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Whitening of the teeth by bleaching is quite popular and is offered by dentists and in some cases non-dentists and pursued by many patients. The two most popular bleaching products are hydrogen peroxide (HP) and carbamide peroxide (CP) in various concentrations. The effect of bleaching on various dental materials has been fairly extensively studied with the results suggesting that bleaching can change the physical properties of dental restorative materials including the surface hardness and roughness as well as leakage.

In a five page article published in the Journal of the Canadian Dental Association, authors J El-Murr, D Ruel, and A St-Georges of the University of Montreal School of Dentistry, Quebec, Canada, provide a comprehensive review of the many alterations in dental restorative materials that can be associated with bleaching and ‘put these changes in restorative materials into clinical perspective and provide practitioners with the evidence to properly answer patient’s questions’ (J Can Dent Assoc, 2011;71:b59).

Assessed is the effect on amalgam, porcelain, ormocer (organically modified ceramic), glass ionomer cement and resin-modified glass ionomer cement, polyacid-modified composite resin (compomer), and composite resins. The authors provide 25 references for the reader interested pursuing information related to the original research.

For amalgam, some properties appear to be changed including elution, microhardness, and surface roughness. But studies assessing metal ion release from bleaching are contradictory. As the authors note, one study appears to suggest that there is no significant release in the release of metal ions associated with use of a 10% solution of CP while two others have found release with varying concentrations of bleach in CP and HP. Even so, the release of mercury, silver, copper and tin did not apparently (per the authors of these two latter studies) reach levels of toxicity as defined by the World Health Organization.

In general, it is reported by the authors that the studies reviewed suggest there could be discoloration with bleaching, especially associated with old amalgams with marginal discrepancies, but generally changes from bleaching as noted above appear minor. As for porcelain material, there is in vitro evidence that prolonged exposure to bleach at 10%-35% may cause porcelain surface change and roughness. However the effect may be different based on the type of glazing (overglazing versus autoglazing) used on the ceramic restoration. At home and in-office studies of HP and CP suggest that there is no effect from 30 days of usage of these bleaching materials. However, the authors conclude it would be best to avoid using bleaching on patients with these restorations.

With respect to organically modified ceramics, one study suggests that bleaching can change the color of the restorations, particularly bleaching at high (35%) concentrations. Several other studies, however, do not support color alteration via bleaching. An additional study suggests that bisphenol A (an estrogen mimicker) is not released from bleaching of these restorations.

In contrast to the above material, the authors cite a number of studies that have evaluated the effect of bleaching agents on glass ionomer and resin modified glass ionomer cements. These studies suggest that surface pitting and other changes may increase with bleaching which may make the restorations more susceptible to different staining solutions such as those associated with red wine, herbal tea, Coca Cola, and coffee. Surface hardness was found to have decreased 23.1% after bleaching with a 35% HP solution in one study. Given these findings, the authors conclude that glass ionomer and resin-modified glass ionomer cement restorations may need to be replaced following bleaching.

The same findings were associated with exposure of compomer resins and composite resins to bleaching with significant effects noted for surface roughness, microhardness, color stability and stain susceptibility. However bleaching did not seem to affect the occlusal margins or produce microleakage. Nonetheless, the authors conclude that more studies need to be concluded before statements can be made regarding the clinical relevance of the changes caused by tooth bleaching.

The authors conclude that “dentists should be aware that the physical properties of some dental restorations may be altered after bleaching” Further, “they should also make sure that their patients with dental restorations are aware of the changes that may occur during whitening, as well as the possibility that their bleached restorations may need to be polished or replaced at the end of the treatment”

Submitted by Dr Jeff Burgess, Editor in Chief