A dental tray with a hydrophobic tooth whitening formulation where the tooth whitening formulation is substantially non-water soluble, and a method of using this dental tray to whiten the teeth. The tooth whitening formulation is primarily comprised of a hydrophobic polymer and a peroxide or a peroxide yielding compound. Preferably the hydrophobic polymer is the condensation product of a silicone resin and an organosiloxane. The dental tray is formed to encompass the front and the rear surfaces of the teeth. The dental tray is comprised of a thermoplastic or thermoset polymer. The teeth whitening formulation is placed into the dental tray and the tray placed against the teeth to be whitened. This is for a sufficient period of time to at least partially whiten teeth. This can be a period of time from about 0.5 hour to 2 hours or more. The substantially non-aqueous tooth whitening formulation is effective over a longer period of time since it is not significantly diluted or removed from the dental tray during the treatment time.