311 Introduction Acrylic resins are the most widely used materials for the fabrication of denture bases. This is due to their acceptable aesthetics, ease of handling, good thermal conductivity, low permeability to oral luids and color stability [1]. Inherent drawbacks of these materials are fracture as a result of fatigue when subjected to intra-oral forces and failure to withstand extra-oral impact forces [2]. Fracture may occur because of insuficient transverse, impact, lexural, and fatigue strengths. Recent advancements in the ield of Dental Materials and the development of newer and more novel forms of denture base materials have enabled acrylic denture base resins to overcome some of these drawbacks. For example, polycarbonate and nylon based materials have been developed to overcome the mucosal irritation and polymerization shrinkage that is associated with the conventional Polymethyl methacrylate (PMMA) resins [3-5]. Over the years, many attempts have been made to improve the impact properties of PMMA in three general directions [6]: the search for, or the development of, an alternative material to PMMA; the chemical modiication of PMMA by the addition of various polymers [7,8] such as a rubber graft copolymer, polyamides, epoxy resin, polystyrene, vinyl acrylic, polycarbonate [9] and nylon [10,11] and the reinforcement of PMMA with other materials, such as carbon ibers, glass ibers and ultra-high modulus polyethylene [12]. Heat, light and microwave polymerization methods have been employed for processing PMMA [13,14]. The addition of copolymers not only modiies mechanical properties of the conventional PMMA but also serves to improve toughness, increase impact resistance and prevent crack propagation. Most manufacturers of PMMA denture resins usually grade their products as “high impact” and claim these materials have new and enhanced strengthening properties, yet there is little or no research to support any strength differences between various versions of these products [15]. Polycarbonate denture base resins are injection molded thermoplastic resins. These materials have a signiicantly lower lexural strength at the proportional limit, a lower modulus elasticity, and a higher impact strength compared to conventional PMMA [16]. Light Activated Urethane Dimethacrylate (UDMA) denture base polymers were developed to surpass contact allergies, laboratory vapors, and the traditional lengthy lost wax technique of investing, lasking and boil-out used with the conventional PMMA materials [15]. This material was promoted on the basis that it does not contain methyl methacrylate monomer and instead contains a urethane dimethacrylate matrix with an acrylic copolymer, micro-tins, silica iller, and photo-initiator system. Triad was the irst system of light activated UDMA denture base polymer, which was advocated because of its biocompatibility, ease of fabrication and manipulation, low bacterial adherence, and ability to bond to other denture base resins. It is not comprised of individual components that need to be measured or mixed [17]. However, the use of UDMA was limited by the low impact resistance and brittleness of the material [18]. This limitation led to the development of a new methyl methacrylate-free denture base material by A Comparative Study of the Mechanical Properties of the Light-cure and Conventional Denture Base Resins Mohamed Hashem 1,2 , Samah O Alsaleem 3 , Mansour K Assery 4 , Emad Braka Abdeslam 5 , Sajith Vellappally 1 , Sukumaran Anil 6 1 Dental Health Department, College of Applied Medical Sciences, King Saud University, Riyadh 11433, Saudi Arabia. 2 Department of Dental Biomaterials, Al-Azhar University, Cairo, Egypt. 3 Senior Registrar in Prosthodontics, King Khalid University Hospital, Dental Department, King Saud University. Riyadh 11433, Saudi Arabia. 4 Chairman, Saudi Board in Prosthodontics at SCHS, Post Graduate Coordinator, College of Dentistry and Pharmacy, Riyadh. Saudi Arabia. 5 Assistant Professor, Department of Removable Prosthodontics. Al-Azhar University, Assiut, Egypt. 6 Professor, Department of Periodontics and Community Dentistry, College of Dentistry, King Saud University, Riyadh, Saudi Arabia. Abstract Purpose: To compare the lexural, tensile and compressive strengths of three denture base materials, namely, Lucitone 550, Bio Carbo Resin, and Eclipse. Materials and Methods: A total of 180 specimens were prepared, with 60 specimens of each material tested. The dimensions of the specimens for each test were made according to the ADA speciication. They were stored in distilled water bath at 37°C for 48 hours before testing. Each specimen was ixed on the table of the Instron universal testing machine. A force was applied at a cross-head speed of 5 mm/min until fracture occurred. Data were analyzed using a one-way analysis of variance (ANOVA) and Tukey’s test (p=0.05) for the lexural, tensile, and compressive strengths among all groups. Results: The lexural and compressive strength values showed signiicant differences between the three denture base materials. However, there was no signiicant difference in tensile strength between Lucitone 550 and Bio CarboResin. Conclusion: Eclipse showed signiicantly higher mechanical properties than polycarbonate reinforced and conventional heat cured acrylic resins, which suggests the use of Eclipse denture base materials as an alternative to traditional denture base resins. Key Words: Flexural strength, Tensile strength, Compressive strength, Denture base materials, Acrylic resins, Light polymerization Corresponding author: Mohamed Hashem, Dental Health Department, Dental Biomaterials Research Chair, College of Applied Medical Sciences, King Saud University, Riyadh 11433, Saudi Arabia, Tel: 00966-500197223; Fax: 00966-11-467-9017; e-mail: drsanil@hotmail.com