Duration of Treatment – Retention of Ingredient (contact time)
Earlier, the concept of diffusion was described as being important for topically applied oxidative tooth whiteners. In order for diffusion to do its work – peroxide must be retained at the tooth surface. This is because diffusion requires a concentration gradient to be effective. Maintenance of this gradient is what retention is all about. The ability of each product to maintain peroxide concentration on the tooth surface varies significantly and is strongly affected by the delivery vehicle employed. In some cases, such as in office higher concentration systems, retention is controlled by the dental professional. In the case of take-home trays, retention is maintained by placing the bleach in a well within the tray and relying on the consumer to put the correct quantity of agent inside. In strip applications, the adhesive strip is what ensures retention on the tooth surface.
Overall, concentration, dose and retention are linked in predicting the effectiveness of tooth whitening systems.