A method of computing oral bone mineral density using a panoramic x-ray system. A reference phantom having a known density is provided. A digital panoramic image of a body part and the reference phantom is obtained by irradiating the body part and the reference phantom. The reference phantom is disposed in a location free from anatomical features and in the same scan line as the body part. A relationship is established 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. Bone mineral density is calculated based upon the established relationship and the known density of the reference phantom.