Gypsum Products in Dentistry

Gypsum Products in Dentistry

• Heating gypsum in a boiling 30% solution of CaCl2 or MgCl2 results in the production of a high-strength die stone (Type V), characterized by its small particle size, high density, and strength.

• Die stone is used for creating dental dies, which are precise replicas of prepared teeth used for making crowns, inlays, and onlays.

• Higher expansion (0.1%) is required for die stone to compensate for the solidification shrinkage of certain alloys, which are used as base metals in dental restorations.

Types of Gypsum Products

• Dental plasters have a high water/powder (W/P) ratio, resulting in a high porosity, low compressive strength, and high abrasion resistance. They are also characterized by large, irregular particle sizes.

• Dental stones have a moderate W/P ratio, resulting in moderate porosity, compressive strength, and abrasion resistance. They have smaller, more regular particle sizes compared to plaster.

• High-strength stones have a low W/P ratio, resulting in low porosity, high compressive strength, and abrasion resistance. They have the smallest, most regular particle sizes.

Setting Reaction of Gypsum

• Mixing hemihydrate gypsum powder with water reverses the dehydration reaction, resulting in the formation of dihydrate through crystallization.

• Increasing water temperature accelerates the setting process.

Advantages and Disadvantages of Epoxy Resin Materials

• Epoxy resin materials can be used with rubber impression materials.
• These materials cannot be used with agar or alginate impressions as the water in the impression hinders the polymerization reaction.
• Epoxy resin materials are viscous, which prevents them from reproducing fine details as well as dental stones.
• They exhibit a shrinkage of approximately 0.1% during hardening.
• They are more expensive than other dental materials.

Casts and Dies

• Casts and Dies are positive replicas of teeth and structures used for observation and diagnosis.
• Casts are used primarily for observation and diagnosis.
• Dies are positive replicas of the prepared tooth on which inlays and crowns are made.
• Dental plaster, stone, and high-strength stone are the most common materials used for casts and dies.

Ideal Properties

• Dimensional accuracy: The model or die should accurately reflect the size and shape of the original structure
• Abrasion resistance: Resistance to scratching during carving of wax patterns
• Good strength and smooth surface: For proper handling and aesthetics
• Reproduction of fine details: To capture important features of the impression
• Compatibility with all Impression materials: Essential for a proper fit and adhesion
• Color contrast with wax patterns: For easy distinguishment during construction
• Easy and quick manipulation: For efficient fabrication
• Non-injurious to health: Safety for both the patient and the technician
• Economics: Cost effectiveness for the overall treatment
• Reasonable setting time: For efficient workflow

Gypsum Products

• Gypsum is a naturally occurring mineral, also known as alabaster.
• Gypsum products are produced by heating the gypsum mineral, which is then ground into a powder.
• Calcination is the process of heating gypsum to create hemihydrates, which are used in dental applications.
• Different types of Gypsum products:
  • Type I: Impression plaster, used for final impressions for edentulous patients
  • Type II: Model plaster, used for diagnostic casts and articulation of stone casts
  • Type III: Dental stone, used for making full or partial denture master casts and orthodontic models.
  • Type IV: High-strength dental stone, used for die construction in fabrication of cast restorations (crowns & bridges)
  • Type V: High-strength, high-expansion dental stone, used for construction of dies on which base metal alloys will be cast.
• Factors influencing Gypsum Properties:
  • Manufacturing Method: Techniques like heating in open air or under steam pressure influence particle size and shape.
  • Particle Size and Shape: Smaller, more regular, and less porous particles offer higher strength.
  • Water/Powder Ratio (W/P): Determines the properties of the mix.
• Setting Reaction:
  • When Gypsum hemihydrate is mixed with water, it forms dihydrate crystals during a crystallization reaction.
  • Crystal growth leads to setting expansion, a crucial property for casting procedures.
  • Hygroscopic expansion: Additionally, soaking Gypsum in water after mixing can lead to expansion due to additional crystal growth.
• Setting Time:
  • Working time: Time for the mix to be workable.
  • Initial Setting time: Time when the mix partially sets, causing loss of gloss.
  • Final setting time: Time when the reaction is complete, although handling may be possible after 30 minutes.
• Factors affecting setting time:
  • W/P ratio: Higher water proportions slow down the setting process.
  • Spatulation: Rapid and prolonged mixing accelerates setting.
  • Temperature: Increased water temperature can accelerate setting until a certain point.
  • Impurities: Presence of impurities can accelerate setting.
  • Fineness: Finer particles accelerate setting.
  • Accelerators and Retarders: These chemicals can modify the setting time.
• Manipulation:
  • Use proper techniques for mixing to avoid air bubbles and ensure a uniform and smooth mix.
  • Ensure a good flow of material onto the impression surface.
  • Allow the mix to set for 45-60 minutes.
  • Disinfect the model after separation from the impression.

Advantages and Disadvantages of Gypsum

Advantages

• Inexpensive and easy to use.
• Good accuracy and dimensional stability.
• Ability to reproduce fine details.

Disadvantages

• Not ideal mechanical properties (low abrasion resistance).
• Brittle nature can lead to fractures.
• Potential issues with alginate impressions, leading to a softer surface.

Electroplated Dies

• Electroplating involves depositing a layer of pure metal (silver or copper) onto the impression.
• Electroplating Mechanism: An electric current causes the dissolution of an electrolyte into ions, which then precipitate onto the impression.
  • Anode: Positive electrode, usually a metal bar.
  • Cathode: Negative electrode, the impression.
  • Electrolyte: Solution containing metal ions.
• Different Electroplated Dies: Copper plating is often used for compound or silicone impressions, while silver plating is preferred for polysulfide or silicone impressions.
• Advantages: Hard, smooth metallic surface, excellent reproduction of fine details.
• Disadvantages: Expensive, time-consuming, and sensitive technique.

Amalgam Dies

• Amalgam is a similar material to filling materials, using an Ag-Sn alloy mixed with mercury.
• Advantages: High surface hardness, reproduction of fine details and sharp margins.
• Disadvantages: Restricted to rigid impression materials, long setting time, separating medium required, good thermal conductivity.

Low Fusing Metal Dies

• Low fusing alloys: Have low melting points, allowing them to be melted and sprayed onto the impression, forming a metal shell that can be filled with dental stone.
• Example: Bismuth-tin alloy, melting point 138°C.

Acrylic Resin Dies

• Self-curing acrylic resin: Used for die construction, requiring water-free impression materials because water can retard polymerization.
• Advantages: More abrasion resistance than stone dies.
• Disadvantages: Polymerization shrinkage, but fillers help reduce this.

Epoxy Die Materials

• Two-component system: Resin and hardener (polyamine) that react in a polymerization reaction.
• Advantages: High abrasion resistance, stronger than high-strength stone.
• Disadvantages: Does not reproduce fine details as well as stone due to high viscosity, some shrinkage during hardening, expensive.
• Toxicity: Hardener liquid is toxic and should not contact skin.

Ceramic Dies

• Specialized ceramic: Supplied as powder and liquid, mixed and fired according to manufacturer's instructions.
• Advantages: Hard and strong die.
• Disadvantages: Shrinks during firing, expensive and sensitive fabrication technique.

Cement Dies

• Silicophosphate cement: Can be used with all impression materials.
• Advantages: Harder than stone dies.
• Disadvantages: Brittle and fractures easily in thin sections, setting contraction occurs.

Explore the crucial role of gypsum products in dentistry, from die stone to dental plasters. Learn about their properties, applications, and the importance of expansion in dental restorations. This quiz will test your knowledge on high-strength die stone and other gypsum types used in creating dental impressions.