Biomaterials 24 (2003) 1705–1712 Transmission electron microscopic investigation of a Pd–Ag–In–Sn dental alloy W.H. Guo a,1 , W.A. Brantley a, *, W.A.T. Clark b , P. Monaghan a,2 , M.J. Mills b a Section of Restorative Dentistry, Prosthodontics and Endodontics, College of Dentistry, The Ohio State University, 305 West 12th Avenue, Mailbox #191, P.O. Box 182357, Columbus, OH 43218-2357, USA b Department of Materials Science and Engineering, The Ohio State University, Watts Hall, 2041 College Road, Columbus, OH 43210, USA Received 7 April 2002; received in revised form 27 July 2002; accepted 26 November 2002 Abstract With the price volatility of palladium, there has been renewed interest in palladium–silver alloys for metal-ceramic restorations in dentistry. The microstructures of a popular Pd–Ag dental alloy were investigated in the as-cast and simulated porcelain-firing heat- treated conditions, using transmission electron microscopy. In the as-cast condition, the microstructure was strongly influenced by microsegregation, and contained the face-centered cubic Pd solid solution matrix, a eutectic structure with lattice parameters that varied for the two phases, and a face-centered tetragonal (fct) precipitate. After heat treatment, the lattice parameters for the two phases in the eutectic structure were uniform, and discontinuous precipitates with f011g matrix habit planes and dislocations appeared in the matrix. An unusual nanostructured constituent was found in the fct set of eutectic lamellae in the heat-treated alloys. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Pd–Ag dental alloy; Transmission electron microscopy; Microstructure; Eutectic; Discontinuous precipitation 1. Introduction Popular palladium–silver dental alloys for metal- ceramic restorations typically have compositions ran- ging from about 50–60% Pd and 30–40% Ag, and contain small amounts of low melting point metals, such as Zn, In and Sn, to improve castability by increasing the fluidity of the molten alloy; In and Sn also promote strong bonding to dental porcelain [1–4]. These alloys were introduced nearly three decades ago, with the first Pd–Ag dental alloy (Cameo-Lite, J.F. Jelenko & Co., Armonk, NY, USA) marketed in 1973 and the first patented Pd–Ag dental alloy (Will-Ceram W-1, Wil- liams/Ivoclar, Amherst, NY, USA) introduced in 1974 [1]. The Pd–Ag alloys have the highest elastic modulus and sag resistance during porcelain firing of all noble metal casting alloys, excellent porcelain-metal bond strength, favorable handling characteristics, ease of soldering, and satisfactory tarnish and corrosion resis- tance [1–8]. Their principal disadvantage has been a tendency to produce an esthetically unattractive yellow– green tint in dental porcelain, because of volatilization of Ag from the alloy and ion exchange with Na in the porcelain; this problem has been alleviated with the development of new brands of dental porcelain [3,4,9,10]. With the recent volatility in the price of palladium, there has been renewed interest in Pd–Ag alloys for metal-ceramic restorations, since these alloys are considerably less expensive than the high-palladium alloys, which had previously [11] achieved widespread popularity as economical substitutes with excellent mechanical properties for traditional gold-based casting alloys. Several investigators have studied the microstructures of commercial Pd–Ag dental alloys in both the as-cast and simulated porcelain-firing heat-treated conditions. Mezger et al. [5] found that five Pd–Ag alloys mainly consisted of a face-centered cubic (fcc) matrix phase with a lattice parameter determined by X-ray diffraction between 0.396 and 0:398 nm; and had heterogeneous *Corresponding author. Tel.: +1-614-292-0773; fax: +1-614-292- 9422. E-mail address: brantley.1@osu.edu (W.A. Brantley). 1 Present address: Center for Biological and Environmental Nano- technology (CBEN), Rice University, P.O. Box 1892, Houston, TX 77251-1892, USA. 2 Present address: Marquette University School of Dentistry, P.O. Box 1881, Milwaukee, WI 53201-1881, USA. 0142-9612/03/$-see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0142-9612(02)00564-1