Research Mentor: Dr. Paul Buonora California State University Long Beach

1. Synthesis of Varying Length Polyhedral Oligomeric Silsesquioxane Methyl-Methacrylate (POSS-MMA) and its Effect on Viscosity and Polymerization Shrinkage of Neat Dental Resin Formulations Research Mentor: Dr. Paul Buonora California State University Long Beach

2. Outline • Introduction • Materials/Methods • Results • Conclusions/Summary • Future Experiments • Acknowledgements

3. What are dental restorative materials? • A mixture of one to several monomers that are able to polymerize or copolymerize upon light-curing (i.e. composites) • Materials usually consisting of methacrylate ester functionalities (i.e. BisGMA/TEGDMA)

4. What should these materials be able to do? • Should have: high resistance to erosion, degradation, and thermal stresses • Retain high tensile and compressive strength, while being biologically inert or bioactive. • Should be easily mixed and placed as an unset paste, have short working and setting times, react rapidly, and give color and translucency which match that of the natural tooth

5. Drawbacks of current materials • High viscosity – these materials become difficult for dental clinicians to extract from tubes designed for small scale applications like placement on teeth • Large polymerization shrinkage – these materials tend to shrink in volume after curing with blue light (foods and liquids can accumulate in these cavities and cause more tooth damage)

6. Polyhedral Oligomeric Silsesquioxanes • Inorganic-Organic Hybrids • Strictly defined inorganic cubic structure of alternating array of silicon and oxygen atoms • Eight pendant side chains tethered to cube center • Inorganic unreactive center and organic reactive side chains

7. POSS Structure * Soluble in methylene chloride

8. Why POSS? • Provides a new class of monomer having the potential to reduce both viscosity and shrinkage • Its defined nano-sized architecture offers a unique opportunity to modify its octameric sites through the addition of organic groups tethered to its vertices • Provides a multitude of possibilities for the synthesis of hyperbranched dendrimer systems.

9. Materials/Methods • Starting Compounds: • POSS • allyloxytrimethylsilane (varying lengths) • BisGMA / TEGDMA • Solvents/Reagents/Catalyst: • methylene chloride, toluene, methanol • triethylamine, triphenylphosphine, methacryloyl chloride • Pt(0)-divinyltetramethyldisiloxane [Pt(dvs)]

10. Materials/Methods • Instruments/Techniques: • Perkin Elmer Paragon 1000 FTIR spectrometer (4 scans) • Eft-90 H1/C13 NMR spectrometer (90 and 400 Mhz) • Standard Thin Layer Chromatography (solvent: 50:50 ethyl acetate/hexane)

11. Materials/Methods • Brookfield CAP 2000 dynamic mechanical analyzer - Visible Light Curing Apparatus (λ = 460nm)

12. The experiment • Synthesize POSS-MMA of varying side-chain lengths • Incorporate these varying POSS-MMA moieties into a resin matrix forming a constant 40/40/20 (% wt) formulation of BisGMA/TEGDMA/POSS-MMA respectively • Assay for pre-polymerization viscosity (poise) and polymerization shrinkage after blue-light curing (equation: % shrinkage = [1-duncured/dcured] x 100%) *d = density

13. Control • POSS-MMA having allyloxytrimethylsilane chains of 3 carbons in length *n indicates the # of carbons present within the parenthesis • Viscosity and Polymerization Shrinkage data of other formulations will be compared to values found in control

14. Synthesis of POSS-MMA species • Step 1: Octasilane-POSS + Allyloxytrimethylsilane Pt(dvs) Octakis[(3-trimethylsiloxypropyl)dimethylsiloxy]-silsesquioxane (POSS-TMSP) Octasilane-POSS

15. Synthesis of POSS-MMA species • Step 2: POSS-TMSP + Anhydrous Methanol CH3OH Octakis[3-hydroxypropyldimethylsiloxy) octasilsesquioxane (POSS-HP) POSS-TMSP

16. Synthesis of POSS-MMA species • Step 3: POSS-HP + Methacryloyl Chloride Octakis(methacryloxypropyldimethylsiloxy) octasilsesquioxane (POSS-MMA) POSS-HP

17. Results *POSS-MMA FTIR Spectra

18. Results *POSS-MMA H’NMR Spectra

19. Trials Viscosity (Poise) Shrinkage (%) 1 1.33 15.2 2 1.34 15.5 3 1.31 14.9 Results Table 1. Viscosity (poise) and % Polymerization Shrinkage of 40/40/20 ratio of BisGMA/TEGDMA/POSS-MMA oligomer. Trials were conducted on control mixtures containing allyloxytrimethylsilane species 3 carbons in length.

20. Description of Resin Formulations Viscosity (Poise) Polymerization Shrinkage (%) BisGMA/TEGDMA/POSS-MMA*3 1.33 15.1 BisGMA/TEGDMA/POSS-MMA*4 1.24 13.4 BisGMA/TEGDMA/POSS-MMA*5 1.12 11.2 BisGMA/TEGDMA/POSS-MMA*6 0.87 9.6 BisGMA/TEGDMA/POSS-MMA*7 0.75 7.1 BisGMA/TEGDMA/POSS-MMA*8 0.73 5.9 BisGMA/TEGDMA/POSS-MMA*9 0.72 4.3 BisGMA/TEGDMA/POSS-MMA*10 0.72 3.8 Results Table 2. Description of the Resins Formulated, Pre-polymerization Viscosity, and Polymerization Shrinkage. All ratios of BisGMA/TEGDMA/POSS-MMA mixtures have a 40/40/20 ratio according to percent weight (wt%). Numbers following an asterisk indicate the carbon length of POSS-MMA side chain groups.

21. Results A) B) *Plots illustrating the effects of methacrylate chain length on A) viscosity and B) polymerization shrinkage.

22. Conclusions/Summary • Using allyloxytrimethylsilane yields an efficient route in the synthesis of POSS-MMA • Incorporation of POSS-MMA into resin matrix causes decreased viscosity and polymerization shrinkage (up to a certain point) of neat dental resin formulations • Viscosity decreased through low weight to volume ratio • Polymerization shrinkage decreased through amount and distance of methacrylate bonds in matrix

23. Future Experiments • Study how incorporating POSS-MMA affects other physical/mechanical properties • Study other silsesquioxane compounds (i.e. cyclic version) • Other novel di- and tri- methacrylate monomers

24. Acknowledgements • Dr. Buonora • Romina Panoussi/Teresa Phan • Dr. Mason/Dr. Archie • Howard Hughes Medical Institute

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