This is a short segment from my clinical endodontic technique presentation. Schilder's principles of developing apical shape results in better apical debridement and facilitates more complete and effective clinical obturation. This slide series portrays my interpretation.
One does not know how many lateral canals or complex ramifications may exist before beginning root canal treatment. Schilder's principles of cleaning and shaping describes the use of a precurved file series, used repetitively, passively, and with constant flushing of irrigant to prevent the accumulation and settling of apical debris. If one spends enough time in the case and performs an adequate number of recapitulations, the idea is that complex apical ramifcations will fortuitously and randomly be found with the tactile sensation of a "catch". This technique is as important today as it was when Herb introduced the concept. There is no current technology available to image the minute accessory canals and deltas but we are coming close with improved resolution in CBCT technology. One will never have much of a chance of treating complex anatomy completely if deep shape is not developed by creating adequate access and coronal taper. The current fad to restrict access with conservative occlusal preparations is an impediment to adequate debridement and eliminates all opportunities to treat complex root canal systems appropriately. Inadequately extended access fails to show filled apical ramifications upon obturation.
In some instances, the removal of gross pulp tissue from major ramifications suffices, but leaving gross communicating unclean space is unwise. Host defense, may play a role in a successful outcome but it certainly doesn't predictably excuse poor technique.
Coronal enlargement is not required to accommodate a precurved file, which is flexible and can be inserted easily. The larger and stiffer files should be precurved less as they are less important during exploration. The coronal enlargement is simply necessarry to introduce an adequate amount of irrigant and evacuate debris, which is an important objective. Achieving a direct line and better access to the apical third prevents block outs and more efficient access to the apical third of the root. There are numerous advantages to prudent coronal enlargement but the exact dimenstions should be strategically planned to specifically suit each individual case. Improving the canal prep convenience form eliminates apical “hurdles”. Many observed poor results are primarily related to rushed over-use of rotaries, too little time spent cleaning the apical third with hand files, under-shaping the apical prep, and then fitting a thin, crinkled, feather-tipped gutta pecha cone which is poorly cut back with no apical tug back.
The more time you spend performing apical recapitulations the cleaner and smoother the apical prep becomes eventually clearing and cleaning more of the complex apical anatomy. The currently available rotary files all tend to function the same and are excellent at shaping a single path to the terminus, but grossly ineffectual in debriding the apical third of the root. The small files hold the curve for one or two introductions, the larger files less so, but the objective is to have the arc of the curve act on the canal walls not the tip via the "envelope of motion" (Boston University Thesis, Dr. Robert Kaufmann). With the introduction of rotary files, the subtle nuances of curving and using hand files to develop a deep, clean shape in the apical third has been educationally neglected. We need high level science which will compare the efficacy of root canal debridement developing shape quickly with rotary files rather than classic slower techniques that let irrigants work with "slow" apical shape development. My suspicion is that slower shape development with more time allowing irrigant action will prove to be more successful.
In my opinion we should talk more about what cleans canals and shaping only in terms of how proper shaping facilitates debridement..
In summary, there is no substitute for spending time in a case going through numerous recapitulations with precurved hand files while flooding with irrigant.
Key Learning Points:1. There is a fine line between developing “deep shape” and a blow-out rip of the apex: one virtually guarantees success and the other creates a need for surgery. 2. Each presented root canal system requires a unique thoughtful plan for cleaning and shaping. 3. Apical portal of exit (POE) diameter is dependant upon the needs to address the unique anatomy of a root canal system.