Nonsurgical endodontic therapy can be challenged by any of the following iatrogenic errors: perforations, blocked canals, ledged canals, and broken files. This article will focus on the proper management of ledged canals.
Ledged canals can be formed during the biomechanical preparation of the canal system, mostly in curved canals. There are 2 major causes for the creation of ledged canals1: inadequate extension of the access opening to allow straight access to the apical part of the root canal2-6, and using a noncurved stainless steel instrument that is too large for a curved canal.2-5,7,8
Other contributory factors involved in ledge formation include the following: tooth type, canal location, working length, the master apical file size, the clinician’s level of expertise and experience in endodontics, and root canal curvature. One study revealed that the maxillary left second molar had the highest incidence of ledging, and the degree of the canal curvature also had an influence on ledge formation.9 Another study showed that experienced endodontists had significantly fewer ledged canals than less experienced operators, and that there was a higher incidence of ledge formation in retreatment cases.4 In addition, the type of canal was found to have an effect on the incidence of ledging. The mesiobuccal (MB), mesiolingual (ML) and distobuccal (DB) canals of molars exhibited a significantly higher ledge incidence rate than the distal and palatal root canals. This study also shared the same conclusion as mentioned earlier that canal curvature was the most significant variable affecting the incidence of ledging.4
Histologically, complete calcification of the apical third of the canal system does not occur. In reality, this clinical perception is due to the clinician’s lack of ability to establish patency, and/or a lack of patience to do so. The incidence of ledge formation, when using flexible files (such as Ni-Ti files), is reduced when compared to conventional stainless steel K-type hand files.6,10 The introduction of Nickel Titanium (Ni-Ti) alloy to the endodontic world by Walia6 in 1988 revolutionized the way the canal system is shaped, however the improper use of Ni-Ti rotary instruments has resulted in procedural mishaps.11 Despite the advancement of modern Ni-Ti files, ledge formation during root canal therapy is still inevitable in certain cases. Once a canal is ledged, the endodontic treatment becomes difficult to complete, often resulting in compromises.
There are many techniques available to assist in negotiating a ledged canal, and usually these involve prebending the tip of K files. The size 10 prebent file is the key instrument used in identifying the original canal.8 Prebending of an appropriate file plays a vital role in the negotiation of a ledged canal. This article will present 2 case reports in which ledged canals were bypassed using a modified conventional method with a BUC 1A ultrasonic tip (Obtura Spartan), a CPR-8 ultrasonic tip (Obtura Spartan), and 2 prototype endodontic explorers with No. 10/.08 tapered tips—one with a diamond-coated tip, and the other with a smooth-surfaced tip.