Abstract: BACKGROUND: The implant fixed complete denture for mandibular edentulous jaws has become one of the main clinical restoration methods. Mechanical studies on different implant designs can help clinical selection of implant designs in line with biomechanical principles, which is beneficial to maintain the long-term stability of implant dentures.
OBJECTIVE: To establish the models for the distribution of different implant sites with the same cantilever length, and to analyze the influence of implant sites, the symmetry of implant distribution and the number of implants on the stress distribution around the abutment, implant, and bone tissue.
METHODS: Cone beam CT data of an edentulous mandible were selected. The cone beam CT data, implant, abutment, and crown restoration data were used to create finite element model of different transplantation sites and regions, and different number of implants. The premolars and molars regions were bilaterally subjected to a vertical load of 150 N. The software was used to calculate the stress of the abutment, implant, and bone tissue, and then statistical analysis was performed.
RESULTS AND CONCLUSION: (1) When the frontmost implant was closer to the front, the stress on the abutment, implant and bone tissue would gradually decrease. For four implants, when the number of implants located at and before the lateral incisor was 2, the bone tissue stress value was the smallest, and there was a statistical difference in the stress value with 1 and 0 implants (P < 0.05). For five implants, when the frontmost implant site was located at and before the lateral incisor, there was a statistical difference in the stress value with the canine and later (P < 0.05). Therefore, when the length of the cantilever was fixed (10 mm in the experiment), the foremost implant of 4 or 5 implants should be placed in the lateral incisor and the front site. When there were four implants, the number 2 of implants before the lateral incisor was a better choice (2) When the cantilever length and anterior-posterior spread (the distance between the frontmost implant and the two farthest implants) remained unchanged. The symmetry of the model had no statistical difference in the stress distribution around the abutment, implant and bone tissue (P > 0.05). Therefore, the implants were not arranged in accordance with the principle of symmetry when the cantilever length and anterior-posterior spread remained unchanged. (3) When the number of implants was four, the stress around abutment and implant was significantly larger, and the difference in stress was statistically significant with five and six implants (P < 0.05). Therefore, five or more implants are better for the implant fixed complete denture.

Key words: material, oral cavity, implant denture, mandibular edentulous jaws, the implant fixed complete denture, finite element analysis, stress, implant number, implant site, cantilever length