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Numerical Analysis of the Response of Superelastic Alloy Dental Implants

Natural teeth are surrounded by a tissue called periodontal ligament. When a load is applied on the teeth, has a natural damping provided by this tissue, which is also responsible for the paralysis of mastication when a very hard object is cold between the teeth. Since the forces applied on implants, during chewing or during a parafunction are transmitted directly to the bone bed for lack of the periodontal ligament. An overhead in the bone-implant system may lead to a unwanted bone resorption or even fracture of components of the delicate system.

The use of superelastic alloys as components of this system may lead to an energy absorption, good for the bone-implant system. The league would be responsible for the artificial damping, first performed by the periodontal ligament.

The objective of this work is to design and analyze a three-dimensional model of a adjacent bone-implant system using a finite element program, quantifying the energy dissipated in the system through the areas of hysteresis in the stress versus deformation curve of superelastic alloy (NiTi) and force versus displacement curve of the point of application loading. The measurement of energy absorption by the system will be the difference of the energy transmitted to the system on the loading and the energy needed for unloading the same. Will be evaluated the effect of energy dissipation of the material used for making implant abutments as a result of applied forces.

The phenomenon of shape memory material occurs when the heating of a NiTi alloy leads to the transformation of the martensitic phase in austenitic phase. Materials with shape memory may have a superelastic behavior defined as the ability to return the material to its original shape at a constant temperature and near the temperature of complete austenitic transformation, but only by eliminating the tension that is deforming the material. This phenomenon is the result of a martensitic transformation induced by deformation of the material.

Lagoudas et al. (2003) report that there is a dissipation of energy by martensitic transformation that can reach very high values, such as 80-90%. This is an indicative of the possibility of using superelastic materials for making devices that have the function of absorbing energy.

The bone-implant system consists of the supporting bone (cortical bone and marrow bone), pin implant, prosthetic component (abutment and abutment screw), implant-supported prosthesis (crown and copping) and the loads. The model used excludes the screw of the abutment and the dental crown, which would make the problem more complex.

The cortical bone is the bone part with better mechanical properties and where the implant does its mechanical locking. The tensions are less dissipated in this region, which may explain the occurrence of bone loss. The pin implant is the replacement of the tooth root. The components of the prosthesis, also called abutments, which are the intermediate elements between the pin implant and the implant-supported prosthesis, are fixed by screws that are retained on the internally thread of the pin implant.

The computational model seeks to represent a section of mandible in the region of the first molar. This is a three-dimensional analysis and simplified geometry.


Figure 1 - Model: prosthesis and cortical and marrow bone.

First we obtained the force-displacement curves at the point of greatest displacement of the abutment, with the use of titanium and NiTi. After measurements were made at the application point of load (which represents the total energy of the system), where the area of the loop was measured, obtaining the energy dissipated in the loading and subsequent unloading. The amount of energy absorbed in the complete cycle was measured in percentage. The energy absorption was observed in the order of 13%. This value is not high, but justified the continuation of studies by improving the model and approach the problem as well as adjustments in the design of the implant.

NiTi has a different behavior under cyclic loading, so a dynamic study with emphasis on material fatigue must also be designed for its continued use be provided. According to Nemat-Nasser et al. (2005), for dynamic loading cycles, the energy absorption capacity of the alloy tends to a stable value for the number of cycles. The making of an abutment in NiTi can be a viable process for impact absorption, and easily applicable clinical use, because the abutment would be compatible with commercial systems of implants existing.

TEAM: Vicente Tadeu Lopes Buono, Estevam Barbosa de las Casas, Ana Maria Gontijo Figueiredo, Édson Antônio Ferreira, Carlos Alberto Cimini Jr. and Ronan Almeida Faustino.

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