prostho 3rd lab script,border molding

8/3/2019 Prostho 3rd Lab Script,Border Molding

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Prosthodontics LAB 3 -Part1

*Border Molding*

The Dr started the lab by reviewing the steps of fabricating a complete denture

that we took in the previous two labs.

Clinic ; The Primary impression is made by using stock trays with differentimpression materials

1- Impression Compound (brown in color).

2-Alginate (Irreversible hydrocolloid).

***The Stock trays may be metal or plastic

Perforated For Alginate

Non-perforated For Impression compound

LAB: Then we made the Initial/diagnostic/primary/study cast as a preparationfor the second clinic.

Clinic: We make the secondary /final impression by using Custom Trays.

Customs Trays could be made by:

1- Light cured Acrylic.

2- Cold/self cured Acrylic.3-Heat cured Acrylic.

4-Shellac.


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Light Cured Acrylic Cold Cured Acrylic(Powder+liquid)

Long Working time

Easy to manipulate

Stable after cured

Brittle (not flexible)

Difficult to repair.

Slightly more expensive

High surface tension

(impression compound doesnt

stick well )

**if the surface (thin layer) is

exposed to air it will remain sticky,

oxygen inhibitors can prevent its

formation.

Limited working time

Not that much easy to

manipulate.

More flexible (if it breaks you

can take a little bit from the

same material and stick it

together)

We use Porcelain glade bowl

for mixing.

Low surface tension (easy to

stick green stick impression

compound on its surface )

** The stages :1. Wet sandy stage

2. Strengystage

3. Doughy stage Operative stage

4. Rubber stage.

Shellac:

Thermoplastic sheet (we expose it to heat then adapt it on the cast )

It distorteseasily (if you leave it on the bench or expose it to heat in border

molding)

Brittle

Cheap

Not effective as light cured Acrylic.

Which Material is more accurate?

The light cured acrylic is more stable and doesnt make

significance changes in shape after it's cured (the reaction will

stop).

Cold/Self cured acrylic changes its shape as the chemical reaction

continues after the fabrication.


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The materials which are used to make trays are used to make baseplate

of the record block, too.

BORDER MOLDING (FOR LIMITING STRUCTURES ):

**It is made using Green Stick impression compound( Tracing Compound).

- Impression compound + Green stick impression compound are chemically

similar, but with different composition ratio.

- Green stick will soften at lower temperature.

We have to cover as much as possible from the denture baring area and extend

as much as possible within the area of functioning muscles and soft palate and

must ends at the post dam area (in front of the vibrating line ).

How to Border Mold?After making a custom tray I put it in the patient mouth then I start adding green

stick impression compound ,section by section.

Why I dont take the 2nd

impression directly with wash material?

1-You need enough time to move all the moving muscles individually within 2-3

minutes (sometimes it's difficult in one go), and you can go back and see if the

denture is retentive ,but this is hard to do with wash materials.

2- If you make a mistake you can correct it ,not like the washing materials

3-Give me the chance to make sure that I did a full seal.

Border Molding differs in the post dam area and the buccal-labial sulcus in

the place where we put the green stick material.

Impression compound 55-56 C Soften by hot water

Green Stick51-52 C Soften by Flame


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Buccal-labial vestibule No green stick inside (we can add it

outside to increase the width)

Post dam area Inside the tray.

The tray should be shorter than the sulcus by 2 mm ,and behind the vibrating

line by 1mm.

In the buccal sulcus I have a space to put the green stick in, but in the back I

dont have a space, so I put the green stickinside the tray in order to fix my

denture.

In the Lower trays :

-There is No post dam area so all the green stick will be on the borders

which will increase the extension according to the movement of

muscles.

-Some text books recommend adding green stick inside the retromolar

pad area because it is a compression area.

The thickness of the border will vary according to the muscles movement.

The stages for border molding:1- Take the tray check it in the patient mouth and see if it's stable and fixed.

* If it fits in the cast that doesnt mean it should fit in the mouth of the

patient.

2- Check if the depth of the sulcus = 2 mm in the patient mouth by moving themuscles ,because in primary impression it is not necessarily that the muscles

movement was accurate .

If the space is small I have to shorten it by trimming while the

patient is present.

If the space is big I use border molding OR re-make the tray again !


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FOR GREENSTICK:1- Soften it slowly by flame; pass it several times not for a long period of

time.

*if I leave it in the flame it burns and bubbles.

*I have to do it gradually (I heat only about 1-2 cm)

2- Then I temperate it with warm water, because if I put it directly in the

patient mouth it will burn him/her.

3- I wet my fingers also, so I can mold it and form a conical head and add it

to the rim of the tray.

4- Shape it with my wet fingers.

How can I know if the tray reaches the soft tissues or

not??

The surface of mucosa is slightly rough.

So if the surface of the tray is shiny then it does NOT reach the rough

surface of the mucosa.But if the surface is Matt then it reaches it.

NOTE :You should heat the old part of the green stick in order to stick the

new material easily.

**To mold the posterior part we ask the patient to swallow.

Buccal-Labial-Buccal- Posterior

OR

Buccal-Buccal-Labial-Posterior The posterior part is always at the end

OR

Labial-Buccal-Buccal-Posterior


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Bring the cheek upward, outward,downward.

Bucco-frenum area backward, forward

Labio-frenum down, right and left

Backward I push it a little pit and ask the patient to swallow (if he can)

When the patient opens and closes his mouth and moves it right and left

the coronid process will make the buccal vestibule in the upper posterior

part narrower ,so if we dont do this movement during taking the

impression this area in the denture will be thick. In the result the denture

will fall from its space or it will hurt the patient.

In the Lower : the sequence always is Buccal before lingual.

- We need the tongue to move forward, right, and left and toward the roof

of the month.

Once the border molding is finished we have to check if it's correct.

In the upper we have to activate the muscles to determine:

1- It is not over extended.

2-Not short (under extended )

I check retention, I put the denture in the patient mouth then I press a little

pit of air outside, and if I have peripheral seal all the way round then I try

to remove the tray but the negative atmospheric inside will prevent

moving the tray.

Remove the wax spacer after border molding then I put my wash

material.

The thickness of the spacer = Thickness of impression material

1- ZOE: base: zinc oxide

Catalyst: eugenol (red)

2-Polyether

3-Addition silicon

4-Condensation silicon.


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ZOEDoesnt require adhesive

Addition silicon require adhesive

Condensation silicon require adhesive

Polyether require adhesive

When I put the wash material I have to repeat all the movement I did

before for the cheek, lip and the soft palate.

Silicon is good for bony undercuts.ZOE when it sets it is rigid when there is no under cuts.

For ZOE: Maxilla: 8 cmbase

8 cmcatalyst

Mandible: 6 cm catalyst

6 cm base

Polyether ( more hydrophilic than other silicon materials)

**ZOE is chemically set so it's affected by temperature, if the weather is hot we

put the base and the catalyst in the refrigerator, to prolong the working time ,and

humidity will work as an accelerator.

We use orange oil to clean ZOE.

The dimensional stability is better in addition silicon and polyether.


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Prosthodontics LAB 3 Part 2

Green Stick ImpressionCompound (tracing compound) :

is made from: wax +resin+filler+a color

*So it is not just made by wax

It is used for border molding of custom trays to make final

impressions.

It might be sticky but it is called a green stick impression compound.

Sticky wax :

Yellow in color.

Made of wax + resin.

It is used for sticking purposes.

At room temperature it is hard, when we heat it,it becomes sticky

like honey because it is mainly used from bees' wax

Utility wax:

Soft at room temperature.

Have many uses so that it's called utility.

Red or transparence

It is used in the clinic to fix an impression tray or in orthodontics

treatment, etc.

Gypsum type 2 (Plaster) is used for pouring the primary cast.

Gypsum type 3 (dental stone ) is used for pouring the secondary cast.

**it has less water so it's stronger.


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- In the final impression we need every single detail inside the mouth and the

cast shouldnt contain bubbles so to avoid that I do more vibration than the

primary impression .

- I need a container around the impression to prevent the gypsum it from

going to the edges when I pour it up. In a process that is called beading and

boxing.

- We use boxing wax that we put it around the impression

- The wax that we use to separate the wax from the impression is called

beading wax.

- When we pour silicon we have to make good vibration, and we spray it with

a chemical that decreases the surface tension.

The End

Done By: Enas Salameh

prostho 3rd lab script,border molding

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