Abstract: BACKGROUND: Clinical trials have shown that the diameter and shape of implants affect the implant effect, but effect of the length of implants on different implant types is still controversial.
OBJECTIVE: From the perspective of healing process simulation, finite element technique was used to analyze the mechanical differences of different implants after implantation. 
METHODS: CAD software was used to establish three kinds of implants (conventional implants, short implants and ultrashort implants) and bone meal geometric models. The loss of maxillary 16 teeth (first molar) was simulated to establish the maxillary sinus internal lift model. The finite element model was established after dividing the mesh and imposing boundary conditions. Loading was selected in the adjacent teeth from 3 to 5 months postoperatively, and loading in the implant from 6 to 9 months. Biomechanical analysis of the implant and its surrounding soft and hard tissues was performed after solving for the optimal implant to find the best implant. 
RESULTS AND CONCLUSION: (1) The maximum displacements were concentrated in the cervical part of the implant, and the displacements of the three kinds of implants were less than 100 μm during vertical loading. The displacement change of conventional implants during the whole healing cycle was the minimum. When adjacent teeth were loaded, the maximum displacements of short and ultrashort implants were similar, and the difference between the displacements of them increased when implants were loaded. (2) During lingual loading, the displacements of the three kinds of implants were more than 100 μm. The maximum displacement occurred on the lingual side. When the adjacent teeth were loaded, the displacement of the conventional implant was the maximum; when the implant was loaded, the displacement of the ultrashort implant far exceeded that of the conventional and short implants. (3) During lingual and distal mid loading, the maximum displacements were concentrated in the cervical part of the three kinds of implants. The displacements of the implants were all larger than those during vertical and lingual loading. When adjacent teeth were loaded, the displacement of conventional implants was greater than that of short and ultrashort implants. When the implants were loaded, the displacement differences among the three kinds of implants were significantly reduced, and the maximum displacements appeared in the implant neck. (4) The stresses on the alveolar bone in the ultrashort implant group were 81.62 MPa and 73.35 MPa for lingual and distal mid loading, respectively. The stresses on the alveolar bone in the rest of the models were less than 53 MPa. (5) Results concluded that conventional implants should be preferred for implant restorations, followed by short implants and finally ultrashort implants. Inclined loading is more likely to cause implant failure than vertical loading.

Key words: dental implant, finite element, implant, internal lifting, biomechanics, bone meal