LESSON 2 - STRUCTURE AND PROPERTIES OF CAST DENTAL ALLOYS

Alloy

A crystalline solid with metallic properties composed of two or more chemical elements, where at least one is a metal and all are mutually soluble when molten

Alloy System

All possible alloyed combinations of two

or more elements (e.g. the binary gold-silver system includes all variations from 100% gold to 100% silver)

All possible composition combinations

Ternary Alloy

An alloy containing three elements

Quaternary Alloy

An alloy containing four elements

Metal

An element or alloy whose atoms readily lose electrons to form positively charged ions. Physically, metals are typically opaque, ductile, relatively malleable, lustrous, and good conductors of electricity and heat

Dental amalgams

which contain mercury (Hg), silver (Ag), tin (Sn) and copper (Cu)

High noble (HN) alloys

which contains at least 40 wt% gold (Au) and 60 wt% of noble metals Highest gold content

Noble (N) metal alloys

which are typically based on palladium (Pd) as the main noble metal with a total noble metal content of at least 25 weight percent. Noble metal alloys may also contain gold, silver, copper, gallium (Ga), indium (In), platinum (Pt), and tin (Sn).

Predominantly base (PB) metal alloys

which contain less than 25 wt% of noble metals, are most commonly composed of one of the following groups: nickel and chromium (Ni-Cr); cobalt and chromium (Co-Cr); iron, carbon, and chromium (Fe-C-Cr); commercially pure titanium (CP-Ti; and titanium-aluminum and vanadium (Ti-AI-V).

High Noble (HN)

Noble metals <25%, Gold no gold requirement

Noble Metal Alloys (Semi-precious)

Noble metals ≥25%, Gold no gold requirement

High Noble Metals (Precious)

Noble metals ≥60%, Gold ≥40%

Polymers

are formed through chemical reactions that convert large numbers of low-molecular-weight molecules (powder(

monomers

large, very high-molecular-weight long-chain macromolecules. (Liquid)

Resins

are compositions of either monomers or macromolecules blended with other components to provide a material with a useful set of properties.

Thermoplastic Polymers

undergo a reversible change when heated. they melt into a liquid that you can mold into a new shape. When they cool down, they harden again. If you don't like the shape, you can heat them up and melt them all over again.

Thermosetting Polymers

undergo an irreversible chemical change when heated or

cured. Once they are formed into a solid shape, they are locked in place forever. If you heat them up again, they won't melt—they will just burn or char.

Biocompatibility

ability of a biomaterial to perform its desired function with respect to a medical (or dental) therapy, without eliciting any undesirable local or systemic effects in the recipient or beneficiary of that therapy

(1) material properties,

(2) the design of the dental device, and

(3) the biocompatibility of component materials.

Three major factors are linked to the success of dental materials:

1. The chemical nature of its components

2. The physical nature of the components

3. The types and locations of patient tissues that will be

exposed to the device

4. The duration of the exposure

5. The surface characteristics of the material

6. The amount and nature of substances eluted from the

material

The biocompatibility of a material depends on: