Effect of Model Parameters on Finite Element Analysis of Micromotions in Implant Dentistry
Micromotion between dental implant and bony socket may occur in immediate-loading scenarios. Excessive micromotion surpassing an estimated threshold of approximately 150 μm may result in fibrous encapsulation instead of osseointegration of the implant. As finite element analysis (FEA) has been applied in this field, it was the aim of this study to evaluate the effect of implant-related variables and modeling parameters on simulating micromotion phenomena. Three-dimensional FEA models representing a dental implant within a bony socket were constructed and used for evaluating micromotion (global displacement) and stress transfer (von Mises equivalent stress) at the implant-bone interface when static loads were applied. A parametric study was conducted altering implant geometry (cylinder, screw), direction of loading (axial, horizontal), healing status (immediate implant, osseointegrated implant), and contact type between implant and bone (friction free, friction, rigid). Adding threads to a cylindrically shaped implant as well as changing the contact type between implant and bone from friction free to rigid led to a reduction of implant displacement. On the other hand, reducing the elastic modulus of bone for simulating an immediate implant caused a substantial increase in displacement of the implant. Altering the direction of loading from axial to horizontal caused a change in loading patterns from uniform loading surrounding the whole implant to localized loading in the cervical area. Implant-related and bone-related factors determine the degree of micromotion of a dental implant during the healing phase, which should be considered when choosing a loading protocol.
Figure 1. Three-dimensional finite element models of dental implants: dental implants with and without threads (a); finite element (FE) model of a bony implant socket with cortical and trabecular bone (b). The area surrounding the implant is designed as an intermediate layer allowing the elastic modulus to be set independently. FE model of a single implant embedded in a bone segment consisting of cortical and trabecular bone (c). The elastic properties of the bone immediately surrounding the implant and the remaining bone can be set independently (calculations were done on a complete model; for illustration purposes, the model is cut in half). Figure 2. Reference landmarks on the implant and on the bone were used to illustrate micromovement of the components. Figure 3. Von Mises equivalent stress (a) and global displacement (b) of an osseointegrated cylindrical implant axially loaded with 200 N.
Figure 4. Von Mises equivalent stress (a) and global displacement (b) of an osseointegrated screw-shaped implant axially loaded with 200 N. Figure 5. Von Mises equivalent stress (a) and global displacement (b) of an immediate screw-shaped implant axially loaded with 200 N. Figure 6. Von Mises equivalent stress (a) and global displacement (b) of an osseointegrated screw-shaped implant axially loaded with 200 N with contact type between implant and bone modeled as force fit. Figure 7. Von Mises equivalent stress (a) and global displacement (b) of an osseointegrated screw-shaped implant axially loaded with 200 N with contact type between implant and bone model led as friction contact (friction coefficient 0.3). Figure 8. Von Mises equivalent stress (a) and global total displacement (b) of an osseointegrated screw-shaped implant horizontally loaded with 20 N. Figure 9. Von Mises equivalent stress (a) and global total displacement (b) of an osseointegrated screw-shaped implant horizontally loaded with 20 N and axially loaded with 100 N.
Overview of displacement values recorded for both the implant and bone landmark reference points and implant micromotion values calculated.
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