A variety of gypsum products are used in dental practice, each tailored to specific clinical tasks. Here’s a detailed look at their main clinical applications, with explanations.
1. Impression Making (Type I: Impression Plaster)
·
Purpose: Used historically for taking
preliminary dental impressions, particularly in edentulous (no teeth) cases.
·
Properties: Rigid, inelastic, and sets quickly
(3–5 minutes).
·
Advantages: Clean fracture on removal from minor
undercuts, low cost.
·
Limitations: Now mostly obsolete for impressions
due to brittleness and difficulty removing from undercuts without breaking;
replaced by alginate and elastomers.
·
Modern use: Still occasionally used for recording
bite registrations (centric jaw relation).
Type II: Model (Dental) Plaster
·
Purpose: Creation of diagnostic (study) casts,
mounting casts on articulators, molds for denture processing.
·
Properties: Lower strength and higher porosity –
easy to trim and inexpensive.
·
Example Uses:
o
Study
models for analysis and case presentations (orthodontics, prosthodontics)
o
Base
material for building up custom trays or secondary casts
o
Attachment
of casts to articulators (mounting plaster, Class 1; has controlled expansion
for accuracy)
Type III: Dental Stone
·
Purpose: Fabrication of working casts for
complete and partial denture construction, orthodontic models, and diagnostic
purposes.
·
Properties: Higher strength and lower porosity
than plaster; suitable for working casts that need more durability and
accuracy.
·
Example Uses:
o
Master
casts for removable appliances or prostheses
o
Molds for
investing waxed-up dentures before processing
o
Models
for orthodontic appliances and aligner fabrication
3. Die Preparation for Fixed
Prosthodontics
Type IV: High-Strength,
Low-Expansion Dental Stone (Die Stone)
·
Purpose: Making precise dies for crowns,
bridges, inlays, onlays—whenever fine detail and accuracy are required.
·
Properties: Very high strength, minimal setting
expansion, excellent surface hardness; minimal distortion after setting.
·
Uses:
o
Dies for
wax patterns in fixed prosthodontics
o
Master
models for CAD/CAM milling
o
Models
for implant-supported restorations
Type V: High-Strength,
High-Expansion Dental Stone
·
Purpose: Used similarly to Type IV, but
specifically when the casting alloy shrinks more (like base-metal alloys), so
the additional setting expansion compensates for this.
·
Properties: Highest available strength, highest
controlled expansion (up to 0.3%), required for base-metal casting
·
Uses:
o
Dies and
models for working with high-shrinkage alloys
o
Precision
removable partial denture frameworks
4. Mounting on the Articulator
·
Materials: Usually Type II (mounting plaster) or
specialized mounting stones
·
Purpose: To attach upper and lower dental casts
to the articulator accurately. Mounting stone is chosen for fast set, low
expansion, and easy trimming.
·
Properties: Needs to set quickly (3 min), with
controlled expansion (important so occlusal relation is not disturbed)
5. Orthodontic Casts
·
Materials: Mainly Type II (plaster) for study
models or Type III (stone) for working models[2]
·
Purpose:
o
Recording
of pre- and post-treatment tooth positions
o
Design
and construction of orthodontic appliances (braces, retainers)
o
Diagnostic
measurements and case planning
·
Properties: Needs moderate strength, dimensional
stability, and good detail reproduction
6. Prosthodontic Use
·
Materials: Mostly Type III stone for
complete/partial denture models, and Type IV/V for fixed prosthetic work.
·
Applications:
o
Master
casts for full and partial dentures
o
Models
for occlusal adjustments, esthetic planning
o
Working
models for wax-up and processing of prosthesis
7. Endodontic Working Casts
·
Materials: Typically Type II or III, depending on
required detail and strength
·
Purpose:
o
Fabrication
of working casts to study canal anatomy or fit endodontic posts
o
Pre- and
post-endodontic treatment assessment
·
Properties: Need for accurate reproduction of
detail, stable base for measurement and planning
Visual Summary Table: Clinical
Gypsum Product Applications
|
Application |
Gypsum Type |
Key Property |
Example Procedure |
|
Impressions |
Type I (Plaster) |
Clean fracture, fast set |
Edentulous impression, bite
record |
|
Diagnostic Models/Mounting |
Type II (Plaster) |
Moderate strength, easy trim |
Study model, case mounting,
trial base |
|
Working Casts/Removable Pros. |
Type III (Stone) |
Stronger, stable |
Denture base, ortho appliance,
cast partials |
|
Precision Dies (Crowns/Bridges) |
Type IV (Die Stone) |
High strength, low expansion |
Crown & bridge dies,
implant master |
|
Hi-Expansion Dies (Casting Base
Metal) |
Type V (Die Stone) |
High strength, high expansion |
RPD frameworks, large bridges |
|
Articulator Mounting |
Type II, Spec. Mounting Plaster |
Fast set, low expansion |
Mounting max/mand casts |
|
Orthodontic Models |
Type II or III |
Detail, white color |
Ortho study models, working
casts |
|
Endodontic Working Casts |
Type II or III |
Reproducible, cost-effective |
Root post, canal shape
assessment |
Key Points
·
Using the
correct type of gypsum for each clinical application is essential: Type II for study models/mounting, Type III
for working models, Type IV/V for dies, and so on.
·
Modern
dental labs often use pre-packed stones (specialized versions) for tailored
mixing, setting, and expansion properties.
·
Always
follow manufacturer instructions for manipulation for reliable, repeatable
results in the clinic and lab.