1 INTRODUCTION
Dental amalgam, in widespread use for over 150 years, is one of the oldest materials used in oral health care[1]. It has been estimated that 75 % of all single tooth restoration are amalgam restoration and that this percentage has remained stable for many years[2]. For an amalgam restoration to be successful, it must be stable and resistant to the solvents and stresses of the oral environment. Several characteristics of the material are important such as susceptibility to corrosion, dimensional change, creep, strength, elastic modulus, and fracture resistance, determine the structural stability of the material[3].
Compressive and tensile strengths of core materials are thought to be important because core build-ups usually replace a large amount of tooth structure and must resist multidirectional masticatory forces for many years[4]. The value of strength of restorative materials should be close to the value of strength of the tooth structure. Compressive strength is only one of the criteria for the selection of core material, but it is a crucial one[5].
Creep is the time-dependent inelastic deformation of materials that are used at temperatures that are close to their melting points. Expressed in absolute temperatures, the melting point of the major matrix phase (?1) in dental amalgam is 400 K, whereas it is used at the mouth temperature of 310 K for a ratio of 0.8. In metals, ratios that exceed 0.5 are considered to be a forerunner for examining creep behavior[6].
The setting reaction for amalgam involves a dimensional change. The overall effect may cause a slight final expansion or a slight final contraction [7]. Excessive contraction lead to a large marginal gap between the material and the cavity[8]. Expansion lead to extrusion of the material out of the cavity[9].
These characteristics are influenced by several factors, including Hg/alloy ratio, condensation technique (i.e., the amount of porosity), and trituration conditions[10,11].
Hasheminezhad et al. [12] investigated the effect of copper content on compressive strength of dental amalgams. Addition of copper content to dental amalgam alloy causes an increase in compressive strength and hardness. Gaurav Solanki [13]found that high copper containing amalgam was be much better than low copper alloy containing amalgam in respect to strength, corrosion resistance, durability and resistance to tarnish. The tooth restored with high copper amalgam did not have any kind of marked expansion or condensation after its setting after 24 hrs. creep were also minimized.
The aim of this work is to investigate the effect of copper content on mechanical properties of dental amalgam.