Abstract
Prevention of erosive tooth wear requires deeper understanding of the complex physico- chemical interactions that occur between acidic solutions, physical challenges, and human enamel surfaces, in both a natural unpolished state and polished enamel. The aim of this PhD is to investigate the interaction between dietary erosion and toothbrush abrasion for protection of enamel from erosive tooth wear.The research methods involved in vitro research on both polished and natural human enamel samples which were sectioned and mounted into 3D printed moulds. The erosive model used throughout the investigations included erosion from 0.3 % citric acid at pH 2.7 and abrasion using a linear brushing machine with toothbrushes set to apply 1 brush/second with a load of 290-295 grams. A non-contacting laser profilometer (NCLP) measured quantitative data on bulk tissue loss, using step height change as ISO standards for polished samples and for unpolished surfaces. The digital scanning and measurement workflow was optimised to accurately quantify lesion depths. Qualitative images were obtained from light microscopy and SEM.
The first experiment measured step height change between acids and abrasion on polished and natural enamel with increasing times of citric acid exposure and number of brush strokes. The results demonstrated statistically significant higher step heights for polished vs. natural surfaces (P<0.001), however, this was not observed after erosion and abrasion separately (p=0.209). SEM analysis enabling a comparison of the subsurface prisms between the groups. The second experiment determined the effect of human saliva and sodium fluoride toothpaste (at 1450 ppm) on the same wear model to quantify tissue loss. A statistically significant difference in step height was found between natural human saliva and artificial saliva (P<0.002) with shallower step heights observed in the natural human saliva group, the same observed for fluoride and fluoride- free surface treatments (p=0.029) after four cycles. A combination of natural human saliva and fluoride toothpaste resulted in the shallowest step height compared to other combinations (p=0.049, p=0.007, P<0.001) after four cycles. The third experiment compared electrical and manual toothbrushing on the same model. Statistically significantly higher step heights were observed on samples exposed to electrical than manual toothbrushing (P<0.001). The fourth experiment assessed the potential of a polyvinylsiloxane replication technique to accurately measure erosive lesions for both NCLP measurements and visual characterization via microscopy. The overall accuracy between direct and silicone replicate measurements was 0.13 (+0.57/-0.31) µm for erosion and 0.12 (+0.99/-0.75) µm for erosion/abrasion (P>0.05) and there was no statistically significant difference between then (P>0.05), furthermore the silicone replicated the visual wear features.
The results of this research demonstrated the significance of an outer layer of enamel in resisting dietary-based acids to tooth wear. These differences were not observed after individual erosion and abrasion and revealed the presence of a subsurface demineralisation which might be vulnerable to mechanical force. These results highlights the interaction of erosion and mechanical wear on enamel, which has implications for how preventative advice and treatment modalities need to be delivered.
| Date of Award | 1 Feb 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | David Bartlett (Supervisor), Rupert Austin (Supervisor) & Saoirse O'Toole (Supervisor) |