Lecture 2, Dental Amalgam II (Script)

8/4/2019 Lecture 2, Dental Amalgam II (Script)

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Dental Material II

Lecture # 2 Amalgam (part 2)

The doctor started this lecture by skipping the slides of the last one and she made a

general review about what have been discussed.

So, last Wednesday we started talking about amalgam which is coming in starting

material, so we talked about some advantages and disadvantages of amalgam, whyitis used commonly, we said it is mainly used for class I and class II procedure

restoration, we went through (composition, classification according to the particles

shape, the setting reaction and different types of phases or compounds that are

form after the alloy react with mercury ,we talked which is stronger than the other,

which is more susceptible to corrosion and then started talking about certain

properties specific for amalgam ).

When we talked about properties like strength, toxicity and compatibility these are

general , but there are certain properties that specific for amalgam. Tarnish for

example, creep and corrosion, each one is caused by certain factors and need the

certain outcomes in the filling. then we talked about other physical properties like

expansion and contraction, and we said that; what we want is very small amount of

either bit expansion or bit contraction, otherwise if there is excessive contraction

there will be Micro leakage, and if there is excessive expansion then extra pressure

on tooth structure occurand may cause fracture especially in large fillings. So thetooth surface is destructed and then no structure remaining. That is why the

manufactories add certain material in certain percentages to minimize this effect.

Slide21 ..2


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We will continue the physical properties which is the strength, its general property

but regarding amalgam it has high compressive strength and its tensile (shear)

strength is much lower, so its a brittle material (like enamel for example) it has

high compressive strength but tensile is weak. That is why its a proper to used

in posterior area in the mouth because the load there is higher than in anterior area

which the force reaches up to 500N. If you remember from summer semester we

said that the posterior teeth toleratea higher load compared to anterior teeth. Soamalgam is good in these areas because it can handle the stress very well!!!

Thats why even it is not esthetic like composite or white fillings it is moreappropriate uses especially if we have a large class I cavity for example or largecavity that involve in mesial or distal surfaces of the tooth. We can place compositeor white fillings but they are weaker, they will not last for as many years as amalgam.

Composite or white fillings could be used posteriorly but patient need tochange it frequently, whereas Amalgam could last for many years.

Now high copper amalgam:the amalgam that is used today is high copper content , so when the copper is highit will capture the Tin(sn) & prevent its reaction with mercury SO it prevents gamma 2phase formation. so amalgam will be less susceptible to corrosion with a betteramalgam filling it will not broken easily inside the oral cavity. It is easily effected byacids or bases or whatever inside the oral cavity or what we eat and drink. So highcopper amalgam is better compare to low copper amalgam and develop

strength quicker.

So high copper amalgam resist tarnish better, resist corrosion better, and thestrength develops much better than low copper amalgam. So in general theseamalgam have better properties (the one which has high percentage of copper).

Amalgam is strong filling, but it has to be certain or minimal thickness of (1.5-2mm) amalgam to be strong, otherwise if it is placed in thin section it will be weak.For the people who have lab yesterday we talked about class I cavity, we said the

minimum depth or the depth must be at least 1.5mm. if the thickness of amalgam(1.5 - 2mm) it is OK !! BUT (if your cavity is only 1mm depth and therefore amalgam1mm thick, the amalgam fracture easily) it is weak in thin section!

So its strong material as long as it has minimal thickness (1.5-2mm).

Slide22 ..3


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This cavity was built (shown in the slide), part of this cavity was too shallow thatswhy some people were telling you go deeper go deeper your cavity is too shallow (inthe lab)! Because you go less than 1.5mm, so if we do too shallow cavity for apatient later on when the patient start using the amalgam filling when he start eatingfor sometimes, it will break off because it was too weak.

So this part of filling brake off because it is too thin (its less than 1.5mm) after its

fracture there will be space all around the filling which may cause Micro leakage orrecurrent carries.

So amalgam is not strong in thin section, at least it should be 1.5mm thick it can be2 or 3 depends on your case inside the tooth.

You drill the cavity you excavate the caries you keep following caries until you

excavate the caries you adjust the shape of your cavity like (floor, smooth, line

angels undercut , mechanical retention) then you replace your amalgam.

Now if there are thin walls all around amalgam,( enamel, is weak in thin section)thats why when you drill cavities it has underlined enamel or enamel that wasweaken by caries, it should be removed because even if you place amalgamunderneath it will break because it has similar properties (similar as amalgam).

When you learn to do class II cavity (occlusion, mesial and distal surfaces),sometimes all the dentine under enamel has caries so it doesnt acceptable to putamalgam under enamel, because it will break.

Enamel is a strong material, but it needs to supported by dentine for it to handle thestress inside the oral cavity even if you place amalgam underneath the enamel willnot be the same as when dentine support the enamel, enamel will be too weak andbreak off ,which will cause fracture of amalgam , micro leakage and caries.

Slide23 ..

Most of amalgam available now in clinics is high copper amalgam, spherical oradmixed so admixed mean (spherical and irregular particles together). Now

spherical amalgam has higher surface area less mercury to be mixed with it(that reduce the risk of mercury) which is good.In the other hand the admixed need more mercury to wet the powder, because theyhave a low surface compared to spherical amalgam .

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You as clinician you dont increase or decrease mercury, this is already make thecapsule by manufacture. The ratio between alloy and the mercury is already placedin the capsule.

Spherical strength is little bit higher compared to admix amalgam, so it has higherstrength after one hours and 24 hours when condense it will be softer. And usually itshrinks a little bit more compared to admixed amalgam. And it is softer when

condense that means it does not require high force when you condense it insidethe oral cavity compare to admixed amalgam or lathe cut amalgam.

Slide24 ..

These are available or how amalgam is supplied by different companies .

Slide25 ..This is just a table in your text book , so it is just a comparison between the two type(spherical and admixed) both are called high-copper amalgam .So spherical amalgam has higher strength after 1 hour or 24 hours thats why sometypes of amalgam you can actually start making polishing and finishing before 24hours, because it is strong enough and they will not be broken! But ideally we shouldwait 24 hours to set then we start doing polishing & finishing .

So you noticed that dimensional changes after 24 hours strength is similar and creep

is less. but generally speaking spherical amalgam is stronger.

Slide26 ..

So this is capsule or representation of the capsule, which contain the mercury But if

you dont handle the capsule properly you expose yourself to mercury, if for example

you start opening the capsule OR if it is not placed correctly inside the machine that

shake the amalgam capsule, the capsule can be opened and may you be in the risk

to expose to mercury.

In general ,liquid here is exposed to mercury, the capsule has two end ;one has

powder (alloy or metal) the other contains the mercury (liquid) and between them

there is membrane. Once the capsule start shaking in the amalgamator or the

machine this membrane will break off and mercury will be mixed with the powder.

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some types of capsule you have to activate which means these will be button at one

end then press it to break the membrane and then place it in the machine .

All of this are available in the instructions on the box containing the capsule. So

either immediately in the amalgamator or sometimes you need to activate it first

(press the capsule to break the membrane or the barrier between the mercury and

powder) and then place it in the amalgamator .

Regardless ,,, the powder in one end, liquid (mercury) in the other end and then

placed in the amalgamator. Now the amount or size of the filling depends on the

amount of mercury and powder placed on the capsule, one capsule can contain

what we called a single mix or double or more depending on the size of your cavity.

If you have small cavity u can use the capsule with single mix, so these are enough

for one small cavity. If your cavity is large we use a large amount of amalgam.

Slide27 ..

So this is the amalgamator you going to see it in the lab, it has an arms with two

ends, capsule is placed between them and then the machine start to shake .

Now there's a recommended time for mixing, just like your impression material, the

mixing by the amalgamator is specific, there is a digital screen on the amalgamator

that you can use it to set the time (10 15 9 second) depending on the

manufacturer instruction, however sometimes we over mix it or under mix it this isn't

good.

Because if you over mix it or mix it for longer than the recommended time the

amalgam will start to set quickly, so you are accelerating the setting time and you

will not have enough time to fill your cavity with amalgam because it will start to set

very soon and you will not have enough time to carve it properly so working time will

be less and it will contract more increase in setting contraction.

Now if it's mixed less than the recommended time the mixture will be dry (There

wasn't enough time to mix the mercury with the powder to wet the powder with the

mercury) giving crumbly, graining mix. For example if the manufacture time is 12sec

and I mixed it for 7 sec the mercury will not wet the powder and mixture will remain

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dry) So over mixing or under mixing is not good and again I can't really use this as

filling material because it doesnt set properly.

You need to know that the amalgam is placed gradually in the cavity layer by

layer, so you don't take the mixed amalgam and place it as one mold in your cavity,

it's placed in layers and condensed in layers.

So if your working time is very short you won't have enough time to fill up the cavity

because amalgam start to set, and we don't want the amalgam to become hard while

we are still carving or still filling the cavity, we need it to be little bit soft so you can

control it better (shape it) the way we want it it's easier to adapt it to the wall of the

cavity and can fill any space that may exist and easier to carve to restore the

morphology.

Slide 28 ..

Placement and condensation :

In general, there is an amalgam carrier or amalgam gun, you will see it in the lab, we

use it to place layers of amalgam and condense them layer by layer vertical and

lateral condensation to fill any space that might be present.

The cavity should be over filled so that when we carve it, and the excess mercury is

removed we make sure there's no spaces (micro leakage) left without being filledwith amalgam.

Q: In case of amalgam shortage do we add more amalgam or we do have to remove

it and do it all over again?

Answer: if you didn't over fill you cavity or over filled and carved a little bit more than

you should. You have two choices depending on the state of the amalgam, if it's

still soft you can add more, however if it started to set you can't add any more

because amalgam doesn't stick to each otherunlike glass ionomer cement for

example which stick to each other.

So a cavity with glass ionomer cement we can add more ever after setting but in

case of amalgam we can't. Generally when you reach the point of carving and then

you found out that part of it was deficient the amalgam had started to set already so

you have to do it again.

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Slide 29 ..

Burnishing and carving :

In the lab we were introduced to instrument including a burnisher which has ball,

round end which is usually used before we start carving to remove excess fromupper surface of amalgam filling and use it to burnish or make the surface shiny and

smooth after the amalgam started to set, usually finishing and polishing is done after

24 hour.

Note if the book mentioned details of how to do burnishing and carving you are not

required to memorize them.

We need to know that :

# Amalgam need to be placed in thick section not less than 1.5 mm.

# Usually placed in layers and condensed vertically and laterally to adapt amalgam

at the cavity wall.

#Over fill the cavity so that no deficient areas are created.

#Polishing and finishing after 24 hours.

Slide 30 ..

Polishingis a very good step to do due to :

1/ minimize tarnish.

2/ increase smoothness.

3/ decrease plaque retention.

4/ decrease corrosion.

5/ more comfortable to the patient.

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Amalgam is retained mechanically(you have to shape the cavity in a certain way so

that the amalgam will stay and not fall off).

Not chemically like glass ionomer cement (the shape of the cavity doesnt matter it

will stick to enamel and dentine by chemical reaction). However in some cases like

white filling or composite we need to do a certain surface treatment of enamel and

dentine to make it rough and then attach composite, this is type of mechanicalretention called micromechanical.

Now just a comparison between low copper amalgam and high copper amalgam

which generally has better properties, they are stronger because they have less

gamma 2 phases and they are less susceptible to corrosion so they corrode slowly

and because they shrink just a little bit compared to low copper amalgam, they can

be associate with sensitivity due to minimal spaces but its negligible.

Now lowcopper amalgam expanda little bit, but high copper amalgam contracta

little bit ,again you only want very low contraction or expansion up to 1 to 4 % .

Slide 32 ..:

Some people tried to use the idea of chemical retention to bound amalgam and

minimize the space between amalgam and cavity wall so they used in what we call

(Bonding agent) which are used with white filling or composite. I don't want you to

memorize because nobody use it this just for knowledge when using composite orwhite filling we need to use something to bond it to enamel and dentine for that we

use a bonding agent which is a resin material like liquid, in this case they tried to

apply this liquid on the surface of the enamel and dentine and they conjugate it with

amalgam and allow it to set.

In some experiments they said that this will minimize the space that might be

created, for example due to amalgam shrinkage and if we have less space we have

less chance of(micro leakage, recent caries and sensitivity) , so bonding agent

means a liquid which used between amalgam and enamel and dentine. Anothermethod is by using white filling between amalgam and cavity walls, but it's not used

nowadays because it's not effective.

Slide 33 ..

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Now mercury safety is very important to know about it especially later on when you

start using it in the lab or when you open your private clinic you need to protect

yourself from mercury.

You need to consider: 1)Patient. 2)Operator/yourself. 3)Environment.

That's why in case of excess amalgam we can't just throw it away, there are certain

ways or methods to store excess amalgam.

1/ In clinics we need to have a jar that contains water and when there excess

amalgam after filling the tooth you need to throw it in this jar. Because this water will

absorb any mercury vapor so it will eliminate the danger of mercury .

2/ Good ventilation is required in the clinic so that the vapor won't accumulate.

3/ the instrument in case of sterilizing them either by placing them in an oven orautoclave the reminder amalgam on instrument needs to be cleaned, because if

there is amalgam on the instrument and put it in the oven the heat will cause

mercury vapor which is dangerous because you will smell it.

4/ carpet in the clinic need to be avoided because it's easy for the amalgam particle

to be captured by the carpet and they difficult to clean compared to regular floor "free

carpet ", and theres a table in your book for these safety methods.

There are many ways you can be exposed to mercury one of them is skin contact

(avoided by wearing gloves, masks, glasses ), also vapor inhalation or ingestion, for

example removing an old filling if we are not using strong suction these small

amount of amalgam can be swallowed by the patient. So we can use Rubber dam

isolation used when we want to remove an old filling or replacing your filling, rubber

dam which is a sheet of rubber that is placed around the tooth so it will isolate it from

the rest of the oral cavity

Of course we reduce exposure to mercury vapor by using amalgam capsule and

amalgamator should have a certain chamber so when it mixes or accidently open the

chamber will be isolated in that closed chamber.

Some types of condenser are placed on a hand piece we call them ultra sonic

condenserso they are not manual, they vibrate that will lead to some heat10


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production, this heat will lead to mercury vapor production thats why we dont use

them .

Slide 38 ..

They tried to produce amalgam that doesn't contain mercury so they replaced themercury with "Gallium" however gallium didn't have good properties such as those

found in mercury so it's not as strong and more susceptible to corrosion, so we don't

use it.

Good luck dentists Done by :

Sana'a Qasem

Ruba Ghanim

Noor Bdeir

Ala'a khalaf

Hard work makes u stronger , mistake makes u smarter ,

success keeps u in shape BUT

only GOD give u the power to go on ..

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Lecture 2, Dental Amalgam II (Script)