GOWTHAMA RAAJ K.C. Tamil Nadu Dr. M.G.R. Medical University MAY

COMPARATIVE EVALUATION OF IMPLANT DESIGNS: INFLUENCE OF DIAMETER, LENGTH AND TAPER ON STRESS AND STRAIN IN THE MANDIBULAR SEGMENT - A THREE DIMENSIONAL FINITE ELEMENT ANALYSIS

GOWTHAMA RAAJ K.C.

Dissertation submitted to the Tamil Nadu Dr. M.G.R. Medical University in partial fulfillment of the requirements for the degree of Master of Dental Surgery in Prosthodontics including crown and bridge and implantology

Under the guidance of Dr. P. Manimaran HOD and Professor of Prosthodontics J.K.K.Nattraja Dental college and Hospital Komarapalayam.

2015-2018

Tamil Nadu Dr. M.G.R. Medical University

MAY 2018

Declaration

I hereby declare that this dissertation entitled COMPARATIVE EVALUATION OF IMPLANT DESIGNS: INFLUENCE OF DIAMETER, LENGTH AND TAPER ON STRESS AND STRAIN IN THE MANDIBULAR SEGMENT - A THREE DIMENSIONAL FINITE ELEMENT ANALYSIS is a bonafide and genuine research work carried out by me under the guidance of Dr. P. Manimaran, H.O.D. and Professor of Prosthodontics J.K.K. Nattraja Dental College and Hospital Komarapalayam

GOWTHAMA RAAJ K.C. Postgraduate student in Prosthodontics J.K.K.Nattraja Dental College and Hospital Komarapalayam

Endorsement by the Head of the Department and Principal

This is to certify that the dissertation entitled COMPARATIVE EVALUATION OF IMPLANT DESIGNS: INFLUENCE OF DIAMETER, LENGTH AND TAPER ON STRESS AND STRAIN IN THE MANDIBULAR SEGMENT - A THREE DIMENSIONAL FINITE ELEMENT ANALYSIS is a bonafide research work done by GOWTHAMA RAAJ K.C. under the guidance of Dr. P. Manimaran H.O.D. and Professor of Prosthodontics J.K.K.Nattraja Dental College and Hospital Komarapalayam

Dr. P. Manimaran Dr. A. Sivakumar Head of the Department of Prosthodontics Principal J.K.K. Nattraja Dental College and Hospital J.K.K.Nattraja Dental College and Hospital Komarapalayam Komarapalayam

I hereby declare that the Tamil Nadu Dr. M.G.R. Medical University shall have the rights to preserve, use and disseminate this dissertation in print or electronic format for academic / research purpose.

Komarapalayam GOWTHAMA RAAJ K.C. Date: -12-2017 Postgraduate student in Prosthodontics J.K.K. Nattraja Dental College and Hospial

Komarapalayam

Certificate - I

This is to certify that the dissertation entitled COMPARATIVE EVALUATION OF IMPLANT DESIGNS: INFLUENCE OF DIAMETER, LENGTH AND TAPER ON STRESS AND STRAIN IN THE MANDIBULAR SEGMENT - A THREE DIMENSIONAL FINITE ELEMENT ANALYSIS is a bonafide research work done by GOWTHAMA RAAJ K.C. in partial fulfillment of the requirement for the degree of Master of Dental Surgery in Prosthodontics including crown and bridge and implantology

Dr. C. Dhinesh Kumar Dr. P. Manimaran Co-Guide and Reader Guide and HOD Department of Prosthodontics Department of Prosthodontics J.K.K. Nattraja Dental College J.K.K. Nattraja Dental College Komarapalayam Komarapalayam

Komaraplayam Date: -2018

CERTIFICATE - II

This is to certify that this dissertation work titled COMPARATIVE

EVALUATION OF IMPLANT DESIGNS: INFLUENCE OF

DIAMETER, LENGTH AND TAPER ON STRESS AND STRAIN IN

THE MANDIBULAR SEGMENT - A THREE DIMENSIONAL

FINITE ELEMENT ANALYSIS of the candidate

GOWTHAMA RAAJ K.C. with registration Number 241511101 for the award of MASTER of DENTAL SURGERY in the branch of Prosthodontics including crown and bridge and Implantology. I personally verified the urkund.com website for the purpose of plagiarism check. I found that the uploaded thesis file contains from introduction to conclusion pages and result shows 0% percentage of plagiarism in the dissertation.

Guide & Supervisor sign with Seal.

ACKNOWLEDGEMENT

I express my profound gratitude and respect to my guide Dr. P. Manimaran, M.D.S., HEAD OF THE DEPARTMENT, postgraduate Department of prosthodontics for his invaluable council and encouragement not only this study but throughout my postgraduate course. I will always indebted to him for his wholehearted support in study.

I am extremely thankful to Dr. A. SIVAKUMAR M.D.S., Principal, J.K.K Nattraja Dental college & Hospital for his kind help and permitting me to use the facilities in the institution.

I am thankful to Dr. C. Dhinesh Kumar M.D.S., Reader, Postgraduate – Department of prosthodontics for giving me constant guidance, support and for giving a final shape to this study. This dissertation has been the fruitful outcome of his immense patience support, expert guidance and advice from beginning to end of this study.

I am thankful to Dr. Saisadan M.D.S., Reader for all the inspiration and guidance he has provided throughout my postgradutation.

I am thankful to Dr. Abirami M.D.S., Senior lecturer, for her instant help, support and motivation rendered throughout this study.

I am thankful to my senior Dr. S. Uthayana Raaja and juniors Dr. Preethi suganya and Dr. Sandhya for their concern and support.

I thank Dr. V. Prabu Raja, B.E., M.E., PhD, Associate professor, Department of mechanical engineering, CAE lab, PSG College of technology, Coimbatore for allowing me to work and taught to me about the software used in this study.

I thank Dr. Kumaresan, B.A., M.A., M.Sc., M.Phil, PhD, Principal, Laxminarayana Arts and Science College for Women, Dharmapuri, for helping me out in doing the statistical analysis of study results.

Finally I thankful to my parents Mr. P. Chidambaram, Mrs. K. Thilagavathy and my sister Dr. K.C. Keerthana Sri for an immense support, help and motivation throughout this study.

ALL FAME TO ALMIGHTY TABLE OF CONTENTS

S. No. Description Page No.

Introduction 1. 1

Aim and objectives 2. 6

Review of literature 3. 8

Finite element methodology 4. 27

Materials and methods 5. 33

Photographs 6. 34

Tables and graphs 7. 51

Statistical analysis 8. 60

Results 9. 79

Discussion 10. 81

Summary and conclusion 11. 87

Bibliography 12. 90

LIST OF FIGURES Fig. No. Description Page No

1. 3D view of mandible and two dimensional sketch of five 40 mandibular segment from CBCT scan 2. Generation of virtual geometric model 41 3. Co-ordinate system 42 4. Contact Establishment 42 5. Meshed model 43 6. Boundary conditions- Fixed support 43 7. Loading conditions 44 8 (a) Stress and strain analysis in 3.5x10mm implant 44 Load 1 - Axial (100N) 8 (b) Stress and strain analysis in 3.5x10mm implant 45 Load 2 - Buccolingual (50N) 8 (c) Stress and strain analysis in 3.5x10mm implant 45 Load 2 - Mesiodistal - (50N) 9 (a) Stress and strain analysis in 4.3x10mm implant 46 Load 1 - Axial (100N) 9 (b) Stress and strain analysis in 4.3x10mm implant 46 Load 2 – Buccolingual (50N) 9 (c) Stress and strain analysis in 4.3x10mm implant 47 Load 3 - Mesiodistal (50N) 10 (a) Stress and strain analysis in 3.5x11.5mm implant Load 1 - Axial 47 (100N) 10 (b) Stress and strain analysis in 3.5x11.5mm implant Load 2 - 48 Buccolingual (50N) 10 (c) Stress and strain analysis in 4.3x10mm implant 48 Load 2 - Mesiodistal (50N) 11 (a) Stress and strain analysis in 4.3x11.5mm implant Load 1 - Axial 49 (100N) 11 (b) Stress and strain analysis in 4.3x11.5mm implant Load 2 - 49 Buccolingual (50N) 11 (c) Stress and strain analysis in 4.3x11.5mm implant Load 2 - 50 Mesiodistal (50N)

LIST OF TABLES

Table No Description Page No.

1. Mechanical properties of different material used in the model 36 2. Contact Type between the Three Dimensional Models 36 3. Load (force) and magnitude 37 4. Von mises Stress (MPa) produced under Axial load 100N Load-1 52 (G1) Implant size 3.5x10 mm 5. Von mises Stress (MPa) produced under Axial load 100N Load-1 (G2) 52 Implant size 4.3x10 mm 6. Von mises Stress (MPa) produced under Axial load 100N Load-1 52 (G3) Implant size 3.5x11.5 mm 7. Von mises Stress (MPa) produced under Axial load 100N Load-1 53 (G4) Implant size 4.3x11.5 mm 8. Von mises Strain produced under Axial load 100N Load-1 53 (G1) Implant size 3.5x10 mm 9. Von mises Strain produced under Axial load 100N Load-1 53 (G2) Implant size 4.3x10 mm 10. Von mises Strain produced under Axial load 100N Load-1 54 (G3) Implant size 3.5x11.5 mm 11 Von mises Strain produced under Axial load 100N Load-1 54 (G4) Implant size 4.3x11.5 mm 12 Von mises Stress (Mpa) produced under Non Axial load (Bucco lingual) 54 50N Load-2 (G1) Implant size 3.5x10 mm 13 Von mises Stress (Mpa) produced under Non Axial load (Bucco lingual) 55 50N Load-2 (G2) Implant size 4.3x10 mm 14 Von mises Stress (Mpa) produced under Non Axial load (Bucco lingual) 55 50N Load-2 (G3) Implant size 3.5x11.5 mm 15 Von mises Stress (Mpa) produced under Non Axial load (Bucco lingual) 55 50N Load-2 (G4) Implant size 4.3x11.5 mm 16 Von mises Strain produced under Non Axial load (Bucco lingual) 50N 56 Load-2 (G1) Implant size 3.5x10 mm 17 Von mises Strain produced under Non Axial load (Bucco lingual) 50N 56 Load-2 (G2) Implant size 4.3x10 mm 18 Von mises Strain produced under Non Axial load (Bucco lingual) 50N 56 Load-2 (G3) Implant size 3.5x11.5 mm 19 Von mises Strain produced under Non Axial load (Bucco lingual) 50N 57 Load-2 (G4) Implant size 4.3x11.5 mm 20 Von mises Stress (Mpa) produced under Non Axial load (Mesio distal) 57 50N Load-3 (G1) Implant size 3.5x10 mm 21 Von mises Stress (Mpa) produced under Non Axial load (Mesio distal) 57 50N Load-3 (G2) Implant size 4.3x10 mm 22 Von mises Stress (Mpa) produced under Non Axial load (Mesio 58 distal)50N Load-3 (G3) Implant size 3.5x11.5 mm 23 Von mises Stress (Mpa) produced under Non Axial load (Mesio distal) 58 50N Load-3 (G4) Implant size 4.3x11.5 mm 24 Von mises Strain produced under Non Axial load (Mesio distal) 50N 58 Load-3 (G1) Implant size 3.5x10 mm 25 Von mises Strain produced under Non Axial load (Mesio distal) 50N 59 Load-3 (G2) Implant size 4.3x10 mm 26 Von mises Strain produced under Non Axial load (Mesio distal) 50N 59 Load-3 (G3) Implant size 3.5x11.5 mm 27 Von mises Strain produced under Non Axial load (Mesio distal) 50N 59 Load-3 (G4) Implant size 4.3x11.5 mm 28 Statistical analysis of cortical bone - Load 1 Axial (100N) 61 29 Statistical analysis of Cancellous bone - Load 1 Axial (100N) 61 30 Statistical analysis of Implant - Load 1 Axial (100N) 62 31 Statistical analysis of cortical bone - Load 2 Buccolingual (50N) 62 32 Statistical analysis of Cancellous bone - Load 2 Buccolingual (50N) 63 33 Statistical analysis of Implant - Load 2 Buccolingual (50N) 64 34 Statistical analysis of cortical bone - Load 3 Mesiodistal (50N) 64 35 Statistical analysis of Cancellous bone - Load 3 Mesiodistal (50N) 65 36 Statistical analysis of Implant - Load 3 Mesiodistal (50N) 66

LIST OF GRAPHS S. No Description Page No

1. Mean Stress values in cortical bone - Load 1 Axial (100N) 68 2. Mean Strain values in cortical bone - Load 1 Axial (100N) 68 3. Mean Stress values in Cancellous bone - Load 1 Axial (100N) 68 4. Mean Strain values in Cancellous bone - Load 1 Axial (100N) 69 5. Mean Stress values in Implant - Load 1 Axial (100N) 69 6. Mean Strain values in Implant - Load 1 Axial (100N) 69 7. Mean Stress values in cortical bone - Load 2 Buccolingual (50N) 70 8. Mean Strain values in cortical bone - Load 2 Buccolingual (50N) 70 9. Mean Stress values in Cancellous bone - Load 2 Buccolingual (50N) 70 10. Mean Strain values in Cancellous bone - Load 2 Buccolingual (50N) 71 11. Mean Stress values in Implant - Load 2 Buccolingual (50N) 71 12. Mean Strain values in Implant - Load 2 Buccolingual (50N) 71 13. Mean Stress values in cortical bone - Load 3 mesiodistal (50N) 72 14. Mean Strain values in cortical bone - Load 3 mesiodistal (50N) 72 15. Mean Stress values in Cancellous bone - Load 3 mesiodistal (50N) 72 16. Mean Strain values in Cancellous bone - Load 3 mesiodistal (50N) 73 17. Mean Stress values in Implant - Load 3 mesiodistal (50N) 73 18. Mean Strain values in Implant - Load 3 mesiodistal (50N) 73

Introduction

INTRODUCTION

A key factor for the success or failure of a dental implant is the manner in which stresses are transferred to the surrounding bone. Load transfer from implants to surrounding bone depends on the type of loading, the bone–implant interface, the length and diameter of the implants, the shape and characteristics of the implant surface, the prosthesis type, and the quantity and quality of the surrounding bone39. The finite element analysis (FEA) is an upcoming and significant research tool for biomechanical analyses in biological research. It is an ultimate method for modelling complex structures and analysing their mechanical properties. FEA has now become widely accepted as a non-invasive and excellent tool for studying the biomechanics and the influence of mechanical forces on the biological systems.

The finite element method (FEM) is basically a numerical method to analyse stresses and deformations in the structures of any given geometry77. The structure is discretized into the so called ‘finite elements’ connected through nodes. The type, arrangement and total number of elements impact the accuracy of the results. FEA allows researchers to predict stress distribution in the contact area of the implants with cortical bone and around the apex of the implants in trabecular bone. The biomechanical load management is dependent on the nature of the applied force and the functional surface area over which the load is dissipated. The principal factors that influence the load transfer at the bone implant interface includes implant geometry which includes diameter and length, thread pitch, shape, depth in the case of threaded implants, the type and magnitude of loading, implant material properties, quality and quantity of the surrounding bone, type of loading in prosthesis, surface structure, surgical procedures,

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INTRODUCTION and the nature of the bone–implant interface78. FEA is capable of providing detailed quantitative data at any location within the mathematical model. Thus, FEA has become a valuable analytical tool in implant dentistry65. Stress analysis of dental implant is very necessary for the investigation of bone turnover and maximum anchorage success. Incorrect loading or overloading may lead to distributed bone turnover and consequent implant loss.

Previous literature have shown that the cortical bone-implant interface has a higher concentration of stress and implant having greater diameter produces minimum stress. Bone quality also influences the long term success of implant treatment, poor bone quality reduces the success rates. Load transfer to bone implant interface depends on number, position, design, geometry of the implant, abutment connection, quality and quantity of surrounding bone. Since clinical determination of stress and strain distribution in bone is not possible, therefore an alternative technique should be used. So here finite element (FE) analysis, which is a reliable method, is used to determine the information about stress and strain in implant-bone structure57.

This study was made to analyse the stress and strain distribution patterns in implants with different diameter and length under axial and non-axial loading conditions in both cortical and cancellous bone using finite element analysis study.

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INTRODUCTION

TERMINOLOGY

DENTAL IMPLANT a prosthetic device made of alloplastic material(s) implanted into the oral tissues beneath the mucosal and/or periosteal layer and on or within the bone to provide retention and support for a fixed or removable dental prosthesis; a substance that is placed into and/or on the jaw bone to support a fixed or removable dental prosthesis28.

ABUTMENT- the supplemental component of a dental implant that is used to support and/ or retain any fixed or removable dental prosthesis28

CORTICAL BONE – the peripheral layer of compact osseous tissue28

CANCELLOUS BONE – the reticular, spongy or lattice-like portion of the bone; the spongy bone tissue located in the medulla of the bone; this bone is composed of a variable trabecular network containing interstitial tissue that may be hematopoietic28.

C.T. SCAN X-RAY- radiography in which a three-dimensional image of a body structure is constructed by computer from a series of plane cross-sectional images made along an axis — called also computed axial tomography, computerized axial tomography, computerized tomography33.

YOUNG’S MODULUS - eponym for the constant of proportionality expressed in the stress strain plot as the slope in the elastic region where elastic recovery occurs upon release of the stress inducing the strain; usually given the symbol E28.

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INTRODUCTION

Poisson's ratio is the ratio of transverse contraction strain to longitudinal extension strain in the direction of stretching force. Tensile deformation is considered positive and compressive deformation is considered negative. The definition of Poisson's ratio contains a minus sign so that normal materials have a positive ratio. Poisson's ratio, also called Poisson ratio or the

Poisson coefficient, or coefficient de Poisson, is usually represented as a lower case Greek nu, .

VON MISES STRESS - it is a geometrical combination of all the stresses (normal stress in the three directions and all three shear stresses acting at a particular location. Since it is a stress, it is measured in Pascal2.

VON MISES STRAIN - It is an index gained from the combination of principle stress at any given point to determine at which points stress occurring on the x, y and z axis will cause failure2.

FINITE ELEMENT ANALYSIS - It is a numerical method of structural analysis based on the principle of dividing a structure into a finite number of small elements that are connected with each other at the corner points or nodes. For each element its mechanical behaviour can be written as a function of the displacement of the node2.

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AIM AND OBJECTIVES

AIM & OBJECTIVES

AIM:

 To evaluate the influence of variable length and diameter of implant on stress distribution in cortical and cancellous bone.

OBJECTIVES:

 To understand the pattern of stress and strain distribution around implant surface with variable length and diameter under axial and non-axial loading conditions.  To understand the response of cortical and cancellous bone, under axial and non-axial loading conditions.

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REVIEW

LITERATURE

REVIEW OF LITERATURE

Meijer et al (1992)57 investigated the influence of stress distribution of a three layered flexible coating of poly active substance on a titanium implant in bone. On vertical loading, the application of a flexible coating reduced the compressive and the tensile radial stress.

Variations in composition and thickness of the coating did not affect the results significantly.

Lewinstein et al (1995)48 used two dimensional finite element method to analyse the IL system for supporting cantilever prosthesis, a special ball attachment and surrounding bone. Effective and maximum stresses in tension and compression were determined. In this study the observation was, in the IL system that support the cantilever prosthesis dramatically lowers the stresses in the bone, cantilever and implants.

Richter et al (1995)23 quantifies the vertical forces applied to dental implants during oral functions. Implants in the molar position that were fixed to a premolar with a prosthesis withstand maximum vertical force so 60 to120 N during chewing. Single molars and premolars carried maximum vertical forces of 120 to 150N. Clenching in centric occlusion caused a load level of approximately 50 N for both natural and artificial abutments. Occlusal pre maturities on the implant restoration that were less than 200 μm in height showed no significant increase of the implant load level.

Zyl et al (1995)63 used three dimensional finite element stress analysis method to determine the distribution of stress in an around a model of six implants in a stimulated human mandible.

A load of 100 N was applied at different intervals along the cantilever segment. There was a decrease of stress that reached a minimal level at 15 mm along the cantilever segment.

Thereafter a progressive increase in stress in the lingual and buccal plates was demonstrated.

Kaukinen et al (1996)36 studied the influence of occlusal surface design on the longitudinal success of implant treatment is believed to be significant, but it is not well understood. This study used a method to apply quantified vertical forces to a food substance and record the forces

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REVIEW OF LITERATURE and strain transmitted through cusped 33 and cuspless 0 occlusal design specimens to a simulated implant-retained prosthesis and the supporting bone. The results of this pilot study indicated that the occlusal configuration and cusp angulation of implant retained prostheses play a significant role in force transmission and the stress-strain relationship in bone.

Papavasilou et al (1996)26 used three dimensional finite element analysis and examined effects of:

 Types of edentulous mandible

 Veneering materials

 Absence of cortical bone

 Different intra-mobile elements

 Loading of cortical bone

 Loading directions and levels

Five different models were created and these models were loaded with 20N magnitude in axial and oblique (12 degree). Two different types of mandibles were modelled i.e. A3 type and C3 type. Two types of intra-mobile elements i.e. delrin and titanium with respect to a single

IMZ implant (11x4 mm) were placed. The prosthesis attached to the implant with acrylic resin veneered gold or porcelain fused to metal (PFM) restoration. Stress distribution patterns were compared and interfacial stress were monitored toward cortical bone (0.8 to 15 MPa). Summary of this study are minor stress increases were associated with smaller mandibles, no differences were found with type of veneering materials, absence of cortical bone increased interfacial stress, oblique load increase stress 15 times and 200N loads increased stress 10 times.

Conditions for bone micro fracturing were associated with oblique loads, high occlusal stress magnitudes and the absence of cortical bone.

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REVIEW OF LITERATURE

Wadamoto et al (1996)53 evaluated a 3D morphometric method to acquire date for the bone implant interface around a HA coated titanium alloy dental implant during initial healing. Three implant were placed in the mandible of monkeys and the surface bone contact ration in the buccal, lingual, mesial and distal directional were computed. Computer graphics were generated by the integration of data for serial ground surfaces obtained at 75μm intervals of the tissue block involved with the implant. The values of bone contact ratio (BCR) for the whole implant surface in the three implants were 80.8%, 68.1% and 68.8% and the bone value ratio

(BVR) values were the volume of cortical bone. These results may contribute to the development of realistic FEA models on biologic bone structures around the implants.

Barbier et al (1998)6 examined the influence of axial and non-axial occlusal load on the bone remodelling phenomena around oral implants in an animal experiment and stimulated in FEA.

The axial and non-axial loading conditions were introduced by inserting a bilaterally supported fixed partial prosthesis and a cantilever FPD on two IMZ implants in the mandible of beagle dog. Strong correlations between the calculated stress distribution in the surrounding bone tissue and the remodelling phenomena in the comparative animal model were observed. It was concluded that the highest bone remodelling events coincided with the regions of highest equipment and that the major remodelling differences between axial and non-axial loading were largely determined by the horizontal stress component of the endangered stress.

Brosh et al (1998)79 evaluated the influence of abutment angulation on stress and strain along the implant bone interface. The two experimental techniques, strain gauges and photo elasticity were used and compared for the analysis. Identical vertical loads applied on pre angulated abutment produced higher stress at the coronal zone of an implant compared with the straight abutment.

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REVIEW OF LITERATURE

Hobkirk et al (1998)40 tested the hypothesis that functional mandibular deformation influences force distribution in the jaw/ implant/superstructure complex. Six Branemark implants were mounted in an acrylic resin replica of an edentulous mandible, which was suspended in a frame that stimulated the natural situation. It was conclude that functional mandibular deformation is a significant factor in the design of mandibular implant stabilized prosthesis and calls into doubt the value of modelling techniques that do not allow for this phenomenon.

Stegaroiu et al (1998)43 assessed stress in bone around titanium implants using three treatment designs for a partially edentulous mandible, under axial (AX), buccolingual (BL) or mesiodistal

(MD) loads. The 3D FEA method was used. For each of the loads highest stress was calculated in the model with cantilever prosthesis supported two implants (M2). Less stress was found in the model with a conventional fixed partial denture on two implants (M3) cortical bone stress was high, comparable to that calculated for M2 under same load. When axial or mesiodistal load was applied to M3 the cortical bone stress was low similar to that found in M1.

Teixeira et al (1998)80 developed a 3D FEA model of an osseointegrated implant that could accurately simulated the stress distribution in the peri implant compact and cancellous bones.

In this study a 3D model construction was first evaluated with respect to minimal model length represented in a section of the mandible and also with regard to effect of decreased element number by unification of elements far away from the implants on stress distribution for saving computer memory and calculation time. Analysis of stress distribution followed by 100 N loading with the fixation of the most external planes of the models indicated that a minimal bone length of 4.2 mm of mesial and distal sides was acceptable for FEA representation.

Moreover, unification of elements located far away from the implant surface did not affect stress distribution. These results suggested that it could be possible to develop a replica FEA

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REVIEW OF LITERATURE implant model of the mandible with less range and fewer elements without altering stress distribution.

Wyatt et al (1998)10 used Branemark implants to support fixed partial prosthesis which appears to be a highly successful treatment alternative for restoration of the partially edentulous patient.

Satisfactory treatment outcomes are possible for a broad range of patients using various implant, abutment and prosthetic components as was documented in this 1 -12 follow up study.

Sato et al (1998)71 investigated the effectiveness of element downsizing on the construction of a 3D FE bone trabecular model with different element size 600,300,150 and 75 Micro meter).

Downsizing of elements from 600 to 300 Micro meter is suggested to be effective in the construction of a 3D FEA.

O’Mahony and Williams et al (2000)60 determined elastic modulus values in three orthogonal directions for cancellous bone taken form edentulous jaw and related these values to apparent density (bone density and volume fraction. These results facilitated more accurate modelling of the mandible in future finite element studies. Young’s moduli were greatest in the mesiodistal direction followed by the buccolingual and inferio-superior direction. The mesiodistal and buccolingual directions could not be shown to be different. This suggested a model of transverse isotropy for cancellous bone in the jaw that be elastic isotropy occurred in the transverse plane, i.e. in the mesiodistal and buccolingual direction with the symmetry axis directed along the inferio-superior directions.

Ress et al (2001)69 examined the importance of the supporting structures of a tooth during modelling was sell as analysing the stress distributions within a tooth. A 2D plane strain FEM of a lower second premolar was developed, supported by periodontal ligament and alveolar bone. Two 50N vertical loads were applied and stress were recorded. It was concluded that

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REVIEW OF LITERATURE both the periodontal ligament and alveolar bone are important when undertaking the FEAA of teeth.

Akca et al (2002)32 compared the data obtained from an in vitro strain gauge analysis of an implant supported fixed partial denture with its 3D FEA model and a mathematical model in which human simulation was provided. A static vertical load of 50N was applied at certain location to simulated centrally positioned axial and laterally positioned axial loading for SGA and 3D FE stress analysis. A statistically significant increase in strain levels were recorded between loading types in the SGA (p<0.05) Strains obtained from SGA were higher than for

3D FEA. However there was compatibility on the determination of the quality of induced strains under applied load between two methods.

Cruz et al (2003)51 analysed the stress distribution around a cuneiform geometry implant using accurate three dimensional model that had a finer mesh than commonly found in the literature.

A mechanical model of an edentulous mandible was generated from computerised tomography

(CT SCAN) with the implant placed in the left first premolar region. A 100 n axial load was applied at the implant abutment and mandibular boundary conditions were modelled considering the real geometry of its muscle supporting system. They concluded that the cuneiform geometry distributed the stress in a smooth pattern with a stress concentration in the cortical region. No considerable apical stress concentrations were found. The modelling methodology, conditions of the support and the load system and the finest anatomic and functional variation played important roles in the results.

Jeffcoat et al (2003)52 compared the efficacy of Hydroxy apatite coated threaded endoosseous dental implants and HA coated cylindrical end osseous dental implants with that of the machined titanium threaded endoosseous dental implants. Each 120 edentulous patients received different types of implants in a randomized design using 5 or 6 implants. A Kaplan

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REVIEW OF LITERATURE meier analysis was used to compare the proportion of ailing implants to each type of implant design. This analysis revealed that 95.2% of machined titanium threaded implants experienced less than 2 mm of bone loss p<0.06) over 5 years, the success rate tended to favour HA coated implants.

Lang et al (2003)47 examined the dynamic nature of developing preload using FEA in an implant complex that was modelled with a screw bore to provide the thread helix in the model design. Even the co-efficient of friction on the development of preload amount in the implant complex during and after abutment screw tightening was also determined. They concluded that using FEA a torque of 32 Ncm applied to the abutment screws in the presence of coefficient of friction of 0.26 resulted in lower than optimum preload for the abutment screws. To reach the desired preload of 75% of the yield strength, using a torque of 32 Ncm, co-efficient of friction between the implant components should be 0.12.

Lin et al (2003)12 analysed the biomechanics in an implant/tooth–supported system under different occlusal forces with rigid and non-rigid connectors by adopting a nonlinear finite element (FE) approach. Materials used in this study are, model containing implant (placed in the second molar position) splinted to the mandibular second premolar was constructed.

Nonlinear contact elements were used to simulate a realistic interface fixation between the implant body and abutment screw and the sliding keyway stress-breaker function. Stress distributions in the splinting system with rigid and non-rigid connectors were observed when vertical forces were applied to the tooth, pontic, implant abutment, or complete prosthesis in

10 simulated models. Result shows that the displacement obtained from the natural tooth increased 11 times than that of the implant, and the peak stress values within the implant system increased significantly when vertical forces acted only on the premolar of a fixed prosthesis with a rigid connector. The values seen in the splinting prosthesis were not significantly

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REVIEW OF LITERATURE different when vertical forces (50N) were applied to the pontic, molar (implant) only or the entire prosthesis, respectively, regardless of whether rigid or non-rigid connectors were used.

Moreover, the peak stress values in the implant system and prosthesis were significantly reduced in single- or multiple-contact situations once vertical forces on the pontic were decreased. Minimization of the occlusal loading force on the pontic area through occlusal adjustment procedures to redistribute stress within the implant system in the maximum intercuspation position for an implant/tooth–supported prosthesis is recommended.

Eskitascioglu et al (2004)30 investigated the effect of loading at 1 to 3 different locations on the occlusal surface of a tooth on the stress distributions in an implant-supported mandibular fixed partial denture (FPD) and surrounding bone, using 3-dimensional finite element analysis.

A 3-dimensional finite element model of a mandibular section of bone (Type 2) with missing second premolar and its superstructures were used in this study. A 1-piece 4.1 X 10mm screw- shape ITI dental implant system (solid implant) was modeled for this study. Cobalt-Chromium

(Wiron 99) was used as the crown framework material and porcelain was used for occlusal surface. The implant and its superstructure were simulated in a Pro/Engineer 2000i program.

Total loads at 300 N were applied at the following locations: 1) tip of buccal cusp (300 N), 2) tip of buccal cusp (150 N) and distal fossa (150 N), or 3) tip of buccal cusp (100 N), distal fossa

(100 N), and mesial fossa (100 N). Results demonstrated that vertical loading at 1 location resulted in high stress values within the bone and implant. Close stress levels were observed within the bone for loading at 2 locations and 3 locations; the former created the most extreme stresses and the latter the most even stresses within the bone. With loading at 2 or 3 locations, stresses were concentrated on the framework and occlusal surface of the FPD, and low stresses were distributed to the bone.

Dincer Bozkaya (2004)18 investigated the effects of external geometry and occlusal load magnitude on bone failure modes for 5 commercially available dental implant systems. Five

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REVIEW OF LITERATURE different implant systems; Ankylos, Astra, Bicon, ITI, and Nobel Biocare, comparable in size, but different in thread profile and crest module shapes, were compared using the finite element method. Type II bone quality was approximated and complete osseous integration was assumed. Occlusal loads of varying magnitudes (0 to 2000 N) were applied on the abutments supporting single tooth restorations at 11.3 degrees from the vertical axis with a 1-mm offset.

Total overloaded bone area, where tensile and compressive normal stresses fell outside of the recommended limits of 100 and 170 MPa respectively, was investigated for different load levels. Result shows that moderate levels of occlusal loads up to 300 N, the compact bone was not overloaded by any of the implant systems. At the extreme end of the occlusal load range

(1000 N or more) the overloading characteristics of implants may be dependent on geometric shape.

Mordefeld et al (2004)55 investigated and evaluated retrospectively the treatment outcome of

WP Mk II implants used in maxillary and mandibular posterior region. Fifty two patients treated with seventy eight WP Mk II implants of 5mm diameter, length 7 to 13 mm placed in the posterior segment of the maxilla and mandible were chosen. Patients under study were recalled for general health and prosthodontics and radiographic examinations. Of seventy-eight implants, eight had been lost by the time of re-examination. The survival rate was 89.8%. They concluded that it is advisable to used wide implants longer than 8.5mm in the posterior areas to minimize the risks for failure, as these regions present higher masticatory loadings, greater lateral forces and sometimes compromised quality.

Kitamura et al (2005)43 observed average marginal bone resorption of about 1 mm after the first year of functional loading, which is followed by an annual loss of approximately 0.1 mm, has been reported in stable implants. However, finite element analyses on bone stress around implants have been limited to analysing the bone stress in the absence of any bone resorption.

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REVIEW OF LITERATURE

Three-dimensional finite element analysis was performed to compare the bone stresses in a non-resorption model with those in four models with bone resorption of two depths (1.3 and

2.6 mm) and types (horizontal resorption and angular defects). Axial and bucco-lingual forces were separately applied to the center of the superstructure and the maximum equivalent stress was calculated. The main tendencies of bone stress (highest stress concentration around implant neck, higher stresses under bucco-lingual than axial load, as well as in the cortical than cancellous bone) were the same in the non-resorption and resorption models. Bone stress distributions were similar in the non-resorption and horizontal resorption models, but differed from those in the angular defect models. Moreover, the changes of the bone stress value with resorption depth differed for the two resorption types. Thus, in FEA, accurate simulation of the marginal bone shape in the implant neck region is advisable.

Petrie et al (2005) 18 analysed and compared systematically the relative and interactive effects of implant diameter, length, and taper on calculated crestal bone strains. Three-dimensional finite-element models were created of a 20mm premolar section of the mandible with a single end osseous implant embedded in high or low density cancellous bone. Oblique (200-N vertical and 40-N horizontal) occlusal loading was applied. Implant diameter ranged from 3.5 to 6mm, total implant length from 5.75 to 23.5mm, and taper from 0 to 141 degree were taken for study, resulting in 16 implant designs. Result shows that when the diameter of the implant is increased

3.5 fold reduction in crestal strain, increasing length caused as much as a 1.65 fold reduction, whereas taper increased crestal strain, especially in narrow and short implants. Diameter, length and taper have to be considered together because of their interactive effects on crestal bone strain. A wide and relatively long, untapered implant appears to be the most favourable choice.

Narrow, short implants with taper in the crestal region should be avoided, especially in low density bone.

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REVIEW OF LITERATURE

Jingade et al (2005)38 used finite element method to detect the stress distribution in three situations namely a) Comparison of stress distribution in a single implant with the narrow ceramic occlusal table and wide ceramic occlusal table, b) comparison of stress distribution in two implants supporting a three-unit bridge, one model with implants placed parallel to each other and the other with one implant placed in angular position to the other. c) Compare the difference in the stress distribution in six implants and four implants supporting mandibular over denture. The three-dimensional (3-D) finite-element mesh model was modelled with the standard dimension of the implant with 11mm long and 4mm. Result shows that the number of implant, design and placement of implant plays an important role in success of implant prosthetic treatment.

Xi ding et al (2009)82 analysed stress distribution in bone around implants of different diameters on immediate loading. Three mandible models, embedded with thread implants (ITI,

Straumann, Switzerland) with diameters of 3.3, 4.1, and 4.8 mm, respectively were developed using CT scanning and self-developed Universal Surgical Integration System software. Result shows that when increase of implant diameter, stress and strain on the implant–bone interfaces significantly decreased, especially when the diameter increased from 3.3 to 4.1 mm.

Siddharth Shelat et al (2011)75 investigated the effect of two different abutment types on stress distribution in the bone around an implant under two loading conditions, vertical load and combined load (vertical + angle of 45°). Implant of 4.2 × 12 mm2 was used. Two 2-piece implant systems, Internal Hex and External Hex implant-abutment complex were used. The implant-abutment complex was embedded in bone and subjected to static load of 100 N vertically and a combined load (vertical + 45° angulation). Finite element analysis shows that the maximum Von Mises stress occurred in the region of the compact bone under all loading conditions irrespective of the type of abutment use. Significant reduction in Von Mises stress

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REVIEW OF LITERATURE was observed at the boundary between compact and spongy bone because of relatively low elastic modulus of spongy bone.

Saluja et al (2012)72 used finite element method to investigate the level of stress distribution to maintain a strong and healthy bone. The design efficacy of the Indigenous titanium Dental implant “INDIDENT” developed by INMAS was studied using finite element stress analysis.

Abacus software has been chosen for the analysis and the models are constructed as three- dimensional Solid models. The boundary conditions for each case remains same. The amount of load applied is equal for all the cases as 100 N. The study involved the modelling of mandible and the dental implant meshed together. The stress generated was calculated by Finite element method using Abacus software. The different parameters used in this study for FEA simulation were stresses developed due to variation in length and diameter variation. The results indicated that the stress concentration and distribution was not effect by the length variation of the

Implants. Stress concentration was same at the neck of hole and which can be reduced after suitable chamfering of the hole. The stress distribution on the effect of diameter variation indicates that if the diameter of implant was increased the contact surface also increases and simultaneously stress pattern was reduced.

Mohapatra et al (2012)44 investigated the effect of implant design on the stress distribution in the framework, implant, and surrounding bone, using a three-dimensional finite-element analysis. Finite element model of a mandibular section of bone with implants placed in the first and second premolar region was created to support a distal cantilever fixed partial denture.

Four models were created in this study. Result shows that showed that the maximum stress overall was in the cervical portion of the secondary abutment. When used in combination, the maximum stress was when the two-piece implant was used as secondary abutment. The one- piece implant showed less stress compared to its counterpart when used as secondary abutment.

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REVIEW OF LITERATURE

The maximum stress distribution in the bone was around the neck region of the secondary implant.

Jayaraman et al (2012)37 observed the stress absorbed by the bone around mini over‑denture dental implant with and without acrylonitrile O‑ring under two different loading conditions. A three‑dimensional finite element analysis using Pro‑E mechanical finite element software was used to check the stress absorbed by the bone with and without acrylonitrile O‑ring. The implant and the mandible where modelled from the data obtained from C.T. scan and optical projector using reverse engineering process. Two different loading conditions of 80 N and 220

N were determined and the analysis was done. The result showed at lower loads (80 N), there was not much difference in the stress absorbed by the cancellous bone with or without acrylonitrile O‑ring, but at higher loads (220), there was difference in the stress absorbed by the cancellous bone with (0.03508 MPa) and without acrylonitrile O‑ring (3.874 MPa) which showed that significant stress was absorbed by the acrylonitrile O‑ ring. This study proves that higher loads during para functional movement were absorbed by the acrylonitrile O‑ring increasing the success of the implants.

Hao-Sheng Chang et al (2013)31 investigated the stress distributions in an implant, abutment, and crown restoration with different implant systems, in various bone qualities, and with different loading protocols using a three-dimensional finite element model. Eight three- dimensional finite element models with 16 test conditions containing four types of dental implants embedded in two different bone qualities (types II and IV) under 100-N axial and 30_ oblique loading forces were applied to analyse the stress distribution in the crown restoration, abutment, abutment screw, implant, and supporting bone. Result shows that the von Mises stresses in the cortical bone were mostly greater in the tissue-level implant (MK III) than in the bone-level implant (Active) of the NobelBiocare system. However, von Mises stresses in

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REVIEW OF LITERATURE cancellous bone were mostly greater in the bone-level implant (Active) than in the tissue-level implant (MK III) of the NobelBiocare system.

Stuart J McNally et al (2013)56 studied the effect on stress in bone with variable diameter using finite element analysis. Dental implants that are 2.0 mm in diameter or smaller

(mini‑implant, small diameter implant) have been advocated as an acceptable alternative to conventional diameter implants (3.0‑5.0 mm diameter) for definitive oral restoration. A finite element analysis (FEA) study was designed to ascertain if reduction of implant diameter to 1.8 m would increase cervical bone stress and result in non‑physiologic stress in the investing bone. A finite element model of a 1.8 mm × 12 mm titanium implant was produced through micro computed tomography scanner. Observation shows that the crestal bone stress was increased and Von Mises stress (an average of 300 MPa) exceed the trabecular and cortical bone yield stress of 100 MPa and 33 MPa respectively. The results indicate that, for implants of 1.8 mm diameter, normal occlusal forces can induce stresses that are destructive to investing bone.

Desai et al (2013)14 compare the stresses, strains, and displacements of double versus single implant in immediate loading for replacing mandibular molar. Two 3D FEM (finite element method) models were made to simulate implant designs. The first model used 5‑mm‑wide diameter implant to support a single molar crown. The second model used 3.75-3.75 double implant design. Anisotropic properties were assigned to bone model. Each model was analysed with single force magnitude (100 N) in vertical axis. This FEM study suggested that micro motion can be controlled better for double implants compared to single wide‑diameter implants. The Von Mises stress for double implant showed 74.44% stress reduction compared to that of 5‑mm implant. The Von Mises elastic strain was reduced by 61% for double implant

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REVIEW OF LITERATURE compared to 5mm implant. Within the limitations of the study, when the mesiodistal space for artificial tooth is more than 12.5 mm, under immediate loading, the double implant support should be considered.

Bholla et al (2014)8 analysed the biomechanical factors like angulation of the abutment that may have a profound influence on the stress levels on bone for long-term function of implant- supported prosthesis using FEA method. The model resembles the maxillary bone, and the material properties similar to the bone are introduced in the model and clinical loading conditions were simulated. Von mises stresses occurring for four angulated abutments (0, 15,

20, 25 degree) in compact and cancellous bone, thick and thin compact bone and subjected to axial and combined loading. Result shows that Von Mises stresses (ΣEmax) were higher in the cortical bone compared to the cancellous bone and were concentrated in the crestal (facial) region in both types of bone. Von mises stress values of 0, 15 degree abutments in thin bone and 0, 15, 20 degree abutments in thick bone were within the physiological remodelling zone.

Stress values for a 25 degree abutment in both types of bone were above the resorption limit.

Stress values were higher due to combined loading compared to axial loading irrespective of the angulation or quality of bone present. Clinically, within a load of 178 N angulated abutments up to 20 degrees can be placed in the anterior maxillary zone.

Pedram Iranmanesh et al (2014)34 investigated the effects of prosthesis material types on stress distribution of the bone surrounding implants and to evaluate stress distribution in three- unit implant-supported fixed dental prosthesis. A three-dimensional (3D) finite element fixed dental prosthesis model of the maxillary second premolar to the second molar was designed.

Three load conditions were statically applied on the functional cusps in horizontal (57.0 N), vertical (200N), and oblique (400N, θ = 120°) directions. Four standard framework materials were evaluated: Polymethyl methacrylate, base-metal, porcelain fused to metal, and porcelain.

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REVIEW OF LITERATURE

Result shows that the maximum of von Mises stress in the oblique direction was higher than the vertical and horizontal directions in all conditions. In the bone-crestal section, the maximum von Mises stress (53.78 MPa) was observed in PMMA within oblique load. In fixed dental prosthesis, the maximum stress was generated at the connector region in all conditions.

Sarfaraz et al (2015)73 evaluated the stress distribution pattern in the implant and the surrounding bone for a passive and a friction fit implant abutment interface and to analyse the influence of occlusal table dimension on the stress generated. CAD models of two different types of implant abutment connections, the passive fit or the slip‑fit represented by the Nobel

Replace Tri‑lobe connection and the friction fit or active fit represented by the Nobel active conical connection were made. The implant and abutment complex was placed in cortical and cancellous bone modeled using a computed tomography scan. This complex was subjected to a force of 100 N in the axial and oblique direction. The results showed that overall maximum

Von Misses stress on the bone is significantly less for frictional fit than the passive fit in any loading conditions stresses on the implant were significantly higher for the frictional fit than passive fit. The narrow occlusal table models generated the least amount of stress on the implant abutment interface.

Eazhil et al (2016)20 evaluated the impact of implant diameter and length on neighbouring tissues around the implant. Tapared implants of different diameter and length were numerically analysed using bone–implant models developed from computed tomography generated images of mandible with osseointegrated implants. The impact of implant with various diameters on stress distribution was examined using implants with a length of 13 mm and diameters of 3.5 mm, 4.3 mm and 5.0 mm. Implants with a diameter of 4.3 mm with lengths of 10 mm, 13 mm,

16 mm was developed to examine the impact of various implant length. Results shows that

Maximum von Mises stresses were located around the implant neck. It was demonstrated that

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REVIEW OF LITERATURE there was statistically significant decrease in von Mises stress as the implant diameter increased.

Gizem (2017)19 used finite element analysis to determine the implant location, number, and diameter to support a maxillary implant supported overdenture. Three-dimensional models of an atrophic maxilla, dental implants, and ball attachments were modelled, and different loading conditions were applied to simulate realistic conditions. Six models with different numbers and diameters of implants, including mini-dental implants and differently located implants, were formed, and stress values were compared by implementing a finite element analysis. The study showed that, as the implant number increased, decreased stress values were observed in peri- implant bone and implants in the maxillary implant supported overdenture prosthesis.

However, changes in implant diameter had no significant effect on stresses. Increasing the implant diameter was not advantageous; the use of mini-dental implants may be a viable alternative method. However, using four implants for maxillary implant supported overenture is indicated.

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FINITE ELEMENT ANALYSIS

METHODOLOGY

FINITE ELEMENT ANALYSIS METHODOLOGY

Finite element analysis method (FEA) allows detailed visualization of any kind of structures that indicates about the distribution of stresses and displacements. FEA software provides a wide range of simulation options for controlling the complexity of both modelling and analysis of a system11. Similarly, the desired level of accuracy required and associated computational time requirements can be managed simultaneously to address most engineering applications. FEA which is an engineering method of calculating stresses and strains in all materials including living tissues, teeth model, restorative materials and dental implants for scientific checking, and validating the clinical assumptions. FEA is capable of providing detailed quantitative data at any location within the mathematical model. Thus,

FEA has become a valuable analytical tool in dentistry. A more recent method of stress analysis, generally developed in 1956 in the aircraft industry was the FEA77. This technique was used widely only in aerospace engineering at first but slowly due to the flexibility of the method to model any complex geometries and provide instant results, it made its presence felt in dentistry in early 1970’s.

Software using for Finite element Analysis:

 ANSYS

 Adina

 Free CAD

 HYPERMESH

 ABAQUS

 CALCULIX

 Autodesk Simulation

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FINITE ELEMENT ANALYSIS METHODOLOGY

Application of finite element analysis in dentistry39:

 Stress distribution in bone-implant interface

 Stress distribution in bone using various design of implants

 Stress analysis in prosthesis and implant interface

 Stress analysis in abutment and screw of implant

 Plastic and viscoelastic behaviours in materials

 Tooth-to-tooth contact analysis

 Contact analysis in implant structures

 FEA has been used in orthodontics to study growth and development.

 Interfacial stress in restorations

 To study stress distribution on supporting structures in relation during designing of

fixed and removable prostheses

 To investigate stress distribution during cavity preparation and root canal treatment in

endodontics.

 Nonlinear simulation of periodontal ligament property

Steps involved in Finite Element Analysis:

1. Development of virtual geometric model

2. Import the VGM in ANSYS workbench

3. Applying of material properties to the three dimensional models

4. Co-ordinate system (Three dimensional axis)

5. Establishing contacts between the models

6. Meshing of models

7. Boundary conditions

8. Application of loads

9. Analysis of results

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FINITE ELEMENT ANALYSIS METHODOLOGY

Methodology:

1. Development of the geometric model

The first step before an FEA model can be obtained is the creation of a virtual geometry model (VGM). Usually VGM are created by several software, some of them are:

 Creo parametric by PTC

 Solid works by Dassault systems

 Auto CADD mechanical by Autodesk

 Auto CADD Inventor by Autodesk

In this study Creo 2.0 parametric by PTC is used for modelling and assembling of model structures.

2. Import the VGM in ANSYS workbench

After generation of virtually designed models it is imported in the ANSYS workbench

software for analysis.

3. Applying of material properties to the three dimensional models:

Engineering data is the material property applied to the three dimensional models that convert the models into objects. In this study Young’s modulus and poisons ratio are applied to the models. In general, material behaviour can be classified into five categories: Nonlinear elastic phenomena (return to original conditions after deformation, not following a specific pattern), plastic phenomena (deformation without return to original conditions), elastoplastic phenomena (partly elastic and partly plastic behaviour), viscoelastic phenomena (return to original conditions after deformation is time-dependent), and viscoplastic phenomena (time- dependent deformation without return to original conditions). Material properties greatly influence the stress and strain distribution in a structure. These properties can be modelled in

FEA as isotropic, transversely isotropic, orthotropic and anisotropic. In most reported studies, an assumption was made that the materials were homogenous and linearly isotropic39. This

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FINITE ELEMENT ANALYSIS METHODOLOGY classification is based on the mechanical properties of a material in relation to the directions of each of the axes (X, Y and Z).

Isotropic materials are defined as those that present the same properties in every direction.

Anisotropic materials are defined as the materials with properties that are different along all the directions.

Orthotropic materials are defined as the properties of materials are same in two direction and different in the third direction.

4. Co-ordinate system (Three dimensional axis):

Three dimensional axis (X, Y, Z axis) will be assigned by the software. This is an important step because, visualization of the model by rotation, zoom, pan options. This step is used also for application of loads in particular or multiple axis and certain angulations for analysis and interpretation of result.

5. Establishing contacts between the models:

Contact between the models decides the stress distribution though the applied force. In

ANSYS workbench, types of contacts are bonded, frictional, frictionless, force frictional sliding, rough, no separation. Type of contact between the models decides the movement of the models while mathematical analysing by the solver. Results will vary according to the contact establishment.

6. Meshing of models:

Once the Virtual geometry model has been obtained and establishment of contacts it should be processed to generate the finite element mesh, several software options are currently available and can be used for FEA mesh generation, with satisfactory results, particularly ANSYS (Swanson Analysis Systems, Houston, PA,USA) and MSC/Nastran

(MSC Software Corporation, SantaAna, CA, USA). The finite element mesh comprises spatial coordinates represented by quadrilateral elements combined and arranged to produce

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FINITE ELEMENT ANALYSIS METHODOLOGY different geometric shapes – triangle, tetrahedrons and hexahedrons (most commonly the latter two). The quadrilaterals used in mesh generation are connected by nodes, resulting in a complex 2D or 3D net, which allows the transport of mathematical equations between the coordinates.

7. Boundary Conditions:

Zero displacement constraints must be placed on some boundaries of the model to ensure an equilibrium solution. The constraints should be placed on nodes that are far away from the region of interest to prevent the stress or strain fields associated with reaction forces from overlapping with each other. Fixed support is used as a boundary condition in this study.

8. Application of loads:

Load (Force) was applied in particular axis or multiple for results generation. In this study

Three forces are applied to the implant model. They are

 Axial load 100N

 Non-axial (buccolingual) load 50N

 Non-axial (mesiodistal) load 50N

9. Analysis and evaluation of results:

Once force and time properties have been properly defined, the software performs a series of calculations by mathematical equations and yields the simulation results. These are presented according to a colour scale where each shade represents a different degree of movement, tension or compression.

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Materials

and

Methods

MATERIALS AND METHODS

MATERIALS USED IN THIS STUDY:

 CBCT scan of a patient with edentulous mandible

 Computer with higher end configuration for faster processing of data.

Software:

 Carestream 3D imaging

 Corel Draw X7

 Creo 2.0 parametric by PTC

 Workbench V17.0 by ANSYS

METHODOLOGY:

Steps involved in finite element method are:

I. Finite element modelling (CREO 2.0 Parametric by PTC)

Construction of geometric model

a. Modelling of the bone

b. Modelling of implants with abutment

c. Preparation mould space in cortical and cancellous bone model

d. Assembling of bone models and implant model with abutment

II. Finite element analysis (Workbench 17.0 By ANSYS)

1. Import designed three dimensional model in workbench by ANSYS

2. Applying of material properties to three dimensional models

3. Co-ordinate system (Three dimensional axis)

4. Establishing contacts between the models

5. Meshing of models

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MATERIALS AND METHODS

6. Boundary conditions

7. Application of loads

8. Analysis of results

a. Equivalent Von Mises stress

b. Equivalent Von Mises strain

I. Finite element modelling: (CREO 2.0 Parametric by PTC)

Construction of geometric model:

a. Modelling of bone:

CBCT scan of patient with completely edentulous mandible was taken. The

scanned file was opened as DICOM frames in Carestream 3D imaging, in that

software frontal view, coronal view, 3D view, sagittal view were seen. In frontal

view, five regions in the posterior region of the mandible were chosen and that

regions shows both cortical bone and cancellous bone layers respectively. These

regions in the image are drawn as two dimensional layers with the same dimension

and shape using Corel draw X7.0 software (Fig. 1) these two dimensional sketches

were imported to creo 2.0 parametric software and by using extrude command 3D

cortical and cancellous three dimensional bone models was generated. The generated

models were saved as (.PRT) files. (Fig. 2)

b. Modelling of implant and abutment:

Nobel replace select tapered implant and tri channel narrow and regular platform

abutment was chosen with diameter and length 3.5x10mm, 4.3x10mm, 3.5x11.5mm

and 4.3x11.5mm. The implant considered was tapered type which is straight parallel

walled slightly tapered implant with variable thread design. Implant model is

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MATERIALS AND METHODS

prepared by using measuring instruments like vernier calliper and screw gauge.

These measurements are builds as models feature by feature. Implant and abutment

are modelled together not separately because the analysis was made only in bone

and implant. Options used for creating 3D implant models are Boolean operations,

revolve, extrude etc. the modelled implants were saved as (.PRT) files.

c. Preparation mould space in cortical and cancellous bone model:

By taking the modelled implant as reference, moulds were created in cortical bone

with respective cancellous bone. Likewise (5 bone sets X 4 implants) 20 cortical

bone with the respective cancellous bone moulds are generated. The moulds were

saved as (.PRT) files separately. (Fig. 2)

d. Assembling of bone and implant model with interface

The moulds of cortical bone with the respective cancellous bone and implant were

assemble as .ASM file. This assemble file was exported as (.IGES) file format. Like

this way 20 (.IGES) file 3d assembly models were created. (Fig. 2)

II. Finite element analysis (Workbench 17.0 By ANSYS)

1. Import designed three dimensional model in workbench by ANSYS

Generated three dimensional assembled models were imported in the workbench

software.

2. Applying of material properties to three dimensional models

For the execution and accuracy of the programme and interpretation of the results,

two material properties were utilized i.e. young’s modulus and poisons ratio. The

cortical bone, cancellous bone and implant with abutment presumed to be linearly

elastic, homogenous and isotropic. Although cortical bone has anisotropic material

characteristics and possesses regional stiffness variation, they were modelled

isotropic, due to the unavailability of sufficient data and difficulty in establishing the

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MATERIALS AND METHODS

principle axis of anisotropy. The corresponding elastic properties such as Young’s

modulus ( and poisson’s ratio ( of cortical bone, cancellous bone and implant were

determined according to literature survey.

Table 1 shows the material properties applied to the cortical bone model, cancellous

bone model and implant model.

Table 1: Mechanical properties of different material used in the model

Material Young’s modulus( Poisson’s ratio ( Reference (MPa) Cortical bone 13000 0.30 9,71

Cancellous bone 690 0.30 9,71

Implant (Titanium) 102000 0.35 9,71

3. Co-ordinate system (Three dimensional axis)

Workbench generates the three dimensional axis (X, Y, Z) for visualization of model

and application of load in particular axis. (Fig. 3)

4. Establishing contacts between the models

Contact between the models are given in table 2 (Fig. 4)

Table 2: Contact Type between the Three Dimensional Models

Materials Cortical bone Cancellous bone Implant

Cortical bone -- Bonded Frictional

Cancellous bone Bonded -- Frictional

Implant Frictional Frictional --

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MATERIALS AND METHODS

5. Meshing of models

After contact establishment between three dimensional models are meshing was done.

Type of mesh was used in this study is FINE type, for interpretation of more accurate

results. (Fig. 5)

6. Boundary conditions

Constraints were applied on the distal end of the model in all three axes and omitting

support at the bottom permitted bending of the model. These aspects make the model

more realistic representation of the clinical situation (Fig. 6)

7. Application of loads

The magnitude of applied loads was within physiologic limits and direction of

application of the loads simulated the clinical conditions. Loads are directly applied

onto the abutment. The prosthesis was not modelled for ease of fabrication of model

and also for simplification of interpretation of results. The loads applied are shown in

table 3: (Fig. 7)

Table 3: Load (force) and magnitude

Load Magnitude

Axial 100 N

Non-axial (Bucco Lingual) 50 N

Non-axial (Mesio Distal) 50 N

8. Analysis and results:

These 20 models were analysed by post processor i.e. solver and results were

displayed in the form of colour coded maps using von mises stress and strain

analysis. Von mises stress values are defined as the beginning of deformation for

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MATERIALS AND METHODS

ductile materials. Metallic implants failure occurs when the von mises stress values

exceed the yield strength of an implant material. Von mises stress are most

commonly reported in FEA studies to summarize the overall stress state at a point.

For statistical analysis the implant with size 3.5x10mm, 4.3x10mm 3.5x11.5mm

4.3x11.5mm were named as group G1, G2, G3 and G4 respectively. The reading are

made by using probe (Fig. 8) in the software by selecting the desired point in the

analysed models. Here the readings are taken in cortical and cancellous bone

implant interface region and surface of the implants. For each models the readings

were taken in these regions respectively.

Cortical bone

 Cancellous bone o Coronal part o Middle part o Apical part

 Implant o Coronal part o Middle part o Apical part

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PHOTOGRAPHS

Fig 1. 3D view of mandible and two dimensional sketch of five mandibular segment from CBCT scan

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PHOTOGRAPHS

Fig 2: Generation of virtual geometric model

(a) Cortical bone model (b)Cancellous bone model

(d) Cortical bone mold (e) Cancellous bone mold

(f) Assembled Model

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PHOTOGRAPHS

Fig 3: Co-ordinate system

Fig 4: Contact Establishment

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PHOTOGRAPHS

Fig 5: Meshed model

Fig 6: Boundary conditions- Fixed support

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PHOTOGRAPHS

Fig 7: Loading Conditions Load 1 - Axial - (100N) Load 2 - Bucco lingual – (50N)

Load 3 - Mesio distal – (50N)

Fig 8(a): Stress and strain analysis in 3.5x10mm implant Load 1 - Axial (100N) Stress distribution pattern in Stress distribution pattern in cortical and cancellous bone implant