Orthodontic Materials Flashcards
Components of fixed appliances?
Arch-wires
Brackets
Bonding agents
Auxiliary components
What is used to harden wires?
Work hardening
Effect of work hardening?
Increased yield strength and hardness = springy
Reduced ductility
Useful properties for orthodontic wires explain
a) stiffness
b) elastic range
a) controls amount of force applied to teeth - higher force = rapid movement
b) Wire will try to spring back to original shape = straighten
Treatment usually requires different levels of wire stiffness. Explain
May be difficult to engage stiff wires with grossly misaligned teeth
Start with low stiffness = slower movement
Replaced with increasing stiffness as treatment progresses - move smaller distances quicker
What dictates wire stifness?
Choice of alloy
Degree of cold working
Dimensions of wire
How does dimensions of wire effect stiffness?
Larger radius = stiffer
If rectangular - larger width and height
Longer wire = lower stiffness
Effect of mutlistrand wires
Combination of smaller (less stiff) wires of same alloy = low stiffness used in standard bracket size
Reason for joining multiple short wires?
Short wires = stiffer
Consequence of joining multiple short wires?
Soldering and welding can lead to recrystallisation - reduction in mechanical properties
Properties of wires. Explain
a) Corrosion resistance
b) friction
a) wires in mouth for long periods of time = corrosion can lead to loss of strength and biocompatibility issues
b) successful treatment requires wire to slide through brackets = high friction no sliding
Most common alloys used for arch wires
Stainless steel 18% Cr, 8% Ni
Ni/Ti
Beta titanium
Properties of stainless steel archwires?
High modulus of elasticity
High proportional limit
Ductile - can be joined
Properties of Ni/Ti
Low modulus of elasticity - (early treatment)
high proportional limit = good spring back = large movement slowly
Low ductility - cannot be joined
Grades of Ni/Ti alloys
Conventional
Shape memory alloys - super-elastic (addition of Cu)
