How does tooth sensitivity relate to cavities?

Rita Medwid

If your tooth is sensitive, it may be due to a cavity, or a fracture, a leaky filling, gum recession, gum disease, acid erosion or clenching and grinding to name a few. If the tooth is sensitive to cold and sweets, it may be decay or gum recession. Sometimes a new filling is all you need. If the root area of the tooth is sensitive, then desensitizing toothpaste may work well, or fluoride varnish from the dentist. You should not ignore tooth sensitivity because it can lead to further problems of decayed teeth or the need for a root canal. Try to see your dentist rather than putting up with the discomfort or avoiding certain foods.

Tooth sensitivity may be a symptom of a cavity. Tooth sensitivity refers to a mild or sharp pain you experience when eating or drinking something hot or cold. However, tooth sensitivity may also be caused by other factors, including teeth grinding (bruxism), brushing teeth too hard, and even some dental treatments like tooth whitening. If you experience tooth sensitivity, it is important to talk to your dentist. Your dentist can determine whether a cavity is the cause, and properly treat this condition.
Recession of the gums away from the teeth can make them more susceptible to sensitivity. Recession of the gums combined with an increased incidence of periodontal (gum) disease, can expose tooth roots to plaque. If you experience sensitivity, see your dentist. He/she can help determine the cause.
Teeth can be sensitive to cold, hot, sweets and biting pressure. I will limit my response to sensitivity to cold. Sensitivity to cold may be the most common complaint of dental patients. The most common reason for tooth sensitivity to cold temperatures may be recession of the gums. Enamel is Mother Nature’s blanket of protection over teeth, but enamel ends slightly below the gums. Dentine comprises the bulk of the tooth below the enamel and includes the root. Dentine contains extensions from the pulp which make it responsive to thermal changes.

When the gums recede, the root of the tooth becomes exposed. The root is much more susceptible to temperature changes. Another reason for cold sensitivity is a crack in the tooth. Cracks develop in teeth from excessive repeated force, as in chewing hard objects or grinding the teeth. Cracks can penetrate beyond the enamel into the deeper parts of the tooth.

A third reason that teeth can be sensitive to cold is a dental restoration (filling or crown). Dental restorations can conduct cold deeper into the tooth. They also expand and contract differently than tooth when exposed to thermal changes.

A fourth reason for sensitivity to cold is pulpitis. Pulpitis is an inflammation of the dental pulp, commonly called the nerve. Inflammation of the pulp can occur for many reasons; so many that entire chapters of dental textbooks have been devoted to the topic of pulpitis.

A final cause of cold sensitivity comes from decay. Decay breeches through enamel into the dentine. As decay becomes more extensive and deeper, the tooth becomes progressively more sensitive to cold.
Abraham Speiser
"Cavities" in this question relates to tooth decay known professionally as dental caries.

STAGE 1: NO SENSITIVITY -- Caries is a bacterial process which results in loss of calcium from the calcium rich outside of the tooth leaving a calcium depleted chalky tooth surface called a white spot. When this process occurs on the crown of the tooth, the white spot is in the hard enamel shell of the crown. There is usually no sensitivity at this point of the dental caries process. 

STAGE 2: MUCH SENSITIVITY -- As the caries penetrates deeper into the tooth, it reaches the junction between the outer enamel and the internal hard tissue of the tooth called dentin. There are VERY SENSITIVE free nerve endings at the dentin-enamel junction. Caries at this junction results in tooth sensitivity, usually due to stimulation by cold, hot or sweets. Sometimes sensitivity is spontaneous. 

STAGE 3: LESS SENSITIVITY -- Sensitivity usually decreases once the caries penetrates deeper into dentin (less free nerve endings). Caries causes the white spot to disintegrate leaving nothing but a hole (a cavity). When food gets into the cavity, pressure on the dentin causes sensitivity.

STAGE 4: SENSITIVITY RETURNS -- when caries gets very deep into the dentin and closer to the dental pulp (nerve of the tooth). At this point, the tooth is about to abscess. 

Two more twists to this relationship between sensitivity and cavities are older age (root cavities) and younger age (teenage cavities). Both are more prone to sensitivity. Roots have no enamel, so older age root caries attacks the free nerve endings in the dentin immediately. Younger age teenage caries is caused by a more virulent strain of bacteria, which can penetrate the chalky white spot down to the free nerve endings at the dentin junction even before the caries reaches the free nerve endings.

When teeth are sensitive, patients may avoid them in brushing and flossing. This can lead to an accumulation of plaque. The plaque can cause cavities. Sensitive teeth can also be a sign of cavities. If your teeth are sensitive, you should see your dentist.

Teeth Sensitivity can be a symptom caused by many conditions. One condition that causes sensitivity is having cavities. Sensitivity could be too hot, cold, or sweet. Since the tooth structure becomes soft and more porous with a cavity, the outer enamel layer can no longer protect the tooth sufficiently and causes the tooth to become sensitive. Removing the infected portion of the tooth and restoring it with a proper restoration should alleviate the problem

Romesh Nalliah
The presence of tooth sensitivity does not necessarily mean you have a cavity. And having a cavity does not necessarily mean you will have sensitivity. This brings up two important issues:
  1. Sensitive teeth should be attended to as soon as possible becuase it could be a simple solution (like desensitizing toothpaste) or a minor filling.
  2. You should have regular check-ups with a dental professional because cavities don't always cause discomfort.
Having sensitivity could be related to cavities, gum recession, tooth injury or nerve problems. Since there could be a broad range of diagnoses, there could also be a broad range of solutions and you should see your dentist as soon as possible.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.