Intraoral Anatomy (Lamina Dura, Alveolar Crest, Cancellous bone)

• Lamina Dura

  • What is it

    A radiograph of sound teeth in a normal dental arch demonstrates

    that the tooth sockets are bounded by a thin radiopaque layer of

    dense bone (Fig. 8-6). Its name, lamina dura (“hard layer”), is

    derived from its radiographic appearance. This layer is continuous

    with the shadow of the cortical bone at the alveolar crest. It is only

    slightly thicker and no more highly mineralized than the trabecu

    lae of cancellous bone in the area. Its radiographic appearance is

    caused by the fact that the x-ray beam passes tangentially through

    many times the thickness of the thin bony wall, which results in

    its observed attenuation (the eggshell effect). Developmentally, the

    lamina dura is an extension of the lining of the bony crypt that

    surrounds each tooth during development.

  • Normal

    

    

  • Bone

    

    

• ALVEOLAR CREST

  • What is it

    The gingival margin of the alveolar process that extends between the teeth is apparent on radiographs as a radiopaque line—the alveolar crest (Fig. 8-8).

  • Normal

    The level of this bony crest is considered normal when it is not more than 1.5 mm from the cementoenamel junction of the adjacent teeth. The alveolar crest may recede

    

    The length of the normal alveolar crest in a particular region depends on the distance between the teeth in question.

    • anterior region,

      the crest is reduced to only a point of bone, between the close-set incisors.

    • Posteriorly,

      it is flat, aligned parallel with and slightly below a line connecting the cementoenamel junctions of the adjacent teeth. The crest of the bone is continuous with the lamina dura and forms a sharp angle with it.

• PERIODONTAL LIGAMENT SPACE

  • What is it

    Because the PDL is composed primarily of collagen, it appears as a radiolucent space between the tooth root and the lamina dura.

    This space begins at the alveolar crest, extends around the portions of the tooth roots within the alveolus, and returns to the alveolar rest on the opposite side of the tooth (Fig. 8-9).

    

  • Width

    The PDL varies in width from patient to patient, from tooth to tooth in the individual, and even from location to location around one tooth (Fig. 8-10). It is usually thinner in the middle of the root and slightly wider near the alveolar crest and root apex, suggesting that the fulcrum of physiologic movement is in the region where the PDL is thinnest.

    

• CANCELLOUS BONE

  • What is it

    The cancellous bone (also called trabecular bone or spongiosa) lies between the cortical plates in both jaws. It is composed of thin radiopaque plates and rods (trabeculae) surrounding many small radiolucent pockets of marrow.