prosthodontics lab 4, baseplate

8/3/2019 Prosthodontics LAB 4, Baseplate

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In the edentulous there is no teeth so there is no reference to construct a

complete denture

If you bite , teeth contact will prevent you from biting more , the ideal occlusion is

when the upper mesio buccal cusp on the mesial fissure of the lower third molar

Teeth will maintain the anterioposterior + the lateral + the vertical relationship ,

and all of these relations are lost in the edentulous patient ..

the edentulous patient will have a compromised esthetics , a compromised

speech , and also the chewing ability is compromised ..

to get back all of these compromised things as it were we have to do what we call

rehabilitation

rehabilitation : to give the edentulous patient the ability to talk very well , to

chew very well with a good appearance , by fixing the the anterioposterior + the

lateral + the vertical relationship ..


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to do rehabilitation we need a device that allow us to increase or decrease the

vertical dimension easily , and to move the mandible anterioposteriorly and

laterally ..

this device we call it ( record block ) .. which is a block used to register the vertical

relation and the horizontal relation ..

the requirements of this record : easy to use , strong when its fabricated , allows

easy addition and removal , cheap material , give us an accurate registration ,

allows for easy marking on the articulator , allows for setting of the teeth ,and its

have to be rigid and dimensionally stable ..

record block = base plate + rim ..

the rim is usually wax rim , as it easy to adjustment and easy to remove ..

base plate :


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base plate could be made from different materials :

1 _ wax

the main disadvantage of wax base plate is : easily distorted ( not rigid ) ,

and not dimensionally stable . so we use a wire ( 1 mm in diameter ) to

make the wax stronger

2 _ acrylic ( light cure , self cure , heat cure )

Self cure has different names : auto cure , cold cure and auto ploymirizing ..

Light cure and self cure are easy to use , cheap , rigid , but it easy to shrink

and it is brittle when its thin ..

Self cure give nicer base plate than light cure , but light cure is easier to

use than the self

Self cure is toxic

Heat cure used also for final denture

Self cure : powder and monomer , we mix it with a glass cup not rubber

because it will be hard to remove ..


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The polymer is : polymethyl methacrylate

The monomer is : methyl methacrylate

The stages for acrylic setting ( self cure ) :

1. Separate powder and liquid ( monomer )

2. Sandy stage after mixing

3. Fibrous or string stage

4. Doughy stage ( we make the base plate on this stage )

5. Rubbery stage ( the setting start here and heat will be released as it an

exothermic reaction )

6. Hard or set stage


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3 _ shallac

Shallac is a thermoplastic material , its brittle

( its used but not common ) ..

4_ metal

We use metal especially with patients who have allergy from acrylic,

The most used material are light and self cure ( light cure more than the self )


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Differences between base plate and special tray :

Base palte is constructed on the master cast , while special trayconstructed on primary cast

Base plate reaches the sulcus to the land area ( the functional depth and

width of the sulcus ) , while the special tray is 2 mm shorter than the

sulcus

no handles and no finger rest with the base plate

no spacer no stopper with the base plate

base plate will be converted to the final dentureso its better to be as

thin as possible ( 1mm ) - without compromising the strength of the

material -, while its not a big deal if the special tray was thick a little bit

as we will use it just to take an impression

thicker special tray is better than the thinner one ( but not bulky ) ..

thinner base plate is better than the thicker ( but not flexible ) as

we dont want the final denture to be thick ..

we need to make lines or grooves ( roughening ) on the base plate , as it

will be attached with the wax rim


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mistakes the students usually do:

first , its more important to be accurate with the base plate than with the special

tray , as it will be converted to the final tray ..

bad adaptation , and the result is shrinkage ( space between the base

plate and the cast

use nails to do the adaptation ( this will make a mark , and will cut the

acrylic ) so always use your soft tissue part of the finger or rubber of apensile

we need a good adaptation to reach the functional depth and the

width of the sulcus

the acrylic is short , or it doesnt reach the land area , so we will have a bad

record ( it must reach the land area not to be movable )


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Notes

in the upper we reach to the vibrating line , in the lower we reach 2 to 3

thirds of the retromolar area

we need a tongue space for the lower

the special tray or the base plate that fit a cast , doesnt fit another cast

usually patients have under cuts especially in the upper labially , so we have

to block these under cuts with a wax , then we construct the base blate (

the same thing with the special tray ) ..

even if the under cuts filled with wax , it will appear in the final

denture .. we just do this to be able to remove the base plate

easily without damaging the cast

if its hard to remove the base plate ( especially after the shrinkage ) you can use

Vaseline or cold mould seal or suckingin water for 5 minutes , to avoid

damaging of the cast ..


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cold mould seal consist of sodium alginate ,its a separating solution but

its thin so it will not separate between the base plate and the soft tissue ,

and whet its dry it easy to be removed , we will us it in the final acrylic

processing ..

the deepest point of sulcus is the functional deep ,that we want to reach

with the base plate

sucking in water may cause hydroscopic expansion for non setting gypsum

while after setting, expansion occurs just after keeping the product for a

long period of time ..

gypsum has 2 types of strength : wet strength and dry strength ,

dry is about 3 times more than the wet , but they have the same

dimension as the molecules are already set .

unset acliric can attach to set acliric ..

done by amr sadi

prosthodontics lab 4, baseplate

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