lab prostho 10 (1) (1)
Post on 14-Apr-2018
224 views
Embed Size (px)
TRANSCRIPT
7/30/2019 Lab Prostho 10 (1) (1)
1/13
1
A,
7/30/2019 Lab Prostho 10 (1) (1)
2/13
2
Very important note: you should watch the video on the CD the CR gave
us.. It helps a lot.. And sorry for any mistake.. It wasn't easy, the dr.
explained a lot on his cast model.. I tried my best. ERRARE EST
HUMANUM ! .
There was a video about the procedures of fabrication of cobalt-
chromium partial denture.So, we are going to do a quick review of the laboratory steps and then
you'll go the central lab to see the Casting machine and casting furnace.
What are the steps for the fabrication of Co-Cr PD?
LaboratoryClinic
Primary cast (dental stone III)Primary impressionWe do initial surveying and design
We fabricate custom tray
Tooth \mouth preparationa-Secondary cast (Master )b-Verification surveying and final designc-Block out and reliefd-Duplicate master cast in Agar-Agar or
Addition silicon- you get the REFRACTORY CAST made
of Phosphate bounded investment
material.e-Fabricate wax pattern
f-Complete the investment process
:sprout and investment
g-Casting
h-De-investment and cut sproutsi-Finishing and polishing metal
framework
Secondary impression (Alginate)
Mounting and teeth settingJaw Relationship record and Metal
framework try in
Wax try-in
Acrylic processing
Finishing and polishing
Insertion
7/30/2019 Lab Prostho 10 (1) (1)
3/13
3
1- The initial survey and design are important to formulate thetreatment plan.
2-
Custom trays are not always necessary, they are necessary fordistal extensions and marginal edentulous areas ,short
bounded saddle areas don't require custom tray.
3- Mouth preparation in general involving extraction , tooth rest ,guide planes (all discussed earlier ). If we are to do border
molding we do border molding
4- The secondary impression is done using Alginate ,we need anelastomeric material we can't use a rigid material unless
there's an edentulous area ,such as addition silicon
,dimensional silicon or Polysulphides5- Points from e-f are done on the refractory cast.6- We put a wax rim on the metal framework and we do Jaw
relationship record in the same visit.
7- The acrylic processing is done on the master cast, mountingand teeth setting is on the master cast , the finish and polish is
on the master cast; so the master cast after we do duplication
we keep it.
Very quickly :
Edentulous pt , we take primary impression ,using stock traysusing alginate for primary impression ,we can use utility wax to
modify alginate trays( different from edentulous ones). We pour
it we end up with primary cast made out of stone , we do initial
surveying and design , we use it have an idea about the treatment
procedure. In the lab, you do custom tray (two layers of spacersnear the teeth and one in the edentulous area )
we make final impression and we end up with final cast (mastercast) type 3 dental stone or type 4 di-stone ;
the final cast will have rest and guide planes on them ; this castwill have the right tissue contour to fit the PD ; the master cast I
can't pour the metal ,because won't stand the temp. in
Centigrade's it's very high necessary to do the casting ; So I do
block out and relief ;
shaped block out for the clasps
7/30/2019 Lab Prostho 10 (1) (1)
4/13
4
arbitrary block out to simplify the duplication relief to make room for the acrylic which decides where the
internal finish line will be .
In order to duplicate we need a special material , we usually use
a silicon type material , additional silicon ,it's flow able and we
use special molds to duplicate ; we end up with a mold which is
a copy of the cast ;or we can use Agar Agar (thermoplastic
setting ,while silicon chemical set);
*Agar Agar is thermoplastic and hydrocolloid; water sensitive and can be
re-used in the lab. While silicon can't be reused to do duplication butcan be report ;
** Distinction : silicon can be used to make only one copy of one cast
but I can pour it many times. Agar Agar I can be use to make copy of
many casts I can mount it and use it many times but I can only pour it
ones.
Now I have the mold , copy of secondary cast, I'm going to pour it in amaterial stronger than master cast which can withstand high
temperatures.
I'll use investments materials ( because the Co-Cr-Mo (Cobalt-
Chromium-Molybdenum) alloy has very high melting temp , so I use
phosphate bounded investment . I mix it up , I have special liquid with
high silica content ; I pour it up then sets and dries ;when I remove it
,sometimes the surface is not very hard,
there's a thin layer of something that shines on the surface; what I do to
remove it? I have a hot bath of bees wax, when it's hot I soak cast in it
and I take it out again, the surface will absorb some of the bees wax , it
will make the surface harder ;technically can't scratch the cast even by
mistake during wax patter , so I do hardening of my refractory cast with
bees wax.
http://www.springerlink.com/index/CK37284X6N60W584.pdfhttp://www.springerlink.com/index/CK37284X6N60W584.pdfhttp://www.springerlink.com/index/CK37284X6N60W584.pdfhttp://www.springerlink.com/index/CK37284X6N60W584.pdf7/30/2019 Lab Prostho 10 (1) (1)
5/13
5
on the master cast , what am I going to do? I want to make the metal
frame work , so what I do is the wax pattern ,there are special wax
patterns fabricated by companies so we have : nice even thickness steeled sheet wax ,for the palate mesh work -latex work I-bar ginigivally approaching clasp -circumferential clasps inlay wax to make the rest and meet everything together ;
** In wax pattern we make the external finish line ; the internal finish
line formed by the relief.
Everything which is wax will turn into metal .
The problem is , this is not like acrylic , I can't just make another mold
and open it again , so what I do is similar to acrylic fabrication ,I need
to make lost wax process but the technique which I use is the sprout
technique ; instead of making two-part mold I make one part mold
;what I do is I place a sprout ( a conical sprout) ;the objective of
sprout when it's completely enclosed in investment is to allow thewax to escape ,to evaporate and burn out and for the metal to go
inside to fill the mold .
So how do I do the mold? I put it in a mold former, I seal it ,I mix my
investment in a similar technique which I used with stone (in a
vacuum mixer )we pour it and we end up with something like a block
,but when I remove the funnel ,there'll be a space , then I put it in the
furnace at high temperature approximately 1000 C . for 2 things:
setting expansions, from chemical reaction of setting andthermal expansion , because when I increase the temp it will
became larger
And when my mold is hot the material (metal) will flow mucheasier ,if my mold is cold and I pour metal inside it , it will cool
down before it goes to the details ;so I warm it to allow
expansion to compensate for the contraction of metal when it
cools * I heat it up to allow metal to flow inside it .
7/30/2019 Lab Prostho 10 (1) (1)
6/13
6
I need to machines to do casting, I need a machine to heat up my
mold and another to melt the metal and pour the metal inside the
mold .** one is called the "CASTIING MACHINE " and the other is "CASTING
FURNICE" .
So I put the mold in the oven ;I leave it for several hours ,there's a
special cycle to allow the wax to evaporate without destroying the
mold. When it reaches the right temperature ,I take the mold out the
oven and I put inside the casting machine ,in the casting machine
either using a flame or using an electric coil ;the metal inside thiscontainer is heated and becomes liquid metal ; I need to get this
liquid metal inside the mold (I don't hold it by hand ,there's a special
machine) there are two basics techniques :
1- centrifugal casting force: it start rotating very fast so that the metal
inside will flow outside the opening of the machine and it'll go inside
the mold, inside the mold because it's rotating so fast, the metal
goes in the details of the mold
2- vacuum casting ,(the air force will press on the metal pushing it
inside; the air is hot air ); of course the machine is different from
centrifugal.
The temperature source can be either flame or induction casting(electric
coil)
// The casting process is on the CD the Cr gave .
After casting we'll move the mold from the casting machine and let it
cool down, usually changes in color, it becomes white; inside it will be all
metal ,so I'll tap it and inside I'll find something like to indicate where
the sprout former were; I'll get the sprout and the metal casting .I use a
special machine called "SAND BLASTER" ,is a very simple design, it has a
tube with an opening at the top , with air pressure and Aluminum Oxide
Abrasive container ..
7/30/2019 Lab Prostho 10 (1) (1)
7/13
7
the air will bring the Aluminum Oxide inside the tube and out of the tip
it'll start shooting the aluminum oxide sand and we use it to abrade; the
investment will become clean; if I use a bur maybe I'll hit the clasp or
destroy the machine ,so the way I