Amalgam Flashcards
Define amalgam
Any alloy of mercury with another metal other metals
Defne dental amalgam
Essentially an alloy of silver =, mercury and tin with some other metals aded to modify the properties
State the chemical reaction that forms amalgam
Ag + Sn=> Ag3Sn
What shapes can the alloy powder particles be in?
Lathe cut
Spherical
What is amalgam made up f?
Amalgam powder (made up of silver , copper etc)
AND
liquid mercury
Let the 3 possible reagins the can occur when liquid mercury and amalgam powder are mixed together?
- 3Ag+Sn=>Ag3Sn
- 2Ag+3Hg=>Ag2Hg3
- Hg+7Sn=>Sn7Hg
State the gamma reaction that occurs when liquid mercury and amalgam powder are mixed together
3Ag + Sn => Ag3Sn
State the gamma 1 reaction that occurs when liquid mercury and amalgam powder are mixed together
2Ag + 3Hg => Ag2Hg3
State the gamma 2 reaction that occurs when liquid mercury and amalgam powder are mixed together
Hg + 7Sn => Sn7Hg
Which of the 3 reactions that occur in amalgam the most problematic?
The gamma 2 reaction :
Sn7Hg
What is the gamma 2 reaction responsible for?
- Corrosion
2, Creep - Decrease in strength
What do we ad to amalgam to reduce the gamma 2 phase?
Copper
State the gamma 2 reaction when copper I added
AgCu + Sn7Hg => Cu6Sn5 + Ag2Hg3
Name the 4main ingredients that makeup modern amalgam powder
- SIlver
2, Tin - Copper
- Zinc
State the percentage weight of silver in modern amalgam powder
65%
State the percentage weight of tin in modern amalgam powder
29%
State the percentage weight of copper in modern amalgam powder
6-13%
State the percentage weight of zinc in modern amalgam powder
2%
What is the IDEAL ratio of powder to liquid in amalgam
Ideally final amalgam restoration should contain less than 50% mercury
What is the problem with trying to mix powder with less than 50% mercury?
It is very difficult as the mixture is too dry
How do we overcome the problem of too dry amalgam mix?
By increasing the amount of mercury BUT then later removing in when we are packing
How do we remove the excess mercury the setting our amalgam filling?
During packing the excess mercury indrawn to the top and hen we scrape it away during carving
Describe spherical amalgam powder particles
They are softer and more flowable
Describe lathe cut amalgam powder particles
Less flowable
Good for building up late amounts missing tooth structure
Give some advantages of amalgam
- Has good compressive strength
- Good wear resistance
- Kind to opposing teeth
- Easy to use
- chemically set
- Cheap
- Radio-opaque so can be seen on radiographs
What are the disadvantages of amalgam
- It is non-adhesive
- It’s weak in thin sections
- It’s a thermal conductor
4 It’s Unaesthetic - Can become a plaque retentive factor
Give some properties of amalgam
- Non adhesive
- Weak in thin sections
- Thermal conduction / expansion
- Corrosive
- Unaesthetic
6 Reactions (lichenoid reactions)
When would we place an amalgam filling?
- Class I and class II caries
- Areas where heavy occlusal forces are encountered
- Where aesthetics are not important
- Building up broken teeth prior to crowning
What qualities must our cavity have before we place an amalgam filling
- Clean walls
- No unsupported enamel prisms
- Undercut
- Cavosurface angle greater than 90
- Amalgam-margin angle greater than 70
- Cavity must be greater than 2mm
What is an undercut ?
When the base of the cavity wider than the top
What is retention?
The prevention of the amalgam filling from being puled out vertically
What type of retention is displayed in amalgam?
Retention is macro molecular
When may an undercut not be sufficient ?
When a cusp of the tooth is completely missing
What do we NOT use anymore to keep amalgam in place if a cusp is missing?
Pins
Why do we no longer use coins when placing an amalgam restoration?
The pins can:
Go into the pulp
Weaken the tooth
What do we do instead of placing pins?
Create pits and grooves
Does phishing improve the life expectancy of amalgam restorations?
NO
What is the problem with polishing amalgam?
Amalgam takes 24 hrs to set so you can’t polish straight away
Also polishing generates heat which may irritate the pulp
Compare he median age of replacement of amalgam with composite
Amalgam = 15 yrs Composite = 8 yrs
Compare the average life span of amalgam and composite
Amalgam = 12 yrs Composite = 5 yrs
What is the main reason for failure for both amalgam and composite?
Secondary caries
Does amalgam or composite have a greater risk of developing secondary caries
Risk of secondary caries was 3.5 times greater in composite than amalgam
Does amalgam perform better in large or small restorations?
Large
How much of amalgam is made up of mercury|
Approx 50%
What state of mercury is toxic?
Mercury vapours is highly toxic
When are mercury vapours released in dentistry?
Mercury vapours are released from amalgam fillings during chewing and toothbrushing
What has amalgam been blamed for?
- Neurotoxicity
- Kidney disfunction
- Reduced immunocompetence
- Birth defects
- Effects on oral & intestinal bacteria
What has reared shown on the effect f amalgam on our health?
It has never been convincingly show that the negligible levels of mercury entering the body from amalgam fillings have any impact on general health
What is the main reason mercury is being phased out?
Due to its detrimental affect on the environment
What happens when mercury enters the environment?
It s converted by bacteria into Methy mercury in fresh and salt water
Why is methyl mercury dangerous?
It is highly poisonous
How do we dispose of amalgam in the clinical skills labs?
Put empty capsules and waste amalgam in the receptacles provided ◦ Clean the heads into the designated sink (This has a separator on it)
Report any spillages
