Fig. 3 The root canal in this tooth contains necrotic infected debris. The objective in endodontics is to remove the debris without extruding any through the apical foramen. It makes good sense to use a technique which cleans the coronal part first and then the apical portion.
Ultrasound has been used to activate specially designed endodontic files. Ultrasound consists of acoustic waves which have a frequency higher than can be perceived by a human ear. The acoustic energy is transmitted to the root canal instrument, which oscillates at 20 40,000 cycles per second, depending on which unit is used. The superior cleaning effect is achieved by acoustic streaming of the irrigant and not, as originally thought, by cavitation. Irrigation with sodium hypochlorite is necessary, although some of the ultrasonic units are not designed to accept sodium hypochlorite through the system and, if water is used, they will be less efficient in their cleansing effect. Even when units designed to take sodium hypochlorite are used, daily maintenance must be carried out to prevent damage, particularly to metals, because the irrigant is corrosive.
Ultrasound has been used to activate specially designed endodontic files. Ultrasound consists of acoustic waves which have a frequency higher than can be perceived by a human ear. The acoustic energy is transmitted to the root canal instrument, which oscillates at 20 40,000 cycles per second, depending on which unit is used. The superior cleaning effect is achieved by acoustic streaming of the irrigant and not, as originally thought, by cavitation. Irrigation with sodium hypochlorite is necessary, although some of the ultrasonic units are not designed to accept sodium hypochlorite through the system and, if water is used, they will be less efficient in their cleansing effect. Even when units designed to take sodium hypochlorite are used, daily maintenance must be carried out to prevent damage, particularly to metals, because the irrigant is corrosive.
The irrigant passes down the shank of the instrument and into the root canal, producing a continuous and most efficient system. Acoustic streaming is produced by the rapid file oscillations in the irrigant within the root canal. With more recent developments, ultrasonic machines are now largely used for their efficient irrigation properties rather than for canal shaping.