Silicones

Silicones
Ideal for impressions for fixed prosthodontics i.e. crowns/bridges
2 Main types: Condensation or Addition

Condensation Silicones
Older than addition silicones with poorer properties
Base paste + accelerator paste
Base: polydimethyl siloxane + colloidal silica or microsized metal oxide filler
Accelerator: alkyl silicate, stannous octate, inert filler

Condensation silicones, also known as polysulfide silicones or simply “condensation silicone impression materials,” are a type of dental impression material used in dentistry.

Composition: Condensation silicones consist of two main components: a base paste and a catalyst (activator) paste. These pastes contain the following key components:

1. Base Paste: The base paste primarily contains a silicone polymer with siloxane bonds. It may also include fillers, plasticizers, and other additives to achieve desired physical properties. These fillers enhance the material’s mechanical strength and tear resistance.
2. Catalyst Paste: The catalyst paste contains a catalyst (often stannous salts, such as stannous octoate) that initiates the cross-linking reaction between the base and catalyst pastes. This chemical reaction results in the formation of an elastic, set impression material.

Properties and Characteristics: Condensation silicones exhibit various properties and characteristics that make them suitable for dental impressions:

• Good Detail Reproduction: They are known for their ability to accurately capture fine details of dental anatomy and oral structures.
• Dimensional Stability: These materials offer good dimensional stability over time, meaning the impression retains its accuracy and shape even if stored for an extended period.
• Elasticity: Condensation silicones are elastic and flexible, making them easy to remove from the mouth without tearing or distortion.
• Hydrophilic: Some condensation silicones are designed to be hydrophilic, meaning they readily accept moisture. This property is beneficial when dealing with a wet oral environment, as it helps prevent distortion of the impression.
• Setting Time Options: Different setting times are available, allowing dental professionals to choose a material with an appropriate working and setting time for their specific clinical needs.
• Taste and Odor: They are generally well-tolerated by patients due to minimal taste and odor.

While condensation silicones have been widely used in dentistry, they have seen a decrease in popularity due to advancements in other impression materials like addition silicones and polyether materials. However, they are still suitable for many clinical situations and may be preferred by some dental professionals for specific applications.

Addition Silicones

Addition silicones, also known as vinyl polysiloxanes or polyvinyl siloxanes (PVS)

Composition: Addition silicones are part of the silicone elastomer group and are composed of a base paste and a catalyst (activator) paste. These two components are mixed together in equal proportions to initiate a chemical reaction and form a set, elastic material.

Properties and Characteristics:

• High Accuracy: Addition silicones are known for their exceptional accuracy and precision, making them a preferred choice for taking detailed impressions of teeth, gums, and oral structures. This accuracy is crucial for the fabrication of dental restorations like crowns, bridges, dentures, and orthodontic appliances.
• Dimensional Stability: Addition silicones exhibit minimal shrinkage and excellent dimensional stability over time. This ensures that the impression remains accurate, even if it is stored for an extended period before being used in the dental laboratory.
• Excellent Detail Reproduction: They have the ability to reproduce fine details of dental anatomy, making them suitable for capturing the intricate features of teeth and soft tissues.
• Hydrophobicity: Addition silicones are hydrophobic, which means they do not readily absorb moisture. This property is valuable when dealing with a wet oral environment, as it helps prevent distortion of the impression.
• Tear Resistance: They have good tear resistance, which is beneficial when removing the impression from the mouth or when handling it in the dental laboratory.
• Quick Set Times: Addition silicones offer various setting times, allowing dental professionals to choose the appropriate material for their specific requirements. Some materials have fast-setting options, which can be advantageous in time-sensitive procedures.

Comparisons

Addition silicones (addition-cured silicones) and condensation silicones (condensation-cured silicones) are two common types of dental impression materials used in dentistry. They have differences in terms of their chemistry, properties, and applications. Here’s a comparison between addition and condensation silicones:

Chemistry:

1. Addition Silicones:
   • Chemistry: Addition silicones, also known as polyvinyl siloxanes (PVS), polymerize through an addition reaction. They do not produce byproducts during the curing process.
   • Safety: They have minimal to no odor or taste, which is generally well-tolerated by patients.
2. Condensation Silicones:
   • Chemistry: Condensation silicones, also known as polysulfide silicones, polymerize through a condensation reaction, producing byproducts such as alcohol or water during the curing process.
   • Odor and Taste: They may have a noticeable odor and taste, which can be less pleasant for patients.

Properties:

3. Accuracy:
   • Addition Silicones: Known for their exceptional accuracy and precision, making them a preferred choice for capturing fine dental details.
   • Condensation Silicones: Also offer good detail reproduction, though they may be slightly less accurate compared to addition silicones.
4. Dimensional Stability:
   • Addition Silicones: Known for excellent dimensional stability, retaining accuracy over time.
   • Condensation Silicones: Offer good dimensional stability but may be less stable than addition silicones over extended periods.
5. Elasticity:
   • Addition Silicones: Highly elastic and flexible, making them easy to remove from the mouth without distortion.
   • Condensation Silicones: Also exhibit elasticity but may not be as flexible as addition silicones.

Hydrophilicity:

6. Addition Silicones:
   • Some addition silicones are hydrophilic, meaning they can capture moisture and work well in a wet oral environment.
7. Condensation Silicones:
   • Typically, condensation silicones are hydrophobic and may not readily accept moisture, which can lead to impression distortion in a wet environment.

Setting Time:

8. Addition Silicones:
   • Offer various setting times, allowing for flexibility in clinical use.
9. Condensation Silicones:
   • Also provide options for different setting times to accommodate specific clinical needs.

Applications:

10. Addition Silicones:
    • Preferred for highly accurate impressions in various dental applications, including crown and bridge work, removable prosthodontics, orthodontics, periodontics, and prosthodontics.
11. Condensation Silicones:
    • Suitable for a wide range of dental applications, although they may be less commonly used than addition silicones in modern practice.