1. A method of computing oral bone mineral density using a panoramic x-ray system, comprising the steps of: providing a reference phantom having a known density; obtaining a digital panoramic image of a body part and the reference phantom by irradiating the body part and the reference phantom, the reference phantom being disposed in a location free from anatomical features and in a same scan line as the body part; establishing a relationship between a region of the image corresponding to a portion of the body part and a region of the image corresponding to the reference phantom; and calculating bone mineral density based upon the established relationship and the known density of the reference phantom.