Review of Cobalt Chrome Denture Design Concepts














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 edentulous space, 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.
Be careful, when u want to determine Kennedy classification remember that it is <<
different to look directly at the saddles or to look at the prosthesis that is supposed
.to replace missing teeth















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-end
(saddles) Mod I (not class III Mod I
Did you notice that the patient in the right picture has no 1st premolars, maybe * *
they 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
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
Polished surface should be shaped correctly to enhance retention and stability <<
.by muscular forces
Place teeth in neutral zone (e.g. where there's balance between inward and <<
(outward forces from cheek and tongue


Here in the picture, in the lower left quadrant (e.g.
your right side) teeth are set in their neutral zone compared to that in the right
quadrant (e.g. your left side) where teeth are set out of their neutral zone
((going lingually
Doing this will lead to NO interferences with the tongue, then better neuromuscular control and better denture stability and then better retention



















The material for the impression surface (e.g. denture fitting surface)
>> Denture base = is that part of removable partial denture that rests on oral mucosa and to which prosthetic teeth are attached
>> Ideal denture base has:
- Accuracy of adaptation to tissues
- Non-irritating surface that is capable of receiving and maintaining good finish
- 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
- 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 the
inherent 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
- Acrylic resin
>> Indicated in
- 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 importan




















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
































>> 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
Support = the resistance to vertical force directed towards the mucosa (e.g. to << (prevent the sinking of the denture into the mucosa
:Support in RPDs can be <<
Mucosa-borne >> only found in acrylic transitional RPDs (coz there's no rest - seat preparation on teeth to deliver occlusal forces to abutment teeth, look at (a) (below
Tooth borne >> found in Cr-Co RPDs restoring short span bounded saddles -
(look at (B) below). Support comes from mesial and distal abutment teeth
Tooth-mucosa borne >> found in Cr-Co RPDs restoring free end saddles and -
long span bounded saddles (look at (C) below). Support comes from abutment tooth/teeth and mucosa
























Planning support
Planning support
This actually depends on 3 important factors that should be interrelated together <<
to understand how much support we need for the prosthesis and how much support we
:can get from the remaining natural teeth. Those 3 factors are
 Root surface area of abutment teeth
>> 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

































>> 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
























>> 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?
>> 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:


















- 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




















>> 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 polished surface
- 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
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

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 of the 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.

1










- Appearance

image







>> 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
image









- 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 cariesin the presence of gingival recession and xerostomia
>> Occlusally approaching clasps are more hygienic than gingivally approaching ones


- 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)

image











B- Clasp design (flexibility ) (The more the flexibility the more the retention)
image









>> 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  lexibility 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).

image












- 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  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 clasps when 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 occlusally approaching clasp and good flexibility and retention is the Mesiodistal width of molars. So for molars occlusally approaching clasps but for premolar Gingivally approaching clasps.

image








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.

image










- Occlusion
>> 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.
image









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.

1










Another indication for ring clasp is when the suitable undercut is located lingually not buccally because th tooth is tilted, so this time the clasp will encircle the tooth from the buccal side to the lingual side to engage the undercut.

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 the fact it will irritate the buccal mucosa and the cheek.

image










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
- 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 be rotation, 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)

1










- Here in the picture, we have Gingivally approaching 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  will move downward and mesially thus preventing distal tipping (e.g. the clasping system won't act as an extraction forceps)
image












- Here in the picture, we have the RPI system, 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

image











- 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
- 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.
image














** Bracing
- Bracing = the resistance to displacement of the denture in both anteroposterior 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)
- 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 …)
image      image











- 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)
image










- 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.
image












>> Protect the soft tissues
- Borders of a maxillary major connector should be 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
image











- 3 mm in the mandible while 6 mm in the maxilla because in the mandible the sulcus tends to be shallower

- Borders should run parallel to the gingiva margins of the remaining teeth. Because we want to reduce plaque accumulation and to reduce crossing with the gingival margin
image











- Gingival margins must be crossed at righ angle. In order to reduce the contact between the delicate gingival margin and the minor connector

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>> Provide a means for placement of one or more dentures bases
- Different major connectors can be used according to the number and location of edentulous spaces

image











>> 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.
image











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.

image











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 and rounded contours and angles. This will give the patient more comfortable sensation and less plaque accumulation

image















- Maxillary major connectors:
1- Palatal bar
image













- 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
image










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

image












4- Anteroposterior palatal bar
- Narrow Anteroposterior variation of anterioposterior palatal strap
- Anterior bar is flat and similar to palatal strap in cross section.

image













- 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 bea effect" which enhances the rigidity of the major connector. So, all major connector designs with anterior and posterior components exhibit the "L beam effect" 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 the
horseshow 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)
image













Consists of a thin band of metal running along the lingual surface of the - remaining teeth and extending 6 to 8 mm onto the palatal tissues
The main disadvantage of horseshoe major connector = its tendency to - flex, 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 use - either wide palatal strap or complete palatal coverage (we need them to (be rigid enough, not to flex under loading

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.

image










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 also maximizes distribution of forces, and it enhances thermal conductivity (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 or a complete palate is indicated.
- 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)
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- 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
- 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

image







- 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
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- 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 the dental bar is indicated instead
- 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

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- 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 and the 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, x - (absent

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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 periodontal -
support and need stabilisation
A labial/buccal bar is rarely indicated -



** Minor connectors
Minor connectors that join clasp assemblies - to major connector (green colour in the
(picture Minor connectors that join indirect -
retainers to major connectors (orange colour (in the picture Minor connectors that join denture bases - to major connectors (purple colour in the (picture

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

Open construction <<
Need more interocclusal space than mesh -
because the metal is thicker  Setting of teeth is easier (that's why it isn't - always true to say that open lattice needs more interocclusal space since teeth in here get in (between the transverse slots

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Mesh construction <<
Need less interocclusal space because the -  metal is thinner Setting of teeth is very difficult (we might - trim the entire tooth to be able to set it (properly If used it allows us to do relining later on -

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Indirect retention

Is useful in a tooth-mucosa borne denture to help prevent -lifting of the saddle away from the mucosa Is provided by either a rest (top picture) or a maxillary - major connector (bottom picture) placed on the opposite side of the axis of rotation

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


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