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What is Frequency of ultrasonic preparation is: and explain in detail?
Ultrasonic preparation: 

Consists of a peeso electric ceramic unit that generates ultrasonic waves which activate a magnetostrictive hand piece.
The hand piece produces movements of the shaft of the file between 0.001 to 0.004 inches in a frequency of 20,000 — 25,000 / sec.
NaOCI is used as irrigant solution.
Increased thermal and mechanical ability of the irrigating solution removes debris and tissue effectively and removal of smear layer is also efficient.