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Questions and Answers
Which of the following is a characteristic of elastomers?
What is the process of converting the elastomeric base into a final rubber-like material called?
Which of the following impression materials was introduced in the 1960s?
What are the two main problems of hydrocolloid impression materials that elastomers aim to solve?
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Which of the following is NOT a type of elastomeric impression material mentioned in the text?
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What is the primary advantage of elastomeric impression materials over hydrocolloids?
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Which of the following is a major advantage of polyether rubber impression materials compared to polysulfide and condensation silicone?
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Which elastomeric impression material undergoes the largest dimensional change upon setting?
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Which of the following properties is NOT time-dependent for viscoelastic materials?
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What is the primary reason for the stiffness of polyether rubber impression materials?
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Which statement is true regarding the hydrophilicity of polyether rubber impression materials?
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Which elastomeric impression material exhibits the best elastic recovery from deformation?
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What is the advantage of using an automated mixing system for polyether rubber impression materials?
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What is the approximate polymerization shrinkage of polyether impression materials within 24 hours?
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Which impression technique is commonly used with polyether rubber materials?
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Which statement about the dimensional accuracy of elastomeric impression materials is TRUE?
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Which property of elastomeric impression materials is NOT affected by their consistency (viscosity)?
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What is a limitation of polyether rubber impression materials regarding storage?
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Study Notes
Elastomeric Impression Materials
- Elastomers are rubbery materials composed of long chainlike molecules (polymers) that can recover their original shape after being stretched.
Definition of Elastomer
- Elastomer is a synthetic rubber formed by chemical reaction, known as polymerization.
- They are rubber-like in nature and composed of polymers (ADA No. 19: Non-Aqueous Elastomers).
Uses of Elastomers
- Impression for crown and bridge.
- Very short working time (2.5 minutes) that can be reduced by using thinner.
Polyether Rubber
- Composed of a polyether molecule with an ethylene imine ring and a polyether sulfonate ester.
- Cross-linked polyether rubber with excellent impression accuracy and dimensional stability.
- Properties:
- Stiff and difficult to remove without rocking.
- Break seal and rock slightly to prevent tearing due to low tear resistance.
- Negatively affected by H2O, saliva, and blood.
- Can be dispensed from automated extruder and mixer (ESPE PentaMix).
- Pleasant mixing and ease of handling.
- High cost.
- More accurate than polysulfide and condensation silicone.
- High stiffness and good surface detail reproduction.
- Bitter taste.
- Easily poured in stone.
- Storage of impressions is critical; must be kept dry to maintain dimensional stability.
Mixing Techniques
- Hand mixing.
- Auto mixing.
- Double mix technique (multiple mix) - single impression (One step).
Factors Affecting Working and Setting Time
- Temperature.
- Working and humidity.
- Viscosity.
Dimensional Changes on Setting
- All types of elastomeric impression materials undergo dimensional changes on setting.
- Addition silicone: smallest change (0.05% shrinkage due to polymerization).
- Polyethers: -0.2% shrinkage.
- Polysulphides: -0.4% shrinkage.
- Condensation silicone: largest change (0.6% shrinkage).
Dimensional Accuracy
- Polysulphide: 0.4% polymerization shrinkage in 24 hours.
- Condensation silicone: 0.6% polymerization shrinkage in 24 hours.
- Addition silicone (PVS): 0.05% polymerization shrinkage in 24 hours.
- Polyether: 0.2% polymerization shrinkage in 24 hours.
Elastic Recovery from Deformation
- Addition silicone: shows the best recovery from deformation (99.5%).
- Condensation silicone: 99.5% recovery.
- Polyethers: 98.9% recovery.
- Polysulfides: shows the poorest recovery (96%).
Viscoelastic Mechanical Properties
- Time-dependent properties.
- Higher rate of deformation, higher tear strength (sudden pull).
- Elastic recovery: the amount of rebound after a cylinder of material is strained 10% for 30 seconds.
Detail Reproduction
- All elastomeric impression materials can reproduce 0.02mm wide line except the very high viscosity 0.075mm line.
- Compatible with gypsum.
Hydrophilic vs Hydrophobic
- Strain in compression: measure of flexibility.
- Low consistency is more flexible than high consistency.
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Description
This lecture covers the chemistry, form of supply, setting reactions, manipulation techniques, and properties of elastomeric impression materials in dentistry. Topics include impression plaster, zinc oxide eugenol, rigid impression compound, impression waxes, reversible/irreversible hydrocolloids, polysulfides, silicones, and polyethers.
