Abstract: Objective: To study the morphological changes of molar and premolar teeth with root canal treatment as well as its effect on periodontal tissues. Methods: Thirty cases with healthy periodontal tissues and thirty cases with chronic periodontitis were selected. After root canal treatment, 15 cases were randomly selected for inlay or crown restoration. Extra oral scanner was used to scan the plaster models and Geomagic Qualify12.0 was employed to perform the best fitting alignment and 3D comparison of the data before and after the restoration. Elastase and prostaglandin E2 in gingival crevicular fluid before and after treatment were analyzed by ELASA. Results: The morphological changes of the teeth with crown restoration in the proximal-occlusal surface , the proximal-gingival end in the buccal sides as well as the proximal-gingival end 1/2 in the lingual side were greater than that of inlay restoration. For the teeth of chronic periodontitis which received initial periodontal treatment, the levels of prostaglandin E2 and elastase in the gingival crevicular fluids were all significantly reduced and they were statistically significant after one year's restoration. Conclusion: The quantities in morphological changes for the original shape of the teeth in the buccal-lingual side due to crown restoration are greater than that of inlay restoration, but there is no significant effect on the periodontal tissues.

Key words: Morphology of tooth, Inlay restoration, Tooth defect, Initial periodontal treatment Imaging, Three-dimensional