A wide variety of ceramics, glasses, and glass-ceramics have been used in dental applications. (Hench 1993; Clark and Anusavice 1991; Day 1995). The relatively smaller scale and primarily compressive loads have combined to make in applications in dentistry less challenging than in orthopaedic surgery. Examples include dental implants, cementation agents, and restorative materials.
6.2.1
Traditional Porcelains
Dental porcelains have been used for nearly two centuries to repair diseased and decayed teeth (Day 1995). Approximately 80% of all fixed prostheses placed in the United States are composed of porcelain-fused-to-metal. Today, porcelains are also used for the cosmetic treatment of broken or discolored teeth. Veneers can be cemented to front teeth, and bridges can be used to replace lost teeth. Three-tooth bridges are fabricated by fusing the porcelain to a metal substrate. Dental porcelains are generally made by blending two components, typically a partially fused potassium aluminosilicate feldspar (leucite) and a fully fused alkali—alkaline-earth— aluminosilicate. Leucite is added to raise the thermal expansion coefficient of the system to more closely match that of the metallic alloy substrate (in prosthodontic devices such as crowns and bridges). The second, glassy component controls the melting characteristics of the mixture. Additives produce the desired optical properties, including color and fluorescence. A typical metal substrate would be an 80Ni-20Cr alloy. Good adhesion of the porcelain depends on good thermal expansion matching as well as a preoxidation step to produce a monolayer of Cr2O3 to ensure good oxide adherence and overall strength.
6.2.2
Other Ceramics for Dental Reconstruction
As pointed out , alumina ceramics have been used in dental applications. Relatively pure alumina, including the single crystal sapphire form, has been used as dental implants, as well as in jaw bone reconstruction. An alternative to traditional dental porcelains are glass-ceramic prosthetics, which offer many benefits including ease of fabrication, low processing shrinkage, high strength, translucency control,
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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