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BAB 2 TINJAUAN PUSTAKA 2.1 Acrylic Resin Acrylic resin is the material most commonly used for removable denture base is composed of long polymer chains of methyl methacrylate units repetitive called polymethylmethacrylate. The resins are formed by bending the plastic molecules combine multiple methyl methacrylate (Craig et al., 2004) 2.1.1 Type of Acrylic Resin According to Craig et al. (2004) there are two types of acrylic resin are: a. Type heat c
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  BAB 2 TINJAUAN PUSTAKA 2.1 Acrylic Resin Acrylic resin is the material most commonly used for removable denture base is composed of long polymer chains of methyl methacrylate units repetitive called  polymethylmethacrylate. The resins are formed by bending the plastic molecules combine multiple methyl methacrylate (Craig et al., 2004) 2.1.1 Type of Acrylic Resin According to Craig et al. (2004) there are two types of acrylic resin are: a. Type heat cured polymer, which is a type of acrylic resin polymerization process occurs after heating at a given temperature.  b. Type cold cured polymer, acrylic resins are the type that does not require heating in the  polymerization process. Acrylic resin composition According Combe (1992) and Anusavice (1996) acrylic resin composition: a. Heat cured acrylic On powder (powder) containing: 1. Polymer (polymethylmethacrylate) as the main element 2. Benzoyl peroxide as an initiator: 0.2-0.5% 3. Reduces Translucency: Titanium dioxide 4. Dye in the polymer particles can be adapted to oral tissues: 1% 5. Fiber: fibers resemble small blood vessels  While the fluid (liquid) contains: 1. Monomers: methyl methacrylate, a clear liquid that evaporates easily. 2. Stabilizer: 0.006% hydroquinone as a barrier polymerization inhibitor during storage. 3. Cross linking agent: 2% Ethylene glycol dimetacrylate, useful help connecting the two so that the polymer molecules into long chains, and to increase the strength and hardness of acrylic resin. According to Craig and Power (2002), while the base material for artificial teeth are the most commonly used type of heat cured poly methyl methacrylate.  b. Self cured acrylic Similar in composition to the type of heat cured, but there are additional activators such as dimethyl-p-toluidine in liquidnya. 2.1.2 Polymerization of Acrylic Resin Polymerization is a reaction to the establishment of the few pieces of polymer monomer, functionally can take unlimited, and an exothermic reaction. Function of monomer in the reaction between the monomer and polymer, is a plastic mass produce because most polymers soluble monomers. During the period of dissolution is not expected to occur polymerization, this  period is called the physical reaction between the powder and the liquid (Craig et al., 2004). According Combe (1992) there are two kinds of polymerization processes, namely: a. Condensation reaction The reaction between two or more molecules to produce molecules by eliminating smaller molecules such as water.  b. Addition reactions Chemical reaction between two or more molecules to large molecules to the formation of small molecules without eliminating. Methacrylateyang polimethyl acrylic resin commonly used as a   base material removable dentures usually melalaui addition reaction, based on the mechanism of  polymerization process through the following stages (Craig et al., 2004): 1. Initiation and activation Polymerization process requires the driver of a free radical is a highly reactive material and having the initiator, can be formed by the decomposition of peroxide. In this reaction one molecule of benzoyl peroksidadapat form two free radicals. Free radicals is what will drive the  polymerization initiator and called activated peroxide by breaking through heating or the  provision of other chemicals, such as dimethyl-p-toluidine or tertiary amine or mercaptan with UV irradiation or radiation of electromagnetic waves. 2. Propagation Is the formation of polymer chains from the reaction between the active molecules with other molecules. Chain spread (propagation) occurs because the activated monomer reacts with other monomers, and so forth until a lengthening chain and activated monomers bind to each other. 3. Termination Chain termination arising from a reaction between two mutually growing chain to form a stable molecule. 2.1.3 Acrylic Resin as a Denture Base Base materials for removable dentures should ideally meet the following criteria (Noort, 1994): a. Non-toxic, irritant and is not affected oral environment that is not soluble or absorb oral fluids.  b. Have sufficient mechanical strength, among others: 1. High modulus of elasticity resulting in a very thin size has sufficient power. 2. Proportional high limit, so that the denture is not easy to change shape when the load gets  pressure. 3. Transverse flexural strength or power greater.  4. Have a great impact strength, so it does not break easily if dropped. 5. Has a large strengthyang fatigue and surface roughness in order to use enough resistance to abrasion. c. Has a thermal expansion according to dental materials, have a higher melting point of the material and liquid food into the mouth. d. Has a thermal expansion according to dental materials e. Does not change shape during manufacture and use. f. Easy to manufacture and cost effective. g. Easy to repair h. Easy to clean. Until now acrylic resin is still used as a denture base material in the field of dentistry for acrylic resin has the properties of both the aesthetic and the relative strengths and easily manipulated but its shortcomings, have properties of porous acrylic resin (Combe, 1992). 2.1.4 Denture Cleaning Mechanism There are two ways that are often made for cleaning dentures, which is done by mechanical means or instrument ultrasonic toothbrush cleaner, how chemistry is done by soaking the dentures in the solution to cleaning materials. Cleaning by mechanical means using a toothbrush with or without abrasives are effective in removing plaque, but if done repeatedly can cause wear of the acrylic resin plate that can later lead to denture becomes retentive (Rianti, 2003; Sesma et al., 2005). Chemical cleaning is done by soaking the denture cleaning solution. According to Silva et al study. (2009) stated that the brushing treatment followed by immersion is effective and efficient to kill bacteria and fungi. Soaking dentures in a cleaning solution can be carried out throughout the night, 2 hours, 1 hour or 30 minutes depending on the cleaning agents used (Sesma et al., 2005)

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