Silicone Impression Materials: Condensation and Addition Types

Mercaptan

Disadvantages: Unpleasant smell and color, can cause stains on clothing, requires a custom tray, prolonged polymerization time, slow elastic recovery in deep undercuts.

Condensation Silicones

Elastic impression materials based on polymethylsiloxane, hardened by a polymerization process in the presence of a catalytic reactor.

Chemical Composition

• Base: Polymethyl siloxane (base), silica (filler).
• Catalyst: Ortoalquilico silicate (reactor, crosslinking agent), tin octanoate (catalyst or accelerator), oily diluent (if liquid), thickening agent (if paste).

Chemical Reaction

Tin octanoate --- Polymethylsiloxane (base) + Ortoalquilico silicate (reactor) = Silicone + Alcohol

Secondary Product: Alcohol.

Commercial Presentation

Presentations: Pasta-Pasta (PP), Pasta-Liquid (PL), Putty (P), Paste (M), Putty-Liquid (ML).

Consistencies: L (Light body), R (Regular body), P (Putty), Putty.

Proportions

• PP: Equal lengths.
• PL: Length of paste x amount of liquid.
• MP (Putty-Paste): Volume of putty x length of paste.
• ML: Volume of putty x amount of liquid.

Times

• Labor Time: L: 2–4 min; R: 3–5 min; P: 2–2.5 min.
• Polymerization Time: L: 6–8 min; R: 6–10 min; P: 6–10 min; Putty: 2 min.

Condensation Silicones: Manipulation Technique

Mixing methods:

• P-P and P-L: Circular motion.
• M-P (Putty-Paste): Mixture with spatula and then manually.
• M-L (Putty-Liquid): Slots are made in the putty, the liquid is added, mixed with a spatula, and then mixed manually.
• M-M (Putty-Putty): Manual mixing.

Properties

• Tear Strength: 99%.
• Flexibility: 5%.
• Flow: 0.1%.
• Low tear resistance.
• Dimensional Stability: 1/2 hour.
• They are hydrophobic.

Uses

• Main Uses: Making impressions for crowns and fixed prostheses, sometimes removable partial prostheses (PPR).
• Secondary Uses: Record of occlusion.

Evaluation

• Advantages: Standard trays are used, acceptable smell, taste, and color, clean handling technique.
• Disadvantages: Short working time, limited shelf life, the catalyst is irritating.

Addition Silicones

Biomaterials based on elastic silicone impression materials, finished with vinyl groups and silane groups (hydrogen), which harden in the presence of a catalyst by an addition polymerization process.

Synonyms

Vinylsilicones, polysiloxane vinyl, polyvinyl.

Chemical Composition

• Base: Hydrogen-based silane/siloxane and silica filler.
• Catalyst: Vinyl siloxane accelerator, chloroplatinic acid catalyst, silica filler.

Chemical Reaction

Chloroplatinic acid (catalyst) --- Siloxanes silanes (base) + Siloxanes chloride (accelerator) = Vinylsilicones