PROS- RPD Design Flashcards
Contains RPD design & Tooth modification
What is the part of the denture that the arrow is pointing to?
This is the denture flange and it is the replacement tissue which extends into the vestibular sulcus
Why can kennedy class IV not have a modification?
As the most posterior saddle defines the classification. Therefore, if the patient had another saddle it would be used for classification & the kennedy class IV would be reffered to as the modification.
Compare denture support?
Using teeth for support directs the load through the PDL of the abutment teeth.
Using mucosa for support distributes the load over a wide area. This uses the hard palate and saddles.
Which tooth should we pick to provide support
Those teeth with the largest root area.
What is a denture rest?
This is the metal bit attached to the tooth that allows distribution of the load down the abutment teeth.
What are the functions of the rest?
- Preventing movement of the RPD towards the mucosa
- Distributing the occlusal load
- Supporting the placement of clasps
- Preventing the over-erruption of unopposed teeth
- Providing bracing on the anterior teeth
- Determining the axis of rotation for free end saddle RPDs.
What is important when designing an occlusal rest?
The rest should come down to the midline of the tooth. So it is large enough for the force goes down the long axis of the tooth .
It should not be placed on an occlusal contact point (as this would be very uncomfortable for the patient)
What is important for incisal rest design?
An incisal rest should only be used on the lower arch (it is unaesthetic on the upper)
What is an advantage of a cingulum rest?
The cingulum rest applies the stress at a lower level.
This means there is less rotational force, meaning the tooth is less likely to break.
Why is it rare to have a metal rest in an acrylic denture?
The metal rest is encorporated mechanically to the acrylic base which produces a pottential weak point in the denture (leading to denture failure)
Where do we place rests on a bounded saddle?
On either side of the saddle area
Where do we place rests on a free end saddle?
The opposite side of the tooth to the saddle.
This is to prevent torquing
Why is having a small surface area of mucosal support inadvisable?
As it will place pressure at the gingival margin and acclerate bone resorption causing denture failure.
Why are mucosa only dentures not recommended on the lower arch?
As the mucosal support on the lower arch is limited.
You can only use the buccal shelf.
What is an ‘every’ RPD design?
This is an open designed denture which spreads the load and keeps the gingival margins healthy.
The denture is kept in the mouth by the frictional contacts between the artificial teeth and the abutment teeth.
What is the arrow pointing to in this denture and what is the function?
The arrow is pointing to wire stops.
These prevent distal drift of the posterior teeth.
We want to prevent this drift as it would cause the loss of the frictional contacts resulting in the denture falling out.
What is Axial Torque?
When movement of the tooth one way causes the root to move the other. This causes breakdown of the Periodontal ligament.
What can we do if the chosen rest position is an occlusal contact point?
- We can move the rest onto the opposite side of the tooth
- Complete a preparation for the rest (requires drilling into a healthy tooth)
What is retention?
What prevents the denture from being dislodged.
Compare the two types of retention?
Direct retention- prevents vertical displacement of the denture.
Indirect retention- prevents rotational displacement of the denture.
How can we achieve retention?
- Mechanically- using clasps
- Muscular forces (over time lingual and buccal muscles will hold the denture in place)
- Physically- using
Adhesion- saliva on the denture
Cohesion- substances within saliva
- Through frictional contacts.
What are guideplanes
Guideplanes are paralell surfaces that provide frictional contacts.
What are clasps?
A metal arm that contacts the tooth in an undercut in order to prevent the removal of a denture base.
Compare guideplanes to clasps
Guideplanes don’t deform over time giving you long term retention.
Clasps deform.
How does the clasp move into place?
The clasp deforms over the bulbosity of the tooth.
How does a rest help clasp function?
The rest prevents the clasp slipping down and damaging the tooth or gingival margin.
Where do you find the undercut on upper posterior teeth?
On the buccal.
Where do you find the undercut on lower posterior teeth?
The lingual.
L-lower L-lingual
Describe an occlusally approaching clasp.
This clasp comes to the undercut across the occlusal surface of the tooth.
It is used for molars.
What is a gingivally approaching clasp
This comes to the tooth crossing the gingival margin. (It comes from the sulcus)
It is used for anterior teeth, canines and premolars.
(It is also known as an I-bar clasp.
Why do we use a gingivally approaching clasp for the anterior teeth, canines and premolars?
It is the only way we can guarentee the 15mm of length that is needed in order to achieve retention.
What is a self reciprocating clasp?
This is a clasp where the clasp metal extends to where the reciprocal arm would be.
Describe the function of the reciprocal arm.
The clasp arm applies a horizontal force to the tooth when it comes in contact.
The reciprocal arm is also in contact on the opposite side.
The reciprocal arm counteracts the force to prevent tooth movement when the clasp is flexing over the bulbosity.
Why do we aim for a triangular patten of retention?
So that you will always have one retainer preventing the dislodging of the plane of the other 2 retainers.
What is the RPI?
A stress relieving clasp system used to prevent stress on the last abutment tooth of a free-end saddle.
What are the components of the RPI?
A- Rest (an occlusal rest on the mesial)
B- Proximal plate (placed adjacent to the saddle)
C- I bar clasp
How does the RPI clasp prevent pressure?
The I bar and the proximal plate come out of contact with the tooth when the patient chews.
How do we achieve indirect retention for free end saddles?
By moving the supporting element away from the saddle area at 90º from the clasp axis
What provides indirect retention?
- Major connectors
- minor connectors
- saddle
- rest
- denture base
What is the connector?
The rigid part of the partial denture that unites the other components.
What is a minor connector?
Thes join components such as rests to other components and the major components.
What is the function of the minor components?
They transfer functional stresses to and from the abutment teeth.
What should you expect in a minor connector?
It should finish above the survey line on teeth
It should cross the gingvial margin at right angles.
It should cover as little gingival margin as possible.
What are the major connectors?
These connect components on one side of the arch to components on the other side of the arch:
What should you expect in a major connector?
- They should not cover the gingival margins
- They should have as few edges as possible
- Cover as little tissue as they can.
What are the two types of major connector?
- A plate connector
- Bar connector
Discuss plate connectors
These are used for mucosa support dentures. (therefore not recomended in mandibular as there is not much to provide support)
They cover the gingival margins
Discuss bar connectors
These connectors require less mucosal coverage.
They are much thicker to maintain rigidity.
they are used in the mandibular arch as there is less space.
Compare a lingual and sublingual bar.
A lingual bar is behind the teeth
A sublingual bar is below the tounge- this is more difficult to place as the floor of your mouth moves when you move the tounge.
How do you decide to use a lingual bar or a lingual plate?
There needs to be an 8mm space from the floor of the mouth to the gingival margin for a bar.
If you don’t have the space, a lingual plate is used instead.
Discuss the advantages and disadvantages of the anterior/ posterior bar.
Advantages:
little gingival coverage
rigid connector
relief of the gingival margins (prevents food impaction)
Disadvantages:
The many edges may be uncomfortable
As diameter is thinner, there will be thicker cross sectional metal.
Posterior bar provides less support to the free end saddle.
Discuss the advantages and disadvantages of a full palatal coverage.
Advantages:
rigid connector
Wide relief of the gingival margins
Support across the hard palate for the free end saddle
Less edges
Thinner cross section
Disadvantages:
Mucosa is covered so there is no natural sensation.
What is the function of major connectors?
- To provide indirect retention
- To assist stability through resisting functional forces in a horizontal direction.
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What is beading?
When you carve into the impression 3mm away from the gingival margin in order to produce an intimate contact between the denture and the tissue.
This prevents food ingression.
Compare open and closed saddle designs.
The open saddle design has no gingival coverage. This allows clearance and saliva to go through. It also reduces irritation of the gingival tissues. e.g. minor connectors connected to the saddle.
The closed saddle design has more contact. It provides greater retention but increases irritation to gingival tissues. e.g. minor connectors that also attach to the cingulum of the tooth.
Name this denture design:
Mid palatal strap
Name this denture design:
Full coverage plate.
Name this denture design
Anterior bar
Name this denture design
Horseshoe
Name this denture
Posterior bar
Name this denture type
Anterior posterior bar.
What type of denture is this?
A lingual bar
What type of denture is this?
A lingual plate
what type of denture is this?
a dental bar
What type of denture is this?
A sublingual bar.
Why should retention be close to the saddle area?
As the saddle area is the location of the dislodging force.
Discuss the location of indirect retention in relation to the clasp.
The indirect retention should be seperated from the clasp by the clasp axis.
Without this separation. It is not retentive.
What is an undercut?
The area under the maximum bulbosity of the tooth
Compare the different types of undercuts.
Soft tissue undercuts- The contour of the alveolar ridge that would prevent the vertical placement of a denture. These can also cause the base to get caught-making removal more difficult.
Hard tissue undercuts- The portion of a tooth surface between the gingival margin and maximum bulbosity where you can place a clasp.
How do we identify undercuts?
By surveying the teeth- where you use a graphite marker to draw lines on the teeth.
You try and get the point of the graphite marker into the gingival crevice. If there is an undercut this is not possible.
The undercut is measured as the space between the two lines.
Why do we alter the path of insertion?
To get rid of the undercuts
What is blocking out and why do we do it?
blocking out is putting wax in the undercuts (where we place the connectors and clasps would go)
We do this so that the RPD doesn’t gointo places it shouldn’t be (i.e. the undercuts)
What is the function of Pin and Post dams?
Compare them
These are ridges which improve the adhesion of the denture.
Pin dam- A shallower groove on the anterior 5mm away from the gingival margin to prevent food slipping under the denture.
Post dam- A ledge on the posterior of the upper denture in the palatal surface.
