Definitive Cast and Dies Flashcards
what is the definitive cast
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
what is a die
the positive reproduction of the form of a prepared tooth in any suitable substance
what is a die pin
a metal pin used in the stone casts to remove die sections and replace them accurately in the original position
a good cast must be
- 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
the die must be:
- 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
what are the advantages of the full arch cast
- guide to occlusal surfaces and contours
- ease of articulation
-development of optimum occlusion - development of optimum pontic adaptation and esthetics
what are the materials sued for die fabrication
- gypsum prpducts
- amalgam dies
- epoxy resins
- electro deposition of metals
- flexible die materials
-refractory materials
what are the advantages of gypsum products
- compatible with all impression materials
- ability to reproduce fine detail and sharp margins
- dimensiional accuracy and stability
- easy to use
what are the disadvantages of gypsum products
susceptibility to abrasion
what are the ADA specifications for die gypsum products
- 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)
what are the properties of die materials
- accuracy
- reproduce fine detal: 20 micrometers wide-line)
- strong and durable
- color
what strength and durability factors do die materials need to be
-strength- wet strength/dry strength
- resistance to shearing forces (edge strength)
- abrasion resistance
what color properties do die materials need to have
- contrast to wax
- scanning visibility for CAD CAM
what are the properties related to water: powder ratio
- 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
what are the advantages of auto mixing
- homogenous
- more strength
- intended expansion
what properties are directly proportional to the W/P ratio
- setting times and manipulation
increased water = (directly related)
increased setting time and increased fluidity
what properties are inversely related to water: powder ratio
strength and setting expansion
increased water = (inversely related)
decreased compressive strength and decreased setting expansion
what interactions are there to be aware of with gypsum
- 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
what will excessive disinfectant solution or water do to gypsum
can give unset or powdery gypsum at the surface
what will excessive use of alcohol- based surfactants or debubblizers do
create surface issues like softness or chalkiness
describe mechanical vacuum mixing of gypsum- what does it do and how to use it
- helps eliminate porosity
- strengthens the cast
- 20 seconds/425 rpm/ >25mmHg
over spatulation =
decreased working time
how do you retain dimensional accuracy and strength
- 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
how much does the strength increase from 1 hour to 24 hours
doubles
what is the alginate impression 2 pour technique
-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
describe the solubility of gyspum
- gypsum immersion in water-> linear dimension decreases per every 20 minutes of immersion
- immersion in water saturated with calcium sulfate will decrease solubiity
describe the accuracy of gypsum
- reproduce fine detail - 20 micrometer wide-line
- avoid sludge formation - cast trimming
- scrubbing cast will remove surface detail
what is the relationship between surface hardness and abrasion resistance
surface hardness does not equal abrasion resistance
what is surface impregnation done with
cyanoacrylate cement
what contributes to abrasion resistance
- surface impregnation
- strengthened products
what strengthening products contribute to abrasion resistance
-resin (CAD-CAM)
- epoxy resin
what are the indirect die systems
- solid cast/separate dies- multiple pour systems
- removable dies
- digitally milled cast-die
describe solid- cast/separate die system
- single (separate) die for wax coping and margins
- solid cast for waxing proximal contacts and occlusion
describe removable dies
-retained by pins in a base - stone or plastic
- one die used for entire wax pattern- proximal contacts, occlusion and margins
what are the types of anti-rotational dowel pins
- straight dowel pin
- curved dowel pin
- di-lok tray
- pindex system
- accutrak system
what casts are made in the solid cast- separate die system
- 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
what are the advantages of the solid cast- separate die system
- simple fabrication- requires minimum trimming
- provides a rigid relation for FPD components
- better contours and emergence profile whilst wax pattern fabrication
what are the disadvantages of the solid cast- separate die system
- the wax pattern must be transferred from die to cast- destroy internal adaptation of wax
- sometimes difficult to seat wax pattern on the cast
what are the types of removable die systems
- wet cast, or pre-pour technique
- dry cast or pour-post technique
what are the advantages of the removable die systems
- requires less manipulation of wax pattern
- reduces chance of breakage and distortion
- handling of restorations is easier
what are the disadvantages of the removable die systems
- technique sensitive
- margin or pin damage by improper saw cuts
- error in pattern if die does not re seat accurately
what are the requirements for removable die systems
- dies must return to exact original position
- dies must remain stable even when inverted
- master cast must be easily mounted on an articulator
describe the solid pour
- check interproximal contacts, solder relation on rigid cast
- verify fit of casting or margin at try in
- can be used if original is damaged
describe digitally milled casts
- 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
what are the advantages of digitally milled casts
- superior reproduction of the master die in terms of dimensional accuracy
- these differences are likely of little clinical significance
what is the technique of solid cast- separate die
- 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
describe the 1st pour of the solid cast- separate die
- 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
describe the technique of removable die system- Pindex system
- 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)
what is the technique of pinning the cast
- 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
describe the base fabrication of the pindex system
- 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
describe the technique of dies sectioning in the pindex technique
- 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
what is the purpose of die trimming/ditching
- 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
what are the drawbacks of ditching
because the instrument used for finishing the margins of wax pattern will rest on this area, its angulation can be exaggerated by the undercut
what contributes to the emergence profile
- 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
describe the technique of die trimming
- 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
what should you avoid in die trimming and why
- sharp ditching of the die apical to the margin
- can cause over contouring of the wax pattern and weakening of the die
where are the die hardening agents applied, what do they do, and what are they
- finish line
- abrasion resistance and surface impregnation
- cyanoacrylate cement
what do die spacers/die relief agents do
-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
where are die spacers/die relief agents applied
within 0.5mm of finish line
where are die lubricators applied and what do they do
- 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
describe articulation of the definitive cast
- 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
what is interocclusal registration necessary for
to orient the dies of prepared teeth to the opposing occlusion
what are the material requirements for the interocclusal records
- no resistance to closure
- rigid when set
- dimensional stability
- accuracy
what are the materials used for interocclusal records
- rigid,fast set VPS
- CAD-CAM scanning
- plaster (for RPD)
-ZnOE paste - resin (rigid)
- wax-Allu wax- dont use for FPD
describe rigid fast set VPS as an interocclusal record material
least rigid, most efficient
- always some rebound
describe resin as an interocclusal record material
technieuq sensitive
time consuming
describe occlusal registration
- 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
what are the steps to occlusal registration
- 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
