Endodontic Access Opening and Canal Location

Endodontic Triad

The endodontic triad is the basis of endodontic therapy:
- Biomechanical preparation.
- Microbial control.
- Complete obturation of the canal space.
Proper access to canal orifices and apical foramina is crucial for achieving the goals of the triad.
The ultimate goal is to create an environment where the body can heal itself, and adequate access is key to achieving endodontic success.

Basic Concepts

The pulp complex is a continuum from the pulp horns to the apical foramina.
Accessing the coronal portion of the pulp complex allows for pulp removal and facilitates locating and debriding root canals without compromising tooth structure.
Cleaning and shaping the pulp complex involves four stages:
1. Pre-access analysis.
2. Removal of the pulp chamber roof.
3. Identification of the pulp chamber floor and root canal orifices.
4. Instrumentation of the root canals.

Pre-Access Analysis

Analysis of tooth anatomy and surrounding tissues is the key.
Identify the coronal portion (pulp chamber) and radicular pulp.
Law of Centrality: The pulp chamber is in the center of the tooth at the level of the cementoenamel junction (CEJ).
- This law is consistently true only at the CEJ level and is unrelated to occlusal anatomy.
- The initial penetration should be directed towards the center of the CEJ, ignoring the clinical or restored crown.
- Prosthetic crowns can be misleading because their anatomy is not always centered over the CEJ.

Step 1: Identifying the CEJ

Physically identify the shape and position of the CEJ using a periodontal probe to explore its circumference.
Select a penetration point on the occlusal surface, which may be unrelated to the occlusal anatomy.
The correct penetration point is determined by radiographic examination, periodontal probing, and a mental picture of the CEJ perimeter.

Step 2: Law of Concentricity

Law of Concentricity: The walls of the pulp chamber are concentric to the external outline of the tooth at the level of the CEJ.
- This law aids in extending access properly; if there's a bulge in the CEJ, the pulp chamber extends in that direction.
- If a tooth is narrow mesiodistally, the pulp chamber will also be narrow mesiodistally.

Step 3: Determining Tooth Angulation and CPFD

Determine tooth angulation using radiographs and clinical observation; cone beam tomography can aid in faciolingual angulation.
Measure the distance from the cusp tip to the furcation (Cusp Tip-Pulp Floor Distance, or CPFD) on the radiograph.
Set the bur short of this length to prevent furcation perforation.
Direct the bur towards the center of the CEJ, parallel to the long axis of the tooth, and set it short of the furcation to avoid perforation.

Step 4: Selecting Initial Penetration Point

The entry point on the occlusal surface is variable and depends on the CEJ perimeter, tooth angulation, and CPFD.
Recommendations about starting at a particular point (pit or fossa) can be misleading; the internal anatomy dictates the outline form.
The outline form may be triangular, trapezoidal, or irregular.

Technique of Access

Step 1: Remove Defective Restorations and Caries

Remove all defective restorations and caries before beginning the mechanical portion of the access to prevent bacterial contamination.

Step 2: Bur Selection and Penetration

The choice of bur shape and type is up to the clinician (#4 carbide, round diamond, or #557 taped fissure bur are common).
Special metal cutting fissure burs are available for prosthetic crowns.
Penetrate the occlusal surface at the point determined by pre-access factors (CEJ perimeter, tooth angulation, CPFD).
Advance the bur towards the center of the mentally imaged CEJ until a drop is felt or the handpiece touches the cusp.
A drop-off will only be felt when the pulp chamber is at least $2mm$ deep; teeth with calcified pulp chambers should be considered for referral.

Step 3: Unroofing the Pulp Chamber

The goal is to completely remove the pulp chamber roof.
Avoid looking for orifices until the roof is completely removed to prevent gouging or perforation.
Orifices will be revealed once access is complete.
Two ways to unroof the chamber:
1. Place a straight bur and move it laterally, parallel to the long axis of the tooth.
2. Place a round bur into the access, engage laterally under the remaining overhang, and withdraw occlusally.
The roof is continually shaved away until the access is complete.
Determining when access is complete requires understanding the Law of Color Change.
- Law of Color Change: The color of the pulp chamber floor is always darker than the surrounding walls.
- The floor-wall junction is where the light walls meet the dark floor and traverses the entire pulp chamber floor.
- Access is complete when the floor-wall junction is visible $360$ degrees around the chamber floor.
- If the junction is not seen in one portion, additional overlying structure must be removed (restorative material, reparative dentin, or pulp chamber roof).
Clear identification of the floor-wall junction is the most important aspect of the accessing phase.
If this can’t be achieved, consider referral.

Orifice Location

The number of root canal orifices cannot be known prior to treatment; radiographs and averages are helpful, but often insufficient.
Visualize the full extent of the pulp chamber floor and use anatomic landmarks to determine the number of orifices.

Laws for Identifying Orifice Locations

Law of Symmetry 1: Except for maxillary molars, the orifices are equidistant from a mesial-distal line through the center of the pulp chamber floor.
Law of Symmetry 2: Except for maxillary molars, the orifices lie on a line perpendicular to a mesial-distal line through the center of the pulp chamber floor.
Law of Color Change: The pulp chamber floor is always darker than the walls.
Law of Orifice Location 1: The orifices are always located at the junction of the walls and the floor.
Law of Orifice Location 2: The orifices are located at the vertices of the floor-wall junction.

After clearly seeing the floor-wall junction, these laws can be used to identify the exact position and number of orifices.
Knowledge of the laws of symmetry immediately indicates the presence and location of additional orifices.
Ignore black dots, indentations, or white dots observed anywhere else (chamber walls or dark chamber floor) to avoid perforation.
The vertices/angles of the geometric shape of the dark chamber floor specifically identify the position of the orifice; if the canal is calcified, penetrate at the vertex to remove reparative dentin.
The Laws of Orifice Location 1 and 2, along with the Law of Color Change, are reliable indicators of second canals in the mesiobuccal roots of maxillary molars (MB2).

Applying the Laws

These laws can be applied to any tooth, especially when unexpected or unusual anatomy is present.
Knowledge of chamber-floor-anatomy guides the observer to realize the number of canals present.
The number of orifices does not necessarily correlate to the number of canals; a single orifice may have multiple canals.

Problem Solving During Access

Problem: Unable to Observe Pulp Chamber Floor Due to Excessive Bleeding

Cause: Pulp tissue in the chamber or canals.
Remedy:
- Enlarge the access by removing the pulp chamber roof (avoid touching the floor).
- Place hemostatic agents in the chamber.
- Use a barbed broach to remove the tissue.

Problem: Unable to Observe Pulp Chamber Floor Due to Inadequate Removal of Pulp Chamber Roof

Cause: Improper selection of initial access penetration point or inability to see the floor-wall junction $360$ degrees around.
Remedy: Return to a round or tapered bur and shave back until the floor-wall junction is visualized.

Problem: Unable to Observe Pulp Chamber Floor Due to Restorative Materials Impinging onto the Pulp Chamber

Cause: Inadequate removal of all restorative material before access (especially Class V restorations).
Remedy: Remove all restorative material before beginning the access.

Problem: Calcification/Pulp Stones

Cause: Degenerating pulp.
Remedy: After removing the pulp chamber roof and cessation of bleeding, use a large smooth round bur (#6) to smooth the floor and delineate the floor-wall junction.

Problem: Unable to Observe Pulp Chamber Floor Due to Inadequate Light

Cause: Access too small, presence of crowns/restorations, or lack of smooth surfaces on walls/floor.
Remedy: Enlarge access, remove restorations, use accessory light (LED headlight or surgical operating microscope), smooth irregularities on walls/floor with round burs.

Problem: Unable to Observe Pulp Chamber Due to Loss of Orientation

Cause: Using occlusal surface as a reference point, failure to observe tooth orientation, losing sight of CEJ circumference, or improper angulation.
Remedy: Proper pre-access observation, mental imaging of the CEJ, remove rubber dam to regain orientation, appropriate angle of penetration.

Problem: Floor Perforation

Cause: Premature attempt to identify orifices, failing to measure occlusal-furcal distance, improper identification of floor-wall junction, or inadequate access.
Remedy: Remove the entire pulp chamber roof before identifying orifice location, observe floor-wall junction $360$ degrees around, set bur at length less than occluso-furcal distance, and direct accessing bur toward the center of the CEJ perimeter.

Problem: Lateral Chamber Wall Perforation

Cause: Failing to mentally image the CEJ, improper angle of access entry, or using occlusal anatomy to begin access.
Remedy: Remove the entire pulp chamber roof, observe floor-wall junction $360$ degrees around, direct accessing bur toward the center of the CEJ perimeter, and choose the initial penetration point based on the CEJ imaged perimeter.

Problem: Unable to Identify All Orifices

Cause: Failure to establish complete access, lack of delineation of a distinct floor-wall junction, presence of restorative materials, or presence of calcifications.
Remedy: Perform a complete access, smooth the pulp chamber floor to remove calcifications and delineate the floor-wall junction and use the laws of pulp chamber floor anatomy to identify the positions of orifices.

Summary

To increase the success rate of endodontically treated teeth, remove as much of the pulp complex as possible.
Find all root canal orifices by utilizing the laws of anatomy of the pulp chamber floor.
Have an access that permits the visualization of the pulp chamber walls meeting the floor $360$ degrees around.