Review of Cobalt Chrome Denture Design 97-2003

8/2/2019 Review of Cobalt Chrome Denture Design 97-2003

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Review of Cobalt ChromeDenture Design Concepts

Le

c

tured: Dr. Anas Al-Ibrahim

In the name of Allah

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Sequence of Designing

Saddles (yellow color)

Support (red color)

Retention (green color)

Bracing and reciprocation (blue color)

Major and minor connectors (black

color)

Indirect retention

Review of completed design

Kennedy Classification

Class I: Bilateral free-end saddle.

Class II: Unilateral free-end saddle.

Class III: Unilateral bounded saddle.

Class IV: Anterior bounded saddle, across the midline.

>> When you give Kennedy classification determine the most posterior edentulousspace, see if it is (class I,II,III or IV), then consider all other edentulous spaces

anterior to it as modifications

>> All Kennedy classifications except for class IV have modifications.


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In the above pictures you are looking at the prosthesis no directly at the saddles

inside the patient's mouth

In the left picture, this prosthesis is supposed to replace upper left 2nd premolar

posteriorly (e.g. unilateral bounded) and the 6 anterior teeth, so Kennedy classification

is class III Mod I (not class I Mod I or II

In the right picture, this prosthesis is supposed to replace lower right and left 6s and

7s and also the 4 incisors, so Kennedy classification is class I (e.g. bilateral free-endsaddles) Mod I (not class III Mod I

**Did you notice that the patient in the right picture has no 1st premolars, maybethey were extracted for ortho purposes in the past :P :P

**Saddles

The design of the occlusal surface

>> Always use narrower and shorter occlusal table in distal extension saddles

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Here in the picture, in the lower left quadrant

(e.g. your right side) we have made the occlusal

table shorter (excluded the 7 and only replaced

5 and 6) and narrower (buccolingually) compared

to that in the right quadrant (e.g. your left side).

Doing this will lead to less forces on the

denture, then more retention and better

adaptation by the patient

We can exclude the 7 in most cases to make the occlusal table shorter

The base extension

>> Maximum coverage in distal extension saddles

Here in the picture in the lower left quadrant

(e.g. your right side) we achieved maximum

extension and maximum coverage compared to that

in the right quadrant (e.g. your left side)

Doing this will lead to more surface area to aid in

cohesion and adhesion (e.g. better retention by

means of physical forces) and also will enhance

muscular control over the polished surface

leading again to better retention

The design of the polished surface

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- Biologically compatible with tissues

- Thermal conductivity

- Light-weighed

- Good aesthetics

- Dimensional stability

- Sufficient strength and resistance to fracture/distortion/deformation

- Self cleansing

- Low cost

>> Functions of denture base:

- Aesthetics

- Support

- Retain artificial teeth

- Transfer occlusal forces to abutment teeth via rests

- Prevent vertical and horizontal migration of remaining natural teeth

- Eliminates food traps

- Stimulate underlying tissues

>> Denture base materials:

- Metal

>> Indicated in

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- Tooth supported partial dentures (e.g. short span bounded saddles)

where relining is rarely needed

- Inadequate interarch space

>> Metal bases are thinner than acrylic bases (but still have adequate strength),

should be designed with maximum extension and without any sharp margins

>> Metal bases Advantages:

- Maintain their accuracy of form without change inside the patient's mouth

compared to acrylic bases

- Provide excellent intimate contact with tissues (e.g. accurate fitting)

- Have no later internal strains release that lead to deformation as what we have

in acrylic resin bases

- They are naturally cleaner than acrylic bases and they actually have theinherent cleanliness property which contributes to healthy oral tissues

- Are thermally conductive unlike acrylic bases which have thermal insulating

effect. Thermal conductivity is important for the acceptance of the patient and

the health of the tissues (the patient will feel that this drink for example is too

hot and so won't burn his mucosa)

>> Metal bases disadvantages:

- Not aesthetically good

- Relining difficulty

- Restoring normal facial contours can't be achieved when there's extreme

residual alveolar bone loss

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- Acrylic resin

>> Indicatedin

- Distal extension saddles and long span bounded saddles where we expect

bone resorption and might need relining

- When there's extreme loss of residual alveolar bone and we want to

restore normal facial contours

- Adequate interarch space

>> Acrylic resin bases should be of adequate strength and bulk

>> Acrylic resin bases are attached to the major connector via minor connectors

(e.g. open lattice or mesh) so that when we have acrylic resin bases we actually have

acrylic and metal together (thus requiring more interarch space) but when we have

metal bases we actually have metal only (thus requiring less interarch space)

Here in the picture, the black arrow points to the

tissue/cast stop in distal extension bases

metal framework, this stop:

- Enables me to check fitting of the metal

framework without any rocking

- Support the framework (e.g. prevent

downward movement)

- Support the framework during packing and processing of acrylic resin.

So tissue/cast stop in distal extension bases is extremely important

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Here in this photo prosthetic teeth are about to

be attached to metal base in the bounded saddle

area via mechanical interaction (e.g. beads,tags ...) without any acrylic

The junction between saddle and abutment tooth.

>> The junction between the saddle and the abutment teeth is either opendesign (as

in the left picture) or closed design (as in the right picture)

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>> The advantage of the open design over the closed one is the fact that it is more

hygienic and doesn't aid dental plaque accumulation

>> The advantages of the closed design over the open one is the fact that is more

aesthetic and also associated with guiding plane preparation which will enhance

retention by means of friction and creates path of insertion. It is somehow cleansable

>> The only case in which we can prepare guiding planes on abutment teeth and use

the open design is when the clinical crown height of abutment teeth is too long,

but in general guiding planes preparation is done when the closed design is used

** Support


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Planning support

Support gained from each tooth is dependent on the type of the tooth and its

periodontal health

>> The picture on the right above represents

the root surface area of all teeth, you can see

that the largest root surface area is for molar

teeth (2.7) and the smallest root surface area

is for lower incisors (1.0), so molars give the

maximum support while incisors give the least

support compared to other teeth. Molars won't

give the same amount of support if their

periodontal health is compromised (as here in the picture on the

right) because when periodontal health is compromised, and

there's reduced periodontal support and attachment loss, root

surface area is reduced and so the support

The extent of the saddles

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>> In the left picture above, we have bounded saddles, thus we don't need that

much support from teeth.

While in the right picture above, we have extensive saddles (e.g. free-end

saddle), thus we need to maximize support by adding more support

components, having maximum extension and coverage of the denture base

(especially in maxillary RPDs) and also using double rest (as in the picture below)

instead of one rest (especially in mandibular RPDs)

The expected force on the saddles

>> This actually depends on:

- The length of the edentulous space >> we need less support for edentulous

span restoring 2 missing teeth than we need for edentulous space restoring 3 or 4

missing teeth. As the length of edentulous span increases we expect the vertical

forces to increase as well thus we have to compensate for this by maximizing the

support

- The nature of the opposing occlusion >> we need less support if the

opposing occlusion is a prosthesis (e.g. complete denture) than if it is natural

dentition because we expect less vertical forces in case of opposing complete

denture than if we have opposing natural teeth

** Tooth support for distal extension saddles

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>> The major component for support is the rest

>> Where to place the rest in distal extension saddles, away from the saddle

area (e.g. mesially) or toward the saddle area (e.g. distally)?

- When placed mesially, we will have more favorable vertical delivery of occlusal

forces to abutment teeth (as seen in the picture above)

- When placed distally, we will have distal tipping of

the abutment tooth (as seen in the picture below)

>> You should know that the issue of where to place the

rest in distal extension saddles is still controversial,

because there will be rotation of the denture base toward the abutment

tooth and other remaining teeth due to the slope and curvature of the

residual ridge, this is why there's nothing causing distal tipping, however in

general we like to place rests mesially (away from the saddle area) in distal

extension saddles

** Partial denture support

>> Support components include:

- Rests (occlusal, incisal and cingulum)

- Maxillary major connector (provides maximum extension)

- Saddles

- Rigid part of the clasp arm, why?

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>> Because the rigid part of the clasp arm lies over the survey line, and it will

act as a rest without embracing any undercut

** Retention

>> Retention = the resistance to removal away from the supporting tissues

>> Retention is either:

- Direct

- Indirect (this is mainly useful in distal extension RPDs)

>> Retention of RPDs:

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- Inherent physical forces

>> Adhesion and cohesion

>> Here we need maximum coverage and large surface area to be covered

to be effective

- When we have few missing teeth (as seen in

the picture above) we won't need maximum

coverage to enhance retention by means of

physical forces because the retention gained by

the clasps is enough

- When we have so many teeth missing (as

seen in the picture below) and extensive free-end

saddles then we will need to maximize the

coverage to enhance retention by means of

physical forces beside the retention gained by the

clasps

>> Usually more effective in acrylic partial dentures than with Cr-Co RPDs

- Neuromuscular control

>> By the act of the surrounding musculature on

the polished surface of the denture

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>> Neuromuscular control is extremely important when it comes to mandibular

bilateral distal extension saddles denture, because we have forces coming

from the tongue and the cheek, so we need to shape the polished surface

correctly to enhance retention my means of neuromuscular control on the polishedsurface

- Mechanical

>> By the use of:

A- Guide planes

Here in the picture, the dotted line represents

the path of insertion; the other line represents

the path of displacement. Path of insertion is

what we have at the new tilt while path of

displacement is what we have at zero tilt. If

we have such path of insertion as in here then

the only way to dislodge the denture is by

applying forces along its path of insertion.

When vertical forces try to dislodge the

denture at this path of insertion, then the

denture base will engage the undercuts directly and thus enhancing its retention.Always remember that guide planes are direct not indirect retainers

because the principle idea of guide planes functioning is the same as that of the

clasps which engage undercuts under vertical forces. When path of insertion =

path of displacement (e.g. didn't gain new tilt) then there's no need for guide

planes and direct retention will only be gained by the clasps

B- Attachments

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C- Clasps

>> The most important components for mechanical retention

>> Clasps are mainly classified into:

- Occlusally approaching clasps

>> E.g. the ring clasp (in the lower picture to

the left)

- Gingivally approaching clasps

>> E.g. I-bar which is the most commonly

used one. We have also T-bar

>> Comparison between occlusally and gingivally approaching clasps:

- Retention

>> Premolar tooth for the clasp to be of good retention we need

enough length (e.g. enough flexibility).

Occlusally approaching clasps are okay for molars, because molars have

enough Mesiodistal width (about 15 mm) and this will cause the clasp

to have enough length then good flexibility and retention.

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Premolars have less Mesiodistal width than molars (about 7 mm), so

clasps on premolars won't be so long as they are on molars teeth.

Cr-Co alloy is very rigid especially if it is very short.

So occlusally approaching clasps made of Cr-Co alloy won't be of enough

length neither flexibility nor retention when placed on premolars.

For molars we can go for occlusally approaching clasps, for premolars

we can go for either gingivally approaching clasps or wrought wire

clasps.

>> Periodontally involved tooth ideally

only the terminal third ofthe occlusally

approaching clasp should be below the survey

line.

Unfortunately, in most of the cases we can't

achieve this, so that more than the terminal

third of the clasp will be below the survey line,

and this will lead to displacing forces and

harmful effect on abutment tooth.

This is why we prefer Gingivally approaching

clasps over occlusally approaching ones when

we have Periodontally involved teeth, because

in Gingivally approaching clasps only the tip

contacts the tooth and this lead to less displacing forces on the abutment

tooth.

- Appearance

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>>Gingivally approaching clasps are better aesthetically

Here in the picture the clasp is engaging a distobuccal undercut, which is

aesthetic.

>> Tooth-coloured clasps

- Polyoxymethylene clasps

- Coloured clasps >> aesthetic

- Very thick clasps >> so that they need

more Mesiodistal width of the tooth

(so that they can be longer and more

flexible) and deeper undercut

- Very expensive

- Aid plaque accumulation (less hygienic)

- Its disadvantages are more than the advantages

- Hygiene

>> Gingivally approaching clasps might increase plaque accumulation

>> Gingivally approaching clasps might increase the risk of root caries

in the presence of gingival recession and xerostomia

>> Occlusally approaching clasps are more hygienic than gingivally

approaching ones

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- Occlusion

>> Occlusally approaching clasps might require in most of the cases tooth

reduction in order to provide adequate space for the rigid part of the clasp

that is supposed to be over the survey line, this reduction might be done

for the clasped tooth or the opposing tooth.

- Gingivally approaching clasps have nothing to do with occlusion

>> Factors on which effectiveness of clasps depends:

A- Tooth shape

>> Depth of undercut the deeper the undercut the more retentive

the clasp

>> Steepness of undercut

Here in the picture, both tooth #1 and #2

have the same depth of undercut so that

the overall retention would be the same,

but the undercut in tooth #1 is steeper than

that on tooth #2, which means the initial resistance for vertical

displacing forces in tooth #1 would more than that in tooth #2 but the

overall retention would be the same (only the initial resistance to

displacing forces will be different)

B- Clasp design (flexibility)

(The more the flexibility the more the retention)

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>> Section

- Round >> in here the flexibility if the clasp is the same in all

directions (vertical and horizontal)

- Half-Round >> in here the flexibility of the clasp is more in

the horizontal direction than in the vertical. We need the clasp

to be more flexible in the horizontal direction because most of

displacing forces are vertical

>> Length the longer the clasp the more flexible it is

>> Thickness reducing the thickness by 1/2 will increase the

flexibility by 8 times

>> Alloy

- The most commonly used alloys to

fabricate clasps include: S.S, Cr-Co

and gold

- Gold is more flexible than S.S, and

S.S is more flexible than Cr-Co

(Gold>S.S>Cr-Co)

- Here the picture represents

comparison between S.S (blue), Cr-Co

(black) and gold (pink). The black circle represents the proportional

limit (the limit after which the alloy undergoes permanent

deformation).

- Cr-Co alloy has a value of stiffness that is twice that of the

gold alloys. Which means, we need double the force needed to bend

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gold alloy for a distance to bend the Cr-Co alloy for the same

distance. (Gold alloy has twice the flexibility of Cr-Co)

- Hardened S.S has the highest proportional limit. Proportional limit

of gold and Cr-Co are comparable.

>> The choice of the retentive clasp:

There are a number of factors that are important to consider when choosing the

appropriate retentive clasp. When to use gingivally approaching clasps, when to

use occlusally approaching clasps, and when using occlusally approaching claspswhen to use ring clasp. Those factors are:

- Appearance

>> Gingivally approaching clasps are better aesthetically than occlusally

approaching ones, so in aesthetic zone use Gingivally not occlusally

approaching clasps

- Length if the clasp

>> The only Mesiodistal width that is suitable for good

length occlusallyapproaching clasp and good flexibility and

retention is the Mesiodistal width of molars. So formolars occlusally approaching clasps but for premolar

Gingivally approaching clasps.

If for a reason or another we need to use occlusally

approaching clasp on a premolar tooth then it should be

wrought wire rather than a rigid cast Cr-Co wire.

- Occlusion

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>> Gingivally approaching clasps don't compromise the occlusion and need

no occlusal reduction as occlusally approaching clasps do, so if we have

problem in the occlusion we better choose Gingivally not occlusally

approaching clasps

- Position of the undercut

>> In most of the cases when we survey the cast we will find that

suitable undercuts are further away from the edentulous space

and this is ideal actually.

Here in the picture we have a missing tooth

between the 1st molar and 1st premolar teeth, the

suitable undercut on both teeth is below the

survey line and farther away from the

edentulous space. On the molar we have

occlusally approaching clasp and on the premolar

we have Gingivally approaching clasp.

Sometimes we will survey the cast and we will find the suitable undercut

closer to the edentulous space, then if I extend my clasp the usual way

it will be shorter, to overcome this we might use the ring clasp.

Here in the picture, the suitable

undercut is located buccally and

closer to the edentulous space, so we

used a ring clasp, which encircles the

tooth from the lingual side to the buccal

side to engage the undercut.

Another indication for ring clasp is when

the suitable undercut is located lingually not buccally because the

tooth is tilted, so this time the clasp will encircle the tooth from the

buccal side to the lingual side to engage the undercut.

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In the RPI system the I-bar should engage a suitable undercut on the

midpoint of the tooth or slightly anterior (mesial) to it. Other

Gingivally approaching clasps can be placed where the suitable undercut is,

it doesn't matter as it matters with the I-bar specifically.

- Health of the periodontal ligament

>> For Periodontally involved teeth we prefer using Gingivally approaching

clasps over occlusally approaching ones

- Shape of the sulcus

>> Here in the picture, we have a premolar

tooth, suitable to be clasped by Gingivally

approaching clasp, but we have a ridge

undercut, this interferes and contraindicates the

placement of Gingivally approaching clasps for thefact it will irritate the buccal mucosa and the

cheek.

We call the gingivally approaching clasp that irritates the buccal mucosa

and the cheek and aid in plaque accumulation and is preferably not placed

because there's a ridge undercut the "cabbage catcher" clasp

>> The RPI system:

- Definition = this is a design that permits the denture to rotate on the

distal abutment teeth without causing any damage to remaining oral tissues

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- Main components include:

> R - Rest, placed mesially on the most

distal abutment tooth. More vertical

loading, transmits less torque

> P - Proximal plate. Designed so as not

to transmit torque to abutment when

saddle is loaded

> I - I-bar. Disengages tooth when saddle is loaded

- Here in the picture, we have occlusally

approaching clasp and a rest on the

most distal tooth directed distally

(toward the edentulous space). Under

vertical loading on the saddle, there will berotation, the distal rest is the point of

rotation, the clasp will engage the

undercut and there will be distal tipping

of the abutment tooth (e.g. the clasping system will act as an extraction

forceps)

- Here in the picture, we have Gingivallyapproaching clasp and a rest on the

most distal tooth directed mesially

(away from the edentulous space). Under

vertical loading on the saddle, there will be

rotation, the mesial rest is the point of

rotation, the I-bar will disengage the

abutment tooth and the guiding plane

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will move downward and mesially thus preventing distal tipping

(e.g. the clasping system won't act as an extraction forceps)

- Here in the picture, we have the RPIsystem, mesial rest, I-bar and

proximal plate, the blue colour

represents the saddle before loading

and the purple colour represents the

saddle after loading, under vertical

loading the there will be rotation, the

mesial rest is the point of rotation, the

proximal plate will move downward and

mesially to prevent distal tipping of the

abutment tooth and the I-bar will

disengage the undercut and the

abutment tooth

- For the proximal plate to be effective (e.g. to be able to move

downward and mesially when the saddle is loaded), guiding plane should

be prepared on the gingival part of the distal surface of the most

distal tooth

** Reciprocation

- Reciprocation = the resistance to horizontal forces exerted on a tooth by a

clasp during either insertion or removal of a denture

- Components of reciprocation >> reciprocal arm or reciprocal plate

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- For the reciprocal component to be effective, guiding

plane preparation should be done.

- Here in the picture, the top one, no guiding plane

preparation was done, A and B before loading, A' and

B' after loading. After loading, the clasp will engage the

undercut and the reciprocal component will disengage

the tooth, thus no effective reciprocation. The

bottom one, we have prepared guiding planes on lingual surface of abutment

tooth, A and B before loading, A' and B' after loading. After loading, the clasp

will engage the undercut and the reciprocal component will move up with the

retentive component while still engaging the tooth thus effective

reciprocation.

** Bracing

- Bracing = the resistance to displacement of the denture in both antero-

posterior and lateral directions (horizontal plane)

- In reciprocation we specifically talk about the clasp and the tooth, in

bracing we talk about the whole denture

- Bracing occurs when the denture is fully seated but reciprocation occurs

during removal and insertion of the denture (e.g. when the clasp is effective)

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- Bracing component >> any component that covers the vertical part of the

ridge or the teeth is a bracing component (e.g. the major connector, the saddle

)

- Here in the left picture, the rigid component of the Cr-Co RPD that covers the

vertical part of the ridge resisted horizontal forces and thus dislodgement. In the

right picture, the rigid component of the Cr-Co RPD that covers the vertical part of

the anterior teeth resisted antero-posterior forces thus dislodgement

** Major connectors

- Major connector =joins the components on one

side of the arch with those on the opposite side (blue

circle in the right picture)

- Minor connector = joins the other components,

such as rests and clasp to the major connector (red

circles in the right picture)

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- Anything in the denture rather than the rests, clasps and major connector is

actually a minor connector

- Requirements for major connector:

>> Be rigid

- Rigidity permits broads distribution of applied

forces

- Rigidity enhances effectiveness of other

components of the RPD.

>> Protect the soft tissues

- Borders of a maxillary major connector shouldbe located 6 mm away from the free gingival

margins (as in the right picture)

- Borders of a mandibular major connector

should be located 3 mm away from the free gingival

margins

- 3 mm in the mandible while 6 mm in the maxilla because in the mandible

thesulcus tends to be shallower

- Borders should run parallel to the gingival

margins of the remaining teeth. Because we

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want to reduce plaque accumulation and to reduce crossing with the gingival

margin

- Gingival margins must be crossed at rightangle. In order to reduce the contact between the

delicate gingival margin and the minor connector

>> Provide a means for placement of one or more

dentures bases

- Different major connectors can be used accordingto the number and location of edentulous

spaces

>> Promote patient comfort

- Anterior border of a maxillary major connector should not end on

the anterior slope of a prominent rugea.

Here in the top picture the anterior border of the

maxillary major connector ended on the anterior slope of

the prominent rugea area which isn't favourable because

it will interfere with the tongue, then speech and also

might traumatize the rugea area.

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Here in the bottom picture the anterior border of the

maxillary major connector ended on the posterior slope

not the anterior one (so that it is in harmony with the

rugea area and not very thick or prominent). This is

favourable because it won't interfere with tongue neither

the speech nor traumatizing the area.

We care about this in Cr-Co but not in acrylic because acrylic has better

adaptation to tissue (e.g. better cohesion and adhesion) but Cr-Co is still a

metal and thus it has poorer adaptation to tissues, so we should keep this in

mind always and end the anterior border of the maxillary major connector on

the posterior slope not the anterior one.

- Borders of a maxillary major connector should cross palatal midline

at right angle. Because I need the maxillary major connector to be the

thinnest in the midpalatine suture area.

- Tori should be avoided as much as possible.

Because the mucosa overlying them is very thin and

irritable easily traumatized

- Major connector should exhibit smooth androunded contours and angles. This will give the

patient more comfortable sensation and less plaque

accumulation

- Maxillary major connectors:

1- Palatal bar

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- Rarely indicated, honestly it is rubbish, shouldn't be used

- We won't be able to use it, because in order to be rigid enough it should be

very very thick and it won't be comfortable to the tongue

- Narrow half oval with its thickest point at the centre

2- Palatal strap

- One of the most commonly used maxillary major

connectors

- It consists of a wide band of metal with a

thin cross-sectional dimension

- Comfortable and might be used for most of the

cases especially long span bounded saddles cases. They can be also used

for class I and II Kennedy but not that much

3- Anteroposterior palatal strap

- Consists of two palatal straps, each should

be at least 8 mm in width to be of good rigidity

- Can't be used if we have a massive tori

(because each strap is 8 mm in width), in this case

anterioposterior palatal bar is used instead

4- Anteroposterior palatal bar

- Narrow Anteroposterior variation of

anterioposterior palatal strap

- Anterior bar is flat and similar to palatal strapin cross section.

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- Posterior bar is half oval and similar to palatal bar in cross section

- The two bars are joined by flat longitudinal elements on each side of the

palate

- Indicated in: torus palatines cases

- In both anterioposterior palatal bar and anterioposterior palatal strap, we

have the anterior part covering the vertical part of the palate, while the

posterior part covers the horizontal part of the palate, so that the major

connector will be in 2 planes at the same time, leading to the "L beam

effect" which enhances the rigidity of the major connector. So, all major

connector designs with anterior and posterior components exhibit the "L beameffect" and have very good rigidity.

5- Horseshoe

- Indicated in: torus palatines cases,

Periodontally involved teeth (so that we extend

the major connector to cover teeth to splint them),

prominent midpalatine suture (because thehorseshow is the only major connector that doesn't

cover any part of the midpalatine suture, unlike

anterioposterior palatal strap and anterioposterior

palatal bar which has its posterior part covering

part of the midpalatine suture)

-Consists of a thin band of metal running along the lingual surface of theremaining teeth and extending 6 to 8 mm onto the palatal tissues

-The main disadvantage of horseshoe major connector = its tendency toflex, because it isn't rigid enough and this is why it is contraindicated in

free end saddles (class I and II Kennedy

-It is preferable for free end saddles (class I and II Kennedy) to useeither wide palatal strap or complete palatal coverage (we need them to

be rigid enough, not to flex under loading

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6- Complete palate

- Anterior border should be kept 6 mm from

gingival margin or cover the cingula of anterior

teeth (if teeth are mobile and periodontally involved

and need splinting)

- Posterior border should extend to the

junction between the hard and soft palate.

Acrylic post dam area at the distal end of the major connector in the opinion

of the doctor is better (e.g. enhances retention more) than metal beading

which he thinks isn't effective at all

- It is very very good, because it provides ultimate rigidity and support,

it alsomaximizes distribution of forces

, and itenhances thermalconductivity (even better than acrylic resin)and it is also less porous than

acrylic resin so more hygienic

- It isn't comfortable for the patient

- Conclusions about the maxillary major connectors:

-If the remaining teeth are periodontally involved, a wide palatal strap ora complete palate is indicated.

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- If a torus is present and is not to be removed, anterioposterior palatal

bar, anterioposterior palatal strap (if not massive), or horseshoe major

connector may be used

- Horseshoe major connector shouldn't be used routinely because of the

possibility of flexure

-A palatal bar is very rarely indicated

- Mandibular major connectors:

1- Lingual bar

- Half pear shaped in cross section

- The broadest portion of the bar is

located at its inferior border

- Maximum cross-sectional dimension is

Oriented vertically (so it gains its rigidity

from its height not width)

- At least 8 mm of sulcus depth must be present

- Rigidity isn't always good because many errors might occur during the

processing of the lingual bar that will compromise its thickness thus the

ultimate rigidity

- Hygienic and tolerable by the patient

2- Sublingual bar

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- Maximum cross-sectional dimension is oriented horizontally (so it gains its

rigidity from

its width not height)

- Needs special impression technique

To record functional depth and width of

the sulcus accurately

- Needs less sulcus depth than lingual bar

(coz its widest cross-sectional diameter is horizontally oriented not vertically)

- The most rigid type of mandibular major connectors

- Sublingual bar is thicker in width, while lingual bar is thicker in length, but

finally the thickness of the sublingual bar (where we use speacial impression

technique to record the full width and depth of the sulcus) is more than that

of the lingual bar thus more rigidity

- Hyginic and tolerable by the patient

3- Dental bar

- Covers part of the lingual surfaces of the

anterior teeth

- Clinical crowns should be long enough

- Very thick (in height) and not always

tolerable by the patient

- It is hygienic

- It's rigidity isn't always good because many errors might occur during

the processing

- When using lingual or sublingual bar is contraindicated (e.g. shallow sulcus

depth, high muscle attachment, high frenal attachment ...) , then using thedental bar is indicated instead

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- Can be used to splint periodontally involved teeth when their clinical

crowns are long

4- Kennedy bar

- Consists of dental bar and lingual bar

- The upper bar (dental bar) should

Present a scalloped appearance(in order

Not to interfere with the tongue)

- Rarely indicated because it is technically

Difficult to fabricate

- Indicated when the dental bar is indicated (e.g. when lingual and sublingual

bars are contraindicated)

- Can be used to splint periodontally involved teeth

- Kennedy bar is better than dental bar major connector because the upper

part of it (e.g. the dental bar it has) is thinner and more tolerable and less

irritating to the patient than the dental bar major connector itself

- We will compensate for the thinner dental bar (the upper component) by

adding lingual bar (the lower component) to enhance rigidity of the major

connector

- Lingual bar used in here doesn't require great sulcus depth and it is also

narrower than lingual bar major connector

5- Lingual plate

- Covers most of the lingual surfaces of the teeth,

the gingival margin andthe lingual aspect of the

ridge

- Rigidity is achieved by thickening the

Lower border to a bar like section

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- Indicated when lingual and sublingual bars

are contraindicated and also when we have periodontally involved teeth (its

main indication actually is to have periodontally involved teeth, and it is the

most important type of mandibular major connector to splint periodontally

involved teeth)

- Main disadvantage >> it aids plaque accumulation (not hygienic)

- Its rigidity is good, also tolerable by the patient

6- Labial/buccal bar

- Runs across the mucosa on the facial surface of the mandibular arch

- Limited space and increased length makes it difficult to achieve rigidity

- More effective when used for short spans

- Indicated when we have lingually tilted premolars, and mandibular tori

- Poor tolerance by the patient, because we have limited space between teeth

and cheek thus it will be very irritating

- It isn't always rigid because we have minimal space and thus minimal

thickness and rigidity

- It is hygienic

-Mandibular Major Connectors Comparison ( present, ? Uncertain, xabsent

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-Conclusions about the mandibular major connectors-Lingual bar and sublingual bar are routinely used

-Lingual plate can be used when there is insufficient depth of sulcus,inoperable mandibular tori, and for patient with high muscle or high lingual

frenum attachment

-Lingual plate is also indicated when anterior teeth have poor periodontalsupport and need stabilisation

-A labial/buccal bar is rarely indicated

** Minor connectors

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-Minor connectors that join clasp assembliesto major connector (green colour in the

picture

-Minor connectors that join indirectretainers to major connectors (orange colour

in the picture

-Minor connectors that join denture basesto major connectors (purple colour in the

picture

-Minor connectors that serve as approach arms for vertical bar type clasps (bluecolour in the picture), these include


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-Is useful in a tooth-mucosa borne denture to help preventlifting of the saddle away from the mucosa

-Is provided by either a rest (top picture) or a maxillarymajor connector (bottom picture) placed on the opposite

side of the axis of rotation

** References

-A Clinical Guide To Removable Partial Dentures : Davenport et al-A Clinical Guide To Removable Partial Dentures Design : Davenport et al

Done by

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Tahany Mazen Abu Al-Teen

Who appreciates ART is no less than who creates it... What if we arein a position to create it guys ;) .. Shine on

I insisted to have my last lecture summarized in the field of Prosthodontics

because the first lecture I summarized was in Prosthodontics;1st lecture summarized >> was the 7th lecture in the course of

Introduction to dentistry, 24/7/2007, was lectured by Doctor Bilal

Mas'oud

Last lecture summarized >> is a review lecture in the topic of Cr-Co

RPD design concepts, 1/5/2011, was lectured by Doctor Anas Al-

Ibrahim

And there are so many lectures in between; each one of them is a whole

experience for me and a pleasant journey where I sailed in the mind of each

lecturer, trying to figure out the unique way he thinks and exploring his

perception of the topic he lectured in my own way , I actually found myself insummarizing, as I found unlimited ultimate passion that can't be described.

I do love you Dentistry. This is my true feeling as I know I might be living similar

experiences while attending any other school because it is me maybe who

determined the way it should go and end, however I can't deny how much being a

dentist polished and finished every single detail of my personality and also

designed the geographical map of my life.As I'm going back to the old times when I was a first year dental student and

exploring all those friends who showed up, remained, gone, the old ones who are

still here and the new ones who were never there and now they are here, I just

feel a sparkle shining everywhere in the air, charging my soul with unexplained

amount of positive energy and warmth .. And yeah I now realize that it doesn't

matter the way we begin it as it matters the way we end it .. We can begin it

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anyway but we should always end it the proper way .. I know that sometimes it is

a must that we begin doing things the proper way to continue doing them the

proper way and end them properly too but how many of us can guarantee this??!!

There's still hope that we can end in the right trail whatever path we were

following all these old times .. We just need a little faith and believe a littlepush.. And too much patience

And how much having the right people around is essential, as I know that we are

also lucky enough to have the "not right" people around sometimes because you can

learn from those people what you can't learn from any others .. you can know

more about yourself, the way you deal with certain situations, the way you might

force certain people to look at you, and what they might be expecting from you,

and lot of other things .. so never consider yourself unlucky to suffer from

anyone just because you didn't pick him carefully .. What is now a wound, is a

healed scar later, and how many scars we need to have to learn??!! The more we

have the more we learn .. and the more we learn the luckier we are.And as a second space maintainer has longer median survival time than the first

one not because it is technically better but because our perception for the case is

now better, Re-Friending (let's call it) who was supposed to be "not right" in the

past might be a rewarding friendship and experience in the future .. friendshipscan happen anytime, and relationships can never be deadly ended .. we are

supposed to get maturer .. and so our perception .. what was supposed to be

vague in the past, is supposed to be clearer (not totally clear) now.At the end, who we are now is what matters .. And what those experiences

carved in our image about life is what matters as well..As I'm looking back to the old Tahany and exploring the updated version of me ;P

I just laugh hhhhh .. though I used to love the old me since PARTs of her are

still somewhere here, but I'm so satisfied about whom I get .. we might lose

ourselves at certain tracks .. it doesn't matter, having a new adventure and

adding a new experience to our life, what matters is to understand the gift

everyone of us is blessed to have (the true You ) and try to get ourselves tothe right track again .. nothing is more relaxing, honest, rewarding than being

You and only You whatever you are trying to prove.

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I would like to thank the 8 lettered word "Thank You" since it helped me a lot to

express my pleasure to deal with lot of people and lot of experiences in the past

and still do.. and now I can feel this word is weak and disabled to help me as it

used to in the past .. you Mom and Dad, Amani (my soul twin), Wa'el, Na'el and

also 3addoool .. who believed in me from the beginning and never stopped doing so

.. you are my gift .. I would never be me without you standing beside me all the

way through .. you are my treasure .. and as I'm trying to get better and

better, only you I want to make proud of me .. thanks for all the love, the

care .. thanks for being my HOME .. thanks for being so GREAT and so PERFECT

.. Thanks ^ the last number in the world .. for everything u did and u still do and

u will do in the future enshalla .. your ability to give is unlimited.And you my friends .. all of you .. what would I say? .. with you I traveled

through so many cultures .. knew loads of stuff .. and shared so many wonderful

amazing indescribable moments .. Thank you for letting me part of your life ..

thank you for considering me a sister of yours .. thank you for all those laughs,

stand ups, happiness tears, successes, craziness, and so many other things that I

feel grateful to live and experience while you are around .. I do love you all ..

and I wish we can keep on touch as much as we can in the future .. I'm not

creating any drama scene in here .. LoL .. I just wish we can and I hope wewill

I hope I could leave a good reason for anyone of you to remember me .. I hope I

could leave a good impression .. precise secondary impression with a good

impression material .. so that when I meet you in the future you would be

remembering me..Shine on guys .. keep on believing .. get more passionate .. love what you do

before you have the chance to do what you love .. appreciate people more ..Aspire before you inspire .. appreciate beauty before you would be able to create

any .. be ALIVE guys .. be ALIVE Thank You

Documents

Review of Cobalt Chrome Denture Design 97-2003