The invention relates to a device for viewing the inside of a mouth of a patient (13). The viewing device includes a penetrating ray emitter (2) capable of viewing an inner portion (14, 22, 23, 27, 28, 31, 32, 33, 34, 35, 36, 37, 50, 51, 62, 63) located under an outer surface of a member placed in the mouth. According to the invention, the device includes a pair of augmented reality glasses (1) having an optical lens through which a user (6) of the pair of glasses (1) can see the inside of the mouth and a viewing camera capable of recording an image of what the user (6) sees through the optical lens. A central unit is suitable for correlating first images, corresponding to those recorded by the viewing camera, with second images, corresponding to those recorded by the penetrating ray emitter (2).