Abstract: BACKGROUND: In oral implant repair, soft tissue level implants are different from bone level implants, which adopt non-embedded surgical methods. A good neck design can promote bone bonding or reduce marginal bone absorption and facilitate the formation of stable soft tissue sealing. Therefore, the neck structure design of implants is one of the key factors for the success of implant repair.
OBJECTIVE: To simulate and analyze the stress distribution of implant components and implant-bone interface during the restoration of mandibular molars with four different smooth collar implants using three-dimensional modeling and finite element analysis software. 
METHODS: The cone-beam CT image data of a patient undergoing mandibular first molar implantation were selected, and the mandible model was established by Mimics 21.0 software. The mandible model was imported into Solidworks 2018 software. Smooth neck implant models were constructed as follows: the standard conventional cervical implant (2.8 mm in height, 4.8 mm in diameter), standard wide cervical implant (2.8 mm in height, 6.5 mm in diameter), aesthetic conventional neck implant (1.8 mm in height, 4.8 mm in diameter), and aesthetic wide neck implant (1.8 mm in height, 6.5 mm in diameter). The four models were repaired with pure titanium base table and zirconia full-crown screw fixation. The von-Mises stress distribution of implant components and the implant-bone interface in four groups of different smooth collar implants were compared and analyzed under vertical and oblique loadings. 
RESULTS AND CONCLUSION: (1) Whether it was vertical loading or oblique loading, the peak values of von-Mises stress were located in the neck region of the implant, and the peak values of von-Mises stress at the implant-bone interface were located in the cortical bone region of the neck region of the implant. (2) When using the same smooth collar implant, compared with the vertical loading group, the peak values of Von-Mises stress were greater in the four different smooth collar implants in the oblique loading group. (3) Under vertical or oblique loading, the maximum von-Mises stress of the standard implant group was greater than that of the standard implant group, and the maximum von-Mises stress of the aesthetic implant group was lower than that of the aesthetic implant group. (4) The maximum von-Mises stress on the implant-bone interface in the wide-neck standard implant group was lower than that in the other smooth cervical implant groups, regardless of vertical or oblique loading. (5) The results showed that the stress distribution of implant components and implant-bone interface was different with different smooth collar implants.

Key words: smooth collar, stress, finite element analysis, implant prosthesis, bone level of implant edge, loading mode, bite