Prosthodontics Laboratory 8

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Prosthodontics Laboratory 8 : Design principles or RPD .

Done by : Enas Salameh and Osama Yousef .

A few notes before we get started:

Please make sure to download this script and view it digitally, the design ofthe RPD requires the use of colors.

As youll see , weve added lots of pictures for each case . But the picturesare showing a patient mouth remember we dont do the design process

inside the patient mouth this is only for educational purposes.

Always refer to the pictures.

In order to make the design for the partial denture that you are working on as a

dentist, you have to know all components of partial dentures in order to choose the

most appropriate one in its specific location. In the clinics there is an

examination sheet (that contains all the details about what different componentsof the denture design are going to be (rest, clasps, missing teeth and other details).

It's a two dimensional sheet that represents 3-D design, you should include all

the information in the patient mouth and not only the ones represented on the cast;

such as teeth mobility, depth of the sulcus ,opposing teeth , type and location of

restorations on teeth , all this information are important for the design and for your

choices that you will make


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There is a general and initial sequence that we should follow when making the

design (Acquiring the 2D information):

1- Determine missing teeth and which teeth are going to be replaced becausewe don't replace all the missing teeth2- Outline the saddle area.

3- Determine the location and type ofREST for support when the patientcloses his mouth. ( support = rest )

4- Determine the location and type ofdirect retainers (clasps) for retentionwhen the patient opens his mouth. ( retention = clasps )

5- Choose which major and minor connectors are most appropriate toconnect all previous components together.

6- Double check to make sure your design requires indirect retention or not,sometimes the design might not need an indirect retention. Other times and

might need it.

7-Refine the design.If you follow this sequence you will end up with a good design.

This sequence is the simplest and initial sequence for making a design and it

doesnt take into account a lot of other information.

It works well on a piece of paper assuming that the patient is (2-diminsional) ,but

patients are living people with movable soft tissues , mobile teeth, restorations

,crown and bridges .So its good for my initial design .

So , in parallel with the previous sequence there are also other steps we can make

(Acquiring the 3D information ) :

1- First, I need to Survey the cast to determinea) I need to know where the survey line is on the teeth.b) I need to know the favorable and unfavorable undercuts


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c) I have to locate the undercut whether it's on the mesial or the distal,what's the point of bringing the clasp down from the mesial to the

disto-facial surface if it has no undercut.

2- Check the opposing teeth to see if the occlusion will allow me to put a clasp onthis site or not, because sometimes there is no enough room for it , or theocclusion is not favorable ( there is super-erupted teeth there ) .

3- Determine the functional depth of the sulcus.4- Caries orrestorations (according to the type of restoration you either put a

rest or not ,in composite and GIC you can't put a rest there ,However, in

amalgam you can put a rest when the remaining thickness of amalgam is 2 mm

,if it's less than 2 mm I can't put a rest on it because it will break down ).

In severe cases of broken tooth ,you can put a crown on it ,on the crown you

can put the rest (the crown has metal inside it which is better to go with themetal of the partial denture and the metal is the part of the crown that should

be in contact with the rest not porcelain )

5- Periodontal health of the toothMobility (grade I,II,III ) the amount ofincorrect movement of a tooth due to the surrounding periodontal disease or

gum disease , this classification with or without the disease :

Grade 0 : No apparent mobility (healthy tooth) Grade 1 : : buccolingual movement which is less than 1 mm ( minimum

movement) ,used for support but questionable to be used for retention(used wrought wire clasp on it).

Grade 2 : buccolingual movement that is 1-2 mm ( moderate movement ),not a good abutment. Some doctors wont use it for neither support or

retention and if you used it youll probably going to have to plan for

failure

The sequence of surveying :1- Anterior-posteriorGuide planes2- Laterally retention3- Make sure there are no interferences soft

or hard.

4- Check for esthetics


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Grade 3 : sever buccolingul movement greater than 2 mmwith (severemovement) vertical depression ( comes up and down ) (always we need to

extract them).

3. Check if there is bleeding on probing or not. ( gum inflamed or not )

4. Crown to root ratio, in some teeth there is much gingival recession, and just

1/3 of the tooth is inside the bone but the rest of it is all exposed which is not good

for support. Sometimes you may have a lower first molar that is weaker than

lower incisor.

For such teeth (mentioned above) it changes what type of rests and retainers I may

use ,and also sometimes I need to do something calledPlanning for failure.

Cobalt chromium RPD is a definitive prosthesis but not permanent, definitive

means that at this time this is the best prosthesis that you can provide the patient

with. But you know that for example within 5 or 6 years the patient is going to lose

his two lower central incisors. Then you have 3 choices:

1- After 6 years extract the teeth and make a new prosthesis.

2- Make a transitional prosthesis for the next 6 years (not a very good choice).

3- More intelligent option: design the prosthesis in a way that even though its

definitive but it can be modified later on.

So your first choice is to use a lingual bar for this case but because you know that

the two centrals will be lost later on, design the denture with lingual plate so that

the metal will reach anterior teeth, when the teeth are extracted you can send it tothe lab and attach teeth to the original prosthesis, this is called Designing for

change or designing for failure.

At the end of collecting information about the case that you have, combine the 2

previous sequences ( both 2D and 3D information ) and see how the 3D affect


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your initial design and modify it or refine it and you also have to see if the design

is hygienic , esthetic ,non-esthetic and so on.

Each design differs from

others, and we can't discuss

10000 different designs together, so you have to know the different component of

the design, their indications and contra-indications .However; the way to simplify

it is by having different classifications for dentures (Kennedy's Classification).

The use of classifications is important for communications between dentist-dentist,

dentist-technician, and this classifications represent the number of missing teethwhich is important as each type of group of missing teeth indicates a general type

of design, but they don't represent the access of rotation is it away or toward the

tissue.

The other type of classification is the type of support:

Tooth- Borne: Class III and short class IV Tooth-Tissue borne :Class I, class II and long class IV ( in very very

rare cases class lll )

There are two main movements inside the mouth:

1- Away from the tissue which requires retention.2- Toward the tissue which requires support/restsYou have to look at each specific case to know whether it requires direct

retention and/or indirect retention, and the type of support that it requires.

What is the simplest design? Class III designs.

Our next talk will involve talking about the most common and conventional RPD

designs .


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1-Kennedy class III: usually requiresQuadrilateral design.

this is Kennedy class III modification one, with 4

abutments ,the design is like a table with 4 legs

which is stable .For support and retention there are 4

corners, even if there were teeth instead of the

modification area I still want a quadrilateral

design ,and in very rare cases I may use a tripodal

design . ( see images 1 and 2 ) .

2-Kennedy class II :Like the case which we were working on in

lab,Kennedy class II modification one .

What type of design you probably have?

there are 3 abutments ,so it is called tripodal

design like a chair with 3 legs , it's acceptable

but not that much great .( image 3 ,4)

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3-Kennedy class I :Like a chair with two legs, the design will have two

abutments, you can balance it but if you use it too

much ultimately it will fall over.

This design is called bilateral design .because we

will have a rotation around this axis .( images 5 ,6).

4-Kennedy class IV :Depending on the length (extensive) of the

edentulous area it can be bilateral or

quadrilateral designs, because a short span

class IV will have 4 abutments, just like

tooth-borne prosthesis so the design will be quadrilateral design.

Where is in long span class IV it's like a reverse for class I so it will be a bilateral

design. So its either bilateral or qudraletral depending on the length.

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By looking at Kennedy classifications and knowing whether it's tooth supported or

tooth-tissue supported you can understand the general design that you are going to

have, but what complicates things is the modifications spaces and indirect

retention.

After talking a general idea about the design you should place rests, retention,

connect everything together, double check if you need indirect retention.

That mean I need to know denture components very well.

The next talk will involve rather a quick revision about the different components of

the RPD design.

A) Extraoral rests:

1- Occlussal Rests (mesial or distal ) :- Near the edentulous space (in

bounded saddles)

- Or Away from edentulous

space (in distal extension)

Occlusal rests are not esthetic but they are very good because they are near the

long axis of the tooth, they load the tooth axially, and you have to have a good

relation with opposing teeth. (image 7 ) .

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2- Cingulum Rests: are on the lingual surface of the tooth. They are good abutmentson canines, they are closer to the axis of rotation than incisal rests , more esthetic

than others .However, the problem is that we can usually place them in maxilla but

in the mandible there is not enough cingulum enamel to place it effectively,

sometimes yes but usually no.(image 8 ).

3- Incisal Rests: they are good rests but they are notesthetic and they are too far away from the axis of

rotation, the rest will come over the mesial or the

distal part of the incisal ridge .the are used on

anterior teeth which are not strong enough,and the

root of the teeth are not effective ,so this type of

rests is my last choice.( image 9 ) .

B) Inraoral rests:but were not going to talk about

them in this semester.

When the patient bites down or the denture comes away the clasps can do lots of

damage to the last teeth which are on the arch because the teeth move very little

and the tissue moves a lot. (The posterior area is having lots of movement ; hence

its the soft tissue while the front area which is the teeth is having a less movement

the difference in the amount of motion creates access of rotation .

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Which mean these last teeth will take on lots of load,

and its my job to take advantage of the natural teeth

and put a rest and clasp on them but its also my job to

design the clasp in such a way that theres a stress

release. So I dont want to burden these teeth , Idchoose between moving the denture ( falls out ) or to

burden these teeth Id choose to let the denture falls

because I dont want to lose these natural teeth due to

too much load.By StressDistribution:

1-Non-stress releasing :a) Circumferential clasp :1- simple circlet

(aker clasp),comes from the edentulous area

2-Reverse circlet (comes away from the

edentulous area)

b) Ring clasps: go all around the tooth especially with mesiolingualundercuts.( image 10 )

c) Embrasureclasps (two simple circlets) double Akers clasps. ( image 11)d) C-clasp (hair-pin clasp) (image 12) 1- difficult to fabricate

2-Not very hygienic3- the tooth has to be tall enough to compensate

with it

4- Its difficult to adjust inside the patient mouth ,any wrong move will destroy the clasp.

** Not our favorite choice but it's one of the

choices

Try to use the best choice, but sometimes you

have to go down till you reach the most

unaesthetic.

** Sometimes I can re-contour enamel to

change the survey line

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If the undercut is located on

the distobuccal surface of the

tooth ,the rest will be on the

mesio-occlusal surface and

the retentive arm will be onthe buccal surface and the

reciprocal arm on the lingual

surface of the tooth simple

circlet circumferential clasp

(image 13 ).

However if the undercut is onthe mesiolingual surface,we

use reverse circlet instead of

putting the rest on the mesial

I put it on the distal and the

clasp starts from the distal and

comes to the undercut, but the

other choice is to use ring

clasp .the rest is on the mesialand go around the tooth until I

reach the mesiolingual

undercut .( image 14 )

My choice to the clasp depends on type of support and the location of the

undercut on the tooth (mesial/distal , Buccal/lingual)

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2-Stress releasing:

In Kennedy class I, class II and long span class IV there will be rotation of the

denture, when the patient bites down I don't want the clasp to engage the tooth

so I use stress releasing clasps.

1. RPI clasp2. RPA clasp3. Combination clasp.4. Reverse circlet in rare cases.

Why the location of the rests and clasps is important in

tooth borne prosthesis and especially tooth-tissue borne

prosthesis?

In bounded saddle areas (tooth-borne) like the image

15, the rests will be on both abutments near the edentulous

area, the rest should be as close as possible to the area where support is needed and

where the load will be on. So if the patients bites down on the first abutment there

will be support from the rest on that tooth, and if he bites on the other abutment the

rest on it will provide the support too, and if the occlussal force is on the

edentulous area the support will be distributed to both rests.

In toothtissue borne prosthesis the

case is different .The following

example is wrong, we wrote it just

to show you why we don't put the

rest near edentulous area in tooth-

tissue borne dentures:

In this example the rest is near the

edentulous area and the guide plane is

attached to it plus a normal survey

line with simple circlet clasp ( like

image 16).

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( look image 17 from here )

when the patient bites down I

don't need retention ,I need

support ,the soft tissue will be

compressed ,but the rest will notcompress , it will take support

first after the tissue ,so what I

have here is a seesaw, the rest is

the fulcrum axis and a rotation

axis on the rest ,everything

behind the fulcrum is going to

go down ,everything in front

of the fulcrum will go up ,so when the patient bites down will be as he isextracting his tooth which is a bad design , and when

eating sticky food the denture will go up and the clasp

will go down ,so this system is bad .So the idea to put the rests near the edentulous area in

tooth-tissue was bad, there are luckily other systems and

designs that will help me overcome this, lets check them

out :

There are multiple solutions:

1- RPI : instead of putting the rest mesially put it distally,with a guide plane and an I-bar. ( image 18 , 19)

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Where is the fulcrum axis?

When the patient bites down he

will continue closing until he

finds a hard thing on the toothwhich is the rest, so we moved

the fulcrum axis and not like the

previous example. And as you

know anything behind the

fulcrum will go down, in this

case its the I-bar clasp. And

ofcoruse anything in front will

go up.( image 20 ).

In other words the RPI will

remove the stress from the tooth that's why it is a stress releasing design, the

clasp will move away from the undercut.

When I don't want retention the clasp goes down when I need retention the clasp

becomes engaged .so it's a good clasp.

For RPI we have to two ways to build the design:

The first one is called Kroll design in which we have short guide plane(1/3 or 1/2 of the occlussal gingival height of the tooth) ,and the retentive tip

is mid facially or slightly mesiofacially ,

The other design is Kradovich which is to put the tip distofacially which wedon't follow .

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2- RPA Design: it's similar toRPI but A represents Aker

(occlusally approaching

clasp) which is connected

to the guide plane not therest .When the patient bites

down the clasp will go down

because it's below the

fulcrum ,so it's an acceptable

design but it's not esthetics

and the I-bar is much more

flexible because it's longer

and it won't hurt the tooth that much .( image 21)

RPI is better than RPA but they work by the same mechanic in which the

rest is found mesially and the clasp disengages when the patient bites and

the clasp engages when the mouth is open. (images 18 , 19 and 21)

3-What if I cant put the rest on the mesial and I

need to put it on the distal? I should think of

something that will provide some retention and

at the same time it wont hurt the tooth.

Ill change the material of the clasp ; Ill use a

wrought wire (0.8mm) , cross we said that its

fibrous not granular and the -section is circular ;

these proprieties gives the wrought wire its

flexibility . ( image 22).

We put a bracing arm on the lingual which is cast reciprocation, when the patientbites down it will engage the tooth but the amount ofengagementminimal. So if

I had to use the rest on the distal Ill follow up this concept which is called

combination clasp, 0.8 mm wrought wire and cast reciprocation as a bracing arm

on the lingual which will certainly give me the minimum amount of engagement *

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between the clasp (wrought wire ) and the tooth , keep in mind this is not my first

choice .

So as a general rule : I bar first choice, and RPA wrought wire (combination ) 2nd

choice , RPI is the best choice in esthetic and flexibility

The next compound that were going to discuses is the major connectors.

Superior border should be at least 3 mm from gingival margin.

If 3 mm is not possible then extend the borders into cingulae.

TYPE INDICATIONSLingual Bar 1- If the functional depth of the lingual sulcus is

greater or equal to 8 mm.2- First choice for tooth-borne RPD Contraindicated in the presence ofmandibular tori.

Lingual Plate 1- If the Functional depth is less than 5 mm.2- When future loss of natural teeth is anticipated .3- If lingual tori are present.4- Periodontal splinting of teeth.5- When posterior teeth have been lost and

additional indirect retention is desired.


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Double lingual Bar

(Kennedy)

1- When contact with remaining mandibularanterior teeth is indicated but open embrasures

exist.

Labial Bar 1- Mandibular teeth are severly inclined lingually.2- Large lingual tori that cannot be removed.3- Labial Vestibular depth should allow superior

borders to be at least 3 mm below the gingival

margin.

First choice is lingual bar the bar itself is

5mm and I need 3 mm between the bar andthe soft tissue of the free gingival margins

and I also need 1 mm below at the bottom

where the suclus is . This will gives a total

of 9 mm . Some might remove the 1 mm

below resulting in 8 mm total but 8 is the

minimal .( image 23)

General Notes :

They should be at least 6 mm away from gingival margins, if this is notpossible then extend borders into the cingulae .

Width of the major connector is proportional to the required support.

Palatal Bar anteroposterior width is less than 8 mm.

Palatal Strap anteroposterior width is between 8-12 mm.

Palatal Plate anteroposterior width is greater than 12 mm.

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TYPE INDICATIONS

Midpalatal Strap 1- Tooth-borne RPD when posterior teeth aremissing.

2- (may be used for tooth-tissue borne RPD whenminimal palatal support is required)

Anterior palatal strap

(Horseshoe)

1- Tooth borne RPD when anterior teeth aremissing.

2- When palatal torus can't be removed.*Contraindicated in tooth-tissue borne RPD.

Anteroposterior Palatal

Strap

1- Tooth-borne /tooth-tissue borne RPDs whenreplacement of anterior and posterior teeth is

required .2- If palatal torus cannot be removed.

Modified palatal Plate 1- Tooth tissue borne RPD.2- When complete palatal coverage is not required

or not acceptable for the patient.

Provides great support than previous designs.Complete (full) palatal

plate

1- Long span bilateral tooth-tissue borne RPD withor without anterior tooth replacement.

2- Whenever maximum muco-osseous support isdesired.Cannot be used in presence of torus.

Palatal Par 1- Short span class III replacing one or two teethon each side.

Should be avoided as possibleAnteroposterior palatal

Bar

1- When anterior and posterior abutments arewidely separated.

2- Short span class III replacing one or two teeth oneach side.

NOT first choice in maxillary majorconnectors.

Contraindicated in patient with reducedperiodontal support.


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In Summary : In the mandible ,I need 3 mm distance between the major connector

and the gingival ,but if I don't have this 3 mm I use a plate that cover the cingulum

and I have to use a plate instead of a bar .

In the Maxilla, I need 6 mm between the major connector and the teeth.

In both maxilla and mandible, the distance between two adjacent minor connectors

should be equal or greater than 5 mm I leave this space because self-cleansing and

hygienic reasons, but if the distance was less than 5 mm I should cover

everything using a plate.

Lattice Meshwork (more room for teeth interocclusaly) Metal base (beads retention) provides best type of retention but it can't be

relined, so it's usually good for small spaces (e.g. a bounded area consisting

of only one tooth ) .

Now we turn out attention into another subject which is indirect retention.

A) I the bounded area:

If there is a bounded area, what stop the movement of the partial denture upward

are the direct retentions (retentive arms of the clasps) on both abutments.

B) In the tooth-tissue borne:

Well do as we did earlier Ill put a bad example just to show you a few concepts:


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If you look at the picture (24) you can see we

have a free end with no teeth, we have a rest

and clasp. So far weve talked about how we

are handling the load that is acting on the

denture or the seating force, but now Iminterested in knowing how the denture will

react against the displacing force (retention).,

so lets say that there is a displacing force

coming on the denture (a force that is acting

on it maybe from the patient or anything

else)? the first thing that is going to stop it

from going up is the clasp tip so the axis of

rotation is now not on the rest but on theclasp, this axis of motion is causing a

movement in the denture and although the

clasp is preventing the denture from going out

(support) its creating a rotational motion in

the denture.

What should I do to remove this axis of

motion on the tip of the clasp thus removing

this unwanted movement? What Ill do is that

I extend the partial denture forward and

putting a rest on the tooth that is in front

of that point. ( image 25)

Now if it tries to rotate, the rest we just added will prevent this rotational

movement and because it provides retention far away from the edntuonlus space (

or in the other side of rotational axis ) and because its not a clasp it is called :

INDIRECT RETIENTION . (image 25).

Kennedy class I and class II and long span class IValways need indirect

retention, plus in rare cases in class III where there is no retainer on one corner

you have to put indirect retainer.

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Now that we nearly finished the theory part of this lab , were moving into a much

easier subject which is the design

Advice: Solve as many designs as possible, the more designs you work on the

better

There is a color coding that you have to follow during

designing the denture (it may differ from one book and another

but this one that we follow in JUST):

Abutment selection -------------(Yellow) Missing teeth ---------------------(put an X ) Rests-------------------------------(Purple) Connectors ,major or minor ---(Grey) Direct retention------------------(Red) Indirect retention----------------(Green) Resin retention------------------ (Black)

Case 1: Maxillary arch with 3 missing teeth on both sides, the teeth

are (5,6 and 7) . Kennedy class III modification 1 , (image 26)

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The following data you have to write are found in the paper given to you earlier ,

above at the top of the page youll have :

First, determine the missing teeth and what type of Kennedy classification you

have

Kennedy class III modification 1 (write it down on the top of theexamination paper).

Determine what is the support classification (tooth-tissue borne or tooth-borne )

tooth-borne in this case.

In this case, where I should put my abutments?

They should be near the edentulous area, so the

abutments will be (4 and 8 ) on both sides and they

are sound teeth, so mark them with yellow color onthe paper .( image 26 ).

Second: Outline the saddle area. ( image 27 ).

Third: Determine the location of the rests (support)

with purple color .In tooth-borne design they should

be near the edentulous area like the picture ( 28), so

it depends on the space created by the edentulous

area.

Fourth: Determine the location and types of direct

retainers; the simplest clasp assembly is occlusally

approaching wrought wire (simple circlet clasp) ,so

you have 4 clasps, each clasp has retentive arm on

the buccal surface of the tooth (marked by an arrow

at its end) and a reciprocating arm on the lingual

surface (marked with a small point at its end).(image

29).

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Fifth, I need now to connect everything together

by choosing the most appropriate minor and major

connectors .for the minor connector as we have a

maxillary denture we commonly use meshwork that

will provide more room.( image 30 ).

For Major connectors it depends on how large the

edentulous spaces are ,in this case I have 3 missing

teeth on both sides and the abutments provide me

with support and I don't need additional support from

the major connector, so there will be 2 choices ,the

simplest one will be the mid-palatal strap which

should be 8-12 mm anteriposteriorly,if it's more than

12 mm it will become a plate . (image 31).

If the number of missing teeth on both sides is more

(like from canine to 3rd molar) then I can open up the

center and use anterposterior palatal strap.

Sixth, If I look at this design and draw an axis of

rotation ,and the denture tries to go up, the clasps

on the abutments will prevent this movement

therefore I don't need indirect retention on the

opposing side even though there is a rest there

anyway, that's why in Kennedy class III

modification one usually doesn't require

indirect retention .

But let's say that I can't put a clasp on the anterior

abutment on the premolar because of esthetic and

mobility reasons, I will still have 4 rests for support that's why it's called

quadrilateral design in term of support ,however; if the denture tries to come out in

this abutment ,I don't have a clasp that prevents this movement ( so here I need

retention ) so I must have an indirect retention (rest) on the opposing 3 rd molar

,since it's already there then the problem is solved , I just need to put a green color

on it to indicate its an indirect retention .(image 32).

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So first as we said were going to color the primary

abutments with the color yellow. ( image 34).

After that were going to put the rests mesially or

distally , depending as we said on the edentulous

areas . But NOTE the canine I put it on thecingulum not on the mesial or distal. (image 35).

Case 2: Mandibular arch with 4,5 and 6 missing on the right side and

5 on the left the functional depth of the sulcus lingually is 6 mm

,buccaly on the right side of the patient is 3 mm and on the left side is

6 mm . ( image 33 ) .

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After that we mark the edntonuls areas , and lets

assume we have an undercut that is 0.25 mm as in

the picture. ( image 36 ) .

( look at image 37 while reading this ) Now that Ihave support I look for retention and were going

to use a regular clasp and a reciprocation arm on

the right molar . On the canine what should I put

here? You might say I want to put an I-bar , but I

cant put it here in this situation because the

functional depth in that area is 3 mm and the

minimum for the I-bar is 4 mm and I also cant

use gingivally approaching clasp because of thedepth of the sulcus (3 mm). I can use an occlusaly

approaching clasp or wrought wire clasp. Well go

with the regular C-clasp (although its not good

esthetically )

On the left molar where I have an undercut on the

mesio-lingual what should I do? I have several

choices :

I can try and create an undercut by contouringor adding materials to the tooth or even drill a

small cavity (0.5 mm) and this is called

DINPLE inside the tooth in the other areas of

the tooth where there is no undercuts BUT this

is usually not a very good idea and I have to

avoid it where make it my last choice

So lets see what other options I have here, simple circuit ( image 38 )? I cantuse that here because of the undercut, what about reverse circuit (image 39)? It

actually works I can use it, but Ill have to change the location of my rest and

itll complicate my design. What are the other options? What about the ring

clasp? the ring clasp is very long as you can see , so we have two options for the

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ring clasp A) we put a rest on the distal and in

addition to the mesial rest ( two rests image 40 )

B) or we add something called strut or bracing

strut . ( image 41).

But probably the best choice here is to go with the

ring clasp with or without the

distal rest (the second rest).

What about the premolar, what

type of clasps Im going to put

here? Because the functionaldepth there is 6mm I can place

an I-bar ( image 37).

And now we need to combine

everything together, on the right side Ill put a lattice . and

on the left side where we only have one tooth its

preferable to put a metal base ( notice how we draw it its

very important) . ( image 42) .

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Now we need to select a major connector the function depth in the middle as we

said is 6mm, my first choice is lingual bar but with 6mm depth can we use lingual

bar? No, the next choice is lingual plate , and while using the lingual plate I have to

cover the cingulum for the teeth involved as in the picture ( 43 ) but note the

drawing is not very accurate on the cingulum .

With the lingual plate , two problem rise :

Now after Ive put the major connector, I want to refine my design, at the leftside where I have an edentulous area consisted of only one missing tooth and

bounded by the molar and the premolar. Weve put clasps on the molar and

premolar. But you have to know that when we have only one missing tooth

there is no need to have two teeth with both clasps, so now I can either

remove the I-bar from the premolar or the ring clasp from the molar as long

as one of them will still provide support for the missing tooth.

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Another thing is that the lingual plate covers the right caninenow you ask yourself am I going to avoid the lingual plate in

that area and make like a window ( or space ) or am I going to

cover it with the lingual plate ? What determine the answer is

that can I leave 3mm for the free gingival margins and 5mmfor the plate, in this case probably not because itll become too

crowded and itll be a fine space for sticky food to get into .

But remember sometimes I need to

create that space especially if Im

using the lingual bar. (Image 44 :

shows the shape of the windows if we

didnt put the plate on the tooth ) .

(Image 45: shows how we plated thatspace and now its covered with

lingual plate).

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Note the dr in this case didnt specify the functional depths just to

ease things for us.

Keendy class ll , mod 1 . With 4, 5 and 6 missing on the right and

5,6,7 and 8 on the left . This is as you know tooth-tissue borne, andas we said we already know that we need indirect retention . ( image

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We start solving this design as always , marking the

primary abutments yellow .( image 47 ).And then as always Im going to draw the rest for support

for the right side its a bounded eduntolues area so I have

to be near it . on the right however I dont have a bounded

edntolues space but I have a distal extension in this

case as you already know I have to put the rest

away from the distal extension which is on this

case the mesial.( image 48).

Now I look for retention , on the right canine Im

going to put a gingvally approaching I-bar or RPI

system ( again remember the dr didnt give the

functional depth to make things clear , dont bother

yourself with it ) I added a regular c-clasp for the

molar and for the premolar on the left I added

RPI system also . ( image 49).

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For the minor connectors were going to use

meshwork . An important note when drawing

the meshwork is that you have to draw it

probably it should go over just the crest of the

ridge and lingually it should be about 1/3 ofthe distance from the crest of the ridge to the

mid-palatine raphie . (Unfortunately the dr

drawing was very unclear in the demo , I

couldnt see his drawing , so stick with his

directions and the following drawing is not

that accurate : image 50 ).

For the major connector its probably either modified palatal plate or anteieor-

postieor paltal plate. The doctor asked what if I put a torus at the middle the answer

would be ? as we know from the mid material its going to be ant-post palatal plate

.And if the torus reaches the vibrating line we go with a horse-shoe . The dr added

a small torus at the middle and he went with the ant-post palatal plate.

Now a question rises, when putting the ant-post palatal plate , where should it meet

with the teeth ? Should I put the plate on the right premolar (meaning should I

plate the right premolar?) or I dont have to put the plate and let it be free on the

lingual surface with its reciprocating arm ? I can do either one, many dentist wouldrather stay away from the gingival and just put a finger or arm ( of plate ) on the

reciprocating arm and continuing the plate . (image 51 , notice how the plate is

coming out from the rest as an extension and the tooth is not plated ). On the

posterior as you remember I need to cross the midline at right angles , and I want

to cover as much of the edentulous area as possible . Another question rises, should

I put the plate on the lingual surface of the right molar or should I start the plate at

only the mesial surface at the rest? the answer is actually is to start putting the plate

on the mesial as long as I have a distance of 6 mm .( image 51 notice the red line is

the midline and the plate is with right angle to it.).

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Now lets evaluate the axis of rotation .

Remember this case is tooth-tissue borne

and to evaluate the axis of rotation putyour pen down on the paper , start from the

back where the distal extension is and not

where the bounded settle . After that start

moving you pen like the images ( 52 ) and

then draw the rotational axis passing by the

clasps as in ( 53).

Now you can see we have an axis or

rotation that passes from clasp tip toclasp tip . So what do I need on the

other side of this axis of rotation ? I

need a rest that is going to provide

me with indirect retention , luckily I

already have that on the right canine

. But now I have another problem,

what if the patient bites here (star

on image 51 ) what will happen tothe other side ? ( which is the right

canine ) the clasp will start harming

the tooth and tries to extract the

tooth as we said earlier , for this

very reason some dentist prefer not to put a clasp on that right canine or put a very

weak clasp ( wrought wire ) .

Remember that in tooth-tissue borne I care about both the forces that are acting

away from the tissue and toward the tissue on the distal extension areas. so inshort the axis or rotation should be looked at away from the tissue and toward the

tissue .

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As always we start by identifying the primary

abutments and coloring them yellow.( image 55)

And then as always were going to place the

rests, again notice how we placed the rest of the

right premolar on the mesial (away from the

distal extension area).(image 56).

Keendy class 1 . With 5,6,7 and 8 missing on the right and 4,5,6,7and 8 missing on the left . functional depths as in image 54

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After that were going to place the clasps ,

starting from the left canine where the

functional depth is 2 mm , I can add

combination clasp ( which we already said

its a wrought wire and cast reciprocation onthe lingual surface ) . On the right premolar I

can add an I-bar since I have 6 mm ( so Ill

put an RPI system here ) .(image 57).

For the minor connector , well go with the lattice

but notice we only draw 2/3 the way and leave 1/3

at the end as in the picture.(image 58).

Now whats my major connector ? as always my

first choice is always lingual bar , and because I

have 9 mm funcational depth at the middle and

lingual bar requires at least 8 mm in that case I

can place a lingual bar . Now on the right

premolar the question rises again , am I going to

put the plate on the tooth or extend an arm that

is attached to the plate ? Well in this case since

the premolar has a limited space ( it has 3 mm

but no 5 mm mesio-distally ) were going to put

the plate on it ( plate it ) . In the left canine I can

make an arm that is attached to the plate , there

is no need to plate it . Why ? because here the

canine has enough space and unlike the

premolar .( Image 58 notice how the canine is

not plated and the premolar is ).

~The end.

Done by : Enas Salamah and Osama Yousef.

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Documents

Prosthodontics Laboratory 8