Treating the Twinge

Q. What causes dentinal hypersensitivity?

A. The cause is exposed cementum, which can erode away with exposure to certain foods, drinks, and aggressive tooth brushing techniques.

Q. What is abfraction and can it lead to dentinal hypersensitivity?

A. Abfraction, by definition, is a cervical defect caused by occlusal forces. When abnormal occlusal forces are transmitted down the long axis of the tooth and concentrate in the cervical area, abfraction can occur. The theory is that this results in the breakdown of the enamel and dentin, causing microfractures, microcracks, and, essentially, weakening of the tooth. This may or may not contribute to sensitivity.

Q. Will dental hygienists visually see a ditching of the cementum or dentin area?

A. No, because these cracks are microscopic. The theory is that anything that happens in this area tends to be multifactorial so it is difficult to say that a given problem or a specific lesion is an abfraction lesion or an abfraction problem. Abfraction usually occurs along with something else like toothbrush abrasion or chemical erosion. But certainly, the abfraction process starts out as a microscopic phenomenon.

Q. Why aren’t all exposed dentinal surfaces hypersensitive?

A. Fortunately, some natural protective mechanisms exist and exposed dentinal tubules will seal themselves over time in many instances just by the accumulation of minerals from saliva. However, this doesn’t happen every time. It is patient specific.

Q. Approximately how many people suffer from some dentin hypersensitivity?

A. This varies immensely. I have seen studies quote numbers as low as 5% and as high as 60% of patients experiencing sensitivity in at least one of their teeth.^1-6 It varies according to the different populations studied but hypersensitivity is fairly prevalent. Certainly in periodontal patients, it tends to be even higher. I’ve seen estimates on periodontal patients that are close to 100% with sensitivity in at least one tooth.^5-7

Q. Why does it appear as though post-periodontal surgery hypersensitivity dissipates more quickly than other types of sensitivity?

A. In nonperiodontal patients, we’re not sure precisely what causes the sensitive areas. With periodontal patients, the scaling and root planing visit is likely the cause. In some of these cases, the natural protective mechanisms take care of the sensitivity, whereas in others, where the cause is unknown, patients’ natural defense mechanisms may not be working very well.

Q. Is hypersensitivity on other surfaces, such as the crown, as common as the root surface?

A. The incidence is much less on the crown than on the root surface. The occasional patient has enamel eroded away from the crown or abraded away from the crown due to bruxism. In some of these erosion patients, sensitivity exists but as a general rule, sensitivity is more prevalent on the root surface than anywhere else.

THERAPIES

Q. Please describe the various types of therapies to treat hypersensitivity.

A. There are two ways to treat dentinal hypersensitivity. One is to seal the dentin mechanically by closing the dentinal tubules. The other approach is to alter the nerve response to a stimulus. The professionally-applied treatments typically are geared toward closing the dentinal tubules. Fluorides, oxalate preparations, resin-based materials, and calcium phosphate are used for this.

Patient-applied products usually alter the nerve response. Desensitizing toothpastes are an example. They contain 5% potassium nitrate, which is designed to change the response of the nerves that transmit a pain impulse to the brain after repeated use. With potassium nitrate, the stimulus still exists, the dentinal tubules are still open, but the nerve doesn’t fire.

Q. Is it appropriate to use both strategies in combination?

A. Yes, it makes sense to combine the in-office and patient-applied treatments. Sensitivity is such a variable problem from one patient to the next and both treatments are effective.

Q. Is toothpaste the only patient-applied option?

A. Home-applied fluoride is available and it seals the tubules; it does not alter the nerve response. Another approach is a potassium nitrate gel. It looks like a fluoride gel but contains potassium nitrate. It’s a very convenient product that is used in a tray that patients apply themselves. The gel uses the same active ingredient as desensitizing toothpaste, just in a gel form. Patients put it in their custom tray and apply it to their teeth for 15 to 20 minutes. It’s really convenient for patients who are whitening their teeth because they already have a custom tray.

THE WHITENING FACTOR

Q. What percentage of whitening patients experience hypersensitivity?

A. There is about a 50% chance that a patient undergoing at-home whitening will experience sensitivity, but it tends to be mild.⁸ Mild sensitivity refers to patients experiencing a little twinge when drinking something cold or when breathing in cold air. A 10% chance exists of moderate sensitivity, where the twinge of pain is greater or sensitivity may happen more frequently. A 4% chance exists for severe sensitivity. The good news is that even with the relatively severe sensitivity, it goes away quickly.

Q. Why do some teeth become hypersensitive following or during whitening?

A. We’re not sure at this point. Currently, a history of tooth sensitivity is our best predictor.

Q. Should patients with a history of sensitivity pretreat their teeth with a potassium nitrate product before undergoing whitening treatment?

A. Patients with a history of sensitivity are more likely to experience it during the whitening process. Potassium nitrate can be used to reduce the possibility. Patients can use desensitizing dentifrices for 2 or 3 weeks before starting the whitening process and then continue on during the process.

Q. For patients who are using the whitening trays, should they use potassium nitrate before or after whitening?

A. The potassium nitrate gel should be put into the tray first, leaving it in for 15 or 20 minutes, then replacing it with the whitening gel. A recent study showed that this is effective for many patients.⁹ Some bleaching agents now contain densensitizers in the bleaching gel itself, which have been studied and deemed effective.^10-11

Q. Is there a protocol for sensitivity treatment?

A. Remember that pain is very specific to each patient. Don’t be afraid to try three or four different treatments if the first one is not effective. The best approach is to start with patient-applied products because they are relatively inexpensive, several teeth can be treated at once, and they’re simple to use. There is no magic bullet—nothing is 100% effective in 100% of patients.

REFERENCES

1. Murray L, Roberts AJ. The prevalence of self-reported hypersensitive teeth. Arch Oral Biol. 1994;39(Suppl.):129S-135S.
2. Fischer C, Fischer RG, Wennberg A. Prevalence and distribution of cervical dentine hypersensitivity in a population in Rio de Janeiro, Brazil. J Dent. 1992;20:272-276.
3. Liu HC, Lan WH, Hsieh CC. Prevalence and distribution of cervical dentin hypersensitivity in a population in Taipei, Taiwan. J Endod. 1998;24:45-47.
4. Irwin CR, McCusker P. Prevalence of dentine hypersensitivity in a general dental population. J Ir Dent Assoc. 1997;43:7-9.
5. Rees JS, Addy M. A cross-sectional study of dentine hypersensitivity. J Clin Periodontol. 2002;29:997-1003.
6. Taani S, Awartani F. Clinical evaluation of cervical dentin sensitivity (CDS) in patients attending general dental clinics (GDC) and periodontal specialty clinics (PSC). J Clin Periodontol. 2002;29:118-122.
7. Chabanski MB, Gillam DG, Bulman JS, Newman HN. Clinical evaluation of cervical dentine sensitivity in a population of patients referred to a specialist periodontology department: a pilot study. J Oral Rehabil. 1997;24:666-672.
8. Jorgensen MG, Carroll WB. Incidence of tooth sensitivity after home whitening treatment. J Am Dent Assoc. 2002;133:1076-1082.
9. Leonard RH Jr, Smith LR, Garland GE, Caplan DJ. Desensitizing agent efficacy during whitening in an at-risk population. J Esthet Restor Dent. 2004;16:49-55.
10. Tam L. Effect of potassium nitrate and fluoride on carbamide peroxide bleaching. Quintessence Int. 2001;32:766-770.
11. Pohjola RM, Browning WD, Hackman ST, Hackman ST, Myers ML, Downey MC. Sensitivity and tooth whitening agents. J Esthet Rest Dent . 2002;14:85-91.

From Dimensions of Dental Hygiene. February 2006;4(2):24, 26.