DEFINITIVE Cast and Dies Flashcards
What is a definitive (master/working) cast?
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
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 stone casts to remove die sections and replace them accurately in the original position
A good cast must be:
- 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
Die must be:
- 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
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 used in die fabrication?
- Gypsumproducts
- Amalgam dies
- Epoxy resins
- Electro deposition of metals
- Flexible die materials
- Refractory materials
Advantages of gypsum products:
- Compatible with all impression materials
- Ability to reproduce fine detail and sharp margins
- Dimensional accuracy and stability
- Easy to use
Disadvantages of gypsum products:
- Susceptibility to abrasion
What is ADA stone type I and II?
impression plaster/model and mounting plaster
What is ADA stone type III?
dental stone (general purpose casts) Yellow
What is ADA stone type IV?
high strength / lowest expansion (die stone) Green
What is ADA stone type V?
high strength / high expansion (die stone)
What are the properties of die materials?
- 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)
Use the _______ amount of water necessary to obtain proper manipulation of stone following manufacturer’s recommendations
least
Add powder to liquid or liquid to powder in mixing bowl for proper mixture
powder to liquid
What are the advantages of auto-mixing?
- Homogenous
- Morestrength GYPSUM
- Intended expansion
What is directly proportional to the water:powder ratio?
setting times and manipulation
* ↑water = ↑ setting time; ↑ fluidity
What is indirectly proportional to the water:powder ratio?
strength and setting expansion
* ↑water = ↓ compressive strength
* ↑water = ↓ setting expansion due to less material per volume
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
Excessive __________ solution or water can give you unset or powdery gypsum at the surface
disinfectant
Excessive use of alcohol-based surfactants or ___________ can also create surface issues like softness or chalkiness
debubblizers
What are the benefits of vacuum mixing gypsum?
- Helps eliminate porosity
- Strengthens the cast
How do you vacuum mix?
20 seconds / 425 rpm/ >25mmHg pressure
* Over-spatulation → decreased working time (material sets quicker)
What is wet strength?
Wet strength is how the gypsum resists breaking when wet
What is dry strength?
Dry strength is how the gypsum resists breaking when dry
Strength of gypsum ________ from 1hr → 24hr
doubles
What is the alginate impression two 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 min)
Gypsum immersion in water = Lineardecrease in characteristics per every ____ minutes of immersion
20
Immersion in water saturated with _______________ will decrease solubility (think diffusion and osmosis)
calcium sulfate
What is the surface hardness of gypsum?
Gypsum is a soft material that can be scratched easily
How do you increase the abrasion resistance of gypsum?
adding surface hardeners
What are the types of anti-rotational dowel pins used in die creation procedures?
- Straight dowel pin
- Curved dowel pin
- Di-lok tray
- Pindex system
- Accutrak 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 of a solid cast separate die system?
- 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
What are the disadvantages of of a solid cast separate die system?
- 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
What are the two types of removable die systems?
- Wet cast, or pre-pour technique
- Dry cast, or post-pour technique
What are the advantages of removable die systems?
- Requires less manipulation ofwax pattern
- Reduces chance of breakage and distortion
- Handling of restorations is easier (porcelain margins)
What are the disadvantages of removable die systems?
- Techniquesensitive
- Marginor 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
What is important for a 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
What is a digitally milled cast?
An intraoral scan of the abutment tooth produces an STL file, and a resin cast is fabricated
What are components of the 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 are the disadvantages of digitally milled casts?
Equipment needed to scan and mill/print in office
What is a separate die?
- 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
What are the steps for pouring an individual die section?
- 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
What are the steps of the 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
* Mark finish line - Articulate the master cast
* Interocclusalrecord in MIP - Preparation for waxing
* Die relief (cement spacer)
* Die hardening (finish line)
What are the steps for base fabrication?
- 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
What are the steps to die sectioning?
- 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
What is the purpose of die trimming/ditching?
- Die is trimmed to remove areas correspondingto the gingival tissue
- Die contour approximates the root and emergence profile
- Provides access to margin
- Smooth surface
What is the drawback 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
How do you make the emergency profile?
- 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
What is the technique for die trimming?
- 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
What should you avoid with die trimming?
Sharp ditching of the die apical to the margin:
→over-contouring of wax pattern (angulation of wax carver)
→weakening of the die
What are the reasons for die hardening agents?
- Protect finish line
- Improve abrasion resistance
- Impregnate the surface
- Typically cyanoacrylate cement
What are the reasons for die spacers/die relief agent?
- 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
What are the reasons for die lubricators?
- 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
What is important to know about articulation?
- 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 an interoccusal record necessary for?
An interocclusal registration is necessary to orient dies of prepared teeth to the opposing occlusion
What are the material requirements for interocclusal records?
- No resistance to closure
- Rigid when set
- Dimensional stability
- Accuracy
What are the different interocclusal record materials available?
- A rigid, Fast-set VPS
- CAD-CAM scanning
- Plaster (Removable Prostheses)
- ZnOE paste – not used anymore
- Resin (rigid)
- Wax–Alminaxwax
What is the process for an 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
