Prostho Lec 5

7/29/2019 Prostho Lec 5

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Minor connectors & Rest and Rest set

Today we will continue talking about the parts of the (RPD) and we talk last time about major connector

and how to design a partial denture which is the most important thing you should learn in this course

because your job as a dentist is to design the denture and to make sure that the technician made it

properly.

We are going to talk about two things: Minor connectors & Rest and rest seat.

*The minor connectors: essentially they are considered the extension of the major connectors, and they

connect major connectors to other components of the denture, the major connector is like the vertebral

column and the minor connectors are like the limps.

*Rest and rest set:

rest: it is the part of the metal frameworkthat sits on the top of the teeth.

Rest set: it is the area of the tooth that accepts the rest.

Minor connectors have many functions:

1- Joint everything together.2- Stress distribution ( like any connectors)3- Maintain the path of insertion.

Anything that have a contact with the teeth helps provide a path of insertion whats the meaning of this:

the space between the teeth is limited and when we place the partial denture we dont want it to fall in

any direction, you will see that we will prepare the teeth we trim the enamel in a strategic way so that the

partial denture slide in its place.

If I had two teeth adjacent to each other a class 3 partial denture I will have an undercut from both

sides, so what I do is prepare a parallel surfaces I will sacrifice a small amount of the enamel to create a

mutually parallel surface.

Types of the minor connectors:

Four basic types:

1-Proximal: Guide plane2-Embrasure: Connects to auxiliary rest3-Retentive: For denture base, denture base retention - gridwork4-Approach arm: For gingivally-approaching clasps


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In the picture you can see a part of the metal

framework that connect the rest to the major

connector (A) and it runs between the teeth

at the embrasure on the lingual side this

type of minor connectors is called Embrasure

minor connector, if you see here at the distal

side of the premolar (B) we have a rectangularpiece of metal that contact the distal proximal

of the tooth where the partial denture goes in

and out it will slide agents the prepared distal

wall of the tooth it is called a proximal plate

or a guide plate, just like we have a rest and

a rest set we have:

Guide plane: on the tooth.

Guide plate: on the metal frame work.

You can see a network of metal (C) this will be pared inside the acrylic it will help hold the acrylic to the

partial denture this is called Retentive minor connector.

You have made a C shape clasp in the lab thats the first type of clasps (hand made) the other type of the

clasps are caste as a part of the metal framework and it may be above the survey line or below it in the

next lectures you will know more about it and thats the fourth type of the minor connectors which are

Approach arm.

*A* Proximal minor connectors (Guide plane):

which are essentially extension of the guiding planes, they are rectangular in shape, theredimensions is from 1.5mm to 3mm in height, it tapers towards occlusal so it dont interfere with

teeth that they are going to sit on, so its not even in thickness its thick at their base and as you go

up it will become thinner, they often the origin for rests and/or clasps, and its shifted slightlylingually to: Increases rigidity, Enhances reciprocation, Improves esthetics.

*Here we can see a guide plate and

its connected to a clasp and a rest.

*Here we have a guide plate that connected to

an anterior tooth like a canine, and as you see

its small, and does not extend to far labial or

buccal so it will be more esthetic.


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*here you can see the flat surface of this premolar and you can see this guide

plate will slide against guide plane on the tooth, and you can see the space

underneath the plate a triangular space this space is because the tooth is

egg shape and below the maximum bulging of it there will be an undercut,

if the metal goes in the undercut it wont get in nether out of it, so you have

to block out this space in the acrylic partial denture we block the spaces with

plaster, but in metal we will block it with wax .. And you will learn about it

later as the Dr. said, and because we block this space we will have a dead

space under the guide pate.

*B* Embrasure minor connectors:

which are essentially attached to the long rest or the lingual surface of the teeth.( like the proximal guiding

planes , only they run as fingers like projection for a major connectors to the rest on the occlusal surfaceusually in a place is not near the edentulous area , so if its near the edentulous area its called the

proximal minor connector, if its between teeth its called the embrasure connectors .

they are often associated with rests, but not clasps, it joins major connector at right angles, it contact

teeth above height of contour (survey line) which mean that there is a relief area, this relief placed so

connector not directly on soft tissue, it is triangular in shape in cross section and the tip of the triangle will

wedge between the two teeth and compress on the tissue, so we should free this area otherwise it will

harm the tissue, and weaken the teeth we may block it out, or we can trim the metal.

his is an example of an embrasure rest you can see

we have a rest here that its base minor connector

hould stay away from the gingival margin it should

be 5-6 mm in width and 4-5 mm in length as in the

picture,so it can have self cleansing and dont

ccumulate food, and you will know how to design

t later in this course.


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*C* Denture base renters (Gridwork):

The aim of the R.P.D is to have teeth and the teeth should have an artificial gingiva that made of acrylic, this

gingiva should be attached to the other parts of the R.P.D so we use Denture base renters, the main function

for them is to connect the acrylic to the metal (major connector), there is no chemical connection between

the metal and the acryl so it has to be mechanical connection, we will make spaces in the metal that the acryl

will go inside it and when it sets(polymerized) it will be fixed to the metal.

We have different designs ofDenture base renters we have:

1-LATTICE : its like a ladder ()

characteristics : large spaces, more bulk, more control, more work, (Superior retention) Interferes with setting

of teeth, and thicker metal .

2-MESH:its like network

characteristics: small spaces, flatter, potentially more rigid, easier for technician, more space for teeth, and

less retention for acrylic if openings are small.

LATTICE

MESH


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*Both of the two types sandwich the metal: that means we have acrylic on the top and in the bottom of the

metal so it would be fixed properly to it.

*we have a third technique which is the metal base with nail head we have thing is coming out from the

metal we have bead retention, nail head retention, usually when we check there shape, its just like a

Mushroom, so essentially we have an extension and the acrylic will go underneath these extension, and

usually there are amount of them, so if you look here there is a small ball on the metal:

Ifyou take a cross section thats what we will see : the acrylic will fit under these space , or in rare cases, I

actually can weld wires on the metal to improve retention


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* because the metal base with nail head has thin metal base its the most design that allow us to set the

teeth properly because we have good space to work with and the mesh is the second and the lattice comes

third according to teeth setting

*On the mandible the distal extension base:

-like connection for kindey class I & class II

_ Extend 2/3 of the way from abutment tooth to retromolar pad

_ Never on the ascending portion of the ridge only reach horizontal part

*On the maxilla :

_ Gridwork(minor connector):

2/3 ofthe length of from abutment to the hamular notch & we dont go to tuberosety .

_ Major connector:

extends fully to the hamular notch bcz on the end of tuberosety we cant place metal & acrylic bczits an area

where isnt much resorbtionbcz no teeth over there .

Bead, Nailhead, Wire Retention**

- Metal bases cast to fit directly to tissue

- Therefore, no relief beneath

- Projections provide mechanical retention for acrylic

- Improved oral hygiene; enhanced thermal stimulation; excellent for cases with limited interocclusal

clearance

**the disadvantages:"sometime the tissue of the patient change or I have error on processing my denture so I have to trim

it if my denture is mesh work or lattice work acrylic will touch tissue (plastic) so I can trim it easily buthere I have cobalt chromium its very hard also with time the patient will have residual ridgeresorbtion even he is partially dentate so I want to attach new acrylic as relining material but if the base is

metal I cant reline it "

- Difficult to adjust and reline; acrylic attachment is weaker than gridwork design

- Usually limited to short-span, tooth bound edentulous areas with well-healed ridges (which will probably not

require relining)

Facially just over the crest of the residual

ridge (extend labialy) why we dont reach

the sulcus? 1-bcz metal in sulcus will

interfere with setting of teeth

2-bcz acrylic translucent so metal will

appear (esthetic reason)

**so we provide more retention to acrylic

On class IV


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_ Mechanical retention of denture base resin

_ Allows the acrylic resin to flow under the gridwork

_ Relief wax is placed in the edentulous areas

_ 1 mm of relief

** how we do reliefing on the lab? By adding wax on the master cast where I want to relief then I make a copy

of the cast by using investment material ( a material that withstand high temperature so we can pour metal on

it) so all stone & wax will be converted to investment .

**the worse thing on mesh working & lattice working that they take up space but more easy to adjust .

*the dark grey metal frame work & light gray is acrylic & tooth on top acrylic go above metal & bellow it also

inside it the place where the acrylic meet the metal in the polished surface on the top we have something

called finish line (end line) junction between acrylic & metal called external finish line . the acrylic in the

fitting surface which touch the tissue (under surface ) also meet metal beneath the minor connector called

internal finish line .

Space where acrylic go in & above

Relief:* to make this space on patient mouth we

have to relief this area by using wax


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The finish /end line : its the Junction between acrylic and metal

Acrylic is not strong and to make it stronger we need to make it about 3 mm thick at least

(and we cant do that it will be so thick with the metal) , so we need to make the acrylic at

the right angle with the metal when possible ,, I should end up with a junction between the

acrylic and the metal at about right angle.

so well have two junction

external finish line(e) : the line where the

metal meet the outer polished side of acrylic .

internal finish line(i) : the line where the

metal meet the inner surface of acrylic ( that

touching the tissue ) .

We would like The external finish line to be 90 degrees but we sometimes make it at

slightly less than 90 degrees to give me some additional mechanical retention, to keep the

acrylic inside the metal ,so you can see this slight undercut which will help to keep the

acrylic inside the metal so we can make it 90 degrees or slightly less.


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The second is considered wrong why ??

Because its obtuse, you can see the acrylic here is thin , here is going to be thin , this is can

fracture and break.

Tissue stop

Which is a piece of metal that you put in your design in order to stand the pressure and

give support for the metal mesh work , preventing the metal from going down from the

acrylic .

When I do packing there is will be a heavy pressure on the metal , how can I prevent the

metal from going down ?? by tissue stop.

How do I create ?

In the wax Im going to cut out a square , the square will expose the tissue so the metal will

go into the square and it will give positive on the fitting surface of the metal.

Rest & Rest seat

You can divide the rest into : primary rest and auxiliary rest

the primary which we will talk in this lecture and the auxiliary which provide indirect

retention.


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or into : posterior rest and Anterior rest

Thats mean we also have occlusal rest, and for anterior teeth we have either : lingual rest,

cingulum rest or incisal rest .

the golden role is never make your rest seat in the dentin

when you make a rest you should prepare your teeth and cut some part of it to make a

place for the rest but remember that you should make the rest seat in the enamel and you

should not reach the dentin ( because it cant stand compression )

all acrylic dentures are tissue supported , because they have no extension on the teeth,

the patient bites down and the mucosa takes the compression and takes the occlusal load .

I want to take the support from something which is stronger , which is the teeth because

they are supported through the periodontal ligament.

periodontal ligament has an average thickness of 0.2 mm thick and its designed in a much

better pattern to withstand the occlusal force.

regardless if the denture is tooth supported or tissue supported I want to take the

maximum support from the teeth.

The purpose of the rest is to getsupportand something called indirect retention. how?

by directing the forces applied to the tooth axially not vertically , because the vertical force

on the teeth will result in moving the teeth and may cause trauma to it as well as the tissue

will get traumatic if the forces applied to it .

There are three main designs for the rests :

Occlusal rests used to premolars and molars (usually on marginal ridges)

singular restused to the canine ( specifically to the maxillary because mandibulars dont

have enough enamel )

incisal rests used to anterior teeth ( at the incisal edge of the tooth )


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*********** The requierments of occlusal rests ***********


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So usually we use the explorer to chick the rest seat angle and to be sure that this angle is

rounded not sharp )

So this is the conventional form, if I have an adjacent tooth , I can place rests on back to

back teeth. If there are no missing teeth or the rest between two teeth , I dont have to put

it in the middle I can place it further toward the lingual more esthetic.


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Back to the embrasure rest, it extend toward the facial and the lingual and you can see the

slight concavity to make room for the retentive arm thats going to the facial and the

reciprocating arm thats going to the lingual .

Cingulum rest : usually the maxillary canine is better than the mandibular one, why ?

Because it has a larger cingulum, so usually these rests are difficult to place in the

mandibular canines , in mandible sometimes we have to place incisal rests.

So the maxillary canine has thicker enamel while the mandibular one has less ! its aninverted v- shaped but its rounded its not sharp v , its almost semi lunar.

Its less than 90 angle , if I take a cross section bucco-lingualy you can see that the angle

is less than 90, I have a catch . the depth should be a 1mm deep so that I have enough

thickness of cobalt chromium, there should be no undercut when I do the preparation. If I

prepared it incorrectly, Ill end up with a rest thats too close either to the incisal edge or

to the gingival margin. So it just be above the cingulum.


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When we prepare this rest , it shouldnt interfere with the opposing teeth.

Now , what if I dont have enough tooth structure in the canine ?

Either I put a crown on the tooth then put the rest, or I stick the rest to the tooth using

composite sometimes bonded metal , its called Resin-bonded rest.

Here if you take a look to the lingual surface we actually stick a piece of metal here on the

lingual surface and in this way we can place rest on top of it. Unfortunately, they tend to

deboned ( they become loose with time ). So here we have the bonded rest, can you see

the metal on the lingual surface ? no preparation needed; it sticks to the tooth surface. We

have special cement that sticks to both metal and enamel but after several years it tend to

deboned. Sometimes its better to put an incisal rest or crown the entire tooth and shape

the rest within it.

The end

Forgive us if there is any mistake and sorry for being late


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Prostho Lec 5

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