Rationale of Determination of Working Length

The significance of determining the working length are listed below:

1) The calculation determines how far into the canal the instruments should be placed and worked and thus how deeply into the tooth the tissues, debris, metabolites, end products, and other unwanted items should be removed from the canal.

2) You will realise that by determining the working length you will be able to limit the depth to which the canal filling may be placed.

3) It will affect the degree of pain and discomfort that the patient will feel following the appointment.

4) If calculated within correct limits, it will play an important role in determining the success of the treatment and, conversely, if calculated incorrectly may lead the treatment to failure.

The working length determination establishes the apical extent of instrumentation and the ultimate apical level of root canal filling. Failure to accurately determine the length of the tooth may lead to apical perforation and overfilling with increased incidence of post-operative pain. In addition, you might expect a prolonged healing period and increased failure due to the incomplete regeneration of cementum, periodontal ligament, and alveolar bone. Failure to determine the working length of the tooth accurately may also lead to incomplete instrumentation and under filling with attendant problems like persistent pain and discomfort from inflamed shreds of retained pulp tissue. In addition, ledge formation may be developed, short of the apex, making adequate treatment or re-treatment extremely difficult. Finally, apical percolation may develop into the unfilled “dead space” at the apex. This could result in a continued peri-radicular lesion and increased incidence of failure.

It is normally felt that the proper point to which the root canals should be filled is the junction of the dentin and the cementum and that the pulp should be severed at the point of its union with the periodontal membrane. The cementodentinal junction (CDJ) is the anatomical and histological landmark where the periodontal ligament begins and the pulp ends. Root canal preparation techniques aim at to make use of this potential barrier between the contents of the canal and the apical tissues. It is generally accepted that the preparation and obturation of the root canal should be at or short of the apical constriction.