SACM - United Kingdom
Permanent URI for this collectionhttps://drepo.sdl.edu.sa/handle/20.500.14154/9667
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Item Restricted Impact of Zinc Oxide Nanoparticles on Model Resin Composite Properties and Strategies for Optimisation(University of Manchester, 2025) Alayed, Abdulaziz Ali; Watts, David; Silikas, NikolaosZinc oxide nanoparticles (n-ZnO) have been widely used in various fields, including dentistry, due to their potent antibacterial properties. Additionally, their white colour closely resembles that of natural teeth, making them an attractive candidate for aesthetic restorative applications. However, despite these advantages, the incorporation of n-ZnO may adversely affect certain material properties, which require further investigation or optimisation. This thesis investigates the effects of n-ZnO additions into model resin-based composites (RBCs), with a focus on properties during polymerisation, optical and mechanical performance, and hygroscopic characteristics; aiming to evaluate their drawbacks and find strategies to improve them. Model RBCs were formulated using a trimodal dimethacrylate resin monomer system (Bis-GMA, TEGDMA, and UDMA) and inert barium glass powder, silica nanoparticles and systematically varied amounts of n-ZnO (0-5 wt.%). The photoinitiator systems consisted of camphorquinone (CQ), ethyl 4-(dimethylamino)benzoate (EDMAB), and diphenyliodonium hexafluorophosphate (DPI). The concentrations of each component were varied depending on the experiment. Depth of cure (DoC) and degree of conversion (DC) were measured using Vickers hardness and FTIR spectroscopy, respectively. Increasing n-ZnO concentrations significantly reduced DoC. However, it was found that the binary initiator system (CQ/DPI/EDMAB) enhanced DoC and the maximum rate of polymerisation (RPmax) compared to the unary system (CQ/EDMAB). Reducing photoinitiator concentrations also improved DoC. Light transmission (LT%) and shrinkage strain (SS) were measured under different irradiance conditions: 1200 versus 2000 mW/cm². n-ZnO significantly reduced LT% from 48–53.9% at 0 wt.% to 11.9–14.6% at 4 wt.%, depending on irradiance and time. Shrinkage decreased with increasing n-ZnO and glass powder loading, ranging from 6.9% to 5.1%. The irradiance mode significantly affected transmission but not material shrinkage. Water sorption, solubility, hygroscopic expansion and Zn2+ ion release were evaluated using multiple techniques. Long-term (168 days) water immersion experiments showed that n-ZnO reduced water sorption and solubility, although increasing hygroscopic expansion. The magnitudes of sorption and solubility remained within ISO 4049:2019 limits. Volumetric expansion ranged from 1.6% to 1.9%. ICP-MS analysis showed a gradual increase in Zn²⁺ release with increasing n-ZnO concentration, up to 675.1 ppb with 5 wt.% n-ZnO. Martens hardness (HM), indentation modulus (EIT), and indentation creep (CIT) were measured after 0 (baseline), 7 and 28 d water storage. At 1200 mW/cm², increasing n-ZnO up to 4 wt.%, increased HM to 355 N/mm² for baseline readings. In contrast, with 4 wt.% n-ZnO cured at 2000 mW/cm², HM significantly decreased to 207 N/mm². Water aging negatively affected HM and EIT, while CIT remained unaffected. These findings provide new scientific insights into resin-composite systems incorporating n-ZnO. They reveal the potential for fine-tuning property outcomes through choice of the photoinitiator system and light-irradiation conditions. These composites are essentially of the ‘flowable’ type and have depths-of-cure appropriate for base layers in deep cavities. But that is exactly where incorporation of powerful antibacterial agents such as n-ZnO are most needed.27 0Item Restricted CAD CAM Ceramics. A Review of the Scientific Literatures(Saudi Digital Library, 2025-04-04) Alsurayyie, Fatimah; Claydon, NicholasAbstract This study aims to provide a review of the literature on CAD/CAM ceramic restorations, focusing on their clinical properties compared to conventional restorations. In addition to manual searching, three scientific databases were searched for study designs that address at least one of the outcomes of interest regarding CAD/CAM ceramic restorations, including in vitro, in vivo, systematic, and narrative reviews. Up-to-date evidence supports an equivalent outcome of CAD/CAM to the conventional, including superior wear characteristics compared to the standard metal-ceramic restorations, with polished monolithic zirconia showing particularly promising wear characteristics compared to other ceramics. However, there are conflicting results regarding the abrasiveness of lithium disilicates compared to monolithic zirconia, though all were found to cause more wear than natural teeth, and the importance of surface treatment (polishing, glazing) was emphasized. Translucent monolithic zirconia improved aesthetics. However, it requires adequate thickness to compensate for the reduced strength (≥1.0 mm). There were deficiencies in long-term clinical trials regarding longevity; the available short- to medium-term studies showed high survival of CAD/CAM ceramic restorations (>90% at 5 years), expecting better performance with continuous technological development. Moreover, CAD/CAM workflow helped reduce laboratory time spent on restoration fabrication, which is necessary for increasing productivity. Based on laboratory and short-term clinical studies, the potential for CAD/CAM to surpass traditional methods is promising. However, the clinical evidence supporting CAD/CAM ceramic restorations is still not extensive. Therefore, well-conducted large clinical studies are needed to confirm the promising long-term performance of CAD/CAM ceramic restorations. Moreover, to help in the continuous enhancement of the material.12 0