Synthesis and characterization of non shrinking nanocomposites for dental applications 1

SYNTHESIS AND CHARACTERIZATION OF
“NON-SHRINKING” NANOCOMPOSITES FOR
DENTAL APPLICATIONS










SOH MUI SIANG
(BSC, BSc(Hons), MSC), NUS










A THESIS SUBMITTED
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF RESTORATIVE DENTISTRY
NATIONAL UNIVERSITY OF SINGAPORE
2006

i
ACKNOWLEDGEMENTS


I
nterdependence is a higher value than independence.

This thesis is the result of multi-disciplinary collaboration that involved people
from the Department of Restorative Dentistry, Faculty of Dentistry and the
Institute of Materials and Research Engineering (IMRE) whom I would like to
express my sincere gratitude.

I would like to thank Associate Professor Jennifer Neo Chew Lian, Head of
Restorative Dentistry, National University of Singapore for the opportunity and
support given to me throughout the course of my postgraduate study.

I would also like to thank and express my sincere gratitude to my supervisors,
Associate Professor Adrian Yap U Jin and Dr. Alan Sellinger for giving me the
opportunity to undertake this research. It is indeed my great honor to work and
learn from them. Despite their heavy work duties, they never fail to make time for
sharing research knowledge, for invaluable discussions and for giving scientific
advice. Their patience, constant guidance, encouragement, support and motivation
contribute much to the success of this research project.

I would also like to thank Research Scientist, Dr. Low Hong Yee for help and
invaluable discussions throughout the course of this project. Her patience and time
is most appreciated.


ii

I would also like to thank Dr. Sundarraj Sudhakar whom has been such a great
mentor and friend. His advice, guidance, help and encouragement have been of
great value in fulfilling this thesis.

Special thanks are also extended to Senior Laboratory Officer, Mr Chan Swee
Heng for his kind assistance, generous help and time. It is indeed a great pleasure
to work with him. His resourcefulness never fails to impress me.

I would also like to thank “big brother” Mr Chung Sew Meng for his guidance on
the use of the Instron machine. His generous help and assistance has been most
invaluable.

Heartfelt thank is also extended to Ms Jane Ong Lay Hoon, Ms Ng Bee Wee and
Mdm Ek Ben Lai for their constant administrative help and support. Without their
help, administrative work would not have been that smooth and easy.

Special appreciation is also extended to all my friends especially to Xiaoyan, Mee
Yoon, Thelese, Elaine, Christine, Zien, Wahab, Xiuwen, Soon Yee, Vicky, Yuan
Yuan, Dr. Sum Chee Peng, Saji and those countless others who have helped me in
every little way.

I would also like to show my appreciation to my sister, Mingjuan for help and
suggestions given in the completion of this thesis.

Finally, I am deeply grateful to my family, especially my parents, for raising me
to believe that with determination, dedication and enthusiasm you can achieve any
goal you can dream of. Their kind understanding, encouragement, support and
love throughout the years of my education have made this possible.

iii

TABLE oF CONTENTS



Foreword

Acknowledgements
i

Table of Contents
iii

Summary
vi

List of Tables
viii

List of Figures
xi

List of Publications


xix
Chapter 1

INTRODUCTION

1.1 Composite Resins – An Alternative to Dental
Amalgam
1.2 Research Objectives

1

3
Chapter 2

LITERATURE REVIEW


2.1 Chemically Cured Composite Resins
2.2 Light-activated Composite Resins
2.3 Organic Matrix
2.4 Inorganic Fillers
2.5 Silane Coupling Agent
2.6 Limitations of Current Dental Composites
2.6.1 Polymerization Shrinkage
2.7 New Resin Technology
2.7.1 Ring-opening Monomers
2.7.2 Liquid Crystalline Monomers
2.7.3 Branched and Dendritic Monomers
2.7.4 Ormocers
2.8 Nanotechnology with Dental Composites

5
6

8
10
11
12
12
15
15
18
20
20
21


iv
Chapter 3

RESEARCH PROGRAMME


3.1 Research Overview
3.2 Research Programme
32
33

Chapter 4


INORGANIC-ORGANIC SSQ AS SYNTHETIC
PLATFORMS

4.1 Introduction
4.2 Materials and Methods
4.3 Results and Discussions
4.4. Conclusions

39
42
45
51

Chapter 5


SYNTHESIS AND CHARACTERIZATION OF
SSQ-BASED MONOMERS: DI(PROPYLENE
GLYCOL) ALLYL ETHER METHACRYLATE
SIDE CHAINS


5.1 Introduction
5.2 Materials and Methods
5.3 Results and Discussions
5.4. Conclusions


52
53
68
99
Chapter 6

SYNTHESIS AND CHARACTERIZATION OF
SSQ-BASED MONOMERS: PROPARGYL
METHACRYLATE SIDE CHAINS


6.1 Introduction
6.2 Materials and Methods
6.3 Results and Discussions
6.4. Conclusions


101
102
110
142
Chapter 7

SSQ-BASED MONOMERS AS COPOLYMERS

7.1 Introduction
7.2 Materials and Methods
7.3 Results and Discussions
7.4. Conclusions


143
144
145

181

v
Chapter 8

EXPERIMENTAL SSQ-BASED
NANOCOMPOSITES


8.1 Introduction
8.2 Materials and Methods
8.3 Results and Discussions
8.4. Conclusions


182
183
189
211
Chapter 9

GENERAL CONCLUSIONS AND FUTURE
PERSPECTIVES


9.1 General Conclusions
9.2 Future Perspectives

212
215

References
220

vi
SUMMARY


The aim of this study was to design and develop novel low shrinkage
nanocomposites based on SSQ (Polyhedral Silsesquioxane) for dental
applications. SSQ based nanocomposites with various types of methacrylate
and/or epoxide functionalities were synthesized based on inexpensive starting
materials. The 8 synthesized SSQ compounds obtained in high yield were viscous
liquids at room temperature and formed soluble hybrids when formulated with
existing dental-based monomers in different proportions. The synthesized
materials were characterized chemically using FTIR, NMR, DSC, TGA and SEC
to confirm polymer structure and purity. Physico-mechanical properties such as
post-gel polymerization shrinkage, indentation hardness and modulus of the
synthesized materials and their formulated neat resins were then investigated and
compared with unfilled 1:1 (control) Bis-GMA / TEGDMA materials (typical
monomers used in dental composites). All samples investigated were cured using
a dental light-curing unit at 500mW/cm
2
for 40 seconds. At all time intervals,
shrinkage associated with the control was found to be significantly higher than all
SSQ based materials and their formulated neat resins. However, both hardness and
modulus of the control were found to be significantly higher than all SSQ based
materials and most of the formulated neat resins. It was observed that the addition
of as little as 5 wt% SSQ nanocomposites into the control monomers significantly

reduced polymerization shrinkage while maintaining useful mechanical properties.
Based on the study results, four promising materials were selected and developed
into experimental nanocomposites (S1 – S4) by reinforcing with 63 wt% of
commercial fillers. The experimental nanocomposites (S1 – S4) were then

vii
characterized for their physico-mechanical properties such as polymerization
shrinkage, hardness, modulus, depth of cure, degree of conversion and water
sorption. Results obtained were compared with various commercial dental
composites (Filtek Supreme [FS], Filtek Flow [FF] and Filtek A110 [A110]). At
60 minutes post-gel polymerization, shrinkage associated with the experimental
nanocomposites and commercial products ranged from (0.31 ± 0.03) to (0.42 ±
0.03)% and (0.54 ± 0.03) to (0.84 ± 0.07)% respectively. At all time intervals,
shrinkage associated with the experimental materials was found to be significantly
lower than the commercial products with depth of cure greater than 2mm obtained
for all materials. No significant difference in hardness was observed between S1,
A110 and FF. Modulus associated with S1 and S4 was found to be higher if not
equal to A110 and FF. The degree of conversion of S4 was also found to be higher
than A110. Water sorption obtained for all experimental nanocomposites was
found to be significantly lower than the commercial products and met the ISO
requirement of less than 40 μg/mm
3
. With the results obtained, we conclude that
SSQ based nanocomposites show potential for use as dental restoratives and
present a promising approach to achieve novel low/non–shrinking nanocomposite
based dental materials.

viii
LIST OF TABLES


Table 2.1
Classification of dental composites by filler particle
size.

10
Table 5.1
Size Exclusion Chromatography (SEC) data of
synthesized SSQ compounds.

83
Table 5.2 Thermogravimetric Analysis (TGA) data of synthesized
compounds.

86
Table 5.3
Differential Scanning Calorimetry (DSC) data. 89

Table 5.4
Mean linear percent polymerization shrinkage at the
various post-light polymerization time intervals.

93
Table 5.5
Results of statistical analysis.

94
Table 5.6
Hardness values of synthesized compounds.

96
Table 5.7
Modulus values of control and synthesized SSQ
compounds.

97
Table 5.8
Comparison of mean hardness values of the various
synthesized compounds to control.

98
Table 5.9 Comparison of mean modulus values of the various
synthesized compounds to control.

98
Table 6.1
SEC data of compounds E - H.

127
Table 6.2 Thermogravimetric analysis data of compounds E - H.

130
Table 6.3
DSC data for compounds E - H.

133
Table 6.4
Mean linear percent polymerization shrinkage at the
various post-light polymerization time intervals.

135
Table 6.5
Results of statistical analysis.

136
Table 6.6
Hardness values of synthesized compounds.

138
Table 6.7
Modulus values of control and synthesized SSQ
compounds.

139
Table 6.8
Comparison of mean hardness values of the various
synthesized compounds to control.

140

ix
Table 6.9
Comparison of mean modulus values of the various
synthesized compounds to control.

140
Table 7.1
Mean linear percent polymerization shrinkage at the
various post-light polymerization time intervals of
control and binary blend of compounds A - D with
control in 5, 10, 20 and 50 wt% of SSQ nanocomposite
ratios respectively.

149
Table 7.2
Results of statistical analysis of post-gel linear
shrinkage.

152
Table 7.3
Hardness values of the control and binary blend of
compounds A - D with control in 5, 10, 20 and 50 wt%
of SSQ nanocomposite ratios.

155
Table 7.4
Elastic modulus of the control and binary blend of
compounds A - D with control in 5, 10, 20 and 50 wt%

of SSQ nanocomposite ratios.

158
Table 7.5
Results of statistical analysis of mean hardness data. 161
Table 7.6
Results of statistical analysis of mean modulus data. 161
Table 7.7
Mean linear percent shrinkage of control and binary
blend of compounds E - H with control in 5, 10, 20 and
50 wt% of SSQ nanocomposite ratios respectively.

167
Table 7.8
Results of statistical analysis of post-gel linear
shrinkage.

170
Table 7.9
Hardness values of the control and binary blend of
compounds E - H with control in 5, 10, 20 and 50 wt%
of SSQ nanocomposite ratios.

172
Table 7.10
Elastic modulus of the control and binary blend of
compounds E - H with control in 5, 10, 20 and 50 wt%
of SSQ nanocomposite ratios.

175

Table 7.11
Results of statistical analysis of mean hardness data. 178
Table 7.12
Results of statistical analysis of mean modulus data. 178
Table 8.1
The experimental and composite materials evaluated.

185
Table 8.2
Mean linear percent polymerization shrinkage at the
various post-light polymerization time intervals.

191
Table 8.3
Results of statistical analysis. 192

x
Table 8.4
Mean hardness of the different materials.

197
Table 8.5
Mean modulus of the different materials.

198
Table 8.6
Statistical comparison of hardness between materials.

199
Table 8.7

Statistical comparison of modulus between materials.

200
Table 8.8
Mean degree of conversion of the different materials.

202
Table 8.9
Results of statistical analysis of the mean degree of
conversion.

202
Table 8.10
Depth of cure of the different materials. 206
Table 8.11
Statistical comparison of depth of cure between
materials.

206
Table 8.12
Results of water sorption obtained for the different
materials.

209
Table 8.13
Results of statistical analysis. 209

xi
LIST OF FIGURES


Figure 2.1
Chemical activation of dibenzoyl peroxide to produce free

radical for polymerization.

6
Figure 2.2
Chemical structure of Bis-GMA monomers. 7
Figure 2.3
Light activation mechanism.

8
Figure 2.4
Chemical structures of common base monomers used in
dental composites.

9
Figure 2.5
Structure of MPTS, a typical silane coupling agent used in
dental composites.

11
Figure 2.6
Chemical structures of SOCs containing methylene
groups.

16
Figure 2.7
Chemical structures of SOC-substituted methacrylate. 16
Figure 2.8
Cationic polymerizable SOC. 17
Figure 2.9
Chemical structures of cycloaliphatic diepoxide and

polyol.

18
Figure 2.10
One example of near room temperature liquid crystalline
dimethacrylate.

19
Figure 2.11
Branched liquid crystalline bismethacrylates.

20
Figure 2.12
Synthesis of SiO
2
nanostructures. 21
Figure 2.13
Transmission electron micrographs of a hybrid, nanomer
and nanocluster (Courtesy of 3M ESPE).

24
Figure 2.14
The Stöber process. 26
Figure 2.15
Example of commercially available methacrylate silanes.

28
Figure 2.16
Mono-methacrylate functionalized POSS
TM

. 29
Figure 2.17
POSS
TM
-MA. 30
Figure 2.18
Epoxy functionalized POSS
TM
structure. 30
Figure 2.19
Siloxane dendrimers.

31

xii
Figure 3.1
Example of SSQ-based monomers synthesized using Pt-
catalyzed hydrosilylation reaction.

34
Figure 4.1
Some common structures of silsesquioxane. 40
Figure 4.2
Silsesquioxanes produced by hydrolysis and condensation
of trialkoxy- or trichlorosilanes.

40
Figure 4.3
Synthesis of hydridosilsesquioxane, (HSiO
1.5

)
n.
41
Figure 4.4
Synthesis of “Octaanion”.

43
Figure 4.5
Synthesis of Octa(hydridodimethylsiloxy)silsesquioxane,
(HMe
2
SiOSiO
1.5
)
8.


44
Figure 4.6
29
Si NMR for the “octaanion” silsesquioxane.

46
Figure 4.7
1
H NMR of Octa(hydridodimethylsiloxy)silsesquioxane,
(HMe
2
SiOSiO
1.5

)
8
.

47
Figure 4.8
13
C NMR of Octa(hydridodimethylsiloxy)silsesquioxane,
(HMe
2
SiOSiO
1.5
)
8
.

48
Figure 4.9
29
Si NMR of Octa(hydridodimethylsiloxy)silsesquioxane,
(HMe
2
SiOSiO
1.5
)
8
.

49
Figure 4.10

FTIR spectrum of
octa(hydridodimethylsiloxy)silsesquioxane.

50
Figure 5.1
Synthesis of compound A (SSQ with 8 equivalents of
DPGAEM).

54
Figure 5.2
Synthesis of compound B (SSQ with 6 equivalents of
DPGAEM and 2 equivalents of VCE).

55
Figure 5.3
Synthesis of compound C (SSQ with 4 equivalents of
DPGAEM and 4 equivalents of VCE).

57
Figure 5.4
Synthesis of compound D (SSQ with 2 equivalents of
DPGAEM and 6 equivalents of VCE).

59
Figure 5.5
VIP light-curing unit. 61
Figure 5.6
Diagrammatic representation of the experimental set-up
for the assessment of polymerization shrinkage.

63
Figure 5.7
Strain-monitoring device. 64

xiii
Figure 5.8
Depth-sensing microindentation test set-up. 67
Figure 5.9
1
H NMR of compound A. 71
Figure 5.10
13
C NMR of compound A. 72
Figure 5.11
29
Si NMR of compound A. 73
Figure 5.12
1
H NMR of compound B. 74
Figure 5.13
13
C NMR of compound B. 75
Figure 5.14
29
Si NMR of compound B. 76
Figure 5.15
1
H NMR of compound C. 77
Figure 5.16
13

C NMR of compound C. 78
Figure 5.17
29
Si NMR of compound C. 79
Figure 5.18
1
H NMR of compound D. 80
Figure 5.19
13
C NMR of compound D. 81
Figure 5.20
29
Si NMR of compound D. 82
Figure 5.21
α and β-trans isomer arising from Pt-catalyzed
hydrosilylation of epoxy substituents on the cube.

83
Figure 5.22 SEC chromatogram for compound A. 84
Figure 5.23
SEC chromatogram for compound B. 84
Figure 5.24
SEC chromatogram for compound C. 85
Figure 5.25
SEC chromatogram for compound D. 85
Figure 5.26
TGA profile of compound A. 87
Figure 5.27
TGA profile of compound B. 87
Figure 5.28

TGA profile of compound C. 88
Figure 5.29
TGA profile of compound D. 88
Figure 5.30
Representative DSC plot for compound A. 90
Figure 5.31 Mean shrinkage during light polymerization.

92

xiv
Figure 5.32
Mean linear shrinkage at various post-light
polymerization time intervals.

93
Figure 5.33
Mean hardness values of control and synthesized SSQ
compounds.

96
Figure 5.34
Elastic modulus of control and synthesized SSQ
compounds.

97
Figure 6.1
Synthesis of compound E (SSQ with 8 equivalents of
PM).

103

Figure 6.2
Synthesis of compound F (SSQ with 6 equivalents of PM
and 2 equivalents of VCE).

104
Figure 6.3
Synthesis of compound G (SSQ with 4 equivalents of PM
and 2 equivalents of VCE).

106
Figure 6.4
Synthesis of compound H (SSQ with 2 equivalents of PM
and 6 equivalents of VCE).

108
Figure 6.5
Oxysilylation reaction associated with allyloxy chemistry. 111
Figure 6.6
1
H NMR of compound E. 113
Figure 6.7
13
C NMR of compound E. 114
Figure 6.8
29
Si NMR of compound E. 115
Figure 6.9
1
H NMR of compound F. 116
Figure 6.10

13
C NMR of compound F. 117
Figure 6.11
29
Si NMR of compound F. 118
Figure 6.12
1
H NMR of compound G. 119
Figure 6.13
13
C NMR of compound G. 120
Figure 6.14
29
Si NMR of compound G. 121
Figure 6.15
1
H NMR of compound H. 122
Figure 6.16
13
C NMR of compound H. 123
Figure 6.17
29
Si NMR of compound H. 124
Figure 6.18 α and β-trans isomer arising from Pt-catalyzed
hydrosilylation of propargyl and epoxy substituents on the
cube.
126

xv
Figure 6.19

SEC chromatogram for compound E. 127
Figure 6.20
SEC chromatogram for compound F. 128
Figure 6.21
SEC chromatogram for compound G. 128
Figure 6.22
SEC chromatogram for compound H. 129
Figure 6.23
TGA profile of compound E. 130
Figure 6.24
TGA profile of compound F. 131
Figure 6.25
TGA profile of compound G. 131
Figure 6.26
TGA profile of compound H. 132
Figure 6.27
Representative DSC plot for compound F. 133
Figure 6.28
Mean shrinkage during light polymerization. 135
Figure 6.29
Mean linear shrinkage at various post-light
polymerization time intervals.

136
Figure 6.30
Mean hardness values of control and synthesized SSQ
compounds.

138
Figure 6.31

Elastic modulus of control and synthesized SSQ
compounds.

139
Figure 7.1 Mean shrinkage of control and binary blend of compound
A with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios during light polymerization.

146
Figure 7.2
Mean shrinkage of control and binary blend of compound
B with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios during light polymerization.

147
Figure 7.3
Mean shrinkage of control and binary blend of compound
C with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios during light polymerization.

147
Figure 7.4
Mean shrinkage of control and binary blend of compound
D with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios during light polymerization.

148
Figure 7.5
Mean linear shrinkage of control and binary blend of
compound A with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios at various post-light polymerization
time intervals.

150

xvi
Figure 7.6
Mean linear shrinkage of control and binary blend of
compound B with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios at various post-light polymerization
time intervals.

150
Figure 7.7
Mean linear shrinkage of control and binary blend of
compound C with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios at various post-light polymerization
time intervals.

151
Figure 7.8
Mean linear shrinkage of control and binary blend of
compound D with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios at various post-light polymerization
time intervals.

151
Figure 7.9
Mean hardness values of control and binary blend of
compound A with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios.

156
Figure 7.10 Mean hardness values of control and binary blend of
compound B with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

156
Figure 7.11
Mean hardness values of control and binary blend of
compound C with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

157
Figure 7.12
Mean hardness values of control and binary blend of
compound D with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

157
Figure 7.13
Mean elastic modulus of control and binary blend of
compound A with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

159
Figure 7.14
Mean elastic modulus of control and binary blend of
compound B with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

159
Figure 7.15
Mean elastic modulus of control and binary blend of
compound C with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

160
Figure 7.16
Mean elastic modulus of control and binary blend of
compound D with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

160
Figure 7.17 Mean shrinkage of control and binary blend of compound
E with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios during light polymerization.
164

xvii
Figure 7.18
Mean shrinkage of control and binary blend of compound
F with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios during light polymerization.

165
Figure 7.19
Mean shrinkage of control and binary blend of compound
G with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios during light polymerization.

165
Figure 7.20
Mean shrinkage of control and binary blend of compound
H with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios during light polymerization.

166
Figure 7.21
Mean linear shrinkage of control and binary blend of
compound E with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios at various post-light polymerization
time intervals.

168
Figure 7.22
Mean linear shrinkage of control and binary blend of
compound F with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios at various post-light polymerization
time intervals.

168
Figure 7.23
Mean linear shrinkage of control and binary blend of
compound G with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios at various post-light polymerization
time intervals.

169
Figure 7.24

Mean linear shrinkage of control and binary blend of
compound H with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios at various post-light polymerization
time intervals.

169
Figure 7.25
Mean hardness values of control and binary blend of
compound E with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

173
Figure 7.26
Mean hardness values of control and binary blend of
compound F with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

173
Figure 7.27
Mean hardness values of control and binary blend of
compound G with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

174
Figure 7.28
Mean hardness values of control and binary blend of
compound H with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

174

xviii
Figure 7.29
Mean elastic modulus of control and binary blend of
compound E with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

176
Figure 7.30
Mean elastic modulus of control and binary blend of
compound F with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

176
Figure 7.31
Mean elastic modulus of control and binary blend of
compound G with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

177
Figure 7.32
Mean elastic modulus of control and binary blend of
compound H with control in 5, 10, 20 and 50 wt% of SSQ
nanocomposite ratios.

177
Figure 8.1
Diagrammatic representation of the experimental set-up

for the assessment of polymerization shrinkage.

186
Figure 8.2
Mean shrinkage during light polymerization.

191
Figure 8.3
Mean shrinkage post-light polymerization. 192
Figure 8.4
Mean hardness of the different materials. 198
Figure 8.5
Mean modulus of the different materials 199
Figure 8.6
Mean degree of conversion of the different materials. 203
Figure 8.7
Depth of cure of the different materials. 207
Figure 8.8
Mean water sorption obtained for the different materials. 209
Figure 9.1
Polymerization of the epoxy groups using the 3
component initiating system.

216
Figure 9.2
Synthesis of cyclohexyl BZO. 217
Figure 9.3
Hydrosilylation reaction of SSQ with 8 equivalents of
cyclohexyl BZO.

218
Figure 9.4
Ring-opening of cyclohexyl BZO upon polymerization. 218









xix
LIST OF PUBLICATIONS


Sections of the results/ related research in this thesis have been presented,
published, accepted for publication or are submitted.

International Papers
1. Soh MS, AUJ Yap and A Sellinger, Dental Nanocomposites. Current
Nanoscience, 2, 4 (2006) 373 -381. (United States)
.

2. Soh MS, AUJ Yap and A Sellinger, Methacrylate and Epoxy
Functionalized Nanocomposites based on Silsesquioxane Cores for use in
Dental Applications. European Polymer Journal, 43 (2007) 315-327.
(Europe).

3. Soh MS, AUJ Yap and A Sellinger, Physicomechanical Evaluation of

Low-shrink Dental Nanocomposites based on Silsesquioxane Cores.
European Journal of Oral Science (Accepted for publication).

4. Soh MS, AUJ Yap and A Sellinger, Effect of Chain Modifications on the
Physico-mechanical Properties of Silsesquioxane-based Dental
Nanocomposites. Journal of Biomedical Research Part B. Applied
Biomaterials (Submitted for publication).

5. Soh MS, AUJ Yap and A Sellinger, Silsesquioxanes-based
Nanocomposites as Copolymers for Low Shrinkage Dental Composite.
Biomacromolecules (Submitted for publication).

6. Soh MS, AUJ Yap and A Sellinger, Synthesis and Characterization of Low
Shrinking Silsesquioxanes-based Experimental Nanocomposites for Dental
Applications. Biomacromolecules (To be submitted for publication
pending invention disclosure).

xx
Conference Papers

1. Soh MS, Sellinger A and Yap AUJ, Synthesis and Characterization of
New Nanocomposite Monomers for use in Low Shrinkage Dental
Restorations. Paper presented at 2
nd
IMRE Poster competition, 21 July
2004, Singapore.

2. Soh MS, Sellinger A and Yap AUJ, Synthesis and characterization of new
monomers for dental restorations. Paper presented at 19
th

International
Association for Dental Research (South-East Asian Division) Annual
Meeting, 3-6 September 2004, Koh Samui, Thailand.

3. Soh MS, Yap AUJ and Sellinger A, Mechanical characterization of new
monomers synthesized for dental restorations. Paper presented at 3
rd

Scientific NHG Congress, 9-11 October 2004, Singapore.

4. Soh MS, Sellinger A and Yap AUJ, Low Shrinkage Nanocomposites based
on Silsesquioxane Cores for Applications in Dental Composites. Paper
presented at 3
rd
International Conference on Materials for Advanced
Technologies (ICMAT) 2005, Singapore.

5. Soh MS, Sellinger A and Yap AUJ, The Development of Novel Low
Shrinkage POSS based Nanocomposites. Paper presented at 20
th

International Association for Dental Research (South-East Asian Division)
Annual Meeting, 1-4 September 2005, Malacca, Malaysia.

6. Soh MS, Yap AUJ and Sellinger A, Mechanical Properties of Novel
Nanocomposites Developed for Dental Restorations. Paper presented at
Combined Scientific Meeting (CSM) 2005, Singapore.

7. Soh MS, Sellinger A and Yap AUJ, Low-shrinking Novel POSS Based
Nanocomposites Developed for Dental Applications. Paper presented at

Combined Scientific Meeting (CSM) 2005, Singapore.


xxi
8. Soh MS, Sellinger A and Yap AUJ, The Development of Novel Low
Shrinkage POSS based Nanocomposites. Paper presented at SERC Inter-
RI Poster Symposium, 19 September 2005, Singapore.

9. Soh MS, Sellinger A and Yap AUJ, Post-gel Polymerization Shrinkage of
Novel Low-shrinking POSS Based Nanocomposites. Paper presented at
84
th
Annual General Session of the International Association for Dental
Research, 28-1 July 2006, Brisbane, Australia.

Awards
1. Soh MS, Sellinger A and Yap AUJ, The Development of Novel Low
Shrinkage POSS Based Nanocomposites.

Awarded Best paper in Dental Materials Research Category in 20
th

International Association for Dental Research (South-East Asian Division)
Annual Scientific Meeting, 1-4 September 2005, Malacca, Malaysia.

2. Soh MS, Sellinger A and Yap AUJ, Synthesis and Characterization of
New Nanocomposite Monomers For Use In Low Shrinkage Dental
Restorations.

Awarded IMRE Poster Competition 2004 3

rd
Prize.