Dentin Hypersensitivity

What is the cause of dentin hypersensitivity?

Sensitivity is associated with open dentinal tubules. A disturbance of the fluid within the dentinal tubule occurs when a stimulus, like hot or cold, comes in contact with the tooth surface. The fluid movement then stimulates the nerve endings located near the pulp, causing the nerve membrane to depolarize, thereby inducing pain. This process only occurs if the dentinal tubules are open at the tooth surface. Two conditions precede open tubules:

1. The protective positioning of the gingiva is altered to expose enamel and/or cementum.
2. Enamel or cementum is lost, exposing dentin.

If the exposed dentinal tubules remain open, sensitivity is likely to occur. Once hypersensitivity is diagnosed, there are two treatment options: occluding the tubule opening and/or precipitating the tubule lumen to prevent fluid disturbance or preventing depolarization of the nerve.

Hypersensitivity can result when gingival recession and tooth surface loss occurs. What is the physiologic process that leads to hypersensitivity?

The stage is set for hypersensitivity when there is a loss of tooth structure, either cementum or enamel.

Root sensitivity comes into play in the presence of recession combined with cementum loss. Sensitivity can also exist on the crown of the tooth if enamel is lost and dentin is exposed. If sensitivity originates from the crown of the tooth, recession isn’t necessarily a prerequisite.

Dental hygienists often look at the cementoenamel junction (CEJ) and root tissue as the source of sensitivity. When we see a tooth that has no visible recession, can the patient really be experiencing sensitivity?

Yes, theoretically sensitivity can originate anywhere on the crown. For instance, if a crown prep is done and enamel around the CEJ is inadvertently removed, some sensitivity may exist there, but you can also get it from the occlusal surface. This is what is difficult. A clinician is alerted to expect the possibility of sensitivity in an area with recession. However, sometimes an area has slight recession and dentin exposure that are not visible to the naked eye so with placement of an instrument or air, the patient unexpectedly reacts.

Are there other forms of tooth structure loss that can lead to hypersensitivity?

Anything that removes the tooth structure can cause sensitivity. Certainly, abfraction, attrition, abrasion, and erosion can all lead to sensitivity. Attrition is tooth-to-tooth wearing away. Abrasion is wear caused by contact between a tooth and some other object, like a toothbrush, fingernail, pen, or a pencil. Abfraction occurs when there are lateral forces that may be quite minor but repeated over time during occlusion can cause microscopic pieces of enamel to break off and break away. The appearance of abfraction is often confused with abrasion. An interesting mechanism that contributes to loss of tooth structure is erosion combined with abrasion. This can occur when an individual consumes an acidic food/beverage (including diet or regular soda) and then immediately brushes with toothbrush/dentifrice. For example, consuming acidic foods or beverages or drinking soda, diet or regular, immediately followed by brushing can lead to tooth structure loss and sensitivity. Practitioners often do not consider this combination of erosion and abrasion when questioning patients about their dietary and oral hygiene habits. Try asking patients with sensitive teeth whether they drink orange or grapefruit juice every morning followed by brushing their teeth. If so, this combination could be the source of their discomfort.

Please describe the current therapies used to treat dentin hypersensitivity.

So many different types of therapies exist that treatment can be confusing. The fact that some products work for some people and not for others is because the different categories of products have different ways of impacting what’s going on with the fluid transmission in the tubules. This is why there is such a variety of products available. Treatments that decrease the ability of the nerve to react can provide relief as well as other products that either occlude the ends of the tubules or form precipitates within the tubule lumen.

Dental hygienists can recommend one modality and evaluate its effectiveness. If the particular therapy doesn’t work, then another treatment can be tried.

If the aim is to impact the nerve response, what types of products can be used?

The easiest and most often recommended as a first line of defense is over-the-counter desensitizing dentifrice, in which the active agent is potassium nitrate. The abrasives in toothpaste can also occlude the tubules. For a patient with severe dentin hypersensitivity, I would start with a more definitive treatment, such as in-office treatments or a prescription concentration home regimen. See Table 1 for a list of professionally applied treatments for dentin hypersensitivity.

What is the role of oral hygiene and biofilm in hypersensitivity?

People who over brush and are too fastidious about removing biofilm often develop hypersensitivity, but on the other hand, plaque biofilm products that get within the tubules when plaque is left on the tooth can lead to irritation of the nerve and manifest as sensitivity. This can be confusing. Should patients brush a lot or a little? It’s similarly confusing with the smear layer. On the one hand, it is beneficial to have a smear layer because it helps seal off the tubules and reduce sensitivity, but by brushing and keeping teeth really clean, the smear layer gets brushed away. It’s not surprising that hypersensitivity is often referred to as an enigma.

What are some of the newest therapies to treat hypersensitivity?

There are newer delivery methods. A professionally-applied product now comes in a syringe where the solution can be applied exactly where you want. It uses soft-needle foam dispensing tips. The mineralizing agent NovaMin, used in hip bone regeneration, has recently been introduced as a hypersensitivity agent.

Esthetic cervical restorations used to provide a physical barrier against hypersensitivity have also greatly improved. In earlier times, you didn’t have a very smooth margin so you were trading one problem for another. It was easy to get gingival inflammation around class five restorations, but the newer products now have eased these problems. They are thinner, the margins are better.

What do you see in the future of treatment for hypersensitivity?

Sensitivity is a vital area of research and development because it is a common problem. Also with the increasing popularity of tooth whitening, treatments for hypersensitivity will only continue to grow.

From Dimensions of Dental Hygiene . September 2005;3(9):30, 32.