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Prostho 4 > 2. Working Casts > Flashcards

2. Working Casts Flashcards

1
Q

What are the limitations of plaster? (4)

A
  • the low resistance to fracture
  • dimensional instability
  • technique sensitivity
  • low resistance to wear by abrasion
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2
Q

What can affect the properties of the stone (cast)? (4)

A
  • the setting time
  • the porosity
  • the setting expansion
  • the strength
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3
Q

What should you do before pouring the cast? (3)

A
  • wash the impression under cold water to remove saliva and mucus
  • disinfect
  • dry but leaving a shiny surface of the material
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4
Q

What type of stone is poured? Why? (2)

A

High strength type IV

To prevent surface abrasion

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5
Q

Where do we start pouring stone? (2)

A

Over tooth preparation

then add stone from distal area and let it flow mesially

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6
Q

How much height should there be for pouring of the casts? why?

A

2.5cm for correct handling of the die

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7
Q

How long should the stone be left to dry?

A

1 hour

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8
Q

What are the different types of casts? (5)

A 
Study cast
Diagnostic cast
Working cast (master cast) 
Antagonist cast
Casts for corrections
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9
Q

What kind of impression can create a study cast? (3)

A
  • Alginate
  • silicone
  • digital
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10
Q

What are study casts made of?

A

Plaster

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11
Q

What is the purpose of a study cast once mounted on the articulator? (4)

A
  • Study occlusal relationships.
  • Treatment planning.
  • Customize articulator (PCPI and Bennett angle).
  • Make provisional dentures.
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12
Q

What type of impression can create a diagnostic cast?

A
  • alginate
  • silicone
  • digital
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13
Q

What is a diagnostic cast made of?

A

Usually plaster

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14
Q

What is a diagnostic cast used for? (5)

A
  • Waxing of restorative contours to evaluate and plan restorations
  • forsee esthetics
  • forsee occlusion
  • show patient final look of treatment
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15
Q

What is the purpose of the working cast?

A

To manufacture the final prothesis over

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16
Q

What impression gives you the working cast? (3)

A
  • sIlicone
  • polyether impressions
  • digital
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17
Q

What is important for a working cast?

A

Must show a clear finish line

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18
Q

Where is a working cast mounted?

A

Must be mounted at the office

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19
Q

What is a working cast made of? (3)

A
  • type IV plaster
  • Epoxy resin
  • investment material
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20
Q

What is important to remember about impression pouring for a working cast? (2)

A
  • impression has to be poured twice

- double pouring only if it is an elastomeric impression (PVS)

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21
Q

How is a working cast mixd?

A

With vacuum mixers

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22
Q

What happens with the gingiva on working casts?

A

Trimmed to show the finish line

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23
Q

What are the disadvantages of working casts with removeable dies? (2)

A
  • alteration of contact point

- relation with the gum has been removed

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24
Q

What are the advantages of working casts with removable dies? (2)

A

◦ Dies can be removed individually

◦ Eases laboratory work

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25
Q

What are the advantages of working casts without removable dies? (2)

A
  • contact point not altered

- relation with gum is kept (avoiding over/undercontoured margins)

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26
Q

What are the disadvantages of working casts without removable dies? (2)

A
  • harder to see finish lines esp at proximal surfaces

- harder lab work

27
Q

What type of impression is needed for the antagonist cast? (2)

A
  • alginate

- silicone

28
Q

What is an antagonist cast? (3)

A

• Full-arch.
• Very important to be accurate too.
• Will condition the quality of the occlusion of the final
restoration.

29
Q

What is a cast for correction? (2)

A
  • for correcting a denture

- ex. readapt the margin of the restoration

30
Q

What impression is used for a cast for correction?

A

Silicone

31
Q

How long should the vacuum mixer be used for impressions? (2)

A

15-20 seconds

*air bubbles and blowholes free

32
Q

What is important to remember about using the plastic vibrator for pouring impressions?

A

Tray is palced over but never resting over the impression material

33
Q

How long should the cast dry for?

A

1 hour

34
Q

What is the procedure of creating a working cast with no removable dies?

A
  • put cast in moisture chamber for 12 hours
  • mount on articulator
  • trim cast to show finish line
35
Q

how do you trim a cast to show the finish line? (2)

A
  • n. II scalpel

- Bur

36
Q

What are the main requirements for removable dies? (3)

A
  1. The dies must return to their exact original positions.
  2. The dies must remain stable, even when inverted.
  3. The cast containing the dies must be easy to mount on an articulator.
37
Q

What 4 variables can affect the quality of the working cast during its fabrication and use?

A

1- accuracy of the impression procedure,
2- accuracy of the cast/die system
3- inherent setting expansion of the dental stones used
4- precise repositioning of the removable die

38
Q

What are the desirable characteristics in a removable die system? (3)

A
  • Ease of fabrication and reassembly of the working casts
  • stability of the dies
  • accurate positioning of the dies
39
Q

A removable die is a ______ for every die

A

individualized cast

40
Q

Every die contains …

A

the preparation of every tooth

41
Q

What are the different die systems? (6)

A
  • Conventional brass dowel pin.
  • Bafix.
  • Pindex.
  • Zeisser.
  • Accutrac.
  • Di-Lok.
42
Q

Dies must return to…

A

their original position accurately

43
Q

Die should be..

A
  • stable over the base (even for upper casts)

- removable even if the casts are mounted

44
Q

Which cast should be mounted on the articulator? (removable die or no die)

A

the removable dies cast

45
Q

Which removable die casts are the pin techniques? (3)

A
  • conventional technique
  • pindex system
  • zeiser system
46
Q

Which removable die casts are the tray techniques? (3)

A
  • accutrac system
  • di-lok system
  • bafix system
47
Q

What removable die casts are neither the pin or tray techniques? (3)

A

Geller system

48
Q

Which casts cannot be poured before?

A 
Zeiser
Dilock
Accutrac
Bafix
Pindex
Geller
49
Q

How are the pins positioned in conventional technique for removable dies? (3)

A
  • Dowel pins are positioned in the center of the prepared tooth and edentulous area
  • In impression before pouring
  • pins are stabilized with hairpins
50
Q

How do you pour the conventional die technique? (3)

A

Two pour technique

  1. pour cast. Trim and apply petroleum jelly
  2. pour base on a base former

*paper clips are placed in order to provide retention for the second pour stone

51
Q

How do you separate the dies in a conventional technique?

A
  • using a saw

- cuts are made distal and mesial to the tooth

52
Q

What do you do after trimming in the conventional die technique?

A

removal of gingival stone to the finish line

53
Q

How are the pins positioned in a pindex system cast?

A
  • Reverse drill press is used

- drills parallel holes from underside of trimmed cast

54
Q

How is the pouring done for a pindex system?

A

one step with enough thickness (20mm height)

55
Q

How is trimming done for the pindex system?

A

Trimming must leave a flat and stable surface

56
Q

How are the positions of the pins marked in a pindex system?

A

Marked with pencil over the occlusal surface

57
Q

How are pins cemented in the pindex system?

A
  • With cyanoacrylate resin
58
Q

What happens after cementation of pins in a pindex system?

A
  • sleeves placed on top of the pins

- utility wax placed to avoid second layer of stone filling them

59
Q

How many pines per die in a pindex system? (4)

A
  • two pins per die
  • two pins for the edentulous area
  • two for the unprepared tooth

*each die or section should have two pins or a double pin

60
Q

Which die system is the most accurate? Why?

A

Zeiser

b/c the base is plastic = more stable

61
Q

How do you do the zeiser system? (2)

A
  • can section and trim the models depending on the needs of the case
  • the model mounted on the articulator is the removable die model
62
Q

What is the bafix system? (2)

A

One step pouring system for removable dies

Base and impressions are poured at the same time

63
Q

What is the accutrac system?

A
  • one pour technique:

impression and tray poured at the same time

Prostho 4 (2 decks)

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