The Effect of Early Coronal Enlargement on the Ability to Accurately Determine the True Size of the Apical Terminus

Dr. Herbert Schilder’s publications (1967’s Vertical Compaction of Warm Gutta Percha and 1972’s Cleaning and Shaping of the Root Canal System) have revolutionized the practice of endodontics, although they went widely unrecognized until the 1990s. We now have a good understanding of the complexity and interconnectedness of the root canal system anatomy, the diversity and pathogenicity of the microbes most commonly associated with endodontic disease, and the limitations of current treatment protocols to completely eliminate those pathogens.

A key determinant of successful endodontic treatment is the negotiation of the root canal pathway from the coronal orifice to the apical termination of the canal. Successful negotiation of the canal allows the dentist to create a glide path, which can be followed by successively larger nickel-titanium rotary shaping files. With appropriate shaping, we have deeper penetration of NaOCL into the root canal system, which facilitates chemical destruction of organic debris and bacteria.

Traditional cleaning and shaping protocols, which were developed in the 1960s and taught mostly unchanged through to the 1990s, stressed quickly getting working length with an initial apical instrument, then using a step-back method to shape the canals. The master apical file was determined to be 3 ISO files larger than the first instrument to bind at working length. As our understanding of root canal anatomy increased, it became apparent that instrument binding occurred most often in the coronal half of the canal and not in the apical third as previously documented. This led to incomplete cleaning of the apical third and underfilling of the canal with gutta percha (the cause of the dreaded overfill).

The concept of early coronal enlargement (ECE), as described by Dr. Cliff Ruddle, addresses this conceptual flaw in the treatment protocol. ECE quickly removes constrictive dentin from the coronal half of the canal prior to working length determination, creating the opportunity for the dentist to take fine hand files and NaOCL deeper into the complex apical third of the canal with maximum dexterity. An additional benefit of ECE was to delay determination of the apical terminus diameter until after canal shaping had been substantially completed, resulting in a higher degree of certainty.

Wrbas et al, JOE 36:10, designed an in vitro study to gage the effect of cervical preflaring (ECE) on the accuracy of apical file size determination. 40 curved, mesio-buccal canals of mandibular molars where divided into 4 groups of 10. Group 1 had no ECE. Groups 2 (Flexmaster), 3 (Protaper), and 4 (RaCe) were preflared using the instrument manufacturer’s recommendations. The actual canal length was determined by positioning a .06 diameter K-file at the apical terminus of the canal with 5X magnification. Working length was determined by subtracting 1 mm from the actual canal length (a contentious issue for us Schilder-trained endodontists, but I digress). The WL instrument was increased until binding was felt at working length. The binding instrument was fixed with acrylic, the root end sectioned at WL, and the surface area discrepancy between the file diameter and canal diameter determined by computer subtraction software.

Wrbas et al found that by preflaring the canals prior to WL determination, the discrepancy between the file diameter and canal diameter reduced from .66mm (a size 60 file) in group 1 (no ECE) to .15mm with group 4 (RaCe). In other words, when the coronal canal was shaped, the dentist’s ability to accurately determine the apical diameter increased by a factor of 4.

An even better study would have studied the delay of apical file determination, which I call “sounding the apical terminus”, until the canal was completely shaped to a .08 taper (a Protaper F2 red instrument). This process would have allowed for unfettered access to the terminus without calcific constraints.

 

ABOUT DR. HOWARD BITTNER

Dr. Bittner was born and raised in the Surrey/Langley area. Following his pre-dental training at Simon Fraser University, he received his Doctor of Dental Medicine from the University of British Columbia in 1982 and his Certificate in Advanced Graduate Studies in Endodontics from Boston University’s Goldman School of Dental Medicine in 1995.

Dr. Bittner was in private practice in general dentistry for 11 years in Langley prior to his endodontic specialty training. He has a wide background in all facets of general dentistry, with advanced dental training in prosthetic dentistry from respected educational facilities such as Creating Restorative Excellence in Tacoma, Washington, and The Pankey Institute in Miami, Florida. He has been practicing the dental specialty of Endodontics since 1995.

He is a past president of the British Columbia Society of Endodontists, the Dental Specialists Society of British Columbia, and the Concentric Endodontic Study Club. Dr. Bittner is also a guest lecturer in the Faculty of Dentistry at the University of British Columbia.

On November 16, 2012, posted in: News for Doctors by