Numerical simulation on the biomechanical interactions of tooth/implant-supported system under various occlusal forces with rigid/non-rigid connections

The aim of this study was to analyze the biomechanics in an implant/tooth-supported system under different occlusal forces with rigid/non-rigid connectors by adopting a 3D non-linear finite element (FE) approach. A 3D FE model containing one Frialit-2 implant splinted to the mandibular second premolar was constructed. Contact elements (frictional surface) were used to simulate the realistic interface condition within the implant system and the sliding keyway stress-breaker function. The stress distributions in the splinting system and dissimilar mobility between natural tooth and implant with rigid and non-rigid connectors were observed for six loading types. The simulated results indicated that the lateral occlusal forces significantly increased the implant (σ_{I, max}), alveolar bone (σ_{AB, max}) and prosthesis (σ_{P, max}) stress values when compared with the axial occlusal forces. The σ _{I, max} and σ_{AB, max} values did not exhibit significant differences regardless of the connector type used. However, the σ_{P, max} values with a non-rigid connection increased more than two times those of the rigid connection. The σ_{I, max}, σ_{AB, max} and σ_{P, max} stress values were significantly reduced in centric or lateral contact situations once the occlusal forces on the pontic were decreased. Moreover, the vertical-tooth-to-implant displacement ratios with a non-rigid connection were 23 and 9.9 times that for axial and lateral loads, respectively, applied on the premolar. However, the compensated non-rigid connector capabilities were not significant when occlusal forces acted on the complete prosthesis. The non-rigid connector (keyway device) only significantly exploited its function when the occlusal forces acted on a natural tooth. Minimizing the occlusal loading force on the pontic area through occlusal adjustment procedures to redistribute stress in the maximum intercuspation or lateral working position for an implant/tooth-supported prosthesis is recommended.