Table of Contents
- 1 Pulp exposures and Pulp capping
Upon occasion, while filling a tooth, a dentist will expose the bleeding nerve of the tooth. Since the patient is already numb, this does not cause any immediate pain, however it always puts the nerve at risk for eventual death. In order to prevent, or at least delay the death of the dental pulp which would necessitate a root canal or eventual extraction, the dentist may attempt a simple procedure to stop the bleeding and cover up the nerve with a sedative base. This procedure is called a pulp cap. The success of this procedure depends on several factors. If the pulp cap is unsuccessful, the patient will develop a toothache sometime between the time the anesthesia wears off and several weeks after the patient leaves the office.
There are two types of pulp caps:
A direct pulp cap
A direct pulp cap is done whenever the nerve is directly exposed revealing a relatively small bleeding wound. There are two types of pulpal exposures:
A mechanical exposure is generally a small bleeding point caused after all decay is removed from the tooth. It happens when the dentist is attempting to refine the shape of the cavity preparation in order to retain the filling. They often occur in younger patients where the nerve is fairly large, and the tooth structure around it is less bulky. They also happen when the nerve of the tooth forms very close to the occlusal (top) surface of a tooth. If the tooth was asymptomatic (painless) prior to receiving the filling, and the exposure was very small, the prognosis for a pulp cap under these circumstances is fairly good.
A Carious pulp exposure
A Carious pulp exposure often happens when the decay is close to the nerve, and the nerve is exposed while the dentist is attempting to remove it. These exposures are often larger, and the nerve is generally already somewhat inflamed due to the proximity of the decay. The prognosis for a pulp cap on this type of exposure is generally poor.
An indirect pulp cap
An indirect pulp cap is often done in order to prevent exposing the nerve. In this procedure, the dentist intentionally leaves some decay directly over the nerve to prevent any bleeding at all. If the tooth was asymptomatic prior to the procedure, the prognosis for pulpal survival is fairly good, although the tooth will probably need a root canal a number of years later. The decay left over the nerve becomes inactive since the base used over it causes it to harden up over time, and also because the composite or amalgam filling should “waterproof” the cavity sealing off any nutrients that could allow the bacteria in the decay to live.
How a pulp cap is done:
The bleeding from the exposure is stopped. If the pulp is not inflamed to begin with, this can be done applying pressure to the bleeding point with a dry cotton pellet for about three minutes. If this does not work, the bleeding can generally be stopped with a brief jolt from an electrosurge unit. If the bleeding does not stop, then any attempt at pulp capping will fail.
The exposure is then covered with one of three possible bases:
Calcium hydroxide paste
Calcium hydroxide paste (generally combined with other components so it sets hard) is placed over the exposure. Calcium hydroxide is the traditional material used for this purpose. Calcium hydroxide has been shown to cause the living pulp under the exposure to build secondary dentinbetween the base and the underlying nerve tissue.
MTA (mineral trioxide aggregate)
MTA is actually just a form of Portland cement which can be used instead of calcium hydroxide. Prior to applying the MTA, the cavity preparation is disinfected with sodium hypochlorite (bleach). MTA has been shown to be more effective than calcium hydroxide at stimulating secondary dentin formation, and sets harder making a better seal to prevent bacterial penetration into the nerve space. MTA has also been shown to stimulate bone growth in instances in which a dentist mistakenly perforates the tooth during a root canal procedure.
Resin Modified Glass Ionomer (RMGI)
This material is actually a base used under composite filings. Even though it is an off-label use for this material, it has steadily replaced calcium hydroxide preparations as a pulp capping agent. It appears to be more effective than calcium hydroxide in preventing post operative pain as well as long term outcomes.
Before there is a tooth, there is a nerve. The nerve is the organ that actually forms the tooth. In general, the tooth begins forming from the top of the crown and proceeds down toward the apex (tip) of the root. If a tooth is badly injured before the tooth is fully formed, the dentist may attempt a procedure known as apexification. If the nerve is still alive, but a part must be amputated due to the injury, the dentist may be able to coax the rest of the root to form by stopping the bleeding, and placing MTA (mineral trioxide aggregate) over the stump. In many cases, the remainder of the nerve will recover and allow the root to form naturally. In most cases, it will be necessary to do a regular root canal after root formation to prevent early sclerosis and discoloration of the tooth.
In cases in which the nerve is necrotic (dead) the dentist may perform a regular root canal procedure down to the open end of the root, create a 2 mm thick plug of MTA at the end of the root, wait for it to set, and finally fill the remainder of the root with cement and gutta percha.
In general, whenever a root canal procedure seems to have failed, the dentist’s first reaction is to try to redo the root canal in standard fashion. In other words, he or she will try to remove the old root filling materials (usually gutta percha and endodontic cement) and re-instrument the tooth before replacing them. This is not always possible to do since it can be quite difficult to remove the original root filling. It is often impossible to do if a post has been placed in the canal to stabilize the subsequent core for placement of a crown. In cases like this, if the failure can be demonstrated (generally using x-rays) to be associated with one root, it is possible to do a surgical procedure to remove the offending root tip along with any abscess associated with it. This is called an Apicoectomy procedure.
An apicoectomy is done by cutting a soft tissue flap just above the tip of the root canal treated tooth, puncturing through the bone and amputating the root tip. This generally removes any offending dead (or living) tissue and often cures the problem. In some instances, the dentist will prepare a tiny cavity preparation at the tip of the root and seal off the rest of the canal with a tiny amalgam filling. If this is not possible, it is still often possible to melt some gutta percha at the tip of the root to seal it off. This is called a retrofill(retro=”from behind”). Apicoectomies and retrofills are generally thought of as a last resort in an ongoing effort to save an otherwise hopeless endodontically treated tooth. They are especially useful in treating a failed root canal in a tooth with a post and core.
The three images above show a fairly rare, but interesting phenomenon called internal resorption. The x-ray image to the left shows a tooth with a large filling that is close to the nerve. (Click on the images to see them enlarged.) The yellow arrow points to the area of concern. Upon occasion, when a live nerve becomes irritated (in this case due to the close proximity of the filling), it may become “sick” and forget its usual function of remaining inert and keeping the tooth hydrated. When this happens, it may start to eat away at the very tooth that it is supposed to be protecting. The image in the center was taken a little over a year after the first x-ray, and shows a dark (radiolucent) area in the distal (back) root next to the furcation (where the two roots join together). This radiolucency represents a hole in the tooth structure at that point. The nerve simply ate away the tooth from the inside out. This hole is an example of internal resorption. The image on the right shows the extracted tooth in which the defect caused by the resorption is clearly visible.
The reason that this defect is labeled internal/external resorption is that a second phenomenon can cause the same defect. This involves cells in the periodontal ligament which forget their usual function of supporting the root of the tooth. If this happens, these external cells may eat the same hole in the tooth, this time from the outside in. Once the nerve is exposed, as it was in this image, it is impossible to tell from which direction the resorption started.
If the internal resorption is noted before it perforates through to the outside of the boundaries of the tooth, a root canal procedure will stop the process and save the tooth.
WARNING: Once the pulp of the tooth has died or has been removed, the tooth no longer has its hydrating mechanism and becomes somewhat brittle and more prone to fracture. It is important that all back teeth (molars and premolars) that have been endodontically treated be protected with crowns to prevent fracture and to restore their appearance. (This is somewhat less necessary with front teeth because they have a smaller biting table and, as a result, are less prone to fracture in function.)
Crowns are a procedure done in addition to the root canal and increases the ultimate expense of keeping the tooth. However it is well worth doing since it protects the investment of the root canal and is a good part of an overall treatment plan. These teeth have root canals, and have been prepared
to receive crowns.
Above, you see a crown as it is received from the lab where it was fabricated. below you see two crowns finally cemented on the preparations seen above.
Crowns are generally made of porcelain and not only look like teeth, but tend not to stain and can be built to correct the bad appearance of crooked, discolored and malformed teeth. Front teeth are frequently crowned even without root canals just to correct the patient’s smile. This is what the prepared teeth look like immediately
after crowns are inserted.
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