5.3.2 Polymer Composites:
Dental composites essentially comprise a resin matrix (organic phase), a filler-matrix coupling agent (interface), filler particles (dispersed phase), and other minor additions including polymerization initiators, stabilizers, and coloring pigments.
Microstructure of a dental composite
Fillers are used in dental composites to provide strengthening, increase stiffness, reduce dimensional change when heated or cooled, reduce setting contraction, impart radiopacity, enhance aesthetics, and improve handling. Most current composites are filled with radiopaque silicate particles based on oxides of barium, strontium, zinc, aluminum, or zirconium. The resin matrix usually contains dimethacrylate monomers of which BisGMA (Bisphenol A—glycidyl methacrylate) is most popular.
The hardening of dental composites is the result of a chemical reaction between the resin monomers. A rigid and well cross-linked polymer network which surrounds the inert fillers is produced. The degree of cure is influenced by many parameters, which include:
• Addition of polymerization promoters and inhibitors;
• Chemical structure of the monomers;
• Chemical or light energy imparted to activate the reactions;
• Filler composition; and
• Composite shade.
Due to the well-recognized anticariogenic effects of fluoride, fluoride-releasing and polyacid-modified composites are developed. Three different approaches to the development of fluoride-releasing composites have been reported. These approaches involve the addition of water-soluble fluoride salts, matrix-bound fluoride, or fluoride-releasing fillers. The first approach is not ideal because soluble fluoride salts are easily washed out, resulting in a porous structure. This can compromise the physio-mechanical properties of the composite. The second group of materials has been intensely investigated, and
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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