Alternative to NiTi Instrumentation in Root Canal Treatment
About the Author
Dr. Musikant is a graduate of the University of Pennsylvania School of Dental Medicine. He is a member of the American Academy of Endodontists, the Academy of General Dentistry, and the American Society of Dental Aesthetics, and is a member of the board of the First Madison Group. In addition, he is the President and Co-Director of Dental Research at Essential Dental Systems. He has lectured throughout the world and is the author or co-author of more than 185 published articles.
Dr. Musikant has no relevant financial relationships that conflict with the administration of this CE course.
- Informing dentists how to preserve dentin while fully debriding the canal of tissue and creating a space for effective irrigation and obturation.
- To appreciate the connection between canal preparations and its impact on the overall strength and integrity of the root.
- Exposing dentists to the concept of 30º reciprocation with predominantly 02 tapered stainless steel relieved vertically fluted instruments in preparing the canal spaces.
- How 30º reciprocation virtually eliminates separation anxiety allowing the vigorous preparation of the buccal and lingual extensions of highly oval sheath-like pulpal anatomy
- Employing techniques that do away with the potential for the development of dentinal defects and their propagation into full blown vertical root fractures.
- How employing these techniques increases safety reducing both procedural stress and the elimination of the need for frequent instrument replacement that adds significantly to the cost.
This course introduces dentists to common sense insights into the complexity of pulpal anatomy as it is and the best ways to remove it and a circumferentially uniform layer of dentin without sacrificing any more tooth structure than is necessary for adequate debridement, irrigation and obturation.
From my readings of the research, coupled with clinical experience, I have concluded that the use of rotary NiTi is a poor way to shape canals. In light of its popularity (being universally taught in dental schools and widely sold by the largest dental manufacturers under many brand names), you may ask how I substantiate this view.
In this matter, my contention rests on several pressing factors, beginning with the configuration of a large portion of the pulpal anatomy.(1) Evidence has been available for over 100 years that the pulp is typically arranged in highly oval-shaped configurations. In recent years, this understanding has been corroborated by micro-ct scanning, which has allowed us to observe such configurations in rotating three-dimensional presentations. Many times, as the scanners show, the mesio-distal widths of the isthmuses are thinner than our smallest 02 tapered 06 tipped instruments, reflecting the narrow external mesio-distal diameter of the root within which the pulp tissue resides.
Our goal in instrumentation is to remove this tissue while also removing a uniform layer of dentin from the canal walls that may have been infected by bacteria invading the dentinal tubules. There is no evidence, to my knowledge, that the bacteria invade the depth of the dentinal tubules more in the narrow mesio-distal plane than in what is often the far broader bucco-lingual plane. For purposes of cleansing the canal, there is no reason to remove a greater depth of dentin in one plane than in the other. Assuming this is the case (and no evidence currently suggests otherwise), the final shaping of the canal space would involve removing a uniform thickness of dentin from the canal walls and, in doing so, rendering a shape that was more or less similar to the original canal anatomy. The minimum mechanical goal in such cases is to remove undercuts in both the mesio-distal and bucco-lingual planes. By doing this, we can give the blades of the instruments the opportunity to more predictably remove dentin along the length of the canal.
This type of shaping, more often than not, is not accomplished by the use of greater tapered rotary NiTi instrumentation, which leaves large portions of the bucco-lingual plane untouched. Another goal of shaping canals is to prepare a space that can be predictably obturated, the best strategy for which was most emphatically laid down by Dr. Schilder, who consistently demonstrated well-obturated canals when those canals were shaped with a continuous conically shaped taper from orifice to apex. Upon reflection, the goal of dentin preservation accomplished by the uniform removal of dentin in what was originally a highly oval canal does not produce the conditions for optimum obturation of that space when using filling techniques that are mostly dependant upon the adaptation of gutta percha to the canal walls, be it accomplished by room temperature or thermoplasticized techniques.
The emphasis on creating a space for the obturation of gutta percha has evidently eclipsed the preservation of dentin. All the rotating NiTi systems produce significantly tapered shapes. A crown-down technique is employed that accentuates coronal tapers. This type of canal preparation has the added benefit of minimizing the engagement of the rotating NiTi instruments along length, reducing both the torsional stress and cyclic fatigue that the instruments are exposed to, reducing the incidence of instrument separation.
On the one hand, we want to preserve the dentin, maintaining as much as possible the integrity of the root, and on the other hand we may need to remove dentin beyond the initial need to create a space that is more easily obturated while reducing the stresses to the instruments. These conflicting interests can result in excess removal of dentin in the mesio-distal plane when oval canals are being cleansed and shaped.
If one is an advocate of rotating NiTi, one would tend to dismiss such insights, noting a high rate of success, and conclude that such success exonerates and potential drawbacks of greater tapered rotating NiTi preparations. Furthermore, one might suggest that the previous use of K-files was much more difficult and took a lot more time, further justifying the use of greater tapered shaping. To counter that argument, we know that endodontically treated teeth sometimes fail structurally long after treatment. The most logical response to such failures is to preserve as much of the dentin as is practical consistent with effective debridement, cleansing and irrigation. The preservation of dentin should not be compromised by the need to intimately adapt gutta percha to the canal walls.
If we prepare the canal walls with far less taper, widening the preparation in what is often the broader bucco-lingual dimensions while minimizing the preparation in the narrower mesio-distal plane, we now have a space that preserves dentin, but creates an inhospitable space for the close adaptation of gutta percha to the canal walls. This does not mean for a moment that the space cannot be well obturated.The two traditional methods of obutration place the major burden of filling the canal space on the gutta percha. If, however, we flood the canal with an epoxy resin cement that flows far better than the most thermoplasticized gutta percha and follow that with a point that is well fitting in at least the mesio-distal plane and is itself generously coated with more epoxy resin cement, the sealer will be easily driven laterally into any nooks and crannies that may exist in this more conservative preparation, with excess cement escaping laterally. The result is still a three-dimensional fill that accomplished the goal of sealing the canal space while giving the dentist the ability to retreat if it becomes necessary.
The properties of the epoxy resin cement include: deep penetration into the dentinal tubules previously opened with 17% EDTA; complete polymerization without shrinkage; and the ability to bond both chemically and physically to both the gutta percha point and the canal walls. In fact, being a room temperature system, both the gutta percha and the cement will expand as they warm to body temperature, further improving the seal.(2) The result will be the placement of a point that is binding apically, but leaves spaces of varying degrees along the length of the canal that are consistently filled with the epoxy resin cement, preventing voids and having the ability to penetrate the dentinal tubules along length. The observation of lateral canals filled using this technique is proof that the employment of a single cone placed into a canal flooded with cement has the ability to drive that low viscosity cement laterally through any extra portals that may be present.
As you can see, there is a practical alternative to creating a space for the specific needs of either lateral condensation or thermoplastic obturation. This alternative removes the need for excessive removal of dentin. Now the only reason for greater tapered preparations is the safety of the NiTi instruments, whose use in rotation, be it continuous or interrupted, may leave them vulnerable to damage. By substituting 30º reciprocation in place of rotation, we virtually eliminate torsional stress and cyclic fatigue, the two factors most responsible for instrument separation.
Such a substitution has added benefits. When employing rotation, the creation of a glide path is essential. While some manufacturers state that a canal should only be patent to a 10 prior to the use of rotating NiTi, experience suggests a canal preparation to a minimum of 20 makes the use of rotating NiTi more predictable. In either case, the purpose of the glide path is to create a patent pathway for the rotating NiTi instruments. Most dentists consider the glide path to be a miniature version of the space created with the greater tapered NiTi, essentially a conical shape in cross-section that will now have enhanced tapering with the application of the NiTi instruments. As long as conical shapes are considered the ideal shape, the highly oval sheath-like anatomy that truly exists will not be directly addressed. If we appreciate anatomy as it truly exists, we will want to address the thin isthmuses of tissue most often present in the bucco-lingual plane. Logically, the most effective time to address these thin isthmuses is when we are using our thinnest instruments, the ones that have the best chance of invading these narrow spaces.
Up until this point, I have discussed the shortcomings that are impossible to overcome when using greater tapered rotary instrumentation. When addressing initial glide path creation the instruments most recommended are 02 tapered files, whether fabricated from stainless steel or NiTi. Files are designed with a tight, highly horizontal flute orientation along the length of the instrument. The typical K-file has 30 flutes along its working length. They are generally used with a watch winding or twist-and-pull motion. Until a vertical stroke is applied, watch winding will do nothing more than engage and disengage the horizontally oriented flutes from the canal walls. Once we realize that the flutes will only shave dentin away when they are more or less at right angles to the plane of motion, it becomes clear that the tight horizontal flutes of the K-file (or its equivalent) are counterproductive to efficient and effective shaping. This is further emphasized by the fact that the flutes along the shafts of all rotary systems (save the original ProFile instruments) are all vertically oriented, allowing them to shave dentin away as they rotate within the canal. The same design that works for rotary instruments should be applied for the same reason to the initial instruments. In short, I recommend using thin 02 tapered thin tipped vertically fluted instruments to create the glide path. However, using them in 30º reciprocation ensures a high degree of safety against instrument separation, allowing the dentist to apply these thin instruments against the sheath-like isthmuses of tissue that often connect canals along the bucco-lingual plane.
By using a predominantly 02 tapered sequence of instruments, we preserve coronal dentin most obviously in the mesio-distal plane while extending the preparation in the bucco-lingual plane to include the tissue that is present in these sheath-like configurations. We are no longer concerned about greater tapered shaping, as our method of obturation is compatible with much more conservative preparations.
Other points to consider:
- Krasner P, Rankow HJ. Anatomy of the pulp-chamber floor. J Endod. https://www.aae.org/uploadedfiles/publications_and_research endodontics_colleagues_for_excellence_newsletter/spring2010_bonusmaterialb.pdf. Published January 2004. Accessed August 18, 2014.
- Marín-Bauza G, Silva-Sousa YTC, da Cunha SA, et. al. Physiochemical properties of endodontic sealers of different bases. J. Appl. Oral Sci. Published August 2012. Accessed August 19, 2014.
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