Clinical Instructional: Endodontic Cleaning and Shaping and Achieving Deep Shape

Terry Pannkuk, DDS, MScD Instructional, Clinical Endodontic Technique Instruction, Access, Cleaning and Shaping, Obturation

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The goals of endodontic treatment have remained equivocal for decades as issues of periapical tissue cytotoxicity, apical limits of obturation, design of the root canal preparation, and most recently endodontic access design have predominated debate.

The Socratic Method of scientific argument is often disrupted by the 3 “E’s”: Emotion, Ego, and Economics; otherwise there might be universal acceptance of certain logically derived clinical principles. The once unquestioned treatment objective of removing pathogens and inflammatory mediators from the root canal system space has more recently been contested with the trend in health care toward “microinvasiveness”. Any trend for the sole sake of a trend often lacks a foundational path of logic and may present a mouse trap capturing errors of objectivity creating a cult practicing foolishness.

There have been many different styles of root canal preparation from the “Washington Monument Prep” described by John Ingle to the tapering cone with apical patency promoted by Herbert Schilder. My training by Schilder profoundly influenced my endodontic clinical technique, which began a life long scientific validation of my choice through experience and examination of decades of recalled treated roots. The introduction of rotary files has facilitated shaping but not necessarily cleaning of the root canal system. I will highlight my personal understanding of the Schilder technique as he taught me which highlights management of the root apical third.

Two failed cases treated by an experienced and talented clinician with an alternative clinical style will be analyzed as a detailed instructional. I was given permission by this generous respected clinician to dissect all speculated clinical reasons for the failures as my opinion, which I hope, will be discussed thoroughly in the discussion by others.

My opinion: the current teachings of endo are inadequate in the sense that they minimize the importance of proper hand file use combined with copious irrigation irrigation as taught by Herbert Schilder. Rotary files shape but inefficiently clean a complex root canal system (simple ones are rare). Restricting endodontic access though an unusually small occlusal surface outline leads to even poorer debridement with ineffectual access to the apical third of a root.

Endodontic access literally constitutes a “means to an end”, a root end and all lateral root surfaces producing a portal of exit (POE). Access is dictated by numerous clinical parameters not primarily concerning preservation of dentin, which is rarely reduced to a clinically significant degree during the meticulous achievement of necessary endodontic treatment objectives. The external crown preparation design and choice of restorative materials has a much greater impact on the structural integrity of a tooth. A much-ignored tooth strength analysis in endodontics is the von Mises yield criterion often discussed in the prosthodontic literature regarding the physical properties of posts imposing stress on dentin. I cannot find one significant reference to von Mises stress ever having been specifically discussed as it relates to the fracture resistance of endodontically treated teeth, the design of the postendodontic restoration and different internally placed core materials.

The initial endodontic treatment focus should be elimination of disease.

The final endodontic treatment focus should be idealized restoration and returning the tooth to function.

If the initial focus, disease-eliminatiion, is not achieved there is no point in restoring the tooth. Subsequently, if disease elimination results in a tooth which cannot be restored to function, then it should be extracted. In that unfortunate instance, at least the goal of disease elimination was accomplished.

With the logical endodontic treatment objectives in mind, endodontic treatment should proceed in the following sequence:

  1. Aseptic isolation with a rubber dam (if the tooth cannot be aseptically isolated, the tooth should not be treated because it likely cannot be adequately restored)

  2. Direct line access to all root canal orifices dictates the appropriate occlusal outline form, which may slightly vary from tooth to tooth also influenced by ease of access to the tooth itself. Direct line access is achieved when an endodontic file can be placed to the first curve of a root without the infringment of overhanging dentin. Unimpeded access facilitates the later process of apical debridement and the final cone fitting which can be considered a practical litmus test of completed cleaning and shaping of the root apical third.

  3. Orifice widening is next performed to a degree that allows unrestricted file entry to the root apical third, but also allows fortuitous discovery of deep ramifications only achieved by gradual and delicate coronal shape development.

  4. The next step is the repetitious placements of a pre-curved hand file series which Herbert Schilder described as “recapitulations”. Full strength sodium hypochlorite should be used and the pulp chamber and canals should be constantly flooded and cleared not allowing the apical settling and blockage of generated debris.

  5. Irrigant activation with an ultrasonic file provides a great benefit of clearing debris from the root canal system but the root canal system should be prepared to a near complete degree to avoid wedging and separation of the ultrasonic file tip. The ultrasonic tip should be used passively on a low power setting. If used passively and not wedged it can be removed easily if it does happen to separate.

  6. Final shaping of the main apical root terminus allows a gutta percha cone to be fit with smooth tug back to the tip of the root. Depending upon the blotting point of a paper point, the gutta percha cone can be cut back to the determined length. A slight error on the long side is clinically insignificant.

  7. Obturation tends to demonstrate deficiencies or accomplishments during the cleaning and shaping process. A properly fit cone-

a. condensed with multiple waves of condensation using appropriately levels of heat,
b. applied for an appropriate period of time,
c. condensed with an appropriate amount of pressure,
d. utilizing an appropriately sized plugger, and
e. compacted to an appropriate depth

will radigraphically show-

a. Apical deformation of the cone
b. Filling of accessory canals, loops, and fins
c. A homogenous dense filling
d. Apical control suggesting an apical seal

Opinions

Case 1: Child patient with incomplete root formation. The Schilderian clinical endodontic treatment objectives are very challenging to complete with incomplete root development. A Cvek pulpotomy with MTA or similar tricalcium silicate/bioceramic material base is best placed indefinitely until complete root development. If the tooth is abscessed then drainage leaving as much apical pulp as possible is desired to preserve Hertwig’s Epithelial Root Sheath which will allow the best chance of normal root formation over time. If single visit endodontic treatment is performed there is absence of case control, likely a weeping/bleeding canal leading to later stagnation of necrotic tissue/debris and sepsis percolating out the unsealed/uncleaned apices. Meticulous control of dental biology and delayed treatment in this case would have likely led to an improved outcome.

Case 2: In this case the caries and existing restoration should have been removed. There was no reason to minimize the occlusal endodontic outline form because it was unnecessary to preserve the caries and existing amalgam restoration which required removal anyway. This tooth appears to show more than two roots, possibly a radix entomolaris variety. Extending the access outline by removing all caries and existing restorations would have simplified exploration and treatment of the complex anatomy. Molar occlusal outline forms should be rectangles not triangles. The overhanging distal amalgam may have inhibited the flushing and removal of debris with copious irrigation and mechanical filing. A larger opening simply allows better visualization, flushing, and clearing. The wide-banded radiolucency along the entire distal aspect of the distal root might represent a vertical root fracture, which could have been more definitively diagnosed with removal of the amalgam filling. One distal canal appears to have some “splaying’, or condensation spreading of the filling material at the terminus, but the three other apical fillings look like they exist as “floating cones”, or uncondensed apical cones simply fit to, but not adequately sealing the apex. A more complete radiographic “look” would show more splaying and the filling of accessory canals, fins, or loops which occur in most all molars and are demonstrable after most endodontic treatments on a final filling radiograph. The radiographic “look” does not necessarily indicate that all endodontic objectives were achieved but does tend to highlight likely deficiencies.

In summary, the modern practice of endodontic treatment should focus on definitive apical debridement, which may, or may not be highlighted by the root filling. Shaping and curve management is over-emphasized by rotary file manufacturers simply because that is what can be marketed successfully as a true performance characteristic which can be visualized on a radiograph. An all-rotary file technique is also very easy for a non-specialist to perform. Debridement of complex apical anatomy is not efficiently or effectively achieved without the adjunctive use of pre-curved hand files, which is essential for deep shape, more definitive debridement, and more predictable treatment success.

Elimination of endodontic disease should be the first focus but with an end perspective on restorability and returning the tooth to stable function.


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