Intraoral images may be acquired on film or as digital images. Periapical and occlusal radiographs provide images with superior resolution and sharpness. Periapical radiographs commonly are used to evaluate the status of adjoining teeth and remaining alveolar bone in the mesiodistal dimension. They also have been used for determining vertical height, morphology, and bone quality (bone density, amount of cortical bone, and amount of trabecular bone). Although readily available and relatively inexpensive, periapical radiography has geometric and anatomic limitations. When teeth are present, images are typically made with the paralleling technique, creating an image with minimal foreshortening and elongation (Fig. 33-2). Because of variations in the morphology of the residual edentulous alveolar ridge (Fig. 33-3), the ridge may not have the same “long axis” as a tooth. The position of the image receptor may not result in an accurate display of the height of the alveolar ridge as a result of image foreshortening or elongation. Also, placing the image receptor either superior or inferior enough to capture an image of the entire maxillary or mandibular ridge can prove to be challenging. Reportedly, 25% of mandibular periapical radiographs do not demonstrate the mandibular canal. In cases in which the canal is identifiable, only 53% of measurements from the alveolar crest to the superior wall of the mandibular canal are accurate within 1 mm.

Because periapical images are unable to provide any cross-sectional information, occlusal radiographs may be used occasionally to determine the faciolingual dimensions of the mandibular alveolar ridge (Fig. 33-4). Although useful, the occlusal image records only the widest portion of the mandible, which typically is located inferior to the alveolar ridge. This image may give the clinician the impression that more bone is available in the cross-sectional (faciolingual) dimension than actually exists. The occlusal technique is not useful in imaging the maxillary arch because of anatomic limitations.

Although the resolution and sharpness of panoramic radiographs are less than those of intraoral radiographs, panoramic projections provide a broader visualization of the jaws and adjoining anatomic structures. Panoramic units are widely available, making this imaging technique useful and popular as a screening and assessment instrument for preliminary estimations of crestal alveolar bone and cortical boundaries of the mandibular canal, maxillary sinus, and nasal fossa (Fig. 33-5).

Information acquired from panoramic images must be applied judiciously because this technique has significant limitations as a definitive presurgical planning tool. Angular measurements on panoramic radiographs tend to be accurate, but linear measurements are not. Image size distortion (magnification) varies significantly between images acquired on different panoramic units and even within different areas of the same image. Vertical measurements are unreliable owing to foreshortening and elongation of the anatomic structures because the central ray of the x-ray beam is perpendicular neither to the long axis of the anatomic structures nor to the plane of the image receptor. The negative vertical angulation of the x-ray beam also causes lingually positioned objects, such as mandibular tori, to be projected superiorly on the film, resulting in an overestimation of vertical bone height. The anatomic vertical axis varies within the image, particularly in nonmidline areas. Compared with contact radiographs of dissected anatomic specimens, only 17% of panoramic measurements between the alveolar crest and superior wall of the mandibular canal were found to be accurate within 1 mm.

Similarly, dimensional accuracy in the horizontal plane of panoramic radiographs is highly dependent on the position of the structures of interest relative to the central plane of the image layer. The horizontal dimension of images of structures located facial or lingual to the central plane but still within the image layer tends to be minified or magnified, respectively. The degree of horizontal size distortion is difficult to ascertain on panoramic radiographs because the shape of the image layer is configured to a population average, and the anatomic morphology of only a few individuals conforms totally to that image layer. Horizontal image magnification with panoramic radiographs ranges from 0.70 to 2.2 times the actual size, which some manufacturers report as a 1.25 average magnification (at the central plane of the image layer). Errors in patient positioning can further exacerbate measurement error in the horizontal dimension. The deficient dimensional accuracy of the two-dimensional panoramic image is further limite/>