Look, Compare and Perhaps Discuss Two Distinct Methods of Canal Instrumentation
Here is a list of undesirable effects that are produced by the use of continuous and interrupted greater tapered NiTi instrumentation: All these conditions have been documented in research studies and are available on request for anyone interested.
1. Produces a smear layer that clogs lateral spaces reducing the effectiveness of irrigation particularly in the buccal and lingual extensions of oval isthmus-like canals.
2. Produces dentinal microcracks along the length of the canals
3. Removes excess tooth structure in the mesio-distal plane
4. Removes an inadequate amount of pulp tissue in the bucco-lingual plane when the canals are highly oval and isthmus-like in cross section
5. Doesn’t cleanse the canal walls as defined by the original three-dimensional anatomy of the pulpal spaces
6. Are vulnerable to “separation” under a number of conditions
7. Requires precautionary steps to prevent separation that increase the loss of dentin, namely straight-line access and crown-down preparations
8. Are expensive and generally confined to single usage
9. Greater tapers weaken the root’s resistance to vertical fracture
10. Imposes conical shapes despite the oval isthmus-like original pulpal anatomy
11. Sets up conditions that further weaken the tooth during obturation, post placement and function
12. Greater tapered shaping is a requirement, not an option, to be used safely
13. Requires increased enlargement of the glide path using K-files when resistance is encountered
14. Requires expensive torque-sensing reversible motors to reduce the incidence of separation
15. Creates procedural stress for the dentist
16. Internal routing is a necessary procedure that rotary NiTi cannot perform
17. Tends to push debris beyond the apex
18. Are drawn into the canals as they rotate
19. Most rotary flutes are ground in and prone to micro-cracks and breakage more than twisted flutes
20. Irrigation is not nearly as effective when the instruments are significantly larger than the canals they are first entering
21. Multiple factors affect rotary NiTi including: canal curvatures, length, dimensions, resistance encountered, speed of rotation, continuous or interrupted, merging and diverging canals, C-shaped that all impact on the predictably of safe and effective instrumentation.
Now let’s compare the above problems to the impact of 30-45º engine-driven oscillations using stainless steel 02 tapered relieved twisted reamers. Again, the statements below are all supported in the research that is available on request.
1. Short amplitudes of horizontal motion at 3000-4000 cycles per minute (engine-driven oscillations) eliminate the buildup of a smear layer along the entire length of the instrumented canal leaving open dentinal tubules that are more effectively penetrated by the irrigants.
2. Micro-cracks are eliminated in both the canal walls and the instruments.
3. 02 tapers preserve more tooth structure in what is most often the already thin mesio-distal dimension.
4. Removes a uniform layer of dentin from all the canal walls in both the mesio-distal and bucco-lingual planes.
5. Instruments the canal in line with the original pulpal anatomy
6. Virtually immune to instrument separation
7. Does not require steps that sacrifice more dentin. Namely, straight-line access and crown-down preparations
8. They are inexpensive to start with and can be used multiple times before replacement reducing operating costs significantly.
9. Lesser tapered roots are stronger
10. Produces the original shape of the canal in larger form
11. Rarely prepare canals with a taper greater than 02 unless the original anatomy typically in the bucco-lingual plane is greater than 02 to begin with.
12. Essentially, the complete preparation, generally taken apically to a 35-40 is a continuation of the glide path that is initially developed in three-dimensions.
13. The oscillating handpiece is inexpensive
14. Without the concern for breakage, there is minimal procedural stress
15. Because the 02 tapered instruments are as thin as .06 of a mm at the tip they are capable of internal routing as well as reaming
16. Pushes minimal debris beyond the apex.
17. They are not drawn into the canal eliminating the concern about torsional stress
18. Twisted instruments are fabricated without the introduction of micro-cracks that are common to ground instruments.
19. Irrigants are far more effective when the instruments are thinner than the spaces they are shaping (at least in one dimension) and rapidly oscillating
20. Twisted instruments used in 30-45º oscillations are not subject to the multiple factors that impact greater tapered rotary NiTi instrumentation.
These two lists reflect a bias I have towards oscillation of lesser-tapered stainless steel relieved twisted reamers and away from greater tapered NiTi preparations. I believe that the popularity of greater tapered rotary NiTi is based primarily on a comparison with the manual use of K-files. In that comparison, rotary automatically comes out ahead in terms of speed, results and reduction in hand fatigue. That is an artificially limited comparison. Considering the option of 02 tapered oscillating stainless steel relieved twisted reamers opens an entirely new comparison where imo the advantages clearly belong to lesser-tapered instruments used in a non-rotational manner.
Any of the items on either list are worthy of a prolonged discussion and offer extended insights into what we want to accomplish in our endodontic therapy using far less risky methods.