Impression Materials in Dentistry Notes

Impression Materials

Die: A reproduction of a prepared tooth made from a gypsum product, epoxy resin, a metal, or refractory material.

Cast: A dimensionally accurate reproduction of a part or parts of the oral cavity or ex- tra oral facial structures produced in a durable hard material.

Model: A positive full-scale replica of teeth, soft tissues, and restored structures used as a diagnostic aid for the construction of orthodontic and prosthetic appliances.

Polymerization: A chemical reaction that transforms small molecules into large polymer chains.

Syneresis: Expression of fluid into the surface of the gel structure.

Imbibition: Process of water sorption.

Read And Learn More: Basic Dental Materials Notes

A review of impression materials

Polysulphides: Also known as

• First dental elastomers
• Rubber-base impression materials Vulcanizing impression materials
• Mercaptan impression materials
• Thiokol
  • Contains lead dioxide polymer that gives polysulfide its characteristic brown color.
  • The polymerization reaction is exothermic in nature.
  • It has a long setting time of 8 to 12 minutes. it has an unpleasant odor and color. both of these properties cause patients discomfort heat and moisture accelerate the setting time.
  • It is messy and stains clothes.
  • Shows the highest permanent deformation. if maximal accuracy is to
  • be maintained, the cast should be poured within the first 30 minutes.
  • Shows high polymerization shrinkage due to loss of the by-product (water).
  • Polymerization shrinkage and permanent deformation can be minimized by taking a minimum quantity of impression material and by using the custom acrylic tray.
  • Shows the highest tear strength.
  • Hydrophobic in nature. So the impression area should be dried before making an impression.
  • Shows high flexibility and so the material can be released from undercut areas with minimum stress.
  • Causes the lowest cell death count & so biocompatibility is good.
  • Polysulphides are the only impression materials that can be elec- troplated.

Condensation silicones:

• Also known as room temperature (RTV) silicones.
• Highest curing shrinkage due to evaporation of ethyl alcohol byproduct. to avoid this, cast should be poured within the first 30 minutes.
• Less permanent deformation than polysulphides.
• Pleasant color and odor.
• Low tear strength.
• Hydrophobic in nature.
• Flexibility is high when compared with polysulphides. So, the impression can be removed from undercuts without distortion. Has a limited shelf life because of oxidation of the tin component.
• Handling latex globes is contraindicated.

Addition silicones (pseudoplastic impression materials):

• Also known as polyvinyl siloxane or vinyl poly siloxane im- precision materials.
• No volatile by-product.
• Lowest curing shrinkage and lowest permanent deformation with best dimensional stability. So casts can be poured after several hours.
• Extremely hydrophobic.
• Shows the least setting time of all the elastomeric impression materials.
• Handling with latex gloves is not indicated because the sulfur present in the natural latex gloves inhibits the settings of the addition of silicone impression materials.
• Shows good shelf life than condensation silicones.
• Hydrophobic in nature.
• Vinyl impression materials can be disinfected by immersing in 10% hypochlorite or 2% glutaraldehyde solutions.
• Sometimes hydrogen may be evolved and may cause pinpoint voids in stone casts.

Polyether:

• First elastomer is to be developed primarily to function as an impression material. All the other materials were adapted for other uses.
• Stiffest of all elastomeric impression materials. So extremely difficult to remove from undercut areas because of the high modulus of elasticity.
• High tear strength next to polysulphides.
• Dimensionally more stable. The casts can be poured immediately or after several hours, or after several days. Pouring up the im- precision and removing the cast several times does not alter the dimensional stability of the polyether.
• Shows the highest cell toxicity and so the biocompatibility is not good.
• Hydrophilic in nature. (Note: Agar and alginate are also hydrophilic).

Impression Compound (ADA – 3) [SPOTTER]

Applications: For making a primary impression, individual teeth impression

Composition:

• Rosin 30%
• Copal resin 30%
• Carnauba 10%
• Rest-Stearic acid, talc, coloring agents.

2. Alginate (ADA 18) [SPOTTER]

• Type 1 Fast setting
• Type 2 Normal setting

Applications: Impression making

• When there are undercuts in mouths with the excess flow of saliva.
• For partial denture with clasp.
• For making an impression for orthodontic and study models.

Composition:

Esters of

• Alginic acid – 15%
• CaSO4-16%
• Zinc phosphate – 4%
• K Ti fluoride
• Diatomaceous earth
• Nas PO
• Coloring and flavoring agent

Zinc Oxide Eugenol Impression Paste (ADA 16) [SPOTTER]

• Type 1 Hard
• Type 2 Soft

Composition:

Uses:

• Cementing and Insulating medium.
• Temporary fillings
• Root canal filling material.
• Bite registration paste.