Sensitive Teeth

Sensitive teeth are often the first sign of a dental problem. Sensitivity occurs when the  dental nerve sends out signals it shouldn't. Unlike other body parts that register temperature and pressure, the tooth registers only pain. Here are some of the common causes:

  • Dentin sensitivity
  • Cavities
  • Pulpal disease
  • Cracks

Dentin Sensitvity


Why it happens

Dentin is the middle part of the tooth, it's under the enamel and outside of the nerve. Dentin is perforated by countless tiny tunnels running from the nerve outwards. The tunnels are called dentinal tubules. Normally all the dentin is covered by enamel and gums. If the dentin is exposed, tubules can transmit temperature, sweetness, saltiness and acidity to the nerve. Because teeth mostly feel pain, we feel tooth sensitivity.

The treatment of dentin sensitivity is plugging dentin tubules. This prevents them transmitting to the nerve. The easiest and most common method is sensitivity toothpaste. The active ingredient in sensitivity paste soaks into the tooth and plugs the tubules. Dentin sensitivity can also be treated in office by plugging the tubules with a resin sealer, or in severe cases custom desensitising trays.

Sensitive Toothpaste

Sensitive toothpaste plugs the tunnels that transmit signals to the nerve . It needs to be on the tooth long enough, and at sufficient concentration to form plugs. Each time the paste is used the plugs get thicker and more numerous. It may take some time to plug them all, so persistence is required. To speed the process apply paste directly to the sensitive spots with a finger, and let it sit without rinsing. The best time to do this is right before bed. Eating acidic foods can dissolve the the plugs, so you may find the sensitivity returns after having red wine, pineapple, citrus etc.



Why it happens

Bacteria present in the dental plaque ferment sugars. The end products are organic acids, which dissolve the outer tooth layers. When the destruction of tooth becomes deep enough, the dentinal tubules again begin to transmit signals to the nerve, resulting in pain. Because the bacteria produce more acid when sugar is around, the sensitivity from cavities is often more pronounced with foods, particularly sweets.

The cavity on the left is still small, but staining has occurred where acids and bacterial waste penetrated the tubules. Nearer the nerve the tooth is fighting back by depositing calcium into the tubules. If bacteria manage to bypass the blockages, they infect the nerve causing an abscessed tooth. This cavity is between the teeth, and would only be detectable by X-ray, but we see bacterial staining is already half way to the nerve. This is why regular dental X-rays are important.

Pulpal Disease

Chronic Periapical Periodontitis
Chronic Periapical Periodontitis

Why it happens

Inflammation or infection of the nerve inside the tooth. There are several types and stages:

  1. Reversable Pulpitis: Inflammation of the dental pulp. Pulp tissues are alive and may heal if treated properly. Pain is intense on stimulation but lasts less than 10 seconds. Caused by dental trauma, deep filings, crown preparation and cavities.
  2. Irreversible Pulpitis: The inflammation of reversible pulpitis progresses to the point where it cannot heal. Swelling restricts blood flow to the tooth and the nerve begins to die of oxygen deprivation. Pain may pulse with the heartbeat. On stimulation pain lasts longer than 10 seconds and can be spontaneous or throbbing at night. After this stage root canal or extraction will be required
  3. Necrotic Pulp without Periapical Periodontitis: The nerve has died, and the tooth no longer has pain. Bacteria have not yet moved to the bone at the base of the tooth, so there is no pain on biting. In the dental office the nerve is unresponsive
  4. Necrotic Pulp with Acute Periapical Periodontitis: As above, but bacteria are causing inflammation at the root tip. There is pain on biting and possibly throbbing. If severe lymph nodes will swell with a general feeling of sickness.
  5. Necrotic Pulp with Chronic Periapical Periodontitis: The body has walled off the infection. There is minimal pain, but an x-ray shows changes in the bone around the root tip.


A crack has formed under a large filling, resulting in pain on biting.
A crack has formed under a large filling, resulting in pain on biting.

Why it happens

Cracks occur from trauma, excessive grinding or weakening of a tooth from decay or large fillings.

Cracks have a distinctive pattern of pain. In most cases the pain is sharp and intense, lasts for only a moment, and only when chewing. Because the crack needs to be put under flexion in order to hurt, you might not feel it all the time. Pain is often only with hard foods, and even then only occasionally. When you do flex the crack, you will definitely feel it.

Cracks can be one of the harder problems to fix because they do not show up on x-rays and it can be hard to predict where they are going. If the crack turns and exits the tooth above the gumline, it can be fixed with a filling or crown. Cracks that enter the nerve or the root are more complicated and will require root canal and crown if minor, or extraction of the tooth if more severe.