Amalgam part II

Question 1

What is an alloy?

Answer 1

Alloy: a metal made by combining two or more metallic elements, especially to give greater strength or resistance to corrosion

Question 2

Explain how the strength of dental amalgam is affected by different components of alloy

Answer 2

• Spherical alloys: require less mercury/ smaller surface area easier to wet
• Admixed alloys: require more mercury/ lathe-cut particles more difficult to wet

• Low copper alloys: has a gamma 2 reaction. This makes it weak and soft. It corrodes fast, and corrosion yields Hg which reacts with more gamma 2. Corrosion caused volume decrease
• High copper alloys: Reduces creep and prevents gamma-2 formation
High copper alloys have: increased strength, reduced tarnish/ corrosion, and reduce creep which reduces marginal deterioration

Question 3

What is trituration

Answer 3

It is the production of a homogeneous material by mixing component materials thoroughly

Question 4

Discuss the trituration process of dental amalgam

Answer 4

• The object of trituration is to provide proper amalgamation of the mercury and alloy.
• The alloy particles are coated with a film oxide that is difficult for the mercury to penetrate
• This film must be rubbed off so that a clean surface of alloy can come in contact with mercury
• The oxide layer is removed by abrasion during trituration (when it is shaken in the amalgamator)
• The duration and speed of trituration should be just enough to coat/wet all alloy particles with mercury, produce the amalgam matrix, and provide a plastic mix.
• The well mixed mass is homogenous, shiny in appearance, and can be managed easily during condensation. It is plastic enough to condense well.

Question 5

Explain the effects of over trituration

Answer 5

• Over-triturated amalgam is shiny, wet and soft. It is difficult to remove from the capsule
• This happens when it is mixed for too long
• Over-triturated amalgam is weak because of excess matrix production in the microstructure of the resulting set material - which is weaker than the original alloy particles. It has low resistance to condensation
• Amalgam sets prematurely which prevents adequate condensation and adaptation to the walls of the cavity and results in a weakened restoration

Question 6

Explain the effects of under trituration

Answer 6

• Under-trituration results in a crumbly, dry, dull mass that cannot be effectively condensed into the cavity
• The under-triturated amalgam is weak because inadequate matrix forms to hold the amalgam together
• There is not enough time for the mercury to coat all alloy particles and therefore is low in strength
• Amalgam remains soft for a longer time which has lower strength with excessive amounts of porosities, rougher surface and increased corrosion

Question 7

Demonstrate the condensation

Answer 7

• As a general rule - place amalgam within 3 minutes of beginning mix
• Compact and adapt amalgam to the walls, margins and line angles with minimum voids - this influences the strength of the restoration
• During condensation, Hg is brought to the surface
• To reduce Hg left in restoration, overfill the cavity by 1 mm (larger condenser on cavo-surface margin), the mercury-rich excess is carved off
• The lower the residual Hg, the greater the strength and longevity
• Choose appropriate size of amalgam plugger head to condense small increments with rapid movements both vertically, horizontally or laterally to promote a close adaption to all walls and floor of cavity

Question 8

Demonstrate the carving of dental amalgam

Answer 8

• Remove bulk excess with a large spoon excavator
• Shape the restoration by using a large burnisher for approximately 20 seconds, moving from the centre of the restoration outwards beyond the margins
• When consistency becomes stiffer, it is suitable for carving (half hollenback, flat plastic and excavators)
• Carve gently from the enamel towards the centre of the tooth
• Some of the blade edge of the instrument should rest on the tooth surface where possible
• Occlusal anatomy should be shallow
• Ensure there are no overhangs and a properly shaped contact area

Question 9

Demonstrate the finishing of dental amalgam

Answer 9

• Wiping the carved surface with a damp cotton pellet improves smoothness of the restoration
• The amalgam crystallization does not complete until 24 hours after insertion.
• DO NOT POLISH
• Patient should be advised not to eat on the side of the amalgam restoration for the next 24 hours
• Pumice or abrasive paste can be used on a bristle brush to smooth inclines of cusps, being careful not to affect the anatomy of the amalgam