| Summary: | 博士 === 國立陽明大學 === 牙醫學系 === 105 === Conical implant-abutment connections have been developed and become popular due to perfect stability in implant-abutment connections. The good clinical performance of conical connections is believed to be attributable to their large clamping force transformed from the large frictional resistance in the conical interface, which helps two-piece connections function as a single piece. Because chewing processes exhibit a regular pattern of the mandible moving forward and also inward on the working side, the effect is converted to bending and torsional moments on implant systems. The shape of the cross-section of conical connections is round, and the anti-torsional ability is questionable under a torsional moment. Meanwhile, several failed clinical cases of the Ankylos implant system (Densply, Mannheim, Germany) demonstrated conical abutment fractures occurring horizontally at the implant platform level in posterior single-implant restorations. Because of the large frictional resistance in the connection, it was quite difficult to retrieve a tightened fractured abutment, resulting in implant body removal with trephine as a final solution. This is a very serious issue due to the aggressiveness of this treatment.
First, a series of in vitro tests were designed to investigate into the mechanical performance of conical connections under different cyclic loading conditions. Then, with design optimization, a finite element analysis (FEA) study was conducted to obtain a specific conical angle which leads to the best connection stability for the lowest abutment fracture possibility in the Ankylos-based conical implant-abutment connection system.
Through the biomechanical analysis, the axial force in the posterior occlusion was found to play an important role in the stability of conical connections, which not only greatly increases their anti-torsional ability, but also restores their anti-bending ability when an index design was added. Furthermore, with design optimization, this FEA study obtained the optimal conical half-angle (10.1˚) for minimizing the von Mises stress of the abutment. Compared with the original design (5.7˚), the new design demonstrated the four advantages of increasing the rigidities of abutment and implant, diminished bone stress, shortened microgap at the implant-abutment interface, and a more even distribution of stress in the connection.
This study employed a scientific methodology to solve the clinical problem of the potential disadvantages in conical connections and helped ascertain the relationships between the parameters of conical connections and occlusal pattern. This provides more information for both clinic applications and related further research.
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