4691 Journal of Applied Sciences Research, 8(8): 4691-4696, 2012 ISSN 1819-544X This is a refereed journal and all articles are professionally screened and reviewed ORIGINAL ARTICLES Corresponding Author: Amani Ramadan Ali Moussa, Department of Prosthodontic Research, Division of Oral and Dental Research, National Research Center, Giza, Egypt. E-mail: amani.moussa66@yahoo.com Comparative Adaptation Accuracy of Heat Cured and Injection Molded Resin Denture Base Materials 1 Amani Ramadan Ali Moussa, 2 Dalia Yehia Ibrahim Zaki, 1 Hisham Samir El Gabry, 3 Tamer Mahmoud Ahmed 1 Department of Prosthodontic Research, Division of Oral and Dental Research, National Research Center, Giza, Egypt. 2 Department of Restorative and Dental Materials Research, , National Research Center, Giza, Egypt 3 Department Dental Anthropology, Institute of African Research and Studies, Cairo University, Egypt. ABSTRACT Background: Polymethyl meth acrylate (PMMA) resin has been the most commonly used material for denture bases, despite its popularity, PMMA resin is far from ideal. Polymerization shrinkage and release of thermal stresses are the major disadvantages exhibited by the material. In an attempt to overcome dimensional in accuracies of PMMA resin, new thermoplastic resins and alternative processing techniques have been developed. Purpose: The purpose of this study was to evaluate and compare the adaption accuracy of two commercial heat cured resins and an injection molded resin. Materials and Methods: a total of 21 accurate denture bases with the same dimension were fabricated, 14 denture bases were made using conventional compression molding technique (Acrostone, WHW plastic, England and Vertex regular, Zeist, Netherlands), and 7 dentures were processed using injection molding technique (Crystal, Bredent, Germany). The adaptation accuracy was examined using universal measuring microscope. The gap between the resin base and stone cast was measured at canine region and posterior palatal area at five points at 5 points, corresponding to the right and left residual ridge crests, the midline, and the right and left marginal limits of the flanges. Results: The least total gap score measured was for Bre-Crystal followed by Vertex- regular while the highest gap score was for Acrostone group. However, there was no statistically significant difference between the Vertex- regular and Acrostone groups. Conclusion: injection moulded PMMA resin showed superior dimensional accuracy compared to conventional pressure packed PMMA resin. Key words: Gap measurement, Heat cured resin, Injection molded resin. Introduction Polymethyl methacrylate (PMMA) resin has been the most commonly used material for denture bases since 1937 (Memon, 2001 and Yunus et al. 2005). Several studies have reported the desirable properties of PMMA resin, such as biocompatibility, excellent esthetics, insolubility in oral fluids, simple processing technique, and reasonable cost (Anusavive, 1991; Craig, 2002 and Pires-de-Souza et al., 2009). Despite its popularity, PMMA resin is far from ideal (Darbar et al, 1992 6 and Dhiman et al., 2009). Polymerization shrinkage and release of thermal stresses are the major disadvantages exhibited by the material (Anusavice, 2003). Such changes are unavoidable during processing of the resin (Chung-Jae Lee, 2010). The accurate fit of denture base is a principle criterion in the physical mechanisms of complete denture retention (Anthony & Peyton, 1962 and Darvell & Clark, 2000). Nevertheless, the combination of polymerization shrinkage and distortion due to thermal stresses affects the adaptation accuracy of denture base to underlying tissue and creating a microgap (Garfunke, 1983; Baemmert et al., 1990 and Jackson et al., 1993). For a long time, PMMA resin was polymerized using compression molding technique by heating the molded resin in temperature controlled water bath (Takamata & Setcos, 1989 and Phoenix, 2004). In an attempt to overcome dimensional in accuracies of PMMA resin new thermoplastic resins (Memon, 2001 and Parvizi et al., 2004) and alternative processing techniques have been developed (Takamata & Setcos, 1989, Keenan et al., 2003 and Ono et al., 2004). Of these techniques is the injection molding technique; in which the polymerization shrinkage is compensated by continuously injecting resin at certain pressure through a carefully controlled procedure (Young, 2010). Several studies have revealed that injection molding techniques result in fewer dimensional inaccuracies and more accurate denture base than conventional processing techniques (Nogueira et al., 1999; Parvizi et al., 2004 and Ganzarolli et al., 2007)