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Restorative Dentistry Supporting Your Practice

Are there any detrimental effects of tooth-whitening agents on enamel?


A woman is smiling while being at the dentistThis question was submitted by a general dentist: Are there any detrimental effects of tooth-whitening agents on enamel? Some have shown increased microfracture in the enamel seen only under SEM; however, is it clinically relevant?

Dr. Laura Tam, from the Faculty of Dentistry at the University of Toronto, and Dr. Suham Alexander provided this quick initial response



Tooth whitening has become an increasingly popular esthetic service for patients and is well-integrated in dental practices. At-home whitening with carbamide peroxide and hydrogen peroxide (H2O2) was originally part of a complete dental procedure which included the dentist examining the patient to ensure there were no contraindications to treatment with the bleaching agent. However, it has seen rapid growth as an over-the-counter product. The latter products typically have higher concentrations of H202 that are used for shorter time periods.

Safety Concerns of H2O2 Bleaching Products 

The safety concerns regarding potential systemic effects are no longer a primary issue given the H2O2 is limited to the oral cavity and does not reach levels which would induce systemic toxicity. However, patients should be advised not to smoke or drink alcohol while undergoing bleaching treatment as H2O2 can promote tumour growth in the presence of DMBA (tobacco carcinogen) in vitro. 

There are documented local adverse effects of bleaching products.

Tissue Burns

  • Occurs when high concentrations of peroxide are used, mainly in-office bleaching.
  • Improper use of at-home bleaching can lead to mucosal irritation or burns due to prolonged exposure to the active ingredients
  • Usually transient.

Tooth Sensitivity

  • Sensitivity to temperature changes is a common clinical side-effect.
  • Sensitivity is transient and generally does not persist after the cessation of bleaching.
  • Increased risk when bleaching agent is higher concentration or changed more than once a day.
  • Long-term studies regarding effect of H2O2 exposure on pulp lacking.
  • Exercise caution and avoid bleaching in patients with carious teeth, exposed dentin and defective restorations.

Gingival Irritation

  • Irritation linked to the concentration of H2O2 and gingival contact.
  • Mild to moderate occurring 2-3 days after beginning treatment at-home.
  • Usually result of an ill-fitting bleaching tray (at-home) or leak in the gingival barrier protection (in-office).

Effects on Enamel

  • Mineral loss occurs during bleaching but, is not significant as there are remineralization capabilities within the oral cavity.
  • Few changes noted in SEMs of bleached enamel surfaces on a micron scale.
  • Alterations in enamel surfaces attributed to products which use and acidic pre-rinse and low pH gels.
  • Presently, no clinical evidence of enamel effects with the use of at-home bleaching agents monitored by dentists (2 significant cases of enamel damage using OTC products).

Effects on Dentin

  • While bleaching agents are not intended for dentin surfaces, dentin is exposed to bleach in cases of occlusal attrition and root recession.
  • In vitro evidence of decreased dentin mechanical properties following direct and prolonged exposure to at-home bleach.

Effects on Restorations

  • Bleaching may affect the chemical/physical properties of restorative material.
  • Residual bleach within enamel and dentin immediately after the cessation of bleaching significantly impairs subsequent bonding attempts. Therefore, dentists should delay all bonding procedures until at least 1 week has passed after the end of bleach treatment.

Chlorine dioxide bleaching agents are also available and are used mainly in beauty spas and cruise ships. These agents make teeth more susceptible to re-staining, strip enamel from tooth surfaces irreversibly while reducing the enamel’s natural lustre and cause sensitivity.


  1. Li Y and Greenwall L. Safety issues of tooth whitening using peroxide-based materials. British Dental Journal. 2013; 215(1):29-34
  2. Naik S, Tredwin CJ and Scull C. Hydrogen peroxide tooth-whitening (bleaching): Review of safety in relation to possible carcinogenesis. Oral Oncology. 2006; 42:668–674
  3. Tredwin CJ, Naik S, Lewis NJ, Scully C. Hydrogen peroxide tooth-whitening (bleaching) products: review of adverse effects and safety issues. Br Dent J. 2006 Apr 8;200(7):371-6
  4. Tam, LE* and Noroozi, A . Effect of direct and indirect bleaching on dentin fracture toughness. J Dent Res. December 2007; 86:1193-1197


Do you have any particular question on this topic? Do you have any comments or suggestions? Email us at oasisdiscussions@cda-adc.ca

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  1. hardy October 8, 2014

    Enamel is crystal clear. The only way to whiten teeth is to whiten yellow dentin. Therefore vital bleach *IS* intended for dentin. It’s the only way to ‘significantly’ change the colour of teeth. With time, ‘touch up’ bleaching is required because bleach entering dentin stimulated the odontoblasts to lay down more dentin, making teeth yellow again. Repeated vital bleaching prematurely ages teeth, ironically, even though they ‘look’ younger. Additionally, it probably makes teeth more brittle. Patients should be warned of these possibilities.


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