According to the Long Island Business Journal, Wanda and Myrna Ortiz, from Westbury, NY, have received a patent (No. 7,997,898) for an illuminated orthodontic retainer that would allow patients to project images onto their tongues.
The abstract of the patent published by the US Patent and Trademark Office states, "A standard orthodontic retainer is modified on its surface opposite the palate and facing the patient’s tongue with a light, a small battery to provide power for the light means, and a frame beneath the light that allows a template to be removably slid into the frame. The template consists of a design such as a heart, a letter of the alphabet, a symbol, or other design that, when the light is activated, shines the pattern onto the top of the tongue of the user. The template can be made so that the design displayed on the user’s tongue is of any desired color or color combination. Alternatively, the color of the displayed design may be created by the color of the light or by an additional template consisting of an optical filter providing the desired color."
The full text of the patent can be found here.