Materials Science and Engineering A 528 (2011) 1415–1420 Contents lists available at ScienceDirect Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea Optimization of bond strength between gold alloy and porcelain through a composite interlayer obtained by powder metallurgy B. Henriques ∗ , D. Soares, F.S. Silva Center for Mechanical and Materials Technologies, University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal article info Article history: Received 10 June 2010 Received in revised form 12 October 2010 Accepted 18 October 2010 Keywords: Dental restoration Powder metallurgy Porcelain Gold alloy Mechanical properties Composite interlayer abstract The purpose of this study was to evaluate the influence of a composite interlayer (at the metal–ceramic interface) on the shear bond strength of a metal–ceramic composite when compared with a conventional porcelain fused to metal (PFM). Several metal–ceramic composites specimens were produced by hot pressing. To identify which was the best composition for the interlayer several composites, with different relations of metal/ceramic volume fraction, were bonded to metal and to ceramic substrates. The bond strength of the compos- ites to substrates was assessed by the means of a shear test performed in a universal test machine (crosshead speed: 0.5 mm/min) until fracture. Some interfaces of fractured specimens as well as unde- stroyed interface specimens were examined with optical microscope and scanning electron microscope (SEM/EDS). The shear bond strength results for all composites bonded to metal and to ceramic substrates were significantly higher (>150 MPa) than those registered in the upper range of conventional porcelain fused to metal (PFM) techniques (∼80 MPa). The use of a composite interlayer proved to enhance metal/ceramic adhesion in 160%. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Metal–ceramic restoration, in the dentistry field, is still the most reliable method in dental prosthetics, especially when a good adhe- sion of the ceramic to the metal substrate is achieved [1]. The recent trend for all ceramic restorations do not accomplish, yet, for the necessary longevity and clinical failure is often reported pre- maturely [2,3]. Despite its cost, within the available metals used in PFM restorations, a well-approved high gold alloy is still the best option in terms of longevity, functionality, aesthetics, and bio- compatibility, together with ease of manufacture [4]. Also, it is no coincidence that in all testing and development of competing mate- rials, gold is always defined as standard material to be judge against. Therefore, for this study was used a high gold content dental alloy (KERAMIT 750, Nobilmetal, Villafranca d’Asti, Italy). Nevertheless, with the recent increase in gold’s price, reduced-gold content and palladium-based dental alloys are becoming very popular. Also, in some particular economic contexts, base metal alloys constitutes the solutions for low cost dental restorations. As referred above, metal–ceramic dental restorations strongly depend on the success of the bond between porcelain and the metal substrate [1–14]. This is achieved by attaining to the character- ∗ Corresponding author. Tel.: +351 253510220; fax: +351 253516007. E-mail address: brunohenriques@dem.uminho.pt (B. Henriques). istics of compatibility of the materials involved, e.g. choose the metals and ceramics with the proper CTEs (coefficient of thermal expansion). Using metals and ceramics with different CTEs, means that when cooling down from processing (sintering) temperature, both materials will contract at different rates and strong residual stresses will form across the interface. Depending on their magni- tude, these stresses can lead the ceramic to crack or even to separate from the metal substructure. Despite PFM restorations longevity, when compared to all-ceramic restorations, clinical failures some- times occur and the failure rate, due to fracture and exfoliation of porcelain, represents 59.1% of the whole clinical failure [7,8]. In this study, it is proposed the presence of a composite interlayer in the metal–ceramic interfacial zone. This interlayer will eliminate the sharp transition between the materials and, consequently, of their properties. For instance, the Young Modulus of the gold alloy and Ceramco3 are different (100 GPa and 83 GPa, respectively) causing an elastic mismatch that can lead to the microcracks generation and finally to failure. The specimens produced for this study were obtained through the hot pressing powder metallurgy (PM) technique. Powder metal- lurgical (PM) processing was the chosen route in this study because of the ease in controlling the composition and microstructure, as well as shape forming of the specimens. Hot pressing allowed avoiding undesired residual porosity and small cracks, together with a better and quicker compaction and full densification. PM used in rapid manufacturing, in the dentistry field, is starting to 0921-5093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2010.10.054