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Finite Element Analysis of the Mechanical Behaviour of Human

Mandible

A DISSERTATION

Submitted in Partial Fulfilment of the Requirements

For the Award of the Degree of

5 year Integrated Dual Degree Programme

B.Tech (Mechanical Engineering) + M.Tech (Design Engineering)

Submitted By

MRIDUL DHYANI

10/IME/034

Under the Supervision of

MR. ANURAG DIXIT

DEPARTMENT OF MECHANICAL ENGINEERING

SCHOOL OF ENGINEERING

GAUTAM BUDDHA UNIVERSITY

GREATER NOIDA (201312)

May 2015

COPYRIGHT © 2015 GAUTAM BUDDHA UNIVERSITY

ALL RIGHTS RESERVED

FINITE ELEMENT ANALYSIS OF THE MECHANICAL BEHAVIOUR OF HUMAN MANDIBLE

i

Department of Mechanical Engineering

School of Engineering Gautam Buddha University Greater Noida

DECLARATION

I here certify that the work presented in this dissertation entitled “Finite Element

Analysis of the Mechanical Behaviour of Human Mandible” by Mridul Dhyani Roll No.

10/IME/034 in the partial fulfilment of the requirements for the award of the degree of 5

year Dual Degree Integrated Programme B.Tech (Mechanical Engineering) + M.Tech

(Design Engineering) submitted to the School of Engineering Gautam Buddha University

Greater Noida is an authentic work of my own work carried out supervision of Mr. Anurag

Dixit. The matter presented in this Dissertation has not submitted by me in any other

University / Institute for the award of any other degree or diploma.

Date: (Mridul Dhyani)

This is to certify that the above statement made by the candidate is correct to the

best of my knowledge and belief.

Mr. Anurag Dixit

(Supervisor)

Research/Faculty Associate Department of Mechanical Engineering

School of Engineering Gautam Buddha University

Greater Noida India

The viva voce of Mr. Mridul Dhyani (10/IME/034) has been conducted/held on

….………………

(External Examiner)


ii

ACKNOWLEDGEMENTS

I would like to express my deepest gratitude towards my guide Mr. Anurag Dixit for his

guidance and constant support. His academic and moral support was of great value and I

would be forever indebted. Without his zealous motivation this work would never have

gotten complete.

I would also take this opportunity to thank Dr. Satpal Sharma the head of department of

Mechanical engineering in Gautama Buddha University for the patience and the support

he has shown towards me.

I would also like to thank Mr Rohit Priyadarshi for helping through the thesis work.

I sincerely thanks my parents and my friends for their undying support which has been a

pillar of strength for me.

(Mridul Dhyani)


iii

ABSTRACT

The objective of this study is to compute the finite element analysis of the mechanical

behaviour of human mandible. The influence of plate geometry and mechanical stress

distribution on the plate and bone is determined at the same time.

The mandible has a central functional and an aesthetic role. A loss of mandibular continuity

occurs mainly due to trauma tumour or inflammation which may lead to airways reduction

poor swallowing failure to retain saliva impairment of speech and aesthetic disfigurement.

This study aims to investigate the effectiveness of treating the mandibular fracture using

mandible plate by examining the stresses and strains developed in the mandible plate

assembly. The mandible plate is designed using CAD software and subjected to the

masticatory force after assembling the mandibular plate and the mandible bone. The

stresses and strains are evaluated using the Von Mises stress and strain distribution.

It is found that the maximum mechanical stresses and strain occur in the middle of the plate

in the region of the highly notched tapering of the cross-section at a level approximating to

the tensile strength. While maximum stress and strain in the mandibular bone occurs at the

extreme of mandibular bone – plate interface. The material can be removed from the areas

where are stresses are minimal to reduce the material requirement and the cost of

fabricating.


iv

TABLE OF CONTENTS

DECLARATION i

ACKNOWLEDGEMENT ii

Abstract iii

Table of Contents iv

Table of Figures vii

List of Tables ix

Chapter 1: Introduction 1

1.1 Mandibular Anatomy 1

1.1.1 Features 3

1.1.2 Structure 3

1.1.3 Malocclusion 5

1.3 Types of Mandible Bones and Properties 7

1.3.1 Cancellous Bones in Human Mandible 7

1.3.2 Cortical bones in human mandible 7

1.4 Mandibular Fractures 8

1.5 Imaging 10

1.5.1 Panoramic radiography 10

1.5.2 Computed tomography 10

1.5.3 Plain film radiography 10

1.6 Classification 11

1.6.1 On basis of the Location of Fracture 11

1.6.2 On the Basis Type of Fracture 12

1.6.3 On the Basis of Involvement of dentition 13

1.7 Treatment of Mandibular plates 14


v

1.8 Types of Mandible Plates 16

1.8.1 Compression plates 16

1.8.2 Reconstruction plates 16

1.8.3 Miniplates Miniplates 17

1.8.4 Microminiplates 17

1.8.5 Lag screw fixation 18

1.8.6 Bioresorbable plates 18

1.8.7 Three-Dimensional Miniplates 19

1.8.8 Locking reconstruction plates 20

1.9 Material properties of Mandible Plate 20

Chapter 2: Literature Review 22

2.1 Introduction 22

2.1.1 Mandibular bone 22

2.1.2 Classification of the Fractures on Basis of Displacement 23

2.1.3 Classification of the Fractures on Basis of Favourability 23

2.1.4 Classification of fractures on the Basis of Age of Factor 23

2.2 Mandible Plate 23

2.3 Literature on Mandible plate 24

2.4 Literature on Human Mandible 27

Chapter 3: Finite Element Analysis 32

3.1 Finite Element Method 32

3.1.1 Basic Concept 32

3.1.2 Benefits of Finite Element Analysis 33

3.1.3 Applications of Finite Element Analysis 33

3.2 Software involved in the finite element analysis of mandibular plates 34

3.2.1 Solid Works 34

3.3.2 Autodesk Algor 35


vi

3.3 Design of L type Mandible Plate 36

3.3.1 Mandible Plate 37

3.3.2 Lower part of mandible bone 38

3.3.3 Bolt 39

3.3.4 Upper Part of Mandible Bond 40

3.3.5 Analysis of L type Mandible Plate 42

3.4 Developing an H Type Mandible Plate 47

3.4.1 Mandible Plate 48

3.4.2 Mandibular Bone 49

3.4.3 Bolt 50

3. 4.4 Assembling of H type Mandibular Plate1 51

3.4.5 Analysis of H type Mandible Plate 52

Chapter 4: Result and Discussion 56

Chapter 5: Conclusions and Future Scope of Work 58

Refrences 60


vii

LIST OF FIGURES

Figure 1.1 : Human Mandible 2

Figure 1.2 : Malocclusion 6

Figure 1.3 : Percentage Share of Various Causes of Mandibular Fracture 8

Figure 1.4 : Cross Sectional View of Mandible 9

Figure 1.5 : Location of Mandibular Fractures 9

Figure 1.6 : Multiple Mandible Fractures of a Patient 14

Figure 1.7 : Mandibular Plate on Human Mandible 14

Figure 1.8 : A Type of Mandible Plate 15

Figure 1.9 : Reconstruction Plate 16

Figure 1.10 : Miniplates 18

Figure 1.11 : ORIF Using a Resorbable Plate at the Angle Region 19

Figure 2.1 : Relevant Anatomical Features of the Mandible 22

Figure 2.2 : C type Mandible Plate 24

Figure 3.1 : SolidWorks Software User Interface 34

Figure 3.2 : AutoDesk Algor User Interface 35

Figure 3.3 : L Type Mandible Plate and Mandible Assembly (Front View) 36

Figure 3.4 : L Type Mandible Design in 1st Stage of Designing 37

Figure 3.5 : Final L Type Mandible Plate 37

Figure 3.6 : Initial Stage of Designing of Lower Part of Mandibular Bone 38

Figure 3.7 : Lower Part Of Mandibular Bone 38

Figure 3.8 : 1st Stage of Bolt Design 39

Figure 3.9 : Bolt Model Used In Assembly 39

Figure 3.10 : 1st Stage of Designing Upper Part of Mandibular Bone 40

Figure 3.11 : Upper Part of Mandibular Bone 40

Figure 3.12 : Mandibular Plate and Mandible Assembly 41

Figure 3.13 : Von Mises Stress Distribution in Mandible Assembly 43 43

Figure 3.14 : Maximum Stress Area in Mandible Plate 44


viii

Figure 3.15 : Von Mises Stress Distribution in Mandible 44 44

Figure 3.16 : Von Mises Stress Distribution in Mandibular Plate Assembly 45 45

Figure 3.17 : Von Mises Strain Distribution in the Mandibular Bone 46 46

Figure 3.18 : Von Mises Strain Distribution in Mandible Plate 46

Figure 3.19 : H Type Mandible Plate and Mandible Assembly (Front View) 47

Figure 3.20 : H Type Mandible Design in 1st Stage of Designing 48

Figure 3.21 : H Type Mandible Plate 48

Figure 3.22 : Initial Stage of Designing of Lower Part of Mandibular Bone 49 49

Figure 3.23 : Lower Part of Mandibular Bone 49

Figure 3.24 : 1st Stage of Bolt Design 50

Figure 3.25 : Bolt Model Used In Assembly 50

Figure 3.26 : Assembly of Mandible and Mandible Plate 51

Figure 3.27 : Von Mises Stress Distribution in Mandible Assembly 53

Figure 3.28 : Maximum Stress Area in Mandible Plate 53

Figure 3.29 : Von Mises Stress Distribution in Mandibular Bone 54

Figure 3.30 : Von Mises Strain Distribution in Mandibular bone 54

Figure 3.31 : Von Mises Strain Distribution in the Mandible Plate Assemble 55

Figure 3.32 : Von Mises Strain Distribution in Mandible Plate 55


ix

LIST OF TABLES

Table 1 - Properties Of Mandible Bones ........................................................................... ..28

Table 2 - Material Properties of Titanium ............................................................................21

Table 3 - Distribution of Different Types of Elements L Plate ............................................42

Table 4 - Distribution of Different Types of Elements ........................................................52

CHAPTER 1. INTRODUCTION

Page | 1

Chapter 1: Introduction

1.1 Mandibular Anatomy

The mandible or inferior maxillary bone is the strongest largest and lowest bone in the face.

It holds the lower teeth in place and forms the lower jaw.

The mandible has a central functional and an aesthetic role. A loss of mandibular

continuity occurs mainly due to trauma tumour or inflammation which may lead to airways

reduction poor swallowing failure to retain saliva impairment of speech and aesthetic

disfigurement [1]. Surgery is generally required for severe fractures to align and

immobilize the bone so it can heal. Symptoms include pain in the face or jaw with inability

to close your mouth and difficulty in speaking jaw may protrude forward.

The mandible is ossified in the fibrous membrane which covers the outer surfaces of

Meckel’s cartilages. These cartilages form the cartilaginous bar of the mandibular arch and

they are two in number a right and a left. Their proximal or cranial ends are connected with

the ear capsules and their distal extremities are joined to one another at the symphysis by

mesodermal tissue. They run forward immediately below the condyles and then bending

downward. They lie in a groove near the lower border of the bone and they incline upward

to the symphysis in front of the canine tooth.

From the proximal end of each cartilage the malleus and incus two of the bones of the

middle ear are developed and the next succeeding portion as far as the lingula is replaced

by fibrous tissue which persists to form the sphenomandibular ligament. Between the

lingula and the canine tooth the cartilage disappears while the portion of it below and

behind the incisor teeth becomes ossified and incorporated with this part of the mandible.

Ossification takes place in the membrane covering the outer surface of the ventral end of

Meckel’s cartilage and each half of the bone is formed from a single centre which

appears near the mental foramen about the sixth week of fetal life.


Page | 2

By the tenth week the portion of Meckel’s cartilage which lies below and behind the

incisor teeth is surrounded and invaded by the membrane bone.

Somewhat later accessory nuclei of cartilage make their appearance viz a wedge-shaped

nucleus in the condyloid process and extending downward through the ramus a small

strip along the anterior border of the coronoid process and smaller nuclei in the front part

of both alveolar walls and along the front of the lower border of the bone.

These accessory nuclei possess no separate ossific centres but are invaded by the

surrounding membrane bone and undergo absorption. The inner alveolar border usually

described as arising from a separate ossific center (splenial center) is formed in the

human mandible by an ingrowth from the main mass of the bone. At birth the bone

consists of two parts united by a fibrous symphysis in which ossification takes place

during the first year.

The foregoing description of the ossification of the mandible is based on the researches

of Low and Fawcett and differs somewhat from that usually given.

Figure 1. 1 : Human Mandible [2]

http://en.wikipedia.org/wiki/File:Panoramicfilm.JPG


Page | 3

A panoramic radiographic reveals the mandible including the heads and necks of

the mandibular condyles the coronoid processes of the mandible.

Inferior alveolar nerve branch of the mandibular division of Trigeminal (V) nerve enters

the mandibular foramen and runs forward in the mandibular canal supplying sensation to

the teeth. At the mental foramen the nerve divides into two terminal branches: incisive and

mental nerves.

The incisive nerve runs forward in the mandible and supplies the anterior teeth. The mental

nerve exits the mental foramen and supplies sensation to the lower lip.

Rarely a bifid inferior alveolar nerve may be present in which case a second mandibular

foramen more inferiorly placed exists and can be detected by noting a doubled mandibular

canal on a radiograph.

1.1.1 Features

The mineral content of alveolar bone is mostly calcium hydroxyapatite which is similar to

that found in higher percentages in both enamel and dentin but is most similar to the levels

in cementum (50%). Like all bone mature alveolar bone is by weight 60% mineralized or

inorganic material 25% organic material and 15% water. The minerals of potassium

manganese magnesium silica iron zinc selenium boron phosphorus sulphur chromium and

others are also present but in smaller amounts. It is important to note that alveolar bone is

more easily remodelled than cementum thus allowing orthodontic tooth movement. When

viewing a stained histological section the remodelled alveolar bone shows arrest lines and

reversal lines as does all bone tissue.

1.1.2 Structure

On the maxillae the alveolar process is a ridge on the inferior surface and on

the mandible it is a ridge on the superior surface. It makes up the thickest part of the

maxillae.

The alveolar process contains a region of compact bone adjacent to the periodontal

ligament (PDL) which is called the lamina dura when viewed on radiographs. It is this part

which is attached to the cementum of the roots by the periodontal ligament.

http://en.wikipedia.org/wiki/Mandibular_condyles

http://en.wikipedia.org/wiki/Coronoid_process_of_the_mandible

http://en.wikipedia.org/wiki/Inferior_alveolar_nerve

http://en.wikipedia.org/wiki/Hydroxyapatite

http://en.wikipedia.org/wiki/Maxilla

http://en.wikipedia.org/wiki/Human_mandible

http://en.wikipedia.org/wiki/Periodontal_ligament

http://en.wikipedia.org/wiki/Periodontal_ligament

http://en.wikipedia.org/wiki/Lamina_dura


Page | 4

It is uniformly radiopaque (or lighter). Integrity of the lamina dura is important when

studying radiographs for pathological lesions. The alveolar bone or process is divided into

the alveolar bone proper and the supporting alveolar bone.

Microscopically both the alveolar bone proper and the supporting alveolar bone have the

same components: fibres cells intercellular substances nerves blood vessels and lymphatics.

The alveolar bone proper is the lining of the tooth socket or alveolus (plural alveoli).

Although the alveolar bone proper is composed of compact bone it may be called the

cribriform plate because it contains numerous holes where Volkmann canals pass from the

alveolar bone into the PDL.

The alveolar bone proper is also called bundle bone because sharper fibres a part of the

fibre of the PDL are inserted here. Similar to those of the cemented surface sharper fibre in

alveolar bone proper are each inserted at 90 degrees or at a right angle but are fewer in

number although thicker in diameter than those present in cementum. As in cellular

cementum sharper fibres in bone are generally mineralized only partially at their periphery.

The alveolar crest is the most cervical rim of the alveolar bone proper. In a healthy situation

the alveolar crest is slightly apical to the cement enamel junction (CEJ) by approximately

1.5 to 2 mm. The alveolar crests of neighbouring teeth are also uniform in height along the

jaw in healthy situation.

The supporting alveolar bone consists of both cortical bone and trabecular bone. The

cortical bone or cortical plates consists of plates of compact bone on the facial and lingual

surfaces of the alveolar bone. These cortical plates are usually about 1.5 to 3 mm thick over

posterior teeth but the thickness is highly variable around anterior teeth. The trabecular

bone consists of cancellous bone that is located between the alveolar bone proper and the

plates of cortical bone. The alveolar bone between two neighbouring teeth is the interdental

septum (or interdental bone).

http://en.wikipedia.org/wiki/Alveolus

http://en.wikipedia.org/wiki/Compact_bone

http://en.wikipedia.org/wiki/Sharpey_fibers

http://en.wikipedia.org/wiki/Trabecular_bone

http://en.wikipedia.org/wiki/Trabecular_bone


Page | 5

1.1.3 Malocclusion

Mandibular fracture repairs which are generally effective can sometimes suffer from a

number of complications. Some of the commonly occurring complications with ORIF

repairs of mandibular fractures are:

1. Non-union of fracture site

2. Malocclusion of the fracture site

3. Infection of the repair site

4. Nerve damage

5. Bone plate failure

Malocclusion is a significant component of patient morbidity and can result from improper

contouring of the bone plate improper placement or plate failure. A malocclusion occurs

when there is displacement of the fracture site during healing. The resulting misalignment

of the teeth can cause significant discomfort and make mastication difficult for the patient.

Figure 1.3 shows an intraoral picture of a severe malocclusion resulting from fracture.

Malocclusion is difficult for a physician to objectively assess but is easily noticed by the

patient. A malocclusion as small as 5 microns can cause discomfort leaving surgeons little

room for error during ORIF. These small disturbances in the occlusal relationship cannot

be detected by x ray or “bite paper” but can still cause significant discomfort. This

significant demand on surgeons and the bone plate they use to treat patients to perform as

expected [3] [4].

Roughly 18 % of patients who undergo treatment for a mandibular fracture suffer from

malocclusion this most often occurs in patients with fractures of the mandible or mid-facial

region. Malocclusion can be cause by improper placement of bone plates by surgeons.


Page | 6

Figure 1.2: Malocclusion [2]


Page | 7

1.3 Types of Mandible Bones and Properties

1.3.1 Cancellous Bones in Human Mandible

The cancellous bone of the mandibular condyle consists of plate-like trabeculae which are

primarily oriented vertically and anterior-posteriorly. This plate-like trabecular structure is

optimal to resist compressive and tensile deformations during loading of the

temporomandibular joint. The mechanical properties of cancellous bone are determined by

load-bearing capacities such as apparent stiffness (i.e. the stiffness of cancellous bone

measured in a standard compression test) and strength. These properties depend on the

stiffness density and microstructure and of the bone tissue.

Due to the combined variations in density and structure the stiffness of cancellous bone can

vary over a large range. This stiffness can be measured on excised bone specimens in vitro.

In addition non-destructive methods have been developed to predict the mechanical

properties of cancellous bone from its structure since the introduction of modern imaging

techniques for the characterization of three dimensional cancellous bone structure (for

example micro-computed tomography [micro-CT].

Table 1: Properties of Mandible Bone [5][6][7][8]

Young’s

Modulus

Poisons

Ratio

Tensile

Strength

(N mm)

Cortical Bone 8700 0.3 85

Cancellous Bone 100 0.3 1-13

1.3.2 Cortical bones in human mandible

The alveolar process (alveolar bone) is the thickened ridge of bone that contains the tooth

sockets (dental alveoli) on bones that hold teeth. In humans the tooth-bearing bones are

the maxillae and the mandible.

http://en.wikipedia.org/wiki/Bone

http://en.wikipedia.org/wiki/Dental_alveoli

http://en.wikipedia.org/wiki/Tooth

http://en.wikipedia.org/wiki/Maxilla

http://en.wikipedia.org/wiki/Human_mandible


Page | 8

1.4 Mandibular Fractures

One fifth of facial injuries occurring involve mandibular fractures. Mandibular fractures are

often accompanied by a twin fracture on the contralateral (opposite) side. The mandible

may be dislocated to the front (anteriorly) and downwards (inferiorly) but very rarely

posteriorly (backwards).

Figure 1.3: Percentage Share of Various Causes of Mandibular Fracture

If strength is defined as the maximum resultant bending stress prior to fracture in the bone

then the strength of the mandible when loaded on the lateral face is roughly 18 % of that

when loaded as in mastication. Thus the mandible is very prone to fractures when loaded

laterally.

Motor Vehicle Accident

40%

Assault 40%

Fall 10%

Sports 5%

Others 5%


Page | 9

Figure 1.4: Cross Sectional View of Mandible [2]

A study of the cross sectional geometry of the mandible can help to unfold why this bone is

susceptible to fracture. During mastication forces are being applied to the superior face of

the bone through teeth at the alveolar process. However if a person is falls assaulted etc

forces are usually applied along the lateral face of the jaw. Figure 1.5 shows a typical cross

section view the mandible.

Figure 1.5: Location Of Mandibular Fractures [9]


Page | 10

1.5 Imaging

1.5.1 Panoramic radiography

Panoramic radiographs are tomograms which show a flat image of the mandible and where

the mandible is in the focal trough. Fractures are easier to spot leading to an accuracy

similar to CT except in the condyle region because the curve of the mandible appears in a

2-dimensional image. In addition mal-aligned broken or missing teeth can often be

appreciated on a panoramic image which is frequently lost in plain films. Medial/lateral

displacement of the fracture segments and especially the condyle are difficult to gauge so

the view is sometimes augmented with plain film radiography or computed tomography for

more complex mandible fractures.

1.5.2 Computed tomography

Computed tomography is the most sensitive and specific of the imaging techniques. The

facial bones can be visualized as slices through the skeletal in either the axial coronal or

sagittal planes. Images can be reconstructed into a 3-dimensional view to give a better

sense of the displacement of various fragments. 3D reconstruction however can mask

smaller fractures owing to volume averaging scatter artifact and surrounding structures

simply blocking the view of underlying areas.

Research has shown that panoramic radiography and computed tomography similar in their

diagnostic accuracy for mandible fractures and both of them are more accurate than plain

film radiograph. The indications vary by region to use CT for mandible fracture but it does

not seem to add to diagnosis or treatment planning except for comminuted oravulsive type

fractures although there is better clinician agreement on the location and absence of

fractures with CT compared to panoramic radiography.

1.5.3 Plain film radiography

Traditionally plain films of the mandible would be exposed but had lower sensitivity and

specificity owing to overlap of structures. Views included AP (for parasymphsis) lateral

oblique (body ramus angle coronoid process) and Towne's (condyle) views.

http://en.wikipedia.org/wiki/Panoramic_radiograph

http://en.wikipedia.org/wiki/Computed_tomography

http://en.wikipedia.org/wiki/Computed_tomography

http://en.wikipedia.org/wiki/Anatomical_directions

http://en.wikipedia.org/wiki/Commonly_used_terms_of_relationship_and_comparison_in_dentistry

http://en.wikipedia.org/wiki/Sagittal


Page | 11

1.6 Classification

1.6.1 On basis of the Location of Fracture

This is the most useful classification because both the treatment and also signs &

symptoms are dependent on the location of the fracture. The mandible is usually divided

for the purpose of describing the location of a fracture into the following zones: condylar

coronoid process ramus angle of mandible body (molar and premolar areas) parasymphysis

and symphysis.

1.6.1.1 Alveolar

This type of fracture involves the alveolus also termed the alveolar process of the mandible.

1.6.1.2 Condylar

Condylar fractures are classified by location compared to the capsule of ligaments that hold

the temporomandibular joint ( intracapsular or extracapsular ) dislocation (whether or not

the condylar head has come out of the socket (glenoid fossa) as the muscles ( lateral

pterygoid ) tend to pull the condyle anterior andmedial and neck of the condyle fractures.

Examples: extracapsular non-displaced neck fracture. Pediatric condylar fractures have

special protocols for management.

1.6.1.3 Coronoid

Coronoid process is rare to be broken in isolation as the mandible lies deep to many

structures including the zygomatic complex (ZMC). It usually occurs with other

mandibular fractures or with fracture of the zygomatic complex or arch. Isolated fractures

of the coronoid process should be viewed with suspicion and fracture of the ZMC should

be ruled out.

1.6.1.4 Ramus

Ramus fractures are said to involve a region inferiorly bounded by an oblique line

extending from the lower third molar (wisdom tooth) region to the posteroinferior

attachment of the masseter muscle and which could not be better classified as either

condylar or coronoid fractures.

http://en.wikipedia.org/wiki/Alveolus

http://en.wikipedia.org/wiki/Temporomandibular_joint

http://en.wikipedia.org/wiki/Glenoid_cavity

http://en.wikipedia.org/wiki/Lateral_pterygoid

http://en.wikipedia.org/wiki/Lateral_pterygoid

http://en.wikipedia.org/wiki/Anterior

http://en.wikipedia.org/wiki/Anatomical_terms_of_location#Left_and_right_.28lateral.29.2C_and_medial

http://en.wikipedia.org/wiki/Coronoid_process_of_the_mandible

http://en.wikipedia.org/wiki/Zygomatic_process_of_temporal_bone

http://en.wikipedia.org/wiki/Tripod_fracture

http://en.wikipedia.org/wiki/Zygomatic_arch

http://en.wikipedia.org/wiki/Third_molar


Page | 12

1.6.1.5 Angle

The angle of the mandible refers to the angle created by the arrangement of the body of the

mandible and the ramus. Those that fracture involving a triangular region bounded by the

anterior border of masseter muscle and an oblique line extending from the lower third

molar (wisdom tooth) region to the postero-inferior attachment of the masseter muscle are

defined as angle fractures.

1.6.1.6 Body

Fractures of the mandibular body are defined as those that involve a region bounded

anteriorly by the parasymphysis (defined as a vertical line just distal to the canine tooth and

posteriorly by the anterior border of the masseter muscle).

1.6.1.7 Parasymphysis

Parasymphyseal fractures are defined as mandibular fractures that involve a region

bounded bilaterally by vertical lines just distal to the canine tooth.

1.6.1.8 Symphysis

Symphyseal fractures are linear fractures that run in the midline of the mandible (the

symphysis).

1.6.2 On the Basis of Type of Fracture

Mandibular fractures are also classified according to categories that describe the condition

of the bone fragments at the fracture site and also the presence of communication with the

external environment.

1.6.2.1 Greenstick

Greenstick fractures typically occur only in children as it is incomplete fractures of flexible

bone which is present in children. This type of fracture generally has limited mobility.

1.6.2.2 Simple

A simple fracture describes a complete transection of the bone with minimal fragmentation

at the fracture site.

http://en.wikipedia.org/wiki/Masseter_muscle



http://en.wikipedia.org/wiki/Canine_tooth

http://en.wikipedia.org/wiki/Greenstick_fracture


Page | 13

1.6.2.3 Comminuted

The opposite of a simple fracture is a comminuted fracture in this type the bone has been

shattered into fragments or secondary fractures have developed along the main fracture

lines. Comminuted fractures will frequently be caused by high velocity injuries (e.g. those

caused by bullets improvised explosive devices etc.).

1.6.2.4 Compound

A compound fracture communicates with the external environment. The communication in

the case of mandibular fractures may occur through the skin of the face or with the oral

cavity. Mandibular fractures involving the tooth-bearing portion of the jaw are by

definition compound fractures because there is at least a communication via the periodontal

ligament with the oral cavity and with more displaced fractures there may be frank tearing

of the gingival and alveolar mucosa.

1.6.3 On the Basis of Involvement of Dentition

Whether the fracture in the tooth bearing portion of the mandible it is dentate or it is

edentulous the treatment will be affected. Wiring of the teeth helps stabilize the fracture

(either during placement of osteosynthesis or as a treatment by itself) so the lack of teeth

will guide treatment.

When an edentulous mandible (no teeth) is less than 1 cm in height (as measured

on panoramic radiograph or CT scan) addition risks apply because the blood flowing from

the marrow (endosseous) is minimal and the healing bone must rely on blood supply from

the periosteum surrounding the bone. If a fracture occurs in a child with mixed

dentition different treatment protocols are needed.

Other fractures of the body are classified as open or closed. Because fractures that involve

the teeth by definition communicate with the mouth this distinction is largely lost in

mandible fractures. Closed fractures are generally Condylar ramus and coronoid process

whereas angle body and parasymphsis fractures are open.

http://en.wikipedia.org/wiki/Improvised_explosive_devices

http://en.wikipedia.org/wiki/Alveolar_mucosa

http://en.wikipedia.org/wiki/Osteosynthesis

http://en.wikipedia.org/wiki/Panoramic_radiograph

http://en.wikipedia.org/wiki/CT_scan

http://en.wikipedia.org/wiki/Periosteum

http://en.wikipedia.org/w/index.php?title=Mixed_dentition&action=edit&redlink=1

http://en.wikipedia.org/w/index.php?title=Mixed_dentition&action=edit&redlink=1


Page | 14

Figure 1.6: Multiple Mandible Fractures of a Patient in the Right Condyle and Left

Coronoid Process [2]

1.7 Treatment of Mandibular Fractures Using Mandible Plates

Figure 1.7: Mandibular Plate on Human Mandible [9]

Reconstruction may be carried out either with an osteoplasty combined with appropriate

osteosynthesis or merely by alloplastic bridging of the defect using a reconstruction system

without bone. This alloplastic replacement of the mandible may be temporary or definitive

[2].

http://en.wikipedia.org/wiki/File:Multiple_mandible_fractures.jpg


Page | 15

Miniplateosteo synthesis according to [10] is easy to adapt and only requires an intraoral

approach. It is a standard treatment for fractures of the mandibular angle [11][12][13]. To

prevent damage to the roots of the teeth and the alveolar nerve monocortical screws are

applied. It is thought to increase stability and to prevent the postoperative development of a

gap often noticed. In miniplate osteo-synthesis a rigid plate preventing mobility between

the fragments is fixed to the lower mandibular border either using an extraoral or an

intraoral approach according to the AO guidelines [14]. The intraoral approach is used

more and more frequently. Clinical review have shown that these titanium reconstruction

plates currently used for c-type mandibular defects are subject to functional loading which

may lead to fatigue fractures of the plate. This also affects titanium screws holding the

mini-plate.

The cortical bones can also be over stressed and strained due to such loading. This results

in enlargement of the screw holes which then loosen [15] [16]. This indicates that

mechanical weakness may be present in the reconstruction system itself.

Figure 1.8: A Type of Mandible Plate [17]


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1.8 Types of Mandible Plates

1.8.1 Compression plates

Compression plates cause compression at the fracture site making primary bone healing

more likely. These plates can be bent in only two dimensions because of their design and if

they are not contoured properly they are unable to produce compression. It is important to

avoid compressing oblique fractures. They also require bi-cortical screw engagement to

produce even compression along the fracture line. This necessitates their placement at the

inferior border to eliminate damage to the inferior alveolar neurovascular structures or the

roots of the teeth. A higher incidence of complications has been noted in fractures treated

with compression plates. Because of the relatively small cross section of bone surface in

some fractures interfragmentary compression is often not possible. At our centre surgeons

prefer non-compression plates for treating mandibular fractures.

1.8.2 Reconstruction plates

Reconstruction plates are recommended for comminuted fractures and also for bridging

continuity gaps. These plates are rigid and have corresponding screws with a diameter of

2.3–3.0 mm. Reconstruction plates can be adapted to the underlying bone and contoured in

three dimensions.

A problem that may be associated with conventional reconstruction plates is loosening of

the screws during the healing process leading to instability of the fracture.

Figure 1.9: Reconstruction Plate [18]


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1.8.3 Miniplates

These plates have been shown to be effective in treating mandibular fractures. Typically a

superior and inferior plate is required for adequate fixation. An exception to this is in the

mandibular angle region where a superior border plate placed at the point of maximal

tension is sufficient. An advantage of these plates is that they are stable enough to obviate

the need for maxillomandibular fixation and have a very low profile. They are less likely to

be palpable which reduces the need for subsequent plate removal.

Typically screws are placed monocortically but may be placed bicortically when positioned

along the inferior border of the mandible. A minimum of two screws should be placed in

each osseous segment. Smaller incisions and less soft-tissue reflections are required with

these plates when compared to larger plates and they can be placed from an intraoral

approach thus eliminating an external scar. Because these plates are less rigid than

reconstruction plates their use in treating comminuted fractures should be avoided.

A study at our centre evaluated the efficacy of 2.0-mm locking miniplate system versus

2.0-mm nonlocking miniplate system for mandibular fracture and concluded that both

miniplate system present similar short-term complication rates.

1.8.4 Micro miniplates

Their use for mandibular surgery is limited because of their inability to provide rigid

fixation and because they have a tendency for plate fracture during the healing process.

These plates can work well in the midface where the muscular forces are much less than

those acting on the mandible. A recent study found a 30.4% complication rate when 1.3mm

microminiplates were used to provide osteosynthesis for mandibular fractures.


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Figure 1.10: Miniplates [18]

1.8.5 Lag screw fixation

Lag screws can provide osteosynthesis of mandibular fractures. They work well in oblique

fractures and require a minimum of two screws. The lag screw engages the opposite cortex

while fitting passively in the cortex of the outer bone segment. This can be accomplished

by using a true lag screw or by over drilling the proximal cortex. This causes compression

of the osseous segments and provides the greatest rigidity of all fixation techniques. The

proximal cortex should be countersunk to distribute the compressive forces over a broader

area and avoid micro fractures.

The anatomy of the symphysis region of the mandible lends itself to use of lag screws in a

different technique. The lag screws can be placed through the opposing cortices between

the mental foramen and inferior to the teeth.

1.8.6 Bioresorbable plates

Bioresorbable plates are manufactured from varying amounts of materials including poly‐

dioxanone (PDS) polyglycolic acid and polylactic acid. It has been shown that the breakage

of a poly-L-lactic acid (PLLA) plate occurred at 50% of the yield strength required to break

a miniplate. Complications associated with these plates include inflammation and foreign

body type reactions.


Page | 19

Laughlin et al. showed in their study that resorbable plates are equal to the performance of

titanium 2-mm plates regarding healing of the fracture with bone union and restoration of

function. We are also using resorbable plates for routine treatment of mandibular fracture.

Figure 1.11: ORIF Using a Resorbable Plate at the Angle Region. [18]

The common complication which we encountered during their use was screw head fracture

during tightening. Consideration may be given for use in paediatric patients with the under‐

standing of the possible complications.

1.8.7 Three-dimensional miniplates

These miniplates are based on the principle that when a geometrically closed quadrangular

plate is secured with bone screws it creates stability in three dimensions. The smallest

structural component of a 3-D plate is an open cube or a square stone.

Clinical results and biomechanical investigations in a study have shown a good stability of

the 3-D plates in the osteosynthesis of mandibular fractures without major complications.

The thin 1.0 mm connecting arms of the plate allow easy adaptation to the bone without

distortion. The free areas between the arms permit good blood supply to the bone.

A study conducted at our centre showed that there is no major difference in terms of

treatment outcome between conventional and 3-dimensional miniplates and both are

equally effective in managing mandibular fracture.

We believe 3- D miniplates provide good stability and operative time is less because of

simultaneous stabilization at both superior and inferior borders.


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1.8.8 Locking reconstruction plates

In 1987 Raveh et al. introduced the titanium hollow-screw osteointegrated reconstruction

plate (THORP). This system achieves stability between the screw and plate by insertion of

an expansion screw into the head of the bone screw. This causes expansion of the screw

flanges and locks them against the wall of the hole in the bone plate.

Later Herford and Ellis described the use of locking reconstruction bone plate/screw

system for mandibular surgery. This system simplified the locking mechanism between the

plate and the screw (Locking Reconstruction Plate Synthes Maxillofacial Paoli PA) by

engaging the threads of the head of the screw with the threads in the reconstruction plate

thus eliminating the need for expansion screws. Locking plate/screw systems offer

advantages over conventional reconstruction plates.

Advantages of the locking system are the ease of plate adaptation, enhanced stability

without transmitting excessive pressure to the underlying bone, leading to less impairment

of blood supply. The minilocking- system (UniLock 2.0, Synthes, Oberndorf, Switzerland)

developed by the Albert-Ludwigs University of Freiburg in cooperation with the AO/ASIF

Institute (Davos, Switzerland) was evaluated in an in-vitro study by Gutwald and co-

workers and was shown to provide superior accuracy in bone reduction and stability when

compared to conventional miniplates

Typically screws are placed monocortically but may be placed bicortically when positioned

along the inferior border of the mandible. A minimum of two screws should be placed in

each osseous segment. Smaller incisions and less soft-tissue reflections are required with

these plates when compared to larger plates and they can be placed from an intraoral

approach thus eliminating an external scar. Because these plates are less rigid than

reconstruction plates their use in treating comminuted fractures should be avoided.


Page | 21

1.9 Material Properties of Mandible Plate Titanium Ti-6Al-4V (Grade 5)

In addition to this finite elements also take friction into consideration. For an idealized

situation the behaviour of the materials involved was taken as isotropic homogeneous and

linearly elastic. Titanium was taken as material for the reconstruction plate and the screws.

Table 2: Material Properties of Titanium [5] [6][7][8]

Property Value

Modulus of elasticity 114000 𝑁/𝑚𝑚2

Poisson’s ratio 0.33

Shear modulus of elasticity 44000 𝑁/𝑚𝑚2

Thermal coefficient of expansion 8.6 e-006 1/C

CHAPTER 2. LITRATURE REVIEW

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Chapter 2: Literature Review

2.1 Introduction

This chapter will give an insight of the numerous studies that have been conducted on the

treatment of mandibular defects and analysis of mandible plates ranging from

experimental analysis to the computer aided finite element analysis.

2.1.1 Mandibular bone

The mandible or inferior maxillary bone is the name of the lower jaw. It has central

functional and aesthetic role. Adult humans normally have 16 mandibular teeth and 16

maxillary teeth. Mastication (chewing) and speech are principal functions of jaw activity.

Males generally have squarer larger and stronger mandibles than females. The mental

protuberance is more pronounced in males but can be visualized and palpated in females.

The symphysis which happens more in male cannot be not fully fused leaving an

indentation.

Figure 2.1: Relevant Anatomical Features of the Mandible [19]


Page | 23

The mandible consists of the following parts (illustrated in the schematic shown in Figure

(2.1) :

A curved horizontal portion.

Two perpendicular parts the rami or ramus for each one unite with the ends of the

body nearly at right angles. The angle formed at this junction is called gonial angle.

Alveolar process is the tooth bearing area of the mandible (upper part of the body

of the mandible)

Condyle superior (upper) and posterior projection from the ramus which makes the

temporomandibular joint with the temporal bone

Coronoid process superior and anterior projection from the ramus. This provides

attachment to the temporalis muscle.

2.1.2 Classification of the Fractures on Basis of Displacement

The extent to which the segments are separated. When the separation is very large it is

more difficult to bring them back together (approximate the segments).

2.1.3 Classification of the Fractures on Basis of Favourability

For angle and posterior body fractures when the angle of the fracture line is angled back

(more posterior at the top of the jaw and more anterior at the bottom of the jaw) the

muscles tend to bring the fracture segments together. This is called favourable. When the

angle of the fractures is pointing to the front it is unfavourable.

2.1.4 Classification of the Fractures on Basis of Age of the fracture

Whether treated immediately or days later the mandible fractures have similar

complication rates while older fractures are believed to have higher non-union and

infection rates although the data on this makes it difficult to draw firm conclusions.

2.2 Mandible Plate

Reconstruction plates are also used to avoid dislocation of the mandibular due to scars

which would be a major obstacle to later restoration of mastication [20].

http://en.wikipedia.org/wiki/Posterior_(anatomy)

http://en.wikipedia.org/wiki/Anterior


Page | 24

Reconstruction may be carried out either with an osteoplasty combined with appropriate

osteosynthesis or merely by alloplastic bridging of the defect using a reconstruction

system without bone.

Figure 2.2: C type Mandible Plate [19]

2.3 Literature on Mandibular Plate

Kay-Uwe Feller’s [21] computed the load on different osteosynthesis plates in a simplified

model using finite element analysis and to find out whether miniplates were sufficiently

stable for application at the mandibular angle. A computation model using finite elements

was established in order to compute mechanical stress occurring in osteosynthesis plates

used for fixation of fractures of the mandibular angle. In the second part of this study the

data from all in-patients treated for fracture of the mandibular angle were evaluated

retrospectively. It may be concluded that a single miniplate is sufficiently stable to

withstand the reduced masticatory forces in most cases. In patients with poor compliance

and in comminuted fractures it is necessary to consider the use of a stronger osteosynthesis

method. In such cases a stronger plate comparable to the 2.3mm module plate is

recommended.


Page | 25

Robert M laugblin [22] evaluated that the resorbable plates are equal to the performance of

titanium 2 mm plates regarding healing of the fracture with bone union and restoration of

function.specific end points were compared with literature norms for titanium 2 mm

miniplate rigid fixation.theresorbable plates and screws used consisted of an amorphous

injection molded co polymer of L-lactide/D-lactide/trimethylenecarbonate.theresorbable

plates provide the proper strength when necessary and then harmlessly degrade over time

until the load can be safely transferred to the healed bone

Martta Martola (2006) [23] investigated the fracture of titanium plates used for mandibular

reconstruction following ablative tumour surgery. Sixteen titanium reconstruction plates

from sheep mandibles were examined to identify reasons for the plate fractures. The plates

were removed from the mandibular bone and inspected by dye penetrant examination

metallography optical microscope scanning electron microscope and energy dispersive X-

ray spectrometer. Furthermore axial load fatigue tests were performed in two different

environments air and physiologic salt solution 0.9% NaCl to compare titanium behaviour

in air and the human body. The site of crack initiation was the inner curvature of the

reconstruction plate. The cracks grew in a cyclic manner under masticatory loading of the

mandible and the plate. The plate fracture occurred by means of fatigue. The results

revealed that the fatigue properties of the plates may have been impaired by the residual

stresses generated in plate bending. To make the plates function without failure the plates

should match closely with the threedimensional shape of the mandible to avoid any

bending in the operative phase.

Christophe Meyer [24] developed and tested biomechanically a new osteosynthesis plate

designed to stabilize mandibular condyle fractures. Use of a single four holeadaptation

miniplate placed vertically and parallel to the condylar axis where the bone is at its

thickest. Using this technique the plate is put along the compressive strain lines and neither

respects the functionally stable osteosynthesis nor prevents secondary displacement. The

primary stability achieved by TCP was superior to that obtained by single plating

techniques. Trapezoidal condylar plates were able to stabilize sub-condylar fractures in

experiments described and to fulfil the biomechanically required principles of functionally

stable osteosynthesis the various sizes allow these plates to be applied to most cases.


Page | 26

Rudolf Seemann [25] evaluated the treatment of condylar process fractures using the novel

plate. Plate was designed according to finite element calculations in order to optimize

mechanical stability and stiffness. The results revealed that the mechanical stability of the

novel condylar process plate as expected in a finite element model corresponds well with

the clinical outcome because no fractures with plate occurred. This showed that the modus

condylar process plate is sufficient for osteosynthesis of condylar plates.

T. F. Renton [26] studied 205 consecutive patients at the Maxillofacial Unit of The Royal

Melbourne Hospital to assess if adherence to Champy’s principles in placement of

miniplates in mandibular fractures minimises morbidity. 205 well documented cases of

mandibular fractures treated with internal fixation January 1985 to April 1990 were

studied. Outcome was measured by preoperative variables (age gender mechanism of

fracture site and number of fractures nerve function associated injuries and treatment

delay) and postoperative variables (duration of admission duration of intermaxillary

fixation (IMF) malocclusion infection dehiscence union removal of fixation and nerve

function which were assessed and compared. The results show that the preoperative

variables were statistically similar in all groups.

The postoperative variables indicated a statistically higher complication rate for the

transosseous wire group compared with the miniplate groups and morbidity was reduced

in the group following Champy’s principles. The morbidity rates in this study compare

favourably with other studies even though the patients in this study had a much higher

incidence of multiple fractures. Titanium miniplates appear as effective as miniplates

constructed of other materials used in previous studies especially when Champy’s

principles are followed.

K U Feller [27] investigated the combination of microplate and miniplates for

osteosynthesis of mandibular fractures. Recently metal deposition in the direct

neighbourhood of osteosynthesis plates made of titanium or even in peripheral organs have

been reported.


Page | 27

Rudolf Seemann (2009) [28] compared locking and non-locking plates in the treatment of

mandibular condyle fractures. Locking plate’s screws do not migrate into soft tissue when

osteosynthesis fails. Screw loosening was observed only in the non lockingplates. Non

atomic reduction especially occurring with transoral approach should be avoided. The

present study provides the provides the evidence that transoral approach can be regarded to

be a safe surgical technique compaired to other mandibular neck plates like Medartis TCP.

The medartistrilock locking and medartis modus nonlocking condylar plates showed

equivalent complication rates.

Roy E. Nicholson (1997) [29] evaluated and compared rates and timing of exposure of

alloplastic mandibular plates by plate type and tissue reconstruction technique. There was

no significant difference in the exposure rates of different plate types or methods of

reconstruction. The titanium hollow osseointegrating reconstruction plate had a similar

exposure rate compared with the other plates. Size and site of the defect were the only

significant predictors of plate exposure. Radiotherapy and postoperative complications did

not affect the rate of exposure. Extraoral plate exposure occurs less commonly and later in

the postoperative period than intraoral exposure suggesting different causes. Plate type and

type of flap reconstruction do not affect the rate of exposure. This may reflect long follow-

up.

2.4 Literature on Human Mandible

Uckan.E [29] developed two and three dimensional finite element models (FEM) to

simulate the behaviour of a fractured jaw bone and the fixation materials. Mini-plates with

various material properties geometric properties and screw combinations were considered.

Their effects on the variation of maximum stress contours were investigated.

The geometric and material properties of the plate screw and bone were seen to play

important roles in effecting the relative displacement at the fractured surface and the

spatial variation of the maximum stress across the jaw bone. Softer materials yielded less

stress concentrations around the screws while increasing the relative deformation at the

fractured surface and stiffer ones caused higher stress concentrations while decreasing the


Page | 28

displacements. Results were also seen to be dependent on the loading and the need for the

use of patient specific 3D solutions was emphasized.

André Correia [30] presented a methodological procedure to obtain the geometric and

discrete models of a human mandible for numerical simulation of the biomechanical

behaviour of a partially edentulous mandible as a function of cancellous bone density. A

3D finite element method was used to assess the model of partially edentulous mandible

Kennedy Class I with dental implants placed at the region of teeth 33 and 43. The

geometric solid model was built from CT-scan images and prototyping. In the discrete

model a parametric analysis was performed to analyse the influence of cancellous bone

density (25 % 50 % and 75 %) on the development of mandibular stress and strain during

simulation of masticatory forces in the anterior region. Maximum Von Mises stress and

equivalent strain values in cancellous bone were found close to the loading area

(masticatory forces). The peak stress and strain values occurred in the mandibular anterior

region and for the same masticatory force the equivalent stresses increased with bone

density.

T.M.G.J. van Eriden [31] investigated the biomechanical behaviour of the mandibular

bone tissue and of the mandibular bone as a whole in response to external loading. A

survey is given of the determinants of mandibular stiffness and strength including the

mechanical properties and distribution of bone tissue and the size and shape of the

mandible. Mandibular deformations stresses and strains that occur during static biting and

chewing are reviewed. During biting and the power stroke of mastication a combination of

sagittal bending corpus rotation and transverse bending occurs. The result is a complex

pattern of stresses and strains (compressive tensile shear torsional) in the mandible. To be

able to resist forces and bending and torsional moments not only the material properties of

the mandible but also its geometrical design is of importance. This is reflected by variables

like polar and maximum and minimum moments of inertia and the relative amount and

distribution of bone tissue. In the longitudinal direction the mandible is stiffer than in

transverse directions and the vertical cross-sectional dimension of the mandible is larger

than its transverse dimension.


Page | 29

These features enhance the resistance of the mandible to the relatively large vertical shear

forces and bending moments that come into play in the sagittal plane.

A. Ziębowicz [32] performed biomechanical analysis of miniplate osteosynthesis of

mandible fracture. Clinical observations allowed ascertaining that the upper limit of

dislocations of the blocks of a broken mandible in the gap of break under the applied

forces should not exceed 1 mm. Analysis of the state of dislocations showed that

maximum dislocations in two miniplate osteosynthesis systems made of steel and titanium

did not exceeded: 0043 mm and 0051 mm respectively. So the bone fragment

displacements did not exceed the given value of 1 mm which is useful for initiating

electromechanical effects and the generation of flow. The two-miniplate stabilizing system

ensures an appropriate stabilization of the bone fragments because the pressure of

mandible fragments is useful for an appropriate osteosynthesis. The findings of this work

suggest that the finite element analysis can play an important role in the study of the

mechanics of mandibular fractures and may be useful in evaluation of other plate

constructs

Yener Oguz (2009) [33] evaluated the mechanical stresses over the bone and hardware

after sagittal split ramus osteotomy (SRRO) fixed with standard titanium or locking plates

/ screws using finite element analysis. The model was fixed with either 2.0-mm titanium

conventional miniplate / screw or 2.0-mm titanium locking miniplate / screw system and

oblique 200 N bite force was applied. The value of von misses stresses in cortical layer of

the distal segment using locking plate system was higher. However in the cortical layer of

the proximal segment the stresses were higher at the locking plate system.in the spongiosa

layers of both segments stresses were higher with the conventional plate system. Locking

miniplate / screw system spreads the load over the plate and screws and diminishes the

amount of force transferred to each unit.

A.R. Akisanya [34] investigated the validity and limitations of the H-based criterion for

predicting the onset of fracture in bi-material joints with at least one elastic-plastic solid is

examined. The evolution of the plastic deformation at the interface corner is determined

and the solution is compared with the zone of dominance of the elastic H-field.


Page | 30

Asymptotic and elastic/plastic analyses of a double-wedged bi-material joint geometry

have been carried out and the magnitude of the interface corner stress intensity factor was

determined.

The validity of a failure criterion based on a critical value of the stress intensity factor has

been examined. A relationship was obtained between a characteristic length scale of the

joint geometry uniaxial yield strength of the joint materials and the critical intensity factor

Hc. The analysis has focused on one joint geometry the double-wedged bi-material joint

and wedge depth-to-half width ratio.

Another study was published in 1982 by Burkett and Bernstein [35] the research involved

22 men and 23 women divided into three groups (MORA devices placebo devices and no

device) of 15 subjects. Twelve tests including isometric and isokinetic measurements were

conducted three times each without a device. Twenty to 40 minutes after baseline testing

was complete all of the tests were repeated using a MORA device a placebo or no device

according to group assignment. Although the results reveal increases in strength while

using the MORA compared to the control and placebo groups for right and left grip

strength isokinetic quadricep strength isokinetic hamstring strength and isometric

hamstring strength; the study claims the statistical analysis indicates no significant

improvement in strength while utilizing a MORA device.

J.I. Cawood (1985)[36] Small plate osteosynthesis was evaluated by comparing 50

successive cases of mandibular fracture treated by this technique alone with 50 successive

cases of mandibular fracture treated by intermaxillary fixation. The plates show

considerable advantages over other forms of fixation in that they are small malleable and

easy to insert. Furthermore they achieve a high degree of stability. The rate of recovery of

normal jaw function and normal body weight is significantly greater than with

intermaxillary fixation

Jennifer Lamphier (2003) [37] compared the complications associated with open and

closed treatment of mandibular fractures in an urban teaching center over a 4-year period.

Retrospective review of mandibular fracture morbidity associated with treatment by the

oral and maxillofacial surgery service was conducted between 1996 and 2000.

http://www.sciencedirect.com/science/article/pii/0266435685900579

http://www.sciencedirect.com/science/article/pii/S0278239103001472


Page | 31

A total of 721 fractures were recorded with 594 fractures available for review.

Perioperative and postoperative complications were assessed by reviewing patient charts

operative reports and radiographs. Complications were classified by location type of

complication and treatment modality. Standard statistical tests were used to assess

differences between the groups. In an urban area with a high prevalence of poor living

conditions substance abuse and poor patient compliance the treatment of mandibular

fractures by closed reduction resulted in the least number of postoperative complications in

all anatomic regions of the mandible. The mandibular angle fracture had the highest

overall morbidity rate.

.

CHAPTER 3. FINITE ELEMENT ANALYSIS

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Chapter 3: Finite Element Analysis

3.1 Finite Element Method

FEM is a numerical technique for modelling of structures that approximates reality. The

geometric model is divided into a large number of finite elements interconnected by nodes.

This technique is called discretization.

FEM allows detailed analysis of problems where structures bend or twist and indicates the

distribution of displacements and stresses. When factors such as clamping conditions and

loading stress are known the deformations and tensions of these simple elements [37] can

be calculated at each node. Due to the mutual interlinking of the elements (the same

displacement and rotation of the nodes in all dimensions of space) the same applies to the

deformation of the overall structure. In turn ‘derived’ parameters (stresses expansions etc.)

can be calculated from [38].

FEM software provides a wide range of simulation options for controlling the complexity

of both modelling and analysis of a system. The desired level of accuracy required and

associated computational time requirements can be managed simultaneously to address

most engineering applications.

3.1.1 Basic Concept

The subdivision of a whole domain into simpler parts has several advantages:

Accurate representation of complex geometry

Inclusion of dissimilar material properties

Easy representation of the total solution

Capture of local effects.


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A typical work out of the method involves dividing the domain of the problem into a

collection of subdomains with each subdomain represented by a set of element equations to

the original problem followed by systematically recombining all sets of element equations

into a global system of equations for the final calculation. The global system of equations

has known solution techniques and can be calculated from the initial values of the original

problem to obtain a numerical answer.

3.1.2 Benefits of Finite Element Analysis include

Ability to accurately assess the performance & safety of any design prior to manufacture

Identify and resolve design faults early

Minimize cost of materials & maximize product performance.

Speed up time to market

Makes complexity possible

Accuracy

Reduce development costs

Coupled multiphysics analysis

Optimized design after running hundreds of “what-if” scenarios

Simulation driven product development

3.1.3 Applications of Finite Element Analysis

Stress Analysis (stress strain factors of safety fatigue creep etc.)

Vibration Analysis (modal harmonic random transient dynamic etc.)

Thermal Analysis (conduction convention heat transfer etc.)

Magnetic Analysis (flux lines magnetic field inductance lorentz forces etc.)

Impact & Crash Analysis (energy absorption impact time etc.)

Electric Analysis (power generation/consumption thermal losses RF etc.)

CFD (flow velocity multiphase flows etc.)

Coupled multiphysics Analysis

Optimization

http://en.wikipedia.org/wiki/Initial_value


Page | 34

3.2 Softwares Involved in the Analysis of Mandibular Plates

3.2.1 SolidWorks

SolidWorks is a solid modeller and utilizes a parametric feature-based approach to create

models and assemblies. The software is written on Parasolid-kernel.

Building a model in SOLIDWORKS usually starts with a 2D sketch (although 3D sketches

are available for power users). The sketch consists of geometry such as points lines arcs

conics (except the hyperbola) and splines. Dimensions are added to the sketch to define the

size and location of the geometry. Relations are used to define attributes such as tangency

parallelism perpendicularity and concentricity.

SOLIDWORKS files use the Microsoft Structured Storage file format. This means that

there are various files embedded within each SLDDRW (drawing files) SLDPRT (part

files) SLDASM (assembly files) file including preview bitmaps and metadata sub-files.

Various third-party tools (see COM Structured Storage) can be used to extract these sub-

files although the subfiles in many cases use proprietary binary file formats.

Figure 3.1: SolidWorks Software User Interface

http://en.wikipedia.org/wiki/Solid_modeling

http://en.wikipedia.org/wiki/Parametric_feature_based_modeler

http://en.wikipedia.org/wiki/Parasolid

http://en.wikipedia.org/wiki/Power_user

http://en.wikipedia.org/wiki/COM_Structured_Storage

http://en.wikipedia.org/wiki/COM_Structured_Storage


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3.2.2 AutoDesk Algor

AutoDesk Algor software helps engineers easily set up advanced simulations with

vibrational analysis tools including Mechanical Event Simulation (MES) Autodesk Nastran

FEA solver software multi-physics simulations multiCAD format support cloud-solving

options and composites. Typical uses include bending mechanical contact thermal

(conduction convection radiation) fluid dynamics and coupled or uncoupled multiphysics.

Autodesk Simulation’s library of the material models includes metals and alloys plastics

glass foams fabrics elastomers concrete (with rebar) soils and user defined materials.

Autodesk Simulation's element library depends on the geometry and the type of analysis

performed. It includes 8 and 4 node solid 8 and 4 node shell as well as beam and rod

elements. It is distributed in a number of different core packages to cater to specific

applications such as mechanical event simulation and computational fluid dynamics. Under

the ALGOR name the software was used by many scientists and engineers worldwide.

Figure 3.2: AutoDesk Algor User Interface

http://en.wikipedia.org/wiki/Computational_fluid_dynamics


Page | 36

3.3 Designing of L type Mandible Plate

The various parts of the mandible plate and mandibular bone assembly are designed

separately using SolidWorks 2010. Initially the L type mandible plate is designed followed

by lower part of mandibular bone and then the upper part of mandibular bone. The bolts

are designed in a separate file at the end.

After all the parts have been modelled separately they are assembled in a separate file in

SolidWorks 2010 to generate required assembled model for analysis. Finally the assembly

is imported to Autodesk Algor 2010 to perform the Stress and Strain analysis.

Figure 3.3: L Type Mandible Plate and Mandible Assembly (Front View)


Page | 37

3.3.1 Mandible Plate

The mandible plate (shown in Figure 3.5) has been prepared using extrude option

(providing the thickness to the plate) and cut extrude option (constructing groves in the

plate).

Figure 3.4: L Type Mandible Design in 1st Stage of Designing

In the first step the basic design as shown in figure below is created and then extruded 2

mm. Then the basic designed model is cut extrude to remove the unwanted area from the

mandible plate at the middle of the plate and the edges to obtain the desired model as in

Figure 3.4.

Figure 3.5: Final L Type Mandible Plate


Page | 38

3.3.2 Lower part of Mandible Bone

The lower part of mandibular bone (as shown in Figure 3.7) has been prepared using

extrude option (providing the thickness to the mandibular bone) and cut extrude option

(constructing groves for the bolts)

Dimensions: 40 mm * 20 mm * 10 mm

Groves in the mandible plate are of 4 mm diameter.

Figure 3.6: Initial Stage of Designing of Lower Part of Mandibular Bone


mm. Then the basic designed model is cut extrude 8 mm to remove the unwanted area

from the middle of the mandibular plate to obtain the desired modelled part as shown in

Figure 3.6. The circular area is extruded fix the bolts to the mandible bone.

Figure 3.7: Lower Part of Mandibular Bone


Page | 39

3.3.3 Bolt

The seven screws inserted in the bone were modelled as cylindrical pins. The screw to be

used in the mandible is prepared as shown in Figure 3.8. The bolt has a diameter of 4mm

and the length of 9 mm. The bolts in the assembly have been prepared using extrude option

(for providing the bolt design on head & providing the length to the bolt) and fillet option

(the ends).

Figure 3.8: 1st Stage of Bolt Design

In the very first step a circle of diameter 4 mm is drawn which is then extrude 8 mm. the

head of the bolt is created by first drawing a circle followed by extruding 1 mm. The head

of the bolt is extrude cut to provide the design on the top and then fillet the edges to obtain

the model as shown in Figure 3.9.

Figure 3.9: Bolt Model Used in Assembly


Page | 40

3.3.4 Upper Part of Mandible Bone

The upper part of mandibular bone has been prepared using extrude option (for providing

the thickness to the bone and the groves for the bolts) fillet option (providing the desired

shape to the edges) and the revolve option (construct the curved design at the top right end

of the bone) as shown in Figure 3.11.

Figure 3.10: 1st Stage of Designing Upper Part of Mandibular Bone

The thickness of the mandibular bone is 10mm. The basic design of the mandibular bone is

shown in Figure 3.10 which is modified to obtain the final model.

Figure 3.1: Upper Part of Mandibular Bone


Page | 41

3.3.5 Assembling of L type Mandibular Plate

Inner surface of groves on the mandible and the outer surface of the bolts are attached to

each other with the help of concentric mating. While outer surface of the mandible plate

and the inner surface of the bolts are held together by tangent mating. Inner surface of the

plate and the surface of the mandible bone have Coincident mating between them. Surfaces

1 2 3 are constrained and act as the surface boundaries as shown in figure 3.12.

Figure 3.12: Mandibular Plate and Mandible Assembly

It is already known that muscles can only transmit traction and joints can only transmit

pressure the resultants of the vertical components of the muscles responsible for closing

the jaw were assumed as loading tensions. The horizontal muscle forces acting at the joint

and thus counterbalancing each other can be neglected in the further analysis. The vertical

chewing force chosen is 135- 160 N. The higher value i.e. 160 N was chosen for the

analysis. The force is applied in the negative y direction on the upper side of the mandible

plate as shown in Figure 3.10.

2 3

1


Page | 42

3.3.6 Analysis of L type Mandible Plate

Using the sub model technique (separation and refined discretization of a segment of

interest from the overall structure) a sub model with a mandibular angle defect bridged

with a standard reconstruction plate was generated from the mandibular model (rough

model). In this way an optimum balance between accuracy and computing effort can be

attained. After virtual resection which simulates a clinically relevant situation the distal and

proximal fragments were joined with a titanium reconstruction plate. The total number of

nodes in the mandible plate assembly is 27057. The distribution of the different types of

elements used ie. Tetrahedral, pyramid, wedge and brick in the mandibular assembly is

shown in Table 4. There are total 83033 elements in the assembly.

Table 3 - Distribution of different types of elements of L Plate

Tetrahedral Pyramid Wedge Brick

Upper

mandible

9294 2367 401 1432

Lower

mandible 6584 2536 481 3432

Plate 25777 6253 1101 2238

Bolt 1 1486 604 173 895

Bolt 2 1624 611 164 968

Bolt 3 432 230 122 881

Bolt 4 1052 505 176 972

Bolt 5 1172 512 180 871

Bolt 6 2222 851 139 975

Bolt 7 1659 609 146 906

Total 51302 15078 3083 13570


Page | 43

3.3.6.1 Von Mises Stresses [ 𝑁/𝑚𝑚2 ]

The Von Mises Stress is often used in determining whether an isotropic and ductile metal

will yield when subjected to a complex loading condition. This is accomplished by

calculating the mechanical stress and comparing it to the material's yield stress which

constitutes the Von Mises Yield Criterion.

Figure 3.13: Von Mises Stress Distribution in Mandible Assembly

The von mises stress distribution in the mandible plate is shown in the Figure 3.14 and the

maximum value of stress is 1448.5 𝑁/𝑚𝑚2and minimum stress as 0.188545 𝑁/𝑚𝑚2. The

maximum and minimum value of Von Mises stresses in the assembly is 1448.5 𝑁/𝑚𝑚2

and 0.188545 𝑁/𝑚𝑚2 respectively as shown in Figure 3.13.

Von Mises stress distribution on the mandible is shown in Figure 3.15 with maximum and

minimum stress as 173.517 𝑁/𝑚𝑚2 and 0.232426 𝑁/𝑚𝑚2 respectively. The maximum

stress on the mandible is near the bolt on left extreme as shown in the Figure 3.15.


Page | 44

Figure 3.14: Maximum Stress Area in Mandible Plate

Figure 3.15: Von Mises Stress Distribution in Mandible

Max


Page | 45

3.3.6.2 Von Mises Strain

The Von Mises Strain (or Stress) is an index gained from the combinations of Principal

Stresses at any given point to determine at which points stress occurring on the x y and z

axis will cause failure. This calculation method is used for measuring stress and strain

distribution within a ductile material.

Figure 3.16: Von Mises Strain Distribution in the Mandible Plate Assembly

The von mises strain distribution in the mandible plate is shown in the Figure 3.18 and the

maximum value of strain is 0.0168992 and minimum stress as 2.1997 e-006

. The maximum

and minimum value of mechanical strain in the assembly is 0.0257 and 2.1997 e-006

respectively as shown in Figure 3.16.

Von mises strain distribution on the mandibular bone is shown in Figure 3.17 with

maximum and minimum strains 0.0257 and 3.47303 e-005

respectively.

Max


Page | 46

Figure 3.17: Von Mises Strain Distribution in Mandibular Bone

.

Figure 3.18: Von Mises Strain Distribution in Mandible Plate


Page | 47

3.4 Developing an H Type Mandible Plate

The various parts of the mandible plate and mandibular bone assembly are designed

separately using SolidWorks 2010. First the H type mandible plate is designed then the he

lower part of mandibular bone. The bolts are separately designed in a file.

After all the parts have been modelled separately the parts are assembled in a separate file

in SolidWorks. Importing the assembly to Autodesk Algor 2010 to perform the Stress and

Strain analysis.

Figure 3.19: H Type Mandible Plate and Mandible Assembly (Front View)


Page | 48

3.4.1 Mandible Plate

The mandible plate (shown in Figure 3.21) has been prepared using extrude option

(providing the thickness to the plate) and cut extrude option (constructing groves in the

plate)

Figure 3.20: H Type Mandible Design in 1st Stage of Designing


mm. Then the design is made at the top right corner of the mandible using the revolve

option. Then the basic designed model is cut extrude to remove the unwanted area from the

mandible plate at the middle of the plate and the edges to obtain the desired model as in

Figure 3.20.

Figure 3.21: H Type Mandible Plate


Page | 49

3.4.2 Mandibular Bone

The lower part of mandibular bone (as shown in figure 3.23) has been prepared using

extrude option (providing the thickness to the mandibular bone) and cut extrude option

(constructing groves for the bolts) Groves in the mandibular bone are of 4 mm diameter.

Dimensions of the mandibular bone are 40 mm * 20 mm * 10 mm

Figure 3.22: Initial Stage of Designing of Lower Part of Mandibular Bone


mm. Then the basic designed model is cut extrude 8 mm to remove the unwanted area

from the middle of the mandibular plate to obtain the desired modelled part as shown in

Figure 3.22. The circular area is extruded fix the bolts to the mandible bone.

Figure 3.23: Lower Part of Mandibular Bone


Page | 50

3.4.3 Bolt

The seven screws inserted in the bone were modelled as cylindrical pins. The screw to be

used in the mandible is prepared as shown in figure below. The bolt has a diameter of 4mm

and the length of 9 mm. The bolts in the assembly have been prepared using extrude option

(for providing the bolt design on head & providing the length to the bolt) and fillet option (

the ends).

Figure 3.24: 1st Stage of Bolt Design

In the very first step a circle of diameter 4 mm is drawn which is then extrude 8 mm. the

head of the bolt is created by first drawing a circle followed by extruding 1 mm. The head

of the bolt is extrude cut to provide the design on the top and then fillet the edges to obtain

the model as shown in Figure 3.25.

Figure 3.25: Bolt Model Used in Assembly


Page | 51

3.4.4 Assembling of H type Mandibular Plate

Inner surface of groves on the mandible and the outer surface of the bolts are attached to

each other with the help of concentric mating. While outer surface of the mandible plate

and the inner surface of the bolts are held together by tangent mating. Inner surface of the

plate and the surface of the mandible bone have Coincident mating between them. Surfaces

4 5 are constrained and act as the surface boundaries as shown in figure 3.26.

Figure 3.26: Assembly of Mandible and Mandible Plate`

It is already known that muscles can only transmit traction and joints can only transmit

pressure the resultants of the vertical components of the muscles responsible for closing

the jaw were assumed as loading tensions. The horizontal muscle forces acting at the joint

and thus counterbalancing each other can be neglected in the further analysis. The vertical

chewing force chosen is 135- 160 N. The higher value i.e. 160 N was chosen for the

analysis. The force is applied in the negative y direction on the upper side of the mandible

plate as shown in Figure 3.26.

4

5


Page | 52

3.4.5 Analysis of H type Mandible Plate

The sub model technique (separation and refined discretization of a segment of

interest from the overall structure) is used to generate sub model with a mandibular

angle defect bridged with a standard reconstruction plate from the mandibular model

(rough model). In this way an optimum balance between accuracy and computing

effort can be attained. After virtual resection which simulates a clinically relevant

situation the distal and proximal fragments were joined with a titanium reconstruction

plate. The Total number of nodes in the mandible plate assembly is 41095. The

distribution of the different types of elements used i.e. Tetrahedral Pyramid Wedge

Brick in the mandibular assembly is shown in Table 4. There are total 50990 elements

in the assembly.

Table 4 - Distribution of Different Types of Elements H Plate

Tetrahedral Pyramid Wedges Brick

Plate 17268 4750 784 2036

Mandibular

bone 7307 2995 492 4393

Bolt 1 1358 605 154 979

Bolt 2 1178 527 157 958

Bolt 3 814 343 140 698

Bolt 4 1374 597 136 947

Total 29299 9817 1863 10011

3.4.5.1 Von Mises Stress [ 𝑁/𝑚𝑚2 ]

The Von Mises stress distribution in the mandible plate is shown in the Figure 3.28. and

the maximum value of stress is 2237.24 𝑁/𝑚𝑚2and minimum stress as 0.0278873 𝑁/

𝑚𝑚2. The maximum and minimum value of mechanical stresses in the assembly is

2237.24 𝑁/𝑚𝑚2 and 0.0278873 𝑁/𝑚𝑚2respectively as shown in Figure 3.27.

Von Mises stress distribution on the mandibular is shown in Figure 3.30 with maximum

and minimum stress as 287.192 𝑁/𝑚𝑚2 and 0.319609 𝑁/𝑚𝑚2 respectively.


Page | 53

The maximum stress on the mandible is near the bolt on left extreme as shown in the

Figure 3.28 while on the mandibular bone the maximum stress is near 1st grove from the

right as depicted with red in Figure 3.29.

Figure 3.27: Von Mises Stress Distribution in Mandible Assembly

Figure 3.28: Maximum Stress Area in Mandible Plate

Max


Page | 54

Figure 3.29: Von Mises Stress Distribution in Mandibular Bone

3.4.5.2 Von Mises Strain

The mechanical strain distribution in the mandible plate is shown in the Figure 3.32 and

the maximum value of strain is 0.0168992 and minimum stress as 2.1997 e-006

. The

maximum and minimum value of mechanical strain in the assembly is 0.0257 and 2.1997

e-006

respectively as shown in Figure 3.31.

Figure 3.30: Von Mises Strain Distribution in Mandibular bone

Max


Page | 55

Von Mises strain distribution on the mandible is shown in Figure 3.30 with maximum and

minimum strains 0.0257 and 3.47303 e-005

respectively. The maximum strain area is

surrounding the 1st hole on the mandibular plate while most part of the area of the

mandible is having strain levels below the nominal values. The other area where the stress

is little above the other areas is the area surrounding the last screw.

Figure 3.31: Von Mises Strain Distribution in the Mandible Plate Assembly

Figure 3.32: Von Mises Strain Distribution in Mandible Plate

CHAPTER 5. RESULT AND DISCUSSION

`Page | 56

Chapter 4: Result and Discussion

The FEM is an important tool to conduct stress-strain investigations in the field of

biomechanical engineering and to make inferences that will enable more efficient designs

of systems.

Figure 3.13 and Figure 3.27 depicts the Von Mises stresses in the standard reconstruction

plate and the compact bone of the mandible in the region where the plate is fixed by means

of the titanium screws. The theoretical maximum stress was of magnitude 1448.5 𝑁/𝑚𝑚2

in L type plate and 2237.24 𝑁/𝑚𝑚2 in H type plate. The local stress normally will not lead

to spontaneous damage to the plate but will lead to cumulative enlargement of the drill

hole and thus to gradual loosening of the screws. In addition stresses occur in the middle of

the plate in the region of the highly notched tapering of the cross-section at a level

approximating to the tensile strength.

It is assumed that the patient executes several thousand masticatory movements within a

week a dynamic strain would be present due to the large number of changes in loading so

that there was a danger of a fatigue fracture at these points as is also confirmed by clinical

practice. The bone was also subject to extremely severe Von Mises stress in the region of

the drill-hole edge with a maximum of 173.517 𝑁/𝑚𝑚2 in L type mandible plate assembly

and 287.192 𝑁/𝑚𝑚2 in H type mandible plate assembly. The tensile strength of the

compact bone (amounting to about 85 N/mm2 as described by was exceeded by more than

twofold. Unlike metal bone can undergo some plastic deformation but only to a limited

extent. High loading stress will dissipate mechanical energy by forming micro fissures.

These microfissures reflect damage that is irreversible in the short-term. However in the

long run they do not constitute a risk as these zones undergo constant renewal by bone

remodelling. However a constant strain will lead to certain loosening of the screws in the

mandible.

CHAPTER 5. RESULT AND DISCUSSION

`Page | 57

First of all the danger that the entire osteosynthesis system will fail as a consequence of the

extremely high stresses in the postoperative phase was confirmed as already described

several times in the literature. The use of larger screw diameters is not generally possible.

On the other hand a reconstruction plate with a flat-spread design has much more

favourable stress characteristics. This could be utilized and the plate could be made thinner

so that it might be better adapted to the geometry of the jaw even prior to the operation.

Despite use of the appropriate tools the standard plate only allows limited bending.

However care must be taken that these pre-deformations do not have a negative effect on

the geometrical stability of the plate (kinking drill kinking).

The fracture of titanium reconstruction plates has earlier been studied with broken plates

from human patients. In these cases the fracture occurred by means of fatigue caused by

stress concentration. When more than three screws were used for fixation of the plate stress

concentrated in the tapped screw hole and that region was the origin of fracture.

Maxillofacial surgeons are also known to require that the surface and the volume of

‘foreign body material’ in the form of a reconstruction plate be minimized. Hence it is

appropriate to remove material from low-tension zones in further optimizing the plate

without causing the stability of the plate to suffer so that the mechanical stress again

approaches critical levels. There still remains the advantage of the large area of the

interface and thus the pronounced reduction in the tension to which the cortical bone will

be exposed. Even the tensions in the plate itself did not reach critical values.

CHAPTER 5. CONCLUSION AND FUTURE SCOPE OF WORK

`Page | 58

Chapter 5: Conclusions and Future Scope of Work

5.1 Conclusion

The objective of the this study is to compute the mechanical stress and strain on

reconstruction plates and in L and H type mandibular defects and screw–bone interface

used in bridging various mandibular angle defects in a simplified model using finite

element method (FEM). The influence of plate geometry and mechanical stress distribution

on the plate screw and bone was determined at the same time. One fifth of facial injuries

occurring involve mandibular fractures. The mandibular fractures can be can be treated

using reconstruction plates. The L and H type mandibular plates are designed. The

mandible plates are modelled using SolidWorks 2010 while the finite element analysis is

performed using Autodesk Algor 2010. The stress distribution in reconstruction plate

which stabilizes the two bone fragments is presented in Figure 3.11 for L type plate and

Figure 3.25 for H type plate. Individual stress values correspond to the colours according

to the presented scale. The red color in the stress and strain distribution shows the area of

maximum stress distribution.

Stress values were expressed in MPa. The stress analysis has shown that maximum stresses

located on the external side of the plate close to bone plate interface and reached values of

173.517 𝑁/𝑚𝑚2 in L type and 287.192 𝑁/𝑚𝑚2 in model 2 and did not exceed the yield

stress of both biomaterials. Enlarging the internal thread diameter of the screws to 1.5 fold

(4 mm) reduces the stress on the components of the osteosynthesis system to less than one

half in comparison to 2.7mm. The notched edge of the plate concentrates stress.

The stresses occur in the middle of the plate in the region of the highly notched tapering of

the cross-section at a level approximating to the tensile strength. The stresses at these

points can be reduced either by changing the design of the plate. The areas on the mandible

plate where the stresses are way below limit the material can be removed so as to minimize

the use of material. The foreign material in the human body should be least possible to

avoid complications.


`Page | 59

The effect of the masticatory forces on the mandible plate assembly post operation causes

loosening of the bolts which can cause loss of the bone if the stresses are about the nominal

limit. This can cause complications which can make the healing process of the mandibular

fractures difficult.

5.2 Future Work

There is a large scope of work which can be which can be done in various ways.Dye

penetrant examination a non-destructive test method for detection of surface defects in a

material can be performed to find out the eventual initiation of cracks in the plates

indicating future fracture. Altering the number of bolts used in order to keep the

mandibular plate in place on the human mandible can also be essential step in reducing the

stresses and presence of foreign material in the human body. The placement of the bolts on

the mandible plate assembly can be altered so as to obtain the least stress and strain

possible. The bolt length and diameter can be changed to observe the change in stresses

generated in the human mandible. The Mandible Plates should be designed to have smooth

geometry with no edge notches. The plates should also be thicker and wider in the inner

curvature to make them more resistant against the biting forces.

Moreover the material should be corrosion resistant biocompatible and strong in tensile

and fatigue properties. Along with titanium as a plate material titanium alloys stainless

steel and carbon fiber composites may be considered. With the assumptions made

regarding loading stress further investigations on stress and strain developing in the

bridging of other types of mandibular angle defects are planned using the geometric model

of a human mandible and FEM. Even further design iterations and fabrication of the testing

apparatus. Further numerical simulation can be created to predict bone plate performances

in the apparatuses and also to better predict the deformation of the plate. The beam models

can be developed to include large deformation assumptions in order to more accurately

predict the forces needed to deform the plate.


`Page | 60

Locking miniplate / screw system can also be used in place of the conventional mandibular

plates. Combination of micro and mini plates can also be used to treat mandibular

fractures.

The advent of resorbable plates and screws opens a new arena for the treatment of

mandible fractures in the pediatric population. Rigid fixation techniques have evolved from

larger thicker plates to smaller low-profile plates while maintaining adequate fixation. The

use of endoscopic techniques may broaden the indications for open reduction of condylar

fractures. Vascularized bone flaps are option for a functional and aesthetic reconstruction

with the free fibula flap remaining the gold standard for mandible reconstruction.

Reconstruction with alternative flaps such as scapula iliac crest and radial forearm flaps

results in good.

http://emedicine.medscape.com/article/870075-overview

http://emedicine.medscape.com/article/870075-overview

`Page | 61

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