Dowel design optimization in an endodontically treated single-rooted tooth: a finite element stress

218 Pages·2017·2.31 MB·English

by  Supanee Buranadham

University of Iowa
Iowa Research Online
Theses and Dissertations
Summer 2000
Dowel design optimization in an endodontically
treated single-rooted tooth: a finite element stress
analysis
Supanee Buranadham
University of Iowa
Copyright 2000 Supanee Buranadham
This dissertation is available at Iowa Research Online: https://ir.uiowa.edu/etd/191
Recommended Citation
Buranadham, Supanee. "Dowel design optimization in an endodontically treated single-rooted tooth: a finite element stress analysis."
PhD (Doctor of Philosophy) thesis, University of Iowa, 2000.
https://doi.org/10.17077/etd.tnijlb98
Follow this and additional works at:https://ir.uiowa.edu/etd
Part of theOral Biology and Oral Pathology Commons
DOWEL DESIGN OPTIMIZATION IN AN ENDODONTICALLY TREATED
SINGLE-ROOTED TOOTH: A FINITE ELEMENT STRESS ANALYSIS
by
Supanee Buranadham
A thesis submitted in partial fulfillment
of the requirements for the Doctor of
Philosophy degree in Oral Science
in the Graduate College of
The University of Iowa
July 2000
Thesis Supervisor: Associate Professor Clark M. Stanford
Copyright by
SUPANEE BURANADHAM
2000
All Rights Reserved
Graduate College
The University of Iowa
Iowa City, Iowa
CERTIFICATE OF APPROVAL
_______________________
PH.D. THESIS
_______________
This is to certify that the Ph.D. thesis of
Supanee Buranadham
has been approved by the Examining Committee
for the thesis requirement for the Doctor of Philosophy
degree in Oral Science at the July 2000 graduation.
Thesis Committee: ___________________________________
Clark M. Stanford, Thesis Supervisor
___________________________________
Steven A. Aquilino
___________________________________
John C. Keller
___________________________________
Vijay K. Goel
___________________________________
Joon B. Park
ACKNOWLEDGMENTS
I would like to thank Dr. Clark M. Stanford, Dr. Steven A. Aquilino, Dr. John C.
Keller, Dr. Vijay K. Goel and Dr. Joon B. Park, for their service on my thesis committee.
I would especially like to thank my mentor for the past six years, Dr. Clark M. Stanford
for his support, intellectual stimulation, patience and input on this project as well as my
prosthodontic education.
To Dr. Steven A. Aquilino goes my deep sense of gratitude. His backing and
encouragement were invaluable. His clinical expertise, knowledge and dedication to
patients and students inspire me to be a better prosthodontist and a better teacher.
I would like to extend a special thanks to Dr. M. Ashgar Bhatti who never got
tired of answering my questions on finite element analysis. I would also like to thank Dr.
Piyawat Phankosol for his interest in helping me develop as a researcher and a
prosthodontist since I was an undergraduate student.
My great gratitude goes to the Anandamahidol Foundation which was my sponsor
for my entire education here.
Most of all, I would like to thank my family, especially my parents who never let
me quit anything. Their love, support and encouragement have enabled me to attain my
goals.

ii
ABSTRACT
Improper dowel design can cause the failure of a restoration in an endodontically
treated single-rooted tooth. A three-dimensional finite element stress analysis was used
to evaluate stress patterns on an endodontically treated single-rooted tooth restored with a
tapered dowel and core and a complete crown under an angular load applied to the tip of
the crown. Results showed that, on the loading side, peak dentin and cement tensile
stresses were located at the level of the alveolar crest and at the crown margin,
respectively. Increasing the diameter and/or stiffness of the dowel decreased these peak
stresses; however, it increased the dentin and cement stresses at the dowel apex level, and
at the bone level, respectively. The role of the dowel length was to change the location of
the stress concentrations in the dentin occurring at the dowel apex. A large and short
dowel or a large and stiff (200 GPa) dowel might cause the root fracture to occur across
the dowel apex region. The ferrule had no effect on both the dentin and cement stresses
below the alveolar crest level. Increasing the ferrule height diminished the stress
propagating in the cement layer from the crown margin toward the tooth-core junction. If
root fracture occurred, the model predicted a horizontal fracture when the cement layer
was perfectly intact. A vertical root fracture was predicted when the cement was broken
at the crown margin on the loaded side. The ferrule effectively prevented the vertical
fracture. Reducing the bone height resulted in increasing the dentin and cement stresses at

and below the bone level. Extending the crown margin toward the bone level increased
the cement stress at the crown margin. With an application of the composite theory, it
could be demonstrated that while dowels might increase the stiffness of the system, it
might not strengthen the tooth under a transverse loading. In conclusion, dowel diameter,
dowel length (below the alveolar crest), dowel material, and ferrule are important factors
in predicting the failure of the dowel-core restoration. All factors have to be considered
together in the dowel design.
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TABLE OF CONTENTS
LIST OF TABLES ............................................................................................................. iv

LIST OF FIGURES .............................................................................................................v

CHAPTER I INTRODUCTION ..........................................................................................1
Purpose of the Study .........................................................................................4

CHAPTER II REVIEW OF THE LITERATURE...............................................................5
Historical Perspectives ......................................................................................5
Types of Dowels ...............................................................................................5
Cast Dowels and Cores ..............................................................................6
Prefabricated Dowels .................................................................................8
Functions of Dowels .......................................................................................10
Reinforcement .........................................................................................11
Clinical Failures of Teeth Restored with a Dowel-Core ................................13
Factors Contributing to Dowel Failures .........................................................18
Dowel Types and Surface Configuration ................................................18
Retention ..........................................................................................18
Marginal Leakage .............................................................................21
Stress and Fracture Resistance .........................................................21
Threaded Design .......................................................................21
Threaded Design vs. Non-Threaded Design .............................22
Non-Threaded Design ...............................................................23
Dowel Diameter .......................................................................................25
Retention ..........................................................................................26
Stress and Fracture Resistance .........................................................26
Dowel Length ..........................................................................................27
Retention ..........................................................................................28
Stress and Fracture Resistance .........................................................29
Remaining Tooth Structure .....................................................................30
Dentin Thickness ..............................................................................30
Ferrule Design ..................................................................................31
The Amount of Ferrule..............................................................33
Bevel Metal Collar ....................................................................34
Non-Metallic Dowels ......................................................................................35
Carbon-Fiber Reinforced Epoxy Resin Dowels ......................................35
Zirconia Dowels ......................................................................................37
Woven-Fiber Composite Materials .........................................................38
Stress Analysis ................................................................................................38
The Finite Element Method ............................................................................39
Brief History ............................................................................................39
Basic Description .....................................................................................40
Stress, Strain, and Hooke's Law ..............................................................44
Generalized Hooke's Law .................................................................47
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Finite Element Method in Stress Analysis ..............................................48
Types of Elements Used in Dowel-Core Stress Analysis .......................49
Plane Element ...................................................................................50
Axisymmetric Element .....................................................................50
3-D Solid Element ............................................................................50
Finite Element Studies in Dowel-Core Stress Analysis .................................51
General Limitations of Finite Element Study .................................................55

CHAPTER III EFFECTS OF REMAINING CORONAL TOOTH STRUCTURE
AND DOWEL DIMENSION ON TENSILE STRESSES IN THE
DENTIN AND THE CEMENT LAYER .......................................................57
Introduction .....................................................................................................57
Study Hypotheses ....................................................................................60
Materials and Methods ...................................................................................60
Tooth Models ...........................................................................................62
Finite Element Modeling .........................................................................67
Applied Boundary Conditions and Load ..........................................77
Model Examination ..........................................................................79
Examination of Displacements .................................................79
Examination of Interelement Discontinuities of the Stress
Contour Plot ..............................................................................79
Convergence Test ......................................................................79
Assumptions of the Model ...............................................................80
Analysis ...................................................................................................80
Broken Cement Layer Models .................................................................81
Results.............................................................................................................82
General Stress Distribution in Dentin ......................................................83
General Stress Distribution in Cement Layer ..........................................90
Factors Influencing Dentin and Cement Tensile Stresses .....................101
The Effect of Dowel Diameter and Length ....................................101
Dentin Stress ...........................................................................101
Cement Stress ..........................................................................104
The Effect of Ferrule ......................................................................106
Dentin Stress ...........................................................................106
Cement Stress ..........................................................................107
Broken Cement Layer ............................................................................109
Discussion .....................................................................................................113
Mode 1: Horizontal Root Fracture ........................................................114
Multiple Regression Analysis ........................................................115
Mode 2: Vertical Root Fracture .............................................................118
Reinforcement .......................................................................................120
Application of Composite Theory ..................................................120
Prediction of the Transverse Modulus ....................................121
Prediction of the Transverse Strength .....................................122
Limitations .............................................................................................124
Material Properties .........................................................................124
Models ............................................................................................124
Interfaces ........................................................................................125
Prediction Equations ......................................................................125
Clinical Implications .............................................................................126
Conclusions ...........................................................................................126
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CHAPTER IV EFFECTS OF DOWEL MATERIAL STIFFNESS AND DOWEL
DIAMETER ON TENSILE STRESSES IN THE DENTIN AND THE
CEMENT LAYER ........................................................................................128
Introduction ...................................................................................................128
Study Hypotheses ..................................................................................133
Materials and Methods .................................................................................133
Assumptions of the Model .....................................................................134
Analysis .................................................................................................135
Results...........................................................................................................135
Dentin Stress ..........................................................................................135
Cement Stress ........................................................................................140
Discussion .....................................................................................................145
Dentin Stress ..........................................................................................146
Multiple Regression Analysis ........................................................149
Reinforcement ................................................................................152
Cement Stress ........................................................................................155
Limitations .............................................................................................156
Clinical Implications .............................................................................156
Conclusions...................................................................................................157

CHAPTER V EFFECTS OF REDUCED ALVEOLAR BONE HEIGHT ON
TENSILE STRESSES IN THE DENTIN AND THE CEMENT
LAYER .........................................................................................................158
Introduction ...................................................................................................158
Study Hypotheses ..................................................................................162
Materials and Methods .................................................................................162
Assumptions of the Model .....................................................................168
Analysis .................................................................................................169
Results...........................................................................................................169
Dentin Stress ..........................................................................................169
Cement Stress ........................................................................................171
Discussion .....................................................................................................173
Limitations .............................................................................................176
Clinical Implications .............................................................................176
Conclusions...................................................................................................177

CHAPTER VI SUMMARY AND FUTURE DIRECTIONS .........................................178
Summary .......................................................................................................178
Future directions of study .............................................................................183

APPENDIX ......................................................................................................................184

BIBLIOGRAPHY ............................................................................................................193
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LIST OF TABLES
Table 1. Examples of prefabricated dowels. ........................................................................9
Table 2. Average crown and root lengths (mm). ...............................................................61
Table 3 . Average root diameters and recommended dowel sizes (mm). ..........................62
Table 4. Modeled tooth and dowel diameters at different locations (mm). .......................65
Table 5. Variations of the FE models ................................................................................67
Table 6. Elastic properties of material modeled. ...............................................................68
Table 7. The dentin stress difference* in different dowel designs. .................................115
Table 8. The least squares estimates of the regression coefficients, the estimated
standard errors, and the analysis of variance (R2 = 0.98, SE = 2.24). ....................116
Table 9. The predicted dentin stress difference* in different dowel designs. ..................117
Table 10. Elastic constant of dowel materials and dentin (GPa). ....................................131
Table 11. Variations of the FE models. ...........................................................................134
Table 12. Dentin tensile stress changes (in percentsa) at the alveolar crest level
when compared to the control model. .....................................................................138
Table 13 Dentin tensile stress changes (in percents) at the dowel apex level (6-mm
long) when compared to the control modela ...........................................................139
Table 14. Average cement tensile stress changes (in percents) at the crown margin
when compared to the control modela ....................................................................144
Table 15. The dentin stress differencea in different dowel designs. ................................147
Table 16. The least squares estimates of the regression coefficients, the estimated
standard errors and the analysis of variance (exclude the dowel width) (R2 =
0.96, SE = 2.92). .....................................................................................................149
Table 17. The predicted dentin stress differencea in different dowel designs. ................150
Table 18. Variations of the FE models ............................................................................162
Table 19. The ratio (in percents) between the dentin stresses at the dowel apex level
and at the alveolar crest ..........................................................................................171
Table 20. Raw data of Chapter IH. Dentin tensile stresses recorded in models of a
tooth with C:R = 11:14 with or without a cast dowel-core. ....................................184
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