EUROPEAN JOURNAL OF PAEDIATRIC DENTISTRY VOL. 15/3-2014 317 F. Sengul, T. Gurbuz, S. Sengul* Department of Pedodontics, Faculty of Dentistry, Ataturk University,Erzurum, Turkey *Department of Hydraulic, Faculty of Engineering e-mail: fsengul@atauni.edu.tr ABSTRACT Aim The purpose of this finite element analysis (FEA) study is to evaluate and compare the stress distributions at the primary molars and restorative materials according to the material used. Materials and methods A total of 12 3D models of Class II cavities in primary molars plus one control model were analysed. Study Design: Three-dimensional FEA was used to compare stress distribution on enamel, dentin and restoration surfaces of cavities. Statistics: Stresses occurring under occlusal forces were compared with the von Mises criterion. Results The highest von Mises stress values at the enamel and restoration of restored tooth 84 were computed. On the basis of these results, all materials were ranked on enamel stress as: flowable composite resin (FCR)> compomer> resin modified glass ionomer cement (RMGIC)> giomer composite resin (GCR)> hybrid composite resin (HCR)> amalgam. Moreover, ranking of materials on restoration stress was FCR<co mpomer<RMGIC<GCR<amalgam<HCR. Conclusion A restorative material with appropriate elasticity module, able to balance stress concentrations, should be used to increase the survival rate of both the hard tissue of the tooth and the restoration material. Finite element analysis of different restorative materials in primary teeth restorations Keywords Finite element analysis, Primary teeth, Class II cavities, Restorative materials, Giomer. Introduction Restorations should be strong enough to resist the intra-oral forces; in fact, as a result of bite forces, restored teeth are exposed to mechanical stresses. Therefore, biomechanical principles have an important part in the clinical success of restorative materials. Formation and distribution of forces, caused by teeth and surrounding tissues, directly affect the prognosis of restorative treatment [Sonugelen and Artunç, 2002]. Recently, finite element method (FEM) was used to assess the durability of different restorative materials under chewing forces in a fast and economical way [Asmussen and Peutzfeldt, 2008; Hubsch et al., 2002; Ausiello et al., 2001; Toparli et al., 1999; Lin et al., 2001]. In the prosthetic, restorative, endodontic, orthodontic, surgical, and periodontal fields of dentistry, many studies of finite element stress analysis (FEA) are available [Simsek et al., 2006; Koca et al., 2005; Gungor et al., 2002]. A literature search of FEA in primary teeth resulted in only one three-dimensional (3D) FEA study in which Gurbuz et al. [2008] evaluated the success of different restorative materials in crowns in which the mushroom-shaped undercut technique was used.. The purpose of this FEA study was to evaluate and compare the stress distributions at the primary molars and restorative materials according to the restorative material used. Materials and methods Head and neck tomography images of a six-year-old girl were selected from the archive of the Department of Radiology, Faculty of Medicine, Ataturk University. Images were acquired through a spiral computer tomography (CT) (Aquillion 16, Toshiba, Tokyo, Japon). A 3D model was prepared from the images with MIMICS 10.01 (Materialise Software, Leuven, Belgium) software. ANSYS Workbench 10.0 (Swanson Analysis Systems, Inc., Houston, PA, USA) software was used for the 3D FEA. The model was transferred to SolidWorks 2005 (SolidWorks Corporation, Massachusetts, USA), a 3D computer-assisted design and manufacturing program. Then 3D solid models of primary maxillary and mandibular molars, suitable for the stress analysis of SolidWorks, were created (Fig. 1). The cortical bone was modeled by creating 1 mm thickness inward the surface of the jaw models. Consequently, cortical and cancellous bone layers were modeled as two separate parts. 3D models of Class II cavities in primary molars were modeled as described by the Suwatviroj et al. [2003]. The digitally prepared cavity sizes are given in figure 1d. Cavities were prepared with a cavosurface angled 90 degrees. The axial walls of approximal cavites were modeled with a slope of 5 degrees. Also, the axio- occlusal and sharp-cut edges of inner cavity walls were softened in dentin (Fig. 1d). The simplest approximation to the probable nature of occlusal contacts is where the jaw and teeth are located at 1 mm from the occlusal contacts in the SolidWorks