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).
2. Cast and Model Fabrication
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)
· 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
· 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.