Root Canal Catheterization

Relationships of the pulp chamber to the clinical crown
Law of centrality: the floor of the pulp chamber is always located in the center of the tooth at the level of the CEJ
Law of concentricity: the walls of the pulp chamber are always concentric to the external surface of the tooth at the level of the CEJ
Law of the CEJ: the CEJ is the most consistent, repeatable landmark for locating the position of the pulp chamber
Table 2.2

Krasner and Rankow’s proposed laws [2]
Law relationships of the pulp-chamber floor
Law of symmetry 1: except for maxillary molars, the orifices of the canals are equidistant from a line drawn in a mesial-distal direction through the pulp-chamber floor
Law of symmetry 2: except for the maxillary molars, the orifices of the canals lie on a line perpendicular to a line drawn in a mesial-distal direction across the center of the floor of the pulp chamber
Law of color change: the color of the pulp-chamber floor is always darker than the walls
Law of orifice location 1: the orifices of the root canals are always located at the junction of the walls and the floor
Law of orifice location 2: the orifices of the root canals are located at the angles in the floor-wall junction
Law of orifice location 3: the orifices of the root canals are located at the terminus of the root developmental fusion lines
After locating the point of the entry, the access preparation should be initiated using the appropriate bur. Bur selection depends on clinician preferences and the type of material (natural or man-made) that you are cutting. Usually #2 round bur will be used with small teeth and #4 round bur used with larger teeth. There are also other burs such as a tapered fissure bur which cuts efficiently through prosthetic restorations. Tapered diamond, Endo Z bur, and 245 burs can be used also. The drilling should be carried on until a “drop” is felt. Caution must be taken since this drop is not applicable in teeth with shallow pulp chamber as defined by pre-treatment radiographs. De-roofing should be attempted until the pulp chamber is completely uncovered. No attempts should be made to locate the orifices until de-roofing is completely finished. Then the canals can be observed. Any unsupported tooth structure should be removed for restorative assessment.

2.2 The Shaping Concept

After adequate access opening has been prepared, a sharp endodontic explorer is typically used to locate the orifices and to assess for straight-line access. Pre-flaring the coronal third should be carried out with the goal of creating a “funnel” at each canal orifice so that instruments easily “drop into” the canal without the clinician having to “search and find” canals. Gates Glidden burs and many other “orifice opener” instruments are available for creating such funnels without gouging the pulpal floor. All dentin triangles in anterior teeth and dentinal overhangs in posterior teeth are removed to reveal orifices and establish straight-line access to the middle third of each root canal. Preparation in this manner makes the subsequent steps easier and faster while eliminating any unnecessary bending of instruments which can later lead to broken instruments and ledged canals.
Schilder (1974) described the cleaning and shaping process, often called “instrumentation,” in great detail. He emphasized the importance of achieving certain objectives that result in successful endodontic treatment [1]:

  • A continuous funneled and tapered preparation from apical to coronal third.
  • As a result of this continuous taper, the smallest diameter should be kept apically and largest diameter coronally.
  • The apical foramen should be kept as small as practical.
  • The apical foramen should be kept in its original geographic location.
  • When the canal is shaped, it should be shaped in three dimensions and the preparation should be a continuous funnel to the apical area.
A continuous funneled and tapered preparation ensures adequate delivery of irrigants close enough to the working length, and it exposes lateral canals by shortening its length. Tapered preparations increase the contact between the file and dentinal walls, whereas in parallel preparation it is less likely to have such contact. Obturation also will be enhanced with funneled preparations, and compaction forces are distributed evenly resulting in a better seal.
The diameter of the root canal should be as small as the canal preparation apically. This kind of preparation will transmit the compaction forces to the smallest area including lateral canals, fins, and isthmus. This results in denser compaction of gutta-percha. Caution must be taken not to weaken the coronal structure by creating too large of a taper. This is particularly true in teeth that have internal resorption.
Clinicians, during root canal therapy, frequently deviate from the canal’s original path thereby creating a new artificial path, commonly called “transportation” of the canal. This is most often caused by the rigidity of the instruments and their inability to accurately follow the curves of the canals. One objective of proper root canal instrumentation is to minimize transportation because it can result in unnecessarily removing of healthy dentin and incomplete debridement of the harmful contents within the main canal. However, conservative straightening of the canal’s coronal third is often desirable in order to achieve better access to the apical third. Transportation of the foramen is one of the most common reasons for wet or bleeding canals, which can result in chronic persistent inflammation and failure of root canal therapy. The rigidity of the metals creates a lever effect when the instrument goes around a curve. This exerts a lateral force, which can lead to transporting the foramen. In severe cases, a lateral perforation through the side of the root is the result. Creating straight-line access to at least the mid-root of the canal helps to reduce this level effect and reduces the lateral force of the instrument leaning against the side wall of the canal. The use of copious amounts of irrigation during instrumentation also helps prevent accumulation of dentinal shavings and canal blockage that also cause instruments to deviate away from the canal’s original path.
The following biological objectives are necessary for adequate root canal preparation:

(a)

Confine the instrument to the root canal space without preparing the surrounding bone.
 
(b)

Care should be taken not to force or push the root canal content to the periradicular area.
 
(c)

Removing and debriding the root canal content meticulously.
 
(d)

Completing vital and non-vital cases in one visit if the chance of successful treatment is not compromised by doing so.
 
(e)

Creating sufficient space for effective irrigation and intracanal medicaments to accommodate the periradicular discharges as a result of inflammation caused by instrumentation.
 

2.2.1 Hand Instrumentation

There are essentially two primary techniques to shape the root canal system using hand files. They are step-back and crown-down technique.

  • Step-back technique [3]
    This technique involves completing instrumentation of the apical third first and then debriding the remainder of the canal by “stepping back” coronally from the working length with successively larger instruments, in 0.5–1 mm increments.
  • Crown-down technique [4]
    In this technique the coronal third is flared first, using Gates Glidden drills or similar instruments to remove the obstructions from coronal and middle third. The apical third is negotiated and completed last. Pre-curved files are advocated during this technique.
In many instances, clinicians use a combination of both crown-down and step-back techniques as they are not mutually exclusive of each other.

2.2.2 Rotary Instrumentation

Endodontic instruments typically have design features as described in Table 2.3.

Table 2.3

Rotary endodontic instrument components
File components
Definition
Role
Flutes
The groove in the working surface used to collect debris
Debris collection depends on the depth, design, and finish
Land
The non-cutting part of the file, which is a metal projection away from the center of the file
Reduces file engagement and keeps the file centered
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Sep 10, 2016 | Posted by in Endodontics | Comments Off on Root Canal Catheterization
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