaxation
Clinical Application
This stress relaxation leads to distortion of elastomeric impressions. Waxes and other thermoplastic materials like compound undergo relaxation after they are manipulated.
Friction
Wear
It is a loss of material resulting from removal and relocation of materials through the contact of two or more materials
Adhesion and Cohesion
Adhesion is the force which causes two different substances to attach when they are brought in contact with one another. When the molecules of the same substance hold together the forces are said to be cohesion
Viscosity
It is the resistance offered by a liquid when placed in motion, e.g. honey has greater viscosity than water.
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.