The effect of the solute on the structure, selected mechanical properties, and biocompatibility of Ti–Zr system alloys for dental applications D.R.N. Correa a , F.B. Vicente a , T.A.G. Donato b , V.E. Arana-Chavez b , M.A.R. Buzalaf c , C.R. Grandini a, ⁎ a UNESP — Univ. Estadual Paulista, Laboratório de Anelasticidade e Biomateriais, 17.033-360, Bauru, SP, Brazil b USP — Universidade de São Paulo, Faculdade de Odontologia, Departamento de Biologia Oral e Biomateriais, 05.508-900, São Paulo, SP, Brazil c USP — Universidade de São Paulo, Faculdade de Odontologia de Bauru, Departamento de Ciências Biológicas, 17.012-901, Bauru, SP, Brazil abstract article info Article history: Received 20 May 2013 Received in revised form 12 September 2013 Accepted 22 September 2013 Available online 28 September 2013 Keywords: Ti alloys Microstructure Mechanical properties Biomaterials New titanium alloys have been developed with the aim of utilizing materials with better properties for applica- tion as biomaterials, and Ti–Zr system alloys are among the more promising of these. In this paper, the influence of zirconium concentrations on the structure, microstructure, and selected mechanical properties of Ti–Zr alloys is analyzed. After melting and swaging, the samples were characterized through chemical analysis, density mea- surements, X-ray diffraction, optical microscopy, Vickers microhardness, and elasticity modulus. In-vitro cytotox- icity tests were performed on cultured osteogenic cells. The results showed the formation essentially of the α′ phase (with hcp structure) and microhardness values greater than cp-Ti. The elasticity modulus of the alloys was sensitive to the zirconium concentrations while remaining within the range of values of conventional titani- um alloys. The alloys presented no cytotoxic effects on osteoblastic cells in the studied conditions. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Titanium alloys have been widely used as biomaterials, especially for orthopedic prostheses and dental implants. Titanium has replaced Co–Cr alloys and 316L stainless steel due to its excellent corrosion resistance, mechanical properties, and biocompatibility. The aim of the develop- ment of titanium alloys is to create materials with improved properties for use as implants that can be used for a long period of time [1]. The Ti–6Al–4V alloy has been singled out as a good alternative for application in orthopedic prostheses because it possesses good mechan- ical and corrosion resistance, as well as a much lower elasticity modulus than cp-Ti [2]. However, there are reports that vanadium and aluminum ions can lead to neurological problems, such as Alzheimer's disease, and adverse reactions in tissues over an extended period [3]. Therefore the need exists for the development of new titanium alloys, mainly with the addition of niobium, molybdenum, tantalum, and zirconium, i.e., el- ements that have no cytotoxicity. Titanium displays allotropic transformation at around 883 °C, changing from an α phase (hcp crystalline structure) to a β phase (bcc crystalline structure). Titanium also presents metastable phases, which are dependent on processing conditions, as hexagonal martens- ite α′ and orthorhombic α″ phases. With respect to their microstruc- ture, titanium alloys are classified according to their phase proportion and can be near α, α, α + β, near β, and β. The mechanical properties of titanium alloys are directly related to their microstructure [4]. The α-type titanium alloys are characterized by good corrosion re- sistance and resilience, and higher elasticity modulus than β-type al- loys. The main applications of α-type titanium alloys are in dentistry because they have significant weldability, hardness, and tensile strength, which are favorable properties for this application [5,6]. Al- though the standard material for removable partial denture framework is still cobalt–chromium alloy. The major difference between titanium alloys and cobalt–chromium alloys lies in their modulus of elasticity. It is known that the modulus of elasticity of titanium alloys is about half that of cobalt–chromium alloy, which increases its resiliency and makes it more like gold alloys. Because these applications are located in a region of the body where there is intense mechanical work and in- teraction with different corrosive substances, α alloys are used predom- inantly as removable partial dentures and dental crowns [5,7]. This property would allow for the retentive clasp arm of removable partial denture to construct shorter arm length than it is possible with co- balt–chromium alloy and to be placed in deeper undercut and on abut- ment tooth. This characteristic is useful in clinical situations when the abutment tooth is not a molar tooth and has to be concerned about an esthetic or periodontal health case. Zirconium is considered a neutral element when added to a solid so- lution with titanium because it has an identical allotropic transformation with a similar phase transition temperature. When in a solid solution with titanium, in both α and β phases, it promotes hardening and slows the speed of phase transformation. This element has great solubil- ity in both crystalline phases of titanium and can form alloys of various proportions, as well as increase mechanical strength (such as tensile strength, hardness, and flexural strength) and improve corrosion poten- tial. Earlier studies have shown that the formation of solid solutions with Materials Science and Engineering C 34 (2014) 354–359 ⁎ Corresponding author. Tel./fax: +55 14 3103 6179. E-mail address: betog@fc.unesp.br (C.R. Grandini). 0928-4931/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msec.2013.09.032 Contents lists available at ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec