Errors in Access Cavity Preparation

Unfortunately errors can occur during the preparation of endodontic opening. Most are a result of failure to follow the access guidelines and others are due to lack of understanding of the internal and external tooth morphology. Major problems or errors in endodontic access preparation arise due to:

1) Failure to identify and excavate all caries and to remove unsupported, weak tooth structure or faulty restorations.

2) Failure to establish proper access to the pulp chamber space and root canal system.

3) Failure to identify the angle of the crown to the root and the angle of the tooth in the dental arch.

4) Failure to recognize potential problems in access openings through crowned teeth or teeth with excessively large restorations.

Many errors occur during access preparation due to under-preparation i.e., the desire to limit the removal of tooth structure. Believing that conservation of enamel and dentin will aid in the stability of the tooth during treatment and better retain the future restoration, one tends to prepare an access of minimal size. This would result in restriction of direct access to the apex, causing incomplete removal of debris, insufficient preparation of dentin walls, failure to discover additional canals, and inability to produce maximal condensation of the canal filling.

Other errors in access preparation include gouging, perforation, ledge formation, instrument breakage and these errors occur due to failure to adhere to the principles of access opening.

a) PERFORATION at the labio cervical is caused by failure to complete convenience extension toward the incisal, prior to the entrance of the shaft of the bur.

Failure to complete convenience extension cause perforation

b) LEDGE formation at the apical-labial curve is caused by failure to complete the convenience extension. The shaft of the instrument rides on the cavity margin and “shoulder”.

c) BIFURCATION of a canal is completely missed, caused by failure to adequately explore the canal with a curved instrument.

Failure to prepare access cavity due to bifurcation of canal

d) APICAL PERFORATION of an invitingly straight conical canal. Failure to establish the exact length of the tooth leads to trephination of the foramen.

Apical perforation of straight conical canal

e) INCOMPLETE preparation and possible instrument breakage caused by total loss of instrument control. Use only occlusal access, never buccal or proximal access.

Instrument breakage due to loss of instrument control

f) BROKEN INSTRUMENT twisted off in a “cross-over” canal. This frequent occurrence may be avoided by extending the internal preparation to straighten the canals (dotted line).

Straighten the canal when instrument twisted off

g.) PERFORATION into furcation caused by using a longer bur and failing to realise that the narrow pulp chamber had been passed. Measure the bur against the radiograph and the depth to the pulpal floor marked on the shaft with Dycal.

Perforation into furcation of molar

It is therefore, important to follow the principles of access opening and to understand the internal and external tooth morphology while preparing access for an endodontic treatment.