ENDODONTICS - Root Canal Therapy
One of the
most difficult diagnoses in dentistry is Cracked tooth syndrome.
The patient generally presents to us with sharp pain on chewing
in a certain area of his mouth, but he frequently cannot tell
us which particular tooth hurts. It is generally a back tooth,
and it becomes plain which tooth it is when the dentist has
the patient bite on piece of wood placed on top of the correct
As a rule, the dentist cannot see any problem with the tooth,
either clinically (in the mouth), or radiographicly (on an
may have no fillings or decay, or it may have an intact filling
with no visible associated problems. Nothing looks wrong,
but the patient feels sharp pain when he applies biting pressure
to the top of the tooth. Symptoms of sharp pain to pressure
accompanied by no visible signs of problem with the tooth
are the hallmarks of cracked tooth syndrome.
can be further confirmed when the dentist uses an instrument
that rests on one part of the tooth at a time. There is frequently
sharp pain when the pressure is applied to only one particular
cusp (the pointed parts of a back tooth), and not to others.
If the tooth has a crack in it, the pain is caused by movement
of the affected cusp. The other cusps generally prove to be
non painful when the same pressure is applied. The "movement"
of the fragment is usually microscopic, and not visible to
the naked eye.
Prior to extraction,
the crack in this tooth was difficult to see, as in the left
hand image. The right hand image shows how the tooth really
looks once the pieces are splayed apart. This crack happened
to go directly through the dental pulp (nerve) which was still
alive prior to extraction. This tooth was extremely sensitive
when pressure was applied to the lose fragment. Note: The
darkness in the crown of this tooth is due to staining from
an amalgam filling which is not visible in these images.
can a tooth have a crack, but show no outward signs of a crack?
When a real crack
occurs in a vital tooth (one with a living nerve), the crack frequently
does not propagate all the way through the tooth. This type of
crack is called a greenstick fracture because, like a green branch
from a tree, the fracture may be mechanically present, but the
unbroken segments of the branch hold it together.
The crack usually
propagates through sensitive parts of the tooth (the dentin),
many times involving the living nerve. When pressure is applied
to the cracked piece of the tooth, a tiny bit of movement of that
piece places pressure on the nerve, or other sensitive tooth structure
and even though the movement is tiny, it hurts a lot! Since the
tooth cannot heal itself, the pain is always present whenever
pressure is applied to the biting surface of that tooth.
will not go away until one of two things happen.
The cracked piece
of tooth may break off relieving the pain when pressure is applied
to it. When this happens, the tooth can usually be repaired with
a crown or a simple filling and the patient (and tooth) lives
happily ever after.
The nerve may
die as a result of the repeated assaults placed on it by the moving
fragment of tooth. When this happens, the pain to pressure may
stop, but the dead nerve leaves the patient vulnerable to a dental
abscess unless a Root Canal, and subsequent crown are done.
teeth be saved?
That depends on
the nature of the crack. The only portion of a cracked tooth that
can be repaired is that part above the gum line! Some categories
of cracked tooth can be saved and some cannot. The real difficulty
for the dentist is trying to determine the category of crack the
tooth has. Since these teeth usually remain intact, and since
the crack is not visible, it can be nearly impossible for the
dentist to make this decision for the patient. Whenever we are
dealing with a cracked tooth, the patient must understand that
whatever treatment the dentist prescribes, and no matter how hard
he tries, the tooth may still be lost eventually! Repair of any
tooth thought to be cracked is always risky, and no guarantees
can be made about the outcome.
way to repair a cracked tooth involves three steps:
Perform a root
canal on the tooth. This procedure is absolutely necessary if
the crack has propagated through the nerve space because in this
case, the nerve will eventually die causing an abscess. While
this procedure is not necessary if the crack does not involve
the nerve, there is really NO WAY FOR THE DENTIST TO DETERMINE
IF THIS IS THE CASE.
Place at least
two posts in the roots of the tooth. Often, once a root canal
is begun, the dentist can look into the pulp chamber and actually
see the crack in the floor of the chamber. If this is the case,
then the crack can be stabilized by placing posts in the roots
on either side of the crack. This procedure is NOT indicated if
it can be determined that the crack runs through the orifice of
one of the canals. The only way to do this is by visual inspection.
Unfortunately, the crack is not always visible to the dentist,
even once the root canal procedure has been started and the chamber
Crown the tooth.
This procedure is always indicated for back teeth with root canals,
even if there is no crack in the tooth.
of cracked teeth
As you can see
from the diagrams on the right, this category of crack remains
above the gum line in its entirety. This is the type that is most
likely to simply break off one day while the patient is eating.
This type of fracture generally does not involve the nerve, so
after the lose fragment breaks off, the patient suffers no more
pain to pressure. The exposed live dentin may be sensitive, but
a trip to the dentist can result in a simple repair with an amalgam
or composite filling.
If the fractured-off
piece is very large, it is usually advisable to place a crown
on the tooth in order to prevent fractures in other areas of the
Note that while
most of the other categories of fractured tooth require root canals
for their continued survival, this one does not. Unfortunately,
unless the fractured fragment has actually broken off, it is difficult,
if not impossible to tell which category of fracture the dentist
is dealing with
of crack goes well below the gum line, and generally below the
level where the jawbone starts. If the fragment breaks off, it
is likely to remain attached to the gums, and can be quite painful
until the dentist removes it. Once the fragment is removed, the
tooth is similar to the supragingival fracture above, except that
the level of the necessary repair can be so far below the gum
line, that periodontal surgery may be necessary to expose the
margin so that a crown can be placed.
The nerve of the tooth is most often not damaged by this type
of fracture, but because of the extent of the tooth lost, it is
often wise to perform a root canal and post and core before placing
a crown on the tooth.
this type of crack can remain unbroken and sensitive to pressure
for years, so that it may be impossible to differentiate this
category of crack from the more serious ones discussed below.
of survival of this type of tooth depends upon how far below the
gum line the crack propagated. The deeper below the gum line the
crack propagates, the less likely that repair will preserve the
tooth for long.
Sometimes, a crown
will bind the pieces together and eliminate the pain upon pressure.
Generally, a root canal is advisable as well since if the fracture
extends very far down the root, it has probably come very close
to the nerve, or may even have effected it directly. There is
no way to tell unless the fragment breaks off first.
vertical furcation fracture
is the place where the tooth splits into two or more separate
roots. A crack like this always involves the nerve of the tooth.
In addition, since both pieces of the tooth are held in position
by the bone, this type of crack seldom separates all the way.
This category of fracture MAY be fixable with a root canal, a
post and core (with posts in both roots) and a crown. Unfortunately,
although the fragments may be very effectively splinted by the
posts and the crown, the crack still exists between the roots.
Even though the crack may not even be visible to the naked eye,
nature may still reject the tooth. (Nature works on all scales,
including the microscopic, and even a tiny crack may be noticed
by the body's defenses and evoke an abscess in response.)
We generally expect
about 50 to 60 percent of these to last 5 years or longer if they
are properly repaired with a root canal, post and core and crown.
Many last indefinitely. Some will fail inside of a year.
Not all cases
involving cracks in teeth are occult, or difficult to diagnose.
Some are quite obvious. The image at the left shows a clinical
case of vertical furcation fracture that appeared in my office
several weeks after a patient had a minor accident. Click the
image to see how this case unfolded. There are many images on
the linked page and I hope that dental students will find it helpful.
Oblique Root Fractures
do not involve the crown of the tooth at all. The broken fragment
is generally entirely below the gum line, most often entirely
under the bone.
Root fractures, especially if they are close to the crown of the
tooth like #1 to the right, are generally fatal (for the tooth).
It may be possible to save the tooth for a while with a root canal,
and a post that extends down the fractured root, past the fracture
line, but the tooth will eventually be lost to an abscess of the
bone surrounding the crack. We see about a 10 to 20 percent success
rate in situations like this.
close to the tip of the root, as in #2 have a better chance of
survival. We generally perform a root canal procedure down to
the point of fracture, and ignore the broken fragment at the tip.
This frequently is resorbed by the body, and the tooth loses all
its pain to pressure, and lives happily ever after. We expect
about a 60 to 90 percent survival rate of five or more years for
teeth like these if properly treated (depending upon how close
to the tip of the root the crack lies).
fractures happen most frequently in teeth that have been endodontically
treated (ie. in teeth that have had root canal therapy), or in
teeth in which the nerve has been dead for a long time. As discussed
on the root canal page, the nerve in a tooth has a hydrating function
which keeps the tooth structure somewhat elastic, and therefore,
resistant to fracture. When the nerve in a tooth dies, the tooth
will become brittle and prone to fracture.
Vertical root fractures are most frequently seen in teeth with
posts. The x-ray image on the left shows such a fracture. Sometimes
the stress on the tooth due to the placement of a post can cause
the fracture, and upon occasion, the stresses on the tooth during
bruxing or even normal function can transfer through the post
and break the root.
This type of fracture
is considered catastrophic, and the patient will eventually need
the tooth removed to avoid chronic abscesses. In the case of the
patient with the tooth in the x-ray above, at the patient's request,
we simply removed the broken fragment and allowed the tissues
around the root to heal. The patient was able to keep the tooth
for a few more years before the periodontal (gum) condition deteriorated
and the tooth had to be extracted.
This image below
is an x-ray of a tooth under a cantilever bridge. A cantilever
bridge is one in which an unsupported pontic (false tooth) "hangs
off" the end of a fixed bridge. A cantilever
bridge is always
a bit unstable because it places extra torque on the abutment
teeth. In this case, the extra force resulted in the fracture
of the tooth supporting the bridge. The x-ray shows a lateral
periodontal abscess, but it does not clearly show the actual fracture
that has caused it.
The image shows the
tooth once it was extracted.
In this case, the bridge was cut in
the mouth between the offending tooth and the remainder of the
bridge. The vertical root fracture in the tooth is clearly visible
in this image. In this case,
the fracture was not caused
by a post, as in the example above, but by excessive forces placed
upon the root of the tooth
by the cantilever.
Apical root fractures
at the apex (tip of the root), while not generally fatal to the
tooth, are still some of the most difficult to deal with. This
type of crack causes mild to moderate pain to pressure even when
the nerve has been removed via a root canal. They cannot be stabilized
with either a crown, or a post in the root. The pain to pressure
comes from the fact that the moving fragments exert pressure on
the surrounding bone.
These teeth are often simply tolerated by the patient because
the pain to pressure, though persistent, is much less severe after
a root canal is performed. Unfortunately, only about 50 percent
of these survive for five or more years after treatment with a
root canal and a crown because some people have immune systems
that will not tolerate a fracture in this part of a tooth. It
is usually worth a try, but don't be surprised if the tooth must
be extracted in a few years.