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RPD design > RPD design > Flashcards

RPD design Flashcards

1
Q

What is a Kennedy class I?

A
  • Bilateral free end saddle
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2
Q

What is a Kennedy class II?

A
  • Unilateral free end saddle
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3
Q

What is a Kennedy class III?

A
  • Unilateral bounded saddle posteriorly
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4
Q

What is a Kennedy class IV?

A
  • Anterior bounded saddle
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5
Q

How do you include mod in Kennedy class? Use with an example of Kennedy Class III mod 1?

A
  • Work form the most posterior part of mouth to identify which kennedy class fits the pt
  • Then any additional (smaller) gaps = no of mods

Picture is K class III mod 1 as has unilateral posterior bounded saddle with 1 more saddle

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6
Q

What is the checklist of things you need to include when designing your RPD?

A
  • Saddles (What teeth need to be replaced)
  • Support (resisting movement towards soft tissues)
  • Retention (resistance of movement away from soft tissues)
  • Reciprocation/bracing (resistance of side to side movement / lateral forces)
  • Indirect retention
  • Major connectors
  • Minor connectors
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7
Q

What is meant by support? What are the two types?

A
  • Resistance to movement towards soft tissues
  • Can be tissue borne or tooth borne
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8
Q

How can support be provided by mucosa born source?

A
  • Extends acrylic to full functional sulcus depth
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9
Q

How can support be provided by tooth borne source?

A
  • Occlusal rest seat
  • Cingulum rest seat
  • Incisal rest seat
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10
Q

Where are rest seats usually placed?

A
  • Placed on the tooth surface nearest the saddle on either side
  • Mesially if part of RPI system (furthest side of tooth from saddle)
  • Can also be placed on crowns of abutment teeth if planned correctly and in advance
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11
Q

Why do we want tooth borne support?

A
  • Additional benefits of proprioception from the PDL of the abutment teeth
  • Less damage to the gingivae
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12
Q

What can occur if the rest seat is not placed so that it is flush with the tooth surface?

A
  • Plaque trap
  • Prop open the bite leading forces in wrong direction
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13
Q

What is the meaning of retention? How can is be achieved?

A
  • Resistance of movement away from soft tissue (prevent denture being dislodged by sticky toffee)
  • Mechanical or Muscular (cheeks)
  • Can also be adhesive forces (saliva suction seal)
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14
Q

How is mechanical retention achieved? What requirements do we need?

A
  • Clasps that engage a 0.25mm undercut on tooth
  • Terminal 1/3rd engages undercut
  • Need 1mm minimum clearance from gingiva from the tip of clasp due to flexion (want to avoid gingival trauma)
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14
Q

What can too much flexion of a clasp cause ? How can this be avoided?

A
  • Distortion of fracture
  • Choose correct material as the force required to flex the clasp over maximum bulbosities of teeth needs to be > force attempting to dislodge denture
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15
Q

What is the diamater and min length needed of Cast co-cr alloy for
a clasp?

A
  • 0.25mm diameter
  • 15mm min length
16
Q

What types of clasps are there ans what are they used for?

A

Occlusally approaching clasp for molars and premolars
- C clasp
- Ring clasp (when undercut not in easy area for C clasp to engage) Needs rest distally and mesially

Gingivally approaching clasp (aesthetics)
- I bar
- L bar
- T bar (mandibular canines)
But need 4mm sulcus depth and only contacts tooth at tip
Contraindicated in buccal undercut of 1mm depth / 3mm from gingival margin

17
Q

What is reciprocation?

A
  • Resistance of side to side movement
18
Q

How is reciprocation achieved?

A
  • Placed opposite to retentive clasp to assist in preventing unwanted movements/ stresses of abutment teeth

Done by
- Reciprocating arms provide some resistance and allow flexion so retentive arm doesn’t get too much pressure and break
- Reciprocating clasp still need to engage undercuts
- try and circle tooth by 180degrees

18
Q

What is bracing? What can you use to help with this?

A
  • General resistance to lateral movements exerted on dentures by
  • Maxilla
  • Flatter ridge (more movement)
  • Major connector and flanges
19
Q

What is indirect retention?

A
  • Resistance to rotation around a fulcrum axis
  • Providing indirect retention moves the fulcrum of movement
20
Q

What is a fulcrum axis?

A
  • line of rotation
  • Imaginary line between most post rest seats on the end of each arch
21
Q

What is the clasp axis?

A
  • Imaginary line between clasps on opposite sides of arch
  • When multiple use one closest to saddle as major one
22
Q

What are the principles of indirect retention?

A
  • Retentive clasps should always be between the saddle and indirect retainer
  • Retentive clasps should be as close to saddle as possible, whilst the indirect retainer is as far away from saddle as possible.
  • Try not to have movements that will force pressure on a tooth/ortho movement.
23
Q

What do minor connectors do?

A
  • Connect the components such as rest seats to main body either saddle or major connector
24
Q

What do major connectors do? What do we want the connector to be? What do we not want the connector to be?

A
  • Join the components of RPD

Want and don’t want
- Rigid not bulky
- OHI friendly
- Not impinge on gingivae
- Wide coverage if maxillary to spread occlusal load
- Keep away from ant teeth and incisive papilla

25
Q

What are the maxillary major connector types?

A

Palatal plate
- Leaves gingiva free
- Rigid
- Simple design
- Keep away gingival margins
- but pts may not like bulkiness

Ring connector
- Allows speech function and taste
- Used when saddles widely distributed in arch
- Palatal tori
- 15mm between anterior and posterior

26
Q

Mandibular major connectors ? pros and cons

A

Sublingual bar
- Need 3mm gingival margin clearance and 2mm actual hieght of bar (5mm total clearance)
- 4mm thickness for rigidity

Lingual bar
- Must be 3mm from gingivae
- 4mm height bar and 2mm thick for tongue (tot 7mm depth needed )
- Problem if prominent lingual frenum or mandibular tori

Lingual plate
- Avoid if possible- encourages periodontal disease and caries.
- Covers lingual aspects of teeth + gingivae.
- When teeth are poor prognosis and not enough gingival clearance.
- Plaque trap

Labial bar
- Lingually inclined teeth
- Swinglock dentures: hinged labial bar – useful when very little undercut present.

Acrylic
- Advantages/Indications = low cost and ease of modification, immediates, poor prognosis teeth, transitional, young patients in growth.
- Careful design as commonly known as ‘gum strippers’.
- Be aware of spoon dentures and modified spoon dentures. – These are not commonly used anymore.
- Keep 3mm borders from all gingival margins. (3)
- Can add SS wire clasps posteriorly- typically used as stops to prevent distal drift and for added retention.
- Connector has to be bulky to avoid flexure etc- patients may complain about function (temperatures of food) and speech (lisps).
- Flanges can also brace the denture.

27
Q

What is an RPI system and why is used?

A
  • Occlusal Rest, distal Guide Plane, Gingivally approaching I bar
  • Used to prevent distal movement/tipping of abutment tooth to a free end saddle.
28
Q

How does an RPI work?

A
  • Allows the free saddle to rotate slightly without damaging the soft tissues or abutment tooth.
  • As the denture is pushed into the tissues, it rotates around the mesial rest- the plane and I bar disengage from the tooth and remove any harmful torque forces.
  • Need this flexibility and adaptability of this system so that the saddle does not apply unwanted/ unfavourable force to the tooth.
29
Q

Why might you modify unfavourable survey lines?

A
  • High survey line- too close to occlusal load
  • Clasp visible
  • May interfere with mastication or get caught on the occlusal surface when being placed in the mouth and engaging.
30
Q

What are guide planes?

A
  • Parallel surfaces cut by clinician on abutment teeth which are used to control the POI + add stability
31
Q

What are the advanatges of guide planes?

A
  • Increase stability as it resists displacement forces in any direction (except path of displacement)
    reciprocate
  • Continuous contact with tooth – helps clasp retention
    prevent clasp breaking/stretching
    ensure patient inserts and removes the denture along the planned path
  • Improve appearance as can adapt the saddle to fit snug against guide planes- minimising gaps
32
Q

What are the requirements for a rest seat?

A
  • Not interfere with occlusion or cause unwanted forces on tooth
  • <90 degrees slope
  • Need vertical loading
  • Flush with tooth to avoid plaque trap
  • 1mm thick , 1/3width and 1/3 length of tooth
33
Q

What is meant by path of insertion?

A
  • A change to path of displacement the improves retention
34
Q
A

RPD design (1 decks)

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