Design Principles for Oxidative Tooth Whitening: Factors Affecting Dentinal Hypersensitivity

Transient dental hypersensitivity is a common side effect of topical bleaching.³⁹ Tooth sensitivity can be a significant barrier to full utilization of vital tooth bleaching by many patients.^40-42 It is important to understand that the etiology of tooth bleaching sensitivity is an entirely separate mechanism from dentinal hypersensitivity via thermal/tactile stimuli.

The etiology for the development dentinal hypersensitivity has been extensively studied. The prevalence of sensitivity with bleaching depends on a variety of factors, however concentration of bleaching is often associated with hypersensitivity complaints, as highlighted earlier. While still not completely understood, a few aspects are clear. First, the source of the increased hypersensitivity is clearly in the pulp, as this is where the nerves are located within the teeth. Hypersensitivity is commonly observed in patients without exposed dentin; hence the bleaching does not have to expose dentinal tubules to produce the effects. In animal studies, application of peroxide solutions to the teeth produced inflammatory responses in the pulp of treated animals.^43-46 This was confirmed in human studies with bleaching of teeth in adolescents scheduled for orthodontic extraction.^46-51

The picture that emerges is that bleaching treatments produce minor inflammation of pulp, which in turn elevates the response of pulp nerves. The inflammation could be caused by the over diffusion of peroxide into the pulp itself or it has been proposed that it may be accentuated by dehydration effects which occur from anhydrous thickening agents in the gel that deliver the bleach. Even though these compositions are hydrophilic, they in fact pull water from and dehydrate the teeth.

With this increased inflammation the nerves may become more responsive to external stimuli, including temperature changes. The response to this minor inflammation includes expression of increased catalase in the pulp which can act to degrade further influx of peroxide in the interior of the tooth. This mechanism explains multiple clinical observations including: elevated hypersensitivity during application of the bleach; hypersensitivity directly following application of the bleach; development of resolution of hypersensitivity during chronic bleaching procedures; and lastly, the resolution of hypersensitivity following bleaching.

While tooth whitening with peroxidative methods has a good record of safety, researchers continue to innovate with treatments which are designed to reduce side effects of dentinal hypersensitivity. There is no contraindication for treating dentinal hypersensitivity via a product whose mechanism of action is tubule occlusion, and it does not impact efficacy as the peroxide is able to diffuse to the chromogen. In fact, using a product that occludes tubules or contains potassium salts may reduce the sensitivity associated with hydrodynamic pull on pulpal fluid while the pulp is inflamed.⁶¹