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Creating Endodontic Access through Crowns
As restorative dentists, we are inundated with new materials and techniques daily.
Continuing education is vital in order for us to keep current on new and innovative
treatment plans and newly developed instrumentation. We also must consider the
biological impact of our work. One of the most experienced and least desired side
effects of any dental procedure is the need for endodontic therapy. Doctors often must
make decisions to perform a precautionary root canal prior to restorative treatment
because there is the lingering fear that a root canal may be necessary sometime down
the road. That decision is not easy, we often feel strained at condemning a tooth to
endodontic treatment. In addition, the patient may not understand the need to perform
this precautionary treatment, which although not immediately mandatory, will present
them with added cost and anxiety.
Often we choose the route of conservative dental treatment based upon our education
and better judgment for the patient’s dental health. The dilemma arises when planning
a restoration such as a crown for the tooth. Deep areas of decay may indicate that the
pulp has been contaminated by bacteria. This situation forces us to decide as to
whether to do endodontic therapy and becomes based on the past experiences we have
had in similar situations and our educational training. The aggressive treatment plan
calls for either doing the endodontic treatment or sending the patient to a specialist.
But we can only make the initial assessment based on subjective criteria, as we have no
way of knowing if there has been direct infiltration into the pulp of bacteria.
The real world scenario that causes us to rethink our treatment planning occurs when a
tooth, which had recently been restored, now needs endodontic treatment. No one has
escaped this dilemma! Let’s consider the case where a tooth that had a large amalgam
present, with no pain except that which is provoked by cold fluids. We see clinically a
partially broken amalgam with what looks like minimal recurrent decay. As we remove
the amalgam, we notice that the decay is not extensive, although closer to the pulp than
we feel comfortable with as the initial preparation was deep. The dilemma… What
course of action do we take? We must inform the patient of all options. The first option
is to explain to the patient that root canal therapy would be in their best interest, but
we must also explain the cost and emotional involvement that accompanies this
treatment action. In the interest of patient relations, finance, and conservative
treatment, we also must present the fact that root canal therapy is not mandatory at
this time under these present conditions and that a restoration can be placed in lieu of
the root canal. Most patients will elect to choose the latter form of treatment. In this
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case, we place a bonded core, prepare the tooth, make a temporary crown, and wait for
a short time to see if any sensitivity or pain develops. After a re-evaluation we can then
decide if RCT is necessary. We have done our patient the humane and ethical service
they chose. The crown is cemented sometime later, and everything is fine.
Experience tells us that this treatment planning sometimes is very short term. The
beautiful crown we placed now has a tooth under it that has signs and symptoms of
pulpal dismay. We must now elect to send this patient to an endodontist for treatment.
The dilemma created for us at this point is to figure out what to do after the root canal
has been completed. Assuming the crown is intact except for the access opening, we
could place a bonded resin and explain to the patient that it should last for a long time
without problems, and also can be easily replaced if needed. However, we all know that
once the integrity of the crown has been violated it is not the same restoration we
placed initially. Creating access through a crown can cause weakening and fracture of
the ceramic material. Sometimes it happens upon access; sometimes it happens on a
delayed basis.
Access through a crown is an important step to the longevity of that restoration. In the
case described, the crown was new and it would be desirable to maintain that crown for
an extended time. After all, the root canal was in itself an investment and the patient (or
the insurance carrier) is reluctant to pay for a new crown. In the case of an older crown,
the longevity might not be such an issue as replacement is planned. The timing of the
treatment becomes a factor and the old crown may need to function for a while as a
transition.
Since access through a crown is important, there are some considerations that need to
be recognized. We will be cutting through crowns that are either all-metal, metalceramic, or all-ceramic (i.e., Procera, Cercon, etc.). The basic rule of thumb for cutting
through these materials is the following:
 Use diamonds on ceramic and precious metal
 Use carbides on non-precious metal
Diamonds cut by abrasion, this action is very similar to how sandpaper works. Because
ceramics are a brittle material, using a carbide can damage the surface due to the
vibration (chatter) associated with the bur design. Diamonds are suited for ceramics as
the mechanism of grinding, this is accomplished by essentially scratching the surface
with the particles at high speeds, lends itself to a smoother cut with less vibration. The
hardness of the diamonds is also less likely to be affected by the ceramic substrate it is
cutting.
Carbides on the other hand cut by slicing or shearing small particles of material. This
action is more suited to cutting non-precious metal as a more efficient cut can be gained
resulting in a smoother surface. Although a diamond is harder than the metal, its use is
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not desired because a diamond creates slurry as it cuts. This slurry limits visibility and
also causes clogging of the diamonds cutting surface, greatly decreasing efficiency. The
action of the blades on a carbide bur is more suitable for the cutting of metal.
It is a good idea to mention the term chatter here. Bur chatter causes vibration, and
vibration is not good when it comes to drilling. Chatter relates to the burs and also to
the handpiece that holds them. If a bur shank is not manufactured concentric, a
whipping action may occur as it rotates. This whipping action can cause the tip of the
bur to become eccentric and not contact the substrate equally. A handpiece needing
repair that does not secure a bur tightly, thus, placing the bur out of concentricity will
allow the bur to ‘swim’ and rotate erratically, creating the undesirable chatter.
To gain access through a particular crown, we must consider what material was used to
construct this crown. Following are the rules which guide me when cutting different
substrates:
Full cast non-precious metal: use carbides only (figures 1, 2)
Ceramo-metal: use diamonds to gain access through the ceramic. Once the metal is
exposed, use carbide for penetration through the metal substrate (figures 3, 4)
All-ceramic: use diamonds only. This also applies to the newer bi-ceramics, such as
crowns with aluminum oxide and zirconium cores. (Figures 5, 6)
Figure 1: Endodontic access being
created with a Great White #6
surgical length bur.
Figure 4: Step 2 creates endodontic
access to the tooth using the GW #6
surgical length and a plunge cut
technique, drill through the metal
coping until the tooth is exposed.
Figure 2: Access hole upon
completion. Note the added length
of the surgical bur, this allows for
proper posterior access in tight
cases.
Figure 5: Because of there unique
qualities, it is best to use a diamond
when creating endodontic access
through all-ceramic crowns.
Figure 3: Gaining access through
a PFM crowns require two steps.
Step 1: Trim away the porcelain
with a Piranha #801-016 Diamond
to expose the metal coping.
Figure 6: Piranha Diamond #856016 used to create access without
causing undue damage to the crown.
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Use a medium grit #801-016 Piranha Diamond (SS White) for cutting through the
ceramic portion of PFM and all-ceramic crowns. After access has been successfully
created, switch to a #856-016 Piranha Diamond to flare out the canal and create
adequate working space with proper visibility (figure 7). Medium grit diamonds cause
less vibration due to the smaller diamond particle size as compared to a coarse or
supercoarse diamond, which can cause undue chatter. The lower cost of a disposable
diamond makes this the best choice for my purposes.
For cutting through the metal, portion of a PFM and full cast non-precious crown, I use a
Great White #6 surgical length carbide bur manufactured by SS White (figure 8). It is a
carbide that cuts very efficiently and smoothly, even through the hardest metals.
Figure 8: Great White Surgical Length #6
Figure 9: The evolution of carbide burs
Figure 7: Piranha Diamond #856-016
For greater efficiency and less vibration, it is important to use a cross-cut fissure bur
(rather than a plain fissure bur) when cutting through metal. The Great White burs have
been engineered with sharpened dentates and an increased cutting surface (figure #9).
These features reduce vibration while increasing cutting ability significantly.
With both types of burs, the use of water spray is imperative to both clear the cut
material from the bur, and of course to keep from overheating.
CONCLUSION
Identifying the proper instrument to task, even when speaking of rotary instruments can
minimize time and effort. As restorative dentists, we can increase the quality of our
patient care and become more efficient in our efforts by using the proper diamond or
carbide to cut any given substrate. Active communication between dentist and
endodontist can also aid in patient care. The need to save a crown is a financial issue for
the many patients and one that is desirable for the dentist. By using the proper
instrument to task to create endodontic access through the many types of restorative
substrates that are in use today, a higher percentage of crowns can be saved and not
replaced.
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