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Metal Framework RPD.doc - MY TOOTHY by xiangpeng


									Our lecture today is about metal framework RPD and introduction to survey
in the previous slides (the last lecture)

Steps we do for metal RPD, Now a patient comes to your clinic, firstly we do
a history examination and diagnosis, hopefully if we need a refer, you refer
at this stage Ex. if there are composite teeth or periodontal disease
(gingivitis or periodontitis) you have to refer, don’t start taking alginate
(irreversible hydrocolloid) for primary (diagnostic cast) if the mouth isn’t
prepared, we have something called mouth preparation.

Mouth preparation is all other treatment have done and the last treatment
motility is the prosthodontics. SO,, Don’t do a partial denture if the patient
has active gingivitis why?

Because the prosthesis itself also will increase the gingivitis and we end
with severe gingivitis, always we need a prosthesis that maintains the
health of the remaining tissue.

SO we do history examination, if we need a refer we do, diagnosis and start
taking a primary impression by an alginate, don’t use for ex. Impression
compound because the patient has some remaining teeth, we can use a
rubber material for primary impression but it’s so expensive and the setting
reaction take 4-5 mins, on the other hand alginate 1 min (quick) and cheap

We end with primary impression , then we reach to (fabricate) the primary
cast , some cases you need to mount on the articulator to analyze the
occlusion , and some direct cases we have 1-2 teeth messing we don’t need
to articulator just hand articulation enough .

Then you do treatment planning for ex. Removable partial denture, then
you need to design the removable partial denture metal or acrylic, if it is
acrylic most of the time easy designing because the acrylic is tissue
supported and you apply clasps to abutment teeth (any abutment teeth
adjacent to the edentulous area should have clasps) we have clasps
according to the number of undercuts doing that after doing the survey line

So, again the steps mounting, treatment planning, surveying (because
without surveying we don’t know the location and the depth of the
undercuts) after this we design the RPD, we don’t design PRD before the
surveying. (The doctor explained this more & more)

We have metal acrylic RPD and acrylic RPD, so we have primary model the
next step if we need to mount on the articulator or if not it depends on the
case and the amount of teeth missing, then primary cast after that survey
the primary cast, then designing process after this step in metal acrylic RPD
we have to do tooth modification (not optional).

But in Acrylic RPD it’s optional we don’t do tooth modification if we have
suitable undercuts and if the teeth are not tilted most of the time we don’t
need to. In Metal acrylic RPD (metal framework RPD) because they are
components that need preparation on the teeth for ex. We have
component called rest and rest should have rest seat, rest seat is not found
on the tooth as anatomical structure so we have to do tooth modification
process called tooth alteration technique or tooth preparation for
removable partial denture, tooth modifications to guide the insertion of
partial denture.

So, we prepare undercuts if we don’t have or if we have deep make them
shallower and after this we prepare also seats for the rests.

One of the advantages in acrylic RPD we don’t need to do tooth
modifications , metal we need to do , at least if we have suitable undercuts
and suitable planes we need to do rest seats preparations .

After we do tooth modifications we take final impressions, final impressions
we can’t use zinc oxide eugenol why ? ? because this material is
contraindicated for dentate or partial edentulous patients this situation if
we need to take final impression for dentate and edentulous areas but
some time as in kenndy class I and class II we need to take an impression
only for the edentulous area , but general speaking the material of choice
is rubber materials like polyether , silicon rubber or polysulfide , the most
widely use is silicon rubber ( keep it ) mainly addition silicon ,mainly of
medium viscosity ( we have the viscosities heavy , putty, light ,medium ,
silicon rubber) .

We use for metal RPD secondary impressions we use the medium viscosity
additional silicon not condensational silicon .

Can we use light or heavy ?? yes sometimes we do combinations light with
heavy , light with putty but light alone not . Medium alone is the most
widely use .

If we ask ME (DR). I quote from the DR " I prefer the light with putty or
the light with heavy ,light because it’s more accurate for rest seats areas ,
undercuts areas and guide planes areas to become very accurate "

Now ,do we need all the time to take impression with a rubber materials ??

Ideally yes ;

 but sometimes we take it by alginate , to ME (DR) I rarely take by alginate
final impression for metal framework RPD Why? Because we now there is
many disadvantages of the alginate like synergies , imbibitions, distortion ,

tear resistance is low all of this can affect on the accuracy of the impression
, and one advantage over rubber that rubber is hydrophobic and if we have
not good moisture control of saliva lead to voids in impression , alginate
hydrophilic doesn’t care that much about saliva contamination or presence.
then we take final impression for final model , as I told you we have metal
framework and final model …….which type of gypsum ? dental stone or
modified dental stone (type III or type IV) and we don’t use type I or II ;
because they are weak .

we hope that gypsum can tolerate a high temperature of casting ,because
we have metal which going to be casting , so need this gypsum to tolerate
high temp. of casting that reach in Co-Cr sometimes to 1 thousand C degree

And the model can’t tolerate more than 150 C ,

So what do we need ?

We need to copy the secondary model into anther material that can
tolerate a high temp. ( the dr will show this demo in lab ) so we do
impression material to secondary model by rubber materials or agar agar
materials , and we pour this impression by special material ,investment
material that can tolerate high temp. of casting , So we convert the
secondary model to investment model and the process called duplication
process .

So we duplicate the secondary model into investment model to tolerate
high temp.

Then we make the wax up on the investment model and then casting , the
result metal framework for the removable partial denture .

Now , there is a clinical step , we do Try-In to the metal framework to check
all component of framework and the insertion .

Then we do jaw relation registration, can be needed at this stage also can
be 30: 00

Then setting of teeth ,after setting we do another Try-In for teeth in wax
and metal framework like CD we check phonetics ,aesthetics ….etc .

After this we do processing of acrylic and it’s converted into metal
framework RPD with acrylic teeth and acrylic denture base joining this
teeth .

The Dr discussed this briefly but every topic will be covered in the lab or lec.

And after this we need to review step , and review it isn’t optional step,
it’s compulsory visit .

Now the component of metal framework RPD we have :

    -   Supporting components
    -   Retentive components
    -   Reciprocating and placing components
    -   Direct retainers ( specially for class I and class II )
    -   Major and minor connecters
    -   Artificial teeth

Every partial denture should have all of these components , even direct
retainers although mainly in class I and class II but we can use it in class III
& IV to provide direct retention

Supporting component :

    - Saddle area : the artificial teeth and the acrylic joining artificial teeth
      are found there , And we have different designs of this area .

    - Proximal plate (guiding plate) : we have the proximal plate and
      guiding plate , proximal plane and guiding plane what the difference
      for the tooth is plane and metal is plate .

    - Major connectors : it joins all the component of the RPD together
      (right side component to the left side component )

    - Minor connector : it connects any component to the major connector
      , we have rest , minor connector and major connector ,minor
      connector joins the rest to major connector ,so any component join
      any component to the major connector it’s called minor connector .

    - Clasp assembly : should have rest for support , retentive arm for
      retention which engaged the undercut . and another arm which
      doesn’t engage the undercuts called reciprocal arm , so for every
      clasp we have 2 arms . in all the framework the only component that
      engaged with undercut is retentive arm .

    - And we have rests we named them according to surface for example
      rest on the occlusal rest we called them occlusal rest or on the
      cingulam of canine we called them cingulam rest .

     Supporting area we have rest ooclusal rest and incisal rest (on incisal
    edge of anterior teeth) , in acrylic RPD as I told you it’s mainly tissue
    support , but sometimes we have also achieve some clasps on teeth or
    rest .

    In metal framework we have teeth –supported as in class III or dually –
    supported (teeth and tissues) as in class I , class II and long-span of class
    IV , although class III is teeth-supported and in maxillary we have tissue-
    supported from the major connector but the main support from the
    teeth, we don’t called tissue – supported it’s an extra support from the
    tissues but the design is called teeth-supported .

    In lower (mandible) because the major connector has small surface area
    we don’t rely on connector to provide support also the main support is
    achieved by rests , and if it’s dually supported by rest and denture bases
    (saddle areas ) but not from major connector

    Retentive component mainly clasps and we have 2 types of retention in
    metal framework :

    - Retention by friction ( not common)
    - Retention by clasps

    Sometimes we make crown for the patient in the crown we incorporate
    a component or sleeve called matrix which can provide retention for
    the final denture , we have component called Matrix and component
    called patrix called male-female components

    So we have the patrix fitting on the matrix without need for clasps called
    attachment , semi- precision attachment or precision attachment
    depends on the case.

    Sometimes we make clasps for Ex. on the canine , if the canine need to
    crown , we can make space on the crown and then the patrix will fit in

    this space , this will provide retention ,stability and support without the
    need to clasps and this it’s called attachments .

    Now if there was machined called precision attachment

    And casting called semi-precision attachment , because it isn’t 100%
    accurate .

    Advantages of attachments mainly is elimination of clasps , so you can’t
    see metal .

    But the disadvantages:

    1- they need crowns on teeth that extra cost

    2- complicate procedures

    - difficult to repair and place-

    - and least defective on teeth with short clinical crowns because they
    need minimum to 3-4 mm, so if we have small crowns there is a
    problem .

    We don’t have specific component for bracing (stability) but any
    component that rigid and prevent lateral and rotational movement of
    the partial denture during function called bracing component like major
    connector, minor connector, and reciprocal clasps.

    Major connector that connects all the parts through minor connector.

    Lastly, we have the teeth and bases

    We need to know how to design RPD acrylic or metal we need to survey

    Surveying to determine the undercuts, no way to design RPD specially
    metal without surveying.

    The main step before designing is survey to know the location, the
    depth of undercut or if we need modification of the teeth or not.

    So survey is compulsory step.

    Sometimes we do double survey one before designing process and one
    after, for primary model and for master model just to confirm your
    design. Ideally should do double survey.

    We can skip one that relate to master cast but for primary cast it is
    compulsory. at the end you need to have a marker any area are apical to
    survey line called undercut and this is what we need to block or you
    need to relief to retentive arm of the clasp, proximal undercuts if deep
    we need to block them, buccal undercut we need them for retentive
    arm of the retention, lingual undercuts sometimes we block them it
    depends on the case.

Surveying is diagnostic procedures we need it for diagnosis and to design
   the removable partial denture, also you need to know which undercuts
   we need to block.

The components of surveyor are:

    1- Undercut gauges usually 0.25, 0.5 mm and 0 .75 mm or 0.1, 0.2, 0.3
       inch, this gauges determine the depth of undercuts.

    - How do we know if it is 0.25, 0.5 or 0.75 mm?
       On every undercut gauges there is strip and line, 1 line means 0.25 2
       lines is 0.5 or 3 lines is 0.75 mm
    2- Chisel which we need to block the undercuts.
    3- Analyzing rod which we need to analyze the undercuts to see the

     4- Grafting marker which we need to draw line on the cast after we use
        the analyzing rod
     5- And the survey itself has disks , arms , adjustable arms ( that you to
        go where ever

     And we need to do survey on abutment teeth or another teeth or
     sometimes edentulous areas because some edentulous areas are have
     undercuts and we have to block the undercut area.

     so the survey not only for the teeth but also for edentulous area .

                              THE END
 Done by : Bara’ al –sahra’a


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