There is a significant difference between getting a white line to the end of the root on a radiograph versus treatment which provides a biologic three-dimensional cleaning, shaping and obturation of the root canal space from the orifice to the minor constriction of the apical foramen.
In the pursuit of ideal cleaning and shaping, the question remains: does the size of the final master apical preparation matter?
While some endodontic equipment and techniques might be faster than others, the final result that accentuates the potential for healing is the parameter that matters most. Despite advertising, cleaning and shaping of the root canal system is not a menu driven experience. Canal anatomy is far too unique, much like fingerprints, upon which to impose a menu driven regimen.
Cookbook methods for shaping canals are doomed to failure as soon as the root is found that is not suitable for the given technique. Iatrogenic events of all types will result very quickly when instruments and concepts are imposed onto the root canal system as opposed to the root imposing the technique onto the clinician. One method of treatment does not satisfy the needs of all canals.
Shaping the root canal system properly can first off be performed by carefully examining the given anatomy of the tooth presenting for treatment. Assessing the tooth pre-operatively is done by radiographic means and viewing the access to the tooth that is available as well as what will be accessed through.
The patient’s opening, being adequate or limited, will also affect the ability of the clinician to get at the tooth. Multiple angles of radiograph can give a significant view of the three dimensional nature of the root canal system. It is essential that the radiographs be diagnostic and not elongated or foreshortened. Excellent anaesthesia, a rubber dam and high quality visualisation and magnification (ideally a surgical operating microscope) are used to have the greatest command over the operative site. All of the above is a basic precursor to addressing the apical foramen in root canal treatment.
In addition to the above, knowing to what diameter and taper the canal space should be prepared is key. While common tapers and tip sizes of preparation will vary with philosophy and training, worldwide taper and tip size tends to be approximately .04 size 20 or .06 and size 25. A strong argument can be made via the endodontic literature that these traditional tip sizes and tapers are too small.
In the context of the above question, size matters. In other words, if a canal is prepared to a .04 taper size 20 tip size, it might be possible to have a master point or carrier inserted into he canal to the end of the root but would this fulfil the biologic requirements of root canal therapy? The simple answer is no. Accomplishing the task of properly cleaning and shaping the root canal system in three dimensions requires knowing to what size the canal should be ideally shaped based on its original dimensions. In other words, one size does not fit all in relation to shaping and ultimately filling canal systems.
Not all canals should be filled arbitrarily to a given canal taper and diameter even though such a diameter and taper might provide a white line to the apex. In the most general sense, small canals can be opened to smaller dimensions and larger canals must have a larger final prepared canal shape and diameter.
The final apical diameter must be determined not by some arbitrarily defined point but ideally by first knowing what the actual diameter of minor constriction of the apical foramen. Using a-.02-tapered hand file to determine the diameter of the minor constriction of the apical foramen can ‘gauge’ the apex and help the clinician determine what the final apical file should be. If, for example, a #25 hand file binds at the minor constriction, that is the diameter of the canal at the narrowest point in the apical architecture.
Instrumenting the apical 3-4 mm of the canal down to the minor constricture can go far toward providing optimal cleaning and shaping. In practical terms, if in our example, the minor constricture is a 25 initially, the final prepared diameter can easily and safely be prepared to a 50 or 60 with the correct rotary nickel titanium instruments (not hand K files).
The K3 rotary nickel titanium file system (RNT) system (SybronEndo) and the LightSpeed System alone or in combination are both excellent methods with which to achieve these larger apical preparations safely and efficiently. A future column will discuss more specifics with regard to this technique.