Lecture 13, Dental Porcelain I (Script)

8/3/2019 Lecture 13, Dental Porcelain I (Script)

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Dental Porcelain (1(

Dental Material II Lecture # 13

Last lecture, we've talked about Metals. It has some relation

with Ceramic. To make crown, we use porcelain to cover metal

crown, right?

Today we talk about ceramic or Dental Porcelain. Ceramic is the

general term. So we will specifically talk about Dental Porcelain.

Dental Porcelain that we are going to talk about has many

advantages;

1. Very esthetic material. Available in many shades that similar to

dentin shade and ..

2. It is biocompatible which do not cause any irritation.

3. Porcelain is a hard material so it is very strong especially in

compressive strength but in the same time the tensile or shear is

weak especially in thin section.

For another example is amalgam or enamel. So in thin section they

are very weak.

4. It has high wear resistance.

5. It resistant toward stain.

And the problems are,

1. Since it has very high wear resistance and very high compressive

strength, it cause abrasion or wear of natural teeth. If we have

upper opposing crown and a natural tooth, it can cause some wear

to enamel. Because it is very hard.

2. Porcelain is brittle material. It has low tensile strength but high

compressive strength. Like enamel, like amalgam, Glass IonmerCement but GIC has moderate compressive strength not high.

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3. It is difficult to re-polish if we want to adjust it with bur because

sometime when we have place the crown or bridge and it has very

high force. You need to reduce it with the bur. It becomes a little bit

rough so you have to re-polish it because it is a hard material.

So these are the advantages and disadvantages of Porcelain

but still the advantages outnumber the disadvantages so it is a good

material to be used. Previously it used to be use acrylic. But in

comparison, Porcelain is a much better material.

So these are examples of bridge; a) Three-unit bridge with

the metal tooth here which are extracted – we call it Pontac. So

these 2 crown will fit on to both side of the extracted tooth.

For example Lateral Incisor has been extracted, Central and

Canine will be prepared, a part of tooth structure will be removed. A

crown will fit the Central and Canine, in the middle it will be the

Lateral Incisor replacing the extracted Lateral Incisor.

So we call the part of extracted tooth a Pontic and these two

crowns that fit on the prepared teeth are called a ----? They support

the Pontic, they'll support the structure that replace the extractedtooth.

This is three unit of bridges, can be four, five unit of bridges;

whatever and it can be a single crown or multiple single crown. It

doesn't matter.

So from the inside there is metal core to provide strength and

support and on top of it Porcelain will be layered to provide

appearance and strength. So we have strength from metal and wehave strength and aesthetic from Porcelain, right?

Sometime the whole bridges are made up of Porcelain but the

central part of Porcelain it should be very strong because it has no

metal support. This type of Ceramic or Porcelain is reinforced to

make it stronger, ok? But in Posterior teeth, the best choice is metal

and porcelain together.

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In anterior teeth, teeth are not subjected to high force like

posterior teeth, full porcelain crown can be made but this porcelain

should be reinforced Porcelain. A strong porcelain because there is

no metal supporting it. So there are two type of Porcelain bridges.

So, for aesthetic purpose, full porcelain crown can be made;

there is no metal. It has even better appearance and more natural

appearance but this will be reinforced Porcelain and we'll talk about

it in a few minutes.

The main composition for Dental Porcelain is:

a) Silica

b ) Feldspar which is a binder that bind all component together

c) Clay; either present in very small amount or not present at all

because it weaken the material.

So, we mainly will talk about Silica and Feldspar. Just now we talked

about what Feldspar mean.

In addition, there are pigment added which are different metal

oxides that give different shade and different colors. Either Iron,Copper, Titannium or Cobalt. So each material will give different

color and for each color they give a different shade; Grey, yellowish,

whiter shade etc.

When they manipulate the powder, they add Sugar or Starch

just to manipulate the powder so these components can be mixed

easily together with the material.

SO the basic components are Silica, Feldspar, Pigment for

shade and for easy manipulation starch or sugar added.

So when these components are placed together, they put them

in oven and under very high temperature to fuse them together.

Once they have fuse it together, they will put it in cold water;

very cold water. So, it will become solid like a block and then they

grind it to make very fine particles.

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SO we will get a porcelain powder, the powder is sold to the lab

and we get in form of powder in container; different shade. So when

it is sold as powder in different container, different shade, what does

technician do when he get your impression and pour it into a model?

He pour the powder and mix it with distilled water and start to

place it on your gypsum model to make the shape of the crown. SO

we will just melt the powder and place it layer by layer on top of the

metal crown or the model.

Component mixed together Put under high

temperature Cooled down Grind it Put into container

Sold into laboratory

Porcelain can be classified in many ways;

a) According to the temperature which the component was

fused.

Some type of porcelain need very high temperature to make

denture teeth. Other type of porcelain fuse at low temperature; they

call it Low-fusing temperature and this are the one that we use to

make crown and bridges.

i- High Fusing

ii- Low- fusing

b) According to the esthetic role;

Body porcelain give shade of enamel, some of them are

opaque, some of them are more translucent or more transparent togive shiny appearance; they call it Glaze Porcelain. SO this is

another way to classify porcelain.

i- Body Porcelain : Give dentin appearence; more

yellowish.There're some that give enamel look.

ii- Opaque : To shade color of metal so that the metal will not

be seen.

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iii- Glaze : Give shiny appearance on teeth surface just like our

normal teeth; always surrounded by saliva that gives shiny

appearance.

So when porcelain is added, it'll be added in layer:

Resemble dentin, and then followed by enamel layer so we can

get a natural appearance because natural tooth is formed by pulp

then layer of dentin then layer of enamel. So we get a natural look

of the restoration.

Some dental porcelain also called Stain porcelain so they can

be used to place a stain to make a tooth look more natural because

natural teeth are not perfectly clean and white. Usually natural toothwill have some stain especially in cervical area which are replicated

by certain type of porcelain to get natural appearance.

It is better to get natural appearance like whitish, grayish

teeth. To get more natural appearance, porcelain are available to

provide the stain.

Once the technician has mix the powder with water, they put a

layer of porcelain on top of the metal or a die; a replica of onetooth.It is a model of one tooth.

Usually you make an impression, then you send to the lab and

you get a replica of one tooth; a die. On top of that the technician

adds a layer of porcelain and makes it solidify. Then he will add

another layer. SO what does the technician do after adding the first

layer?

He put it into an oven.

1- Under vacuum: To minimize voids or pores; to make it

stronger.

After that, he should allow to cold slowly. Now, while it come

out from oven and cooling, it will shrink a little bit. That's why the

technician add a little bit more than necessary to compensate the

shrinkage as the material cools down.

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Now, once the layer solidify, he's going to add wax layer until it

reach the natural quality or size of the tooth. So layer by layer of

addition of porcelain.

So this is a comparison between 2 type of porcelain; one is notvacuum and another one is vacuum inside the oven.

Which one is without vacuum? The one on the left. It is obvious.

There are too many pores. So without vacuum, there'll be prominent

presence of pores. The presence of pores will weaken the porcelain

so it is more susceptible to vacuum.

Then, of course we add a layer dentin porcelain and put itinside the furnace and out again and then enamel and then out

again.

This process of glazing the porcelain is called Firing. They place

it inside the oven under high temperature, under vacuum and cool it

down and then another layer before firing. They are using high

temperature to make the material solid.

At the end, to give shiny smooth surface, they add a layer of

glazing porcelain. Glazing Porcelain will also close up any pores or

deformities on porcelain surface. They gave us a nice, even surface;

no irregularities, no imperfection, no voids and shiny. Just like

natural tooth surface.

So, basically these are the steps they made dental porcelain.

Question : What is the difference in composition of Glaze

Porcelain?

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Answer : It just the same unless it's pigment.

Question : How about the particle size?

Answer : Yes, it is. Look, it's gonna be different. The smaller the

particle size, the better the surface finishing.

Ok, let’s start to take about properties. We have talked a little

bit about properties.

1. It is a brittle material in thin section. So, that's why when we

make Porcelain fused with metal; a crown that made up by metal

inside and porcelain on top, the thickness of porcelain should be at

least 1.5 mm. Let say 1.425 mm. The cusp or tip of the cusp, porcelain thickness should be at

least 2.0 mm. Why? Because of the higher occlusal load. So, the

material need to be a little bit thicker. So the metal could be 0.5 mm

or 0.3 mm is acceptable but the porcelain should be at least 1.0 –

1.5 mm. While at the tip of the cusp, incisal edge and functioning

cusp, porcelain thickness should be at least 2.0 mm; where there's

occlusal load or occlusal contact between upper and lower teeth.

This will provide us with enough thickness of porcelain and

prevent fracture.

2. Porcelain has low thermal conductivity and good thermal

insulator.

3. Porcelain is hard material.

Harder than enamel so it could cause wear to opposing tooth.

4. Static fatigue

Now, with time; over the years, after continuous function

performance inside the oral cavity, some failure may occur due to

residual bond within the material itself; Between Silica and

Oxidase.

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So, with time fatigue may occur in porcelain. That's why in

some cases you will find tipping of porcelain. A piece of porcelain is

gone; it's fractured due to fatigue.

Fatigue : Failure of material due to continuous force applicationover a long period of time.

Mainly, fracture of ceramic occur through crack propagation.

Crack start in weak area and continuous until it reach the surface.

That's why a piece of porcelain pulled of the crown.

So this is a crack that propagate until it reach the surface from

the weak area. So any weak spot will be spot where crack occur.

Usually in Porcelain-fuse-to-Metal is made in these area which

porcelain bond to the metal.

Sometimes the bond is not very strong; under stress it will

Porcelain not be able to handle stress very well, it is not binding to

the metal well, so crack will occur until it reaching the surface. It will

propagate inside the material surface may break off.

That's why they try to reinforce the material to prevent crack or

to stop crack from propagating to the surface.

An example is they start to reinforce by using Alumina

(Aluminium; Al2O3). They place a part of Alumina and act as crack

stopper. They will stop the crack from propagate into the whole

thickness of porcelain.

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On the right, this is an example of porcelain which has crack at

one end. This is Alumina particle which able to stop the crack from

propagating to the surface. So this is an example of Reinforced

porcelain with Alumina particles.

What the Alumina particles do?

It prevent propagation of crack from reaching the surface.

Crack Stoppers.

So there're another method to make the material stronger and

prevent fracture or propagation of crack. Technician firing the

material. When the technician put it into oven, the temperature is

high. As it cools down, which layer will be smoother?

The outer layer. It will cool down slowly, at a latter stage it will

shrink a little bit. With shrink, it will compensate stress of the

material. It will become stronger resist fracture more.

Another method is chemically. They change the composition a

little bit; like we said before by adding Alumina, right?

Another method is alloy strengthening. They change somecomposition of the alloy. Porcelain is made up of sodium. One of

example is Pottasium.

So what do they do? They soak the porcelain into solution of

Pottasium. Pottasium and Sodium is + 1, right? But potassium is

larger. Then what happen? Pottasium will do inside the material and

replace Sodium.

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Since Pottasium is larger, it will put forces on the rest of

material thus form compression add higher strength.

Again, there are 2 ways to strengthen Porcelain;

a) Thermal strengthening

b) Ion strenghthening

PORCELAIN SHADE

As I said, Porcelain shade are available by incorporating

pigment or oxide.

These are shade that available in the market. They come in

different container and shade. Some are available with brushes to

apply and mix porcelain.It is mixed with distilled water to make a paste to be

incorporated or added to the metal core.

So these are 2 example of restoration;

B: Porcelain-fused-to-metal crown

A: All-ceramic crown

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From inside to outside. So it end with core porcelain that has

darker shade, followed by porcelain that resemble most superficial

dentin and then Porcelain that resemble to enamel in term of

translucency; it has natural shade of enamel.

Enamel is responsible for the shade of the tooth because

enamel will react with reflection of light. So different shade of

enamel are available. So when we have a metal core inside, an

opaque layer should be placed to cover the dark color of metal.

On top of it, dentin and enamel porcelain is added. So within

the crown, there's color of metal that needed to be covered; add

opaque porcelain. Here (A), opaque layer is not need to be added.

So in term of natural appearance, (A) looks more natural. No metal

underneath, no need to place opaque layer.

So which is stronger? Metal-reinforced porcelain is stronger.

That's why (B) is suitable for posterior while (A) is suitable for

anterior.

Now, there's new type of porcelain that they made all-porcelain

can be at posterior part of the mouth. One of them is called Zirconia.'suddenly a student interrupt with question which I couldn’t

hear'

Answer: Pontac can be made with metal core covered with

porcelain or completely porcelain. You can choose either one for

esthetic reason and cost factor because stronger porcelain is more

expensive because the manufacturing process is more expensive.

Again, way to strengthen porcelain is by adding Alumina. This

alumina can be in form of particle or they can added in form of sheet

of Alumina (but sheet must be used in the palatal surface). Why?

Because it is not esthetic. It is too white. This will add support and

strength.

So, they add particle of Alumina or sheet (make it stronger)

place between layer in palatal surface or labial surface or they

made a core of Alumina then they put Porcelain on top of it.

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What is core? It's like metal core, the same.On top of it they

will place layer of porcelain to resemble natural teeth. This will add

strength and prevent crack formation.

So Alumina is used as:

-Crack stopper

-in form of particle or sheet (unaesthetic)

- Alumina core

On top of it, they will place porcelain, just like a base as

supporting layer.

Now, there are examples of these reinforced ceramic.

One of them is In-Cerum. There are many of them; different

type of porcelain with different composition and they are all

reinforced. They become stronger to overcome the brittleness of

Porcelain of low fracture strength.

So, as I said they mix Alumina powder with water, they painted

to build this core , put in an oven and on top they start adding layer.Before they add layer of porcelain, they have to make sure the core

has even surface. So they add a layer of glass, they painted on top

of this core just to avoid any void. (similar technique with glaze)

Metal Core painted with Alumina Silica Oven (high

temperature) harden

Metal-core will be:

-no void

-Good, strong surface

On top, they add dentin porcelain and enamel porcelain.

Example of In-Cerum

a) Alumina In-Cerum

- 400 – 500 mPa flexural strength

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-contain Mg; slightly weaken material but better esthetic; less

opaque. (may be suitable in anterior part of the mouth)

b) Zirconia (the strongest In-Cerum)

- 800 mPa flexural strength; suitable for restoration in premolar

area.

- Full-porcelain crown; no metal needed.

# Different type of porcelain can be used according to it's

purposes.

-----------------------

Lecture ends here and Dr. Hanan discussed the exam's

questions.

Alhamdulillah, hope this will be helpful. Do refer the slides and

study well.

Written by : Nurul Kauthar Mohamad Khari

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Lecture 13, Dental Porcelain I (Script)