Post on 08-May-2020
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Mechanical Behaviour of Dental Implants
Pedro Miguel Vitorino Borges Bicudo
Mechanical Engineering Department, Instituto Superior Técnico, University of Lisbon, Avenida Rovisco Pais,
1049-001 Lisboa, Portugal
Abstract
Dental implants are majority made of titanium, since this material promotes a stable and functional connection between the bone and
the surface of the implant. Efforts produced during the chewing cycles may interfere with this union, affecting the process of
osseointegration and eventually compromising the stability of the implant.
Given the difficulty in working with bone in vivo, in the present study two implant systems were inserted in polymer samples, known
as Sawbones, which simulate the structure of trabecular bone. On the experimental side, the performance of the implants was
evaluated through fatigue tests. The qualitative analysis of the damage in the structure of the samples was performed using scanning
electron microscope images. The study was complemented with the determination and comparison of stress fields and deformations
at the Sawbone-implant interface using an analytical model of indentation and the finite element method.
The experimental results showed that the performance of the Morse taper implant is greater than the external hexagonal implant
when both are tested cyclically in samples of different densities. It was proven that the diameter, length, density and type of implant-
abutment interface are design variables that affect the behavior of the implants. The numerical results of indentation model are very
similar to those obtained by the analytical model. The results of the penetration FEM model have the same tendency as the
experimental values and the FEM models and analytical indentation with increasing density of the polymer foam. It can be
concluded that, as in foams, the increase of the bone density will induce an increased stability to the implants
Keywords: Dental Implant; Sawbone; Fatigue Tests; Finite Element Method (FEM); Scanning Electron Microscopy (SEM)
1. Introduction
Nowadays, dental implants are the ideal solution for lack of
dentition, being considered the best alternative after natural
teeth. However, in spite of the latest advances recorded in
the dentistry field, implants are still likely to fail.
Complications at the implant-bone interface level, such as
bone loss, occurrence of micromovements and concentration
of tensions at the surface of the bone and the implant, are
very common phenomena, which reveal the need of solution
that keep the stability of the implant and the process of
osteointegration.
A weak primary stability is one of the major causes
contributing to the defect of the implants [1]. Therefore a
high primary stability assures a high resistance of the implant
to micromovements, which is very important for a successful
osteointegration, since the implant shall not be subject to
micromevements higher than 150 μm [1].
The factors that influence the primary stability are bone
density, the type of surface and the surgical technique used.
When an implant is placed, the primary stability will depend
firstly on the quatity and quality of cortical and trabecular
bone available for the fixation of the implant [1]. Thus, bone
desnsity is, amongst all, the most related influencing factor
of primary stability, hence its influence on the mechanical
behavior of the implants.
The literature reveals different studies [2], for a correlation
between the insertion torque values and the bone mineral
density. Friberg studies on bone resistance, allowed the
relation between the level of bone density and the value of
the applied torque inserted. The study reveal: i) low density
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– insertion torque smaller than 30 Ncm; ii) medium density -
insertion torque between 30 and 40 Ncm; iii) high density -
insertion torque values higher than 40 Ncm.
The research in biomechanics is one of the major factors to
achieve long-term success of the dental implants. To
evaluate different types of implants available in the market,
mechanical tests are fundamental, for it is through them that
is possible to analyze the performance of the tested material,
when submitted to different loadings, in different substrates.
Amongst the different possible mechanical tests to a dental
implant, fatigue tests take an important role in the
mechanical characterization of the implants. Throughout
time, the implants will be subject to different types of
loadings, product of the chewing cycles of one individual,
reason why it is of the highest importance to submit them to
these types of tests, under different levels of loading, with
the goal of predicting its life on fatigue.
From a biomechanical prespective, a well-succeeded
osteointegration depends on how the tensions and
deformations are transmitted to the bone and its involving
tissues, being key-factors for the success or defect of a dental
implant. Many variables affect the way tensions and
deformations are transmitted to the bone, such as the type of
loading applied, the length and diameter of the implant, its
geometry and surface, the bone-implant surface, and the
quality and quantity of involving bone. MEF allows to
analyze the influence of each one of the mentioned variables,
and for that reason it has become the most useful and used
tool to locate and predict flaws in any mechanical system.
Moreover, when a structural analysis is applied, it is possible
to determine what are the effects of the deformations and
tensions caused by structural loadings applied on the implant
and surrounding bone.
Given the difficulties inherent to working with trabecular
bone, synthetic polyurethane foams are widely used as
alternative materials to this type of bone in several
biomechanical tests, due to the fact that these materials
present a similar cellular structure and consistent mechanical
characteristics, found in the same order as the ones of the
trabecular bone [3]. Amongst the different possible tests, the
measurement of micromovements in the bone-implant
system when exposed to cyclic loadings is one of the most
important pre-clinical tests to determine whether the
performance of the in vivo implant is possible, and to
evaluate its stability. In the present work, a set of fatigue
tests was performed, according to the ISO 14801 norm, in
which the implants were inserted in polymeric samples, with
different densities, simulating different bone types, with the
intuit of assessing the stability of the implants and evaluate
de deformations level in the bone-implant system. This study
was complemented with an analytical analysis and of finite
elements, where similar geometries to the test specimens
were generated, through which it was possible to determine
deformation fields and bone-implant interface tension, and
finally, compare these results to the medical reality.
2. Materials and methods
2.1. Preparation of test specimens
The insertion material used consists of rigid polyurethane
(PU) foams known as Sawbones. Three types of theses
foams were selected, with the purpose of covering a certain
range of densities. Of the three selected types, the Sawbone
10 is of lower density, Sawbone 12 of higher density and
Sawbone 11 of intermediate density. It is important to
establish a relation between the density of each Sawbone and
the bone density. According to the Misch classification for
bone density, can assume that the Sawbone with lower
density aims to simulate a bone of type D3, which is, a thin
trabecular bone (less dense) and a thin cortical part. The
Sawbone 12, the denser used in the test performed,
represents the characteristics simulated of a bone of type D1,
which corresponds to a dense cortical part with a trabecular
part less dense, and finally, the intermediate density
Sawbone 11, associated to the type D2 bone. In order to
simulate the cortical part of the bone, an epoxy resin was
used to replicate the cortical properties of the bone. Table 1
presents the correspondence between the different Sawbone
types and the bone density according to Misch.
Table 1 - Sawbones and bone density according to Misch
Sawbone Classificação Misch Densidade
10 D3 Baixa
11 D2 Intermédia
12 D1 Alta
For the experimental tests of fatigue, two types of implants
were tested: the external hexagon and the Morse taper with
the respective abutments, represented in figure 1.
The identification of the type of material was made through
the technique of EDS, which allowed identifying the
chemical spectrum of the implants. The results of such
analysis showed that the implants are produced with titanium
commercially pure (Ticp) degree 4.
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Figure 1 –Implants tested
The preparation of the test specimens was made based on the
surgical protocol and the drilling sequence recommended by
the manufacturer. The implants were inserted to a depth of
8,5 mm for the external hexagon and 9 mm for the Morse
taper, given that, to conduct the tests according to the ISO
14801 worse scenario, the implants must be 3 mm above the
test specimen, instead of totally inserted [4]. The implant
insertion was conducted with resource to a dental torque
wrench, where the reading of the applied torque was
possible, as shown in figure 2.
Figure 2 – Preparation of test specimens
The average force applied to the test specimens corresponds
to the lower and upper limits of the average chewing force of
an individual. The lower average force, between 70 and 80
N, corresponding to the lower limit of the average chewing
force and a higher average force, 150 N, corresponding to
the upper limit of the average chewing force. All the tests
had a duration of 120000 cycles, and were conducted at 3 Hz
and R = 0,1. The results were handled through displacement
– number of cycle graphs, with the identification of the
defect site made through SEM images.
2.2. Analytical model for indentation
Several physic problems in the real world involve some sort
of mechanical contact. The mechanical contact problems can
be experimentally study, numerically or through theoretical
models. It was sought on literature a model that aims the
analysis of the behavior of the Sawbone structure, with the
purpose of predicting the deformations that occur when it is
externally solicited by a force. The proposed model is one of
indentation for elastic materials. This seeks, based on the
mechanical theory of contact, to describe the deformation
occurring on the Sawbone, resultant of the contact action
from the implant. The elastic tension fields generated by an
indenter be it of spherical geometry, cylindrical or
pyramidal, although complex, are well defined on the
literature [5]. For a cylindrical indenter, for r<=a, this is, for
a radial distance, r, smaller than the contact radius, a, the
contact pressure distribution is:
(
)
(1)
Below the indenter, uz, is the depth below the original free
surface of the indenter and is obtained by:
(2)
For a cylindrical indenter, the radial tension of the indented
surface is given by:
( )
{ (
)
}
(
)
(3)
The radial displacements at the indented surface are given
by:
( )( )
{ (
)
} (4)
In the expressions 1, 2, 3 and 4, E and v correspond to the
Young's modulus and Poisson coefficient of the indented
sample. For the analytic calculations, a relation of 0,5 for r/a
was chosen, to evaluate deformations and tensions at the
Sawbone structure.
2.3. Finite element method (FEM)
The generation of the finite element model was initiated with
the modulation of two distinct geometries for the implants,
one smooth and other threaded by the SolidWorks 2015
program, as shown in figure 3.
Figure 3 – Smooth and threaded geometries
The generation of the smooth geometry has the purpose of
simplifying the model, which means it was used in a
primarily analysis for the study of tensions and deformations
that occur at the set implant-Sawbone. Sawbone and epoxy
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geometries were also created, to which the two types of
implants were assembled.
Both geometries were imported to ANSYS Workbench 14.5
commercial code. The analysis were made imposing a
convergence to the von Mises tension of 7% for both
modulated geometries, for which at the smooth geometry the
element SOLID186 was used, and for the threaded geometry
the SOLID187, a tetrahedral element, as shown in figure 4.
Some simplifications were made for the simulations. Firstly,
all materials were considered homogeneous, isotropic and
linearly elastic [6, 7]. The mechanical properties of the
materials, namely the Young’s modulus, E, Poisson
coefficient, v, density, ρ and the yeld strength, σy, are the
represented in table 2.
Figure 4 - Implants computational meshes
Table 2 – Material properties
E [MPa] ν Ρ [g/cm3] σy[MPa]
Sawbone 10 23 0,3 0,16 2,3
Sawbone 10 47,5 0,3 0,20 3,9
Sawbone 12 137 0,3 0,32 5,4
Epóxi 16700 0,26 1,64 157
Implant 120000 0,37 4,55 400
Also was assumed that de implants are 100%
osteointegrated. For that, the bonded contact type was used
to simulate the contact between the different surfaces, for
according to this model, there is no separation or slip
between the faces and edges at the contact surfaces. For the
boundary conditions, the lateral faces of the epoxy and all of
the Sawbone faces are constraint to the three directions, x, y
and z. The intensity of loading used corresponds to the two
limit values of average chewing force of an individual,
which means, analysis were made for the different types of
Sawbone applying a statical loading of 70 N and 150 N,
applied at the top of the implant, according to a 30º angle
with the axial axis of the implant, simulating the loading
conditions of of ISO 14081 norm.
A numerical study was also conducted to validate the
equations presented in subchapter 2.2. A representative
geometry, shown in figure 5, was generated for the
indentation model, were the tested sample is a cubical block
with a 15 mm edge, representative of the Sawbone, and the
indenter is the implant of smooth geometry. The
convergence criterion of the mesh was 5% for the von Mises
tension. The boundary conditions are the same as describe
before for the total constraint of the Sawbone walls and of its
base. The loading applied to the indenter axis is of
compressive character, therefore the intensity of the force
used on the indention simulations corresponds to the vertical
component of the resultant force.
Figure 5 – Indenter geometry
3. Results
3.1. Results of fatigue tests
The test results for the two systems used, implant external
hexagon and Morse taper, are arranged according to the type
of Sawbone in which were inserted, as shown in figures 5, 6
and 7. The test curves reveal clear that in a first stage and for
a low number of cycles the materials response is essentially
linear elastic. There is a rapid accumulation of deformation
caused by the bending and stretching of the cell walls. After
this stage, the yield point is where the first cell collapse
occurs. Then, after overcoming this peak, there is a slight
decrease of deformation, a result of the softening of the
material, registering lower deformation values temporarily.
At the end of this phase, it starts a level where the increase
value of the deformation in the material is negligible with
increase of the number of cycles. It is during this phase that
occurs the plastic collapse phenomenon, with formation of
plasticity on the membrane connection nodes of the cellular
material due to the fact that have exceeded the threshold
value of the total plastic moment when applying a normal
force to the cell walls [8].
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a) b)
Figure 6 - Experimental results for Sawbone 10: a) external hexagonal implant; b) Morse taper implant
a) b)
Figure 7 - Experimental results for Sawbone 11 a) external hexagonal implant; b) Morse taper implant
a) b)
Figure 8 - Experimental results for Sawbone 12 a) external hexagonal implant; b) Morse taper implant
The results shown in Figure 5, regarding the Sawbone 10,
show that for the external hexagonal implant there is a clear
difference in the progress of the two curves. In the green
curve, representing the test performed at an average force of
75 N, is not recorded, in the plastic collapse phase, which
starts at around 10000 cycles, an increase in the deformation
amount with the increased number of cycles. Regarding the
red curve, increased to twice the value of the average of the
test force promoted early a sudden increase of deformation
for a low number of cycles, a behavior which tends reduce
during the plastic collapse phase of the material, which is
clearly visible that the gradual increase in the number of
cycles promotes a decrease in strain rate of Sawbone. In the
case of the Morse taper implant the progress of the two
curves is substantially the same, verifying a sudden increase
in the elastic deformation zone until the yield point of the
material and about 20000 cycles starts the plastic collapse
phase, where the variation in deformation value in the
Sawbone is not significant with increasing number of cycles.
Against the behaviour of the external hexagon implant, the
increase of the average strength intensity from 75 to 150 N,
did not cause a change in the material behavior during the
phase of plastic collapse. This means that the structure of
Sawbone was able to accommodate the movements of the
implant when it is subjected to a cyclic load of greater
intensity.
In the external hexagonal implant, the results for the tests
with the Sawbone 11 show, for the corresponding curve of
80 N, an equivalent behavior that was previously registered.
After exceeding the elastic range and the slight softening
material, there has been an increase in the value of the
deformation in Sawbone until the conclusion of the test. For
the test conducted, at an average force of 150 N, it is found
that for about 20000 cycles occurs a gradual increase in
Sawbone deformation. In the Morse taper implant, the results
also show a very similar behavior of the two curves, and for
both specimens, as from the plastic collapse phase begins, it
was found a slight variation of deformation in advance the
number of cycles. Comparatively to the previous recorded
results for Sawbone 10, the deformation values are
6
significantly inferior in this case, being possible to verify a
small variation on the values derived from the increment of
strenght.
Finally, in tests performed with the denser Sawbone, the
results of the external hexagonal implant are the ones
expected. Again, for the loading of lower intensity, there is a
long plateau where the progress of deformation is
substantially constant. When the intensity of the applied
average force passes to 150 N, the deformation rate in
Sawbone also gradually increases. For the Morse taper
implant, once again it is clear that the behavior of the two
curves is almost the same, recording from the plastic
collapse phase and for the two curves shown, the Sawbone
strain rate is practically constant, having no abrupt increase
in strain values up to completion of the test.
Figure 9 – Insertion torque external hexagonal implant
Figure 10 - Insertion torque Morse taper implant
In all tests the values of the insertion torque were recorded,
hence why it is now possible to analyze how this parameter
varies with the density of the foams. Clearly increased the
Sawbone density, leads to an increase of the respective
implant insertion torque. This increase in the torque value
can be explained based on the structure of the cells.
3.2. Results of FEM penetration simulations
The distributions of stress and strain are presented in figures
4.11 to 4.14, manilly, maximum stress values in the implant
and deformations in Sawbone. These are represented in a
color scale, that is, closer to the red, higher the value of the
stress / strain. Amongst the results presented for the smooth
geometry, there was a gradual decrease in the value of stress,
such as deformation, which with the type of Sawbone, and
that this situation happens for both strength intensities used.
Firstly it is noted that in all simulated cases, either the
implant or the Sawbone-epoxy set have not reached the limit
value of the yield stress of its material, meaning, all
components support the loading imposed without deform
plastically. From the point of view of stress analysis, it can
be said that the most favorable situation occurs when using
the higher density Sawbone, beacuse the stress values are
minimized. Taking this into account, it can be seen that for
both strength intensities, there is a 20.45% decrease of the
stress for the less dense Sawbone, and 14.20% for the
Sawbone intermediate density, when compared with
Sawbone of high density, respectively. Regarding
deformations on Sawbone, it is in the less dense than the
highest values occur, and there as the value of density
increases, the amount of deformation decreases, behavior
similar to stress. Given the nature of the applied compressive
force and bending moment generated on the implant, the
maximum deformation occurs at the contact interface
between the implant base and Sawbone, a situation which
occurs for all values of density and intensity strength tested.
a) b) c)
Figure 11 – Deformations in Sawbone of smooth geometry: a) Sawbone 10; b) Sawbone 11; c) Sawbone 12
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a) b) c)
Figure 12 - Stress in Sawbone of smooth geometry: a) Sawbone 10; b) Sawbone 11; c) Sawbone 12
a) b) c)
Figure 13 - Deformations in Sawbone of threaded geometry: a) Sawbone 10; b) Sawbone 11; c) Sawbone 12
a) b) c)
Figure 14 - Stress in Sawbone of threaded geometry: a) Sawbone 10; b) Sawbone 11; c) Sawbone 12
On the results of the threaded geometry, these are very
similar to those previously found for the smooth geometry. It
was found that there is a reduction of the values of stress, as
for the deformation, when there is a increase of density on
the Sawbone. It is for the denser Sawbone that both values
are minimized, a situation which occurs for both strength
intensities. For all the conditions simulated, the materials
don’t deform plastically.
Now comparing the results between the two tested
geometries, the thread geometry provides a reduction in
terms of the stresses anda deformation in the Sawbone. For
the less dense Sawbone, the introduction of threads on the
implant body leads to a reduction of 17.52% in the value of
the stress at the interface, in addition to the value of the
maximum deformation decreases Sawbone 1.92%. For
Sawbone 11, reducing stresses is also evident, dropping the
value of the maximum stress of 15.79% and 4.80%
deformation. Finally, for Sawbone with higher density
tension in the threaded implant compared to smooth implant,
decreases 11.74% while the deformation decreases 4.79%.
The decrease in tension between the two geometries is
justified because increasing the contact area on the interface
contact between the implant and the Sawbone-epoxy set,
maintaining the same degree of loading, an increase in the
area promotes a reduction in the amount of tension.
3.3. Results of indentation simulations
The results of numerical simulations, such as analytical
calculations showed that the deformation values decrease as
the mechanical properties of Sawbone increase, as shown in
tables 3 and 4. The finite element model valid the equations
for the displacement, having experienced a 8.28% error
between analytical and numerical values. Regarding stress
analysis, it appears that the value of the resultant doesn't vary
in function of the Sawbone. The finite element model also
validates the stress equations, having been an error between
the two values of 5.23%.
Table 3 – Numerial results of indentation
Deformation (mm) Tension (MPa)
Force (N) 60,62 129,90 60,62 129,90
Sawbone 10 0,551 1,180 1,180 7,292
Sawbone 11 0,267 0,571 0,571 7,293
Sawbone 12 0,092 0,198 0,198 7,298
Table 4 – Analytical results of indentation
Deformation (mm) Tension (MPa)
Force (N) 60,62 129,90 60,62 129,90
Sawbone 10 0,600 1,286 3,592 7,697
Sawbone 11 0,291 0,623 3,592 7,697
Sawbone 12 0,101 0,216 3,592 7,697
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In figure 15, it can be seen an example of indentation stress
fields and deformation.
Figure 15 – Example of indentation stress fields and
deformation
4. Discussion
There were several differences for the two tested implant
systems. For both, the external hexagonal implant, as for the
Morse taper implant, it was found that the deformation value
decreases as the Sawbone density increases. The SEM
images, shown in figure 16, verify this, once the results were
analyzed, it is observed that the number of collapsed cells
within the affected area is larger for the less dense structure.
Figure 16 – SEM images: Sawbone 10 and 12, respectively
Although this situation occurs for both implants, the
variation range of values for the displacement is smaller for
the Morse taper implant, that is, this type of implant is less
sensitive to load variation when it is tested in the same cell
structure, as shown in figure 17.
From the point of view of the bone structure, a bone-type
D1, being denser and mechanically stronger, is less sensitive
to the variation of masticatory forces.
Another interesting result is found for the case of the less
dense Sawbone, that is, when both the implants were tested
in the worst design condition. For the external hexagonal
system it was found that the plastic collapse phase starts
earlier at about 10000 cycles, and that the curve behavior for
the greater force intensity displays significant differences
compared to the Morse taper implant curve. The difference
of the values recorded can be reflected in the fact that for the
external hexagonal implant, the Sawbone structure doesn’t
accommodate the movements suffered by the implant when
it is loaded cyclically. To make an analogy between the
experimental results and the world of dentistry, this result
may lead to a lower adhesion of bone cells around the
implant, contributing to a delay of osseointegration time,
compromising the long-term success of the implant.
Numerical studies show that the effect of diameter and
length of the implants has an influence on stress distribution
at the bone-implant interface [6, 7]. The increase in diameter
of the implant promotes a reduction in the normal and shear
stresses along the implant-bone interface, promoting a better
distribution of loads to the tissue. In other words, the
increase of the lateral area and implant section reduces the
tensions generated in the cortical bone, stresses arising from
compressive forces, tensile, bending and torsion, wherein the
diameter of the implant have a greater influence compared
with the length [9]. The shape of the Morse taper implant
also helps to explain the better performance during the test,
since the introduction of microthreads in the implant neck
region, as shown in figure 1, helps to minimize the amount
of tension along the zone, resulting in a decrease of bone loss
after the placement of the implant [1].
The implant abutment connection also influences the results
obtained. The performance of the Morse taper system, when
compared with the behavior of the external hexagonal
implant has a higher success rate, meaning, for the same type
of loading the number of cycles to failure is higher thanks to
their locking mechanism, by wherein the clearance between
the implant and the abutment is reduced, eliminating
vibration and micromovements of the connecting srew [10].
The values of the measured insertion torque also show a
clear relationship with the density of Sawbone. There have
been higher torque values when the foam density is higher,
and this result is in line with some studies published. Given
that the three Sawbones are closed cell foams, the air that
lies within each cell has influence on the process. This means
that for larger cells the air which is inside it is at lower
pressure compared to larger cells [11]. Therefore the force
which is necessary to fix the implant in the less dense
Sawbone is lower compared with the densest Sawbone, that
is, the value of the torque is lower for lower densities and
higher for higher density foams.
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Figure 17 – Comparison of the experimental results
Figure 18 - Variation in the deformation values for different Sawbone
Figura 19 - Variation in the stress values for different Sawbone
Establishing a link between these results and bone density, it
was found that measured values haven't exceeded the
recommended maximum torque, this means that the bone
structure is not overloaded at the time of insertion of the
implants.
For the numerical results, it is noted that the maximum
magnitude of the deformation recorded in all the simulations
is in the range of microns, μm. According to the literature,
excessive micromovements between the implant and
surrounding bone can interfere with the process of
osseointegration, having been postulated that such
deformations must not exceed the value of 150 μm [1]. The
simulations results indicate that this threshold value is never
reached, and knowing that the Sawbones are a test material
used to simulate the conditions of trabecular bone, it can be
stated that for the Sawbones 10, 11 and 12, representative of
the type of bone D3, D2 and D1, respectively, the
corresponding micromovements of the implant relative to the
10
bone microstructure proved to be sufficiently low to avoid
the formation of fibrous tissue, favoring the long-term
osseointegration.
In order to compare the results of indentation, with the
penetration results, an analysis between displacement and
stress values for both situations was made and is shown in
figures 18 and 19. However, the fact that the simulations
made with the penetration model have been used the type of
contact bonded, makes that all the components of the
geometry behave as a single body. In order to overcome this
situation, the type of contact between the walls of Sawbone
and epoxy with the implant was changed, for no separation.
This type of contact also used in linear simulations is similar
to bonded, but is permitted a slight sliding between surfaces.
This sliding simulate better the penetration of the implant on
the surface of Sawbone, since the formulation of border
conditions of the indentation model only takes into account
the interactions between the base of the indenter and the
sample surface, non-accounting for the effect of the side
walls of the indenter as it penetrates into the sample. Based
on this analysis, it can be said that the numerical model
indentation validates the analytical equations. However, the
magnitude of strain and stress values, when compared with
the numerical value of the penetration FEM model, it isn’t of
the same order of magnitude, but it is noted the same trend as
the other models. Despite this, the evidenced behavior in the
three situations is the same, which justifies that despite the
analytical model not quantify a priori the value of deflection
and penetration stress, this allows us to understand the
implant behavior when inserted in a PU sample.
5. Conclusions
The analysis of the mechanical behavior of implants
subjected to fatigue tests on different substrates, completed
with an analytical and finite element analysis, revealed
different conclusions. The results of the tests showed that the
performance of the Morse taper implant is greater than the
external hexagonal implant when both are tested cyclically in
samples of different densities. This superior resistance
presented by Morse taper system explains the significantly
increased long-term stability of these implants in clinical
applications. It has been proven that the diameter, length,
density and type of implant-abutment interface are design
variables that affect the behavior of the implants. The
deformation and tension results obtained with the penetration
FEM model exhibit the same trend as the analytical results
and MEF indentation, so that part of a scale factor, the
analytical model of indentation can be a starting point for the
explanation of the experimental results. Obviously the
conditions are different, since experimental tests are dynmic
while simulations and analytical method reproduce static
indentation behaviours.
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[4]. UNE-EN ISO 14801. (2007). “Dentistry. implants.
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[5]. Fischer-Cripps, A. C. (2007). “Introduction to contact
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