Abstract: PURPOSE: To explore the percentage of residual support height (Ph) and the percentage of residual root surface area (Ps) in evaluating periodontal support ability by simulating different stages of periodontitis based on the curved surface modeling. METHODS: Fifteen cone-beam CT (CBCT) images including 420 teeth in total were collected. The data were reconstructed into 3-dimensional teeth models by Mimics software.The 3D surface model of the tooth was then optimized by Geomagic software and then imported into Solidworks software to simulate different periodontal support height. Ph and Ps were measured and calculated to evaluate the consistency of Ph and Ps results in all tooth types. The data were analyzed with SPSS 22.0 software package. RESULTS: RSA in incisors, canines and premolars: coronal 1/3>middle 1/3>apical 1/3. RSA in molars: middle 1/3>coronal 1/3>apical 1/3. Maxillary first molar had the largest RSA, accounting for 11.60% of the dentition, which was about 3.18 times than mandibular central incisor. The difference between Ph and Ps in all types of teeth was statistically significant (P< 0.01). The 95% confidence interval(CI) of the difference between Ph and Ps in the maxillary incisor, mandibular incisor, mandibular canine was between the clinical consistency limit (-15%, 15%). In the remaining tooth types, 95%CI of the difference between Ph and Ps was beyond the clinical consistency limit (-15%, 15%). CONCLUSIONS: For single-root tooth, except maxillary canine, the remaining periodontal support height could replace periodontal support area. For multi-rooted tooth, judging the ability of periodontal support ability only by alveolar bone absorption ratio in 2D index has significant limitations. Full consideration is needed to focus on root morphological discrepancy when determining the extent of periodontal disease.

Key words: Root surface area, Curve surface modeling, Cone-beam CT