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BDS2 CDS > Pros > Flashcards

Pros Flashcards

1
Q

Define indirect retention.

A

Component of a denture that prevents movement away from tissue arising from a rotation of the denture such as in a free end saddle case.

  • or resistance from rotational movement
  • component should be placed as far away from the axis of rotation as possible, and should be placed at 90 degrees to clasp axis
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2
Q

Define retention.

A

Resistance of a denture to vertical displacement.

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3
Q

Briefly describe the problems relating to free end saddles.

A

support is tooth and mucosa - this can cause extra stress and damage on the abutment teeth
can cause rotation (of denture)
can cause tilting (of tooth)

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4
Q

Describe the advantages of an RPI system.

A

stress relief for the abutment tooth
protects the tooth from tilting or rotating
mesial rest prevents rotational movement of denture
proximal plate creates a guide plane which prevents upward movement of denture (provides retention)

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5
Q

List other simple design features which should be used, apart from the RPI system, when designing a free end saddle RPD.

A

occlusally approaching clasp
additional rest that is not adjacent to saddle for indirect retention
extend acrylic part of denture to retromolar pad (or tuberosity of maxilla) for additional support (as this transfers load)

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6
Q

Define support.

A

the resistance of a denture to occlusally directed loads

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7
Q

Give examples of support.

A

occlusal rests, cingulum rests, large area of tissue covered e.g. connector covers the hard palate
optimum extension - retromolar pad, buccal shelf (base of ridge to external oblique ridge)

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8
Q

Give examples of retention.

A

Mechanical (clasps), muscular forces (shape of the denture, lips), physical forces (adhesion, cohesion - saliva)

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9
Q

What materials are each undercut gauge used for?

A
  1. 25mm = CoCr
  2. 5mm = gold
  3. 75mm = stainless steel
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10
Q

What articulator is used to mount casts with?

A

Non-arcon

NB: arcon one is one which resembles the anatomy of jaw I.e. TMJ

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11
Q

What instructions would you give on a lab card for Primary Impressions?

A

Please pour primary impressions in 100% dental stone. Create custom trays using PMMA with 3mm wax spacing and with extra oral handles. Please do not perforate trays. Create occlusal stops. If sufficient teeth, mount casts and survey. Disinfected - circle YES

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12
Q

Why do you need to write a written lab prescription and draw one?

A

To improve communication and so the lab has a better understanding.

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13
Q

What instructions would you write on a lab prescription card for the Master Impressions stage?

A

Please pour impressions in 100% dental stone (if for an acrylic denture) or improved stone (if for an alloy base denture). Mount casts on articulator. Survey casts and block out undercuts in relation to design. Duplicate master casts and mount on to the articulator. Set teeth for tooth trial using shade and mould provided.

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14
Q

If patient does not have sufficient teeth to occlude study casts, what are the options for the lab prescription?

A

Use a wax wafer if there is sufficient teeth for this. Request that primary impressions are poured in 100% dental stone with aid of wax wafer.
If insufficient teeth, send primary impressions and request that the are poured in 100% dental stone and that occlusal rims are constructed.

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15
Q

What thickness is required for rests?

A

0.5mm (1mm at junction with minor connector)

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16
Q

What length of clasp is required?

A

15mm

17
Q

What is the thickness required for a maxillary plate/strap?

A

0.4mm minimum

18
Q

What are the dimensions needed for a maxillary bar connector?

A

6mm width, 1.5mm thickness

19
Q

What is a RPI system?

A

R - mesial rest
P - proximal plate, provides guide plane
I - I-bar clasp engaging buccal undercut on tooth

20
Q

What is a system for denture design?

A 
Outline saddles
Support
Retention
Bracing
Connector
Review design
21
Q

What is the importance of the retromylohyoid area?

A

It provides stability for mandibular dentures

22
Q

What are the pros and cons for palatal plate connectors?

A

pros - well tolerated (few edges), open gingival margins (good hygiene), good rigidity, good support
cons - heavy (can lead to easy displacement), once made position of post dam cannot be altered, covers palate

23
Q

What are the pros and cons for a ring connector?

A

pros - works well with multiple saddles, covers little of palate, can be used if patient has palatinus torus
cons - no support provided, anterior bar can interfere with speech and swallowing, low tolerance (many edges)

24
Q

What are the pros and cons for a lingual bar connector?

A

pros - default, good tolerance, good hygiene (open gingival margins)
cons - no bracing/indirect retention provided, anatomical restraints (lingual frenum, mandibular torus), 8mm sulcus depth required

25
Q

What are the pros and cons for a sub lingual bar connector?

A

pros - good rigidity, good hygiene (open gingival margins), good tolerance, smaller lingual sulcus height required
cons - no bracing/indirect retention provided, very technique sensitive - requires specialised impressions

26
Q

What are the pros and cons of a lingual plate connector?

A

pros - provides bracing/indirect retention, good rigidity, good patient tolerance
cons - poor hygiene, avoid unless patient has good oral hygiene

27
Q

What are the pros and cons for a dental bar connector?

A

pros - provides bracing/indirect retention, good hygiene (open gingival margins)
cons - low tolerance, clinical crowns must be long enough, avoid if anterior spacing

28
Q

What are the pros and cons for a labial bar connector?

A

*used when anterior teeth are lingually inclined, thus preventing use of lingual bar etc
pros - good hygiene
cons - no bracing/indirect retention provided

29
Q

What are the pros and cons of a lingual bar + dental bar (Kennedy bar)?

A

pros - good rigidity

cons - very complex to create, avoid if simpler alternative can be used

30
Q

What components of the RPI system act as reciprocators?

A

the minor connector carrying the mesial rest contacts the mesiolingual surface of the abutment tooth
along with the distal plate, this acts as a reciprocal for the tip of the retentive clasp

31
Q

What is blocking out?

A

preparation of undercut areas on the master cast to provide the common path of insertion for the partial denture
all undercut areas that are not being used in the RPD design are blocked out

32
Q

Why prepare the master cast by blocking out?

A

Failure to correctly prepare the master cast by blocking out unwanted undercuts will results in a denture that will not fit the patients mouth without chair side adjustment.
Adjustment at chair side is time consuming and very difficult to achieve precisely - it could result in an ill fitting denture

33
Q

When surverying casts, the primary casts are firstly tripoded to the survey table. Why is this?

A

Casts are tripoded to the common path of displacement - this orientates the cast to the surveyor table
If the path of insertion in altered, this is also tripoded (in red) to allow orientation of the cast to the surveyor table
Tripod marks also allow the master casts to be placed on to the surveyor to the same path of insertion as the primary casts

34
Q

Once blocking out is completed in all required areas, the maxillary casts sometimes have beading (pin/food dam) and post dam cut into them. What is the post dam? What is it’s function?

A
  • post dam provides a seal at the periphery of the palatal extension of the denture (physical retention)
  • post dam is a groove cut into the surface of the cast
  • the resulting dam on the denture enables an intimate contact with the compressible tissue surface that will prevent air from breaking the denture seal
  • enables denture to have a precise finished edge and enables denture to be thinned at the edge to blend with the tissues due to the rounded beading
  • prevents ingress of food beneath the denture base
  • only used for maxillary dentures where direct retention is augmented by physical forces of retention (therefore less teeth present)
35
Q

What is a pin/food dam? What is it’s function?

A
  • shallow groove is cut on the surface of the cast at the periphery of the baseplate to provide an intimate contact between the denture and the palate
  • the bead produced should be rounded, 0.5mm deep and 1mm wide
  • denture base should be kept clear of gingival margins by 5mm (3mm minimum)
  • beading should stop 3mm from gingival margin
36
Q

What are the different duplication materials? What are the advantages/disadvantages of each?

A 
reversible hydrocolloid (agar gel): reusable, economic, limited shelf life
condensation cured silicone: not reusable, more expensive, more accurate
37
Q

How far away should upper major connectors stop from the gingival margin?

A

5mm

38
Q

How far away should lower major connectors stop from the gingival margin?

A

3mm

39
Q

What can provide stability (resistance to horizontal forces) and indirect retention in a maxillary denture?

A

major connectors

BDS2 CDS (5 decks)

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