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.
