Answer a
Pathways of the Pulp, 8th Ed, Cohen and Burns 2002
Ultrasonic instruments are Piezo electrical units that create an oscillating sinusoidal wave in a file or accessory tip.. They operate at a frequency of 25-30 kHz. (Sonic devices operate at 2-3 kHz)
Applications for ultrasonics are:
1. Root apical preparation.
Advantages over burr preparations are:
a) Better access in difficult to reach areas with small tips.
b) More thorough debridement of tissue and debris.
c) More conservative preparations, follows the canal.
d) Precise isthmus preparations with parallel walls allow better retention of filling materials.
2. Endodontic paste (resin based) removal.
3. Indirect silver point removal.
During silver point removal, direct contact with the point is avoided since the ultrasonic action will erode the silver. The objective is to create a trough around the point to facilitate mechanical instrumentation or use of removal pliers. The ultrasonic unit is used indirectly by contacting the pliers grasping the point.
4. Post removal.
Direct contact with the post loosens the cement that holds it in place.
5. Enhance irrigant effect.
Acoustic streaming and cavitation allows for better clearing of debris.
Used with 17% EDTA, can help eliminate smear layer.
6. Identifying constricted canal orifice.
7. During retreatment, can aid in softening gutta percha.
Prolonged use of ultrasonic files may result in file breakage. Files must be changed out frequently.
In many cases, the ultrasonic is used as an adjunct and not the primary instrument.
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