Normal Radiographic Appearance of the Supporting Structures of the Teeth
The maxilla and mandible are composed of cancellous or trabecular bone located between the dense cortical outer plates. The cancellous bone consists of trabeculae, thin bony rods, and plates, surrounded by areas of bone marrow, presenting a mixed radiopaque and radiolucent radiographic appearance.2 The bone pattern varies among individuals as well as in the different regions of the dental arches.3 The maxilla, especially in the anterior region, has numerous thin trabeculae with many small marrow spaces, displaying a fine granular appearance radiographically.2 The posterior maxilla demonstrates a similar pattern with larger marrow spaces (Figures 3‑4).2 In comparison, the anterior mandible shows thicker trabeculae with a coarser horizontal pattern with fewer plates and larger marrow spaces than the maxilla.2 The posterior regions of the mandible exhibit a pattern similar to the anterior region, but the trabeculae and marrow spaces tend to be larger and sparser (Figures 5‑6).2 A ladder-like effect may be visualized due to the large size of the posterior marrow spaces. Apical to the molar teeth, the trabeculae may be very sparse or appear to be absent, resulting in a very radiolucent radiographic appearance which may be misinterpreted as pathologic.2
Figure 3. Maxillary posterior cancellous bone.
Figure 4. Periapical radiograph of maxillary posterior bone pattern.
Figure 5. Mandibular posterior cancellous bone.
Figure 6. Periapical radiograph of mandibular posterior bone pattern.
Alveolar Bone and Alveolar Crest
The alveolar bone is the teeth-bearing bony process of the jaws. The alveolar crest is the gingival margin of the alveolar process and extends between and around the tooth root(s).4,5 The crest is covered by a thin layer of cortical bone, appearing radiopaque radiographically (Figure 7).3,4 The crestal alveolar bone level ranges from 0.5 to 2.0 millimeters from the CEJ, in health, and follows the plane of adjacent CEJs.4 The shape of the crestal bone varies from narrow and pointed between the anterior teeth and flat and angular between the posterior teeth.3 The crestal shape is dictated by the space or distance between the teeth.2
Figure 7. Bitewing radiograph of posterior alveolar bone crests.
Lamina Dura and Periodontal Ligament Space
Surrounding the tooth root(s) is a layer of dense bone which lines the tooth socket called the lamina dura (LD) (Figure 8).2 This radiopaque structure is contiguous with the alveolar crests.3 The thickness and degree of radiopacity of the lamina dura varies with occlusal function.2 It is thicker and more radiopaque with heavy function and thinner and less radiopaque with loss of function.2 Immediately adjacent to the lamina dura is the periodontal ligament space (PDLS) which contains flexible collagen fibers surrounding and cushioning the tooth root in its bony socket.1 It is a radiolucent structure that begins at the alveolar crest, surrounds the root, and returns back to the crest on the other side of the tooth (Figure 8).2 The periodontal ligament varies in width, demonstrating differences among patients and the dentition itself2 In normal function, the periodontal ligament space appears thinner mid-root and wider at the crest and root apex.2-4
Figure 8. Periapical radiograph of showing the LD and PDLS.