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In-office and at-home whitening services have grown in popularity over the years as patients have sought a more esthetic smile. Today, there are many different types of whitening and bleaching products available to the dental team, varying in primary agent and purpose. For many patients, determining the potential for sensitivity can be accomplished through assessment of past tooth sensitivity as well as their reaction to an explorer or air during an initial examination. Methods for reducing tooth sensitivity are often predicated on whether the treatment is in-office or at-home. Generally, a combination of different strategies will be sufficient to reduce sensitivity and ensure greater compliance with intended treatment. Consequently, patients can glean the benefits of whitening and clinicians can more effectively use these services to boost their practice productivity or influence the success of a restorative case.
Understanding Whitening Sensitivity
When a patient does not complete a prescribed whitening regimen, it can result in disappointment that may challenge the patient-doctor relationship or lead to potentially detrimental word-of-mouth that contributes to a decline in patient recommendations. Thus, understanding how to reduce bleaching sensitivity is vital not only to patient satisfaction, but also to the health of the dental practice's business. Treatment management must include a means by which to handle potential noncompliance. When tooth sensitivity occurs as a result of bleaching, it is most likely caused by penetration of peroxide to the pulp. One study found that over half of patients treated with carbamide peroxide experienced tooth sensitivity and 20% decided not to move forward with treatment because of the unpleasantness.1
Dentin hypersensitivity often appears as a brief, sharp pain associated with exposed dentin that has encountered some form of stimulus, whether it be heat, touch, or other sensations.2 Studies using techniques such as scanning electron microscopy have shown that there is a significant difference between the dentin of teeth that experience hypersensitivity and those that do not.3,4 For example, Absi et al found a higher number of dentinal tubules per unit area in sensitive teeth versus nonsensitive teeth as well as significantly wider diameter of these tubules.3
Anatomical differences can account for why some patients experience no discomfort during whitening while others find it intolerable. Dentin hypersensitivity is commonly attributed to the hydrodynamic mechanism of fluid flow in dentinal tubules, where a pressure change has an impact on mechanoreceptors, leading to the sensation of pain.5 The sensation is directly related to activation of the Aδ nerves.
Another important contributing factor to dentinal hypersensitivity is gingival recession. The latter leads to exposed root surfaces and has been connected to teeth exhibiting excellent oral hygiene and low plaque scores, perhaps as a result of overbrushing. However, a relationship between brushing and gingival recession has not necessarily been supported by the literature. A 2007 systematic review did not find data to support or refute the association.6 Moreover, a 2016 3-year randomized study found that preexisting gingival recession was significantly reduced by brushing with both manual and power toothbrushes.7
A 2018 cross-sectional study found a positive correlation between noncarious cervical lesions, cervical dentin hypersensitivity, and gingival recession.8 Fukumoto et al found the highest level of dentin hypersensitivity in teeth with severe recession but also noted that plaque-free teeth demonstrated greater dentin hypersensitivity than plaque-stained teeth.9 Overall, these studies suggest that greater quality of oral health may contribute to a lower incidence of sensitivity but that certain aspects of good oral hygiene may negatively contribute to hypersensitivity.
Common Whitening Agents and Their Impact on Sensitivity
Common ingredients used in whitening are carbamide peroxide and hydrogen peroxide. In general, hydrogen peroxide products are associated with more prevalent sensitivity, stemming from higher release of oxygen molecules across a shorter duration. Moreover, light sources in heat can further exacerbate this sensitivity. Research has shown that the higher the concentration of these compounds in the whitening treatment, the more likely the patient is to experience sensitivity.10 This demonstrates outright the importance of managing two different factors: (1) the duration of whitening and (2) the concentration of the whitening agent.
Both carbamide peroxide and hydrogen peroxide are oxidizing agents, meaning that they are able to lighten teeth color by freeing oxygen from the dentin. This distinguishes these agents from strict "bleaching" agents, which simply remove extrinsic surface stain. Whitening agents act on dentin for a more thorough removal of stain. Carbamide peroxide in particular is often found in at-home tray bleaching. Clinicians may fabricate individual trays with the intention of patients using a gel on their own outside the office.
Carbamide peroxide in contact with water creates hydrogen peroxide, which is absorbed into enamel rod porosities, where it is then able to penetrate dentinal tubules. It is preferred for at-home treatments because it packs only a third of the punch of hydrogen peroxide. In-office bleaching uses hydrogen peroxide because it is stronger at a lower percentage and can therefore have a greater impact in a shorter amount of time. With a liquid dam in place to guard the gingiva, this treatment is quite effective. These whitening agents are able to act with equal efficacy but in different time frames.
Tray bleaching is usually accomplished at a concentration of about 10% carbamide peroxide, which translates to around 3.5% hydrogen peroxide, but even with such a low hydrogen peroxide concentration, some studies have indicated 25% to 75% incidence of sensitivity.11,12 One study found that sensitivity is especially compelling in leading a patient to discontinue treatment, with 14% of patients deciding to stop treatment for this reason.13 A study from Browning et al found that 77% of individuals will experience sensitivity and will have it for 3 days or less, not a long period of time.14 These researchers highlight the necessity of talking to patients about what to expect with sensitivity during and after bleaching.14
An initial comprehensive examination should include questioning patients about the current sensitivity of their teeth. Asking how their teeth respond to hot or cold stimuli can be especially revealing. It is more difficult to gauge a predisposition for sensitivity from factors such as exposed dentin, gingival recession, or caries. Moreover, the mechanical forces associated with bleaching in trays may themselves heighten the sensation of sensitivity, making it impossible to completely reduce sensitivity even when using the methods delineated in this article. The rigidity of the tray can also have an impact on perceived sensitivity. Patients who grind their teeth can experience sensitivity, and some may even find that wearing a tray with or without a whitening agent can produce sensitivity.15-17 It is nearly impossible to control all variables; therefore, clinicians must respond to the individual needs of patients with proper education and explanations before problems arise.
Reducing Bleaching Sensitivity
Patients who experience significant sensitivity will benefit from using at-home trays with a lower percentage of the active ingredient. A disadvantage of this method is that the treatment will take longer to achieve the desired result; however, it will be more comfortable for the patient. It will also depend more heavily on patients' willingness to consistently carry out the treatment on their own.
These same patients will benefit from using potassium nitrate relief gel in trays every day when they bleach. A 2018 study examining the impact of five 10% carbamide peroxide tooth whitening formulas, three of which contained different concentrations of desensitizing potassium nitrate, found that sensitivity was not reduced during treatment by using potassium nitrate but that it did lead to a significant postoperative reduction of sensitivity.18 Potassium nitrate is effective because of the potassium ions released in its mechanism of action. Studies have concluded that potassium salts may function by preventing the action potential produced in intradental nerves from firing.19,20 Nerve activity is thus a significant contributing factor to perceived pain or sensitivity from whitening. Potassium nitrate can be dispensed through direct application to the bleaching tray or in whitening products that already include the compound.
Another helpful intervention is to have patients brush with potassium nitrate toothpaste 2 to 4 weeks before starting treatment. Potassium nitrate is approved by the US Food and Drug Administration in toothpaste at a maximum concentration of 5%. A 2012 study explored potassium nitrate's impact on sensitivity, with 30 patients divided into one group using 5% potassium nitrate toothpaste and the other group using 3% potassium nitrate mouthwash.21 Both groups showed a statistically significant decrease in dentinal hypersensitivity, with no statistically significant difference between the groups.21 This suggests that either option can be beneficial as a treatment modality, with more options provided to patients who may have different preferences for management.22
Potassium nitrate is widely accepted as an effective desensitizing agent. Success was further demonstrated by Haywood and colleagues in 2001, who found that 16 of 30 patients had tooth sensitivity.23 More than 90% of 12 patients who used a 5% potassium nitrate with 1,000-ppm sodium fluoride gel experienced reduced sensitivity.23 Additionally, one of the main advantages of potassium nitrate is that it is a safe over-the-counter product that patients can use easily whenever it is needed, whether that be actively every time they whiten their teeth or as the situation arises.
One caveat to the use of potassium nitrate in toothpaste is that some patients may experience gingival sensitivity to a different ingredient in certain formulations, specifically sodium lauryl sulfate, which can irritate the tissue and cause patients to misattribute the source of the problem to potassium nitrate. Recently, toothpastes have been developed that include the desired active ingredient without the irritating compound, but it is important for clinicians to carefully select a recommended toothpaste to bypass any conflicting factors.
Some clinicians use fluoride as a treatment adjunct to potassium nitrate because it is assumed that this agent will work toward occluding dentinal tubules or generating a harder enamel surface, thereby creating a barrier that prevents peroxide molecules from penetrating tooth surfaces to reach the dentinal tubules. However, this method may not be effective in preventing small molecules from entering the interstitial space found between the tubules. Nevertheless, a 2009 double-blind randomized clinical study found that the placebo group versus the group that received fluoride treatment experienced a higher-intensity tooth sensitivity.24 This result suggests that fluoride may provide some benefit when combined with other methods, such as potassium nitrate.
For in-office whitening, 600 mg of ibuprofen before the appointment will help to reduce discomfort. It is beneficial to use non-steroidal anti-inflammatory drugs (NSAIDs) for sensitivity reduction because they act rapidly and have a relatively low impact on the body compared with other medications. In a 2009 study by Charakorn and Cabanilla, it was found that 600 mg of ibuprofen reduced tooth sensitivity during in-office bleaching with 38% hydrogen peroxide.25 The reduced sensitivity may have resulted from raising patients' pain threshold so they were better able to tolerate treatment.
In the future, in-office bleaching may benefit from new therapies to reduce sensitivity on-site. A 2018 study by de Paula et al investigated the effect of combining photobiomodulation using low-level laser therapy with 5% potassium nitrate gel.26 The researchers concluded that these therapies together are effective in minimizing pain sensitivity, but they did not observe a significant synergistic effect.26
In-office and at-home teeth whitening are essential components of the modern dental practice's treatment offerings. Their popularity reflects the growing appreciation patients have for cosmetic services. Whitening is a relatively simple treatment that supports the business health of the dental practice. Clinicians can prevent patient dissatisfaction or discontinuation of treatment due to whitening sensitivity by properly explaining the possibility of sensitivity to patients before treatment, completing an examination to test for the presence of sensitivity, and providing options for sensitivity management, including NSAIDs and potassium nitrate products. Ultimately, these efforts can enable patients to have the best whitening experience possible so that they can achieve the tooth shade they desire.
About the Author
Lee Ann Brady, DMD, is a privately practicing dentist and nationally recognized educator, lecturer, and author. With an extensive history in leadership, she is currently director of education of the Pankey Institute. Dr. Brady has also developed a vast library of online instruction at leeannbrady.com and restorativenation.com. She practices in Glendale, Arizona, and is a member of the editorial board for the Journal of Cosmetic Dentistry, Inside Dentistry, and Dentaltown Magazine.
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