Lamina dura

The name lamina dura is applied to the thin layer of dense, cortical bone which lines the root socket of the alveolar process. It is visualized as a thin opacity since it results due to a layer of dense bone.

The thin hypodensity/ radiolucency present along the tooth side denotes the periodontal ligament space and cancellous bone lies on the opposite side of the lamina dura.

The lamina dura can be demarcated around a recent extraction socket.

Coronal image showing socket with 12 and sagittal image showing socket with 38. Lamina dura is demarcated around the alveolar socket.

CBCT is considered better than IOPA/ Periapical radiographs and Panoramic radiographs for detection of lamina dura and PDL space.(1) CBCT can detect bone defects of the cancellous bone and cortical bone separately.

The CBCT volumetric data set consists of isotropic voxels. Majority of the software used for assessment allows multiplanar reformation (MPR) which can generate non-orthogonal 2D images. The MPR modes include Oblique, Curved planar reformation, which can be used to evaluate focused anatomic areas under investigation.

Thus, the differences in the shape and contour of the root/s do not affect the width and/or density of the lamina dura in images derived from multiplanar reconstruction in CBCT as there is no superimposition of anatomical structures or distortion due to insufficient thickness.

The axial, coronal and sagittal reconstructed images without superimposition, magnification and distortion can be used to detect involvement of lamina dura and PDL space in periodontal lesions. Thus lesions showing areas with furcation involvement; buccal and lingual/ palatal bone discontinuity; and intrabony defects can be detected using multiplanar reconstruction in CBCT. (2)

Similarly the complex relationship and borders between teeth and their anatomic structures such as the maxillary sinus and mandibular canal, mental canal and foramen are clearly visualized. This helps to eliminate errors caused due to superimposition in 2D radiography.

Factors to be considered or evaluated in the absence of lamina dura

Integrity of the cortical lining of lamina dura

In majority of cases, the lamina dura can be demarcated from the crestal area along the root length and into the furcation area for a normal tooth.

Previous radiographs

Evaluate earlier images to check if the lamina dura has changed.

Normal anatomic variations

Certain radiolucencies may be noted entering the lamina dura, which could be suggestive of anatomic vascular canals/ foramens.

Coronal images showing nutrient canals i.r.t socket of 43 and 33

External root resorption

In cases of external root resorption, loss of dentinal structure is noted at the affected area. However, lamina dura usually stays intact and can be demarcated

Cross sectional and axial images showing resorption i.r.t the outer aspect of the root of 21. Lamina dura can be demarcated along the resorbed root surface.

Diseases causing discontinuity or loss of lamina dura

Discontinuity in lamina dura is indicative of abnormality, usually suggestive of disease. Most common causes for the absence of lamina dura are periapical inflammatory lesions and periodontal disease.

The common causes for localized loss of lamina dura are – apical abscess, periapical granuloma, periapical cyst, periapical cementosseous dysplasia, osteomyelitis.