Dental Materials Investment Materials PDF

**Investment materials:** it is a ceramic material which is suitable for forming a mold into which molten metal or alloy is cast. The procedure for creating the mold is described as 'investing'. These materials can withstand high temperatures. For this reason, they are also known as refractory mate...

**Investment materials:** it is a ceramic material which is suitable for forming a mold into which molten metal or alloy is cast. The procedure for creating the mold is described as 'investing'. These materials can withstand high temperatures. For this reason, they are also known as refractory materials.  **Requirements of investment materials:** 1. The investment mold must expand to compensate for the alloy shrinkage, which occurs during the cooling of the molten alloy. 2. The powder should have a fine particle size to give a smooth surface to the casting. 3. Manipulation should be easy. It should have a suitable setting time. 4. The material should have a smooth consistency when mixed. 5. The set material should be porous enough to permit air in the mold cavity to escape easily during casting. 6. At higher temperatures, the investment must not decompose to give off gases that may corrode the surface of the alloy. 7. It must have adequate strength at room temperature to permit handling, and enough strength at higher temperatures to withstand the impact force of the molten metal. 8. Casting temperatures should not be critical. 9. After casting, it should break away readily from the surface of the metal and should not react chemically with it. 10. The material should be economical. **General composition of investment:** All investment materials contain a refractory and a binder. a. ***Refractory materials:*** A material that will withstand high temperatures without decomposing or disintegrating and regulate the thermal expansion like silica dioxides such as Quartz, Tridymite and Cristobalite. b. ***Binder:*** A material that will set and bind together the particles of a refractory substance, e.g., gypsum, phosphate and silicate. The common binder used for gold alloys is dental stone (alpha-hemihydrate). The investments for casting cobalt-chromium alloys use ethyl silicate. c. ***Chemical modifiers:*** Chemicals such as sodium chloride, boric acid, potassium sulfate are added in small quantities to modify properties. **Types of investment materials:** - According to the type of binder used, there are three types of investment materials. They all contain silica as the refractory material, and the type of binder used is different. 1. ***Gypsum bonded investment:*** its low-temperature casting investment. It is used for casting gold alloys. They can withstand temperature up to 700°C. 2. ***Phosphate bonded investments:*** its high-temperature casting investment. It is used for metal-ceramic and cobalt-chromium alloys. They can withstand higher temperatures. 3. ***Ethyl silica bonded investments:*** They are an alternative to the phosphate bonded investments, for high temperature casting. They are principally used in the cast of base metal alloy partial dentures. - According to processing or casting temperature, dental investment classified into two types: 1. ***High temperature casting investment:*** a. Phosphate bonded investment. b. Ethyl Silicate bonded investment. 2. ***Low temperature casting investment:*** Gypsum bonded investment. **All ceramic crown investment:** It is phosphate bonded, contained fine-grained refractory fillers to allow accurate reproduction of details and remain undamaged during the firing of ceramic.