prosthodontics laboratory 8 (corrected)

8/11/2019 Prosthodontics Laboratory 8 (Corrected)

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Introduction

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 of

the RPD requires the use of colors.

As youll see, weve added lots of pictures for each case . But the pictures

are showing the patient's 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 and choose the most

appropriateone for your case, you have to know all the components of the partial

dentures. In the clinics there is an examination sheet containing all the details

about different components of the partial denture design (ex. rests, clasps, missingteeth and other details). It's a two dimensional representation of a three

dimensional design, it should include all the information in the patient mouth and

not only the ones that can be seen on the cast (such as teeth mobility, depth of the

sulcus, opposing teeth, type and location of restorations on teeth, shade of teeth),

these are major aspects a dentist must consider during construction of an RPD.


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A systemic and initial sequence should be followed in making the design

(Acquiring the 2D information):

1- Determine missing teethand which teeth are going to be replaced, (not all

teeth should be replaced). explain when teeth are not replaced-2-

Outline the saddle area.

3-

Determine the location and type of reststhat aid in supportwhen forces are

directed toward the tissues. ( rests provide support ).

4- Determine the location and type of direct retainers(clasps) that aid in

retention when forces are directed away from tissues. (Clasps provide

retention)

5-

Choose the appropriate major & minor connectorsto connect all previous

components together.

6-

Double check to make sure if your design requires indirect retention,

sometimes the design might not need an indirect retention.

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 mouths are with

movable soft tissues , mobile teeth, restorations ,crown and bridges .So itsonly

good as an initial design .


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In addition to the initial sequence, there are also other steps we can follow

(Acquiring the 3D information):

1- First, I need to Survey the cast to determine:

a) Where the survey line lies on the teeth.

b) the favorable and unfavorable undercuts.

c)

The position of the undercut whether it's mesial or distal, for the clasp

assembly. (ex, what's the point of bringing the clasp down from the

mesial to the disto-facial surface if it has no undercut there)

2- Check the opposing teeth to see if the occlusion allows me to put a clasp on

this site or not, because sometimes there is no enough room for it , or the

occlusion is not favorable ( there is super-erupted teeth there ) .

3-

Determine the functional depth of the sulcus.

4- Look out forCariesor restorations(according to the type of restoration you

either put a rest or not, ex, Composite and GIC can't hold rests so we dont put

rests there, However, in amalgam you can put a rest if only 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 , and on the crown

you can put the rest (the crown has metal inside it which is better to go with the

metal of the partial denture and the metal is the part of the crown that should

be in contact with the rest not porcelain)

The sequence of surveying :

1- Anterior-posterior Guide planes

2- Laterally retention

3- Make sure there are no interferences soft

or hard.

4- Check esthetics


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5-

Periodontal health of the toothMobility (grade I,II,III ) the amount of

incorrect 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 but if you decide to use it youll have to plan for failure

Grade 3 : severe buccolingul movement greater than 2 mm with (severe

movement) vertical depression ( comes up and down ), needs to be

extracted).

6. Check if there is gingival inflammation. (bleeding on probing)

7. Crown to root ratio, in some cases there is gingival recession, and just 1/3 of

the tooth is inside the bone but the rest of it is 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 called Planning 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 losehis 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).


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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 thatthe metal will reach anterior teeth, when the teeth are extracted you can send it to

the lab and attach teeth to the original prosthesis, this is called Designing for

change or designing for failure.

After acquiring information about your case, combine the 2 previous sequences (

both 2D and 3D information ) and see how the 3D affect your initial design and

modify it or refine it, also check 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 these classifications represent the number of missing teeth

which 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 IIIand short class IV

Tooth-Tissue borne:Class I, class IIand 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.

Classification


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2-

Toward the tissue which requires support/rests

You 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 designs? Class III designs.

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

designs .

1-

Kennedy class III: usually requires Quadrilateraldesign.

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 ) .

1

2


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Depending on the length (extenstion) 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 as in long span class IV it's like a reverse for class I so it will be a bilateraldesign. So its either bilateral or quadrilateral depending on the length.

By looking at Kennedy classifications and knowing whether its 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 means 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) Extra oral rests:

1-

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

bounded saddles)

RPD Components

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- Or Away from edentulous space (in distal extension)

Occlusal rests are not estheticbut 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 goodrelation with opposing teeth. (image 7 ) .

2- Cingulum Rests: are on the lingual surface of the tooth. They are good abutments

on 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 not

esthetic 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 resort.( image 9 ) .

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

them in this semester.

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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 tissuewhile the front area which is the teeth is having a less movement,

the difference in the amount of motion creates an

axis of rotation .

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

and itsmy 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 , Id

choose 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 mesiolingual

undercuts.( 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 hygienic

3- the tooth has to be tall enough to compensate

with it

1

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4-

Itsdifficult to adjust inside the patient's 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

undercu

t is

located

on thedistobu

ccal

surface

of the

tooth

,the rest

will be

on themesio-

occlusal

surface

and the

retentiv

e arm

will be

on the

buccal

surface

and the

reciproc

al arm on the lingual surface of the toothsimple circlet circumferential clasp

(image 13 ).

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However if the undercut is on the 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 mesial and go around the tooth until I reach the mesiolingual

undercut .( image 14 )

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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 attachedto it plus a

normal survey

line with simple

circlet clasp (

like image 16).

( look image 17

from here )

when the patientbites down I

don't need

retention ,I need

support ,the soft

tissue will be

compressed ,but

the rest will not

compress , itwill 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 if he is extracting 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

1 = Fulcrum axis

2 = rotation axis

*Notice how the movement of arrow 4 will make the

clasp harm the tooth as if its the patient extracting hi

Tooth-tissue borne

1

1 = Rest

2= Guide plane

3= I-bar

RPI

1

1


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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)

Where is the

fulcrum axis?

When the patientbites down he will

continue closing

until he finds a hard

thing on the tooth

which is the rest, so we moved the fulcrum axis and not like the previous example.

1 = Rest

2= Guide plane ( short )

3= I-bar ( retentive arm is mid-fiacilly )

4 = soft tissue

5 = survey line

6 = undercut

RPI

RP

*Notice the direction of the clasp in arrow 1 and hit moved down and not harming the patient when

close down

2


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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 designin 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 Kradovichwhich is to put the tip distofaciallywhichwe don't follow.

2-

RPA Design: it's

similar to RPI but A

represents Aker

(occlusally

approaching clasp)

which is connected to

the guide plane not

the rest.When the

patient bites down the

clasp will go down

RPA

1 = rest

2 = guide plane

3 = Aker ( occlusally approaching clasp )

* Notice how the Aker is connected to the guid

2


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because it's below the fulcrum ,so it's an acceptable design but it's not esthetics

and the I-bar is much more flexiblebecause 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 therest 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),we said

that its fibrous not granular and the

cross 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 patient bites 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 * 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.

1 = rest ( notice its on the distal )

2 = wrought wire ( 0.8 mm )

3 = cast reciprocation ( bracing arm

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

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

TYPE INDICATIONS

Lingual Bar 1-

If the functional depth of the lingual sulcus isgreater or equal to 8 mm.

2- First choice for tooth-borne RPDContraindicated in the presence of

mandibular 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 andadditional indirect retention is desired.

Double lingual Bar

(Kennedy)

1-

When contact with remaining mandibular

anterior teeth is indicated but open embrasuresexist.

Labial Bar 1- Mandibular teeth are severely inclined

lingually.2-

Large lingual tori that cannot be removed.

3- Labial Vestibular depth should allow superiorborders to be at least 3 mm below the gingival

margin.

Ma or connectors

2


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First choice is lingual

bar the bar itself is 5mm

and I need 3 mmbetween the bar and the

soft tissue of the free

gingival margins and I

also need 1 mm below at

the bottom where the

sulcus 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 not

possible then extend borders into the cingulam.

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.

TYPE INDICATIONS

Lingual bar 5

1 mm

3 mm

1 = suclus

2= lingual bar

3= free gingival margins

TOTAL = 9

8 MM


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Midpalatal Strap 1- Tooth-borne RPD when posterior teeth are

missing.

2- (may be used for tooth-tissue borne RPD when

minimal 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 when

replacement 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 requiredor not acceptable for the patient.

Provides great support than previous designs.

Complete (full) palatal

plate

1- Long span bilateral tooth-tissue borne RPD with

or without anterior tooth replacement.2-

Whenever maximum muco-osseous support is

desired.

Cannot be used in presence of torus.

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

Should be avoided as possible

Anteroposterior palatal

Bar

1- When anterior and posterior abutments are

widely separated.2- Short span class III replacing one or two teeth on

each side.

NOT first choice in maxillary major

connectors.

Contraindicated in patient with reduced

periodontal 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 inter-occlusaly)

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) In bounded areas:

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

Indirect Retention


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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 onthe denture or the seating force, but

now Im interested 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 the clasp, 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 forwardand 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 edentulous space

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

INDIRECT RETIENTION . (image 25).

notice in 1 which is the clasp , how w

have an axis of rotation as in 2 . And

notice how the denture is rotating is i

2

Notice here how we extended th

denture as in 1 . Notice the anteri

tooth as in 2 which we put on it a r

as in 3 that worked as an indirec

retainer

2


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Kennedy class I and class II and long span class IV always need indirect

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

you have to put indirect retainer.

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 duringdesigning 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 the

examination 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 on

the 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

2

2

2


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surface (marked with a small point at its end).(image 29).

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 commonlyuse 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 3rdmolar) 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 IIImodification 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

3

3

3


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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 rdmolar

,since it's already there then the problem is solved , I just need to put a green coloron it to indicate its an indirect retention .(image 32).

So first as we said were going to color the primary

abutments with the color yellow. ( image 34).

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 ) .

3

3


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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 the cingulum not on

the mesial or distal. (image 35).

After that we mark the edentulous 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 I

have 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

cantput 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 contouring

or adding materials to the tooth or even drill a

small cavity (0.5 mm) and this is called

DIMPLE inside the tooth in the other areas of

the tooth where there is no undercuts BUT this

3

3

3


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is usually not a very good idea and I have to avoid it and make it my last

choice.

So lets see what other options I have here, simple circuit( image 38 )? I cant

use 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 anditll 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 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 functional

depth there is 6mm I can placean 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 problems rise:

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Now after Ive put the major connector, I want to refine my design, at the left

side 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 eitherremove 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.

Another thing is that the lingual plate covers the right canine

now 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 5mm

for the plate, in this case probably not because itll become toocrowded 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 that

space and now its covered withlingual 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, and

as we said we already know that we need indirect retention . ( image46 .


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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 edentulous area so I have

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

edentulous 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 canineIm going to put a gingivally 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

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premolar on the left I added RPI system also . ( image 49).

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 of

the distance from the crest of the ridge to the

mid-palatine raphe. (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 answerwould be. As we know from the mid material its goingto 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 would rather

stay away from the gingiva and just put a finger or arm ( of plate ) on thereciprocating arm and continue 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

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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 .

As always we start by identifying the primary

abutments and coloring them yellow.( image 55)

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Keendy class 1 . With 5,6,7 and 8 missing on the right and 4,5,6,7

and 8 missing on the left . functional depths as in image 54

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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).

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 saidits a wrought wire and cast reciprocation on

the 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 1/3at 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 functional 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

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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.

prosthodontics laboratory 8 (corrected)

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