Definitive Casts and Dies Flashcards
Definitive (Master or 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.
Die:
Positive reproduction of the
individual prepared tooth; used for
wax pattern fabrication.
A good cast must be:
(2)
Bubble free
Distortion free
- Reproduce both (2) tooth surfaces, and be free
of voids
prepared and unprepared
All occluding surfaces must allow for precise — of the
opposing casts
articulation
All relevant — should be reproduced.
soft tissues
* Edentulous spaces and ridge contours involved in FPD
Requirements for the Die:
(4)
- Reproduces the prepared tooth exactly.
- All surfaces must be accurately duplicated.
- The unprepared tooth structure apical to the finish line should be
easily visible (0.5 – 1mm). - Adequate access for carving wax pattern margin.
- All surfaces must be accurately duplicated.
- No bubbles or voids especially along the finish line.
- Adequate access for carving wax pattern margin.
- Establish correct cervical contour of the restoration
Advantages of the FULL ARCH CAST:
(4)
- Guide to occlusal surfaces and contours
- Ease of articulation
- Development of optimum occlusion
- (Development of optimum pontic adaptation and esthetics)
*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)
Desirable Properties of Cast / Die Materials
(4)
- Accuracy
- Reproduce fine detail (20μ-wide-line)
- Strong and durable
- Color
- Strong and durable
(3)
- Strength (wet strength / dry strength)
- Resistance to shearing forces (edge
strength) - Abrasion resistance
- Color
(2)
- Contrast to wax
- Scanning visibility
(CAD-CAM)
Water : Powder Ratio
(3)
- Least amount of water necessary to obtain proper manipulation of stone
- Manufacturer’s recommendation
- Add powder to liquid in mixing bowl for proper wetting.
- Many properties are either directly or inversely related to the
W/P ratio
- Directly proportional:
setting times / manipulation
* ↑water = ↑ setting time; ↑ fluidity
- Inversely related:
strength and setting expansion
* ↑water = ↓ compressive strength
* ↑water = ↓ setting expansion
* (important in gypsum investment)
- — that has already set acts as a catalyst when in contact with
unset — and can cause changes in the set and working times.
Gypsum
Excessive disinfectant solution or water can give you
unset or
powdery gypsum at the surface.
* Make sure that your impressions are clean and only slightly damp before you
pour
- Excessive use of alcohol based surfactants or debubblizers can also
create
surface issues like softness or chalkiness.
Mechanical-Vacuum Mixing of Gypsum
* Helps eliminate —
* — the cast
* time
porosity
Strengthens
* 20 seconds / 425 rpm / >25mmHg
* Over-spatulation → decreased
working time
Dimensional Accuracy and Strength
(4)
- Minimal expansion for procedure
- Surface should be hard and smooth when
removed from impression - Wet strength – Dry strength
- Set in an upright posit
Wet strength – Dry strength
- Strength doubles 1H → 24H
- Set in an upright position
- Prevents stone slumping from cusps
Alginate Impressions: 2-Pour Technique
(2)
- Anatomic pour with Type III Stone: cover vestibule; stack up stone; add
nodules - Base: 2o mix after initial set of anatomic pour or after separation from
impression (45 min).
Solubility: Gypsum immersion in water
Linear dimension ↓ per every — minutes of immersion
20
Solubility: Gypsum immersion in water
Linear dimension ↓ per every 20 minutes of immersion
(4)
- Accuracy: Reproduce fine detail (20μ-wide-line)
- Immersion in water saturated with calcium sulfate (slurry) will decrease
solubility - Avoid sludge formation (cast trimming)
- Scrubbing cast will remove surface detail
Resistance to Abrasion
(3)
- Surface hardness ≠ abrasion resistance
- Surface impregnation**
- Cyanoacrylate cement
- Strengthened products
- Resin (CAD-CAM)*
Pour the impression twice…
(3)
- Check interproximal contacts, solder relation on rigid cast.
- Verify fit of casting or margin at try-in.
- Can be used if original is damaged.
- Removable Dies
(2)
- Retained by pins in a base (stone or plastic)
- One die used for entire wax pattern - proximal contacts, occlusion and margins
- Solid Cast / Separate Dies (Multiple Pour System)
(2)
- Single (separate) die for wax coping and margins
- Solid cast for waxing proximal contacts and occlusion
Solid Cast – Separate Die System
Advantages:
(2)
- Simple fabrication - requires minimum
trimming - Provides a rigid relation for FPD components
Removable Die Systems
(2)
- The die can be lifted and replaced in the master cast with embedded
pins or dowels. - Requires less manipulation of wax pattern
- Requires less manipulation of wax pattern
(2)
- Reduces chance of breakage and distortion
- Handling of restorations is easier (porcelain margins)
Removable Die Systems
* Disadvantage: Technique sensitive
(2)
- Error in pattern if die does not re-seat accurately
- Margin or pin damage by improper saw cuts
Digitally Milled Casts
(2)
- Digital impression systems
*CAM process (Cadent)
*CAM process (Cadent)
(3)
- Milled resin cast
- Sectioned dies
- Articulation
Requirements for Removable Die Systems
(3)
- Dies must return to exact
original position. - Dies must remain stable,
even when inverted. - Master cast must be easily
mounted on an articulator.
Definitive Cast and Die Preparation
Pindex Technique
(6)
- Pouring the impression / cast trimming
- “Pin” the cast and pour base
- Section the cast by sawing
- Die Preparation
* Die trimming
* Mark finish line - Articulate the master cast
* Interocclusal record in MIP - Preparation for waxing
* Die relief (cement spacer)
* Die hardening (finish line)
Definitive Cast Preparation: Pindex Base
* Base is poured — pins/sleeves are
cemented
after
Definitive Cast Preparation: Pindex Base
* 1st pour carefully separated from
cast base.
* Cast base interface should be free of voids
- Each die section must slide out — -
independently
- Yet have adequate stone around pins for — -
strength
- Avoid cutting or abrading a —.
margin
- All sections are — removable from the base.
independently
- Die base should seat flush and be — to cast base.
perpendicular
Definitive Cast Preparation:
Solid Cast – Separate Die
(5)
- Pour individual die section (1st pour)
- Separate cast from impression and 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 (full arch) is mounted on articulator
Definitive Cast – Die Trimming
(4)
- 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
Die Trimming: Emergence Profile
(2)
- The surface of the “un-prepared” tooth apical to the finish line is
left intact. - Stone is removed with scalpel blade below this line.
Cervical Margin: Emergence Profile
(3)
- 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. - ≈ 5mm below finish line
Definitive Cast – Die Trimming
* Trimmed from below and parallel to the margin.
(2)
- Leave small lip of stone below margin.
- Margin trimming is finished with Bard-Parker #25 blade.
AVOID:
Sharp ditching of the die apical to the margin
→ over-contouring (angulation of wax carver)
→ weakening of the die
Definitive Cast: Articulation
(4)
- Ensure accurate tooth - tooth contact.
- Verify contact of incisal pin.
- Accuracy of mounting is critical to accurate occlusion in final
restoration. - Compare intraoral and articulated cast occlusal contacts
Interocclusal Records for Orienting Casts on
Articulator
An interocclusal registration is necessary to orient dies of prepared
teeth to the opposing occlusion.
Interocclusal Records: Materials
*Material Requirements:
(3)
- No resistance to closure
*Rigid when set - Dimensional stability / accuracy
Rigid, Fast-set VPS
(3)
- Least rigid, most efficient
- Always some rebound
- CAD-CAM scanning
- ZnOE paste; Resin (rigid)
(1)
- Technique sensitive, time consuming
- Wax - should not be used for fixed
prosth - WHY?
?
Interocclusal Records: Materials
(3)
*Rigid, Fast-set VPS
* Plaster (Removable Prostheses)
* ZnOE paste; Resin (rigid)
Definitive Cast: Occlusal Registration (MIP)
(3)
- Record the maxillary and mandibular teeth in total contact.
- Stone - stone contact with hand articulation where possible.
- Place record material between prepared and opposing teeth only.
Definitive Cast: Occlusal Registration
(5)
- Reduce 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
