Bartlett, DavidAlmansour, Abdullah2025-05-052025https://hdl.handle.net/20.500.14154/75300The primary aim of this PhD was to investigate if location or site on the enamel surface and sub surface changes after erosion and erosion/abrasion. The methodology involved in vitro testing on polished and natural human enamel molars. The teeth were sectioned and divided into two groups: occlusal and buccal. They were exposed to 0.3% citric acid at pH 2.7 for multiple durations and abrasion applied using non-fluoridated toothpaste for 240 strokes in a reciprocating brushing machine. A white light profilometer was utilised to calculate the mean step height of the erosion scar. Different loading regimens for microhardness testing were used to estimate depth-related changes in the polished enamel subsurface. The objective of the first study was to evaluate the impact of erosion duration on the step height and hardness of the buccal and occlusal polished enamel surfaces. At 5 mins the step height on the occlusal surface was 3.6 ± ( 0.65) µm and on the buccal surface was 3.1 ± (0.60) µm which increased after 60 mins to 32.9 ± (3.43) µm and 30.1 ± (3.34) µm, respectively. There was a significant increase in step height for the occlusal surface. Notably, increasing hardness values were observed for the buccal and occlusal eroded surfaces when the indentation load increased. The second study focused on analysing of polished occlusal and buccal enamel surfaces following erosion/abrasion. Despite differences in step height at the 60 mins mark 32.9 ± (2.8) µm for occlusal and 31.1 ± (1.8) µm for buccal surfaces (p = 0.02), no significant difference in microhardness was detected between occlusal and buccal surfaces. Similar to eroded surfaces, an increase in hardness value was identified in both buccal and occlusal surfaces following erosion/abrasion as the indentation load increased. In the third study, natural freeform enamel surface was subjected to erosion using paired occlusal and buccal natural enamel surfaces. A two-way ANOVA, the step height loss was calculated using a 3D comparison of pre- and post-erosion scans. The analysis did not indicate any significant difference between the occlusal and buccal surfaces (p = 0.09). Following 60 mins erosion, the step height for occlusal surfaces reached 33.84 µm (11.48), whereas buccal was 25.50 µm (11.72). These results offer an important insights into acid exposure's impact on enamel microhardness and step height, on both occlusal and buccal surfaces. Despite results from polished enamel with erosion only, polished enamel with erosion and abrasion and unpolished enamel surfaces has no significant difference on location was observed. Microhardness differences were detected with lower indentation loads showing that although the surface loss occurred there were subsurface changes.232en.Thesis