Role of fem in orthodontics /certified fixed orthodontic courses by Indian dental academy

ROLE OF FEM IN ORTHODONTICS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


INTRODUCTION
In the last decade the application of a well proven
predictive technique the Finite Element Method,
originally used in structural analysis has
revolutionized dental biomedical research. Finite
Element analysis was introduced originally as a
method for solving structural mechanical
problems, which was later recognized as a general
procedure for numerical approximation to all
physical problems that can be modeled by a
differential equation description.

Finite Element analysis has also been applied to
the description of physical form changes in
biologic structures particularly in the area of
growth and development and various branches of
dentistry. Finite element method which is an
engineering method of calculating stresses and
strains in all materials including living tissues has
made it possible to adequately model the tooth and
periodontal structure for scientific checking and
validating the clinical assumptions.

Finite Element Method
– General Review


Finite analysis solves a complex problem by
redefining it as the summation of the solution by a
series of interrelated simpler problems. The first
step is to subdivide (i.e. discretize) the complex
geometry into a suitable set of smaller "elements"
of "finite" dimensions when combined from the
"mesh" model of the investigated structures. Each
element can adapt a specific geometric shape (i.e.
triangle, square, tetrahedron etc) with a specific
internal strain function. Using these functions and
the actual geometry of the element, the
equilibrium equations between the external forces
acting on the element and the displacements
occurring on its nodes can be determined.

Information required for the software used in the
computer is as follows.
1) Coordinates the nodal points.
2) Number of nodes for each element.
3) Young's modulus and Poissons ratio of the
material modeled by different elements.
4) The initial and boundary conditions.
5) External forces applied on the structure.

The boundary condition of these models is defined
so that all the movements at the base of the model
are restrained. This manner of restraining prevents
the model from any rigid body motion while the
load is acting.
The two-dimensional axisymmetric finite element
modeling has been used in most of the previous
research. Although numerical results can be easily
obtained in two-dimensional modeling, it has
some significant shortcomings.

The human is highly irregular in shape, such that
it cannot be represented in a two-dimensional
space and the actual loading cannot be simulated
without taking the third dimension into
consideration. The distribution of various
materials of the tooth structure does not show any
symmetry. Therefore a three dimensional
modeling with the actual dimension must be
preferred for a reliable analysis.

Element Attributes


One can take finite elements of any kind one at a
time.
Their local properties can be developed by
considering them in isolation, as individual
entities.
This is the key to the programming of element
libraries.
In the Direct Stiffness Method, elements are
isolated by disconnection and localization steps.
This procedure involves the separation of elements
from their neighbors by disconnecting the nodes,
followed by the referral of the element to a
convenient local coordinate system.

Summary of the data associated with an
individual finite element.

This data is used in finite element programs
to carry out element level calculations.


Dimensionality:
Elements can have one, two or three
space dimensions. (There are also special
elements with zero dimensionality)


Nodal points:
Each element possesses a set of
distinguishing points called nodal points or nodes
for short. Nodes serve two purposes: definition of
element geometry, and home for degrees of
freedom. They are located at the corners or end
points of elements; in the so-called refined or
higher-order elements nodes are also placed on
sides or faces.

Geometry:
The geometry of the element is defined by
the placement of the nodal points. Most elements
used in practice have fairly simple geometries. In
one-dimension, elements are usually straight lines
or curved segments. In two dimensions they are of
triangular or quadrilateral shape. In three
dimensions the three common shapes are
tetrahedral, pentahedral (also called wedges or
prisms), and hexahedra (also called cuboids or
“bricks”).

Degrees of freedom:
The degrees of freedom (DOF) specify
the state of the element. They also function as
“handles” through which adjacent elements are
connected. DOFs are defined as the values (and
possibly derivatives) of a primary field variable at
nodal points. For mechanical elements, the
primary variable is the displacement field and the
DOF for many (but not all) elements are the
displacement components at the nodes.

Nodal forces:
There is always a set of nodal
forces in a one-to-one correspondence with
degrees of freedom. In mechanical elements
the correspondence is established through
energy arguments.


Constitutive properties:
For a mechanical element these is
the relation that specifies the material
properties. For example, in a linear elastic
bar element it is sufficient to specify the
elastic modulus E and the thermal
coefficient of expansion

Fabrication properties:
For a mechanical element these are
fabrication properties which have been integrated
out from the element dimensionality. Examples
are cross sectional properties of elements such as
bars, beams and shafts, as well as the thickness of
a plate or shell element.
This data is used by the element
generation subroutines to compute element
stiffness relations in the local system.

BOUNDARY CONDITIONS:
A key strength of the FEM is the
ease and elegance with which it handles
arbitrary boundary and interface conditions.
This power, however, has a down side. One
of the biggest hurdles a FEM newcomer
faces is the understanding and proper
handling of boundary conditions

Essential and Natural B.C.
The important thing to remember is
that boundary conditions (BCs) come in
two basic flavors:


Essential BCs are those that directly affect the
degrees of freedom

Natural BCs are those that do not directly
affect the degrees of freedom


Showing the boundary conditions of the model


Linear/non-linear FE-modeling:
The stiffness matrix for a linear
problem remains constant .This means that
throughout the analysis the relation between force
and displacement is linear. If the relation between
force and displacement is not constant at the
different steps of the analysis, the problem to be
solved is called non-linear.

There are different sources of nonlinearity:


•

Material non-linearity generated by nonlinear relations between stresses and
strains.
•
Geometric non-linearity generated by
non-linear behavior of the strain to
deformation and stress to force relations.


Non-linear boundary conditions that are
generated when the boundary conditions are
changing during analysis. A typical case is
the contact problem where two separate
objects are getting in contact with each
other during the analysis.


To solve problems with one or more of the
above types of non-linearity, the solution
has to be calculated in steps where the load
is gradually incremented. At every step the
equations of equilibrium should be fulfilled
within a prescribed error.


Finite element models are created by breaking the
design in to numerous discrete parts or
elements.


Applications of finite element method


 Finite element analysis has been applied to the
description of form changes in biological
structures (morphometrics), particularly in the area
of growth and development.
 Finite element analysis as well as other related
morphometric techniques such as the macroelement and the boundary integral equation
method (BIE) is useful for the assessment of
complex shape changes.

 the knowledge of physiological values of alveolar
stresses is important for the understanding of
stress related bone remodeling and also provides a
guideline reference for the design of dental
implants.
 Finite element method is also useful for structures
with inherent material Homogeneity and
potentially complicated shapes such as dental
implants.

 Analysis of stresses produced in the
periodontal ligament when subjected to
orthodontic forces.
 To study stress distribution in tooth in
relation to different designs.
 To optimize the design of dental
restorations To investigate stress
distribution in tooth with cavity preparation.

 The type of predictive computer model
described may be used to study the
biomechanics of tooth movement, whilst
accurately assessing the effect of new
appliance systems and materials without the
need to go to animal or other less
representative models.

Advantages of FEM


It does not require extensive
instrumentation
Any problems can be split into smaller
number of problems
It is an non-invasive technique


3-D model of the object can be easily
generated with FEM
The actual physical properties of the
materials involved can be simulated
Reproducibility does not affect the physical
properties involved


The study can be repeated as many times as
the operator wants
There is close resemblance to natural
conditions
Static and dynamic analysis can be done


Disadvantages of FEM


The tooth is treated as pinned to the supporting
bone, which is considered to be rigid, and the
nodes connecting the tooth to the bone are
considered fixed. This assumption will introduce
some error however maximum stresses are
generally located in the cusp area of the tooth. The
progress in the finite element analysis will be
limited until better defined physical properties for
enamel, dentin and periodontal ligament and
cancellous and cortical bone are available.

REVIEW OF LITERATURE ON THE
FINITE ELEMENT METHOD


In the general field of medicine, FEM has
been applied mainly to orthopedic research
in which the mechanical responses of bony
structures relative to external forces were
studied. Furthermore, some research has
been carried out in order to investigate the
soft-tissue and skeletal responses to
mechanical forces.

First FEM study in dentistry appeared in
1974,where j.w.farah and r.g.craig did finite
element stress analysis in a restored
axisymmetric first molar


The applications of the FEM in dentistry
have been found in studies by Thresher and
Saito, Knoell, Tanne and Sakuda, Atmaram
and Mohammed, Cook, Weinstein, and
Klawitter, Tanne, Rubin and associates,
Moss and associates, and Miyasaka and
associates.

The application of this theory is relatively
new in orthodontic research. It is the
development of powerful mainframe
computers with extensive memory and
number of improved soft wares that has
now placed finite element analysis in the
hands of orthodontic researchers

It has been shown in previous studies that the
finite element method can be applicable to the
problem of the strain-stress levels induced in
internal structures. This method also has the
potential for equivalent mathematic modeling of a
real object of complicated shape and different
materials. Thus, FEM offers an ideal method for
accurate modeling of the tooth-periodontium
system with its complicated three-dimensional
geometry.

Experimental techniques are limited in measuring
the internal stress levels of the PDL. Strain gauge
techniques may be useful in measuring tooth
displacement; however, they can not be directly
placed in the PDL without producing tissue
damage. The photo elastic techniques are also
limited in determining the internal stress levels
because of the crudeness of modeling and
interpretation.

The force systems that are used on an
orthodontic patient can be complicated. The
FEM makes it possible to analytically apply
various force systems at any point and in
any direction. Experimental techniques on
patients or animals are usually limited in
applying known complex force systems.

It is very important to keep in mind that the
FEM will give the results based upon the
nature of the modeling systems and, for that
reason, the procedure for modeling is most
important.


FEM studies in orthodontics


FEM has already been broadly applied in
orthodontic research. Yettram et al. (1972) were
amongst the first to employ a two-dimensional
finite element model of a maxillary central incisor
to determine the instantaneous centre of rotation
of this tooth During translation. Halazonetis
(1996) used a similar two dimensional model to
determine periodontal ligament (PDL) stress
distribution following force application at varying
distances from the centre of resistance of a
maxillary incisor.

Using more complex three dimensional
models Wilson et al. (1992, 1994), Tanne et
al. (1987, 1988) and McGuinness et al.
(1990, 1991) have studied moment to force
ratios and stress distributions during
orthodontic tooth movement. Cobo et al.
studied periodontal Stresses during tooth
movement

In the field of dentofacial orthopedics,
Finite Element models have been employed
to evaluate the stress distribution induced
within the craniofacial complex during the
application of protraction headgear (Tanne
et aI., 1988, 1989; Miyasaka- Hiraga et al.,
1994), orthopedic chin cup forces (Tanne,
1993), and conventional headgear forces
(Tanne and Matsubara, 1996).

Mechanical properties of bone and FEM


Knowing the mechanical properties of bone is' of
the utmost importance when an FE-analysis of a
bony structure has to be performed. Bone is a
living tissue that models and remodels throughout
life, and thus continuously changing its
mechanical behavior .Moreover a clear
discrimination between cortical and trabecular
bone is not a straightforward procedure especially
in the transition areas.

Having this in mind, it is anyway important to
have a mathematical description (i.e. Young's
moduli and Poisson's ratio) for both cortical and
trabecular bone properties. In cortical bone the
osteons are aligned to the bone's long axis or in
case of short bones along the direction of forces,
therefore cortical bone exhibits a higher Young's
modulus along the direction following the osteon
arrangement than in the other two transversal
directions.

The differences in between the two
transversal directions are much smaller so
that cortical bone is often assumed to be
transversely isotropic in case of trabecular
bone a precise mechanical connotation is
more problematic as mechanical properties
are strongly dependent on the orientation of
the trabeculae.

Cortical bone as well as trabecular bone has
viscoelastic properties. This means that it has
different values for ultimate strength and stiffness
depending on the strain rate during loading. In
addition to this the mechanical properties of the
bone are also depend on age and thus the level of
mineralization .These factors, together with the
uncertainty in the determination of the mechanical
properties, make it impossible to give an ultimate
value for both trabecular and cortical bone.

Moss et al (1985 ajo)
Finite element methods are able to provide
absolute quantitative descriptions of cranial
skeletal shape and shape change with local growth
significance, independent of any external frame of
reference, and, by so doing, eliminate the principal
source of methodological error in customary
roentgenographic cephalometry.

Finite element methods uniquely describe growth
locally. Given the coordinate information defining
the location of the nodes of a series of individual
finite elements at successive times, the FEM
provides an invariant (unique) description of the
time-related shape changes of each finite element
of a given structure independently of the
coordinate system used and referred to its own
initial boundaries. While it is possible to integrate
over the descriptions of all the individual finite
elements so as to provide a summary (global)
description of that same structure, as a whole, the
utility of the FEM increases when the structures
analyzed are subdivided into increasingly smaller
and more numerous constituent elements.

Kazuo Tanne et al (angle 1991)
Investigated stress distributions in the craniofacial
complex by means of the finite element analysis. An
orthopedic 1.0 Kg force was applied on the first molars of
the model in the anterior direction parallel to the occlusal
plane The model was restrained at the region around the
foramen magnum where no linear and angular
displacements were allowed, The analysis was executed
using a computer program, FEM 3 (Fujitu Corp., Tokyo,
Japan). Three principal stresses were determined in the
craniofacial bones and around the sutures.

Stress distributions produced only by an anteriorly
directed force applied to the maxillary first molars
were investigated. Large compressive stresses
were found in the bones around the maxillofacial
sutures in addition to tensile stresses in the
maxillary bone. These biomechanical changes in
the sutures were caused by counterclockwise
rotation and upward displacement of the complex.

they concluded that orthopedic maxillary
protraction forces applied in more downward
directions and/or at more anteriorly located
teeth may eliminate concomitant rotation of the
skeleton and produce more efficient sutural
modifications for subsequent maxillary growth
and repositioning. These considerations will be
effective in terms of normal maxillary growth
direction

G.D. Singh, J.A. McNamara. (Angle 1998)...

Traced cephalographs of 73 pre pubertal
children of European American descent
with untreated Class III malocclusions and
eight mandibular landmarks were digitized.
The resulting eight-noded geometries were
normalized, and the mean Class III
geometry was compared with the equivalent
Class I average. A color-coded finiteelement (FEM) analysis was used to
localize differences in morphology.

they Compared Class III and normal mandibular
configuration for changes in size and FEM revealed
positive allometry of the mandibular corpus and around
supramentale (15% increase in size), with reductions
(30%) between the incisor alveolus and menton. For
changes in shape, mandibular configurations were
predominantly isotropic, with the exception of the
anisotropic anterior region in the Class III subjects.
Incremental growth differences are consistent and
concluded that the absence of physical restraint is
associated with mandibular prognathism.

Iseri et al (1998ejo)
Evaluated the biomechanical effect of rapid
maxillary expansion (RME) on the craniofacial
complex by using a three-dimensional finite
element model (FEM) of the craniofacial skeleton.
The construction of the three-dimensional FEM
was based on computer tomography (CT) scans of
the skull of a 12-year-old male subject. The CT
pictures were digitized and converted to the finite
element model

The final mesh consisted of 2270 thick shell elements with
2120 nodes. The mechanical response in terms of
displacement and stresses was determined by expanding
the maxilla up to 5 mm on both sides. Viewed occlusally,
the two halves of the maxilla were separated almost in a
parallel manner during 1-, 3- and 5-mm expansions. The
greatest widening was observed in the dento-alveolar
areas, and gradually decreased through the superior
structures. The width of the nasal cavity at the floor of the
nose increased markedly.


However, the postero-superior part of the nasal cavity was
moved slightly medially. No displacement was observed in
the parietal, frontal and occipital bones. High stress levels
were observed in the canine and molar regions of the
maxilla, lateral wall of the inferior nasal cavity, zygomatic
and nasal bones, with the highest stress concentration at
the pterygoid plates of the sphenoid bone in the region
close to the cranial base


Dermaut et al (ejo2001)
From 55 frontal tomograms (CT-scans) using the
'Patron' finite element processor, a three-dimensional finite
element model (FEM) of a dog skull was constructed. The
model was used to calculate bone displacements under
orthopedic loads. This required good representation of the
complex anatomy of the skull. Five different entities were
distinguished: cortical and cancellous bone, teeth, acrylic
and sutures. The first model consisted of 3007 elements
and 5323 nodes, including three sutures, and the second
model 3579 elements and 6859 nodes, including 18
sutures.

Prior to construction of the FEM, an in vivo study was
undertaken using the same dog. The initial orthopedic
displacements of the maxilla were measured using laser
speckle interferometers. Under the same loading
conditions, using the second FEM, bone displacements of
the maxilla were calculated and the results were compared
with the in vivo measurements. Compared with the initial
displacement measured in vivo, the value of the
constructed FEM to simulate the orthopedic effect of
extra-oral force application was high for cervical traction
and acceptable for anterior traction.

Jafari et al (angle 2005)
Analyzed the stress distribution patterns
within the craniofacial complex during rapid
maxillary expansion., a finite element model of a
young human skull was generated using data from
computerized tomographic scans of a dried skull.
The model was then strained to a state of
maxillary expansion simulating the clinical
situation. The three-dimensional pattern of
displacement and stress distribution was then
analyzed.

Maximum lateral displacement was 5.313 mm at
the region of upper central incisors. The inferior
parts of the pterygoid plates were also markedly
displaced laterally. But there was minimum
displacement of the pterygoid plates
approximating the cranial base. Maximum forward
displacement was 1.077 mm and was seen at the
region of the anteroinferior border of the nasal
septum. In the vertical plane, the midline
structures experienced a downward displacement.
Even the ANS and point A moved downward.

The findings of this study provide some additional
explanation of the concept of correlation between the areas
of increased cellular activity and the areas of dissipation of
heavy orthopedic forces. Therefore, the reason for the
occurrence of sensation of pressure at various craniofacial
regions, reported by the patients undergoing maxillary
expansion could be correlated to areas of high
concentration of stresses as seen in this study.
Additionally, the expansive forces are not restricted to the
intermaxillary suture alone but are also distributed to the
sphenoid and zygomatic bones and other associated
structures.

Tooth and periodontium


More recent work has attempted to quantify
periodontal proper1ies during instantaneous
tooth movement (Tanne, 1995; Volp et al.,
1996). These studies have allowed the
development of more clinically valid threedimensional finite models of the tooth
(Middleton et al.,, 1997; Jones e t al ,
1998).

Bobak et al (1997ajo)
The finite element method of analysis (FEM) was
used to analyze theoretically the effects of a transpalatal
arch (TPA) on periodontal stresses of molars that were
subjected to typical retraction forces. The purposes of this
investigation were (1) to construct an appropriate finite
element model, (2) to subject the model to orthodontic
forces and determine resultant stress patterns and
displacements with and without the presence of a TPA,
and (3) to note any differences in stress patterns and
displacements between models with and without a TPA.

A finite element model, consisting of two
maxillary first molars, their associated periodontal
ligaments and alveolar bone segments, and a TPA,
was constructed. The model was subjected to
simulated orthodontic forces (2 N per molar) with
and without the presence of the TPA. Resultant
stress patterns at the root surface, periodontal
ligament, and alveolar bone, as well as
displacements with and without a TPA, were
calculated.

Analysis of the results revealed minute differences of less
than 1% of the stress range in stress values with respect to
the presence of a TPA. Modification of bone properties to
allow for increased displacement levels confirmed the
ability of the TPA to control molar rotations; however, no
effect on tipping was noted. Results suggested that the
presence of a TPA has no effect on molar tipping,
decreases molar rotations, and affects periodontal stress
magnitudes by less than 1%. The final results suggest an
inability of the TPA to modify orthodontic anchorage
through modification of periodontal stresses.

Tanne et al (1998bjo)
This study was designed to quantify the magnitude
of tooth mobility in adolescents and adults, and to
investigate the differences in the biomechanical response
of tooth and periodontium to orthodontic forces. The initial
displacement of the maxillary central incisor was measured
in 50 adolescent and fifty adult patients and the
biomechanical properties of the periodontium were
examined using the finite element method (FEM) and
supporting experimental data. The magnitude of tooth
mobility was significantly greater in the adolescent group
than in the adult group.

By integrating the differences in tooth mobility in
both subject groups with analytical tooth
displacements, the Young's modulus of the
periodontal ligament (PDL) was demonstrated to
be greater in the adults than in the adolescent
subjects. The differing biomechanical properties
of the PDL in adults were demonstrated to result
in almost equivalent or somewhat increased stress
levels in the PDL in adult subjects.

It is suggested that this might produce a
reduction in the biological response of the
PDL and thus lead to a delay in tooth
movement in adults.


Provatidis et al (2000)
reports on studies upon five different
hypothetical mechanical representations of the
periodontal ligament (PDL) which plays the most
significant role in tooth mobility. The first model
considers the PDL as an isotropic and linearelastic continuum without fibers; it also discusses
some preliminary visco-elastic aspects.

The next three models assume a nonlinear and
anisotropic material composed of fibres only that
are arranged in three different orientations, two
hypothetical that have appeared previously in the
literature and one more consistent with actual
morphological data. The fifth model considers the
PDL as an orthotropic material consisting of both
a continuum and of fibres. Results were obtained
by applying the Finite Element Method (FEM) on
a maxillary central incisor

It was found that the isotropic linear-elastic
PDL leads to occlusal positions of both
centres in comparison with those obtained
through the well-known Burrstone’s
theoretical formula, while histological
anisotropic fibres locate them apically and
eccentrically.

Jones et al (jo2001)
In this study they developed a 3 D
computer model of the movement of the maxillary
incisor tooth when subjected to orthodontic load
.this was to be used to validate the finite element
based computer model.
The design took the form of a prospective
experiment at a laboratory at the University of
Wales

A laser apparatus, was used to sample tooth movement
every. 0.01 seconds .over a one minute cycle for ten
healthy volunteers when a constant load of 0.39N load was
applied "This process was repeated on eight occasions and
five consistent readings were made this data was used to
calculate the physical properties of the PDL. This was
formed by 15000 four noded tetra hedral elements. Tooth
displacements ranged from 0.012 to 0.133 mm the
maximum strain located at the alveolar bone was thirty
five times less than that of the PDL


Computer-generated 3-dimensional finite element ‘‘meshwork’’ of a
maxillary central incisor, periodontal ligament, and alveolar
bone.


Geramy et al (ejo2002)
Investigated the stress components that appear
in the periodontal membrane (PDM), when
subjected to transverse and vertical loads equal to
1 N. Six three-dimensional (3D) finite element
models (FEM) of a human maxillary central
incisor were designed. The models were of the
same configuration except for the alveolar bone
height. Special attention was paid to changes of
the stress components produced at the cervical,
apical, and sub-apical levels

results showed that alveolar bone loss caused
increased stress production under the same load
compared with healthy bone support (without
alveolar bone resorption). Tipping movements
resulted in an increased level of stress at the
cervical margin of the PDM in all sampling points
and at all stages of alveolar bone loss. These
increased stress components were found to be at
the sub-apical and apical levels for intrusive
movement.

Materials


The finite element method has only recently been applied
to the evaluation of orthodontic attachment. Ghosh et
al(1995) have used three-dimensional FEM models of
ceramic orthodontic bracket designs to determine the stress
distribution and likely mode of cohesive failure within the
bracket when a full dimension stainless steel arch wire is
engaged within the bracket slot. Katona. (1994, 1997), and
Katona and Moore (1994) have used a two dimensional
finite element model of the bracket tooth interface to
assess the stress distribution in the system when bracket
removing forces are applied.

Similarly, Rossouw and Tereblanche (1995) have used a
simplified three dimensional finite element model to
evaluate the stress distribution around orthodontic
attachments during debonding. Katona (1997b) compared
different methods of bracket removal and suggested that
different loading methods resulted in significantly different
stress patterns.
In addition, peak stress concentrations were suggested to
be responsible for attachment failure indicating that mean
stress values were of little value in quantifying the quality
of attachment.

Ghosh and nanda (1995ajo)
This investigation was designed to generate finite
element models for selected ceramic brackets and
graphically display the stress distribution in the brackets
when subjected to arch wire torsion and tipping forces. Six
commercially available ceramic brackets, one
monocrystalline and five polycrystalline alumina, of twin
bracket design for the permanent maxillary left central
incisor were studied. Three-dimensional computer models
of the brackets were constructed and loading forces,
similar to those applied by a full-size (0.0215 ´ 0.028 inch)
stainless steel arch wire in torsion and tipping necessary to
fracture ceramic brackets, were applied to the models.

Stress levels were recorded at relevant points
common among the various brackets. High stress
levels were observed at areas of abrupt change in
geometry and shape.
The Starfire bracket ("A" Company, San Diego,
Calif.) showed high stresses and irregular stress
distribution, because it had sharp angles, no
rounded corners, and no isthmus.

The finite element method proved to be a
useful tool in the stress analysis of ceramic
orthodontic brackets subjected to various
forces.


Finite element model of unit cell


Finite element mesh of cement part
of unit cell


katona et al (1994ajo)
A finite element model (FEM) of an
orthodontic bracket bonded to enamel with
glass ionomer cement was developed. The
loading on the model simulated tensile
loading conditions associated with the
testing of bonding system strength.

The results indicate that peak stress values
increase as the load deflection angulation
increases. If the tensile load is inadvertently
applied entirely on one wing of the bracket,
the stress components nearly double in
magnitude.


Conclusion:
In future with this proviso, computer models of
various types can be used increasingly for
fundamental biomechanics research in dentistry.
They also provide an ideal "test-bed“ for research
and development of new materials for use in
mouth.


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Role of fem in orthodontics /certified fixed orthodontic courses by Indian dental academy

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