Amalgam and gamma reactions Flashcards
What are the 3 phases of gamma reactions?
Gamma phase: silver- tin
Gamma phase I: silver- mercury
Gamma phase II: tin - mercury
Explain the normal reaction that occurs in low - copper amalgams.
During trituration, mercury ‘wets’ the alloy silver- tin (gamma phase) to from:
Gamma phase I: Silver- mercury
Gamma phase II: Tin- mercury
The tin- mercury creates voids in the silver- mercury matrix causing issues such as creep.
Explain the reaction that occurs in admixed high - copper amalgams.
The composition of the alloys in admixed high- copper alloys are different to the compositions in low- copper alloys.
Firstly, the term admixed refers to the fact that there are combinations of lathe-cut and spherical alloys in the composition.
The lathe-cut alloy consists of silver- tin (gamma phase) and the spherical alloys consists of silver- copper.
The gamma phase and silver- copper react with mercury to form gamma phase 1 (silver- mercury). However, instead of going on to form gamma phase II (tin- mercury), the tin reacts with the high copper content in the spherical silver- copper alloy to form new copper- tin (ETA phase).
Explain how the reaction that occurs in admixed high - copper amalgams reduces creep
The new copper-tin particles bind silver- copper and gamma phase I (silver- mercury) together.
Thus, this prevents the formation of gamma II (tin- mercury) as it hinders the gamma I (silver- mercury) from slipping under tensile loads.
Explain the reaction that occurs in spherical alloys high - copper alloys.
Spherical alloys are different in that they are made of silver- tin — copper- tin, (gamma phase and epsilon phase) which reacts with mercury.
This causes the formation of gamma phase I (silver- mercury), and the tin reacts with copper to form new copper-tin (ETA phase)
