Analysis of a dental implant using finite element method.

Vlasceanu, Daniel ; Petrescu, Ioana ; Comaneanu, Raluca Monica 等

1. INTRODUCTION

There are known prosthetic methods by which the fixing work is done by cementing on various types of blunts or mixed-blunts and natural teeth, using different materials.

The disadvantage of these methods is that the prosthetic work is fixed on prosthetic blunts only by cementing and can only be removed by cutting and the emergence of bimetallism and corrosion. (Bratu & Nussbaum, 2001)

There are also known the dental implants that are made of a metallic body of pure titanium, at the top having a conical portion where is linked with the prosthetic blunt.

The disadvantages of these implants are that at the linking of the prosthetic blunt with the implant, in the conical portion, there is the risk of infiltration of secretions and microbial germs, which has a good culture medium and can later affect, for starters the gum layers and then damage the cortical bone and the spongy bone with a compromised implant integration and failure of the total. (Patrascu et al., 2008)

The problem that is solved lies in that the implant made of pure titanium in two surgical stages and integrated into the tissue prevents such infiltrations of secretions and microbial germs inside the implant in the area of attachment.

The implant, fig.1, is composed of an inner-bone and an oral part. Part of the inner-bone implant consists of a cylindrical body provided at the bottom with a slightly conical part and special, very thin spires and at the top with a cylindrical head within which there are the gathering-screwing and the fixation elements of the oral implant. After the surgical phase of implant tissue integration, which lasts 4 months in mandible and 6 months in maxillary, the implant is revealed. In another surgery stage the scarring-bone screw is removed and there is mount a gum complier. After 10-12 days the blunt transfer is mount instead of the gum complier, which is marked along with the homologous implant, after which the work pattern is pour in the laboratory, which contains a faithful copy of the clinical situation. This implant provides the possibility of prosthetic reconstruction, with mixed support, implant-tooth fixed even on natural teeth. (Slavescu et al., 1988)

The dental implant type screw is composed of a lower inner-bone and a high inner oral part. The inner-bone part of the implant consists of a screw implant whose body has a tapered cylinder of 1 degree at the bottom and on that there are some very narrow helicoidally spires, while the upper body has inside a hole in which there are placed the nip-screwing elements of the implant and the fixation element of the oral part of the implant that consist of a hexagonal portion to be screw into the bone and a 45 degrees bowed portion on which there is placed a scarring-bone screw in the superior component. The inner oral component which forms the oral part of the implant can be:

[FIGURE 1 OMITTED]

* A prosthetic straight blunt

* A prosthetic angular blunt

* A prosthetic intermediary blunt

2. FINITE ELEMENT ANASYSIS (FEA)

Finite element analysis (FEA) represents a simulation of mechanical behaviour of structures using finite elements method.

To perform a finite element analysis is necessary to develop a geometrical model of the analyzed structure (Sorohan, Constantinescu, 2003).

Considering the complex geometry of the dental implant, the 3-D geometry model was achieved using a specialized in design program (CATIA).

After obtaining the model using CATIA, it was exported to an analysis program using finite elements method. Next step consisted in meshing process, fig. 2, using a SOLID 45 finite element, fig. 2. SOLID45 is used for the 3-D modeling of solid structures.

The element is defined by eight nodes having three degrees of freedom at each node: translations in the nodal x, y, and z directions. There were obtained 91118 nodes and 50430 elements.

The geometrical model consists of two components: the implant itself made of titanium alloy and mandible, which was approximated by a cylinder having the properties of the bone.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The structure was loaded with a concentrated force equal with the mastication force, meaning 700N. The loading and the constrained model is presented in fig. 3.

3. RESULTS

The next step in the project, after the establishment of the limit and the load conditions, it was made the static simulation of the model.

The obtained results are presented in the following figures.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

The finite element analyses (FEA) of the mandible-implant assemble wants to put in evidence the state of stress and displacement of the implant-bone interface. This stimulation was made for checking the bio-functionality of the dental-implant.

4. CONCLUSION

The results of the simulation, based on the finite elements method, regarding the deformation state are very small as shown in fig.4.

These displacement values meaning 0.027 mm were recorded on the OX axis where the mastication force was applied. This shows that in the mastication process the implant does not suffer major deformations, leading to a good behaviour of it.

The maximum value of the equivalent stress calculated according to von-Mises criterion is not relevant to the model because this value appears where the force was applied.

This fact is eliminated because of the way that the force was applied it induces the appearance of the stress concentrators.

In the rest of the implant structure, the variation of the equivalent stress is included in the normal mechanical behaviour of the material.

Also from fig. 5 the stress transmitted in the mandible is irrelevant, so in conclusion the complex geometry of the implant takes the entire loading.

The fig. 6 concludes that the normal stress that appears in the blunt area of the dental implant can cause deformation that may affect its functionality.

But considering that on the blunt area of the dental implant is covered with the dental crown that is made from ceramics, part of the mastication force effect is taken by it. All in all the stress that appears in the blunt area will be in the admissible limits.

The maximum value of shear stress that is plotted in fig. 7 appears in the head of the blunt is not relevant because of the stress concentrator induced by the action of the concentrated force.

5. REFERENCES

Bratu, D. & Nussbaum, R. (2001). Clinically and technical base of determinate prosthetic, Ed. Signata, Timisoara, Romania

Patrascu, I., Ciocan, L.T. & Miculescu, F. (2008). Biomaterials and prosthetic technologies of oral implant, Ed. Printech, Bucharest, Romania

Slavescu, D.D., Heinrich, B., Constantinescu, M.V., Heinrich, R., Meiler, J. & Koty, T. (1988). Mouth implantation. Practical guide, Ed. Romcartexim SA, Bucharest, Romania

Sorohan, S. & Constantinescu, I.N. (2003). The modeling and finite element analysis practice (in romanian), Ed. Politehnica Press, Bucharest, Romania

*** Ansys tutorial guide

Tab. 1. The elastic properties of materials

Material Elastic Modulus, E, MPa Poisson Ratio, v

Bone 9600 0.28
Titanium alloy 96000 0.36