Access Cavity

Locating Canal Orifices

The main objective of access cavity preparation is to identify the root canal entrances for subsequent preparation and obturation of the root canal system. Access cavity preparation can be one of the most challenging and frustrating aspects of endodontic treatment, some say it is the key to opening the door for successful endodontics. Inadequate access cavity preparation may result in difficulty locating or negotiating the root canals. This may result in inadequate cleaning, shaping and filling of the root canal system. It may also contribute to instrument separation and aberrations of canal shape. These factors may ultimately lead to failure of treatment. Good access cavity design and preparation is therefore imperative for quality endodontic treatment, prevention of iatrogenic problems, and prevention of endodonticfailure. Careful assessment of pre-operative radiographs may indicate the number of canals present and potential challenges to identifying them.

Large pulp spaces and obviously patent canal entrances may be common in younger patients, but as teeth age, secondary dentine is laid down resulting in a reduction in the pulp chamber volume, and size of the root canal lumen. This often results in the loss of helpful anatomical landmarks and changes in the shape of the pulp chamber which will be unique to each tooth. The dimensions of the pulp chamber and location of the root canal entrances will also be influenced by the amount and position of tertiary dentine deposited as a specific response to caries, microleakage and tooth surface loss over the course of a tooth’s life. These insults on the pulp may have a dramatic effect on the size and shape of the pulp chamber. Canal entrances may also become obstructed by pulp stones and other calcifications, making identification even harder.

Time spent accessing the pulp chamber and refining the access carefully will make the other stages easier and more predictable. The aims of access cavity preparation are to:

1. Allow visualisation of the entire pulpal floor

2. Identification of the canal orifices

3. Allow straight line access of the preparation instruments to the canals

4. Create enough space for files during working length determination

5. Provide a reservoir for canal irrigant

6. Provide retention for an adequate thickness of interim restoration and to provide a good seal in a multiple visit treatment.

When trying to locate canal orifices, obviously knowing the root canal anatomy is crucial – knowing where to look. A simple schematic diagram of each tooth can help with this. Canal orifices are found at the junction of the floor and the walls, and if there are root developmental fusion lines then the canals will be located at the end of these. The pulpal floor tends to be darker then the lighter pulp walls.

The following kit helpful in locating the orifices:

1. Good isolation i.e. rubber dam

2. Good lighting

3. Magnification (Loupes or Microscope)

4. Front surface reflecting mirror

5. Non end cutting bur for removing the roof of the pulp chamber

6. Long neck slow speed round burs

7. Ultrasonic scaler

8. DG 16 endodontic probe

Lighting and magnification often go hand in hand. With newer, lighter and more powerful prismatic loupes, visualisation of the canal orifices should be easier than ever. LED technology has allowed for a very bright and concentrated beam of light to be focussed on a specific site. A microscope is ideal as studies have shown that by using a microscope the same operator can locate more canal orifices.

After the initial pulp chamber access, spend time refining the access to allow thorough checking for all canals and to fulfil the above requirements of the access cavity design. Use a tungsten carbide endo Z bur to remove the entire roof of the pulp chamber enabling visualisation of the entire pulpal floor. A long goose neck round bur can be used very carefully to remove overhanging and reparative dentine. Ultrasonics have multiple applications in endodontics, such as pulp stone removal and endosonics, but a fine tip can also be used to locate canal orifices.