prostho script 10

7/30/2019 Prostho Script 10

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Metal Framework Try IN

In this lecture we will talk about 2 topics: the 1st

one is, metal frame work try in

Its a very important issue for you as a dentist so please be aware.

You know that you need to take a primary impression, send it to the lab then you

will get primary cast you will make surveying on it and make the design, you take

the 2nd

impression send it again to the lab to make secondary or master cast.

In the lab they do the wax-up similar to your design then process it to get metal

framework part.

(1)

(2)


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(3)

(4)

(5)


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(6)

What we should do after delivering the metal framework from the lab?

The metal framework should be fitted to the mouthshortly after it is returned from the dental laboratory.

(if you try it after long time you maybe surprise bcz there is movement ofthe teeth or changes in the vertical dimension)

The practitioner must ensure that each framework fitsextremely well

Must be completely passive in the mouth. That mean youshould feel there is retention BUT there isnt any excessive

lateral force on the abutment teeth.

_ look to this picture


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In (A) its a good fitting framework on this tooth; the clasp and the reciprocating

arm are fitting in its true place. BUT in (B) they arent in their true space that

means we will end with lateral force affect the tooth, with time it may lead to

periodontal problems and may cause bone resorption, and the patient may lose

this tooth bcz of malfitting of this tooth.

Examination of Framework:

Was the proposed design closely followed?

1.major connector

2.the finish lines

3.rests been included

4.clasp assemblies present

5.Appropriate sizes, shapes, and position`~` you should make sure that the design which you receive is the same that you

make (the technetion should follow your design)

`~` Each part of the metal framework should be in its true place.

NOTE:

Before you try in the framework you should make sure that every thin is ok.

1-receve the metal framework from the lab

2- Examine the metal framework

3- Try in the metal framework on the master cast

4- Try in the metal framework in the patient mouth


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After you check the metal frame work you will try it on the master cast,(framework should fit tightly against the mastercast)

If everything is good until now, then you can try in patient mouth but before that chick it by

your hand and finger :

*** You should follow the following steps ***

1. Are the rests fully seated in their preparations?


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2. Are reciprocal clasp arms and/or lingual plating in

intimate contact with tooth surfaces?

3. Have finishing and polishing procedures been carried

out correctly?

We polish the polishing surface, the surface away from the tissue to prevent

food & plaque formation.


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4. Is the major connector sufficiently rigid?

To make sure for the rigidity of the major connector, you hold it and try to bend it

by your finger, if it bends easily that mean its a failure one and you should repeat

it.

****NOW TRY IT IN PATIENT MOUTH: ****

Clinical Procedures


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Now bcz of present of saliva and other component in the mouth, its difficult to try

in so, you can use Disclosing media.

You can spray or apply it on the fitting surface of the metal framework then you

try in the patient mouth, if there is any point prevent it to fit then the disclosing

material will remove from its place So its easy to use it BUT its a messy material

when it contact with saliva it dissolve.

You can also use a wax disclosing media its give you 3D presentation (height,

width and depth of the contacting point)

In this pic you notice that you soften it then you apply it as a thin layer on the

fitting surface.


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Then you put it in the patient mouth. Make sure that you apply the pressure on

the rest not on the saddle area. Bcz now there is nothing under the saddle area

and there is a space for the acryl so, if you press it then you end with false

pressure area (removed disclosing media).

After removing the metal framework from patient mouth you notice some metal

shown. So gently you can use several burs to remove the excess metal and polish

and smoothen it.

After that you will put a new layer of disclosing material and try it again until you

have a continuous layer.

The most common area that prevents the MFW to fit in its place is:

1- The root of the clasp (the sides of the rest).

2- The proximal part of the MFW.


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NOTE:

the guide plain should fit passively in its place it shouldnt apply any pressure on

the tooth. You can remove and apply it without harming the tooth.

Now if everything is good you can do some opposing occlusion,

to make sure that the MFW not interfering with the opposing dentition. Its done

by articulator paper. Chick centric and eccentric occlusion.

If you have both upper and lower MFW you should

start with upper and do the occlusion correction

then continue with the lower, then you put both of

them and chick the occlusion.


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IMPORTANT NOTES:

1) The reduction from the metal should not less than 1 mm.2) Corrective grinding procedures should always be performed with great care.3) Practitioner must avoid overcutting the metal surfaces.4) Thickness of the rest should be 1-1.5 mm.5) To measure the thickness of the MFW you can use the metal gauge.

`~` these steps take 10-15 min BUT with 5th year students its take 2 hr!!!

*NOW WE FINISH THE 1ST

PART OF THE LECTURE LETS START WITH THE 2ND

PART*

Special Impression ProceduresThe impressing material that we use is anatomical impressing, that mean if you

use alginate or rubber impression material you make a negative copy of the

anatomical structure in the mouth. Then you end with anatomical cast.


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The aim of special impression procedures is to take impression with slight

pressure the same as the normal functional pressure in the mouth. We dont face

this problem with the short span bonded area bcz the pressure will directly

transfer to the teeth, so, you can use convential impression procedure BUT in the

free saddle area we have a problem bcz the soft tissue move and compress so we

need to use thus special procedure. And its considering a stress area so, we need

to release this stress.

So, our Requirement is:

record the tissues under uniform loading distribute load over as large an area delineate the peripheral extent of the denture

Factors Influencing Support of the Distal Extension Base:

1.Quality of soft tissue covering edentulous ridgeA firm, tightly attached mucosa displaying moderate thickness

(2 to 3 mm) will offer the greatest support (more thickness moreneed for functional force).

2.Type of bone in the denture-bearing area


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Chancellous bone, as compared with cortical bone, is less able

to resist vertical forces.bcz its sharp so excessive pressure on it

end with inflamed tissue)

3) Design of the prosthesis.

4)Amount of tissue coverage of denture base, we try to covertissue as we can BUT we should avoid over extension.


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5)Anatomy of the denture-bearing area.Each denture base must be made to fit the areas that can serve as

primary stress-bearing regions. We use it to get primary support. BUT inthe maxilla these area are cover by a thin layer of mucosa.

In the maxillary arch we dont need to talk functional impression bcz the tissue is

favorable

In the lower the crest of the ridge are not favorable to be a denture bearing area

our aim from using the functional presser is to transform the presser from the

crest of the ridge to the buccal shelf area.


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Indications for special impression procedure:1. mandibular distal extension application2.a long-span anterior edentulous base (normally including at least

the six anterior teeth).

Impression Methods:

1.McLean physiologic impression2.Functional reline method3.Corrected cast procedure

(Selected pressure techniques)

McLean physiologic impression:

a dual impression technique Constructed a custom tray on a diagnostic cast, its only covering

the edentulous area.

A functional impression was made using this tray and a suitableimpression material hydrocolloid "over-impression

Could not produce same Functional displacement Generated byocclusal forces.(actually its a problem)


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We used ZOE or polysulfide or polyether or any rubber impression material.

I return it to the patient mouth using a perforated tray then I will get

an over impression.


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You notice in the picture (previous page) we have 2 colors the blue is the

functional impression and the white is the alginate.

McLean Dis Advantage:

clasps is sufficient :may result in compromised blood flowwith adverse soft tissue reaction and resorption of the

underlying bone

clasps is not sufficient: the denture base will be occlusallypositioned (premature contact)

Functional reline method Done after the partial denture has been completed (done at a

later date) but the maclean is taken during the secondary

impression.

Adding a new surface to the intaglio of the denture base(functional relying) we add the new layer to the fitting surface.

The partial denture is constructed on a cast made from a singleimpression with a soft metal spacer under neath to ensure auniform space for the impression material(we use the spacer tocreate a space for the relaying technique).

The patient must keep the mouth partially open to permitappropriate tissue control and visual assessment

We call it a dual impression technique bcz its use 2 impression material:

1- Functional impression material using functional pressure2- Statiical impressing material (alginate) which is taken during statics (pic-up impression)


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modeling plastic like a green stick is applied to the intaglio(fittingsurface) of the denture base

1mm of modeling plastic is removed from the intagliosurface and an impression is made by ZOE or any rubber

material.

Disadvantage:

failure to maintain the correct relationship between theframework and the abutment teeth during the impression

Failure to achieve accurate occlusal contact following the relineprocedure bcz its must take while the patient opening his mouth

so we cant control occlusion force.


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occlusal discrepancies must be corrected: slight: accomplishedcorrection directly in the mouth, majority of cases: remount on an

articulator.

Corrected cast procedure (selected

pressure techniques) we also, called it alter cast

technique bcz some alteration is done for the master cast during

this technique.

We adding an impression tray after the framework have been

fitted using a chemically activated or light-activated resin. we

use its impression only for the free saddle area.

Undercuts that would interfere with removal of the trayare blocked out


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separating medium is then placed

Tray is adapted to the master cast Boarders trimmed using a laboratory knifeand gently rounded the edge of the tray should be 2 to 3 mm from the depth of the

buccal vestibule


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Border molding for a corrected cast is basically the same as thatfor a complete denture covers

the buccal flange to the most posterior extent the lingual and distolingual flanges


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NOW we end with MFW, border molding and special impression, all of

these components are located in the free saddle area.

So, now we need to relief the crest of the ridge, we do that by

removing parts of the acryl, to make sure these areas not compressed

during this technique.

Also, to make sure that the tissue are relieved we make some pores to

get more retention.


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NOW after we finish we put it on the master cast but before that we

should cut the free saddle area from the master cast. So, its called alter

cast technique. (We cut the free saddle area and place the new

impression structure)

NOTE: in this technique we use the normal impression to make the

master cast, then we use the special impression to use it on the alter

cast.

DONE BY: Hebah ramadneh


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