prosthodontics ll lab 1

7/28/2019 Prosthodontics Ll Lab 1

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Prosthodontics ll laboratory.

Title: Laboratory Introduction.

In this laboratory we will talk about partial removal Prosthodontics, we are goingto talk about the tools we are going to use this semester and then we will talk a

little about some of the partial denture making steps, so lets start.

We will continue learning how to make removable prosthesis , as you remember

last semester we learned how to fabricate a maxillary and a mandibular complete

denture for the edentulous mouth . This semester we will learn how to fabricate

prosthesis for partially dentate mouth (1-15 teeth missing is considered as partial

prosthesis). If a patient came to me with only one single tooth present in his mouth

will I be making a partial or a complete denture for him? Ill be making partial

denture, complete dentures are when there are no teeth present.

You should know that crowns and bridges are not the same term as removal partialdentures, although some use it to describe the removable partial dentures; crowns

and bridges involve having a cemented crowns and bridges, so you should note this

difference when referring to upcoming lectures.

In this semester we have more work to do than the previous semester; we have to

do an interim(provisional) denture and a definitive(metal framework) denture.

In this semester we are going to make wire designing, you must have a set of at

least six colors with you. If you draw your design with only one color you will notget the full marks.


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Last semester we talked about how complete dentures get

their retentive nature via many things one of them is

peripheral seal, the case with partial dentures are different;

we cant have a peripheral seal in them and the reason behind

this is that in complete dentures the borders (flanges) go all the way from suclus to

suclus and to the post-dam area so air cant escape.

In partial dentures the need of having wires or clips are to create a seal to the

denture, the company provides us with wires in these forms.

We need to use specialized tools to bend these wires, they are called Orthodontic

Pliers. Orthodontists have many designs for these pliers if not hundreds , each

design to accommodate each function .

What characterizes the pliers are the geometric shape of the peaks, we have conical

shape , pyramidal and triangular and many other shapes . Sometimes we have three

peaks, sometimes we have peaks of the same shape ( e.g. two peaks , two

triangular . ) sometimes we have them different from each other ( one conical and

one triangular ) and so on , so there are lots of shapes to accommodate the need to

make the design you want .

However the most common types of pliers we use indentistry are actually two: Loop forming Pliers and

Adams Universal Pliers (named after the dentist who

made it; Philip Adam). During this semester we are

going to work with the first one; the loop forming

wires but in the next year we will be working with

Adams pliers during orthodontic training.

Before we start using the loop forming pliers we have

to know how they work, looking at their peaks you can

notice that one of the peaks is sharp and one is conical.

If I bend the wire toward the sharp edge Ill get a sharp

bend depending on how much force you applied. Also

if you bend toward the conical edge Ill get a curve (loop) depending on how much

force you applied.

Loop forming


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Adams pliers (two pyramidal peaks shape) produces a right angle bend which is

much easier to do with this tool than with the loop forming pliers.

Depending on where you put the wire: down at the junction or toward the tip, how

acute the curve is or how wide the curve is the wire will be affected. I f I put it atthe tip Ill have a bigger curve than if I put it at the junction down.

In orthodontics they make a 360 loop (spiral) curve, but in Prosthodontics we dont

do that do you know why? In orthodontics they make these spirals to make springs

in order to make teeth a little mobile when applying the orthodontic treatment. In

Prosthodontics we dont want teeth to move we want them to be firm. So each one

has its own objective.

When you cut the wires without paying attention to a proper way the wire might

bounces off and hit your eye or cause permanent injury, you have to either cover

the both ends or point the wire under the table ( or your lab coat ) so no one will

get hurt . The wires themselves they have a diameter of 0.7-0.8, they are made out

of stainless-steel

As you already know the basics divisions of Prosthodontics are:

The main are:

Removable Prosthodontics ( Complete dentures and Partial dentures ) Fixed Prosthodontics ( crowns and bridges )The subtypes from the two above are: Maxillofacial Prosthodontics (removable or fixed, replace larger parts of the

mouth not only the teeth e.g. face).

Implants Prosthodontics.


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What are the subdivisions of the partial dentures?

Provisional (Temporary/Diagnostic/Interim/Transitional): dont be fooled bythe name temporary, this prosthesis is made out of good materials not like what

the patient thinks when he hears the word temporary. Made out of Acrylic Definitive (Permanent): it is called metal base removable partial denture. Needs

much more work than the provisional .

Why do we have provisional and definitive? When the patient comes his mouth is

not fully healed, he has some teeth that need to be extracted. If I make the final

definitive denture then the patient mouth changes the denture I made would be

useless. So I make the provisional because it is less costly : we only use acrylic and

wire bands, and can last for days or weeks or in some rear cases months, on the

other hand the definitive is more expensive and it is more technique sensitivebecause the base is made out of metal and the gingival rejoin is covered with

acrylic. So in the definitive we have two processing steps: Lost Wax Technique (to

shape the metal) and the other one is to add the acrylic and teeth.

What is the type of metal we use in the metal framework in dentistry?

We either we use high noble (precious), or non-noble (non-precious) but in some

parts of the world like in our country we cant always use high noble materials,

fortunately we have two materials that will do the job just fine : Cobalt-chromium

orNickle-chromieum , although nickel is begin popularly used due to the fact it is

cheap , it is advisable not to use it because it might cause allergy to some patients .

So the material we are going to use in the lab and the one which is advisable is

Cobalt-Chromium.

The cobalt-chromium alloy consists of a highly reactive element (chromium) and a

lower reactive element (cobalt). When the denture is inside the patient mouth many

external factors can promotes corrosion as water and air. Because chromium is

more reactive itll react with these factors and make chromium-oxide on the

surface (little black dots), so we say chromium gives passivity to cobalt. The other

good thing is that when you polish the surface more chromium will come to

surface.


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What are the steps of fabricating a completedenture (clinical steps)?

1. First impression2. Secondary impression3. JRR4. Tryin5. Insertion6. Recall

In partial dentate mouth the space where teeth doesnt exist is called Bounded

edentulous area or less formally settle .

The key to understand partial denture is that each denture has its own steps, not

every denture follow the same formula, consider these following situations :

If we have a patient with only some missing teeth, the depth of the sulcus here is

not important as in the complete denture because I dont have peripheral seal

The depth of the sulcus (flange) in partial denture is not that important, do you

know why? Because I dont really care about the peripheral seal, I dont have to

border mold here. Sometimes if you made a good palatal impression with most of

the suclus impression you dont have to actually take a secondary impression.

I didnt know the jaw releation between the teeth in the complete denture because I

didnt have teeth , but here in the partial denture some teeth are still present and I

can take the patient jaws model and fabricate a denture depending on that relation

without the need to take a jaw relation record

So we dont always need a secondary impression and jaw relation record.

In most cases we like to make try-in but in some very rear cases (e.g. one tooth is

missing) for example I have a patient with only one tooth missing I can make him

a bride in only two visits , the first visit Ill make the impression and in the second

impression we will insert it to him , that simple .


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In the other cases we dont have one tooth missing but we have many missing teeth

or what we call free extensions, so here registering the depth of the sulcus is

important because we want lateral stability at the extensions area (distal extensions

area), we are not looking for a perfect peripheral seal but we just want to register

the maximum denture area. So here it is very important I take a secondaryimpression, jaw relation record and a try in appointment.

All of the previous examples show that each partial denture has its own unique

design. Sometimes I dont need to make J.R.R , secondary impression or a try-in

session . Other times I have to make all these things .

The classification of edentulous ridges:

Lets say you want to communicate with another doctor about your patient

situation , you cant just name each tooth that is missing so the need to invent a

classification system rises , the most popular one is Kennedy Classification which

depends on where the teeth are missing .

After Dr.Kennedy invented this classification they found out that it is not enough

and it doesnt describe all the cases, so another doctor (Applegate) mademodifications to this system , we will know about them briefly.

There is another simple classification which refers to where the denture gets it

support and it is simply known as:

Tooth supported Tissue supported Tooth and Tissue supported

For example looking at an edentulous mouth (no teeth present) we can saythat the type of support is? The answer is tissue supported.


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Another example if I have a patient with teeth at the corners of his mouth,here I can take this as an advantage and make these teeth as a support factor

so here Tooth supported prosthesis

What if we have an area with no teeth and another area with some teeth ,what type of support do I have here ? Here it is a combination of both the

tooth supported and the tissue supported.

So lets talk about Keendy classification (Refer to pictures next page while reading

What Dr.Kennedy did is that he tried to look for the most common edentulous

scenarios among population and he came up with four classes, and they are as

follows:

Before you learn about these classes there is something important you haveto know.As its written above this classification depends on the free spaces

in the mouth. You count the free spaces from the most posterior part and

moving anteroirley .

You only include the teeth that are going to be in your design (e.g. thirdmolars) sometimes this third molar has a week roots so it is not good for

retention so we will not included in the final design , be careful during the

exam read the question asked is it a third molar or not . Class 1: I have teeth in the front with an edeunoules area in the back or what

is called bilateral distal extension.

Class 2 : I have teeth in the front or the back in one side , or what is calledUnilateral distal extension

Class 3 : I have missing teeth in one area but it is bounded by the remainingteeth

Class 4: I have teeth in the back but nothing at the front.Class 1 and 2 are: Tooth-Tissue supported, Class 3 is always tooth supported, and

class 4 is sometimes tooth supported and sometimes is tissue supported depending

on the length of the edentulous area.

What is the difference between class three and four? Class three is bounded and it

doesnt cross the midline, class four is bounded but it cross the midline


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There is another problem; usually teeth when they are extracted are not very

organized as in the pictures, from this situation a modification to the classes above

rises , this modification is calledApplegate modification to Kennedy classification

Consider this example you have a class ll patient with 2 spaces, youll call it class

ll modification 2. I dont count the teeth missing but the spaces created by these

missing teeth and so on. Keep in mind class 1, 2 and 3 have modifications but

class 4 doesnt have modifications.

We made a primary impression using stock trays (can be all metal, all plastic,

porfrrated or non-proffrated ).

And as you already know we choose non-perforated , metal with impression

compound . And Perforated , Plastic or Metal with Alginate.


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And as you know Perforrated are for reslent matierls (e.g. alginate, elastomeric

materials )

Non-perforatted are for impression compound and sometimes for silicon.

Edentulous trays have a semi-circular cross section when we have a patientwith teeth these semi-circular trays are no longer suitable, because it wont

reach the full depth of the suclus and itll hit the cusps and start causing errors

to the impression.

On the other hand Dentate-tray cross section is more rectangular or square andit is more deeper than the other trays , so when you put it inside the patient

mouth itll actually go around the teeth without hitting them so these trays are

called : Dentate trays .

Another tray is the Hybrid trays it is with a rectangular area at the front and acircular area at the back, which class of Kennedy classification do we use this

with? The answer is class 1, so when you have a patient with teeth in the front

and no teeth at the back we use this special type of trays to be better adapted. If

you cant get your hands on any of these special trays you can get the dentate

tray (rectangular) and modify it with impression compound at the back (you

only put impression compound on the edentulous area , because if you put it in

the area where the teeth is itll lock and itll become hard to get it out ), we will

learn this procedure later

For a primary impression for a dentate patient we cant use ridged materials (e.g.

Zinc Oxide Eugnoal or impression compound) because we have undercuts , even if

the patient doesnt have an actual undercuts but each tooth has many undercuts that

will affect the impression ( e.g. cusps , ridges ) .

Instead we will use alginate or any of the elastomeric materials (polysulfide,

polyether, condensation silicon and addition silicon).

As you remember, If we want to increase the retention of the impressioncompound we spray an adhesive to the tray . But most of the students make

mistakes like spraying too much , they dont wait for it to be fully set and finally

when they spray they sometimes hold the denture in the air and start spraying , the

glue will go to the floor and the clinic will be dirty . So please note these things

during your practical years because they are common mistakes.


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Sometimes we use utility wax around the sides to modify the dentate stock trays

(e.g. suclus is more deep we can add utility wax ) .

Why didnt we use the utility wax with impression compound the last semester?

Because utility wax liquefy at about 45-50, and the fusing temperature ofimpression compound is 56-57 so the degrees are similar between them. So what

you have to do is you put the impression compound first, wait for it to cool and

then you add the utility wax

So at the end it is optional to use the adhesive, and to modify the tray with utility

wax and impression compound as needed.

So the material we are going to use today in the lab for a parietal dentate patient isAlginate (Irreversible Hydrocolloid). And some of its characteristics as you know

them by now are: 1) elastic 2) Aqueous (hydrophilic, synerises and ambition ) 3)

Chemically set , cant be modified later .

Revision for gypsum types:

Type l Impression plaster.

Type 2 Dental Plaster: suitable for only two things: A) pouring a primary

edentulous cast ( there are no teeth to distort anything ) B) Mount casts on the

articulator ( we use it in flaking as the first layer ) .

Type 3 Dental Stone: Used with primary and secondary dentate impression.

Type 4 Di-stone

So we will mix according to the manufacture rules (100mg powder = 25-30 liquid),

and as you know we have to not incorporate any bubbles. After you have the

impression make sure you put it in a moist environment, and as you know you thebest thing is to pour it into gypsum immediately. The type of gypsum we are going

to use is dental plaster type ll , but typically you have something between 15-30

min.

Another thing you should note is that Algiante , dental stone and dental palster are

hydrophilic , when you pour them in the impression itll flow easily . But silicon is


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hydrophobic and it doesnt flow very easily so you need to use a small instrument

like a carver to make sure there are no bubbles , also spraying a surfactant will help

and help it flow better and no bubbles are found .

If I have a bubble on the gypsum ( the dental stone ) what will this look like when Ipour the cast ? Negative defect ( a void ) .

After we have our cast , with this cast as you know we are going to make our

custom tray . With the custom tray we are going to take our secondary impression.

What are the differences between the custom tray of the edentulous mouth and the

partially dentate mouth?

The difference is in the thickness of the spacer ( if it was there in the first place ) .

As you already know the spacer is made out of baseplate wax ( they are 1.5-2mmthick ) , in the partially dentate mouth you are going to place two layers of

baseplate wax over the teeth and one layer over the palate and edentulous areas OR

two layers over everything and one over the teeth .

And then we need to make a small windows for the stoppers (over the teeth and on

the edentulous areas if nessery ) .

Then we adapt acrylic (we are going to use light cure as the previous semester) ,

and as you know we adapt the acrylic well ( dont press with your nails , make

handle .. etc ) . Youll notice that the custom tray for the partial dentate is more

bulky than the edentulous tray.

A smart thing to do is if you are going to use alginate as an impression material,

you know that alginate requires holes for retention. You cant make the holes after

the acrylic is set, do it before you it set so itd be easier.

~The end .

The number of deaths in Syria to the date of writing this script is 8818 people, from

that number 618 are kids, and 542 are women. My prayers go to you my country.

prosthodontics ll lab 1

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