Saudi Cultural Missions Theses & Dissertations
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Item Restricted Comparison of an experimental single application two-step 25600 ppm Ammonium Fluoride / 34100 - 48600 ppm Nano-Calcium Fluoride solution vs. a one-step 7700 ppm Ammonium Fluoride varnish for Preventing Enamel Loss from Erosion and Attrition in vitro(King’s College London, 2024) Almejrad, Lamya; Austin, Rupert; Bartlett, DavidIntroduction: The potential for high-fluoride treatments to prevent progression of erosion and attrition is not fully understood. This thesis investigated the effect of an experimental two-step ammonium fluoride/nano-calcium fluoride formulation (25600 ppm NH4F plus 34100 - 48600 ppm CaF2) versus a single-application one-step 7700 ppm ammonium fluoride (NH4F) varnish on step height loss (μm) of polished and natural human enamel undergoing erosion and attrition in vitro. Material and methods: Three restorative dental materials and human enamel (Occlusal vs. Buccal) samples were used to validate the attrition simulation method. Samples were subjected to attritional wear using leucite-reinforced CAD/CAM ceramic antagonists in an electrodynamic wear simulator (200 cycles, 80 N load, 0.7 mm horizontal slide). Following validation, polished and natural (unpolished) enamel samples were pre-treated with either deionized water (DIW negative control), NH4F varnish (positive control) or a two-step NH4F/CaF2 solution. After surface wiping, samples were subjected to erosion (0.3% citric acid solution immersion, pH 3.8, for 5, 10, 15, 20 and 60 minutes) and attrition (200 strokes). Enamel wear was measured using non-contact laser profilometry (NCLP). Enamel surface and sub-surface mechanical testing was conducted using micro- and nanoindentation. Enamel surface and sub-surface qualitative examination was conducted using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Results: The attrition method revealed that the glass ionomer material experienced the most wear, measuring 177.8 μm (±16.9). This was significantly more than the fine particle composite, which showed 22.2 μm (±1.3) of wear, and the micro-filled composite, which had the least wear at 13.6 μm (±1.02) (P < 0.001). Enamel samples from buccal vs. occlusal sources experienced non-significantly different step height enamel wear (P<0.05). The attrition wear generation was consistent with co-efficient of variation <10%. Polished enamel samples treated with surface fluoride treatments showed significantly reduced step height enamel loss vs. control (p<0.001): Mean (SD) enamel loss for DIW treatment was 1.97 μm (±0.14) after erosion and 36.55 μm (±1.79) after erosion/attrition. NH4F treatment reduced loss to 0.58 μm (±0.08) after erosion and 32.71 μm (±2.63) after erosion/attrition (p<0.001). NH4F/CaF2 treatment further reduced loss to 0.41 μm (±0.06) after erosion and 24.08 μm (±3.15) after erosion/attrition (p<0.001). This was supported by the microhardness data: fluoride-treated enamel experienced reduced hardness changes following both erosion and erosion/attrition vs. non-fluoride treated enamel (p<0.001). For natural enamel, the experimental NH4F/CaF2 solution significantly reduced enamel loss after all erosion durations (5, 20, 60 minutes) and after 200 strokes of attrition. After 5 minutes of erosion, enamel loss compared to DIW was significantly reduced (p<0.001). Mean (SD) enamel loss in the NH4F/CaF2 treated group was reduced to 0.21 μm (±0.13) after erosion and 9.82 μm (±1.46) after erosion/attrition in comparison with DIW treated groups which was 0.79 μm (±0.32) after erosion and 15.58 μm (±2.49) after erosion/attrition. The surface and sub-surface SEM and EDS data supported these findings. Conclusion: The two-step ammonium fluoride solution (NH4F/CaF2) reduced step height enamel loss and hardness changes occurring in polished and natural enamel during simulated erosion and attrition in vitro.16 0Item Restricted THE EFFECT OF DISTANCE BETWEEN TWO ELBOWS IN SERIES ON EROSION IN SINGLE AND MULTIPHASE FLOW CONDITIONS(2023-08-01) Othayq, Mazen; Shirazi, SiamackSolid particle erosion is an unavoidable and challenging phenomenon that occurs in elbows and leads to elbows failure. One area of interest is how erosion patterns and magnitude may change when elbows are positioned in series. One curious question is, will the erosion in a second elbow be higher, less, or equal to the first elbow? In the literature, very few investigators have examined erosion in elbows in series where the particles upstream of the second elbow are affected by the underdeveloped flow caused by the first elbow. Thus, it is advantageous to examine erosion in a second elbow with various distances between two elbows installed in series in different flow conditions. Solid particle erosion in elbows in series was investigated in large-scale flow loops experimentally in two-phase and multiphase flow conditions. In this work, sand was used as a solid particle. Before performing erosion measurements, paint removal tests using acrylic elbows were conducted to better understand the erosion pattern and the location of the maximum erosion in the elbows. In addition, the Computational Fluid Dynamics (CFD) approach was used to simulate the investigated cases with different distances between the elbows, particle sizes, and flow conditions to better represent the flow and erosion prediction using the available erosion and rebound models in the literature. The presented erosion measurements showed that the location of the maximum erosion in gas-dominated flow conditions differs from liquid-dominated flow conditions. In gas-dominated flow conditions in 3-inch elbows, the location of the maximum erosion was observed at the centerline of the exterior wall of the second elbow, for instance, from 55 degrees to 75 degrees. However, in the liquid-dominated flow conditions in 2-inch elbows, the location was observed at the end of each elbow, around 84 degrees. The presented experimental data in gas-dominated flow conditions showed that the erosion in the first elbow is higher than in the second elbow. However, for liquid-dominated flow conditions in 2-inch elbows, the experimental results showed that the erosion in the second elbow is higher than the first elbow with the 1D distance between the elbows. The maximum erosion ratio in the second elbow becomes less than the first elbow with the 5D distance between them. CFD has been used also to examine erosion magnitude of the second elbows as compared to the first. The CFD results showed good agreement compared to the experimental data in the first elbow. However, the presented CFD results overpredicted the maximum erosion ratio in the second elbow, especially with a short distance between the two elbows (1D and 2D).9 0