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Fixed Pros I > Definitive Cast and Dies > Flashcards

Definitive Cast and Dies Flashcards

1
Q

what is the definitive cast

A

a replica of the tooth surfaces, residual ridge areas, and/or other parts of the dental arch and/or facial structure 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 the 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 and 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
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5
Q

the die must be:

A
  • reproduces the prepared tooth exactly
  • all surfaces must be accurately duplicated, no bubbles especially along finish line
  • the unprepared tooth structure apical to the finish line should be easily visible (0.5-1.0mm)
  • adequate access for carving wax pattern margin- establish correct cervical contour of the restoration
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6
Q

what are the 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 sued for die fabrication

A
  • gypsum prpducts
  • amalgam dies
  • epoxy resins
  • electro deposition of metals
  • flexible die materials
    -refractory materials
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8
Q

what are the advantages of gypsum products

A
  • compatible with all impression materials
  • ability to reproduce fine detail and sharp margins
  • dimensiional accuracy and stability
  • easy to use
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9
Q

what are the disadvantages of gypsum products

A

susceptibility to abrasion

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10
Q

what are the ADA specifications for die gypsum products

A
  • type I and II: impression plaster/model and mounting plaster
  • type III: dental stone ( general purpose casts)
  • type IV: high strength/lowest expansion (die stone)
  • type V: high strength/high expansion (die stone)
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11
Q

what are the properties of die materials

A
  • accuracy
  • reproduce fine detal: 20 micrometers wide-line)
  • strong and durable
  • color
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12
Q

what strength and durability factors do die materials need to be

A

-strength- wet strength/dry strength
- resistance to shearing forces (edge strength)
- abrasion resistance

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13
Q

what color properties do die materials need to have

A
  • contrast to wax
  • scanning visibility for CAD CAM
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14
Q

what are the properties related to water: powder ratio

A
  • least amount of water necessary to obtain proper manipulation of stone
  • manufacturers recommendations
  • add powder to liwuid in mixing bowl for proper wetting
  • hand mixing vs auto mixingwh
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15
Q

what are the advantages of auto mixing

A
  • homogenous
  • more strength
  • intended expansion
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16
Q

what properties are directly proportional to the W/P ratio

A
  • setting times and manipulation
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17
Q

increased water = (directly related)

A

increased setting time and increased fluidity

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18
Q

what properties are inversely related to water: powder ratio

A

strength and setting expansion

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19
Q

increased water = (inversely related)

A

decreased compressive strength and decreased setting expansion

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20
Q

what interactions are there to be aware of with gypsum

A
  • gypsum that has already set acts as a catalyst when in contact with unset gypsum and can cause changes in the set and working times
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21
Q

what will excessive disinfectant solution or water do to gypsum

A

can give unset or powdery gypsum at the surface

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22
Q

what will excessive use of alcohol- based surfactants or debubblizers do

A

create surface issues like softness or chalkiness

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23
Q

describe mechanical vacuum mixing of gypsum- what does it do and how to use it

A
  • helps eliminate porosity
  • strengthens the cast
  • 20 seconds/425 rpm/ >25mmHg
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24
Q

over spatulation =

A

decreased working time

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25
Q

how do you retain dimensional accuracy and strength

A
  • minimal expansion for procedure
  • set in an upright position to prevent stone slumping from cusps
  • surface should be hard and smooth when removed from impression
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26
Q

how much does the strength increase from 1 hour to 24 hours

A

doubles

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27
Q

what is the alginate impression 2 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 mins

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28
Q

describe the solubility of gyspum

A
  • gypsum immersion in water-> linear dimension decreases per every 20 minutes of immersion
  • immersion in water saturated with calcium sulfate will decrease solubiity
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29
Q

describe the accuracy of gypsum

A
  • reproduce fine detail - 20 micrometer wide-line
  • avoid sludge formation - cast trimming
  • scrubbing cast will remove surface detail
30
Q

what is the relationship between surface hardness and abrasion resistance

A

surface hardness does not equal abrasion resistance

31
Q

what is surface impregnation done with

A

cyanoacrylate cement

32
Q

what contributes to abrasion resistance

A
  • surface impregnation
  • strengthened products
33
Q

what strengthening products contribute to abrasion resistance

A

-resin (CAD-CAM)
- epoxy resin

34
Q

what are the indirect die systems

A
  • solid cast/separate dies- multiple pour systems
  • removable dies
  • digitally milled cast-die
35
Q

describe solid- cast/separate die system

A
  • single (separate) die for wax coping and margins
  • solid cast for waxing proximal contacts and occlusion
36
Q

describe removable dies

A

-retained by pins in a base - stone or plastic
- one die used for entire wax pattern- proximal contacts, occlusion and margins

37
Q

what are the types of anti-rotational dowel pins

A
  • straight dowel pin
  • curved dowel pin
  • di-lok tray
  • pindex system
  • accutrak system
38
Q

what casts are made in the solid cast- separate die system

A
  • the final impression is poured twice to obtain two working casts
  • 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
39
Q

what are the advantages of the solid cast- separate die system

A
  • simple fabrication- requires minimum trimming
  • provides a rigid relation for FPD components
  • better contours and emergence profile whilst wax pattern fabrication
40
Q

what are the disadvantages of the solid cast- separate die system

A
  • the wax pattern must be transferred from die to cast- destroy internal adaptation of wax
  • sometimes difficult to seat wax pattern on the cast
41
Q

what are the types of removable die systems

A
  • wet cast, or pre-pour technique
  • dry cast or pour-post technique
42
Q

what are the advantages of the removable die systems

A
  • requires less manipulation of wax pattern
  • reduces chance of breakage and distortion
  • handling of restorations is easier
43
Q

what are the disadvantages of the removable die systems

A
  • technique sensitive
  • margin or pin damage by improper saw cuts
  • error in pattern if die does not re seat accurately
44
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
45
Q

describe the 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
46
Q

describe digitally milled casts

A
  • an intraoral scan of the abutment tooth produces an STL file and a resin cast is fabricated
  • CAM process: milled resin cast, sectioned dies, articulation
47
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
48
Q

what is the technique of solid cast- separate die

A
  • pour individual die section- 1st pour
  • separate cast from impression ans re pour impression
  • the first pour is sectioned/trimmed into individual die
  • the 2nd pour is completed as a full arch cast with base
  • the solid cast is mounted on articulator
49
Q

describe the 1st pour of the solid cast- separate die

A
  • add stone in small increments
  • if large amount of stone is dropped into preparation voids may be formed due to air trapped
  • build stone to height of approximately 1 inch to make a handle
  • trimming
50
Q

describe the technique of removable die system- Pindex system

A
  • a special drill press, dowels, and plastic sleeves
  • pour the impression then trim the cast to horse shoe shape with flat base
  • pin the cast and pour base AFTER applying a separating medium
  • section the cast by sawing
  • die preparation: die trimming and mark finish line
  • articulate the master cast: interocclusal record in MIP
  • preparation for waxing: die relief(cement spacer), die hardening(finish line)
51
Q

what is the technique of pinning the cast

A
  • use a pencil to mark the desired location of the pins on occlusal surfaces of teeth or preparations
  • place the cast on workable of drill press with red pilot lights on
  • short/thin pins are cemented on lingual then long/thick ones on facial
52
Q

describe the base fabrication of the pindex system

A
  • base is poured after pins/sleeves are cemented
  • apply a thin coat of separating agent on bottom of cast
  • pour the base with flow stone and allow the cast to dry before sectioning
  • first pour carefully separated from cast bae
  • cast base interface should be free of voids
53
Q

describe the technique of dies sectioning in the pindex technique

A
  • saw cuts are marked on facial and lingual aspects
  • sectino 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
54
Q

what is the purpose of die trimming/ditching

A
  • die is trimmed to remove areas corresponding to the gingival tissue
  • die contour approximates the root and emergence profile
  • provides access to margin
  • smooth surface
55
Q

what are the drawbacks 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

56
Q

what contributes to the emergence profile

A
  • the surface of the unprepared tooth apical to the finish line is left intact
  • stone is removed with scalpel blade below this line
  • a properly trimmed die must have the same cervical contour as the tooth
  • adequate access to the margin necessary for carving the wax to the proper emergence profile above 5mm below finish line
57
Q

describe the technique of die trimming

A
  • trimmed from below and parallel to the margin
  • leave small lip of stone below margin
  • margin trimming is finished with bard-parker #25 blade
  • finish line highlighted with red pencil
  • handle should be 1 inch long
58
Q

what should you avoid in die trimming and why

A
  • sharp ditching of the die apical to the margin
  • can cause over contouring of the wax pattern and weakening of the die
59
Q

where are the die hardening agents applied, what do they do, and what are they

A
  • finish line
  • abrasion resistance and surface impregnation
  • cyanoacrylate cement
60
Q

what do die spacers/die relief agents do

A

-provide space for cement while cementing final restoration in mouth
- allows for accurate adaptation of casting on die
- thickness depends on number of coats applied to produce a relief of 10-15 um

61
Q

where are die spacers/die relief agents applied

A

within 0.5mm of finish line

62
Q

where are die lubricators applied and what do they do

A
  • can be used to coat the die directly over the die spacer such as die lub
  • helps in easy removal of wax pattern without adherence to the die
63
Q

describe articulation of the definitive cast

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
64
Q

what is interocclusal registration necessary for

A

to orient the dies of prepared teeth to the opposing occlusion

65
Q

what are the material requirements for the interocclusal records

A
  • no resistance to closure
  • rigid when set
  • dimensional stability
  • accuracy
66
Q

what are the materials used for interocclusal records

A
  • rigid,fast set VPS
  • CAD-CAM scanning
  • plaster (for RPD)
    -ZnOE paste
  • resin (rigid)
  • wax-Allu wax- dont use for FPD
67
Q

describe rigid fast set VPS as an interocclusal record material

A

least rigid, most efficient
- always some rebound

68
Q

describe resin as an interocclusal record material

A

technieuq sensitive
time consuming

69
Q

describe occlusal registration

A
  • record the maxillary and mandibular teeth in MI
  • stone-stone contact with hand articulation when possible
    -place record material between prepared and opposing teeth only
70
Q

what are the steps to 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
71
Q
A

Fixed Pros I (13 decks)

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