Prostho Lab 6
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Transcript of Prostho Lab 6
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7/30/2019 Prostho Lab 6
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7/30/2019 Prostho Lab 6
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Prosthodontics lab 6
Steps of cobalt chromium metal frame work fabrication
There is a difference between a cobalt chromium frame work and all acrylic partial dentures
because there are two steps in the cobalt compared to only one step of the acrylic partialdenture
In the acrylic partial denture we have only one lost wax technique we have only flasking and
packing, in the metal frame work partial denture we have to make the metal frame work
first and then we have to process the acrylic to the metal
Because metal is not like acrylic and because it requires higher temperatures when we reach
the master cast stage we cannot fabricate the final prosthesis from the master cast
Stone can take the temperature of boiling water but it cannot take the temperature of
molten metal so we have to duplicate the master cast to form a refractory cast which is
made out of investment "phosphate bonded investment"
This duplication method gives us two advantages:
1. We reproduce the master cast accurately in a heat resistant material "refractory
material"
2. And we are able to duplicate Block out and Relief
>> so anything that we don't want metal to get into its place we do block out and relief on
the master cast and when it is duplicated it will become part of the investment
Last week you had a master cast and you did: parallel block out "the guide planes", shaped
block out, for the claps we made a step, on the lingual at the survey
line we have a step for the reciprocating arm, for the I bars we have
parallel block out and relief below it, and then we have an extension
with a window and a roof where the tip of the I bar clasp will sit
And the parallel can also be on the lingual surface of the canines and
premolars!
And then you did arbitrary relief; which only helps us in theduplication and has nothing to do with the prosthesis itself
And finally you placed the relief; we said the job of the relief material is to create room
underneath the metal frame work for the acrylic; we need a space beneath the metal in the
final prosthesis so that the acrylic can go there!
And this relief will create an internal finish line, the 90 angled border between the relief
and the cast will create the internal finish line!
The green wax later on will become a space, and then filled with acrylic
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So where the acrylic meets the metal on the palate I will have
an internal finish line because it is underneath the denture
Also on the top between the major connector and the acrylic I
am going to have an external finish line
Do you remember the sandwich analogy?
-the major connector when we come near the ridge it will
flare out
-green wax will turn into acrylic
-the junction between the wax and the metal will be the internal finish line
-on the master cast we can't fabricate the external finish line yet because we haven't done
the pattern wax
So the external finish line we are going to shape it in the wax pattern
>>Internal finish line formed by the relief on the master cast
>>External finish line formed by the pattern wax on the refractory cast
And the acrylic will go into the minor connector the mesh work to give mechanical retention
Major connector
Acrylic
Minor connector
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The internal finish line shouldn't touch the tooth
there is always metal between the tooth and the
acrylic
That is why if you remember we left some space
between the green wax and the tooth! About
1mm
This is a tissue stop just like a tag it is a protection
of the acrylic when we do packing so that the metal
doesn't go down during packing
Finish line means a junction between two different
materials in our case it is between acrylic and metal
So after we did wax up and block out and relief whatwe did?
Duplication with agar agar or silicon
And then we pour it with a refractory material in our case phosphate bonded investment
When we look at the refractory cast what do we see?
Where the wax was we are going to see a positive edge
So there is a ledge which is my internal finish line
And between the tooth and the acrylic there is a space and
an internal finish line
On the other side "bounded saddle" we have palatal,
anterior and posterior finish lines
If you look closely we are going to have a ledge where the
clasps are going to be
On the canine we made a window
And the arbitrary wax will look like just an irregular area filling down the sulcus
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If you take a look at the lower cast the finish line is
at a different place than the maxilla
On the right side of the pic >>
Will the junction between the metal and the acrylicbe at the tongue or the anterior part?
Actually the only internal finish line that I have here is
in the front and over the crest of the ridge
So the area beside the tongue is not an internal finish line
Why is that? Because when we fabricate the pattern wax we will place the lingual bar which
only has a junction in the front
We have no junction between the area on the lingual and the tongue area except in thefront
But on the bounded saddle area all of it is an internal finish line
So here in the pic above the major connector will reach the molar in the back
On the right side there is no teeth posterior for the metal to reach and all of it is going to beacrylic so no internal finish line
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The major difference between the upper and the lower casts is the shape of the major
connector "in our case in the maxilla a plate in the mandible a bar"
We used for the minor connector in our lab for the mandible a lattice for the maxilla a mesh
work!
You have to add the pattern wax to the refractory cast with a specific sequence so you end
up with the right edges and the right margins
We are going to use the prefabricated pattern wax
Some things you have to fabricate it in your hands and other things are ready to be used
The things that come ready are as such:
-the free inlay wax we are going to use it and place it in the rests, to make the guide
planes, tissue\cast stop, and a small amount at the finish line and the junctions; because thefinish line will be a negative area I need to place wax so that when I put other layers of wax it
won't go down
Now the sequence differs in the maxilla from the mandible, after I do the rests
In the upper after I do the rests, tissue stop, and the internal finish line I place the mesh
Then we will place the major connector, the wax is very thin so I have to be very delicate
with it
After I place the palate I have to make a positive margin between the palate and the meshwork an external finish line, it has anterior and palatal border, on the bounded saddle area
I have anterior, posterior, and a palatal border "maxilla"; how to do that? We place an extra
roll of wax, which is about .5 mm thick; we place it above the mesh work BEFORE I place the
palate
So the sequence " maxilla "
-Rests
-Guide planes
-Tissue stop
- Mesh work
-Roll of wax that is going to help me create the external finish line, and some more inlay wax
to make this area thicker
-The palate 'the sheath' 'the major connector' and I have to make sure that I have a nice
right angle at the external finish line
-Reshaped wax for the clasps, reciprocating arms, and the I bar
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In the mandible it will be a bit reversed
Rests tissue stop guide planes Bar 1st
then the mesh work then some wax >>
external finish line, then I put the clasps
Inlay wax is not prefabricated you melt it and use it
*Prefabricated pattern:
They have an orientation you have to be careful when you use it!
You have to make sure which side is up and which side is down "in the clasps it is very very
important"
on the right you can see the mesh work
there is always a rough surface and a smooth
surface
the smooth surface all the time towards the
tissue
And the rounded surface "rough" towards the mouth and the acrylic
And we have the lattice work the same there is a smooth surface and a rough rounded one
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This is smooth toward the tissues "left"
And then you have a rounded surface toward the
acrylic 'or towards you' "right pic"
The roll wax is just a fully rounded wax sheath that helps me raise the external finish line
It is like you draw a line with a ruler and build up wax on top of it! (zai sad shame3!)
After the roll I am going to place the major connector in the maxilla it is a sheath wax
and we have stippled wax like if it is veined so this wax I slightly rough like the rough
surface of the maxilla or the tissue so when the tongue comes against it it is not highly
polished and smooth it stimulates the tongue in a normal way the tissue would
On the other side we have a nice smooth surface
it is about .5 mm thick
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Try to be nice with it and not to play with it that much because the more you play with it the
more you will distort it!
Now we come to the clasps we have a flat surface and a round surface
The round towards the tongue so it stimulates it well the smooth to the cast so it is adaptedwell!
In the clasps it is really important to place the tapered end in the undercut, and the other
end in the minor connector
Which aids in the flexibility of the clasp tip so that cast cobalt
chromium can be flexible without damaging the tooth
So always the tapered tip at the undercut and the broad base
toward the minor connector
And don't use your fingernails! Use the flesh of your fingers
Now the other type of clasps
Gingival approaching clasps have different shapes:
It can be just an I
Or the I can have an extension; for more contact >> this
becomes an L bar
Or it can have two extensions and become a U or a T
The company has made it like U or a T and then you can cut away the pieces the way you
want to! #4 in the picture below:
Or you can just work with clasps like in > tapered end toward the undercut and
broad base toward the minor connector
The gingivally approaching clasps should always in the tooth "window" then it goes straight
down it doesn't g down diagonally, so it goes down 3-4mm then straight back through a
rounded angle then it goes diagonally to the minor connector
Why don't we go back diagonally from the beginning? Because by this we cover a larger area
of the irritable gingiva so we try to cross the gingiva at a rounded right angle
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Such as when we were children and they taught us to cross the street at right angle because
it is the shortest distance
We also fill the bead line with inlay wax in the maxilla
Now Mr. No3man started putting the wax on the refractory cast
Everything in wax on the refractory cast will turn into? Metal
So the wax we use is prefabricated from the company and what we do is just putting pieces
together
So try to keep the cast as clean as possible
There are adhesive wax patterns the one we used is non-adhesive
So first we filled the rests, tissue stop, guide planes, and internal finish lines
Don't too much wax the more you put the more you have to carve away
Dr. advises us to use two instruments one to shape and one to add, you can use some of the
Cons instruments they are very handy here! Amalgam carver for example
The guide planes should be no more than .5mm thick
The squared area on the tooth we call it guide
plane the metal plate that will stand upon it is
called guide plate!
Remember that you cannot have a floating piece
of wax because a floating piece of wax will
become a floating piece of metal all of the
parts have to be connected minor connectors
with major connectors
And we put wax on the bead line and one of its
advantages is to have a strong border that
appears thin to the tongue
So we have an anterior and posterior finish lines the anterior border should finish just
behind the rugae so the tongue slides from the major connector into the rugae onto the
space
Shape the inlay wax that you placed so it is smooth and nice and remember any extra
wax means over trimming of the metal which very hard of course
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So far we did this:
There is one more area that I need to make thicker if this is our relief(B) for example:
When I put my sheath major connector it is going to go like this:
An angle so what we do is that we fill the area beneath it first so when we put the sheath
wax it goes smoothly, and then I can make my external finish line afterwards!
So we are going to place wax on the internal finish lines on the
palate and the teeth
I don't put it toward the sulcus or the hamular notch!
Usually we don't use a lacron carver to do this we use aninstrument that is called PKT (after the dentist Peter K. Thomas) in Arabic they call it addition
because they are used in the addition wax technique, an instrument that look like the
explorer, they are long and thin! They come in different sizes
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Each one takes a different amount of wax so I fill in the internal finish line and I try to
make it ramp so the pattern wax on top will go smoothly on top of it
Ramp =
:^^The guide plate proximal facial line angle
Next step we are going to place the mesh work it is a good idea if u draw it before you
place it
The mesh work doesn't reach the internal finish line remember I told you that the external
and internal finish lines are not at the same level
The external finish line is closer to the teeth than the internal let's suppose that they were
on the same level the area in between will be weak
So we stagger it! We put the two lines into different
levels!
So what I do is like this:
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So there would be at least 2-3mm distance between the two usually the internal finish line
is closer to the center of the palate the reason is that we want more acrylic on the internal
surface so we can reline it in an easier fashion
So the end of the mesh work "external finish line" will be 1-2.5mm at least away from the
internal finish line
How far back in the open hamular notch area should I go? About 2\3s of the crest just in
front of the maxillary tuberosity "behind the tissue stop"
We don't cover the tuberosity because we usually don't have enough space for the mesh
work and teeth!
How far facially the mesh work should go?
2mm down the crest why?
Because the ridge lap will come from the facial and I will have trouble setting the tooth! And
aesthetically the metal shows from the acrylic and it is not very nice
Or you can extend from the facial proximal line angle backwards, or crest of the ridge+2mm!
So this is the area that will be covered by the meshwork we don't go all the way down
facially
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The first you do when you get your pattern wax is to decide which the bottom surface is and
which the top surface is round and smooth
Just adapt it with the flesh of your finger add some inlay wax over the tissue stop to
connect it and to make sure that there is enough bulk where the tissue stop is
Remember everything has to be connected so we fused the mesh work with the guide
plate
So now we have our mesh work in place:
Now before we place the major connector we have to bulk up the internal finish line more
Because wax has to come from the palate and end up on the mesh work as a positive step!
So the rolled wax starts at the guide plate all the way down just at the edge of the mesh
work this will become my external finish line
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So this is our relief area that we put the mesh work on top of it:
And we put the mesh work on top of it:
If we add wax now we will end up with a step and that is not good
So we added some inlay wax down here to help bulk it up
But I also needed an external finish line which we added the
rolled wax for
So we will end up with something like this:
The major connector is going to come from the left and for the major connector not to fall
down and irritate the tongue I need to fill in underneath it like this:
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And then I will put my major connector on top
And with a lacron carver I am going to make the external finish line sharp
And at the end all of this wax will turn into metal no difference between them but I would
have made my internal and external finish lines the way I want to
So now we fill the space between the palate and the internal finish line so that it raises
gradually "ramp"
Now adding the major connector is the breaking step you have to be very careful some
technicians because the palate is concave they add it in two sheaths and seal it in the middle
In a concaved surface if you want to add wax you start to adapt from the center and work
the bubbles and air to the outside
Pattern wax cannot be heated you can pass it once on the flame
Again stippled surface towards you smooth shiny surface towards the tissue
Careful not to destroy the things that you've already done
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If you don't adapt well you will end up with a metal of 2-3mm thick!
When you cut from posterior cut away from the bead line with 1-1.5mm because it will tell
me where to trim later on
Where to cut the external finish line? Just at the external border of the rolled wax!
We extend the major connector to the lingual of the premolar and canine to make the
reciprocation
It is more comfortable to the tongue
You can burnish to blend the green red and blue wax and smooth them down together to
have a right degree angle so use a blunt instrument not a hot one 'not to melt the wax'
just to make them one unit
After burnishing the external finish line we will seal it just touch with the hot lacron carver
Join everything together
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The wax should be continuous
Now we cut the clasp make sure that the smooth surface if toward the tissue
Put the short arm of the clasp on the facial and the long one on the lingual [upper cast]
The clasp doesn't go all the way to the adjacent tooth and it has to reach the rest and the
guide plate!
The long arm of the prefabricated clasp should go on the lingual surface
Now we move to the I bar the tip tapered surface toward the window in the undercut ... it
should cross the gingiva at right angle after wards you can go straight up or diagonal the
longer you make it the more flexible it is but the more the chance of breakage and chance
difficulty during casting
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There should be a connection between the clasp tip and the minor connector and we try to
make it broad
From the free gingival margin and the angle should be at least 3-4mm!
Some text books recommend making a finish line between the acrylic and the I bar!
Now we're done we go back and see if there is anything that I missed or if there is anything
that I can do to make the wax better
Thats it for the maxilla
Now we move to the mandible we are going to lace a lingual bar
The cross section of a lingual bar is half pear shaped
The thick rounded part is toward the flour of the mouth the thin tapered part is toward
the gingiva how far away should it be from thefree gingival margin? At least 3mm the
bar itself should be 4-5mm and we prefer to have 1mm below it
So our minimum is 8 mm thickness from teeth to the depth of the bar
If I don't have this room I cannot use the bar I place a lingual plate!
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So if we don't have enough room (8mm) we use a lingual plate instead of a lingual bar
We either stay away from the gingiva and if we cannot we cover it
If you notice in our casts that we did in the lab the lingual bar extends all the way down to
the bounded saddle area "from the mesial of the 7 all the way around until we reach thepremolar on the other side"
And as we said the external finish line of the mandibular cast "at the open crest area" is in
front "anterior"
-rests
-guide plates
-finish lines
Finish line at the bounded saddle area:
-tissue stop
-major connector "reversed to the maxilla in which we put the mesh before"
If you take a close look at the lingual bar it is rounded at one edge "lower border" and a
tapered upper it has a flat surface and a round surface!
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So the bottom toward the floor of the mouth thin surface upwards smooth surface
towards the tissue rounded surface toward you or the tongue!
So between the gingiva and the connector it is about three mm!
Adapt and cut the excess
The lingual bar under normal teeth has to be half pear shaped in cross section because it is
free above because the tongue has to feel gradual increment going from the tissues to the
teeth but where the artificial teeth are the bar is going to continue into acrylic and it is
going to be thicker not half pear bar!
-lattice work
Just at the ridge of the crest
Just behind the tissue stop! At the distal extension area seal it in front
You can see that the lattice work is separate from the major connector so we have to join
them together
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So you have to fill in the space between the lattice and the major connector everywhere
The wax should be at least .5 mm thick
And now we have to make it thicker at the top to make the external finish line
So we need a definite junction between the metal and acrylic "external finish line" >> roll of
blue wax >> positive edge and it should go anterior and posterior to the guide plates
Make sure you have smooth rounded ends everywhere
At the back we shaped it rounded not to irritate the tongue
Remember to connect everything together
Okay we are using several colors but it will turn into one
material so don't make edges between them they have to
be connected nicely and smoothly
But on the other side "free distal extension side" how are
we going to join the lingual bar with the lattice nicely and
smoothly?
We make a delta "smooth and strong" wider triangle plate
So we have two triangles one from the lattice work and one coming from the lingual bar
Shape the small triangle to be flush with the lattice work
Don't forget to place clasps
Lower long >> facial short tip >> lingual
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Just put it in the step don't go up
I bars same as the maxilla
Remember that the external finish line should be continuous from anterior "guide plate" and
posterior "guide plate" and the palatal
Mandible: rests, tissue stop, guide plates, internal finish lines, major connector, lattice work,
fill in the blanks, clasps
And that's it
Forgive me for any mistake I am so sorry for being late I am so sor ry for the script that it
is long but I tried to write everything and add pix as much as possible
Gd luck in the finalzZ d3waaatkom _
Syria Palestine Asrana I am too small and nothing to say anything