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