by Richard Mounce, DDS
For more on this topic, go to www.dentaleconomics.com and search using the following key words: orifice management, iatrogenic events, RNT, straight–line access, Dr. Richard Mounce.
Clinicians who perform endodontics tend to be goal–oriented, and in a root canal, this goal is often to get to the apex. It is axiomatic that getting to the apex is made most predictable by performing small steps well and in order, where each step follows the previous one both logically and sequentially. Such small steps allow progressive penetration of the root canal system to the apex with minimal chance of iatrogenic events. Performing each step slowly and correctly provides smooth treatment, which saves time and makes the process as efficient as possible — in essence, fast.
Two factors that are often overlooked in creating a final ideal shape are access and management of the cervical dentinal triangle (CDT) — in essence, orifice management. If the management of the orifice is correct, subsequent management of the apical third is much easier and more predictable. The converse is also true. The origin of many iatrogenic events in endodontics is a lack of adequate access and orifice management.
It is not possible to shape the apical third well if the more coronal two thirds have not been prepared correctly. Consider the scenario where a clinician takes a rotary nickel titanium (RNT) file forcefully and repeatedly into an inadequate access and orifices that have not been properly shaped. In this scenario, debris from the chamber as well as the coronal third is literally forced down the roots, which will likely lead to blockages and file separations, among other iatrogenic events.
Alternatively, a more effective way to move forward is to establish straight–line access, ideally under a surgical operating microscope (SOM) (Global Surgical, St. Louis, Mo.). After every step in access creation, debris is removed through irrigation. If a wall of the access is missing, it can and should be rebuilt with composite to give the access preparation four walls in which to hold the irrigant in the chamber.
To complete access:
- The chamber must be fully unroofed.
- All caries must be removed.
- All fracture lines should be examined to see if they progress below the pulpal floor or into any of the canals.
- All the restorations and unsupported tooth structure are ideally removed so that prior to initiating the enlargement of the orifice, the tooth has been stripped back to its healthy tooth structure.
After these steps, the restorability of the tooth should be reassessed. If the tooth has a crown, or if there is any question as to the marginal integrity, caries under the crown, or bridge abutment (this is relatively easy to view under the SOM), the crown or the bridge should be remade. If the treatment is being done by a specialist, it is essential that the communication between the referring doctor and the endodontist be very clear with regard to who will place the buildup, if post space is required, and more.
In any event, once straight–line access has been created, the clinician must remove the CDT before starting down the coronal third. This can be done with a number of potential orifice openers. My chosen instrument is the Twisted File (SybronEndo, Orange, Calif.) because it can be used to shape the entire canal as well as remove the CDT, often with one file, or at most three single instruments.
The motion of TF use is up and away from the furcation and toward the greatest width of dentin. It is important to appreciate the initial diameter of the orifice and what the final prepared orifice diameter would likely be. For example, if the root is relatively fluted (concave at the furcation), the orifice is relatively small, and the canal comes into the chamber at an angle, it is possible to create a perforation with some orifice openers and/or block canals (Gates Glidden (GG) drills and Peezo reamers) if they are used overzealously.
I have not used either of these devices in many years. I believe that any of the commercially available RNT orifice openers, if used appropriately, can be used to shape the orifice more efficiently and safely than GG drills or Peezo reamers.
Excellent apical cleaning and shaping requires achieving straight–line access and proper management of the CDT. Patiently making sure that these two steps are correct before moving apically allows a smooth, and ultimately fast and efficient preparation outcome.
I welcome your feedback.
Dr. Mounce offers intensive, customized, endodontic single–day training programs in his office for groups of one to two doctors. For information, contact Dennis at (360) 891–9111 or write [email protected]. Dr. Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, Wash.