thesis development of novel remineralising antimicrobial brushite cements

182 Pages·2014·11.86 MB·English

THESIS

DEVELOPMENT OF NOVEL REMINERALISING ANTIMICROBIAL
BRUSHITE CEMENTS

Thesis submitted by
Nor Azlina Ismail
BDS (Malaysia)

In partial fulfilment of the requirements for the Degree of
CLINICAL DOCTORATE IN DENTISTRY (PAEDIATRIC DENTISTRY)
UNIVERSITY COLLEGE LONDON

2014

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DECLARATION OF ORIGINALITY

I hereby certify that the work embodied in this thesis is the result of my own
investigations, except where otherwise stated. Information derived from the published
and unpublished work of others had been acknowledged in the text and the relevant
references are included in this thesis.

Nor Azlina Ismail
Eastman Dental Institute, University College London
September 2014

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ACKNOWLEDGMENT

I wish to express my extreme appreciation firstly to Dr Anne Young. Her guidance and
unending quest to understand had profound impact on my skills, my drive and my
philosophy. I thank her for giving me the opportunity and the pleasure of working with
her during this research.

My deepest gratitude also goes to my supervisor Dr Paul Ashley. His excellent
guidance and invaluable assistance enable me to complete my thesis successfully.

I would also like to thank, Dr Wendy Xia, Dr Graham Palmer and Dr George Georgiou
for their help in my experimental works, for which I am much obliged.

The author acknowledges the scholarship and study leave by Ministry of Higher
Education Malaysia and Islamic Science University of Malaysia (USIM).

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Dedication
This work is lovingly dedicated to my husband and both of my sons; for their support,
encouragement, and constant love which have sustained me throughout my life.
Finally, my parents for their unconditional love.

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ABSTRACT

Brushite cements have potential as drug carriers and bone filling materials. They can
also act as a reservoir for calcium and phosphate ions in remineralisation of hard
tissues.
Aim and objectives: To optimize brushite cement properties and assess the effect of
incorporation of a novel antimicrobial ε-polylysine (PLS) into brushite.
Materials and Methods: Powders were mixed with aqueous solutions at a powder to
liquid ratio of 3.3:1 or 4:1 to produce cement pastes and start the setting reaction. The
powder consisted of 1g of monocalcium phosphate monohydrate (MCPM) and 1.23 g
of β -tricalcium phosphate (β-TCP). Two different types of MCPM and different β-TCP
particle size range from 4 micron to 34 micron were used. The liquid phase was
prepared by dissolving PLS powder in aqueous citric acid 800 mM in incrementally
percentages. In control formulations, only citric acid 800 without the PLS was
employed. Biaxial flexural strength and modulus were determined using a ball on ring
jig. Setting kinetics and chemistry were examined using Fourier transforms infrared
spectroscopy (FTIR). Microstructure of brushite cements were examined with scanning
electron microscopy (SEM).
Results: The largest particle size of β-TCP (34 micron) produced the highest flexural
strength of 30 MPa. The handling of brushite cements was better with MCPM 2
(Sigma). This was observed to have much larger flat crystals rather than the more
powdered MCPM 1 from Himed. Powder to liquid ratio 4:1 overall increased the
strength 5 MPa – 7 MPa compared to powder to liquid ratio 3.3:1. High levels of PLS
could be added with only a minor reduction in the strength. Setting time however was
delayed and an alternative anhydrous dicalcium phosphate complex formed rather than
all brushite which is hydrated dicalcium phosphate.
Conclusion: The findings of this research demonstrated that very high levels of PLS
could be introduced into brushite cements without serious detrimental effects on
mechanical properties. PLS however, did delay the setting time and altered the final
chemistry and microstructure of the dicalcium phosphate product.
.
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Table of Contents

DECLARATION OF ORIGINALITY .................................................................................................... 2
ACKNOWLEDGMENT ..................................................................................................................... 3
ABSTRACT ...................................................................................................................................... 5
LIST OF TABLES ............................................................................................................................ 11
LIST OF EQUATION ...................................................................................................................... 12
ABBREVIATIONS .......................................................................................................................... 17
1 INTRODUCTION ................................................................................................................... 20
1.1 Statement of the problem .......................................................................................... 20
2 BACKGROUND ..................................................................................................................... 23
2.1 Tooth loss in children .................................................................................................. 23
2.1.1 Caries ................................................................................................................... 23
2.1.2 Trauma ....................................................................................................................... 23
2.2 Alveolar bone and alveolar ridge resorption .................................................................... 24
2.1.2 Function of Alveolar Bone ................................................................................... 24
2.3 Consequences of alveolar bone loss ................................................................................. 25
2.4 Current methods of alveolar bone preservation .............................................................. 26
2.4.1 Immediate placement of dental implant ................................................................... 26
2.4.2 Decoronation ............................................................................................................. 26
2.4.3 Immediate bone filling of extraction socket .............................................................. 27
2.5 Bone graft material ........................................................................................................... 27
2.6 Biological bone graft material ........................................................................................... 29
2.6.1 Autograft .................................................................................................................... 29
2.6.2 Allograft...................................................................................................................... 29
2.6.3 Xenogenic graft .......................................................................................................... 30
2.7 Alloplasts ........................................................................................................................... 30
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2.7.1 Bioactive glass and Glass ionomer cements .............................................................. 31
2.7.2 Aluminium oxide ........................................................................................................ 32
2.7.3 Polymethylmethacrylate ............................................................................................ 32
2.7.4 Beta tricalcium Phosphate ......................................................................................... 33
2.7.5 Synthetic hydroxyapatite ........................................................................................... 33
2.7.6 Calcium phosphate Cements ..................................................................................... 33
2.8. Hydroxyapatite ................................................................................................................. 35
2.9 Brushite Cements .............................................................................................................. 35
2.9.1 Setting time ................................................................................................................ 37
2.9.2 Mechanical properties ............................................................................................... 39
2.9.3. Shelf-life .................................................................................................................... 41
2.9.4 Injectability ................................................................................................................. 41
2.9.5 Degradation ............................................................................................................... 42
2.9.6 Adhesion .................................................................................................................... 43
2.9.7 Cohesion..................................................................................................................... 43
2.9.8 Bone formation .......................................................................................................... 44
2.9.9 Macroporosity ............................................................................................................ 44
2.9.10 Application ............................................................................................................... 45
2.10 Brushite cements with antibacterial properties ............................................................. 49
2.10.1 Chlorhexidine ........................................................................................................... 50
2.10.2 ε-Polylysine .............................................................................................................. 50
2.11 Citric acid as setting retardant ........................................................................................ 54
2.12 Summary ......................................................................................................................... 56
3 AIM AND OBJECTIVE ........................................................................................................... 59
3.1 Aim: ................................................................................................................................... 59
3.2 Null Hypothesis ................................................................................................................. 59
3.3 Objectives: ........................................................................................................................ 59
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4 MATERIAL AND METHODS .................................................................................................. 61
4.1 Materials ........................................................................................................................... 61
4.1.1 Powder ....................................................................................................................... 61
4.1.2 Liquid .......................................................................................................................... 64
4.2 Methods ............................................................................................................................ 64
4.2.1 Cement and disc preparation..................................................................................... 64
4.2.2 First series .................................................................................................................. 65
4.2.3 Second series ............................................................................................................. 65
4.2.4 Mechanical Property Studies ..................................................................................... 68
4.2.5 Study on setting kinetics ............................................................................................ 72
4.2.6 Scanning electron microscopy (SEM) ......................................................................... 73
4.2.7 Degradation study ...................................................................................................... 74
4.2.8 pH studies .................................................................................................................. 75
4.2.9 Drug release study ..................................................................................................... 75
4.2.4 Data analysis .............................................................................................................. 77
5 RESULTS............................................................................................................................... 80
5.1 Mechanical properties ................................................................................................ 80
5.1.1 Biaxial flexural strength (BFS) ............................................................................. 80
5.1.2 Biaxial flexural modulus (Young’s modulus) ....................................................... 83
5.1.3 Toughness ........................................................................................................... 86
5.2 Microstructure study using scanning electron microscopy (SEM) ............................. 89
5.2.1 Microstructure study of MCPM powder ............................................................. 89
5.2.2 Microstructure study of β-TCP powder .............................................................. 89
5.2.3 Microstructure study of ε-polylysine powder ..................................................... 89
5.2.4 Microstructure study of the set cements ........................................................... 94
5.3 Handling properties .................................................................................................. 103
5.4 Setting kinetics .......................................................................................................... 103
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5.4.1 Reference spectra ............................................................................................. 103
5.4.2 Setting reaction ................................................................................................. 106
5.4.3 Difference spectra ............................................................................................. 112
5.4.4 Absorbance change ........................................................................................... 118
5.5 Degradation study ..................................................................................................... 123
5.5.1 Mass loss of set cements with different MCPM ............................................... 123
5.5.2 Mass loss of set cements with increase wt % of ε-polylysine (PLS) .................. 124
5.6 pH study .................................................................................................................... 125
5.6.1 pH study for formulation with different MCPM’s ............................................. 125
5.6.2 pH study for formulation with increase wt % of ε-polylysine (PLS) .................. 126
5.7 ε-Polylysine release profile ....................................................................................... 127
5.7.1 Calibration curve of ε-polylysine ....................................................................... 127
5.7.2 ε-Polylysine release in water ............................................................................ 128
6 DISCUSSION ....................................................................................................................... 130
6.1 Mechanical properties of brushite cements ............................................................. 130
6.1.1 Biaxial flexural strength (BFS) .................................................................................. 130
6.1.2 Biaxial flexural modulus (BFM) ................................................................................ 131
6.1.3 Toughness ................................................................................................................ 131
6.2 Setting kinetics ................................................................................................................ 132
6.3 Scanning electron microscopy (SEM) .............................................................................. 134
6.4 Degradation .................................................................................................................... 135
6.5 ε-polylysine release study ............................................................................................... 136
6.6 Conclusion ....................................................................................................................... 137
6.6.1 Mechanical properties ............................................................................................. 137
6.6.2 Setting kinetic .......................................................................................................... 138
6.6.3 Microstructure of the cement ................................................................................. 138
6.6.4 Cement degradation ................................................................................................ 138
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6.6.5 pH and drug release study ....................................................................................... 138
6.7 Summary ............................................................................................................................. 139
7 FUTURE WORK .................................................................................................................. 141
7.1 Investigate effect of MCPM Himed ................................................................................. 141
7.2 Investigate effect of Strontium ....................................................................................... 141
7.3 Cohesion study ................................................................................................................ 141
7.4 Cement adhesion to dentine and bone .......................................................................... 142
7.5 Antibacterial study .......................................................................................................... 142
7.6 Cement injectibility ......................................................................................................... 142
7.7 Final composition of the cements ................................................................................... 142
7.8 Cement porosity .............................................................................................................. 143
7.9 Adding polyacrylic acid ................................................................................................... 143
7.10 Comparison to commercial product ............................................................................. 143
7.11 In vivo assessment of brushite cements ....................................................................... 143
8 REFERENCES ...................................................................................................................... 145
9 APPENDIX .......................................................................................................................... 155
Appendix 1: ............................................................................................................................... 155
Appendix 2 ................................................................................................................................ 164
Appendix 3 ................................................................................................................................ 173
ABSTRACT FOR IADR CONFERENCE........................................................................................... 182

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