In Vitro Simulation of Tooth Mobility Resulting from Periodontal Attachment Loss

In our previous studies, we developed the normal periodontal ligament index (nPLI) and the resi-dual periodontal ligament index (rPLI), to estimate residual periodontal ligament support for in-dividual teeth during treatment planning for partially edentulous patients. The purpose of the current in vitro study was to analyze tooth mobility resulting from periodontal attachment loss, and to determine the application range of both nPLI and rPLI. The association of horizontal load-displacement and conditions of attachment loss was measured in triplicate for each anatomical tooth model at 10-minute intervals, using a universal tester at a crosshead speed of 0.05 mm/min, and a load of 0.1 N. The conditions of attachment loss were: (I) 0 mm (cementoenamel junction), (II) 2 mm attachment level, and (III) two-thirds, and (IV) one-half lengths of normal attachment. Except for the upper first molar, lower lateral incisor, lower first premolar, and the lower first molar, the displacement of each tooth type was increased significantly relative to Level I (P < 0.01 or 0.05). Moreover, except for the upper first molar, the displacement of each tooth type at Level IV was significantly increased compared to Level III (P < 0.01). The results indicated that nPLI at two-thirds of normal attachment and greater, and rPLI at less than two-thirds of normal attach