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Chemo-mechanical Characterisation and Biocompatibility of CAD/CAM Composite Blocks

Alamoush, Rasha

[Thesis]. Manchester, UK: The University of Manchester; 2020.

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Abstract

Composite with improved properties for CAD/CAM processed restorations can be produced using high temperature and/or high pressure polymerisation, and innovative filler microstructure and loading. Many new CAD/CAM composite materials have been investigated to evaluate their performance and durability. The overall aim of this research was to assess the mechanical, chemical and biological properties of CAD/CAM composite upon ageing in different oral and food simulating fluids at various time intervals, comparing them to ceramics and to other conventional resin-composite materials where appropriate. The first part of this study evaluated hardness and elastic modulus of CAD/ CAM composite blocks in comparison to CAD/CAM ceramic and tooth structure. It also investigated the effect of filler weight on these properties. It was found that all resincomposite blocks (RCB) had hardness and elastic moduli closer to dentine than enamel. Polymer-infiltrated ceramic network (PICN) exhibited hardness and elastic modulus closer to that of enamel. These properties were positively correlated to filler loading. The hardness of CAD/CAM composite blocks (RCB and PICN) compared to CAD/CAM ceramic was then tested after storage in simulated oral fluids(water, artificial saliva and 75% E/W) for 30 and 90 days. It was found that CAD/CAM ceramic exhibited superior softening resistance (less hardness reduction) than CAD/CAM composite blocks with PICN showed superior softening resistance to RCB. The hardness reduction levels were negatively correlated to the filler loading, and were mostly influenced by 75% ethanol/water (E/W) storage. The sorption and solubility of CAD/CAM composite blocks in comparison to CAD/CAM ceramic were assessed over eight months of storage in water and artificial saliva. It was found that CAD/CAM composite blocks were not as hydrolytically stable as CAD/CAM ceramic and exhibited varying degrees of sorption and solubility, influenced by their resin-matrix composition and the filler weight percentage. In addition, water and artificial saliva were considered comparable as storage media in relation to water sorption. The viscoelastic stability of CAD/CAM composite blocks was assessed under a constant static compressive stress at 24 h in dry conditions and after 3 months of water storage. The PICN material exhibited superior viscoelastic stability compared to RCB in both storage conditions, with predominantly elastic rather than viscoelastic deformation. Monomer elution of CAD/CAM composite blocks and conventional resin-composites was assessed using high performance liquid chromatography in different storage media (water, artificial saliva and 75% E/W) for 3 months. There was minimal or no monomer elution from CAD/CAM composite blocks. Finally, and based on the monomer elution experiment, selected materials (one PICN, two RCB and a conventional resin-composite) were investigated in relation to their influence on human gingival fibroblasts (HGF) and gingival keratinocytes (HGK). All investigated materials influenced HGK proliferation and caused higher cytotoxicity than that of HGF. It was concluded that different manufacturing techniques of CAD/CAM composites had no significant effect on their biological properties and that PICN showed a cytotoxic effect in HGK.