Cavity Preparation & Working Length (WL) Determination

Root canal treatment
To begin root canal treatment several points should be considered

1-Preoperative radiograph

2-Local anaesthesia

3-Tooth preparation

4-Isolation of the

5-Access opening
Entrance into the cavity takes place through the crown of the tooth, gaining entry to the pulp chamber and removing the roof of the pulp chamber. Two handpieces are usually required for this task, which have low- and high-speed ranges of rpm.
For the initial entrance through the enamel surface or resin, metal and ceramic restoration, the ideal cutting instrument is the round-end carbide fissure bur with the accelerated speed handpiece. For porcelain fused to metal or metal-ceramic crowns, the extra coarse dome ended cylinder is effective.
While, for drilling through dentine, dropping into the pulp chamber and removal of roof of the pulp chamber, round burs sizes 1, 2, 4 and 6 with 2 lengths (regular and surgical lengths) are usually used. This drilling through dentine is done with slow-speed handpiece (3,000-8,000 rpm).
The chamber is then cleaned, the vital and inflamed haemorrhagic pulp tissue is extirpated with barbed broach and excellent visibility can be obtained with direct access of the root canal instrument, without bending of the instrument. After that, the radicular cavity preparation can be started.

6-Working length (WL)
Determining the working length is very important to ensure complete debridement of the root canal as close as possible to the apical constriction from 0.5-2 mm from the radiographic apex. This can be undertaken using electronic or radiographic devices.
1. The electronic device measures the root canal length by electrical resistance. However, it should be confirmed radiographically.
2. Radiographic technique shows the instrument that is used to determine the length of the root and shows the apex of this root. The instrument should be less than 3mm from the apex, otherwise another radiograph should be taken