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Title: Development of composites for tooth and bone repair
Author: Panpisut, P.
ISNI:       0000 0004 7226 0581
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2017
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Currently used composites for tooth and bone repair share a similar composition. A major issue with dental composites is polymerisation shrinkage leading to bond damage and increased risk of bacterial microleakage. Concerns with bone composites for vertebral fracture repair (vertebroplasty) include low monomer conversion, high stiffness, and lack of antibacterial agent release. The aim of this study was to develop novel dental composites and injectable bone composites to overcome these limitations. The effects of components on various properties of the materials were also examined. The main components of experimental composites consisted of dimethacrylate monomers mixed with dental glass, mono calcium phosphate monohydrate (MCPM), tristrontium phosphate (TSrP), and polylysine (PLS). The experimental dental composites exhibited higher monomer conversion than a commercial material. The addition of MCPM with TSrP and PLS promoted hygroscopic expansion, apatite precipitation, and early polylysine release. These properties are expected to reduce bacterial microleakage. The incorporation of these additives reduced the monomer conversion and strength of the composites but these were still within an acceptable range. To produce bone composites, the dental composites were modified by replacing a light activated initiator with a chemically activated initiator and decreasing powder to liquid ratio. The pre-cured bone composites exhibited viscoelastic properties and shear- thinning behaviour which are desirable for injectable materials. The use of high molecular weight diluent monomer (polypropylene glycol dimethacrylate, PPGDMA) increased monomer conversion and shelf life of the bone composites. The addition of MCPM and PPGDMA increased strontium release, which is known to promote in vivo bone formation. The use of small glass fillers and fibres improved mechanical properties of the composites. Furthermore, the composites showed fatigue properties that compared favourably with commercially available materials. Modulus of elasticity of the experimental bone composites was, however, too high compared with that of cancellous bone. This could potentially lead to increased adjacent vertebral fracture risk. An attempt was made to decrease the modulus by raising the level of PPGDMA, phosphates, and polylysine. Increasing of PPGDMA improved monomer conversion and reduced the injection force required for the composites. Furthermore, the increase of PPGDMA and phosphates enhanced surface apatite precipitation which is known to enable in vivo bone bonding. The increase of these components also increased polylysine release. This may reduce postoperative infection, which is a life-threatening complication of vertebroplasty. Increasing PPGDMA and phosphates, however, reduced metabolic activity of mesenchymal stem cells limiting optimal levels.
Supervisor: Young, A. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available