Prostho Revision

7/30/2019 Prostho Revision

1/35

1

Revision for midterm material**

Components of the metal framework removable partial denture :1 .major connectors

2. Minor connectors:what connects the major connectors with othercomponents, such us clasps or rests.

3. Direct retainers (also called clasp assembly):


2/35

2

4. Denture Base (Acrylic):

-Major connectors have many requirements:


3/35

3

Advantages of the bead lines:

1-it provides mechanical seal to food and saliva so prevents things from

going in and out underneath the denture

2- Indicates the technician where to stop trimming.

3- Gives strength to the borders because it is a positive edge.

4- It has a retentive function specifically in complete denture becausetheres an extra-thickness at the edge of the border so it will strengthen it,

and the denture will be less prone to breakage.

5- In acrylic RPDs, it counteracts the contraction that occurs duringsetting and cooling of the material .


4/35

4

-The depth is usually no more than 0.50.75 mm , because compressing

the tissue to this depth causes no harm to them , if deeper it will harm the

tissues.

*Types of maxillary major connectors

Mid palatal strap (posterior):

- One of the most common major connectors used in the maxilla, usually

used in bounded saddle (class III),

-It should be 8-12 mm wide....Thickness of the strap is 1.5 mm.


5/35

5


6/35

6


7/35

7

- Complete full palatal plate is the one that provides best support and

rigidity.


8/35

8

- In the maxilla, we tend to use plates and straps more than bars, in the

mandible it's the opposite.

*MANDIBULAR MAJOR CONNECTORS:

- In the mandible, there are NO bead lines


9/35

9


10/35

10


11/35

11


12/35

12

* No straps in the mandible.


13/35

13

*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

*Types of the minor connectors:

-Four basic types:

1-Proximal minor connector: Guide

plate

2-Embrasure minor connector:

Connects to auxiliary rest

3-Retentive minor connector: For

denture base, denture base retention - grid work

4-Approach arm: For gingivally-approaching clasps


14/35

14

):Guide plateProximal minor connectors (-1

- They often considered the origin for restsand/or clasps.

- Its shifted slightly lingually to:1} Increases rigidity2} Enhances reciprocation

3} Improves esthetics.

-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


15/35

15

3- Denture base retention (Gridwork):

-the main function for them is to connect the acrylic to the metal (major

connector)

*We have different designs ofDenture base retention we have:

1-LATTICE: its like a ladder

*characteristics: large spaces, more bulk,

more control, more work, Interferes withsetting of teeth, and thicker metal

2-MESH: its like network

Characteristics: small spaces, flatter,

potentially more rigid, easier for

technician, more space for teeth, andless retention for acrylic if openings are

small.


16/35

16

. Thicker..usually we use it in the*Lattice work

because there is more room in the mandible due to the resorption .mandible

.maxillahinner ...usually we use in theTMesh work *


17/35

17

* Grid work relief

-Relief: is to create space for the acrylic underneath the metal minor

connector

-so we here have the master cast, this sheet of wax is going to create a space

under the metal frame work


18/35

18

*Junction between acrylic and major connector (The finish /end line)

1- External finish line (e): the line where the metal meetthe outer polished side of acrylic.

2-internal finish line (i): the line where the metal meet

the inner surface of acrylic (that touching the tissue).


19/35

19

*Tissue stop- a piece of metal that you put in your design in order to stand the pressureand give support for the metal mesh work , preventing the metal from going

down from the acrylic .


20/35

20

*Functions of the rest and rest seat:

1-Direct forces along long axis of abutment


21/35

21


22/35

22


23/35

23


24/35

24


25/35

25


26/35

26


27/35

27

part of the removable partial denture that goes to the undercutonly(The

)the tip or the terminal third of the retentive armis


28/35

28


29/35

29

-D: deflection

-P: applied force

-L: length E: elastic modulus.. W: beam width

t: thickness


30/35

30

*Direct retainers can be divided into:

Direct Retainers

Designed forTooth-Tissue

Borne.Stress releasingdirect retainers.

Designed forTooth borne.

Non-stress releasingdirect retainers.


31/35

31

*We have four types of Non-Stress Releasing Retainers:

1)Cast CircumferentialOur first choice usually on a posteriortooth starts from above the survey linethats why it is called supra- bulgeclasp

Also called Akers (name of the dentist

who designed it).

Less esthetic and less hygienic than gingivally approaching I-

bar clasps.

More difficult to adjust than wrought wire. (Wrought wire is

softer.)

2)Ring ClaspI use it when the undercut is not

where I want it to be.

Because it's too long it might become

a little bit too flexible, so what they

tend to do sometimes is provide a Supporting Strut on

one surface (two layers of metal like the figure below).


32/35

32

*Disadvantages of a ring clasp:

1-they are very difficult to adjust.

2- They have poor hygiene (especially with the presence of the strut).

.excessive tissue undercutThey are contraindicated when there's-3

3)Double Embrasure ClaspIt extends from the embrasure rests.

It has two retentive arms and two

reciprocating arms.

The main problem with these clasps is

that it can cause wedging

It is quite aggressive because unless youtrim them you will not have enough room

for the rests.

4)Reverse Action ('C') ClaspAlso called Hair-Pin Clasp.

If the undercut is on the mesiolingual

side of the molar, I can do the ring

clasp, or my other choice is to go distal

and then go backwards to the mesial

again if the tooth is long enough- and

it looks like a hair-pin.


33/35

33

It has poor flexibility especially for short crowns so the

abutment has to be long enough to

increase the flexibility of the clasp.

It is not comfortable for the patient

and it's difficult to adjust and it is

esthetically and hygienically poor.

Usually it's our last resort.

It is the least desirable design

REMEMBER

*TOOTH BORNE.Rest Near the Edentulous Space.Non-stress releasing

*TOOTH-TISSUE BORNERest Away From the Edentulous SpaceStress releasing


34/35

34

-we have to imagine the movement of the denture in three dimensions, not

just along the normal axis of rotation

Its the most significant

movement for us as a dentist

This movement is from side to side


35/35

-so keep in mind that if you have an axis of rotation that the partial

indenture is going to rotate around it ,we need to design our component

the axis of rotation to reduce thisbehindof the axis of rotation andfront

amount of movements

- Example 2: Here we can place the rest on the anterior teeth or instead of

doing that we go to the next tooth which is the canine and instead of

putting one rest, we put slightly two equal rests on either side, we divide

the stress on the two teeth on the sides, so, we can have more than oneindirect retainer by dividing it between the right and the left sides.

- Note: stars (*) means that the denture base is going out from the paper

i.e. away from the tissue, so the denture base is going out towards your

eyes whereas the indirect retainers prevent the front part of the denture (in

front of the axis of rotation) from going down or inside the paper

This movement is horizontally

Documents

Prostho Revision