The Mechanical Properties of Moulded and Thermoformed Denture Resins

Removable dentures are mobile dental (prostheses) that are used for replacing missing teeth in patients with partial or complete edentulism. Since 1940, the primary material for the fabrication of removable dentures has been polymethylmethacrylate [1] to [3]. Since then, much effort has been made in the improvement of characteristics of construction materials, affecting the composition of the materials and the addition of external supplements to increase their resilience [4]. The most commonly used method of strengthening polymethyl-methacrylate (PMMA) is impregnation with rubber (butadiene styrene) and the addition of various types of fibres [5]. Further improvement of mechanical properties of PMMA can also be conducted via microwave irradiation, as well as the addition of nanoparticles [6] to [8]. Better utilization of the materials’ potential requires additional examination by the scientific community, because manufacturers are not required to state the full specification of the product, unless the ingredients of the material that have proven to be potentially harmful. Knowledge about each material and of its characteristics is necessary in order to choose the most suitable material for a given clinical situation. According to the Hergravesa [9], the fact that 63% of dentures fracture occurs in the first three years of their use remains a problem in current denture applications [10]. Denture fracture usually appears in the midline of the palate (Fig. 1), due to the cyclic shifting between flexion and extension forces that occur during mastication. This was confirmed by the study of Khasawneh and Arab [11], which reported that 61% of fractures occur in the middle of the palate, which was further verified by in vitro studies by Prombonas and Vlissidis [12]. It has been stated that in the case of a mandibular complete denture, the midline stress field is planar, consisting of low intensity compressive forces and low shear stress. At the same time, the corresponding stress field of the maxillary complete denture is characterized by high tensile stresses and high shear stress. This is of particular importance when The Mechanical Properties of Moulded and Thermoformed Denture Resins Baloš. S. – Milutinović, M. – Potran, M. – Vuletić, J. – Puškar, T. – Pepelnjak, T. Sebastian Baloš1 – Mladomir Milutinović1 – Michal Potran2 – Jelena Vuletić2 – Tatjana Puškar2 – Tomaž Pepelnjak3,* 1 University of Novi Sad, Faculty of Technical Sciences, Serbia 2 University of Novi Sad, Medical Faculty, Serbia 3 University of Ljubljana, Faculty of Mechanical Engineering, Slovenia