Three-dimensional Finite Element Stress Analysis Of The Bar-clip Attached And Implant-supported Overdentures In Edentulous Maxilla

With the development of implantology and prosthodontics, bar-clip attached and implant-supported overdentures become a more desirable method for the treatment of the maxillary edentulous. It is more difficult for implant prosthesis in maxllary edentulous compared with the mandibular edentulous because of bone deficient, osteoporosis and many other factors. Many scholars thought that the biomechanics was the crucial factor for long-term success of implants. If the implanted position in bone, the number of implants and the length of cantilever are unreasonable designed, the stress will not well-distributed. All these factors will result in the absorption of alveolar bone around the implants, loosening, fracture, or failure of the implant prosthesis. As a matured method, three-dimensional finite element analysis was widely used in oral biomechanical research field. The main purpose of this study is to research thestress effect on the bar-clip attached and implant-supported overdentures in edentulous maxilla with three-dimensional finite element method, in view of the position of implants in bone, the number of implants and the length of cantilever design.This study established three-dimensional finite element models of edentulous maxilla with technical sofeware. According to the experimental design, changes the number and the distribution of implants and the length of the cantilever. We applied vertical and 30°lateral loads under the condition of localized load and dispersed load to analysis the stress in implant and the bone around it.The results showed that the stress distributed in the cervical region of implants, facial side, lingual side and the bone interface closed to the bottom of buccal side. The stress concentrated in the cervical region of implants and the bone interface closed to the bottom of facial side. The implants and the metal bars of the bar-clip attached and implant-supported overdentures in edentulous maxilla are linked together, so loading in one side would make a displacement of the ensemble. Therefore, the implants should have a good retention and stability to ensure the stability of the restoration.The results indicated that the stress was evidently increased in both 4 implants groups and 6 implants groups when the implants distributed unevenly. The mental bars of the bar-clip attached and implant-supported overdentures played a role similar to periodontal splints. The bars connected with the implants as an ensemble, reduced the risk of excessive concentrated stress for a single implant. When the implants distributed evenly in the bone, the length of the corresponding mental bars was nearly equivalent, the stress was well-distributed. These were conducive to enhance the stability of the restoration. On the contrary, when the implants distributed unevenly in the bone, the length of the corresponding mental bars was different. There was significant difference between the stress values of two tips of the implant, which made the implants missing balance, loosening and fractured.When 4 and 6 implants distributed evenly in the bone, the stress of 4 implants groups noticeable greater than that of 6 implants groups at same location of the bone interface. There was more osseointergration area when increased the number of implants. Increasing the number of implant can strengthen the stability of therestoration, especially for osteoporotic maxillary posterior region.The results indicated that there was a great influence on the stress by changing the length of the cantilever. The stress of bone interface gradually increased with the increasing of the length of the cantilever. And the stress became greater in the implant which more closer to the cantilever.The conclusions derived from this 3-D finite element stress study are limited to the assumptions made for the composition of the computer model and its boundary conditions. Within the limits of this study, increasing the number of implant, distributing the implants evenly and shortening the length of the cantilever are very important factors to reduce the stress of the bone interface, and also important for the success of implant-supported overdentures in edentulous maxilla.