In addition to the method of approach to the root canal, there have been numerous techniques for the manipulation of endodontic shaping instruments.
Watchwinding and circumferential filing
Watchwinding, or a continuous back and forth rotation with slight apical pressure, rapidly advances a fine file down a root canal. Each slight turn engages the flutes of the file in the canal wall and removes dentine. Only fine files should be advanced to the apex in this way as there is a danger of compacting pulpal debris ahead of the file. If such a blockage occurs it can be extremely difficult to remove.
Once the file has reached the desired length, a push-pull filing action was used, moving the file circumferentially around the canal walls. When using K-type files an attempt was made to file on the outstroke only, again to reduce the apical compaction of debris. Hedstroem files were more efficient for circumferential filing, although these should not be used when watchwinding. Research into canal preparation found two distinct problems with circumferential filing.
The first was a tendency to preferentially file the inside wall of a curved canal. The technique of anticurvature filing was put forward by Abou-Rass et al. Anticurvature filing involves filing predominantly away from the inner curve of a root to reduce the risk of a strip perforation. The mesiobuccal roots of maxillary molars and the mesial roots of mandibular molars are the teeth most frequently at risk. The method is used only in canals with a moderate-to-severe curve.
Watchwinding and circumferential filing
Watchwinding, or a continuous back and forth rotation with slight apical pressure, rapidly advances a fine file down a root canal. Each slight turn engages the flutes of the file in the canal wall and removes dentine. Only fine files should be advanced to the apex in this way as there is a danger of compacting pulpal debris ahead of the file. If such a blockage occurs it can be extremely difficult to remove.
Once the file has reached the desired length, a push-pull filing action was used, moving the file circumferentially around the canal walls. When using K-type files an attempt was made to file on the outstroke only, again to reduce the apical compaction of debris. Hedstroem files were more efficient for circumferential filing, although these should not be used when watchwinding. Research into canal preparation found two distinct problems with circumferential filing.
The first was a tendency to preferentially file the inside wall of a curved canal. The technique of anticurvature filing was put forward by Abou-Rass et al. Anticurvature filing involves filing predominantly away from the inner curve of a root to reduce the risk of a strip perforation. The mesiobuccal roots of maxillary molars and the mesial roots of mandibular molars are the teeth most frequently at risk. The method is used only in canals with a moderate-to-severe curve.
The second finding was that once the file engaged in the coronal part of the root canal, the apical flutes tended not to cut dentine but remain passive. The majority of the filing occurred coronally, which tended to leave underprepared canals which were not fully cleaned.