When to Place Restoratives
Following a Whitening Procedure
By Sachin Seth, B.Sc., D.D.S.
References | About Sachin Seth, D.D.S.
Successful bleaching of teeth can commonly result in anterior resin restorations no longer having an esthetic shade match, which may consequently necessitate their replacement. The replacement of these restorations should be delayed for at least three weeks, because studies have shown that bleaching enamel before performing a resin restoration can significantly reduce the bond strength resulting in early restoration failure. [1-3]
In order to understand the effects bleaching may have on enamel and subsequent bonding to the tooth, it is important to understand how carbamide peroxide and hydrogen peroxide exert their bleaching effects. Carbamide peroxide dissociates into urea and hydrogen peroxide when in contact with saliva. The hydrogen peroxide molecule, being a strong oxidizing agent, penetrates the enamel surface and through the formation of free radicals, will break down pigmented molecules. [4, 5]
Two theories have been proposed for the potential decrease in post bleaching bond strengths. One suggests that the enamel surface becomes altered in its crystalline structure becoming pitted with decreased levels of calcium and phosphorus. This in turn results in an enamel surface that forms a weaker bond with resin. The second proposes that residual oxygen free radicals from the breakdown of hydrogen peroxide may interfere with resin infiltration into the enamel or with resin polymerization. [6, 7]
When examining the scientific body of evidence most studies have been performed on in vitro models that cannot completely simulate the complexities of the oral environment. Comparison of these situations is very difficult, because factors such as hydrogen peroxide concentration, exposure times and storage mediums vary widely from study to study. The inconsistencies in these variables make it difficult to draw any concrete conclusions. However, there exists compelling evidence that there are changes at the enamel surface that may alter the bond strength of resins. Although scientific evidence remains inconclusive, a one-to-three week waiting period is recommended before any resin bonding is performed following any whitening treatment.
References:
- Metz, M.J., et al., Clinical evaluation of 15% carbamide peroxide on the surface microhardness and shear bond strength of human enamel. Oper Dent, 2007. 32(5): p. 427-36.
- Cavalli, V., et al., The effect of elapsed time following bleaching on enamel bond strength of resin composite. Oper Dent, 2001. 26(6): p. 597-602.
- van der Vyver, P.J., S.B. Lewis, and J.T. Marais, The effect of bleaching agent on composite/enamel bonding. J Dent Assoc S Afr, 1997. 52(10): p. 601-3.
- Josey, A.L., et al., The effect of a vital bleaching technique on enamel surface morphology and the bonding of composite resin to enamel. J Oral Rehabil, 1996. 23(4): p. 244-50.
- Basting, R., A. Rodrigues, Jr., and M. Sierra, The effect of 10% carbamide peroxide bleaching material on microhardness of sound and demineralized enamel and dentin in situ. Oper Dent, 2001. 26(6): p. 531-9.
- Potocnik, K., L. Kosec, and D. Gaspersic, Effect of 10% carbamide peroxide bleaching gel on enamel microhardness, microstructure, and mineral content. J Endod, 2000. 26(4): p. 203-6.
- Attin, T., C. Hannig, and A. Wiegand, Effect of bleaching on restorative materials and restorations - a systematic review. Dent Mater, 2004. 20(9): p. 852-61.
Sachin Seth, B.Sc., D.D.S. is a graduate of Dalhousie University in Halifax Nova Scotia where he is now a full time faculty member in the Department of Clinic Sciences.
