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TOOTH BLEACHING—A CRITICAL REVIEW OF THE BIOLOGICAL ASPECTS

NIOM-Scandinavian Institute of Dental Materials, Kirkeveien 71B, PO Box 70, N-1305 Haslum, Norway;

U. Pallesen

Institute of Odontology, Faculty of Health Sciences, University of Copenhagen, Denmark

View larger version (15K): [in a new window]   Figure 1. The formation of hydrogen peroxide from sodium perborate (Eq. 1) (Hägg, 1969) and from carbamide peroxide (Eq. 2) (Budavari et al., 1989). Hydrogen peroxide forms free radicals like hydroxyl and perhydroxyl radicals, and superoxide anions (Eq. 3a) (Gregus and Klaassen, 1995), reactive oxygen molecules that are unstable and transformed to oxygen (Eq. 3b) (Cotton and Wilkinson, 1972), and hydrogen peroxide anions (Eq. 3c) (Cotton and Wilkinson, 1972).

View larger version (70K): [in a new window]   Figure 2. Non-vital tooth bleaching of a discolored tooth in a 21-year-old woman. The tooth had been endodontically treated 6 yrs earlier due to trauma. A slight discoloration, which subsequently became more intense, was visible immediately after the endodontic treatment. (A) Tooth #11 with a dark blue discoloration. (B) The result after 3 wks of internal bleaching with sodium perborate suspended in water and a weekly change of bleaching agent. (C) 5 yrs after internal bleaching. Only slight discoloration is visible, and no re-treatment was necessary. (D) 10 yrs after internal bleaching. Recurrence of the discoloration is visible, and the patient needed re-treatment. The relapse after 10 yrs, however, was not as severe as the discoloration before bleaching, and the tooth could be re-bleached to a satisfying result. Although intercoronal bleaching does not have—as do most other treatments—indefinite durability, the long-term aesthetic and biological results of this treatment are considered to be of high quality.

View larger version (104K): [in a new window]   Figure 3. External root resorption after internal bleaching of teeth #11 and #21. Both teeth had been endodontically treated due to caries 14 yrs earlier. No history of trauma was reported. Two years after endodontic treatment, both teeth were internally bleached by sodium perborate and 3% hydrogen peroxide. Due to an unsatisfactory bleaching result after 3 wks, the treatment was supplemented with in-office bleaching with 30% hydrogen peroxide and heat two times for 30 min each, with an interval of one week. External root resorption was diagnosed 12 yrs later.

View larger version (45K): [in a new window]   Figure 4. External at-home bleaching of discolored teeth in a 13-year-old girl diagnosed with amelogenesis imperfecta. (A) Before treatment, an intense yellowish discoloration of all teeth was visible. Pigments from foods and beverages had penetra-ted the hypomineralized enamel. (B) The result after dentist-guided at-home bleaching of the maxillary anterior teeth (#14, 13, 12, 11, 21, 22, 23, 24) with 10% carbamide peroxide twice daily for 30 min each and for two consecutive weeks. The yellowish discoloration was eliminated in the bleached teeth.

View larger version (78K): [in a new window]   Figure 5. External in-office bleaching of teeth #11 and #21 in a 52-year-old woman. (A) Both teeth had become discolored in the mesial part after restoration of small Class II cavities with composite resin material 20 years previously. This is a known side-effect of some of the first-introduced composite materials. Replacement of the restorations with a new composite material did not remove the discoloration located in the surrounding dentin and enamel. (B) The result after external in-office bleaching with 35% hydrogen peroxide and heat (from two light-curing units) twice and for 30 min each with an interval of one week. Although the restorations were not removed during treatment, an acceptable result was obtained. (C) The result 4 yrs after bleaching. Only slight relapse was visible. (D) 8 yrs after bleaching. A moderate recurrence of discoloration is visible, but the patient did not need re-treatment.

View larger version (102K): [in a new window]   Figure 6. SEM photomicrographs of an enamel surface without (A) and with (B) exposure to a bleaching procedure. The enamel of an extracted human tooth was cleaned with water-spray, and half of the surface was covered with nail varnish (the control). The tooth was then exposed to 10% carbamide peroxide gel for 1 hr two times daily during 3 wks. After each bleaching procedure, the gel was removed by water-spray, and the tooth was stored in water between treatments. At the end of the bleaching period, the nail varnish was removed, and comparative sections of bleached and unbleached enamel were prepared for direct scanning electron microscopy (Holmen et al., 1985). The enamel microstructure of the bleached-enamel surface (B) illustrates an obvious enamel etch caused by the bleaching agent, compared with the unbleached surface (A).

View larger version (7K): [in a new window]   Figure 7. The formula for calculating the safety factor based on general principles for risk assessment (Woodward, 1996).