trends _ re-treatment I Fig. 8a Fig. 8b 6) Assessment and repair of iatrogenic events if possible The two most common iatrogenic events encountered are canal transportations and separated instruments, commonly RNT files. The deeper the instrument fragments, the lesser the chance that they can be retrieved. This said, ideal access, crown removal, use of the SOM and creation of the ideal orifice size can all contribute towards fragment visualisation, even if the fragment is at or slightly beyond a curvature in the apical third of a root. In addition, it is optimal to use the thinnest ultrasonic tips possible that allow the clinician an optimal view of the fragment used in an anticlockwise motion to remove the dentine that binds the fragment. RNT fragments should not be directly vibrated (touched) by ultrasonic tips. Doing so will cause them to shatter. In addition to ultrasonics, there are many systems available that engage the fragment with either frictional retention or possible tube and glue options. Instrument fragments that are entirely beyond the apical curvature and that cannot be bypassed are generally left in place and obturation is placed up to them. In the event of clinical failure with RNT fragments lodged, it may be required to follow NSER with root resection and retrofill. 7) Achievement and maintenance of apical patency Once the canal is evacuated of gutta-percha, the clinician will need to spend as much time as it takes to either achieve apical patency or determine that apical patency is unattainable. Fortunately, in many clinical failures, the apical third of a large number of roots has not been touched owing to an inaccurate determination of working length, as well as an inadequate cleaning and shaping. In any event, in the apical 3 to 4 mm of a root with #6, 8 and 10 hand K-files, the clinician should place one Fig. 9a Fig. 9b roots 4 _ 2009 I 27