The difference between implants and natural teeth
The implant does not have the periodontal ligament of the natural tooth, and is osseointegrated with the alveolar bone. There are proprioceptors in the periodontal ligament, but there is only "bone perception" in the implant. The tactile sensitivity of natural teeth is 8.75 times that of implants. Therefore, natural teeth tend to feel excessive bite force and produce a protective response. Periodontal ligament has the function of damping impact and dispersing bite force. Due to the lack of periodontal ligament, the mobility of the implant in the vertical direction is 3 ~ 5 μm, and the horizontal direction is 10 ~ 50 μm; while the normal teeth are 25 ~ 100 μm and 56 ~ 120 μm, respectively.
Under the action of occlusal force, the movement of natural teeth includes rapid, complex, non-linear movement in the periodontal ligament and linear elastic deformation of the alveolar bone; while the implant has only the linear elastic deformation of the alveolar bone. There are periodontal ligament fibers in different directions in the periodontal ligament, which can resist the bite force in all directions. When subjected to lateral force, the rotation center of the natural tooth is located at 1/3 of the root tip, and the stress can be dispersed in a larger range.
Except for laser etching at the implant-abutment connection, the direction of the fiber around the implant is parallel to the implant. When the implant is subjected to lateral force, the top of the alveolar ridge forms a fulcrum where the stress is concentrated, which increases the risk of bone resorption in the neck of the implant. From the morphological point of view, the implants are mostly columnar or tapered, while the anterior area of natural teeth has a single irregular shape, and the posterior teeth area has multiple. Therefore, the natural tooth has a large contact area with the alveolar bone, which has the advantages of dispersing stress and resisting rotation. In addition, the elastic modulus of natural teeth is close to that of alveolar bone. The elastic modulus of titanium or titanium-zirconium implants used clinically is 5-10 times that of alveolar bone, and the implant-bone interface is prone to appear Stress concentration.
Avoiding occlusal load is the main goal of implant restoration occlusal design. The occlusal surface design can reduce the occlusal surface area by 30%-40%, appropriately reduce the tip inclination, and provide a 1.0-1.5mm flat median fossa. In addition, appropriate crown-to-plant ratio, crown height spacing and cantilever length should also be designed. When the patient's bone density is low, progressive weight-bearing can be used or the surface of the implant can be roughened.
It is recommended that patients with molars wear occlusal pads, follow up in time, and adjust their occlusion. Patients with periodontitis should undergo implant restoration after the periodontitis is controlled. According to the number of missing teeth, the position and area of the teeth, the appropriate occlusal type is selected, and the occlusal plan of implant denture restoration is designed. The occlusal design of implant dentures still needs further research to obtain sufficient evidence-based medical evidence.
Post time: Jul-14-2021