A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
Browse
2 results
Search Results
Item EFFECT OF GLASS JOINS ON PERFORMANCE OF LAYERED DENTAL CERAMIC SYSTEMS(2008) Saied, Mey; Lloyd, Isabel K; Lawn, Brian R; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Layered structures can be used to address the competing needs of systems like dental crown restorations where the exterior needs to be aesthetic and the interior needs to be strong and fatigue resistant. Dental crowns typically have an aesthetic porcelain veneer layered on a strong, fatigue resistant ceramic or metallic core. In current restorations, even when the core is shaped by a computer-aided design and manufacturing (CAD/CAM) or solid-freeform fabrication processes, the veneer is applied in sequential layers. This process is labor intensive, time consuming and may not optimize the long-term performance properties of the veneer layer. If the core and veneer layers were to be independently fabricated and then joined, their individual and the veneer-core system performance could be optimized. Some groups have explored the possibility of joining with filled epoxies, which is easier, but may not be long-lasting. In this project we explore the possibility of using more durable glassy joins. Dense, thermal-expansion-matched (to the core and veneer glass) joins can be fired at temperatures far enough below the melting and/or slumping temperatures to join veneers to cores without degradation. In this study, we design and fabricate joining glasses for bonding porcelain veneers to ceramic cores, specifically to dental aluminas and zirconias. We study the chemical bonding and mechanical integrity of the resulting layers. Finally, we assess the effects of glass joins on performance of layered dental ceramic systems.Item High elastic modulus nanopowder reinforced resin composites for dental applications(2007-08-27) Wang, Yijun; Lloyd, Isabel K.; Greer, Sandra C.; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dental restorations account for more than $3 billion dollars a year on the market. Among them, all-ceramic dental crowns draw more and more attention and their popularity has risen because of their superior aesthetics and biocompatibility. However, their relatively high failure rate and labor-intensive fabrication procedure still limit their application. In this thesis, a new family of high elastic modulus nanopowder reinforced resin composites and their mechanical properties are studied. Materials with higher elastic modulus, such as alumina and diamond, are used to replace the routine filler material, silica, in dental resin composites to achieve the desired properties. This class of composites is developed to serve (1) as a high stiffness support to all-ceramic crowns and (2) as a means of joining independently fabricated crown core and veneer layers. Most of the work focuses on nano-sized Al2O3 (average particle size 47 nm) reinforcement in a polymeric matrix with 50:50 Bisphenol A glycidyl methacrylate (Bis-GMA): triethylene glycol dimethacrylate (TEGDMA) monomers. Surfactants, silanizing agents and primers are examined to obtain higher filler levels and enhance the bonding between filler and matrix. Silane agents work best. The elastic modulus of a 57.5 vol% alumina/resin composite is 31.5 GPa compared to current commercial resin composites with elastic modulus <15 GPa. Chemical additives can also effectively raise the hardness to as much as 1.34 GPa. Besides>alumina, diamond/resin composites are studied. An elastic modulus of about 45 GPa is obtained for a 57 vol% diamond/resin composite. Our results indicate that with a generally monodispersed nano-sized high modulus filler, relatively high elastic modulus resin-based composite cements are possible. Time-dependent behavior of our resin composites is also investigated. This is valuable for understanding the behavior of our material and possible fatigue testing in the future. Our results indicate that with effective coupling agents and higher filler loading, viscous flow can be greatly decreased due to the attenuation of mobility of polymer chains. Complementary studies indicate that our resin composites are promising for the proposed applications as a stiff support to all-ceramic crowns.