Endodontic Access: Paving the Way to the Apex

Dr. Richard E. Mounce, DDS

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Endodontic access is an underappreciated, yet an absolutely vital component of endodontic therapy.

If access is prepared correctly, great endodontic results can follow. If access is underprepared or compromised, it is virtually impossible to carry out the remaining steps to achieve the standard of care.

This column was written to describe the common challenges in access preparation and provide clinical solutions to these challenges.

Restorative dentistry is built principally on the notion of conserving tooth structure where possible. In essence, this means removing both decay and only the tooth structure needed for either mechanical or adhesive retention. This mindset, while essential in restorative dentistry is not directly correlated to endodontic access.

Figure 1: Significant difficulty can be expected in attempting access through #20 (non vital). This bicuspid has three roots and access is being made through a porcelain crown that is part of a three-unit bridge.

In endodontic access, the access opening must be large enough to fully uncover, locate, negotiate, instrument, irrigate and obturate canals. This may be slightly larger than expected in some cases. Empirically, it is my opinion that more often than not, endodontic access is made too small.

Correct access may bear little, if any, resemblance to the access openings depicted in endodontic textbooks. Such textbook pictures assume that there are no coincident fractures, caries, existing restorations, resorption, limitation of opening, etc. These issues must be considered and addressed simultaneously to the location of canals.

Because of these challenges, some access openings must be modified from an otherwise ideal dimension to allow the placement of both hand and rotary nickel titanium (RNT) files.

The correct dimensions of access have been prepared when:

Figure 2: Mani MI Stainless burs.

1. Hand and RNT files are able to enter the canal without deflecting off of axial access preparation walls.
   In other words, the hand and RNT files should reach the point of first curvature without deflecting off the axial access walls because canal wall deflection places unnecessary forces on hand and rotary instruments. These forces diminish tactile and visual control over the file and increase the possibility of fracture and/or canal transportation.
2. Once access is prepared correctly, the clinician should be able to see all the canals in one mirror view. In addition, files should be able to reach the point of first canal curvature without having a curvature placed upon them.
3. The pulp chamber has been fully unroofed.

A comprehensive listing of challenging access scenarios is beyond the scope of this article, but several common technical challenges must be appreciated which necessarily make access more complex. These include:

Figure 3: Rotated lower bicuspid, access will be deviated 90 degrees from mesial to distal to accommodate the location of the canal relative to the usual buccal to lingual orientation.

1. Limited Access – Once the canal is located, whether or not the patient can or will open wide enough to allow full visual and tactile control must be taken into account.
2. Access Through Crowns (porcelain or otherwise) – It should be remembered that crowns are made to fit the occlusion, not to be drilled through. In essence, the anatomy of the crown may have little to do with the location of either the pulp chamber or the orifices themselves.
   In many crowned teeth, it is not possible to see the pulp chamber radiographically because it is obscured by the crown. It is incumbent on the clinician to always be aware of both the vertical depth of penetration in searching for the chamber and canals, as well as the horizontal width of penetration. This is especially complex in the case of a strategic bridge abutment when the tooth is relatively narrow, for example the anterior bicuspid abutment of a bridge.
3. Malpositioned Teeth – Rotated, tipped and otherwise malpositioned teeth are especially challenging, as access will need modification in relation to the expected position of the canals.

Several aids in making access are listed here:

Figure 4: Clinical case using the strategies discussed in the article. Note the straight axial walls leading into the canal orifices. Case treated with the MounceFile rotary nickel titanium Controlled Memory Assorted pack.

1. Where appropriate, a three dimensional radiographic assessment of the tooth can be invaluable as it can tell the clinician the vertical depth where the canal is clearly visible radiographically and its expected location. As I mentioned in a previous column, “cone beam technology is the gold standard for determining the true three-dimensional anatomy of any given root. Without CBCT technology, the next best option is standard digital radiography, taking two or three radiographic angles.”
2. There is no substitute for a surgical operating microscope, during access. Alternatively, at a minimum, loupes can provide the visualization needed for more routine cases.
3. Using new burs for every access improves efficiency. While the carbide and diamond burs used for access are a matter of personal preference, when searching for calcified canals. Mani MI Stainless slow speed burs or Munce Discovery Burs are both excellent means to remove tooth structure safely and efficiently when looking for calcified canals. Ultrasonic tips are another alternative for removal of tooth structure in this scenario.
4. While not directly related to the access preparation, checking for profound anesthesia prior to making access can eliminate the scenario where the patient moves without warning and as a result, inadvertently, the access preparation becomes unnecessarily larger than it otherwise would be.
5. The access prep should be irrigated often and copiously to allow the clinician to fully see both the presence of orifices as well as the color of the pulpal floor where canal location is difficult. A spatial awareness of both the vertical, horizontal and coloration of the chamber cannot be overstated in importance, as access is prepared.

Endodontic access preparation has been discussed. Emphasis has been placed on assessing preoperative risk factors and cognition of the vertical and horizontal dimensions of access preparation and coloration of the pulpal floor when access is being made. It is axiomatic that straight-line access is essential to allow the clinician to properly locate, negotiate, instrument, irrigate, and obdurate canals.