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BDS3 Past Paper By Topic (05-19) > Prosthodontics > Flashcards

Prosthodontics Flashcards

1
Q

What is torus palatine? (1.5)

A

A harmless bony growth on the middle of the roof of the hard palate. Can vary in size

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2
Q

What is the prosthetic significance of torus palatine? (1)

A

Can’t use palatal strap for maxillary RPD – need to remove by surgery or use other type of strap.

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3
Q

What is the management of torus palatine? (1.5)

A

Surgery to remove; leave it; make sure the RPD doesn’t touch that area

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4
Q

How do you assess teeth used as denture abutment?

A
  • Endodontic status (Vital / root-filled)
  • Periodontal status (no mobility or advanced recession, bone loss < 1/3 of total length of roots)
  • Restoration status (quality and quantity) (structural integrity, remaining sound tooth structure)
  • Crown root ratio
  • Crown angulation, inclination
  • Opposing teeth
  • Morphology, number, divergence of root
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5
Q

What is reciprocation? (2)

A

The mechanism by which lateral forces generated by a retentive clasp passing over a height of contour are counterbalanced by a reciprocal clasp passing along a reciprocal guiding plane (reciprocating element may be: retentive arm of clasp; lingual plating; combination of mesial and distal minor connectors) (like (2); remember reciprocation when displaced occlusally; bracing when denture is fully seated)

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6
Q

What is the function of resurveying the master cast? (1)

A

To know the final path of placement, the location of retentive areas, and the location of remaining interference. (The master cast has tooth preparation on it!)

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7
Q

Compare between base line and tripod in surveying (3marks)

A

Both are used to record the degree of tilt of the cast. The base line is recording three lines on the sides of the cast; the tripod is marking three points on the teeth at the same horizontal plane at a specific degree of tilt (easier to transfer to another cast?)

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8
Q

Why are two colours of articulating paper used when checking the fitting and occlusion of RPD? (1)

A

Static occlusion; dynamic occlusion (during horizontal excursion)

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9
Q

Compare and contrast lingual bar and lingual plate (4)

A

No answer

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10
Q

Critically assess the existing denture.

A
  • Retention / support / stability / occlusion / aesthetics / OH
  • Defective components: tooth wear / fracture of clasp / missing tooth / crack
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11
Q

Outline labstages for Co-Cr framework fabrication after the stage of master cast surveying

A
  • Block out unwanted undercut on the master cast after designing the outline
  • Place spacer for acrylic retention mesh
  • Duplication of master cast for refractory model and another duplicated model (use agar x2)

Impression material

Refractory material (phosphate bonded investment)

Strengthen refractory model by drying at 200 degree for 45 mins and soaking in beeswax at 140 degree for 15 s

  1. Outline design on refractory model and make wax pattern
  2. Sprueing attached to wax pattern
  3. Apply detergent on wax surface (to avoid bubbles being trapped)
  4. Embedding the cast in casting ring and ring liner
  5. Pour phosphate bonded investment
  6. Wax burnout at 900 - 1000 degree (also allow expansion to compensate metal cooling contraction)
  7. Co-Cr is melted by electromagnetic induction (in a centrifuge via centripetal force (directed to center)) or by flame at “reducing zone” and moulded to the cast
  8. Cooling → remove investment → sandblast with Al2O3 → remove sprueing → electrolytic polish
  9. Wrought wire clasps may be soldered
  10. Check fitting and occlusal dimension on duplicated model (not master cast)
  11. Final polishing –> delivery
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12
Q

Upon framework try-in, an occlusal interference was found on a rest seat, but the rest seat is very thin already. What could have caused this?

A
  • Insufficient tooth preparation
  • Impression errors
  • Technical and processing errors during framework fabrication
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13
Q

What are the problems associated with design of removable partial denture with free-end saddle? (5)

A 
Inadequate retention
Uneven support
Insufficient stability
Oral discomfort
Damage to support tissue
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14
Q

Explain why inadequate retention is associated with design of removable partial denture with free-end saddle?

A

Absence of most distal abutment

Only rely on muscular control and mucosal coverage

Though indirect retention can resist rotational movement, its effectiveness is highly depends on the distance between rest and axis of rotation / saddle (poor if in extreme SDA case)

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15
Q

Explain why Uneven support is associated with design of removable partial denture with free-end saddle?

A

Support is derived from remaining teeth and mucosa covering posterior edentulous saddles

Mucosa itself may not be uniform in its thickness and displaceability all over the residual ridge

(Cause: impression can’t record anatomical form of teeth and physiologic form of soft tissue simultansously → that’s why the need for altered cast technique

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16
Q

Explain why Insufficient stability is associated with design of removable partial denture with free-end saddle?

A

Poor support and direction retention

Absence of most distal abtument for retentive clasp placement

In case with resorbed ridge, resistance to lateral and horizontal force is reduced

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17
Q

Explain why Oral discomfort is associated with design of removable partial denture with free-end saddle?

A

Factors include fragile or resorbed underlying ridge, uneven support, inadequate retention and stability

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18
Q

Explain why Damage to support tissue is associated with design of removable partial denture with free-end saddle?

A

Abutment teeth may be subjected to torque forces coming from the clasps and aggravated by rotational movement of denture base

Resorption of underlying ridge without relining can further exert damaging torque forces and in turns periodontal destruction of abutment

Poor support and stability may accelerate ridge resorption and induce tissue inflammation

19
Q

What are the concerns of selection of path of insertion in this case (Kennedy Class IV)? (5)

A
  • Zero tilt surveying
    Dead spaces found on anterior edentulous space, flange can’t be used

More retentive as MB undercut present (No need to build undercut with composite)

Simpler to do

  • Posterior tilt
    Eliminate dead spaces anteriorly, and saddle / flange can make better contact to abutment tooth in better appearance

When labial flange is used, bony undercut is avoided as insertion of denture is not along a path a right angle to occlusal plane

Insufficient MB undercut, but can build with composite

20
Q

What are the advantages of posterior tilt?

A
  • Remove anterior dead space, mesial to the abutment teeth

* Avoid soft tissue undercut for a full labial denture flange

21
Q

What are the disadvantages of posterior tilt?

A

Undercuts appear on DB of posterior teeth
• Poor aesthetics (Thicker 2/3 retentive arm on mesial side which is more visible)
• Complicated design as the undercut is on DB

Image available on doc p72

22
Q

What is the purpose of aesthetic try-in? (1)

A
  • Check aesthetic with patients
  • Assist framework fabrication (facilitate position of retention, strengthening pin, metal backing)
  • Production of silicone index for teeth set up
23
Q

What is the thickness of “shimstock”? (1)

A
  • 12 micron
24
Q

The aesthetic try-in was fit to the patient’s mouth. However, at the delivery, there is 3 mm occlusal discrepancy found on the master cast. What will be your advice to the laboratory? (4)

A
  • Wrong jaw registration
  • Retake a bite registration in clinic and instruct technician remount the master cast at correct jaw relationship, adjust occlusal errors and check bite
25
Q

What is the melting point of Co-Cr

A
  • melting range: 1200-1400 oC (while casting temp is 1500oC)
    Ken: from Luk Sir ppt
26
Q

What type of investment will be used for casting?

A
  • Phosphate-bonded investment
27
Q

Discuss the strategic value of 27 and 28 from the //Peri. (4)

Anson: not sure what this means, page 72

A
  • Strategic value considerations
    Tooth position (Whether tooth is in aesthetic zone +
    Whether tooth is the most distally located)
    Tooth function (Act as abutment, Function in mastication)
    Restorative status (structural integrity, remaining sound tooth structure)
    Periodontal status (Root morphology, bone support)
  • Normally the most distal teeth have importance to tx plan, which required for support of prosthesis
  • However, if periodontal and restorative prognosis of 27 is good, 28 won’t be a worthwhile candidate for endodontic or prosthodontic treatment
28
Q

Reason for peripheral under extension of the study cast(3)

A

• Tray selection too small
• Tray incorrectly seated
• Cheeks/lips/etc trapped under tray
Ken: Underfilled tray?

29
Q

Reason for roughness on surface of study cast(3)

A
  • May have been immersed in water (gypsum dissolves in water over time)
  • Some water was left in the impression before it was poured –> weak and chalky gypsum
  • Maybe bubbles in the impression
30
Q

Why snap removal of alginate?(1)

A

Reduce chance of plastic deformation (if stress is applied quickly, then all the energy is stored elastically and the material will not undergo plastic deformation)

A table is given (maybe it’s talking about the metal framework???)

Ken: Alginate has low tear strength, it would tear if removed slowly (found online)

Anson page 72

31
Q

What causes the cast to be too large and how to prevent it?

A

Overexpansion of mold caused by wrong water-powder ratio

Use proper water-powder ratio according to type of casting

32
Q

What causes the cast to distort and how to prevent it?

A

Distorted wax pattern

Manipulate wax at high temperature
Invest wax pattern within one hour after finishing
If need to store, store in a refrigerator

33
Q

What causes rough surface and how to prevent it?

A

Too much debubbliser used on wax pattern

Prolonged overheating of gypsum bonded investment leading to gases leaking out

Prevent:
Use less debubbliser

Use correct heating cycle for burnout procedure

34
Q

What causes fins on surface and how to prevent it?

A

Burnout before investment reached maximum hardness caused mold to crack

Heating ring too rapidly causes too rapid expansion of investment –> cracked mold

Prevention:
Allow investment to set thoroughly before starting burnout

Start burnout with cold furnace; increase temperature gradually

35
Q

What are the ideal rest seat dimensions?

A
  • Saucer-shaped covering 2/3 of marginal ridge & tapering deeper into adjacent fossa to direct forces along the long axis of tooth
  • Minimal thickness of 0.5mm (optimal: 1-1.5 mm)
  • No occlusal interference or undercut (angle between the floor & axial wall should be less than 90 degree)

look at page 72-73 for remarks (other notes)

36
Q

What are the anatomical landmarks in the free end saddle?

A
  • Posteriorly: anterior half to 2/3 of retromolar pad which is fibrous and relatively non-displaceable (the posterior part is movable, made of loose glandular connective tissue)
  • Buccally: buccal sulcus, external oblique ridge, (buccal frenum)
  • Lingually: mylohyoid line, lingual sulcus, retromylohyoid fossa, (lingual frenum, genial tubercle(if extremely resorbed)
37
Q

Advantage of using cobalt-chromium for a partial denture base over using acrylic.

A
  • Strong and rigid
  • High modulus of elasticity (= stiff) –> less bulky than acrylic –> px tolerance
  • Less plaque retentive and soft tissue coverage –> better perio, reduce risk for denture-induced stomatitis
  • Better heat conduction –> better sensation when eating
  • Low risk of allergy (biodegradation of acrylic –> allergy)
38
Q

Disadvantage of using cobalt-chromium for a partial denture base over using acrylic.

A
  • Poor aesthetics
  • Only mechanical (not chemical) bond with teeth
  • Complicated to construct and adjust (no relining allowed)
  • Expensive
  • Not for temporary denture
39
Q

What are the problems associated with design of removable partial denture with free-end saddle? (3)
Walter Lam PPT

A
  1. Downward movement of free end saddle (Support problem)
  2. Upwards movement of free end saddle (Retention problem)
  3. Distal movement of free end saddle (stability problem)
40
Q

Solution to problems associated with design of removable partial denture with free-end saddle? (3)
walter ppt

First problem

A

Ken : From RPD Walter Lam PPT

  1. Downward movement +(solution)
    • Oral discomfort
    • Damage to support tissue due to functional load –> inflammation etc
    • Decreased support as the mucosa on the edentulous ridge is displaceable (Altered cast technique)
    • Distal displacement and stress on abutment tooth

Solutions:
1. Extend the base in the areas of the free end saddle, reduces load per unit on the edentulous ridge)

  1. Use RPI/RPA clasp system to reduce stress on abutment and distal displacement
  2. Use altered cast technique to maximize support from the edentulous ridge
41
Q

Solution to problems associated with design of removable partial denture with free-end saddle?

Second problem

A
  1. Upwards movement of free end saddle (free end saddle move away from the mucosa)

Solutions:

  1. Rigid major connectors
  2. Indirect retainer as far away from the free end saddle/axis of rotation as possible
42
Q

Solution to problems associated with design of removable partial denture with free-end saddle?

Third problem

A
  1. Distal movement of free end saddle

Solutions:

  1. Mesial rest and its minor connector (instead of a distal rest) (RPI/RPA)
  2. Mesial buccal undercut
  3. Mesial-distal grip
43
Q

How to reduce stress on the abutment tooth?

A
  1. Alter-cast technique
  2. Mesial rest (RPI/RPA) **Important
  3. Splint the abutment
  4. Stress breakers (Hinge, disjunct denture)

BDS3 Past Paper By Topic (05-19) (24 decks)

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