| Summary: | This thesis is concerned with the abrasive particles used within toothpastes for oral care products. The dynamic and abrasive characteristics of different particles is analysed using a variety of experimental and observational techniques, in order to discern their suitability as an abrasive agent upon sensitive human tissue such as dentine. It is of particular interest to companies working within Oral Care, to develop an abrasive formula that is both adept at removing surface detritus such as plaque, but does not cause damage to the underlying tissues of the tooth such as enamel and dentine. Further to their role as an abrasive agent for detrital removal, particles are also utilised to act as an aid against dental hypersensitity, by infiltrating and sealing off dentinal tubules. The main focus of this thesis is to study both the individual and collective behaviour of the particles in order to better understand the practicality and influence particles can introduce within oral care and why. The efficacy of the particles is analysed from 3 key perspectives: 1. The abrasive performance of particles under a variety of tribological testing. Particular attention was paid to the wear characteristics of the particles upon key dental tissue. 2. Visualising and understanding the dynamic characteristics of the particles when motivated in an effort to relate these findings to wear observations. 3. To investigate the positive role of some key particles as an aid in dental hypersensitity. It was found that subtle variation in particle size and shape can have a significant effect upon the magnitude of the wear. This shape can affect the abrasive properties in more than one way, either by having a more aggressive shape leading to increased scratching and material removal; or by augmenting the affinity of the particle to agglomerate and operate as an agglomeration when motivated. Nano-manipulation techniques are employed to discern the dynamic characteristics of the particles. Being able to directly observe the particles when manipulated rather than attempt to derive suppositions from wear tracks, leads to a much improved understanding of a particles dynamic traits as well as the characteristics of particle breakdown. A comparison is made between the occlusive efficacies of bespoke precipitated calcium carbonate versus typical ground particles. Clear differences between the particles were observed, highlighting a delicate relationship with the presence of water. The aim of this research is to contribute further understanding of the important role that abrasive particles play within oral care, and to draw conclusions as to what factors play a key role in making a particle aggressive or sympathetic to a substrate surface.
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