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Title: Encapsulation of fluoride for incorporation into orthodontic elastomeric auxiliaries
Author: Mah, Eng Ching
ISNI:       0000 0004 2718 3636
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2011
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The aim of this study was to produce an elastomeric material containing nano or microcapsules impregnated with a fluoride solution, and to mechanically test such a material. Using polycondensation interfacial polymerisation it was possible to produce silica (SiO2) core shell capsules using a water-in-oil technique. The various parameters involved in the production process, namely acid-base concentration along with Alkoxysilane concentration were tested and capsules in the 2 to 10μm diameter range were produced. In general, all the experiments seemed to demonstrate that ammonia was the preferred aqueous base solution for use with 80ml Hexadecane as the oil phase, along with 1 % of the surfactant TEGOPREN and 6g of Alkoxysilane (3g ofTEOS and 2.7g ofDEDMS along with a premix of O.3g DEDMS). Two commercially available mouthrinses, Fluorigard and Corsodyl, were tested as potential active core solutions but in both cases capsules could not be created. This was thought to be due to the other components of each mouthrinse, notably surfactants. It was however possible to successfully encapsulate a 240 ppm sodium fluoride in water solution. Once created, the next challenge was to separate the capsules from the original oil phase, Hexadecane, and to transfer them to water for mixing with the water based polyurethanes under test. This was done by progressive centrifuging and dilution using the non-polar solvent Heptane, the polar solvent Tetrahydrofuran (THF), water and the surfactant INUTEC. The two polyurethanes tested were Neorez 1022 and Neorez 1007 along with a silicone sealant. Of these three materials, Neorez 1007 most closely approximated a polyurethane that might be used in orthodontics. The sodium fluoride containing capsules were embedded in the Neorez 1007 and the material was subjected to tensile testing and observation under SEM. The tensile test demonstrated that addition of sodium fluoride core capsules reduced the force at maximum extension. This may also have been due to the presence of residual THF or Heptane within the capsule containing solution. Although capsules could be seen within the material, they were not evenly dispersed and many appeared to have ruptured. Although INUTEC had been used it wasn't fully miscible in water, making separation of the capsules into the water phase potentially less than complete. It is this that may have led to the presence of the residual Hepatane and THF. To overcome this, an alternative surfactant was tested namely Dow Coming© 190. This permitted more complete separation and dispersion of the capsules into water. Further work is required to determine if capsules fabricated with this surfactant will have less detrimental effects on any potential polyurethane. An investigation using Methylene blue as a partial substitute for the sodium fluoride core demonstrated that much of the active core is lost during the process of separating the capsules from the oil and then dispersing them into the water phase. The precise mechanism of this loss is as yet still unclear. In conclusion this experiment demonstrated how silicon sphere microcapsules, containing an active sodium fluoride solution core, could be produced and incorporated within a water based polyurethane. With further refinement of the production parameters this shows great potential for the fabrication of custom made "smart" materials for use in orthodontics.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available