**4.1 Bone loss**

The radiographic image tends to underestimate the severity of bone loss. The difference between the alveolar crest height and the radiographic appearance ranges from 0 to 1.6 mm, mostly accounted for by X-ray angulation [21].

#### *4.1.1 Amount*

Radiographs are an indirect method for determining the amount of bone loss in periodontal disease; they image the amount of remaining bone rather than the amount lost. The amount of bone lost is estimated to be the difference between the physiologic bone level and the height of the remaining bone. The distance from the CEJ to the alveolar crest has been analyzed by several investigators. Most studies, conducted in adolescents, suggest a distance of 2 mm to reflect normal periodontium; this distance may be greater in older patients [22].

#### *4.1.2 Distribution*

The distribution of bone loss is an important diagnostic sign. It points to the location of destructive local factors in different areas of the mouth and in relation to different surfaces of the same tooth [23].
