Polymeric shells which fit over one or more natural teeth to change the perceived color of the teeth, and optionally to provide orthodontic support. The shells can be prepared by thermoforming selected polymeric sheets which contain optical additives over a physical image of the teeth, or by depositing polymeric compositions containing optical additives over a physical image of the teeth, or by additive manufacturing based upon a digital image of the teeth. The optical additives cause the combination of the shell and the teeth to have a desired appearance. At least part of the shell preferably has transparency greater than 75%, particularly greater than 85%.