As patients and consumers demand not only a healthy mouth but also a perfect appearance, vital bleaching of teeth has gained interest. It has been accepted as one the most effective methods of treating discolored teeth and considered to be a conservative approach towards obtaining esthetic or cosmetic results rather than other methods such as veneering or crowning. Procedures that utilize different concentrations of carbamide peroxide (CP) or hydrogen peroxide (HP) have been commonly used by dentists as "in office" or by patients as "home bleaching" applications. Other than these, over the counter products have been widely used by patients; however they cannot be considered as one of the "bleaching treatments".
The efficacy of bleaching is influenced by many factors like the type, concentration of the bleaching agent, time it is applied, application method used (heat, light, laser, etc.) cause of the stain and the condition of teeth. Procedures apparently rely on an extended period of contact between the bleaching agent and the teeth to accomplish the bleaching. The decomposition of hydrogen peroxide results in oxygen and per-hydroxyl free radicals that oxidize the stained macromolecules and break them down into smaller lighter colored fragments. Then the fragments diffuse across the tooth surface resulting in the bleaching effect (Haywood, 1992; Chen et al., 1993). The oxidation reaction should not exceed the saturation point in which the organic and inorganic elements of enamel and dentin are damaged. Otherwise, the crystals of mine matrix proteins lead to adverse changes in the morphology of the tooth surface and weakened structure (Haywood & Heymann, 1989; Goldstein&Garber, 1995). Studies (Seghi RR&Denry, 1992; Justino et al., 2004; Flaitz & Hicks, 1996; Spalding et al., 2003; Turkun et al., 2002; Bitter, 1992; Lopes et al., 2002; Hegedus et al.,1999; Rotstein et al.,1996; Potocnick et al., 2000; Tezel et al., 2007.) have shown that bleaching agents can cause structural alterations on enamel surface and that the biomechanical properties of the enamel can change. In addition Basting and others (Basting et al., 2001) reported the possibility of formatting of active caries lesions after bleaching process since they diffuse through the enamel by demineralization.
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