The Cracked Tooth Syndrome

 

The tooth 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.

The diagnosis 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.

How 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.  

The pain will not go away until one of two things happen.

1. 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.

2. 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.  

Can cracked 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.  

The safest way to repair a cracked tooth involves three steps:

1. 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. 
2. 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 is empty. 
3. Crown the tooth.  This procedure is always indicated for back teeth with root canals, even if there is no crack in the tooth.

The categories of cracked teeth

Oblique supragingival fractures

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 same tooth. 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

Oblique subgingival fractures

This category 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. Unfortunately, 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.  The probability 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.

 The vertical furcation fracture

The furcation 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

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.   Root fractures 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).

Vertical root fractures

Vertical root 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 shows 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 on the right 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.

 

Vertical Apical root fractures

Vertical 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.

 

The following series of images shows the progression of bony destruction due to the sudden occurrence of a crack in a tooth that happens below the level of the bone:

The x-ray image on the left shows a tooth with a crown and a post.  Note that the level of the bone is at about 2 mm below the margin of the crown on both sides of the tooth in this image.  The center image shows that something is happening to the bone that surrounds the tooth.  The image on the right is the same as the one in the center, except that the bone level has been highlighted.  X-rays are two dimensional projections of a three dimensional object.  The red highlight shows the plate of bone on one side of the  tooth while the yellow highlight shows the plate of bone on the other side.  If you use your imagination, you can see that the tooth is now really sitting in a "bowl" of bone. This represents bone eroded by the presence of the crack in the tooth.  The crack formed because of excess pressure on the tooth.  This caused the root of the tooth to crack from the level of the crown margin to the base of the post.  The images below show the actual root once it was extracted.