518. FATIGUE STRESS RESISTANCE OF SOME COMPOSITE MATERIALS FOR DENTAL FILLINGS. J. MYSTKOWSKA 1,A , A. NIEWCZAS 2,A , P. KORDOS 3,A , J.R. DĄBROWSKI 1,B  VIBROMECHANIKA. JOURNAL OF VIBROENGINEERING. DECEMBER 2009. VOLUME 11, ISSUE 4. ISSN 1392-8716 717 518. Fatigue stress resistance of some composite materials for dental fillings J. Mystkowska 1,a , A. Niewczas 2,a , P. Kordos 3,a , J. R. Dąbrowski 1,b 1 Bialystok Technical University, Wiejska 45 C, 15-351 Bialystok, Poland e-mail: 1a j.mystkowska@pb.edu.pl, 1b jrd@pb.edu.pl Phone: +48857469251; Fax: +48857469248 2 Medical University of Lublin, Karmelicka 7, 20-081 Lublin, Poland e-mail: 2a agatan@neostrada.pl 3 Lublin University of Technology, Nadbystrzycka 38, 20-618 Lublin, Poland e-mail: 3a p.kordos@pollub.pl (Received 29 June 2009; accepted 27 November 2009) Abstract. The paper investigates fatigue stress resistance of some originally made composite materials based on Bis-GMA resin with fluoridated glass and YbF 3 . The material was used to fill in the cavities in teeth extracted for orthodontic reasons. For laboratory tests a mastication simulator was used. The tooth samples were placed in special holders with resin and exposed to cyclic mechanical loads (100 000 cycles) in order to assess their resistance to fatigue stress. The influence of repeatable mechanical loads on the teeth and the structure of the material were investigated. Additionally, the impact of cyclic loads on fluoride release from the composite materials was estimated. Keywords: fatigue stress, fluoride, release, dental fillings, composite materials Introduction Due to their superior mechanical and aesthetic properties, dental composite materials are commonly used as dental fillings. Numerous investigations concerning physicochemical, mechanical and tribological properties of dental composite materials have been intensively conducted [1,2]. In paper [3] an in vitro oral wear simulator was used to compare the susceptibility of different classes of dental composites to marginal breakdown. The reported results are in general agreement with clinical studies stating that microfilled composites show greater marginal degradation than other fillings of this type. On the other hand, microfilled composites show much higher resistance to contact fatigue than other materials, like glass ionomers [4]. Fatigue behaviour of resin composites was analyzed under different environment parameters [5]. It was found that fatigue crack propagation decreased under aqueous conditions and that fatigue cracks detoured around inorganic macro-fillers, but penetrated the organic ones. In the literature available on the subject there is not much information concerning fatigue properties of composite dental fillings. The influence of cyclic loads on forming the gap margin between dental fillings and hard tooth tissues is not specified. The mechanism of crack propagation in the composite material and hard tooth tissues directly adhering to the material is difficult to characterize [6, 7]. Dental filling undergoes mechanical and thermal loads. The process of mastication generates the complicated system of forces in the human oral cavity [8, 6]. Considerable stresses are additionally intensified by stresses resulting from the cyclical changes of a tooth thermal state [9]. Some results on the marginal fissure confirm that all kinds