Elastomeric Impression Materials: Polyvinyl Siloxane and Polyether

What Are Elastomeric Impression Materials?

Elastomeric impression materials are rubber-like substances that set to a flexible, dimensionally stable solid. Unlike reversible or irreversible hydrocolloids (such as alginate), elastomers capture extremely fine detail and resist distortion long enough for stone models to be poured days later. Two types you will use most often in a modern dental practice are polyvinyl siloxane (PVS) and polyether. Both are used for crown and bridge impressions, implant records, and any situation where high accuracy is essential.

Polyvinyl Siloxane (PVS)

PVS, also called addition silicone or vinyl polysiloxane (VPS), undergoes an addition reaction during setting. A base paste and a catalyst paste are combined; the reaction produces no by-products, so shrinkage is minimal and dimensional stability is excellent. PVS comes in multiple viscosities:

• Light body (wash): flows easily, captures fine margin detail, syringed around prepared teeth
• Heavy body (tray material): stiffer, supports the impression in the tray
• Medium body and monophase: used in single-viscosity techniques

PVS has a pleasant, low-odor working experience. Its major weakness is hydrophobicity: moisture (blood, saliva, sulcular fluid) on the tooth surface can cause voids. Modern PVS formulations include surfactants to improve wettability, but good moisture control remains critical. Typical working time is approximately 1–2 minutes at mouth temperature; set time varies by product.

Polyether

Polyether sets by a cationic ring-opening reaction. It produces a stiffer set material than most PVS formulations, which can make removal from deep undercuts more challenging. Its key advantage is natural hydrophilicity: it is far more tolerant of a slightly moist field. This makes polyether popular for implant impressions and cases where perfect moisture control is difficult. Polyether has a distinctive taste and smell that patients notice, and its stiffness means it should not remain in the mouth longer than necessary. Like PVS, polyether is available in light and heavy body, though viscosity options are more limited. Polyether absorbs water if stored in a humid environment, so models must be poured promptly.

Automix Gun Technique

Both PVS and polyether are supplied in dual-cartridge format. The automix gun holds the two-component cartridge and drives equal amounts of each component through a disposable mixing tip simultaneously.

Steps for safe, correct use:

1. Inspect the cartridge. Check expiration date and confirm the material shows no phase separation.

2. Seat the cartridge in the gun per the manufacturer's instructions.

3. Purge before attaching the tip. Express a small amount of each component separately to equalize flow and verify both components advance. Wipe the nozzle ends clean.

4. Attach the mixing tip and lock it.

5. Purge through the tip. Express a small bead of mixed material and discard it. This ensures the first material into the tray is fully mixed.

6. Load the tray using a smooth, steady trigger pull, moving from one end of the tray to the other and filling without stopping to avoid air incorporation.

7. Hand the loaded tray immediately to the dentist or seat it yourself within the manufacturer's stated working time.

8. Leave the mixing tip attached after use; it seals the cartridge opening to prevent cross-contamination of components.

Two-Step Tray Technique and Tray Adhesive

Custom trays improve impression accuracy by creating a uniform, minimal thickness of impression material. Before loading any elastomer into a custom tray, apply a tray adhesive matched to the material type (PVS adhesive for PVS, polyether adhesive for polyether; they are not interchangeable). Allow the adhesive to dry fully—at least 1–2 minutes or per manufacturer instructions—before loading material. Inadequate drying is a leading cause of impression detachment from the tray. A spacer (typically 2–3 mm of wax or foam) used during tray fabrication creates room for wash material in a two-step technique, ensuring even pressure and detail capture.

Reading the Manufacturer IFU

Always read the Instructions for Use (IFU) supplied with each product. Working time, setting time, and storage conditions vary by brand and formulation. Elevated room or patient temperature shortens working time; cool materials extend it. If you are working in a warm operatory, refrigerating cartridges briefly per the manufacturer's directions can give a few extra seconds—but always allow cartridges to return to the temperature specified in the IFU before use.

Safety and Scope of Practice

• Wear gloves, mask, and eye protection whenever handling impression materials; uncured components can cause sensitization.
• Latex contamination inhibits PVS setting. If a patient has a latex allergy or if you have touched latex gloves, change to latex-free gloves and clean the prepared tooth surface before expressing PVS around it.
• Never leave a patient unattended with a set impression in place; stiff materials, especially polyether, require a deliberate but careful removal technique.
• Document all materials used in the patient record, including lot number and expiration date, per your facility's policy.
• As a dental assistant, your role is to prepare, load, and assist with impressions per your state's scope-of-practice regulations. Verify what is permissible in your state before independently seating an impression tray.