English: This section from a panoramic X-ray film depicts the teeth of the lower left quadrant, exhibiting generalized severe bone loss of 30–80%. The red line depicts the existing bone level, whereas the yellow line depicts where the gingiva was originally (1–2 mm above the bone), prior to the patient developing periodontal disease. The pink arrow, on the right, points to a furcation involvement, or the loss of enough bone to reveal the location at which the individual roots of a molar begin to branch from the single root trunk; this is a sign of advanced periodontal disease. The blue arrow, in the middle, shows up to 80% bone loss on tooth #21, and clinically, this tooth exhibited gross mobility. Finally, the peach oval, to the left, highlights the aggressive nature with which periodontal disease generally affects mandibular incisors. Because their roots are generally situated very close to each other, with minimal interproximal bone, and because of their location in the mouth, where plaque and calculus accumulation is greatest because of the pooling of saliva, mandibular anteriors suffer excessively. The split in the red line depicts varying densities of bone that contribute to a vague region of definitive bone height.