Figure 3. Active root resorption lacunae of normal periodontium (A,B) and hypofunctional periodontium (C,D) groups stained with tartrate-resistant acid phosphatase (A,C) and hematoxylin and eosin (B,D). The newly formed resorption lacunae were identified by the presence of TRAP-positive multinucleated cells, the odontoclasts. Root resorption had occurred on the disto-apical third of the distal root facing the alveolar bone in the compression zone. In the hypofunctional periodontium group, the roots were resorbed extensively into dentin after 15 days of orthodontic movement. The black line indicates the resorption lacunar length. PDL, periodontal ligament; B, alveolar bone; T, Tooth; Bar = 250 µm.