Objectives of Access Cavity Preparation

By now you have already understood that access is the most important phase of non-surgical root canal treatment. A well-designed access preparation is essential for an optimum endodontic result. Without adequate access, you will realise that instruments and materials become difficult to handle properly in the highly complex and variable root canal system.

It is therefore, suggested that you try to assess the following features by visual examination of the tooth, and a study of a pre-operative periapical radiographs:

• The external morphology of the tooth.

• The architecture of the tooth’s root canal system.

• The number of canals present.

• The length, direction and degree of curvature of each canal.

• Any branching or division of the main canals.

• The relationship of the canal orifice(s) to the pulp chamber and to the external surface of the tooth.

• The presence and location of any lateral canals.

• The position and size of the pulp chamber and its distance from the occlusal surface.

• Any related pathology.

The objectives of access cavity preparation consist of the following:

1) Remove the entire roof of the pulp chamber so that the pulp chamber can be debrided.

2) Enable the root canals to be located and instrumented by providing direct straight line access to the apical third of the root canals.

3) Enable a temporary seal to be placed securely in order to withstand any displacing forces.

4) Conserve as much sound tooth tissue as possible and as is consistent with treatment objectives.

The ideal access cavity creates a smooth, straight-line path to the canal system and ultimately to the apex. During your practice you will find that when prepared correctly, the access cavity allows complete irrigation, shaping, cleaning, and quality obturation. Optimal access results in straight entry into the canal orifice, with the line angles forming a funnel that drops smoothly into the canal(s). Projection of the canal centre line to the occlusal surface of the tooth indicates the location of the cavosurface line angles. Connection of the line angles creates the outline form. The access cavity preparations for endodontic therapy are designed for efficiently uncovering the roof of the pulp chamber and providing direct access to the apical foramina by way of pulp canals.

It may be prudent to commence access cavity preparation before isolating the tooth with rubber dam in order that the anatomical landmarks, tooth inclination and other helpful features are not lost. You must understand that it is crucial that the root canal does not become contaminated during either access preparation or canal instrumentation, and the tooth should be isolated in an aseptic field as soon as possible. If there is a danger of fracture of the coronal tooth structure, the cuspal height should be reduced to prevent this. If the loss of coronal tissue is extensive, there may be a need to provisionally restore the tooth. The subsequent restoration of the tooth should always be considered first. If you find that the tooth is not heavily restored then only the amount of coronal tissue sufficient for the successful completion of the root canal treatment should be removed. However, if you discover that the tooth is already compromised and will require some form of cuspal coverage restoration, an onlay or a crown, then it may be practical to reduce the cusp height, particularly mesiobuccally in molars, to enable better visualisation of the pulp chamber.