Gum Recession
Receded gum tissue is one of the most common causes of tooth sensitivity. Exposed root surfaces have no enamel and are much more sensitive to temperature.
Diagnosis – Look for a gum line that has receded below where adjacent teeth have. Exposed roots are usually a bit darker than the adjacent crown as well. Sometimes the tooth will have a notched appearance as well.
Treatment – Sensodyne or other sensitivity toothpastes work well after about two weeks of use in most cases. However once treatment is stopped the sensitivity often returns. Dentists have a host of desensitizing medicaments that have improved recently and are quite effective. If the tooth is notched or worn a filling is often indicated as well. Severe recession may need a gingival graft procedure to help replace lost gum tissue.
Decay
Tooth decay is the other most common cause of sensitivity. Early decay is often asymptomatic but as it penetrates the tooth further many people will begin to develop cold sensitivity.
Causes – Bacterial infection of the hard tooth structure which causes irritation of the dental pulp.
Diagnosis – This needs to be done by a dentist. Large cavities visible to the patient are usually quite advanced. A hard diagnosis even for your dentist can be decay developing under old fillings or crowns. These are difficult to detect both clinically and with x-rays. One clue that your sensitivity might be decay is when it does not go away after a few weeks of sensodyne or similar toothpaste use.
Treatment – A filling, crown, or other appropriate restoration. If the decay has advance deep enough into the tooth a root canal may be indicated.