By Richard E. Mounce, DDS
Knowing which obturation technique is best suited to a particular canal anatomy is a skill that comes with experience. In addition to appreciating which obturation technique is most applicable to a given clinical situation is understanding if any modifications of the technique might be required. There is no one-size-fits-all obturation method. This means that the clinician should be willing and able to move between different obturation systems seamlessly, assuming that there is some clinical variation that optimally requires divergence from standard protocol. At times, even when using the same technique, there might be indications for variance. For example, if the clinician is backfilling a lower molar with SystemB via a warm “gun” device such as the Elements Obturation Unit™, he or she may backfill the entire canal in one instance with one squirt and backfill the canals in 3-4 mm segments in another (SybronEndo, Orange, Calif.).
In the most general sense, obturation techniques, irrespective of the material used (gutta percha and RealSeal bonded obturation materials) share common principles (SybronEndo, Orange, Calif.). For example, both of the materials above are available in master cone varieties, obturator-based varieties, and both can be injected (without a master cone). None of these three methods is inherently better than another as each of the above should be principle-driven to achieve the correct obturation, irrespective of the particular method used. Principle-driven in this context means that the obturation should:
- Be three-dimensional
- Be without voids from orifice to apex
- To the greatest extent possible, minimize film thickness and maximize the obturation core material
- Move a heat-softened mass of obturation material into all of the ramifications of the canal space and replicate the internal anatomy of the tooth
It should be noted that this describes more the mechanical goals of obturation rather than the biologic goals. These biologic goals are somewhat different and related to providing an apical seal and ideally eliminating the movement of bacteria in the canal; in essence, trapping any residual bacteria present after cleansing and shaping procedures. To this end, using bonded obturation in the form of RealSeal has been shown to reduce coronal microleakage in vitro and in vivo in a clinically relevant manner relative to gutta percha. RealSeal, in the master cone and obturator-based form is highly biocompatible.
With the above as a background, it is axiomatic that the quality of the obturation is directly related to the quality of canal preparation. Excellent preparation leads to optimal obturation. Ideal shapes for canal preparation include the following characteristics:
- The preparation has narrowing cross-sectional diameters and resembles a tapered funnel
- Patency is maintained
- The canal is left in its initial position
- The apical foramen is left at its original size and position
- The master apical diameter and taper are optimized for ideal irrigation and cone and obturator fit
Number 5 above in the list requires interpretation. The larger the taper, the better — with the caveat that the final preparation avoids unnecessary removal of tooth structure and/or perforation, especially at mid-root. Clinically, this means that a .08-tapered preparation is more ideal than a .06 in the mesial root of a lower molar if there is no iatrogenic risk to its preparation. The Twisted File can easily and predictably prepare a .08 taper in the mesial root of a lower molar relative to a rotary nickel titanium file that has been manufactured by grinding (SybronEndo, Orange, Calif.). It should be mentioned that if the canal can have its master apical taper be prepared with a single .08 tapered Twisted File to the minor constriction of the apical foramen (MC), that the taper will be continuous throughout the preparation and as a result provide “deep body” shape. Deep body shape refers to the continuity of taper that should ideally exist throughout the preparation, especially at the junction of the middle and apical thirds.
Clinical anatomies and their impact on obturation technique decisions
In general, choosing one obturation technique over another should include these general considerations:
1) Canal length. Roots above 25 mm in some hands might be an indication for carrier-based techniques, clinician dependent.
2) Canal curvature. The greater the curvature, the more critical it is that the access and shaping of the coronal third be ideal to allow unrestricted access of instruments and irrigants into the middle and apical thirds. As a result, if the middle third is shaped correctly as well as the orifice and coronal access, the clinician can have optimal visual and tactile control over the use of heat pluggers in the apical third if using a technique such as SystemB.
3) The initial size of the MC and the final size of the apical preparation. The wider the MC and the more open the apex, the greater the indication for the master cone-based techniques or possibly MTA (Dentsply Tulsa Dental, Tulsa, OK) and the less optimal a carrier-based technique becomes. All things being equal, carrier-based materials in this clinical situation will have a greater tendency to unnecessarily extrude sealer and obturation material beyond a relatively open apex. Extrusion becomes more problematic if the apex were to be coincident with the mandibular canal or mental nerve.
4) The presence and/or severity of apical resorption. For reasons very similar to those above in number 3, the more open and irregular; i.e., the further the MC deviates in form from the usual, the less indicated warm carrier-based methods will become.
5) Where the tooth is located relative to whether the clinician is right- or left-handed. Some areas of the mouth are more challenging to reach than others. All things being equal, for example, a right-handed clinician will have a harder time placing an obturator into a lower left second molar mesial root.
6) Experience of the clinician. The more experienced the clinician, the greater the ease with which he or she will be able to switch from one technique to another within the same tooth or from case to case. For example, if an apex is blocked in one root but preparation is ideal in another, the clinician might consider using extrusion of a warm obturation material without a master cone in the blocked canal and a master cone or obturator in the other.
7) Use of the surgical operating microscope (SOM) or other means of visualization. Whether using loupes Class IV 4.8X HiRes Plus Loupes, Orascoptic (Middleton, WI) or the SOM (Global, St. Louis, MO), in either case the clinician will have better tactile and visual control than he or she otherwise would using less magnification and working without additional light sources.
In addition, it is essential that the clinician obtain the correct working length. A master cone or obturator should not be placed until the master apical diameter and taper are optimized and the clinician is absolutely sure that he or she has the correct position of the MC, a determination made by using several means of confirmation.
And finally, the material used for obturation makes a significant difference in the resistance of the obturation to microleakage. In vitro and in vivo, RealSeal has been shown to reduce microleakage relative to gutta percha in a statistically significant manner. I have used RealSeal since January 2004 for all of my obturation.
I welcome your feedback.
Richard E. Mounce, DDS, is the author of the nonfiction book “Dead Stuck” — “one man's stories of adventure, parenting, and marriage told without heaping platitudes of political correctness.” Pacific Sky Publishing. DeadStuck.com. Dr. Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, Wash. Contact him at firstname.lastname@example.org.