A teeth whitening appliance (10) such as a tray includes a seal member (18) which is attached to an interior surface (19) of the tray. The seal member comprises a fabric strip or a gecko adhesive strip which extends around the periphery of the interior surface of the tray adjacent the peripheral or boundary edge thereof. The seal member adheres to the teeth, so as to prevent gel from escaping from the tray when the tray is in place, as well as preventing water/saliva in the mouth from entering the tray, while also being convenient to remove.