Synthesis and characterization of non shrinking nanocomposites for dental applications 1

Physico-mechanical properties such as post-gel polymerization shrinkage, indentation hardness and modulus of the synthesized materials and their formulated neat resins were then investig

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

A CKNOWLEDGEMENTS

Interdependence 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

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

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

Chapter 3 RESEARCH PROGRAMME

3.1 Research Overview 3.2 Research Programme

39

42

45

51

SSQ-BASED MONOMERS: DI(PROPYLENE GLYCOL) ALLYL ETHER METHACRYLATE SIDE CHAINS

5.2 Materials and Methods 5.3 Results and Discussions 5.4 Conclusions

52

53

68

99

SSQ-BASED MONOMERS: PROPARGYL METHACRYLATE SIDE CHAINS

6.2 Materials and Methods 6.3 Results and Discussions 6.4 Conclusions

143

144

145

181

212

215

S UMMARY

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/cm2 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

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/mm3 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

various post-light polymerization time intervals 93

compounds

97

synthesized compounds to control

98

synthesized compounds to control 98

various post-light polymerization time intervals

135

synthesized compounds to control 140

synthesized compounds to control

140

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

shrinkage

152

compounds A - D with control in 5, 10, 20 and 50 wt%

of SSQ nanocomposite ratios

155

compounds A - D with control in 5, 10, 20 and 50 wt%

of SSQ nanocomposite ratios

158

blend of compounds E - H with control in 5, 10, 20 and

50 wt% of SSQ nanocomposite ratios respectively

167

shrinkage

170

compounds E - H with control in 5, 10, 20 and 50 wt%

of SSQ nanocomposite ratios

172

compounds E - H with control in 5, 10, 20 and 50 wt%

of SSQ nanocomposite ratios

175

various post-light polymerization time intervals 191

Table 8.4 Mean hardness of the different materials 197

L IST OF F IGURES

dimethacrylate

19

and nanocluster (Courtesy of 3M ESPE) 24

Figure 3.1 Example of SSQ-based monomers synthesized using

Pt-catalyzed hydrosilylation reaction

34

of trialkoxy- or trichlorosilanes 40

DPGAEM and 2 equivalents of VCE) 55

DPGAEM and 4 equivalents of VCE)

57

DPGAEM and 6 equivalents of VCE) 59

for the assessment of polymerization shrinkage 63

hydrosilylation of epoxy substituents on the cube

83

Figure 5.32 Mean linear shrinkage at various post-light

polymerization time intervals

and 2 equivalents of VCE)

106

hydrosilylation of propargyl and epoxy substituents on the cube

126

polymerization time intervals 136

A with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios during light polymerization

146

B with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios during light polymerization

147

C with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios during light polymerization

147

D with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios during light polymerization

148

compound A with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios at various post-light polymerization time intervals

150

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

compound C with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios at various post-light polymerization time intervals

151

compound D with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios at various post-light polymerization time intervals

151

compound A with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

156

compound B with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

156

compound C with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

157

compound D with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

157

compound A with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

159

compound B with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

159

compound C with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

160

compound D with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

160

E with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios during light polymerization

164

F with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios during light polymerization

165

G with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios during light polymerization

165

H with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios during light polymerization

166

compound E with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios at various post-light polymerization time intervals

168

compound F with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios at various post-light polymerization time intervals

168

compound G with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios at various post-light polymerization time intervals

169

compound H with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios at various post-light polymerization time intervals

169

compound E with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

173

compound F with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

173

compound G with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

174

compound H with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

174

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

compound F with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

176

compound G with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

177

compound H with control in 5, 10, 20 and 50 wt% of SSQ

nanocomposite ratios

177

for the assessment of polymerization shrinkage 186

component initiating system

216

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)

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 2nd 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 19th 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 3rdScientific 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 3rd 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 20thInternational 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

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

84th Annual General Session of the International Association for Dental Research, 28-1 July 2006, Brisbane, Australia

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 3rd Prize