Metallic materials utilized for the construction of intra-oral and implant dental restorations include a wide range of relatively pure metals and multicomponent alloys. Basic corrosion and biodegradation properties of these alloys have been studied by both in vitro and in vivo techniques. These property characteristics have been shown to be dependent on composition and metallurgical state, combinations within a construct, surface conditions, mechanical aspects of function, and the local and systemic host environment. The susceptibility of these metallic materials to various forms of biodegradation will be presented, with emphasis on corrosion.

Biodegradation of restorative metallic systems.

The corrosion of five materials for implant suprastructures (cast-titanium, machined-titanium, gold alloy, silver-palladium alloy and chromium-nickel alloy), was investigated in vitro, the materials being galvanically coupled to a titanium implant. Various electrochemical parameters ECORR, iCORR Evans diagrams, polarization resistance and Tafel slopes) were analyzed. The microstructure of the different dental materials was observed before and after corrosion processes by optical and electron microscopy. Besides, the metallic ions released in the saliva environment were quantified during the corrosion process by means of inductively coupled plasma-mass spectrometry technique (ICP-MS). The cast and machined titanium had the most passive current density at a given potential and chromium-nickel alloy had the most active critical current density values. The high gold content alloys have excellent resistance corrosion, although this decreases when the gold content is lower in the alloy. The palladium alloy had a low critical current density due to the presence of gallium in this composition but a selective dissolution of copper-rich phases was observed through energy dispersive X-ray analysis. ©2000 Kluwer Academic Publishers

Galvanic corrosion behavior of titanium implants coupled to dental alloys.

In vitro corrosion behaviour and metallic ion release of different prosthodontic alloys.

A study was undertaken to determine the defects in the internal microstructure of clasps of cast chromium cobalt removable partial denture frameworks. Ninety cast frameworks were radiographically evaluated for porosity with an industrial radiographic machine. The grain structure of the clasps was analyzed with an optical photomicroscope before and after various heat treatments. The radiographic study showed a large number of internal defects in various parts of removable partial denture frameworks. The grain structure study revealed microporosities randomly distributed within the matrix. Various heat treatments were performed and resulted in no change in the grain structure of the original castings.

Radiographic and metallographic evaluation of porosity defects and grain structure of cast chromium cobalt removable partial dentures

Electrochemical characteristics of high-Pd alloys in relation to Pd-allergy

Binary compositions over the entire range of compositions of the Ag-Pd system are characterized by anodic polarization in Ringer's solution and alternate immersion in 0.5% Na 2S solution. The results show that a wide range of protection and passivation tendencies are introduced with Pd alloying of Ag.

In vitro Corrosion and Tarnish Analysis of the Ag-Pd Binary System

Radiographic analysis of uniform cylindrical castings fabricated by the centrifugal casting technique has revealed that the macroscopic porosity is dependent on the location of the sprue attachment to the casting. This is attributed to the significant pressure gradient associated with the centrifugal casting technique. The pressure gradient results in different heat transfer rates at portions of the castings near and away from the free surface of the button. Consequently, the macroscopic porosity is invariably at portions of the casting close to the free surface of the button. In addition, some optimized sprue-reservoir combinations could be predicted and proved, based on this pressure gradient concept.

T.K. Vaidyanathan

Papers

In vitro Corrosion and Tarnish Analysis of the Ag-Pd Binary System

Correlation Between Macroscopic Porosity Location and Liquid Metal Pressure in Centrifugal Casting Technique