2. 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, Stewart’s 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 you’re going to build a building you need to know the materials that you’ll
use ,you need to know the structures or components of the building which
you are going to design ,for the partial denture it’s 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:
It’s 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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3. 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 that’s fine it’s only going to be on that
side right? we say no we never make removable prosthesis on only one
half of the patient’s mouth, if it’s 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 stability
and retention, remember not all of this prosthesis have a lot of tooth
support , so it’ll 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 there’s a skeleton and there’s 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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4. -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 it’s self cleansing ,if it’s 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 shouldn’t 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 that’s
possible.
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5. 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 shouldn’t be
irritating to the tissues like marginal gingival and midpalatine raphae,
mandibular tori or to the tongue, shouldn’t be too thick , should across from
one side to the other and that’s only in the maxilla , because in the mandible
this can’t 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 know
the 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 it’s not only the coverage
that is important , but also the thickness .
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6. 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 don’t place bead lines in the
mandible. we make a groove which usually about 0.5-1 mm deep and wide and
the metal will go inside this.
Bead line hasn’t 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 there’s 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 , also
it 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 isn’t there .
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7. 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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8. 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 it’s 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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9. 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 it’s not irritating
for the tongue . Dentists don’t like it because it is more flexible,
especially in tooth tissue borne prosthesis.
Its indicated for tooth borne when anterior and posterior teeth are
missing but in different areas, and specifically indicated when a palatal
torus can’t 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 can’t 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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10. Anterior posterior palatal strap:
Relatively popular design, covers large surface area, it’s 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 can’t be covered .
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 .
o It covers less area than modified palatal plate, therefore it
provides LESS support than plate.
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11. Torus
Although it clears part of the palate, irritation occurs due to having
many edges In the connector’s design. So this is an example where
borders are sometimes more irritating than the thickness or the
coverage.
o Note : Palatal plate can be either complete “full “ or modified ,
covering the whole palatal area or only a part of it , respectively.
.
Modified palatal plate:
o In this design, we cover areas that we need to reach the
edentulous areas.
o It is broader than 12 mm, has extend and flat two borders
(anterior and posterior), it gives a lot of support.
o Indicated mainly in tooth tissue supported prosthesis .
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12. A complete full palatal plate:
o It does not necessary cover 100 % of the palate , but usually more
than 90 % of it . the figure below is an example for this .
o The patient does not feel any borders with this design , usually it
reaches the vibrating line and the teeth in all other areas .
o It’s indicated for very large edentulous areas , extensive class I ,
extensive class IV or class III with many modifications .
Here everything
is covered, except
for a small area in
the front.But still
its considered a
complete full
plate.
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13. Split major connector :
o It’s 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 isn’t 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 patient’s
mouth, without a lot of rigidity .
o This is achieved by splitting the major connector, making it more
flexible.
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14. Palatal Bar:
o Bars are rarely used in the palate, because of its thickness.
o Used in very small edentulous areas, like in Kennedy class III .
Or if there’s a very large torus, and we have to work around it .
o It’s thick, and narrow.
Notes:
o Each of these designs provides rigidity and support in different ratios.
o Complete full palatal plate is the one that provides best support and
rigidity .
o However , we don’t want to cover the palate everytime we are making a
prosthesis , due to oral hygiene considerations and preparation
considerations . so only when its really needed .
o In the maxilla , we tend to use plates and straps more than bars , in the
mandible it’s the opposite .
o Bars in the maxilla are exposed to the dorsum surface of the tongue ,
that’s why they are thinner than the lingual bars in the mandible , which
are not exposed to the dorsum surface of the tongue .
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15. MANDIBULAR MAJOR CONNECTORS :
o The first choice for mandibular major connectors is the lingual
bar .
o Lingual bars are made quite thick, because they are below the
tongue and because the distance between the gingiva and the floor
of the mouth is small, making it difficult to place a plate .
In the mandible ,a bar is placed unless the following conditions are
present :
There should be a distance between the bar and the free gingival margin,
at least 3 mm for gingival health and oral hygiene . if it’s not possible to
have this distance , then we have to cover the whole gingiva up to the
cingulam . so the only two choices are either keep a distance away from
the gingival margin or cover the gingiva up to the cingula , means that
leaving a 0 , 1 ,2 mm space between the bar and the gingival margin is not
allowed , because it’ll cause irritation and gingival recession .
The key number in the mandible is 3 mm .
The key number in the maxilla is 6 mm, if the major
connector does not reach to the cingula then it has to be
6 mm away from the gingival margin .
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16. 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 there’s 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
there’s 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 can’t do lingual bar is lingual plate , but it has its contraindications , if
there’s spacing between the teeth ( it would be unaesthetic because it’s going
to appear through these spaces), if there’s 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 that’s when mandibular tori are present.
However , it’s 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 ) .
It’s indicated when the lower anterior teeth is so severely retroclined ,
or there’s a large lingual torus .
Hinge / Swing-lock design , dental bar , sublingual bar . These are other types
of mandibular major connectors .
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17. No straps in the mandible .
For strength , the Bar in the mandible must be 4 mm in width “occluso
gingivally “.
7 mm distance is needed between free gingival margin and the lingual
frenum , and additional 1 mm for the free movement of the frenum ,
which equals 8 mm .
that means to place a bar we have to measure , from the free gingival
margin to the floor of the mouth , if its less than 8 mm we can’t do a
bar , if we have 8 mm and more , then we can ; 3 mm is the distance
between the bar and the free gingival margin , 4-5 mm for the width of
the bar itself , 1 mm for the free movement of the lingual frenum .
(very important )
These measurements are done in the patient’s mouth with a periodontal
probe , before making the design .
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18. Superio inferiorly its 5 mm , thickness is 2 mm .
Advantages of lingual plate : gives support because it sets on the teeth,
gives a degree on indirect retention ( there are rests attached to it).
The shape of a Lingual bar is half bear shaped , broad at the bottom
and rounded at the top . A lingual plate is a lingual bar with a plate
attached to it that reaches the cingulam , so the top part is tapered as
possible , the bottom part is rounded for strength & support .
Double lingual bar is indicated when there are open embrasures to
reduce the amount of the metal that would be shown through between
the teeth . however , it’s irritating for the patient .
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19. Hinge/swing lock design is a ( lingual bar + lingual plate + labial bar ) . it
locks the teeth from lingual and labial surfaces , it’s popular with
extensive kennedy class I . its used for added retention , we want
retention from all anterior teeth not only canine . it’s not very common
these days because we have implants .
Done by: Abeer Abu sobeh
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