| Given the high success rate of implant denture in clinical application, early and late failure is still unavoidable in some cases. The main causes can be attributed to excessive loading or infection resulted from concentration of stress. The implant system should be selected and designed to have good biomechanical properties, so as to ensure the long-term success rate of implant restorations. The stress distribution is subject to a number of factors, such as the implant shape and length, the implant/abutment connection types, the design of superstructure and the selection of materials. Among them, the selection of implant system should be taken into primary consideration, and is also relatively easy to be controlled clinically.At present, there are many implant systems on both domestic and overseas markets, and the greatest difference between them lies in the implant - abutment connection structures. It is of great significance to a higher clinical success rate of implant denture to analyze the stress distribution of different implant-abutment connection structures commonly used clinically in the bone tissues around the implant and to reveal the mechanical effect of different connection designs on the implant and the surrounding bone tissues, so as to find the optimum structure for abutment and implant connection forms. In the available literature, researches on the biomechanical transfer characteristics of implant denture structure are mostly of comparison and analysis of discrete or individual factors, and these results cannot provide full guide in the clinical selection.Experiment 1: Digital modeling for implant-abutment structures based on reverse engineeringDigital modeling for physical implants is an important basis for the FEM analysis of the implant systems. In this chapter, the point cloud data of the implants is obtained by an integrated method, which combines. the optical measurement of implant profile data by 3D optical grating projection with the plane-image measurement of characteristic details. Digital modeling for the seven typical physical implant systems is accomplished by using the method of data processing, region analysis, feature fitting and shape modeling based on the point cloud data.Experiment 2: FE stress analysis of implant-abutment connection typesThe ABAQUS was used to perform FE analysis of the models of the implant-abutment connection structures of the seven internationally known implant systems. Identical experiment conditions were applied for the implant-abutment models of different connections, to obtain the stress distribution at the implant-abutment interfaces of the seven models under five vertical loads, five horizontal loads and five cyclic loads. The following conclusions have been obtained:1. In the implant system with Morse taper connection, the stress is concentrated at the implant-abutment structure, but the stress on the abutment screw is very small.2. The stress level of the implant-abutment in the implant system with Morse taper platform transfer is higher than that of the implant system with dual-hexagon 12-side platform transfer.3. The fixation screw in an outer hexagon connection is subject to concentrated stress and is therefore likely to break. The stress level of mixed inner hexagon inner cone fixation screw is lower than that of the inner octagon, inner trivalve and inner hexagon types.4. Stress is concentrated at the implant recess and three cams of the abutment in the inner trivalve connection.5. Under the action of horizontal load, the stress in components of implant-abutment connection increases substantially, therefore the horizontal load to an implanted denture should be minimized. Experiment 3: FE stress analysis of implant-abutment assemblies in the alveolar bone Implant-bone models were established for seven different structures, and five vertical loads, five horizontal loads and five cyclic loads were applied in incremental magnitude. The ABAQUS software was used for FE analysis, to obtain the stress distribution of implant-abutment assemblies of seven different connections in the jaw bone. The following conclusions have been obtained after comparison and analysis:1. The non-axial loads produce significant effect on the stress distribution in the one tissues around the implant.2. The Anklos and 3i implant systems can reduce the stress concentration in the bone tissues around the implant, favoring the conservation of supporting bone around the implant and extending the service life of the implant.3. The Bego mixed inner hexagon and inner cone structure is superior to outer hexagon, inner trivalve, inner hexagon and inner octagon structures.Experiment 4: Digital design and experiment analysis for personalized abutment.The digital design technology was applied to measure and obtain the curing digital model of a patient. The implant was positioned based on the feature matching technique. The personalized design of the abutment neck edge, angle and shoulder of the patient are implemented by extracting the morphological characteristics of the corresponding adjacent teeth and gingiva. Finally, the CAD design process is completed for the personalized abutment of a patient.Experiment 5:Finite element study of Computer-milled abutment and custom abutment Finite element method was used to compare of difference in computer-milled abtment and custom abutment with 20°angle. The result showed that computer-milled abutment stress uniformly distributed and that can better resist the lateral force and the horizontal loadIn summary, with this research, analysis and comparison was performed for seven typical implant systems in common use internationally under 15 loading conditions, on the basis of reverse engineering and precise modeling and using the powerful ABAQUS FE analysis software, to reveal the mechanical effect of different connection forms on the implant and its surrounding bone tissues and evaluate the advantages and disadvantages of different structures, so as to provide reference for selection by users. In the meantime, a personalized abutment for the China-made implant system has been developed and designed by our own, to enable improving the stability of the China-made implant-abutment connection and realize personalized aesthetic repair of implant denture. |
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