An intra-oral device for positioning oral tissues during medical treatment, for example, radiation treatment. The device includes upper and lower dental arch members configured to engage the maxillary and mandibular teeth or edentulous arch(es) of a patient, respectively. The upper and lower dental arch members are operatively coupled to provide a dental arch assembly. A protective element to displace or depress a patients tongue is secured at a suitable working position with respect to the dental arch assembly. In an embodiment, provision is made for three-dimensional spatial adjustment of the protective element to a desired location, at least during initial fitting and assembly. The device is then secured to allow consistent repetition of the oral tissue positioning from treatment to treatment. The protective element may be configured to engage the tongue of a patient so that the tongue may be selectively positioned for treatment and/or diagnostic procedures.
