02/23/2011 Tooth Bleaching-A Critical Review of the Biological Aspects

Resident: J. Hencler
Date: 02/23/2011

Article title: Tooth Bleaching-A Critical Review of the Biological Aspects
Author: Duhl, Pallesen
Journal: Crit Rev Oral Biol Med 14(4):292-304 (2003)
Type of Article: Review

Introduction:
Tooth discoloration is classifies as intrinsic, extrinsic, or a combination of both. Intrinsic staining is caused by incorporation of chromatogenic material into the dentin and enamel during odontogenesis or after eruption. Exposure of high levels of fluoride, tetracycline, developmental disordered, and trauma to the developing tooth may result in pre-eruptive staining. After eruption, aging, pulp necrosis, and trauma are the main causes of intrinsic staining. Coffee, tea, red wine, carrots, oranges, and tobacco cause most extrinsic staining. Tooth bleaching can be performed externally (vital tooth bleaching) and intracoronally (non-vital tooth bleaching).

Medicaments:
Hydrogen peroxide (H2O2) is the active agent in tooth bleaching. It may be applied directly, or produced in a chemical rxn from sodium perborate or carbamide peroxide. H2O2 acts as a strong oxidizing agent through the formation of free radicals, reactive O2 molecules and H2O2 anions. These reactive molecules attack the long-chained, dark-colored chromophore molecules and split them into smaller, less colored and more diffusible molecules.

Intacoronal Non-vital Tooth Bleaching:
The medicament is placed in the pulp chamber, sealed, left for 3-7 days, and is replaced regularly until acceptable bleaching is achieved. Cervical root resorption is an inflammatory-mediated external resorption of the root, which may be seen after trauma and following intacoronal bleaching and has been reported. Intra-coronal bleaching requires healthy periodontal tissues and RCT that achieves proper obturation and a completely sealed canal orifice to prevent bleaching agent from reaching the periapical tissues.

External Vital Tooth Bleaching:
Four different approaches include 1) dentist-administered bleaching: a high concentration medicament often supplemented with a heat source 2) dentist-supervised bleaching: by means of tray delivered high concentrated medicament for 30 mins to 2 hrs while patient in dental office 3) dentist-provided bleaching: AKA at- home bleaching with custom made tray 4) over the counter products.

Side Effects:
Tooth sensitivity: most common side effect of external tooth bleaching. The mechanisms responsible have not yet been fully established. In vitro studies have shown that peroxide penetrated enamel and dentin and entered the pulp chamber. Histological evaluation revealed mild inflammatory changes.
Mucosal irritation: High concentration of H2O2 is caustic to mucous membranes and may cause burns and bleaching of the gingival.
Alteration of the enamel surface: The enamel surface exposed to bleaching agents underwent slight morphologic changes including loss of the aprismatic enamel layer and changes in the inorganic composition.
Effects on restorations: lab studies report increased mercury release from amalgams exposed to some bleaching medicaments. Also, the bond strength b/t enamel and resin-based fillings was reduced in the first 24hrs of bleaching.

Genotoxicity and Carcinogenicity:
H2O2 has been shown to have a weak local carcinogenic-inducing potential. The mechanism is unclear, but the genotoxic action cannot be excluded, since free radicals formed from H2O2 are capable of attaching DNA.

Summary of conclusions:
Generally, bleaching is safe and its use is widespread. The practitioner should be selective and provide professional bleaching to the patient in which this treatment is clinically justified.

Assessment of article: Good in-depth review of tooth bleaching.