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Fixed > DEFINITIVE Cast and Dies > Flashcards

DEFINITIVE Cast and Dies Flashcards

1
Q

What is a definitive (master/working) cast?

A

A replica of the tooth surfaces, residual ridge areas, and/or other parts of the dental arch and/or facial structures used to fabricate a dental restoration or prosthesis

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2
Q

What is a die?

A

The positive reproduction of the form of a prepared tooth in any suitable substance

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3
Q

What is a die pin?

A

A metal pin used in stone casts to remove die sections and replace them accurately in the original position

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4
Q

A good cast must be:

A
  • Bubble free & distortion free
  • Reproduce both prepared and unprepared tooth surfaces
  • All occluding surfaces must allow for precise articulation of the opposing casts
  • All relevant soft tissues should be reproduced
    — Edentulous spaces and ridge contours involved in FPD
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5
Q

Die must be:

A
  • Reproduce the prepared tooth exactly
  • All surfaces must be accurately duplicated
    — No bubbles or voids especially along the finish line
  • The unprepared tooth structure apical to the finish line should be easily visible (0.5– 1mm)
  • Provide adequate access for carving wax pattern margin
    — Establish correct cervical contour of the restoration
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6
Q

Advantages of the FULL ARCH CAST:

A
  • Guide to occlusal surfaces and contours
  • Ease of articulation
  • Development of optimum occlusion
  • Development of optimum pontic adaptation and esthetics
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7
Q

What are the materials used in die fabrication?

A
  • Gypsumproducts
  • Amalgam dies
  • Epoxy resins
  • Electro deposition of metals
  • Flexible die materials
  • Refractory materials
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8
Q

Advantages of gypsum products:

A
  • Compatible with all impression materials
  • Ability to reproduce fine detail and sharp margins
  • Dimensional accuracy and stability
  • Easy to use
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9
Q

Disadvantages of gypsum products:

A
  • Susceptibility to abrasion
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10
Q

What is ADA stone type I and II?

A

impression plaster/model and mounting plaster

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11
Q

What is ADA stone type III?

A

dental stone (general purpose casts) Yellow

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12
Q

What is ADA stone type IV?

A

high strength / lowest expansion (die stone) Green

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13
Q

What is ADA stone type V?

A

high strength / high expansion (die stone)

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14
Q

What are the properties of die materials?

A
  • Accuracy OF CAST
  • Reproduce fine detail (20μ-wide-line)
  • Strong and durable
    —Strength (wet strength / dry strength)
    —Resistance to shearing forces (edge strength)
    —Abrasion resistance
  • Color
    —Contrast to wax
    —Scanning visibility (CAD-CAM)
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15
Q

Use the _______ amount of water necessary to obtain proper manipulation of stone following manufacturer’s recommendations

A

least

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16
Q

Add powder to liquid or liquid to powder in mixing bowl for proper mixture

A

powder to liquid

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17
Q

What are the advantages of auto-mixing?

A
  • Homogenous
  • Morestrength GYPSUM
  • Intended expansion
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18
Q

What is directly proportional to the water:powder ratio?

A

setting times and manipulation
* ↑water = ↑ setting time; ↑ fluidity

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19
Q

What is indirectly proportional to the water:powder ratio?

A

strength and setting expansion
* ↑water = ↓ compressive strength
* ↑water = ↓ setting expansion due to less material per volume

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20
Q

Gypsum that has already set acts as a catalyst when in contact with unset gypsum and can cause…

A

changes in the set and working times

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21
Q

Excessive __________ solution or water can give you unset or powdery gypsum at the surface

A

disinfectant

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22
Q

Excessive use of alcohol-based surfactants or ___________ can also create surface issues like softness or chalkiness

A

debubblizers

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23
Q

What are the benefits of vacuum mixing gypsum?

A
  • Helps eliminate porosity
  • Strengthens the cast
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24
Q

How do you vacuum mix?

A

20 seconds / 425 rpm/ >25mmHg pressure
* Over-spatulation → decreased working time (material sets quicker)

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25
Q

What is wet strength?

A

Wet strength is how the gypsum resists breaking when wet

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26
Q

What is dry strength?

A

Dry strength is how the gypsum resists breaking when dry

27
Q

Strength of gypsum ________ from 1hr → 24hr

A

doubles

28
Q

What is the alginate impression two pour technique?

A
  • First pour: anatomic pour with Type III Stone cover vestibule; stack up stone; add nodules
  • Second pour: base build up after initial set of anatomic pour or after separation from impression (45 min)
29
Q

Gypsum immersion in water = Lineardecrease in characteristics per every ____ minutes of immersion

A

20

30
Q

Immersion in water saturated with _______________ will decrease solubility (think diffusion and osmosis)

A

calcium sulfate

31
Q

What is the surface hardness of gypsum?

A

Gypsum is a soft material that can be scratched easily

32
Q

How do you increase the abrasion resistance of gypsum?

A

adding surface hardeners

33
Q

What are the types of anti-rotational dowel pins used in die creation procedures?

A
  • Straight dowel pin
  • Curved dowel pin
  • Di-lok tray
  • Pindex system
  • Accutrak system
34
Q

The final impression is poured twice to obtain two working casts:

A
  • one of these casts is sectioned to obtain the individual dies that are
    separated from that cast
  • the other working cast is mounted on the articulator
35
Q

What are the advantages of of a solid cast separate die system?

A
  • Simple fabrication- requires major trimming of only one pour up
  • Provides a rigid relation for FPD components
  • Better contours and emergence profile whilst wax pattern fabrication
36
Q

What are the disadvantages of of a solid cast separate die system?

A
  • The wax pattern must be transferred from die to cast– destroy internal adaptation of wax
  • Sometimes it is difficult to seat wax pattern on the cast
37
Q

What are the two types of removable die systems?

A
  • Wet cast, or pre-pour technique
  • Dry cast, or post-pour technique
38
Q

What are the advantages of removable die systems?

A
  • Requires less manipulation ofwax pattern
  • Reduces chance of breakage and distortion
  • Handling of restorations is easier (porcelain margins)
39
Q

What are the disadvantages of removable die systems?

A
  • Techniquesensitive
  • Marginor pin damage by improper saw cuts
  • Error in pattern if die does not re-seat accurately
40
Q

What are the requirements for removable die systems?

A
  • Dies must return to exact original position
  • Dies must remain stable, even when inverted
  • Master cast must be easily mounted on an articulator
41
Q

What is important for a solid pour?

A
  • Check interproximal contacts, solder relation on rigid cast
  • Verify fit of casting or margin at try-in
  • Can be used if original is damaged
42
Q

What is a digitally milled cast?

A

An intraoral scan of the abutment tooth produces an STL file, and a resin cast is fabricated

43
Q

What are components of the CAM process?

A
  • Milled resin cast
  • Sectioned dies
  • Articulation
44
Q

What are the advantages of digitally milled casts?

A
  • Superior reproduction of the master die in terms of dimensional accuracy
  • These differences are likely of little clinical significance
45
Q

What are the disadvantages of digitally milled casts?

A

Equipment needed to scan and mill/print in office

46
Q

What is a separate die?

A
  • Pour individual die section (1st pour)
  • Separate cast from impression and re-pour impression
  • Thefirst pour is sectioned/trimmed into individual die
  • The 2nd pour is completedas a full arch cast with base
  • Thesolid cast (full arch) is mounted on articulator
47
Q

What are the steps for pouring an individual die section?

A
  • Add stone in small increments
  • If large amount of stone dropped into preparation voids may be formed due to air trapped
  • Build stone to height of approx. 1 inch to make a handle
  • Trimming
48
Q

What are the steps of the pindex system?

A
  1. A special drill press, dowels and plastic sleeves
  2. Pour the impression then trim the cast to horse-shoe shape with flat base
  3. “Pin” the cast and pour base AFTER applying a separating medium
  4. Section the cast by sawing
  5. Die Preparation
    * Die trimming
    * Mark finish line
  6. Articulate the master cast
    * Interocclusalrecord in MIP
  7. Preparation for waxing
    * Die relief (cement spacer)
    * Die hardening (finish line)
49
Q

What are the steps for base fabrication?

A
  • Base is poured after pins/sleeves are cemented
  • Apply a thin coat of separating agent on bottom of cast
  • Pour the base with yellow stone and allow the cast to dry before sectioning
  • 1st pour carefully separated from cast base
    —Cast base interface should be free of voids
50
Q

What are the steps to die sectioning?

A
  • Saw cuts are marked on facial and lingual aspects
  • Section the cast by sawing
  • Each die section must slide out independently
  • Yet have adequate stone around pins for strength
  • Avoid cutting or abrading a margin
  • All sections are independently removable from the base
  • Die base should seat flush and be perpendicular to cast base
51
Q

What is the purpose of die trimming/ditching?

A
  • Die is trimmed to remove areas correspondingto the gingival tissue
  • Die contour approximates the root and emergence profile
  • Provides access to margin
  • Smooth surface
52
Q

What is the drawback of ditching?

A

Because the instrument used for finishing the margins of wax pattern will rest on this area, its angulation can be exaggerated by the undercut

53
Q

How do you make the emergency profile?

A
  • The surface of the “un-prepared” tooth apical to the finish line is left intact
  • Stone is removed with several tools/burs below this line
  • A properly trimmed die must have the same cervical contour as the tooth
  • Adequate access to the margin is necessary for carving the wax to the proper emergence profile
    — ≈ 5 mm below finish line
54
Q

What is the technique for die trimming?

A
  • Trimmed from below and parallel to the margin
  • Leave small lip of stone below margin
  • Margin trimming can be finished with Bard-Parker #25 blade or donut slow speed bur
  • Finish line highlighted with red pencil
  • Handle should be 1 inch long
55
Q

What should you avoid with die trimming?

A

Sharp ditching of the die apical to the margin:
→over-contouring of wax pattern (angulation of wax carver)
→weakening of the die

56
Q

What are the reasons for die hardening agents?

A
  • Protect finish line
  • Improve abrasion resistance
  • Impregnate the surface
  • Typically cyanoacrylate cement
57
Q

What are the reasons for die spacers/die relief agent?

A
  • To provide space for cement while cementing final restoration in mouth
  • It allows accurate adaptation of casting on die
  • Thickness – depending on number of coats are applied to produce a relief ≈10-15μm
  • The tooth preparation of die is painted within 0.5mm of finish line
58
Q

What are the reasons for die lubricators?

A
  • It can be used to coat the die directly over die spacer such as die lube
  • It helps in easy removal of wax pattern without adherence to die
59
Q

What is important to know about articulation?

A
  • Ensure accurate tooth- tooth contact
  • Verify contact of incisal pin on articulator
  • Accuracy of mounting is critical to accurate occlusion in final restoration
  • Compare intraoral and articulated cast occlusal contacts
  • Make sure that the removable die is fully seated
60
Q

What is an interoccusal record necessary for?

A

An interocclusal registration is necessary to orient dies of prepared teeth to the opposing occlusion

61
Q

What are the material requirements for interocclusal records?

A
  • No resistance to closure
  • Rigid when set
  • Dimensional stability
  • Accuracy
62
Q

What are the different interocclusal record materials available?

A
  • A rigid, Fast-set VPS
  • CAD-CAM scanning
  • Plaster (Removable Prostheses)
  • ZnOE paste – not used anymore
  • Resin (rigid)
  • Wax–Alminaxwax
63
Q

What is the process for an occlusal registration?

A
  • Trim the record to include only cusp tips for proper seating
  • Cut back facial to visualize seating
  • Ensure accurate tooth-tooth contact elsewhere
  • Mark with articulating paper
  • Check with shimstock

Fixed (13 decks)

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