4Metal:
5.4.1 Alloys:
Since the introduction of investment casting to dentistry in the early 1900s, alloys have been used for different types of prosthesis including crowns, bridges, dentures, and implants. An alloy is a mixture of two or more metallic elements. The constituents can be a metalloid or a non-metal, provided that the resultant mixture exhibits metallic properties. Dental alloys for fabrication of crowns/bridges can be broadly divided into precious metal casting alloys and alloys for porcelain-fused-to-metal restorations. Precious or high-gold-content alloys are used for inlays, full-cast crowns, and partial-veneer crowns as they are soft and burnishable. Precious metal alloys contain mainly gold, palladium, platinum (which are classified as noble metals), and silver. They also contain limited amounts of non-precious alloying elements like iron, tin, and indium.
Due to aesthetic requirements, most crowns and bridge works are of the porcelain-fused-to-metal (PFM) type. They constitute approximately 70 to 80 percent of all cast restorations used clinically. Alloys intended for use in PFM restorations have several special requirements, such as:
• Melting temperatures must be above that of porcelain application;
• Close matching of thermal properties to those of porcelain;
• High modulus of elasticity; and
• Good corrosion resistance
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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