STANCA BOBOIA, MARIOARA MOLDOVAN, CRISTINA PREJMEREAN, CODRUTA SAROSI, ALEXANDRA ROMAN, IOAN ARDELEAN INFLUENCE OF INITIATION SYSTEM AND FILLER RATIO ON THE PROPERTIES OF NEW FLOWABLE DENTAL COMPOSITES The goal of this study was to measure and analyze the water sorption and mechanical properties of 5 experimental flowable composites with different filling ratios and two types of initiation systems: self cured and light-cured. The samples were analysed, in order to observe the influence of initiation type and the amount of filler on the properties required to satisfy the conditions for dentistry use. We have determined the water sorption and mechanical properties (compressive strength, flexural strength, diametral tensile strength) according to ISO 4049/2000 and international norms ďAmerican Dental Associationís Specification No.27. The measurements were done using a mechanical testing machine Lloyd Instruments-LR5k Plus. Increased water absorption weakens the bonds in the polymer matrix, causing separation of filler by the polymer matrix, filler hydrolytically degrade, leading ultimately to reducing the mechanical resistance, which represents a major step in the characterization of dental materials to be used in dentistry. Among all the mechanical stress from oral cavity, the compression and the tension are the predominant forces, during which are developing the highest forces that dental hard tissues are subject to. The results of this study highlight the relationship between the composition, initiation system of the dental materials and their properties.