Polysulphide Impression Material in Dentistry

Questions and Answers

What is the purpose of sulfur in the accelerator paste of polysulphide impression material?

To increase the setting time

To promote polymerization reaction (correct)

To reduce the viscosity of the material

To improve the flexibility of the material

What is the main advantage of using polysulphide impression material for impressions of crowns and bridges?

It has a high tear strength

It can be used with stock trays

It is more accurate than alginate (correct)

It has a long working time

What is a disadvantage of polysulphide impression material?

It is expensive to use

It has a short working time

It has an offensive odor and taste (correct)

It has a low tear strength

What is the recommended way to mix polysulphide impression material?

Mix the two pastes with a spatula in a swirling and stropping motion Signup and view all the answers

What property of polysulphide impression material makes it suitable for full denture impressions?

High flexibility Signup and view all the answers

Why should the tissue be thoroughly dry when using polysulphide impression material?

Because the material is hydrophobic Signup and view all the answers

What is an advantage of polysulphide impression material over alginate?

It is more accurate Signup and view all the answers

What can be done to polysulphide impression material to improve its dimensional stability?

Electroplate it with copper Signup and view all the answers

Which of the following factors can inhibit the setting time of addition silicone (AS)?

All of the above Signup and view all the answers

Which of the following is NOT an advantage of silicone elastomeric impression materials?

Low cost Signup and view all the answers

Which of the following is a disadvantage of addition silicone (AS)?

Hydrogen gas release during setting Signup and view all the answers

Which of the following properties refers to the resistance to fracture of an elastomeric material?

Tear strength Signup and view all the answers

Which of the following is an appropriate disinfectant for polysulfide and silicone elastomeric impression materials?

All of the above Signup and view all the answers

Which of the following is an alternative name for addition silicone?

Vinyl polysiloxane Signup and view all the answers

Which elastomeric impression material exhibits the highest dimensional stability?

Addition silicone Signup and view all the answers

Which of the following is a factor affecting the dimensional stability of elastomeric impression materials (EMIMs)?

All of the above Signup and view all the answers

What is a characteristic of polyether impression material?

It provides elastic recovery with minimal distortion. Signup and view all the answers

Which statement is true regarding addition silicone materials?

They are known for their excellent dimensional stability. Signup and view all the answers

What is a common property of elastomeric impression materials?

They can undergo elastic recovery after deformation. Signup and view all the answers

What is the ideal manipulation time for elastomeric impression materials after mixing?

Within the first three minutes of mixing. Signup and view all the answers

Which type of silicone is known for curing through a condensation reaction?

Condensation silicone. Signup and view all the answers

What effect does filler content have on the shrinkage of elastomeric impression materials?

More filler content results in decreased shrinkage. Signup and view all the answers

What is the first elastomeric impression material commonly used in dentistry?

Polysulphide. Signup and view all the answers

Which statement accurately describes the stages of polymerization in elastomeric impression materials?

Final set progresses to a solid rubbery mass. Signup and view all the answers

Study Notes

Composition of Accelerator Paste

Contains lead dioxide, dibutyl phthalate, magnesium stearate, and sulfur for polymerization.

Uses of Polysulphide Impression Material

Ideal for impressions of crowns and bridges with a light-bodied injected material.
Heavy-bodied material used in trays optimizes accuracy.
Custom trays increase the precision of dental impressions.
Light and medium-bodied materials are used for full denture impressions.

Properties of Polysulphide

Offers greater accuracy than alginate but less than other elastomeric materials.
Excellent detail reproduction and lowest viscosity among elastomers.
High tear strength and hydrophobic; requires dry tissues for application.
Notable for an unpleasant odor and the longest working time of 4-6 minutes.
Working and setting times are influenced by heat and humidity.
Susceptible to distortion from water loss through evaporation.
Provides good flexibility and elastic recovery; can be electroplated with copper.

Advantages and Disadvantages of Polysulphide

Advantages:
- More accurate than alginate; long working time (4-7 minutes).
- High tear resistance and long shelf life.
- Cost-effective and demonstrates high flexibility.
Disadvantages:
- Offensive odor and taste; needs immediate pouring with dental stone.
- Stains clothing and can experience significant distortion due to water loss.
- Longer setting time (7-10 minutes) and not as accurate as other elastomeric materials.

Mixing Polysulphide Impression

Equal lengths of two pastes dispensed and mixed on a paper pad until homogeneous.
Components include divinyl polysiloxane, inert oils, fillers, platinum salt, palladium, and retarders.

Properties of Addition Silicone

Highest dimensional stability among elastomers.
Good tear strength with excellent surface detail reproduction.
Exhibits the lowest curing shrinkage and lowest permanent distortion.
Can be electroplated with copper and silver.

Advantages and Disadvantages of Addition Silicone

Advantages:
- Adequate strength, high accuracy, and short setting time.
- High dimensional stability with minimal distortion.
Disadvantages:
- Hydrogen gas generation may affect dimensional stability.
- More expensive and hydrophobic.

Factors Affecting Setting Time of Addition Silicone

Sulfur contamination from latex gloves can inhibit setting.
Materials used in gingival retraction cord, such as aluminum sulfate.
Residues from acrylics, methacrylates, and petroleum jelly can interfere with the reaction.

Disinfection Methods for Elastomers

Polysulphide and silicones may be disinfected by immersion.
Recommended exposure time should not exceed 30 minutes; suitable disinfectants include glutaraldehyde, chlorine compounds, iodophors, and phenolics.
Polyether should be immersed with caution; short-term exposure minimizes distortion.

Dimensional Changes in Elastomeric Impression Materials

Curing shrinkage and incomplete elastic recovery are key factors.
Filler content affects shrinkage—more fillers result in less shrinkage.
Loss of water (notably in polyether) and thermal contraction impact dimensional stability.
Timing of pouring impressions also influences the outcome.

Types of Elastomeric Materials

Commonly used elastomeric materials in dental practice include polysulphide, polyether, silicone, and polysiloxane (polyvinyl siloxane).

Curing Process of Elastomeric Impression Material

Polymerization begins upon contact of base and catalyst, proceeding through three stages:
- Initial set: Paste stiffens without elasticity.
- Final set: Paste becomes elastic, evolving into a solid rubbery mass.
- Final cure: Occurs within 1 to 24 hours.

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Description

This quiz covers the composition and use of polysulphide impression material in dentistry, including its application in crowns and bridges.