US Pharm. 2011;36(1):12-15.
Patients occasionally approach the pharmacist with complaints that one or more teeth become painful when exposed to specific types of provoking factors, such as cold or heat. While the cause may be a serious underlying disorder, such as caries or a cracked tooth, the problem is more often due to a relatively trivial condition known as dental or dentinal hypersensitivity.1 Dentinal hypersensitivity is not a direct cause of tooth loss, but patients benefit greatly from advice on prevention and treatment.2 The pharmacist can provide advice regarding recognition, prevention, and treatment, and can refer the patient to a dentist when appropriate.
Dentinal hypersensitivity reportedly affects millions of people.2-4 Experts estimate that 15% to 57% of adults suffer from the condition.1,5 The incidence appears to be rising.
The observed increase in patients seeking help for dentinal hypersensitivity is theorized to be due to several factors.1 First is the lengthening life span and the gradually increasing average age of American residents. Second is the growing trend to fluoridate water supplies, which has allowed larger numbers of people to keep their natural teeth.5 This combination of factors leads to the conclusion that the average age of living teeth is also rising, as fewer people wear dentures than ever before. Older teeth are prone to problems such as dentinal hypersensitivity, because of being brushed and cleaned a greater number of times. Further, such causal factors as gingival regression become more common as people age.
Age-stratified studies confirm the age-related link.1 While those affected range from 20 to 50 years of age, the peak age for onset is between 30 and 39 years.1,5 Research also reveals that females are more prone to the condition than males, possibly due to the fact that women generally clean their teeth more consistently and intensively than age-matched groups of men.1
Enamel covers the crown, the portion of the tooth above the gum line. Enamel is the hardest substance in the body; beneath it is a softer layer of material known as dentin. The roots of the teeth are covered by cementum, and dentin also underlies this substance.6 The etiologic theory of dentinal hypersensitivity builds on the fact that dentin is riddled with many tiny tubules that lead into the tooth, directly to the dental pulp or nerve.1,7 Dentinal tubules are filled with a protoplasmic fluid, which undergoes minute shifts inward or outward in response to specific triggers.8 The movement of tubular fluid is thought to stimulate mechanoreceptors in the pulpal-dentinal area, perhaps through deformation of odontoblasts, which stretches or compresses interwoven nerve fibers to cause pain.7,9 Normally, dentinal tubules are occluded by the overlying dental enamel or the protecting gingival and cementum, preventing these fluid shifts.10
Pain of dentinal hypersensitivity can occur when the tubules are exposed by erosion of the enamel (perhaps caused by ingestion of acidic foods or drinks), caries, periodontal therapy, abrasion, or gingival recession coupled with cementum damage (e.g., caused by vigorous brushing and cleansing of the teeth).6,10-13 Patients notice pain when ingesting cold, hot, or sweet foods or beverages, when an air blast is directed to the teeth, or during routine cleaning procedures. The pain is severe in some patients and only mild in others. In some patients, only a few teeth are affected, but in others all teeth are sensitive.6
The hydrodynamic theory helps patients understand how the common triggers cause dentinal pain.14-17 Cold, the most common trigger, causes contraction of fluid. Heat causes it to expand. Sweet substances (or occasionally salty foods) cause an osmotic shift of fluid in the tubules.6 Air blasted onto dental surfaces dries out fluid in the distal tubule, causing a shift outward.18,19 Mouth-breathing of dry cold air during the winter can cause a similar stimulus.6 Cleaning procedures displace fluid, causing similar shifts.20 Rubbing the area with a periodontal aid or fingernail or even simple brushing can cause the mechanical stimuli that result in discomfort.6 Dentinal hypersensitivity only occurs in permanent teeth.6 Experts also report that acidic foods such as fruit can cause discomfort, perhaps due to the pH differential.
The link to oral hygiene is important to understand.1,6 Evidence suggests that overzealous cleansing regiments induce gingival recession that leads to dentinal hypersensitivity.11 For instance, the teeth easiest to clean (e.g., canines and premolars) have the lowest plaque scores but are more likely to exhibit sensitivity. Teeth that are more prone to brushing trauma due to their location are known medically as vestibularized teeth.6 Buccal tooth surfaces are more susceptible to the condition than often-neglected lingual surfaces. Researchers note that individuals usually brush harder on the side opposite the hand holding the brush: right-handers brush the left side more aggressively, left-handers brush the right side more aggressively.1 As a result, right-handers are more likely to experience dentinal hypersensitivity on the left side of the mouth, and the situation is the exact opposite for left-handed individuals.
While overzealous cleaning of the teeth can lead to dentinal sensitivity, overt dental neglect is also a potential cause of dentinal hypersensitivity.6 In these cases, neglect results in accumulation of dental plaque, in turn causing gingival recession that exposes cementum and dentin.6
Users of smokeless tobacco also undergo gingival recession, and consequently suffer more from dentinal hypersensitivity. Bulimics experience sustained exposure of the teeth to gastric acids and are also prone to the condition.
The epidemiologic factors explained above point to the conclusion that chronic abrasion from brushing too often with firm-bristle brushes induces gingival recession leading to dentinal hypersensitivity.1 Patients should be instructed to choose the softest bristle brush that can be located, and cautioned against using excessive force when brushing. It is also advisable to eliminate or reduce intake of the acidic foods listed in the Patient Information. Many of the foods are components of a varied, healthy diet, and they should not be entirely eliminated. However, patients would be well advised to eliminate the acidic drinks that have no dietary contribution (e.g., caffeinated and noncaffeinated soft drinks).
Usually, pain resulting from dentinal hypersensitivity only occurs when affected teeth contact pain triggers. This helps the pharmacist differentiate it from the constant pain of persistent toothache, which can be caused by such factors as a cracked filling or uncorrected caries.1 However, its come-and-go nature makes it similar to intermittent toothache, which alternates between periods of pain and periods free of pain, persisting until the damaged tooth is repaired or removed. When it is not caused by actual tooth damage (e.g., chipped enamel), hypersensitivity undergoes spontaneous remission in 20% to 45% of patients in 4 to 8 weeks.1 Dental hypersensitivity following root planing usually becomes less noticeable within 2 to 3 weeks.1
Treatment of Dentinal Hypersensitivity
At one time, two ingredients were marketed in nonprescription sensitivity toothpastes: strontium chloride, which is no longer available, and potassium nitrate, the sole remaining ingredient, which is hypothesized to act directly on sensory pulpal nerves. Once sensory nerve fiber membranes have been depolarized, excess potassium from the toothpaste will prevent repolarization, thereby decreasing pain.1
The FDA-labeled age cutoff for hypersensitivity toothpastes is 12 years. These products are not proven safe or effective below this age. Given the hypothesized etiologic factors in causation of dentinal hypersensitivity, it would be rare for patients 12 years and below to experience the condition in any case.
To use potassium nitrate toothpastes properly, patients should be advised to brush with a soft-bristle toothbrush for at least 1 full minute twice daily (morning and evening), using about an inch of toothpaste. Patients should take care to contact all areas where teeth are sensitive. Dental practitioners suggest that patients use a minimum of fluid while brushing, and also that they avoid rinsing the mouth with water after brushing.6 Adhering to these suggestions can prevent dilution and expectoration of the active ingredient of the toothpaste, which would compromise its activity.
The FDA requires the following warning on packages of toothpastes intended for dentinal hypersensitivity: “Sensitive teeth may indicate a serious problem that may need prompt care by a dentist. See a dentist if the problem persists or worsens.”1 The products work slowly, and as long as 2 to 4 weeks may be required before they begin to work. Therefore, all carry labeling indicating that if the problem persists for more than 4 weeks or worsens, an appointment with a dental professional is indicated. The patient should check the formula for the hypersensitivity product to ensure that it also contains fluoride, as some do not. If not, the patient may need to use a fluoridated toothpaste as well.
Possible Future Therapies
Investigators have attempted to discover new methods of preventing dentinal hypersensitivity, although none have gained FDA approval at this time. One avenue consists of searching for impermeable products that can effectively seal the outer opening of the dentinal tubules, thereby preventing the fluid shifts that cause pain. A professionally applied tooth sensitizer that places a layer of amorphous calcium phosphate over dentin has been proven to be effective.14 The outer layer forms into hydroxyapatite, which covers the tubules. Toothpastes that contain calcium and phosphate salts also cover dentinal enamel with a layer of calcium phosphate that can reduce sensitivity.14
Until the 1980s, strontium chloride was available in nonprescription toothpastes as a dentinal desensitizing agent, although it was never proven to be safe and effective. In recent research, however, investigators applied it to hypersensitive teeth with the aid of an iontophoretic unit.3 With as many as three repeated applications, it was found to be safe and effective.
Teeth that hurt have always vexed humans, leading to sleepless nights, reduction in the quality of life, and a hampered ability to eat or drink. Some people may notice that one or more teeth have begun to hurt at very specific times. This pain is not constant like a toothache due to a broken tooth, missing filling, or cavity. Instead, it occurs when they drink hot, cold, or sugared beverages, when the dentist dries out a tooth before a procedure, or after the teeth have undergone dental cleaning and scaling. The problem is known as dentinal or dental hypersensitivity.
Why Are My Teeth So Sensitive?
Several things make your teeth sensitive to cold. One is brushing with a toothbrush that has bristles of medium or stiff consistency. Over many years, your gums may recede, exposing a tooth-root substance known as dentin. When this substance is exposed to the inner mouth, the act of drinking a cold beverage causes small shifts of fluid in the dentin, which you perceive as pain. Women are generally better at cleaning their teeth than men, so they are more likely to have this problem. Smoking, chewing, and dipping tobacco can also cause the gum recession, leading to tooth sensitivity.
Eating and drinking acidic foods and beverages can cause tooth hypersensitivity by slowly dissolving the enamel covering of your teeth, exposing the softer dentin underneath. Acidic foods and drinks include ginger ale, limes or lemons and their juices, wine, cranberry sauce, coffee, vinegar, pickles, cola, oranges juice, plums, cider, grapefruit juice, apples, raspberries, root beer, relish, strawberries, fruit jams/jellies, orange soda, peaches, sauerkraut, blueberries, pineapple juice, cherries, and grapes.
How Can I Prevent It?
You must choose the softest bristle brush you can locate. You should not brush with a great deal of force. Stop use of all tobacco products. Moderate your intake of acidic foods and beverages. Never suck directly on lemons or tart powders that can be bought at convenience store counters; doing so can erode your teeth badly.
How Can I Treat Sensitivity?
Fortunately, your pharmacist can sell toothpastes that may stop the discomfort of dentinal hypersensitivity (e.g., Sensodyne, Crest Sensitivity, Colgate Sensitive). All will have a note on the package indicating that they are for sensitive teeth, with the active ingredient listed as potassium nitrate. The products should not be used in patients under the age of 12 years. To use potassium nitrate toothpastes properly, you should brush with a soft-bristle toothbrush for at least 1 minute twice daily (morning and evening), using about an inch of the sensitivity toothpaste. You should contact all areas where teeth are sensitive. The product labeling will warn you that sensitive teeth may be a sign of a far more serious condition; therefore, you should only use the toothpaste for 4 weeks. After that time, if the problem persists or worsens, you should visit a dentist, who can rule out more dangerous conditions.
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