Strain terms
1. Flexibility
• The maximum flexibility is defined as the strain occurring when the material is stressed to its proportional unit.
Significance
• A larger strain or deformation with slight stresses is an important consideration in orthodontic appliances.
• Impression materials should have large flexibility or elastic deformation to withdraw through severe undercuts without permanent deformation.
2. Ductility
• The amount of plastic strain produced in the specimen before fracture.
• Or the ability of a material to be drawn and shaped into wire by means of tension.
• When tensile forces are applied, the wire is formed by permanent deformation.
• However, malleability of a substance represents its ability to be hammered or rolled into thin sheets without fracturing.
Significance
• High ductility and malleability are useful in adapting metallic restorations to the margins by burnishing.
• Very thin pure direct filling gold foil is available for restorations.
• Orthodontic wires are drawn from cast ingot.
