Archwires

Question 1

Describe the properties of Nickel Titanium (NiTi) wires which make them a common archwire choice in the initial aligning process?

Answer 1

• Shape memory.
• Low stiffness.
• Higer friction than stainless steel.
• Fewer activations needed.
• Good for large deflections with low forces required. Force directly proportional to deflection.
• Early use of NITI rectangular achieve leveling, torque, correction of
rotations

Question 2

Describe the following properties of archwires

Answer 2

Range – distance wire behaves elastically before it deforms permanently.

Formability – The amount of permanent deformation that can occur without fracture.

Stiffness – Higher in SS than NITI, TMA 1/3 stiffness of SS, NITI 1/6 stiffness od SS.
Low stiffness provides the ability to apply lower forces and more consistent force over time

Friction – higher in NITI than SS.
Friction reduces the free sliding movement of tooth along the archwire increased friction can lead to slower tooth movement or loss of anchorage

Annealing – softens wire, permanently changing the elastic property, becoming formable.

Question 3

Describe the properties of a Heat Activated NiTi wire and why it might be prescribed?

Answer 3

Thermally activated shape memory.

Thermal activation can be set at different temperatures (temperature transition range TTR)

Cool down below the TTR and it is less stiff and easily deformed.

Heat above the TTR and it becomes stiff and returns to the original
shape.

Can be copper NITI – increasing strength.

Copper added to lower TTR to oral temperature