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Removable partial denture

24/2/2013

Abeer Abu sobeh

3esam-el3alem

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Prosthodontics II: lec IV.

Title:Maxillary Major Connectors for Metal Framework RPDs.Mandibular Major Connectors for Metal Framework RPDs

The references for this lecture

Chapter 2, Stewarts Clinical Removable Partial Prosthodontics,4th Ed, 2008 (pages 19-36).

Chapter 5, Removable Partial Denture Design - Outline Syllabus,5th Ed, Kroll et al, 1999 (pages 33-45).

Today we are going to be talking about the major components of RPD

structure before you learn how to design, you need to know the components,

if youre going to build a building you need to know the materials that youll

use ,you need to know the structures or components of the building whichyou are going to design ,for the partial denture its similar, you need to

understand the major components and the different choices that you have

for each of this components when you fabricate it ,so the first thing we are

going to learn about :

Components of the metal framework removable partial denture:

The major connector: Its like a skeleton for the partial denture, it connects various parts

together and it transmits the force so that the functional load is

distributed on both mucosa and teeth.

It always extend from one side of the arch to the other.

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It provides support. When the patient bites down on one side it

prevents the rotation of the denture and keeps it in place.

Many patients often come to us in the removable prosthodontics Clinique

and they are missing 2-3 teeth on one side ,and they asking for

removable prosthesis, they say thats fine its only going to be on that

side right? we say no we never make removable prosthesis on only one

half of the patients mouth, if its removable by definition for safety

and for structural reasons:

1)The first reason is for structural, removable prosthesis is not attached

to the adjacent teeth like a bridge, it has to cross the arch for stabilityand retention, remember not all of this prosthesis have a lot of tooth

support , so itll distribute the support from one side to the another .

2)The other reason which is for safety: even if technically we can make it

of one side from the patients mouth we avoid it, because it is so small

,and the problem is if the patient will leave our Clinique he might sneezes

,yawns ,be in an accident ,this might dislodged so the patient can swallow

it or worse aspirate it if it gets lodged in his trachea. So we never make

unilateral or one side partial dentures, they always cross the arch, when

they cross the arch they give us additional stability retention and

support when it cross the palate we get some support from the palate in

addition. Depending on the different components that the major

connector has it provides stability and to some degree it provides

support, like we said theres a skeleton and theres backbone over

prosthesis but we need to have specific requirements when we make this

prosthesis, first of all the materials need to be compatible, the material

that we use we call it: cobalt chromium and there are other alloys that

we can use (like: nickel chromium, high noble alloys -gold alloys-

although it is expensive but it was very popular in the past , titanium

which is difficult to fabricate).

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-The one which is economically and technically most usable it is: cobalt

chromium and nickel chromium, but in general we avoid nickel chromium

because approximately 1/20 people has nickel sensitivity.

Notes:

o Acrylic partial dentures for strength reasons need to be at

least 2-3 mm thick in the cross of the base plate.

o Metal framework partial denture could be make as thinnest

0.5 as routine and could be 0.3-0.4 if it covers the entire

palate.o if the major connector does not reach to the cingula then

it has to be 6 mm away from the gingival margin .

o The distance between minor connectors in the maxilla

should be at least 5 mm (the space needs to be large enough

so its self cleansing ,if its small the food will accumulate in

this area which might cause caries, gingival inflammation ,

and irritation to the patient).o We should cross the gingiva at right angles.

o In the anterior part of the mouth the metal plate -the

major connector often ends in the rugae area.

o The function of rugae area: Phonetics, taste stimulation,

maybe have something to do with nursing in mammals so it

stimulates lactation.

o The posterior border shouldnt end to the vibrating line

because the soft palate is movable.

o The anterior and posterior borders should cross the midline

at right angle so it causes the least irritation thats

possible.

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So, the principle functions for the major connector: Unification & rigidity.

Major connectors has many requirements, the doctor mentioned some of

them: it must be rigid, unifies the different parts together, it shouldnt be

irritating to the tissues like marginal gingival and midpalatine raphae,mandibular tori or to the tongue, shouldnt be too thick , should across from

one side to the other and thats only in the maxilla , because in the mandible

this cant be possible due to the presence of the tongue .

o Rigidity is necessary, if a force is applied on one side of the

prosthesis, it should be distributed to all parts, because as we knowthe edentulous area was not designed to support the occlusal force .

o In a partial denture, we want to distribute the force over a large area

as much as possible, or to other teeth if we can .

Maxillary Major Connectors:

Major connectors in the maxilla have different designs , due to the anatomy

of the maxilla and the variation of Kennedy classes that guides the design of

the prosthesis.

Depending on the class we have (the location of the edentulous spaces),we

have to decide what type of design is the suitable one , and if we need to

make either broad or small major connector . so its not only the coverage

that is important , but also the thickness .

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In maxillary RPDs we place bead lines ( ONLY IN MAXILLA) at the edges

of the major connectors, The bead line is something you scraping in the cast,

so the material of the denture will go in and it will comprise this area it can

be in anywhere in the maxillary denture ,but we dont place bead lines in themandible. we make a groove which usually about 0.5-1 mm deep and wide and

the metal will go inside this.

Bead line hasnt to be between the junction of the movable and non-movable

parts of the soft palate, it provides mechanical seal to food and saliva ,

prevents things from going in and out underneath the denture, indicates the

technician where to stop trimming , gives strength to the borders , it has a

retentive function specifically in complete dentures because theres an extra

thickness at the edge of the border so it will strengthen it ,and the denture

Will be less prone to breakage.

and in acrylic RPDs it counteracts the contraction that occurs during

setting and cooling of the material .

The depth is usually no more than 0.5 1 mm , because compressing the

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

tissues .

As it gets close to the gingiva it becomes shallower and shallower , alsoit should be thin in the midpalatine suture area in order not to irritate

these areas .

We try to finish the edges of the denture ( bead lines ) behind the

rugae not in front of it , because it would be more comfortable for the

tongue , but if the denture ends in front one of the rugae this makes it

less comfortable and more thick . So in the first case the tongue will

pass from the major connector to the rougae , it will keep sliding as if

the border of the partial denture isnt there .

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The junction between the major connector and the acrylic is called

the finish line, in the maxilla it differs in location between the

fitting surface and the polished surface . If they were both on the

same level, the metal will be very thin and might break .

In polished surface: its closer to the teeth . In fitting surface : its

closer to the palate . at the fitting surface we want to cover as much as

we can from the ridge , we might need to reline the base again in the

future .

o Note: major connectors can be designed to add a tooth to the

prosthesis later, this is called planning for future failure.

TERMINOLOGY :

Three main terms: a palatal bar , a palatal strap and a palatal plate .

o Bar > strap > plate , as we go from bar to strap to plate , the shape

gets thinner and broader .

o Bar are more common in mandibular partial dentures , not used

much in the maxilla . Bar is less than 8 mm wide ( lateral dimension

, not thickness ) .

o Strap is between 8-12 mm .

o

Plate is greater than 12 mm wide . ( this is for the maxilla )

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Mid palatal strap (posterior):

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

used in bounded saddle (class III), missing premolars and molars at

one or both sides it has a mid-palatal strap that extends from one side

to the other for retention and rest.

So its used for tooth borne prosthesis. And in some rare cases can be

used in tooth tissue borne prosthesis.

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

o Note: Usually the anterior posterior width is proportional to the

degree of support required, the more the support the greater

the area we need to cover.

o We usually thicken the center to give it more rigidity.

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Anterior palatal strap horse shoe , U shaped :

It covers the edentulous area, goes around anterior part of the palate

and then goes back.

Preferred by patients, not by dentists. Patient like it because it frees

the palate, for taste and temperature sensation and its not irritating

for the tongue . Dentists dont like it because it is more flexible,

especially in tooth tissue borne prosthesis.

Its indicated for tooth borne when anterior and posterior teeth aremissing but in different areas, and specifically indicated when a palatal

torus cant be removed or covered. so for large Kennedy class 1 ,

bilateral distal extension and with presence of torus , I want a lot of

coverage and support but still cant cover the torus , horse shoe

design is the suitable one .

o Note: we may have combinations of: anterior posterior, mid

posterior and so on of these designs.

o Problems with this design : relatively flexible , poor rigidity and

is often misused ( many dentists use it routinely) .

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Anterior posterior palatal strap:

Relatively popular design, covers large surface area, its a rigid design

because it has not only an anterior part but also a posterior one,

middle part of the palate area is cleared to maintain sensation.

Its indicated for both tooth & tooth-tissue borne prosthesis , also

useful if the torus is the in center of the palate and cant be covered .

o It covers less area than modified palatal plate, therefore it

provides LESS support than plate.

If the torus is large, extending to the vibrating line, horse shoe

design is indicated .

If the torus is small and just in the center, anterior posterior

palatal strap is indicated .

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Although it clears p

many edges In the c

borders are someti

coverage.

o Note : Palatal

covering the

.

Modified palatal pl

o In this design

edentulous ar

o It is broader

(anterior and

o Indicated mai

rt of the palate, irritation occurs du

onnectors design. So this is an examp

es more irritating than the thickness

plate can be either complete full or

hole palatal area or only a part of it ,

ate:

, we cover areas that we need to reac

as.

han 12 mm, has extend and flat two b

osterior), it gives a lot of support.

ly in tooth tissue supported prosthes

Torus

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to having

le where

or the

modified ,

respectively.

the

orders

is .

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A complete full pa

o It does not nec

than 90 % of it

o The patient do

reaches the vib

o Its indicated f

extensive class

latal plate:

essary cover 100 % of the palate , but

. the figure below is an example for t

s not feel any borders with this desig

rating line and the teeth in all other a

r very large edentulous areas , exten

IV or class III with many modificatio

H

is

fo

th

it

co

pl

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usually more

is .

n , usually it

reas .

sive class I ,

ns .

ere everything

covered, except

a small area in

front.But still

considered a

plete full

te.

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Split major connector :

o Its a rare design, not seen any more in clinics.

o The objective is for stress relief between the retention and the

support.

o Used when rigidity is undesirable, mainly in maxillofacial

prosthodontics , in such cases part of the palate is gone , the sinus

is open , this area is very movable and there isnt much support that

if I connect it very rigidly to the few remaining teeth , everytime

the patient bites down , a lot of force is applied on the remaining

teeth , which with time may lead to extraction of these teeth .

So we just need a design that keeps the denture in the patients

mouth, without a lot of rigidity .

o This is achieved by splitting the major connector, making it more

flexible.

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Palatal Bar:

o Bars are rarely u

o Used in very sma

Or if theres a v

o Its thick, and n

Notes:

o Each of these designo Complete full palatal

rigidity .

o However , we dont w

prosthesis , due to o

considerations . so o

o In the maxilla , we te

mandible its the oppo Bars in the maxilla ar

thats why they are t

are not exposed to t

sed in the palate, because of its thick

ll edentulous areas, like in Kennedy cl

ry large torus, and we have to work a

rrow.

s provides rigidity and support in diffplate is the one that provides best s

nt to cover the palate everytime we

al hygiene considerations and prepar

ly when its really needed .

nd to use plates and straps more than

site .e exposed to the dorsum surface of t

hinner than the lingual bars in the ma

e dorsum surface of the tongue .

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ness.

ss III .

ound it .

rent ratios.pport and

re making a

tion

bars , in the

he tongue ,

dible , which

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MANDIBULAR M

o The first choice

bar .o Lingual bars are

tongue and beca

of the mouth is

In the mandible ,a

present :

There should be a dist

at least 3 mm for gingiv

have this distance , the

cingulam . so the only t

the gingival margin or c

leaving a 0 , 1 ,2 mm spa

allowed , because itll c

The key nu

The key nu

connector d

6 mm away

JOR CONNECTORS :

for mandibular major connectors is t

made quite thick, because they are b

use the distance between the gingiva

mall, making it difficult to place a pla

ar is placed unless the following co

nce between the bar and the free gin

al health and oral hygiene . if its not

we have to cover the whole gingiva u

o choices are either keep a distance

ver the gingiva up to the cingula , me

ce between the bar and the gingival m

use irritation and gingival recession .

ber in the mandible is 3 mm .

ber in the maxilla is 6 mm, if the major

oes not reach to the cingula then it has t

from the gingival margin .

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e lingual

low the

nd the floor

te .

nditions are

gival margin,

ossible to

p to the

way from

ns that

argin is not

be

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o Lingual plates creates problems in oral hygiene especially in small narrow lower

anterior teeth .

o In the mandible , there are no bead lines . however , we usually relief (wax

spacer ) underneath the major connector ,because theres a certain degree of

motion in the mandible , and depending on either the case is tooth borne Or

tooth-tissue borne, the thickness and location of this relief varies , notice

that in tooth borne the movement is up and down only , in tooth tissue borne

theres rotation .

o In tooth-tissue borne prosthesis , in addition to the lingual bar ,indirect

retention is needed . so there will be extension that goes from the lingual bar

to the lingual surfaces of the teeth to prevent rotation. So , another option

when we cant do lingual bar is lingual plate , but it has its contraindications , if

theres spacing between the teeth ( it would be unaesthetic because its going

to appear through these spaces), if theres crowding.

Double lingual bar ( kennedy bar ) :

Is two lingual bars , one on the cingulam surface and one below .

Labial bar :

Instead of extending the major connector from the lingual, we extend it

from the labial. And thats when mandibular tori are present.

However , its considered the very last choice because the longer the bar

the more flexible it is and the more irritating it is for the patient.

And the rule of 3 mm away from the gingival margin also applies here (

from the labial side ) .

Its indicated when the lower anterior teeth is so severely retroclined ,

or theres a large lingual torus .

Hinge / Swing-lock design , dental bar , sublingual bar . These are other types

of mandibular major connectors .

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No straps in the m

For strength , the B

gingivally .

7 mm distance is nee

frenum , and additio

which equals 8 mm .

that means to place

margin to the floor o

bar , if we have 8 m

between the bar and

the bar itself , 1 mm

(very important )

These measurement

probe , before makin

ndible .

r in the mandible must be 4 mm in wi

ded between free gingival margin and

al 1 mm for the free movement of th

bar we have to measure , from the f

f the mouth , if its less than 8 mm we

and more , then we can ; 3 mm is the

the free gingival margin , 4-5 mm for

for the free movement of the lingual

are done in the patients mouth with

g the design .

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dth occluso

the lingual

frenum ,

ee gingival

cant do a

distance

the width of

frenum .

a periodontal

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Superio inferiorly it

Advantages of lingua

gives a degree on ind

The shape of a Lingu

and rounded at the t

attached to it that r

possible , the botto

Double lingual bar is

reduce the amount o

the teeth . however

5 mm , thickness is 2 mm .

l plate : gives support because it sets

irect retention ( there are rests atta

al bar is half bear shaped , broad at t

op . A lingual plate is a lingual bar with

eaches the cingulam , so the top part

part is rounded for strength & suppo

indicated when there are open embra

the metal that would be shown thro

its irritating for the patient .

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on the teeth,

hed to it).

e bottom

a plate

is tapered as

rt .

ures to

gh between

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Hinge/swing lock design is a ( lingual bar + lingual plate + labial bar ) . it

locks the teeth from lingual and labial surfaces , its popular with

extensive kennedy class I . its used for added retention , we want

retention from all anterior teeth not only canine . its not very common

these days because we have implants .

Done by: Abeer Abu sobeh