Dentinal wear is a complex event system that is dependent on the quality of the dentinal surface and that of the toothbrush and toothpaste used. The wear properties of toothpaste mixtures are commonly characterised by the dentine abrasion it causes. This thesis aims to investigate not only this macroscopic wear but also to further analyse in detail the behaviour of the abrasive particles within toothpaste by analysing the microscopic tribological scratches caused by these abrasive particles to determine the mechanisms of their cleaning behaviour.
This project uses quantitative micro-tribological investigative methods on three different aspects of oral care:
• Calcium Carbonate particles – currently ground calcium carbonates (GCC) are the predominant abrasive particles in many commercial toothpastes. This investigation determines whether the use of uniform precipitated calcium carbonates within these mixtures is advantageous.
• Citrus fibres – citrus fibres are currently a waste product in the food industry, and sometimes used as a thickening agent in low-fat mayonnaise. Testing was done to show how the addition of these dietary fibres into toothpaste mixtures affects overall and microscopic abrasivity of the paste.
• Silica particles with polymer binders – Carbopol polymer binders are currently used in a number of commercially available toothpastes in the market today. Testing was done to determine how differing chemistries of these pastes or the method of addition of them to toothpastes mixtures affects the overall cleaning efficacy of the pastes.
Tribological testing was done to discern the wear characteristics of each paste on dentine and dentine models. Micro-visulisation techniques were then used to understand the scratch characteristics of each abrasive. Nano-manipulation techniques were employed to characterise dynamic primary movement traits. This was employed to directly observe the particles when moved, rather than only assuming dynamic movement from wear tracks.
It was found particle size is not the key factor in determining overall wear or individual scratch tenacity of particles. Instead factors such as geometry and interaction with other particles are most significant in determining how a particle operates and removes substrate material.
This research was carried out to develop an understanding of the abrasive efficacy of abrasive particles within oral care and to help further develop the next generation of toothpaste for Unilever Plc.
