An oral treatment device that emits light onto a user's teeth. The oral treatment device includes an intraoral mouthpiece comprising: a lamp comprising: a flexible sheet body having a front surface and a rear surface; and a plurality of light emitting diodes embedded within the flexible sheet body that generate light which is emitted from the rear surface of the flexible sheet body. The flexible sheet body comprises: a flexible lens plate formed of a biocompatible material. The plurality of light emitting diodes are printed to the front surface of the flexible lens plate, the rear surface of the flexible lens plate forming the rear surface of the flexible sheet body. The rear surface of the flexible sheet body of the lamp having a concave curvature and being exposed so as to form a light emitting surface of the mouthpiece.