prostho iv lec 4 impression making for complete dentures pdf (1)
TRANSCRIPT
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IMPRESSION MAKING FOR COMPLETE DENTURES
Zuhal Syuwa Mohd Yasin &
Siti Nurbaya Mustafa
Khalid Al-Hamad
20-10-2013
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, u’ll 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 technique Records impression in a condition that assumes under the masticatory load
2) Mucostatic/ non pressure Records the impression of the tissue in an anatomical form without pressure
3) Selective compression technique Records impression with more compression on the tissue on certain selected areas on the others.
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 it’s too large,
it will disturb your sulcus area. While if it’s too small, the tissue will collapse and your impression of
the sulces will not be accurate. And i’ve 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 pt’s mouth.
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 under
extended 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 and
because it is elastic, it will be okay with undercuts. But, however, silicone can’t 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 isn’t 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 it’s unstable because it’s hydrocolloids,
so, the humidity will affect it meaning that the alginate will be affected by air ambibition and
absorbtion if it’s 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.
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 . A
tracing 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 it’s non elastic. So
it’s 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 it’s 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 it’s 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 complete
denture, you will end up with flabby anterior ridge. When bone resorbs, soft tissue will have no
support and will end up flabby and that’s 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.
So, once again:
1) Starting with conventional technique, ensure that the border molding has created peripheral
seal.
2) Take the whole impression of maxilla using ZOE or PVS
3) 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 tray
5) 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 without
pressing 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.
ADDITIONAL NOTES 1) Displaceable, flabby area is usually seen on the anterior region of edentulous maxilla
opposing 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 to originl form, and CD fabricated from it will not accurately fit on the recovered tissues resulting 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 in mucostatic 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 Bara’ah and Bay (:
Done by,
Zuhal Syuwa Mohd Yasin
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 with
because the sulcus is shallow and there is
no ridge for the denture to sit on.
Because it’s 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. Not
overextended 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
*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. is
functioning. (swallowing, moving the tongue around, etc.)
- design for patients with poor track records denture stability, a large tongue (tongue
expanded because patient has been edentulous for a long time) or other anatomical
anomaly.
(I’m sorry, I couldn’t 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 impression
compound.
- Model is poured. On this model, upper wax rims and lower special tray is
constructed.
- 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, distally
and 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 pt’s musculature into
a position of balance. (Polyvinylsiloxane putty)
- It will provide an indication of where inward-directed forces from the buccinators
muscles 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
- 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 retentive
because the denture should not interfere with or be displaces by the functions of the
lips, 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 Syafi’e
Sorry if there is any mistakes. All the best to all of us!
Special thanks to Baraa’h and Zuhal.
Done by,
Siti Nurbaya Mustafa