Factors to be Considered when preparing a root canal

With the invention of nickel titanium instruments came the additional question of, “How wide should I make the taper of the preparation?” This essentially split clinicians into two schools of thought.

1. Those who prepare the apex to large apical sizes, such as 40 and above but use narrow tapers (4%).

2. Those who prefer less apical preparation size 20 or size 25 but use a wide taper (6% and above).

Factors to be Considered when preparing a root canal

PULP STATUS

An important factor to consider when preparing a root canal is to establish where the bacteria are likely to be situated.  In acutely inflamed cases the microorganisms are located in the coronal region of the root canal and there are very few, if any microorganisms in the apical region. In necrotic cases we have to assume they are the throughout the root canal system and in the apical ramifications.  The way in which we prepare the canals of these two very different situations should also be different. In inflamed cases or elective root canal treatments there is no need for a wide taper or large apical preparation. Depending on the case stainless steel hand files with a 2% taper may be all that is necessary! However in necrotic cases with large periapical lesions irrigating to the apical region becomes critical. Some investigators recommend the irrigation needle should be placed 1mm from the working length (Chow et al 1983). But in reality we can move the irrigant solutions to the apex by using sonic or ultrasonic activation and having the irrigation needle this close to the apex may be unnecessary.

ANATOMY OF ROOT BEING TRATED

Probably one of the most important factors to consider when preparing a root canal is the shape of the root being treated; because the preparation must be made within the confines of this anatomy. In narrow roots using a wide taper or large apical size to prepare the canal can risk strip perforation or predispose the tooth to fracture in the future. In teeth with thin roots that have large periapical lesions (such as lower incisors) my preference is to prepare the canal using a file with a small apical size but one that has a wide taper for the first few millimetres. This preserves dentine at the apex but creates a region where the irrigant solutions can reach the apex. If the anatomy does not permit the preparation to be made wide enough to allow irrigants to reach the apex then activation of the irrigants and placement of an antibacterial medicament becomes a more important factor.