Assuming you have made the right diagnosis, the tooth truly needs endodontic treatment, and the local anesthesia placed is deemed adequate, your first challenge is to enter the pulp chamber without perforating or removing excess amounts of coronal tooth structure.
The purpose of this article is to present step-by-step hints to help ensure clinical success.
Hint No. 1. Any permanent tooth not worn down occlusally/incisally has a pulp chamber that is situated approximately 7 mm from a cusp tip or an incisal edge.1-3 To slowly gain depth by small degrees leading up to 7 mm is needlessly inefficient, but to go beyond 7 mm in one fell swoop is needlessly dangerous. You have a landmark: 7 mm. By sticking to it, you will gain access in a predictable way without the concern of perforating the floor of the chamber. This hint is an immeasurable help when pulp chambers are narrower than the width of a No. 4 round bur that is often used to create the access.
|Figure 1. The length of the bur head plus the tapered portion of the shank equals 6.50 mm in length, which closely corresponds to a depth slightly deeper than the roof of the pulp chamber when measured from an unworn cusp tip.||Figure 2. This 6.50 mm mark on the shank of a high speed round bur can be easily marked with a colored ink, allowing the dentist to ease it up with the cusp tip.|
|Figure 3. Since we are relying on statistical depth rather than feel, calcified chambers don’t limit the use of this technique in finding the initial opening into the pulp chamber.||Figure 4. Once the roof of the pulp chamber is removed, highly calcified and desiccated canals make it difficult to find the canal orifices.|
Figures 1 and 2 demonstrate control of depth. Figure 3 controls the depth even when the chamber is so narrow that “popping in” is not discernible.
Once access is gained, the entire roof of the pulp chamber should be removed. The canals are often found at the furthest extensions of the chamber. To open less than fully makes the clinician vulnerable to missing canals that may be far too buccally or lingually positioned. However, opening fully does not mean opening more than fully. The roof of the pulp chamber produces a horizontal overlap once the initial entry is made.
Hint No. 2. By using a No. 4 round bur (in most situations) with a light dusting stroke against the walls, the overhanging lip of the roof can be removed without widening the opening beyond that point. With the roof fully removed, the challenge of finding the orifices to the canals remains. This may be made more challenging by the presence of pulp stones, a good deal of secondary dentin, and dried and dessicated remnant pulp tissue as illustrated in Figure 4.
Hint No. 3. If the tissue in the canal is vital, the irrigant that should be introduced is 17% EDTA, a mild acid that chelates the calcium in the dentin making it somewhat softer and, consequently, easier to negotiate. Do not use sodium hypochlorite (NaOCl) initially in vital cases because it tends to coagulate the remnant pulp tissue, making it harder to negotiate through and beyond. If the tissue is nonvital, by all means use 6% NaOCl immediately after gaining entry. Nonvital tissue is rapidly digested in the presence of 6% NaOCl.
Pulp stones take on a yellow color and, while in intimate mechanical relationship with the floor of the pulp chamber, they do not fuse with the floor like secondary dentin does. For this reason, they can often be picked away from the floor with a sharp explorer. Once through the secondary dentin and pulp stones, the canals of a calcified canal may still not be readily apparent.
Hint No. 4. With good illumination and magnification, the floor of the pulp chamber can often be read like a map with dark lines creating a Y or square configuration. The canals are generally at the endpoints of these lines, as illustrated in Figures 5 and 6. A Y configuration in a mandibular molar generally means there are 3 canals, while a square configuration generally means 4 canals. A Y configuration in a maxillary molar is also useful in finding the canals in the same way as mandibular molars. However, a Y configuration here does not mean there are only 3 canals. In fact, 90% of the time in maxillary first molars, an mb2 exists. However, it often becomes common with mb1.
|Figure 5. Please note as illustrated that the canals are generally found at the apices of the line angles describing the shape and dimensions of the pulp chamber.||Figure 6. The canals are also found at the furthest extensions of the dark colored “roadmap” often seen on the floor of the pulp chamber.|
Once the orifices to the canals have been found, they must be negotiated. There are different schools of thought on what type of instrument to use to gain access to the apex. One school of thought recommends stiff instruments to gain access into calcified areas. I completely disagree with this recommendation; until a canal is negotiated, one does not know the state of patency along its length. If the canal is calcified coronally (the way most canals are calcified), a stiff instrument is likely to create an indentation into the dentin that does not lead to the canal. Once indented, finding the true pathway that leads to patency becomes more difficult.
|Figure 7. Reamers (relieved and unrelieved) negotiate canals with less resistance than K-files (Sybron Endo) while recording the curve they are negotiating.||Figure 8. The flutes along a relieved reamer are more vertically oriented, on a shank that is more flexible, making them less engaging while cutting more efficiently and supplying an overall superior tactile perception.|
Hint No. 5. I much prefer reamers; instruments with significantly fewer contact points and more vertically oriented flutes compared to K-files (Sybron Endo) (Figure 7). They engage the canal walls far less and are more flexible. The goal is to find the small opening that leads to continuous patency. This target is best sought out with a thin flexible instrument that can only negotiate a space that is not calcified. It does not have the ability to indent solid dentin, something that is only a detriment in eventually finding the canal orifices. If, in fact, patency is not attained, then more coronal calcified dentin must be removed to reach a depth where at least a small amount of patency is present.
Once the canals are found, the next question is, what they are best shaped with? Even those using rotary nickel-titanium (Ni-Ti) do not employ them until the canals have been widened to a 20. The typical instrument used for this widening is the K-file; K-files engage the canal walls a lot due to the 30 flutes along length, and their horizontal orientation. The high number of flutes creates stiffness in the file, making it difficult to negotiate canals with multiplanar curves. Taken together, the number of flutes, their horizontal orientation and stiffness produce poor tactile perception as these instruments negotiate apically.
Hint No. 6. Use relieved reamers to shape the canals not only up to a 20, but through a 35 or higher (Figure 8). In order to appreciate the use of relieved reamers, one must be aware that they are designed far differently than K-files. There are 50% fewer flutes along their length. The flutes are twice as vertically oriented, and the shanks are far more flexible; a result of the fewer number of flutes, as well as the relief along the working length of the instrument. Together, these 3 design features give the dentist the ability to negotiate to the apex with far less resistance and a superior tactile perception, allowing for operator differentiation between a solid wall and a tight canal. The relieved reamers also represent an asymmetric instrument that can differentiate between a round and oval canal; a critical piece of information that tells the dentist when a canal must be further enlarged.
|Figure 9. The 30º arc of motion provided by the Endo-Express (Essential Dental Systems) provides rapid shaping without distortion as long as patency is maintained.|
Hint No. 7. The use of the 30° reciprocating handpiece allows the dentist to machine the walls of the canal at a rate of 3,000 to 5,000 cycles per minute (Figure 9). As long as the canals are patent, the walls of the canal will not be distorted and the shaping to each sized instrument will take only a few moments.
If one sticks to inefficient K-files, the desire to switch to rotary Ni-Ti is overpowering and well understood. However, the relieved K-reamers operate so efficiently, whether used with a tight watch-winding stroke or in a 30° reciprocating handpiece, that there is no need to incorporate the use of expensive and vulnerable rotary Ni-Ti systems.
Hint No. 8. Use a tapered peeso to better shape oval canals in their wider diameter through the middle third of the canal (Figure 10). One of the stated advantages of rotary Ni-Ti is its inclination to stay centered. Producing a well-centered space in an oval-shaped canal tends to not only leave tissue untouched in the buccal and lingual extensions of the canal, but to create a space that has undercuts in it, further compounding the challenge of removing as much tissue as possible. With the canal shaped by the tapered peeso to at least the middle third, it is unlikely any gross amount of tissue will be left in the recesses of an oval canal; and no undercuts will be present that will prevent larger, more aggressive instruments from removing any residual tissue that may still be present. This advantage is further enhanced by the fact that there is virtually no concern that the instruments will fracture as they become wider and more tapered. They can be worked against the walls of the canal forcefully, something not recommended with rotary Ni-Ti. Figure 11 clearly shows the asymmetrical shape of canals when viewed in the mesiodistal and buccolingual planes.
|Figure 10. The tapered peeso, or Pleezer (Essential Dental Systems), allows the dentist to straighten the coronal curves without removing excessive tooth structure safely and conservatively.||Figure 11. The concept of smooth continuous taper is nullified by the buccolingual radiograph that often presents a cross-sectional diameter much wider than the mesiodistal anatomy seen on clinical x-ray.|
The goal is to create a space that has not only mechanically removed the tissue, but a space that accepts a volume of irrigant sufficient to digest the tissue that has not been mechanically removed.
Hint No. 9. Use the reciprocating handpiece with a 25 relieved reamer as an activator of the irrigants. By running the 25 relieved reamer in each canal for each irrigant 30 seconds, the reamer aids in breaking down the biofilm layer, reducing the microbial load, removing the smear layer, and opening tubules for the greater penetration of the epoxy resin that will eventually be used to seal the canals.
Once the canals are shaped, a process that takes approximately 2 minutes (marked from the time the canal lengths are negotiated and measured), the canals may now be obturated. Again, there are advocates for several different obturation approaches. I believe in room temperature systems that eliminate shrinkage of the obturation materials. The goal is to create a 3-dimensional seal via the core material and the cement.
Hint No. 10. Use the bidirectional spiral cement applicator to thoroughly flood the canals with a low viscosity cement, without driving cement over the apex (Figure 12).4
|Figure 12. Designed to flood the canal with cement without driving excess over the apex, the bidirectional spiral shifts the burden of the fill from the gutta-percha to the cement making obturation far easier and effective.|
By incorporating the bidirectional spiral, the burden of the fill is removed from the gutta-percha. The gutta-percha’s purpose is now limited to being a carrier of additional cement as well as a lateral driver of the cement that has already flooded the canal. Given the low viscosity of the cement, there is no need to go beyond the prefitted point to drive the cement laterally into all the nooks and crannies of the canal space. In highly oval canals, the use of light lateral condensation will create additional space for well-coated secondary points assuring that a 3-dimensional fill is attained. In addition, both the cement and the gutta-percha will expand as they warm from room temperature to body temperature.
TWO CASE EXAMPLES
Using the principles as described above, we can demonstrate how adaptable these hints/tips are to challenging situations. Please remember that, in all the cases, there is virtually no concern about instrument separation or canal distortion.
Below are 2 cases that we (in our Manhattan, NY endodontic practice) shaped and obturated that required the full complement of advantages included with our approach. Please note that in each case, canals had to be traversed, widened, and obturated without creating distortions. The fact that we can do this relatively rapidly at a cost approximately 90% less than rotary Ni-Ti is just one more advantage of a system that derives its strengths from years of common sense experience.
|Figure 13. Preop x-ray of lower third molar.||Figure 14. Trial fit of the gutta-percha points.|
|Figure 15. Final fill. Please note that despite the curved nature of the canals, the size of the apical shaping assuring excellent irrigation, thorough debridement and superior obturation.|
Endodontics was required on the mandibular third molar (Figure 13). The trial fit of the points clearly demonstrates the nondistorted shaping. Please note that the canals remained nondistorted even though the canals were open to a 35 to the constriction, 40 one mm back with a 25/06 overlaid taper (Figure 14). Figure 15 not only demonstrates the excellent fill that can be accomplished using a single room temperature point and the bidirectional spiral to apply the epoxy resin cement, but one can also see a filled lateral canal into the furca.
The next case involved a maxillary second molar that demonstrates the challenges of bayonet-like anatomy. Yet, the relieved reamers were able to maintain the original anatomy even as the canal was opened once again to a 35 at the constriction; 40 one mm back with a 25/06 overlaid taper. There is a great reduction in resistance when the relieved instruments are negotiating apically, giving the dentist a superior tactile perception of what the tip of the instrument is encountering. If the tip of the instrument hits a solid wall, the dentist will know immediately, remove the instrument, prebend it at the tip, and then negotiate around the blockage. This is something that is not that difficult to do in many situations, as long as you know from the start that a wall is being hit (Figures 16 to 19). Once around the blockage, the shaping motion can be generated via the reciprocating handpiece, dramatically shortening the time required for adequate instrumentation.
|Figure 16. The initial x-ray prior to retreatment of the maxillary second premolar.||Figure 17. Initial negotiation of the canal with a relieved reamer.|
|Figure 18. The fit of the gutta-percha point.||Figure 19. The final fill, showing the ability to shape to wider apical preparations without apical distortion even in multiple curved canals assuring a cleaner more irrigated canal that more thoroughly obturates.|
Instruments designed rationally from the get-go, and used in a common sense manner, lead to safe, efficient, cost-effective shaping and obturation. The elegance of any system is usually found in its simplicity.
- Deutsch AS, Musikant BL. Morphological measurements of anatomic landmarks in human maxillary and mandibular molar pulp chambers. J Endod. 2004;30:388-390.
- Deutsch AS, Musikant BL, Gu S, et al. Morphological measurements of anatomic landmarks in pulp chambers of human maxillary furcated bicuspids. J Endod. 2005;31:570-573.
- Lee MM, Rasimick BJ, Turner AM, et al. Morphological measurements of anatomic landmarks in pulp chambers of human anterior teeth. J Endod. 2007;33:129-131.
- Wu MK, van der Sluis LW, Wesselink PR. A 1-year follow-up study on leakage of single-cone fillings with RoekoRSA sealer. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006;101:662-667.
Disclosure: Dr. Musikant holds 19 patents for inventing endodontic products for Essential Dental Systems, a company that he co-founded and of which he is president.