prostho sheet # 7 - Malik Al3esa

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prostho sheet # 7 - Malik Al3esa

Post by Shadi Jarrar on 14/5/2011, 1:16 am

بسم الله الرحمن الرحيم

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Removable Partial Denture Components
Major Connectors



Today's lecture is a continuation of the components of the removable partial denture; we'll talk about major connectors:

A Major connector is the unit of the partial denture that connects the parts of the prosthesis located at one side of the arch with those on the opposite side.

Partial denture can never be unilateral, even if the teeth that are missing are on one side; it has to be extended to the other side for cross arch stabilization

Different components (clasps, rests ... etc) are connected to the major connector with minor connectors.

Major connector basically connects the parts on one side to the other side, to fulfill this function it has to be:
Requirements of major connectors
1. Biocompatible and comfortable for the patient
2. Rigid; if it is not rigid it will be flexed easily under load and it won't be able to fulfill its function which is proper stress distribution.
Flexible major connector would cause forces on the teeth leading to orthodontic movement, bone loss and irritation of the gingiva and soft tissues.
3. It should not interfere with or irritate the tongue.
4. It should not impinge on the oral tissues during removal or insertion of the RPD; this will cause ulceration of the tissues.
5. It should not accumulate or cause food retention or trapping, it should be self-cleansing (easily cleaned), even if food accumulates it should flow away with the saliva.
6. It should contribute to the support of the prosthesis, especially in the maxillary RPD because it extends on top of the palate and hence can take support or can transfer forces to the underlying palate.
It might also aid in indirect retention but they're not in direct retainers.
7. They should cover as minimum tissues as possible (you extend it if we have edentulous areas).
8. Possess smooth rounded edges to avoid discomfort, stress concentration and fatigue.
Angles always cause stress concentration, continuous pressure on stress area (angle) can cause fracture of the teeth.
All the angles in the RPD should be rounded


Mandibular Major Connectors
Types:
1. Lingual Bar.
2. Lingual Bar with Continuous Bar (Open Kennedy).
3. Lingual Plate.
4. Labial Bar.
5. Swinglock.
6. Sublingual bar.
7. Dental bar.

Lingual Bar:
Always use a lingual bar unless there is a contraindication!
Lingual plate has disadvantages that out way its advantages, we only use it if we need it or if there are contraindications for the lingual bar.
If you want to use any of the other major connectors you have to have a justified reason for using them, because the most appropriate is the lingual bar.
• It's a half-pear shaped.
• Very close to the floor of the mouth.
• To be able to use it; the distance between the gingival margin of the tooth and the floor of the mouth should be at least 8 mm. the reason is that for the major connector to be rigid it has to have at least 5 mm height minimum (otherwise it will not be rigid), and there should be a space between the gingival margin and highest border of the major connector (the minimum distance is 3 mm) because this is the biological width of the tooth, otherwise it will cause plaque accumulation, food retention, lack of cleansability and eventually loss of bone and teeth.
• This is one of the contraindications: if the distance between the gingival margin and the lingual bar is less than 3 mm, we cannot use it.
• You should be able to differentiate between the lingual bar and the sublingual bar because they are similar, same dimensions, the difference is that the maximum dimension in sublingual bar is horizontal and the maximum dimension in sublingual bar is vertical.

Advantages Disadvantages

1.Simplicity 1. May not be rigid
• if it is too long
• if there is not enough space to place it correctly
• If you have to provide relief in some areas like in cases of permanent torus)

2. Minimal contact with soft tissues.
• less plaque retention
• better soft tissue stimulation 2. Cannot be used in cases with tori
• there is two Mandibular tori (bilateral) in the premolar area on the lingual side)
• if you cover them with a lingual bar it will be very irritating for the patient and if you relieve it, lingual bar will be very thin (not rigid)
• So preferably if the patient has tori we should not use a lingual bar

3. It does not contact the teeth (very important).
3. Provides no bracing or indirect retention.
• The only function it provides is connection
• You have to have other components to provide proper bracing, stability and indirect retention




Lingual Plate:
• It looks like a lingual bar but with an extension.
• We use it when we don't have 8 mm space for the lingual bar (3 mm clearance and 5 mm for the lingual bar).
• If you can't provide a sufficient space (3 mm in Mandibular 6 mm in maxillary) then cover the tissues intimately.
• We don't leave spaces, because it will result in food accumulation, plaque retention, tissue hyperplasia and loss of the proper function.
• Pear shape lingual bar with thin solid metal piece extended on to the lingual surfaces of the anterior teeth.
• There must be adequate block out and relief for both soft tissue undercuts, gingival margins and undercuts in the proximal areas of the teeth
There should not be a space for food and plaque retention.
• The superior area (upper part) of the plate (which is scalloped in shape) must have intimate contact with the teeth (scalloped) and extended just above the cingulum of the teeth; to prevent food impaction.
Upper border should be in contact with teeth, but we can create a little relief (in the lower part) between the major connector and the underlying gingiva in cases of severe undercut or gingival irritation.
• Must always be supported at each end by an occlusal rest (usually on premolars) to provide some kind of indirect retention and prevent rotation of the framework and labial displacement of teeth.
• Its biggest disadvantages are poor/lack of patients’ tolerance because it is irritating since it's covering the teeth and the need for impeccable oral hygiene (can cause severe soft tissue irritation and caries).
• If the patient has bad oral hygiene this is a contraindication.
• As you can see in slide 13; there is a very close contact between the lingual plate and the teeth, there is no space for food trapping and it needs a skillful technician to do it especially if there is crowding in the anterior teeth, you can also notice the rests that aid in indirect retention.
• In slide 14; if there is spacing between the anterior teeth and you don't want the metal to be visible then you can cut back the metal, this will not compromise the rigidity since it's very thick and rigid.

Advantages and indications
1. Rigid (even if relieved around tori, rigidity is gained from the other parts).
2. Can be used when there is insufficient space for lingual bar (due to gum recession or high frenal attachment).
3. Can provide indirect retention and stability against horizontal forces (indirect retention if rests are added at each end.
(Remember that the major connector is not an indirect retainer, indirect retainer should be horizontal to resist the rotation, and lingual plate is oriented on a slope so the amount of retention gained is minimal).
4. Especially useful with distal extensions with excessive bone resorption; compromised abutments, amount of support provided is minimal, no teeth to provide indirect retention.
5. Can be used to splint periodontally involved teeth and mobile anterior teeth if they are lost they can be added to the old RPD with lingual plate easily.

Lingual Bar with cingulum Bar (Kennedy Bar):
• Used if there is not a sufficient 8 mm distance between the gingival margin and the floor of the mouth since there is two pieces that give some kind of rigidity.
• It is a little bit shorter than the lingual bar.
• To add some kind of rigidity, stability and indirect retention you can use the dental bar (Kennedy bar).

• Rests should be placed at each end of the upper bar mesially at first premolars to prevent the bar from moving inferiorly; (to provide indirect retention).
• The upper bar (dental bar) should be positioned at/extend to the contact points of the teeth, should be half oval in cross-section, 2-3 mm in height (just above the cingulum) and 1 mm thick. Its upper border should be scalloped.
• Lingual surfaces of teeth and interproximal soft tissues are exposed.
• The 2 bars (dental and lingual) are joined by a minor connector at each end located in interproximal spaces.
• As you can see in slide 18; it is 1 mm thick, 2-3 mm in height, and there is a distance that is exposed just above the cingulum till the contact points.
• As you can see in the picture if the teeth are spaced you cannot use such kind of major connectors, it will be visible.




Advantages Disadvantages
1. Indirect retention.
• Since the dental bar is just above the cingulum (at a relatively horizontal surface) it can provide some kind of indirect retention.
• At the end we put 2 rests at the premolars to provide additional retention. 1. More tongue annoyance; because there are 2 bars, and their edges are noticeable by the patient.

2. Horizontal stabilization.
2. Entrapment of food debris is very easy.

3. Stimulation for the uncovered gingival margin; because they it is not covered.
3. Complex design and difficult to make (needs a very skillful technician to make it).



Labial bar
• The connection here is labially rather than lingually.
• We use it very rarely.
• Runs at the Mucosa labial to the anterior teeth.
• It is indicated for malposed or lingually inclined teeth (because insertion of the denture will be very difficult in this case) and where there are prominent inoperable tori.
• Not commonly used because:
1. The labial bar is very irritating for the patient.
2. The labial flange is longer than the lingual flange and since it is longer it is less rigid, if you want to increase the rigidity you have to increase the bulk of the denture and if you increase the bulk it will be uncomfortable for the patient (patient irritability).
3. It does not provide any bracing or indirect retention.

• Labial bar is very rarely used; only when you have severe undercuts, malpositioned teeth or lingually tilted teeth.


Swing lock:
• A little bit advanced, we'll talk about it more in fifth year.
• It has a gate.
• It has some kind of vertical struts contacting the surfaces of the teeth on certain positions.
• A useful modification of the labial bar where the labial component has a hinge on one side and a locking device at the opposite side providing an opening and closing movement similar to a gate.
• The prosthesis is inserted while the lock is opened and this is locked after the denture is fully-seated.
• The denture permitting its insertion in inaccessible labial undercuts.
• It provides some kind of stabilization mainly because of the struts and the vertical arms.
• Especially useful when there are few remaining teeth, compromised stability, compromised support.
• You can actually cover vertical arms with acrylic to improve the aesthetics.
• When there is vertical forces directed towards the denture it will be concentrated on the vertical arms.
• Advantage: force will be distributed on all remaining teeth.
• Disadvantage: if there are higher forces posteriorly (excess forces) it will enhance the mobility of the teeth and end up losing all the teeth.
• Very rarely used, because if it is not properly designed it might cause some harmful forces on the teeth.
• All teeth are used to retain and stabilize the prostheses as the labial bar has small vertical projections contacting labial surfaces of teeth below height of contour. These projections can be replaced with acrylic base for better aesthetics (especially with short or mobile lip).
• Not preferable sometimes because firmly grasped teeth might be subjected to stresses when distal extensions move towards the tissues, although useful when only few mobile teeth are remaining as it helps splinting.


Sublingual Bar
• Half-pear shaped in cross section.
• Maximum dimension is horizontal.
• We can use it when we don't have 8 mm space between the gingival margin and the floor of the mouth (located at the depth of the sulcus).
• To determine the proper depth and width of the sulcus you need a special impression technique.
• If I have 6-7 mm I can use the sublingual bar, less than that then I have to use the lingual plate.



• So the sublingual bar is the first option if the space is reduced between the gingival margin and the floor of the mouth but it's not that small.
• Indications: when there is not enough space for lingual and sublingual bar


Dental Bar
• Dimensions more than 2-3 mm, so you need long teeth and crowns to use such kind of major connector.
• There should not be any spacing, otherwise it will be visible.
• It is not that rigid (it is thin).
• Not preferable.
• Indications:
1. When there is not enough space for lingual and sublingual bar.
2. Poor oral hygiene (lingual plate is contraindicated).
3. When you have long clinical crowns; it provides good bracing and retention.

Advantages Disadvantages
Good bracing and indirect retention
1. Low patient tolerance (whenever you cover the teeth it will be very irritating).

2. Poor aesthetics if spaces are present between teeth
3. Not rigid enough


Maxillary Major Connectors
Types:
1. Palatal Bar
2. Palatal Strap.
3. Antero-posterior Palatal strap.
4. U-shaped Palatal Connector.
5. Complete (full coverage) Palatal Plate.

Palatal Bar
• Palatal bar is narrow, gently curved, half oval with its thickest point at the centre.
• Used only in interim (temporary) prostheses as it lacks rigidity (because it is very narrow).
• Very rarely used, we can use it for a very short period of time.
• To improve rigidity, should be made bulky, and if you make it bulky it will be noticeable and uncomfortable for the patient
• Palatal bar is not really preferable; it provides little support because of its limited width (it is thick but the width is not that much antero-posteriorly).
• Because it has minimal tissue coverage; it provides little support and it can be used in temporary prosthesis or when you have very short span bilateral Class III (o1 or 2 teeth).
• It should never be placed anterior to the first premolar, because it is bulky and it will irritate the patient (causes discomfort).

Palatal Strap
• The thickness is little; however the extension antero-posteriorly is long (minimum 8mm).
• Should not be less than 8mm wide, but its cross-section is thin (more comfortable for the patient), the palate is a very vital area, the more you cover the patient will not be comfortable, palate will be insulated from normal oral stimulations and also you might affect the phonetics for the patient if it was tilted.
• The palate undergoes minimal resorbtion after the loss of teeth so the extra thickness will be useless.
• The most versatile maxillary major connector (most commonly used). The width is increased as the width of edentulous saddle increases.
• Mainly used for class III.
• Increased width provides rigidity and support (since you’ll be covering more of the hard palate).
• May be used in unilateral distal extension but not the bilateral distal extensions, (in class II -with minimal modification on one side- you can use it), but in bilateral distal extensions you need a more rigid major connector more with better support since a lot of teeth are missing so you might need to extend the major connector a little bit further.
• The anterior border should end posterior to the rugae area, but if not possible (if there is distal extension anteriorly) it should end at the rugae valley (keep the border between the valleys), otherwise it will become too bulky.
• The posterior border should end short of the junction of the hard and soft palate.
Advantages Disadvantages
1. Great rigidity with less bulk. Good stress distribution because of its width. 1. 1. The patient may complain of excessive palatal coverage.
2. Offers little interference with the tongue (because of its minimal thickness) 2. 2. Also might be associated with papillary hyperplasia with poor oral hygiene (since the thickness is little then we have to extend it more antero-posteriorly min. of 8 mm) so the patient might complain.
Offers retention through adhesion and cohesion (the major connector should be in intimately contact with the tissues).
3. Might give some indirect retention (depends: if it is extended on the surfaces of the teeth or horizontal surfaces).
If you need an indirect retainer you’ll need to use another major connector other than palatal strap.
Antero-posterior palatal strap (Ring connector)
• Similar to palatal strap, but with 2 straps (thinner antero-posteriorly).
• Very commonly used.
• Composed of 2 palatal straps each is 8 mm (minimum), with longitudinal bars connecting between them
• The middle area is left uncovered which is good; the tissues are not covered so there will be normal stimulation for the tissues.
• It is called ring connector.
• It has excellent rigidity.
• Each strap is at least 8 mm wide but has thin cross-section.
• Borders should be at least 6 mm away from gingival margins or covering the lingual surfaces of teeth (if you cannot provide a space of 6 mm then you should cover the lingual surfaces of the anterior teeth till the cingulum), so either expose the 6 mm or cover it totally.
• The two straps joined by flat longitudinal elements on each side of the lateral slopes of the palate.
Indications for antero-posterior palatal strap:
1. If there are widely separated abutments for ex. Class III with multiple modifications, (multiple saddles with good abutments).
2. Cases with large inoperable palatal tori; it is preferable to remove the palatal torus; if you can’t then you have to expose.
3. Patients who want to avoid palatal coverage.
4. Long edentulous span in class II modification 1 arch (because we want a design that is more rigid so we use anterior posterior palatal strap)
5. Class IV (because there is anterior saddle with components posteriorly).



Advantages Disadvantages
1. Provides good rigidity for relatively low bulk 1. The anterior strap might interfere with phonetics if it covers the rugae area.
2. Used when the patient objects the large palatal coverage 2.There are too many borders (2 anteriorly, on the sides and 2 posteriorly) might be annoying to/irritating for the patient (the anterior strap at highly innervated area and when you cover it the patient will be uncomfortable with this design)
3. Used with maxillary Tori.
4. Provides good support since it covers part of the horizontal surface of the palate.


• Although it is empty from the middle; it is rigid, because there is 2 straps (beams) in 2 different planes  they resist the movement of each other.

• A typical case to use the anterior posterior palatal strap  when there is missing anterior and posterior teeth with too many saddles (since there is many minor connectors in this case that need to be attached to the major connector).

U-shaped Palatal Connector (Horseshoe-shaped connector)
Indications for U-shaped Palatal Connector:
1. We use it mainly with class IV (When there are many anterior teeth that need to be replaced).
2. With palatal tori (at the middle) extending to the posterior border of the hard palate; in this case we can’t use anterior posterior palatal strap.
• Very rarely used; it has so many disadvantages.
• Thin metal band running along lingual surface of remaining teeth and extends on the palatal tissues for 6-8 mm.
• Metal borders end at the junction of the vertical and horizontal slopes of the palate but might be extended to increase rigidity.
• All borders should be gently curved (rounded) and smooth.
• It covers the lingual surfaces of anterior teeth and goes down to the junction between the vertical slope and the horizontal plate of the palate; you can extend it a little bit more if you need more rigidity.

Advantages Disadvantages
1. Reasonably strong 1. When vertical forces are applied on one or both ends it tends to flex and deform.

2. Has moderate indirect retention 2. Cannot be used for distal extension RPD.

3. Has moderate support 3. Greater bulk is required to avoid flexing and to increase rigidity, but results in discomfort, interferes with phonetics and it will be uncomfortable for the patient

4. Poor cross-arch stabilization
So it is one of the least commonly used.
When forces are applied posteriorly, it tends to flex easily.





Complete Palatal Plate (complete palatal coverage)
The picture shows an ideal case when to use this kind of major connectors (all posterior teeth are missing, anterior teeth are present).
We need indirect retainers on anterior teeth (it will be very weak on centrals and laterals)
So if the remaining teeth are compromised, the amount of indirect retention and periodontal support is minimal we need more coverage (more support) of the palate.
Despite the fact that this is a maxillary arch and the degree of resorbtion is less than the lower arch, we need to distribute the forces and the stresses evenly.
We cannot apply a lot of forces on anterior teeth and the saddles so we use the palate since it can provide sufficient support if the connector was properly designed.
• The lingual surfaces up to the cingulum are covered.
• It covers the entire palate.
• Its anterior border should be 6mm away from the gingival tissues or extends up to the cingula of anterior teeth.
• The posterior border should extend to the junction of the hard and soft palate (you can actually get a better seal by making a beading -like a step- posteriorly; this provides better adaptation for the tissues.
• If it was in intimate contact with the tissues it can provide better retention through adhesion and cohesion.




• If you cover the lingual surfaces of the teeth; you have to cover them intimately  if you left a space gingival would enlarge in order to fill the space resulting in inflammation.
• This does not mean engaging every single undercut so the denture is inserted and removed in a difficult way.
• It has to be easily inserted and removed.
• Sometimes severely undercuts cannot be relieved; in this case we should maintain an intimate contact between the major connector and the surfaces of the teeth.
Indications for Complete Palatal Plate
1. Many posterior teeth are missing and need to be replaced, plus periodontally compromised abutments.
2. Kennedy class I with anterior teeth replacement (class I with modifications), and with very poor anterior abutments.
3. Patients with developed muscles and natural lower teeth, in those two cases there will be excessive forces on the denture  we need better stress distribution and better support.
4. Flat highly resorbed upper ridge and shallow vaults where high stability is required, (if the edentulous ridge is resorbed you cannot gain sufficient support).
Advantages Disadvantages
1. Best rigidity and support 1. 1-Soft tissue reaction (hyperplasia of the tissues with poor oral hygiene).

2. Better transmission of temperature and thus better stimulation for underlying tissues.
2. 2- Might interfere with phonetics if it is thick.

3. Little discomfort or effect on speech because of its minimal thickness (if you extend it more this means it won’t be thick).

Remember that the second requirement of the major connectors is to cover as minimum tissues as possible, we use complete coverage when there is an indication (poor abutments, many missing teeth, ridges are highly resorbed ... etc).
You can uncover an area of 6 mm; if you cannot then you have to cover the whole lingual surfaces.
If you expect that posterior teeth will be lost and the anterior teeth eventually will be lost, it might be converted in to a complete denture




If today was your last day
And tomorrow was too late
Could you say goodbye to yesterday?
Would you each moment like your last?
Leave old pictures in the past?
Donate every dime you had?
Would you call old friends you never see?
Reminisce old memories?
Would you forgive your enemies?
If today was your last day
Malik M. Al-Issa
Prostho sheet # 6
Dr. Nadia
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Shadi Jarrar
مشرف عام

عدد المساهمات : 997
النشاط : 12
تاريخ التسجيل : 2009-08-28
العمر : 26
الموقع : Amman-Jordan

http://jude.my-rpg.com

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