prostho iv - lec 4 - impression making for complete dentures.pdf

7/27/2019 prostho IV - lec 4 - impression making for complete dentures.pdf

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IMPRESSION MAKING FOR COMPLETE DENTURES

Zuhal Syuwa Mohd Yasin &

Siti Nurba a Mustafa

Khalid Al-Hamad

20-10-2013


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IMPRESSION MAKING FOR COMPLETE DENTURES

By Dr Khaled

20/10/2013

Part 1

Lets start with impression itself. Lets talk about mucostatic and mucoimpressive. These terms are

related to the viscosity of the material. If you use a viscous material, ull be ending up with making

mucompressive impression. If you use a light viscosity material, theoretically, you will be ending up

with mucostatic impression. The doctors probably ask us in the clinic about these terms, so we

should able to differentiate them.

You have to analyze the anatomy, the primary support area, secondary support area, and the relief

area. The other technique is you will manipulate your technique to press certain areas and to less

press certain area (selective compression technique) .

[RECALL]

from Prostho (1) slide:

Impression Techniques:

1) Mucocompressive/ close mouth/ pressure impression techniqueRecords impression in a condition that assumes under the masticatory load

2) Mucostatic/ non pressureRecords the impression of the tissue in an anatomical form without pressure

3) Selective compression techniqueRecords impression with more compression on the tissue on certain selected areas on theothers.

So thats the idea of the mucostatic and mucocompressive techniques. I hope you will notice after

finishing this lecture, that I would not be using this terms, i will explain to you 3 techniques besides

the conventional techniques in which you will encounter during your complete dentures.

So, go back to our primary visit, usually we use 2 visits for taking the impressions because usually

when we use stock tray, it will not fix the patients mouths. It will be either too large, if its too large,

it will disturb your sulcus area. While if its too small, the tissue will collapse and your impression of

the sulces will not be accurate. And ive told you last time, the most important part of taking the

impressions is to accurately determine the peripheral areas. If you get that right, your impressions

will be succesful. Choosing the impression materials will not make any differences, the main

difference is made by proper border molding stage. So the special tray will help you to make the

adjustment of periphery of the stock tray by border molding and can also help us to plan the

support areas. About the impression materials, if you use a viscous material, you can ask your

technician to put a spacer, according to the material you are using.

So, the objectives of the primary impressions, just to outline the important landmarks on the

primary cast and to fabricate the special tray that you can customize in the pts mouth.


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Choices of materials.

We can use impression compund, silicone or irreversible alginate. The difference is, if the material

is viscous, then you can go away with a slightly under extended tray. Although you use underextended tray, the material will support itself. It happened to your colleague who used a slightly

small tray and not covering the retromolar pad area, i just asked him to add the impression

compound and it would cover the area. The viscous materials will help you to compensate a slightly

(not too much) under extended tray.

If you talk about silicone , rubber material silicone likes condesation silicone or polyvinyl siloxane, it

comes with different viscosity. The difference of the viscosity is related to the fillers. The quantity of

the silicone will be the same, the manufacturer will change the quantity of the fillers. If the fillers are

increased, the materials will be viscous. You can use a putty for the primary impression. The

advantages, again, the viscous material will help you to support itself in the under extended tray andbecause it is elastic, it will be okay with undercuts. But, however, siliconecant be corrected . if its

not an acceptable impression, you have to do all over again. It is very similar to the impression

compund except the impression compound isnt elastic and can be corrected. If your patients have

mild or severe undercuts, you might use alginate or zinc.

Alginate is elastic so you can use with undercuts, however its unstable because its hydrocolloids,

so, the humidity will affect it meaning that the alginate will be affected by air ambibition and

absorbtion if its not be stored properly. So, after taking impression with alginate, you must pour the

cast immediately and be very careful with how you store it until you pour it. Its not very viscous, so if

your tray is not properly extended, you will end up with deficient impression. Refer to the table.


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Impression techniques

So, lets move on to impression techniques. For the conventional technique, you should adjust your

tray to be 2mm short of your sulcus and border mold you periphery tray using a tracing compund . Atracing compound is the same as impression compund but comes as a green stick (tracing compund

is the proper name) . Its component is the same as impression compound but it is less viscous than

impression compund. So, after you border mold the area and make muscle activation as I showed

you last lecture, you just can place the impression material and make the impression.

This is another technique that I learn in UK, where you just adjust your tray as close as the sulcus,

add some tracing compound at the post dam area and some wax spacer. Dr said that its not that

important to know about this techique, you just learn about what we do here in JUST.

Here in JUST, we will use zinc oxide eugenol, its not as hard as compound but still its non elastic. So

its not the best material to be used when there are undercuts. If you have undercuts, you can use

zinc oxide eugenol. If your case is not appropriate, you can ask you supervisor to use silicone.

Zinc oxide eugenol is usually used in a thin section. So, standard, you will not use wax spacer. So

when you write down the lab instruction, dont ask for spacer. The best is not to be used with spacer.

If its in thick structure it wont be accurate.

SLIDE 67

So, that is the conventional techique. Lets move to selective pressure technique.

Now, lets focus on 3 cases. If you get the pt with good ridge, you use conventional technique. But if

the patients dont have good ridge, we have to use special technique. Basically its all about pressure.

How you plan to take the impression and you press certain areas and avoid pressure on other areas.

That will make the differences between these technques. And also a functional impression material,

we are struggling for space for your denture. You really need to accurately determine the space

between the tounge and the cheeks for the lower impressions .

Flabby ridge

A flabby ridge will usually happen when you have extra pressure from the opposing natural teeth

against usually the upper anterior teeth. For example a Kennedy Class 1 (lower) against a completedenture, you will end up with flabby anterior ridge. When bone resorbs, soft tissue will have no

support and will end up flabby and thats not good news for your denture. Your denture needs

stable seat, just like you, when you sit, you need a stable chair, not the one thats moving around.

If you have a pt with flabby ridge, then you have to plan impression to avoid placing pressure on

that area. How do you do? You just simply make a full impression conventionally, you border mold

the periphery areas, make the full impressions, then you outline the area on that patients mouth,

then you translate to impression area, then you cut out that area and then you apply that flabby

area with low viscosity impression material.


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So, once again:

1) Starting with conventional technique, ensure that the border molding has created peripheralseal.

2) Take the whole impression of maxilla using ZOE or PVS3) Draw the extent of the displaceble tissue on the impression taken.4) Remove the drawn area equivalently with the area of the tray, creating a window on the tray5) Hold the modified tray in position and paint the low viscosity material on the flabby area to

record it in a minimally- displaced position.

6) Because the material used for the flabby area is very thin, so it just sits on the area withoutpressing it.Your denture will only compress the area that are good for support and that can

stand pressure, the flabby area will not be compressed.

Window area:

The impression and part of the tray

are removed

A low viscosity material is used

to take the impression of this

flabby area/window area.


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ADDITIONAL NOTES

1) Displaceable, flabby area is usually seen on the anterior region of edentulous maxillaopposing mandibular anterior natural teeth or in the mandibular alveolar ridge when

extensive bone is occured.

2) Soft tissues that are displaced (flabby areas) during impression making tend to return tooriginl form, and CD fabricated from it will not accurately fit on the recovered tissuesresulting in loss of retention, loss of stability and occlusal disharmony of the teeth.

3) Using a custom tray with a window on the flabby area, that flabby areas are recorded inmucostatic state while the remaining areas are recorded in mucocompressive state to

minimize the distortion of tissues while taking the impressions.

Sorry for any unintentional mistakes in this script..Wish you all the best.

Special thanks to Baraah and Bay (:

Done by,

Zuhal Syuwa Mohd Yasin


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PROSTHODONTICS

20/10/13 - Part 2

Definitive Impression

Selective pressure technique

Fibrous (Unemployed) Ridge

- Thin, mobile thread-like ridge- Picture: mandibular ridge, the crest of

the ridge is like a thread. Will move

around when touched.

How to take impression for this ridge?

- Take impression using tracing compound(greenstick). Outline the area again,remove greenstick relating to crestal

tissues

- Apply light-bodied material.- Pressure is to be compressed on the part

which is going to provide support. And

avoid pressure on the thread-like structure.

Flat (Atrophic) Ridge

Class V - Flat ridge with insufficient height and width.

Class VI - Depressed ridge with a cup-shaped surface.

- Border moulding is difficult to start withbecause the sulcus is shallow and there is

no ridge for the denture to sit on.

Because its flat, when we use

conventional technique, we will compress

the tissue underneath the denture.

- The solution is to use admix technique- If we only use impression compound we

will not get accurate details for impression

- Tray should be properly adjusted. Notoverextended or underextended. 2-3 mm

short of the sulcus.

- Border molding should be done right away.Admix - a mucocompressive technique to spread the tissues away

*3 parts by weight of impression compound to 7 parts by weight of tracing compound


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*created by placing the constituents into hot water and kneading with vaselined, gloved

fingers.

*Philosophy is that a viscous admix of impression compound and tracing compound removes

any soft tissues folds and smoothes them over mandibular bone.

Functional Impression

Neutral Zone technique

- It is called the functional technique because we take the impression while the pt. isfunctioning. (swallowing, moving the tongue around, etc.)

- design for patients with poor track records denture stability, a large tongue (tongueexpanded because patient has been edentulous for a long time) or other anatomical

anomaly.

(Im sorry, I couldnt imagine what the doctor was saying, so here is the

summarization of this technique from

http://www.dentistry.bham.ac.uk/cal/impress/nz.htm)

- Primary impressions of the upper and lower jaws are taken using impressioncompound.

- Model is poured. On this model, upper wax rims and lower special tray isconstructed.

- The upper wax rim is adjusted to the prescribed occlusal vertical dimension (OVD).Lower impression is placed in the mouth. It is a resin base with three vertical stops

joined by a wire bent in sinusoidal manner. The stops must contact with the upper

teeth at the selected OVD

- A thick mix of viscogel is then placed around the rest of the lower special tray, distallyand mesially to the occlusal pillars. The pt. is then asked to talk, swallow, drink some

water etc. After 5-10 minutes the set impression is removed from the mouth and

examined. The viscogel material will have been moulded by the pts musculature into

a position of balance. (Polyvinylsiloxane putty)

- It will provide an indication of where inward-directed forces from the buccinatorsmuscles are equaled or neutralised by outwardly-directed lingual forces. (The

neutral zone)

Conventional technique Border mould each muscles alone

Admix technique Border mould the muscles all at once.We have to repeat

all the procedures if we failed to get it with one try
http://www.dentistry.bham.ac.uk/cal/impress/nz.htmhttp://www.dentistry.bham.ac.uk/cal/impress/nz.htmhttp://www.dentistry.bham.ac.uk/cal/impress/nz.htm


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- Indices are then constructed in the lab, by surrounding the impression with plaster.When the viscogel and the tray is removed, a gutter corresponding to the neutral

zone is left behind. The teeth may then be placed into the neutral zone.

- Resulting denture should feel more comfortable and be more stable and retentivebecause the denture should not interfere with or be displaces by the functions of thelips, cheeks and tongue. (areas of minimal conflict)

I complained to Imam Waqee of my weak memory. He advised me to abstain from sins;

Verily, knowledge is a light from Allah, and this light of Allah is not awarded to sinners.

Imam Syafie

Sorry if there is any mistakes. All the best to all of us!

Special thanks to Baraah and Zuhal.

Done by,

Siti Nurbaya Mustafa

prostho iv - lec 4 - impression making for complete dentures.pdf

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