关键词: 前磨牙, 牙周膜面积估算, 附着丧失

Abstract: Objective　Through detecting the changes of the periodontal ligament area during the different attachment levels in premolar teeth，we aim to explore a method of estimating the residual periodontal area of the premolar according to the degree of attachment loss. Methods　Totally 108 premolar tooth were extracted by orthodontic extraction from January 2018 to January 2019 in Shiyan People′s Hospital. On the four axial plane of roots，film material was coated to simulate the periodontal ligament. The lines with different attachment levels were recorded on the surface of the film forming material parallel to the enamel cementum boundary. After the stripped material was scanned，the data of periodontal ligament area were simulated by Photoshop CS2 9.0 and Scion Image 4.0.3. Results　When the level of horizontal attachment level was lost to 6mm，the total area of the periodontal ligament was less than 50%. When the vertical attachment loss level is limited in the buccal or lingual surface，there was at least about 80.9% periodontal ligament area remained，and when the vertical attachment loss level was limited to the mesial and distal surfaces，the remaining periodontal ligament area was at least about 63.8%. When single axis with large percentage of periodontal ligament area vertical attachment was completely lost，and the other axes attachment loss was 2 mm，there was at least about 51.1% periodontal ligament area remained. Conclusion 　While the vertical attachment level of a single axial plane is completely lost，there was still possibility for preservation of premolars，but if the horizontal attachment level is lost to 6 mm or when the vertical attachment of near/far-middle planes is completely lost，and the attachment loss of other axes are more than 2 mm，it will not provide enough periodontal support.

Key words: anterior molar, estimation of the periodontal ligament area, attachment loss