**2. Normal interdental bone**

Evaluation of bone changes in periodontal disease is based mainly on the appearance of the interdental bone because the relatively dense root structure obscures the facial and lingual bony plates. The bone which is present interdentally normally is seen as a radiopaque line beside the periodontal ligament (PDL) and at the bone margin, called as the lamina dura. Because this thin line represents the cortical bone which lining the socket, and change in the angulation of the beam produce changes in its appearance [13, 14].

Crest of the interdental bone normally vary according to the convexity of the proximal tooth surfaces and the level of the cementoenamel junction (CEJ) of the approximating teeth. The faciolingual diameter of the bone is related to the width of the proximal root surface. The angulation of the crest of the interdental septum is generally parallel to a line between the CEJs of the approximating teeth. When there is a difference in the level of the CEJs, the crest of the interdental bone appears angulated rather than horizontal [15] (**Figure 1**).

#### **Figure 1.**

*Crest of interdental bone normally parallel to a line drawn between the cementoenamel junction of adjacent teeth (arrow). Note also the radiopaque lamina dura around the roots and interdental bone.*
