Page 17 - The Beauty and Sorrow in Endodontics (WL and C/S)

Once pulpal tissue is removed, immune cells are no longer able to enter into the canal

system and remove the pathogens within the root canal system. Therefore, if pathogens
remain in the last 1-2mm of the apical canal, they will not be eliminated by the body's

natural defense mechanism. In fact, the bacteria may obtain nutrients from nearby tissue

fluid and release pathogenic byproducts that result in chronic destruction of the periapical
tissue.

Accurate Working Length Determination is Key to the Success of Endodontic

Treatment

The following are some terminology pertaining to working length (WL):

a. Tentative WL; tWL:

There are many ways to determine the tentative WL, and it's better to be short rather

than long. Many research papers have compared different canals in different teeth and
ethnicity and came up with average lengths for each that we can use. In an office with

digital radiographs, the system often has a built-in ruler that can be used to estimate the

tWL. In an office that uses traditional films, as long as the image is not elongated or
foreshortened, a traditional ruler can be used to measure the tWL.

b. Initial WL; iWL:

The initial working length (iWL) is the working length measured on the smallest file

that can peek through the RT; it is essentially the working length measured on the initial
apical file. The most common way to determine iWL is by measuring a straight line from

a point on the occlusal surface of the tooth to the root apex minus 0.5-1mm. This number,
of course, is not accurate as there may be elongation or foreshortening of the radiographic

film. In addition, some authors recommend removing an extra 1-2mm from the pre-
determined length if there is a huge periapical lesion or if there are signs of root

resorption. There are also apex locators on the market that can aid in determining the

iWL, they are classified into different generations based on if they measure resistance,
voltage, or frequency of the current. Two electrodes (one hooked on the lip and one on

the file) measure the flow of electrical current passing through, and when the file contacts

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