The tooth consists of 3 parts: enamel, dentin, and pulp. The enamel is the tough non-porous outer coating of the tooth that is normally the only part of the tooth that can be seen. The dentin is a more porous bony material that lies beneath the enamel, and is softer than enamel. The dentin has microscopic tubules present, which normal allow nutrients to diffuse from the pulp into the actual tooth, to keep the tooth structures alive and healthy. However, when the dentin is exposed to the mouth, the tubules are large enough to potentially allow bacteria to work their way into the tooth, and into the pulp itself. The pulp consists of the blood vessels and nerves that supply both nutrients and sensation to the tooth itself.
Enamel defects may result from trauma to the tooth secondary to impact or chewing of hard objects. In rare circumstances, dogs can get true cavities (caries) similar to those that occur in people. A cavity results from an area of tooth enamel that becomes infected and develops subsequent erosion of the enamel and dentin. Regardless of the cause, enamel defects compromise the normal nonporous surface of the tooth and expose the more porous dentin. This appears as divot or chip missing from the affected tooth. These roughened areas are also very prone to developing yellow to brown staining, and the rough surface allows calculus (tartar) to build up faster than it does on teeth with normal, intact enamel.
When enamel defects are present the affected teeth are more sensitive. Pain can be caused by heat, cold, drying, contact with objects, and certain food substances. In addition, the dentinal tubules are very small, but are still large enough for bacteria to move through them and into the pulp of the tooth. When bacteria invade the pulp, it results in inflammation of the pulp tissue, called pulpitis. This causes irreversible damage and swelling of the pulp, which ultimately results in the death of the pulp (pulp necrosis), and therefore, the tooth. If the pulp becomes necrotic, it becomes a great place to harbor bacteria from the bloodstream, which can result in abscess formation. In addition, it becomes a potential source of chronic pain, as well as allowing leakage of the necrotic contents of the pulp chamber into the system. If this has occurred, then the only two treatment options are either root canal therapy or extraction (discussed later).
The only way to determine if the tooth has become devitalized or abscessed is by taking dental x-rays to evaluate the affected tooth. Dental x-rays are taken under anesthesia in animals. Therefore, we will not know for certain if the affected tooth is living or not, until we are actually performing the treatment procedure. It is also important to be aware that if a tooth has had bacterial invasion through the dentinal tubules, but has not yet abscessed, then there will be no abnormalities seen on x-rays.
If enamel defects are present with no apparent pulp involvement, there are three treatment options:
1) Crown placement.
The strongest restoration for affected teeth is to place an artificial crown on the tooth. Crown placement is the process of placing a manufactured metal or ceramic artificial tooth over the existing tooth structure that has been compromised by enamel defects. The process of placing a crown is a 2-step procedure, both of which require general anesthesia. The first step involves shaping the tooth to receive the crown and making impressions of the tooth that will be used by the dental laboratory to manufacture a metal or ceramic crown specifically made to fit the tooth. In the second anesthetic procedure, which is performed about 2 weeks later, the manufactured crown is cemented in place and any final adjustments are made.
The advantage of crown placement is that it has the least likely chance of failing due to microscopic leakage and bacterial invasion. The disadvantages of crown placement are that it requires 2 separate anesthetic procedures to perform, and that it is more expensive than simple composite restoration.
One feature of crown placement in animals that could be considered either an advantage or disadvantage is that the crowns typically used in animals are made of metal. Therefore, the manufactured crown that is placed is metal colored, rather than the color of a natural tooth. The porcelain crowns that are routinely used in people are too susceptible to breakage when used in animals, and therefore carry an unacceptable risk of failure in the long run.
Complications of crown placement usually occur due to inappropriate chewing behavior by the pet. Be aware that if your pet chews hard materials such as real bones, Nylabones, rocks, cage doors, etc., the crown may be broken from the tooth, or more likely, the tooth will be broken off with the crown still attached.
2) Composite restoration.
This is the second best option. Composite restoration is the placement of a filling material over the defect in the tooth. This will permanently seal the exposed dentinal tubules and will both eliminate sensitivity as well as the chance of bacterial invasion into the tooth. It has the added bonus of making the tooth appear normal, but physically covering up the defect.
Also, be aware that if bacterial invasion has already occurred, but the tooth has not become devitalized or abscessed yet, then this will still occur even if we do a composite restoration. If bacteria have invaded the tooth, but are not causing problems yet, then there is no way to detect this. This is one of the risks of this procedure. Also be aware that the composite restoration can be broken off, just like tooth enamel itself, if the pet has inappropriate chewing behavior (such as chewing rocks or a cage door).
3) Dentin bonding. This is the application of a sealing material to the exposed dentin, in order to seal the ends of the dentinal tubules. The goal is to reduce sensitivity and reduce the chance of bacterial invasion through the dentinal tubules. This is simpler and less expensive than composite restoration, but may not provide as long of protection as composite restoration. Originally, this was thought to protect the teeth for 6-12 months, but recent evidence suggests that this may provide much longer term protection. As a precaution, the procedure should be repeated each time the pet is having a dental cleaning and assessment.