Argen Testing

PHYSICAL/MECHANICAL PROPERTY TESTS

Colour Determination

The colour of a dental alloy is significant aesthetic quality of the material. A patient may desire a rich gold colour for the metal inserted in his/her mouth. Colours range from deep yellow, yellow, pale yellow to white.

Density Determination

The density of a dental alloy is related to the amount of both precious and base metals in the formulation. The density will determine the weight of alloy required for a particular casting application and hence the cost. Density is determined by weighing a sample of alloy in air and then submerged in water. The difference is the weight of displaced water which is a measure of the sample volume. Density is the alloy weight per unit volume expressed in grams per cubic centimeter (g/cm3).

Tensile Test

The mechanical properties of a material are determined by tensile testing. This test utilizes a specifically dimensioned sample cast in accordance with ASTM E8 which is linearly pulled until breaking in a machine which can simultaneously measure the applied load in pound and the deformation of the test unit in inches. The units of interest to be derived from the tensile test are stress or pounds of force per unit cross sectional area and strain or inches of deformation per inch of original gauge length expressed in per cent.

Yield Strength
The yield strength is the stress at which a material starts to exhibit permanent deformation. It is determined by applying the tensile force on an as cast ASTM E8 specimen until the resulting stress/strain curve shows a departure from elastic behavior. For many alloys, this is not a distinct phenomenon and is therefore assigned to that load which correspond to a 0.2% offset from proportionality or 0.2% of strain.

Ultimate Tensile Strength
This is the maximum load per unit area observed during the tensile test. This value generally exceeds the yield strength.

Elongation
Elongation is defined as the percentage change in the length of a tensile test specimen at fracture (ASTM E8). This property directly relates to the burnishability of dental casting alloys. An alloy with a high percent of elongation is easily burnished.

Modulus of Elasticity
This is the ratio of the tensile stress and tensile strain over the elastic (linear) part of the stress/strain curve.

Hardness Test

Material hardness is a measure of the resistance to indentation by a harder material such as tool steel or diamond. Hardness is determined either from the load required to make a specific indentation or the size of an indentation made by a specified load. When samples to be hardness tested are small or thin, microhardness techniques and equipment are recommended for use.

Microscopic Analysis

Metallographic techniques can reveal many important features of a cast alloy. Careful preparation of samples by cutting, grinding, polishing and etching are required to bring out the descriptive structures visible in the metallurgical microscope.

Grain Size and Microstructure
The size of the metal crystals formed during the solidification are revealed by microscopic examination of a polished and etched sample of the alloy. Generally speaking, a fine evenly dispersed grain structure indicated by the appearance of many cells per unit area, improves the performance of the alloy.

BIOCOMPATIBILITY

CORROSION RESISTANCE

TARNISH TEST

PHYSICAL/MECHANICAL PROPERTY TESTS

THERMAL PROPERTIES

PRACTICAL APPLICATION TESTS

QUALITY ANALYSIS TESTING