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Summary of personal endodontic insights
by Barry Musikant on Mon May 16, 2011 7:53 pm
1. Instruments with more vertically oriented flutes shave the dentin away
with far more efficiency than instruments that have more horizontally
oriented flutes. The above statement is predicated on the fact that the
predominant motion used with the instruments is watchwinding. The
instruments we typically use are K-files that have horizontally oriented
flutes, just what we don’t want. We should be using reamers that have more
vertically oriented flutes. Very few if any schools teach this although
it has such noted advocates as Dr. Herb Schilder. Furthermore, once
K-files have finished the glidepath, the subsequent rotary NiTi instruments
are all designed similarly to K-reamers with their more vertically
oriented flutes. This makes sense since rotation is an even more pronounced
form of horizontal motion than watch winding. To drive home the truth that
more vertically oriented instruments make more sense, consider the fact that
the shaving blade is at right angles to the plane of motion when one shaves.
If it were not we would be cutting our face (without removing facial hair).
It is not good for our face and it is not what we want to accomplish when
we attempt to shave away dentin from the canal walls.
2. Once it has been established that reamers with more vertically oriented
flutes are a more efficient design than the horizontally oriented flutes
on K-files, an extension of that logic calls for a flat along the working
length of the reamers because they create two vertical columns of chisels
that further improve the shaving ability of the instruments in addition to
making them more flexible (thinner in cross section) and even less engaging
along length reducing the resistance they encounter when negotiating apically.
This design modification also increases the tactile perception that these
instruments deliver to the dentist giving him a greater ability to
differentiate between a tight canal and a solid wall and directing him when
to remove the instrument, prebend it and negotiate manually around any
impediments encountered. The asymmetric design also gives the instrument the
ability to differentiate between a round and oval canal an attribute that
tells the dentist when he must shape the canal to a greater internal diameter
or at least work all the circumferential walls effectively.
3. Endodontis instruments made from stainless steel actually have more
advantage in usage than NiTi. Where NiTi is superelastic, it also rebounds to
the straight position tending to selectively work the outside walls of curved
canals. Stainless steel can be prebent and if the relieved reamer design is
incorporated a good deal of the stiffness is reduced. Furthermore, the stainless
steel can be treated to make it close to dead soft eliminating any rebound
effect that tends to distort to the outer wall of curved canals.
4. 30º reciprocation virtually eliminates the torsional stress and cyclic fatigue
associated with rotary NiTi that unpredictably leads to instrument separation.
5. By combining treated stainless steel that is designed as a relieved reamer an
instrument has been designed that negotiate thru the canal with minimal resistance
and conforms to the most tortuous canals as they do so. By using these instruments
with either a tight watch winding stroke or in the 30º reciprocating handpiece
separation is virtually eliminated.
6. We can now shape canals to a size that is dictated by the biologic needs of the
tooth rather than limited by the metallurgic properties of the metal used. In short,
we can shape canals to a wider apical dimension if and when called for without fear
of breakage, a fear that in the past has caused us to shape canals more
conservatively than the biologic needs that the tooth demands.
7. The objective of obturation is to create a stable three-dimensional fill. Thermoplastic
obturation cannot produce a three dimensional fill because the materials used in
obturation must shrink as their insertional temperature cools to body temperature,
from 201º C to 37º producing a contraction of the gutta percha between
4-5%. This reality undermines the major investment required to do thermoplastic
obturation and further questions the judgment of employing a system that with just a
little bit of overheating can damage both the integrity of the root and the pdl.
8. Under any circumstances, it is the cement interface and not the gutta percha that
seals the tooth. In that regard, it doesn’t matter whether or not the cement interface
is thick or thin as long as it has properties that ensure its stability. It must also
have additional properties to ensure a good long term seal including the ability to
physically and chemically bond to the dentin and the gutta percha point(s), dimensional
stability during polymerization, high resistance to water degradation, minimal apical
irritation if and when extruded beyond the confines of the root and the ability to be
digested by the macrophage if and when it is extruded into the periapical tissues.
These properties are best found in epoxy resin cements, sealers that
have been used and researched for their use in endodontics for over 65 years.
9. An excellent way to apply the epoxy resin cements is via the bidirectional spiral,
a tool that floods the root with cement while preventing its extrusion beyond the
apex in the process.
10. In highly oval canals, a spreader can be used to create lateral space for the
placement of secondary points, but the force applied to the spreader should never
exceed the weight of ones hand. To use more force can damage the root or cause a
rebound in the highly compressed gutta percha that will create a void when the
force is removed compromising the three dimensional fill we want.
11. Each practioner has different levels of skill, but despite this innate differential,
a system that is designed to shape uniformly, not break in usage that easily adapts
to the canal anatomy without snapping back to the straight position will make life
easier for all independent of the skill level.
12. In order of importance, I would rank the use of relieved reamers over K-files as
the most significant insight we have in improving day to day endodontics. Switching
to reamers entails no change in the present technique of those using K-files.
The only perceived difference will be in the increased ease of use, the ability to
shape to greater dimensions without distortion and the significant reduction in
hand fatigue even when used manually. The second most important insight was
coupling the relieved reamers to the 30º reciprocating handpiece. Together they
eliminate the bulk of the stress encountered in shaping increasingly curved canals.
As more dentists incorporate these changes, we will see wider apical preparations,
less distortion to the outer wall that will produce more consistent fills used with
materials that expand as they warm to body temperature after placement rather than
shrinking as they cool from insertion temperature to body temperature.