Quality of Heat-activated Acrylic Denture Base Resins Cured using Improvised Techniques in

95 Pages·2017·2.97 MB·English

by  Kaaria Mwirigi Mburu

QUALITY OF HEAT-ACTIVATED ACRYLIC DENTURE BASE
RESINS CURED USING IMPROVISED TECHNIQUES IN
PRIVATE DENTAL LABORATORIES IN NAIROBI, KENYA

KAARIA MWIRIGI MBURU, BDS (NBI), V60/75834/2014

Thesis submitted in partial fulfillment of the requirements for the award of Masters of
Dental Surgery Degree in Prosthodontics, Department of Conservative and Prosthetic
Dentistry, School of Dental Sciences, University of Nairobi

AUGUST 2017
DECLARATION OF ORIGINALITY
I, Dr. Kaaria Mwirigi Mburu, V60/75834/2014 of College of Health Sciences, School of Dental
Sciences, Department of Conservative and Prosthetic Dentistry, declare that this thesis titled
“QUALITY OF HEAT-ACTIVATED ACRYLIC DENTURE BASE RESINS CURED
USING IMPROVISED TECHNIQUES IN PRIVATE DENTAL LABORATORIES IN
NAIROBI, KENYA” is my original work.
Where other people’s work has been used it has been properly referenced and acknowledged
according to the University of Nairobi requirements.
I have not allowed and shall not allow anyone to copy my work with the intention of passing it
off as her/his own work.
I understand that any false claim in respect to this thesis report shall result in disciplinary action
in accordance to the University of Nairobi Plagiarism policy.
Signature
Date

i
APPROVAL
This thesis has been submitted with our approval as University of Nairobi supervisors.
Dr. B K Kisumbi BDS (Nbi), MPhil (Manchester), FCID. Senior Lecturer, Department of
Conservative and Prosthetic Dentistry, University of Nairobi.
Signature Date

Dr. J M Nyaga BDS (Nbi), MDS Prosthodontics (Nbi). Lecturer, Department of Conservative
and Prosthetic Dentistry, School of Dental Sciences, University of Nairobi.
Signature Date

Prof. F G Macigo BDS (Nbi), MPH (Nbi), PGD-STI (Nbi), FICD. Associate Professor of
Community and Preventive Dentistry, School of Dental Sciences, University of Nairobi.
Signature Date

ii
DEDICATION

This work is dedicated to our son, Leon Mwaki Mwirigi.

iii
ACKNOWLEDGEMENTS

First, I thank the Almighty God for good health and strength to accomplish this task.
Secondly, I would like to thank the following people:
My supervisors Dr. B K Kisumbi, Dr. J M Nyaga and Prof. F.G. Macigo of the University of
Nairobi, School of dental sciences, for their immense support, forbearance and dedication.
The staff in the prosthetic laboratory of the School of Dental Sciences, University of Nairobi,
who spared no effort to ensure the experimental work was completed in time. Special mention of
Mr. Josphat Miyogo, Mr. Dennis Kota and Mr. Albert Mulewa for going the extra mile.
All the dental technologists who consented to participate in this study and allowed me into their
private dental laboratories.
The staff at the Materials Testing Laboratory at the Kenya Bureau of Standards, in particular,
Dr. Geoffrey Muriira and Mr. Boniface Mbithi for their generosity, dedication and tireless efforts
to ensure the analytical work met international standards. In addition, I would like to thank Mr.
Stephen Ndeti for assisting with the Vickers Hardness Tests.
My employer and sponsor, the University of Nairobi for giving me time off to study and for
waiving the fees.
Mr. Desmond K’Owino of the School of Dental Sciences, University of Nairobi, who helped me
with the data analysis.
And lastly, my dear wife and colleague Dr. Laura Edalia-Mwirigi for walking with me every step
of the way.
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TABLE OF CONTENTS

DECLARATION OF ORIGINALITY .......................................................................................................... i
APPROVAL ................................................................................................................................................. ii
DEDICATION ............................................................................................................................................. iii
ACKNOWLEDGEMENTS ......................................................................................................................... iv
TABLE OF CONTENTS .............................................................................................................................. v
LIST OF TABLES ..................................................................................................................................... viii
LIST OF FIGURES ..................................................................................................................................... ix
ACRONYMS ............................................................................................................................................... xi
DEFINITION OF TERMS .........................................................................................................................xiii
ABSTRACT ................................................................................................................................................ xiv
CHAPTER 1: INTRODUCTION ................................................................................................................. 1
CHAPTER 2: LITERATURE REVIEW ...................................................................................................... 4
2.1 Historical development of denture bases ................................................................................................ 4
2.2 Classification of acrylic denture base materials ...................................................................................... 6
2.3 Processing techniques for acrylic based denture base resins .................................................................. 9
2.4 Improvised curing techniques ............................................................................................................... 10
2.5 Residual methyl methacrylate monomer ............................................................................................... 11
2.6 Resistance to indentation of the denture bases ...................................................................................... 13
2.7 Water Sorption and Solubility............................................................................................................... 14
2.8 Porosity of the denture base .................................................................................................................. 14
CHAPTER 3: STATEMENT OF THE RESEARCH PROBLEM AND JUSTIFICATION ..................... 16
3.1 Statement of the research problem ........................................................................................................ 16
3.2 Justification of the study ....................................................................................................................... 16
3.3 Study objective ...................................................................................................................................... 17
3.4 Hypothesis............................................................................................................................................. 17
3.5 Variables ............................................................................................................................................... 18
CHAPTER 4: MATERIALS AND METHODS ........................................................................................ 19
4.1 Study area.............................................................................................................................................. 19
4.2 Study design .......................................................................................................................................... 19
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4.3 Inclusion and exclusion criteria ............................................................................................................ 19
4.3.1 Inclusion criteria ........................................................................................................................ 19
4.3.2 Exclusion criteria ....................................................................................................................... 20
4.4 Identification of the improvised curing techniques (ICTS) .................................................................. 20
4.4.1 Pilot study .................................................................................................................................. 20
4.4.2 Sample size determination for the exploratory quasi-experiment .............................................. 21
4.5 Data reliability and validity .................................................................................................................. 22
4.6 Laboratory procedures and techniques ................................................................................................. 23
4.6.1 Improvised curing techniques for heat-activated PMMA denture base resins ........................... 23
4.6.2 Improvised curing technique 1 ................................................................................................... 23
4.6.3 Improvised curing technique 2 ................................................................................................... 24
4.6.4 Improvised curing technique 3 ................................................................................................... 25
4.6.5 Heat-activated acrylic resin used for specimen preparation ....................................................... 26
4.6.6 Specimen preparation for residual methyl methacrylate monomer evaluation .......................... 28
4.7 Evaluation for water sorption (Wsp) and water solubility (Wsi) .......................................................... 32
4.7.1 Preparation of test specimens ..................................................................................................... 32
4.7.2 Desiccated specimens ................................................................................................................ 33
4.7.3 Wet specimens ........................................................................................................................... 36
4.8 Evaluation of resistance to indentation ................................................................................................. 37
4.8.1 Specimen preparation ................................................................................................................. 37
4.8.2 Vickers hardness test .................................................................................................................. 38
4.8.3 Denture base porosity ........................................................................................................................ 40
4.8.4 Data analysis and presentation ........................................................................................................... 40
CHAPTER 5: RESULTS ............................................................................................................................ 41
5.1 Use of a thermo-regulated curing bath .................................................................................................. 41
5.2 Reasons given for use of improvised curing techniques ....................................................................... 41
5.3 Improvised curing techniques utilized .................................................................................................. 42
5.4 Evaluation of residual methyl methacrylate monomer ......................................................................... 43
5.5 Resistance to indentation ...................................................................................................................... 46
5.6 Water sorption and solubility ................................................................................................................ 49
5.7 Evaluation for porosity ......................................................................................................................... 50
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5.8 Overall Ranking .................................................................................................................................... 51
CHAPTER 6: DISCUSSION ...................................................................................................................... 52
6.1 Processing techniques for heat-activated acrylic denture base resins. .................................................. 52
6.2 Residual Monomer Content .................................................................................................................. 53
6.3 Denture base porosity ........................................................................................................................... 54
6.4 Water sorption and solubility ................................................................................................................ 55
6.5 Resistance to indentation ...................................................................................................................... 56
6.6 Study Benefits ....................................................................................................................................... 58
6.7 Study Limitations .................................................................................................................................. 58
6.8 Conclusion ............................................................................................................................................ 58
6.9 RECOMMENDATIONS ...................................................................................................................... 59
REFERENCES ........................................................................................................................................... 60
APPENDIX 1: CONSENT INFORMATION ............................................................................................ 67
APPENDIX 2: CONSENT CERTIFICATE ............................................................................................... 68
APPENDIX 3: QUESTIONNAIRE............................................................................................................ 70
APPENDIX 4: DATA COLLECTION TOOL ........................................................................................... 74
APPENDIX 5 : ETHICAL APPROVAL .................................................................................................... 77

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LIST OF TABLES
Table 1: Sample size calculation.………………………………………………………………...22
Table 2: Technical data for heat-cure acrylic resin, LUCITONE 199 ®………………………...27
Table 3: One-way Analysis of Variance test for residual methyl methacrylate levels for
improvised curing techniques and the control cycle……………………………………………..44
Table 4: Fisher’s Least Significant Difference Post Hoc analysis tests for Residual
Monomer………………………………………………………………………………………....45
Table 5: One-way Analysis of variance test for resistance to indentation: ……..........................47
Table 6: Fisher’s Least Significant Difference Post Hoc analysis tests for hardness…...…........48
Table 7: One-way analysis of variance test for water sorption …………...…………………......50
Table 8. Random ranking of the findings of this study where 1 is best and 4 is worst………....51

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LIST OF FIGURES

Figure 1: Apparatus for improvised curing technique 1……….……………………...………...24
Figure 2: Time and Temperatures curves for improvised curing techniques….…………...........24
Figure 3: Apparatus assembly for improvised curing technique 2……………..………… …....25
Figure 4: Heat activated acrylic denture base resin.……………..................................................27
Figure 5: The stainless steel moulds and flat stainless steel covers…………….…..………..….28
Figure 6: Stainless steel moulds mounted in type II gypsum………….…………………….......29
Figure 7: Open denture flasks with residual methyl methacrylate specimens……………...........30
Figure 8: Specimen discs for residual methyl methacrylate monomer evaluation……………...30
Figure 9: Methyl Methacrylate calibration curve ………………….…………..……………......31
Figure 10: Specimen dissolution for monomer extraction………………………………..……..32
Figure 11: Specimen discs for water sorption and solubility………………………………….....33
Figure 12: Calibrated Thermostatic oven…………….…………...…………………………….34
Figure 13: Specimens in self-indicating silica gel ……………………………...………….........34
Figure 14: Samples inside the oven in first stage of desiccation…………..………………........35
Figure 15: Analytical scale ………...……………………………………………….……….......35
Figure 16: Specimen placed in distilled water in the oven ……………………...………….…..37
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