Abstract—The dental composites are preferably used as filling materials due to their esthetic appearances. Nevertheless one of the major problems, during the application of the dental composites, is shape change named as “polymerisation shrinkage” affecting clinical success of the dental restoration while photo-polymerisation. Polymerisation shrinkage of composites arises basically from the formation of a polymer due to the monomer transformation which composes of an organic matrix phase. It was sought, throughout this study, to detect and evaluate the structural polymerisation shrinkage of prepared dental composites in order to optimize the effects of various fillers included in hydroxyapatite (HA)-reinforced dental composites and hence to find a means to modify the properties of these dental composites prepared with defined parameters. As a result, the shrinkage values of the experimental dental composites were decreased by increasing the filler content of composites and the composition of different fillers used had effect on the shrinkage of the prepared composite systems. Keywords—Dental composites, hydroxyapatite (HA), BisGMA, shrinkage. I. INTRODUCTION N modern dentistry, one of the most important issue is esthetically repairing the structural problems of teeth by means of proper materials especially dental composites used mostly as the filing material. Therefore a great number of researches have been carried out for improving the properties of the dental composites throughout the world. Polymerisation shrinkage of dental resin composites is one of the main problems for clinicians during the restoration. Hence, any data on the shrinkage of such dental composites B. S. Oduncu is with the Department of Bioengineering, Yildiz Technical University, Istanbul, TURKEY (e-mail: bilgesema@hotmail.com). S. Yucel is with the Department of Bioengineering, Yildiz Technical University, Istanbul, TURKEY (e-mail: syucel@yildiz.edu.tr). I. Aydin is with the Rheology Group, Department of Chemical Engineering, Engineering Faculty, Istanbul University, Avcilar Campus 34320, Istanbul, TURKEY (corresponding author, phone/fax: +90-212- 5908646; e-mail: i.aydin@istanbul.edu.tr). I. D. Sener is with the Department of Prosthodontics, Faculty of Dentistry, Marmara University, Buyuk Ciftlik S., No: 6, Nisantasi 34365, Istanbul, TURKEY (e-mail: isildamlasener@gmail.com). G. Yamaner is with the Department of Endodontics, Faculty of Dentistry, Marmara University, Buyuk Ciftlik S., No: 6, Nisantasi 34365, Istanbul, TURKEY (e-mail: g.yamaner@gmail.com) could contribute for a successful and proper restoration. Composite materials used in dental restorations consist of a continuous organic matrix phase such as a bisphenol A- glycidyl methacrylate (BisGMA) or urethane dimethacrylate (UDMA) diluted with triethyleneglycol dimethacrylate (TEGDMA) [1], [2] or hydroxyethylmethacrylate (HEMA) reinforced with a dispersed inorganic filler phase such as barium or zinc glasses, quartz, zirconia, silica, hydroxyapatite, etc. [3], [4]. The polymerisation shrinkage occurs as a result of exchanging the van der Waals spaces within the covalent bonds while monomers in the resin matrix are converted into polymer networks by the effect of visible-light [5]. As a result, such polymerisation shrinkage would create contraction stresses within the resin composite restoration as well as internal stresses and various forms of deformations in the surrounding tooth structure. Therefore leakages could occur at the stressed interfacial margin and contact area between the inner surface of teeth and the dental composite producing marginal staining and ultimately recurrent caries. Several publications have determined the influence of polymerisation shrinkage on composite resin restorations [6]– [8]. Therefore, the primary aim of this study was to evaluate the magnitude of the shape change of composite resins obtained in the laboratory. In this study, the shrinkage values of composites prepared were measured by means of a surface laser profiling system (OSP 100A, Uniscan, UK) and the calculated results were compared with the corresponding literature obtained by various methods. The composites, throughout this study, were obtained by using BisGMA (bisfenol A-glycidyl methacrylate) and HEMA (hydroxyethyl methacrylate) as the organic matrix phase and hydroxyapatite (HA), alumina and zirconia as the inorganic fillers with various amounts. The surfaces and hence the volumetric geometry of the prepared composites after curing (polymerisation) by LED type light were obtained by the OSP 100A surface profiling system. As a result, necessary calculations were implemented on the 3D shrinkage geometry constructed by the scan data. This scan was performed by recording “z-axis” data as the “depth” of the composite samples’ surface along the “x-axis” line with the defined steps along “y-axis”. After that, 3D geometries were analyzed by using MATLAB software package. An executable program was written to perform such analysis Polymerisation Shrinkage of Light−Cured Hydroxyapatite (HA)−Reinforced Dental Composites Bilge S. Oduncu, Sevil Yucel, Ismail Aydin, Isil D. Sener and Gokhan Yamaner I World Academy of Science, Engineering and Technology International Journal of Biomedical and Biological Engineering Vol:4, No:4, 2010 130 International Scholarly and Scientific Research & Innovation 4(4) 2010 scholar.waset.org/1307-6892/8448 International Science Index, Biomedical and Biological Engineering Vol:4, No:4, 2010 waset.org/Publication/8448