Abstract
In our previous studies, we developed the normal periodontal ligament index (nPLI) and the residual periodontal ligament index (rPLI), to estimate residual periodontal ligament support for individual 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 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 attachment should be applied, respectively.
Highlights
The occlusal-supporting abilities (OSAs) of remaining teeth are closely related to their physiologic and pathologic periodontal tissue support, and directly affect prosthodontic treatment planning
We developed an index for estimating residual periodontal ligament support and the corresponding occlusal support according to tooth type, by applying these formulae [5]
Since it is difficult to conduct this research in patients with periodontal attachment loss, we performed an in vitro simulation of tooth mobility resulting from periodontal attachment loss. The purpose of this in vitro study was to analyze tooth mobility resulting from periodontal attachment loss, based on our previous studies [5]-[7], and to determine the application range of both normal periodontal ligament index (nPLI) and residual periodontal ligament index (rPLI)
Summary
The occlusal-supporting abilities (OSAs) of remaining teeth are closely related to their physiologic and pathologic periodontal tissue support, and directly affect prosthodontic treatment planning. When designing fixed and removable partial dentures, assessment of the OSA of the remaining teeth is usually based on the assumption that these teeth have normal, optimal periodontal ligament support [3]. Yamamoto et al [4] demonstrated that the formulae derived for estimating the residual root surface area attached to the periodontal ligament for each tooth type can be used to assess tooth prognosis, along with other factors such as mobility, oral hygiene, degree of inflammation, and occlusion. To illustrate the applicability of nPLI and rPLI, an OSA score calculated using these indices for the remaining teeth, and corresponding to Eichner’s subclasses of partial edentulism, was charted by numerically assessing the average occlusal support [7]. The resulting OSA score, based on nPLI and rPLI, was proposed as a suitable tool for epidemiologic research on the progression of tooth loss and the survival rate of prostheses
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