Impression Materials: Comparing Silicones and Polyethers

What "hydrophilicity" really means in an impression material, the chemical difference between polyvinylsiloxanes and polyethers, and why neither works well in a completely wet operative field.

Elastomeric impression materials are mainly divided into polyvinylsiloxanes (PVS, or addition silicones), polyethers and, to a lesser extent today, condensation silicones and polysulfides. Reversible hydrocolloids, once widespread, have been progressively abandoned in clinical practice due to the need for dedicated heating equipment and trays with internal water circulation, now replaced almost everywhere by more practical alternatives.

The concept of hydrophilicity, often cited in impression material marketing, has a precise technical meaning tied to the contact angle between a water droplet and the material's surface: an angle below 90 degrees indicates hydrophilicity, one above 90 degrees indicates hydrophobicity. In strictly chemical terms, the only truly hydrophilic impression materials are hydrocolloids; polyethers interact favorably with water through hydrogen bonds, but in practice this interaction also involves partial dissolution of the water-soluble plasticizers contained in the formulation, which partly alters the material once set. Addition silicones, historically hydrophobic, have been improved with the addition of surfactants that increase their surface wettability (hydroactivity) — an important practical improvement, but not equivalent to genuine chemical hydrophilicity.

Clinically, an important point to keep in mind is that neither material produces an acceptable impression in a completely wet operative field: both silicone and polyether, in contact with excess fluids, show reduced or absent adaptation to the structure being reproduced and significant loss of detail. In a partially moist environment, however, the polyether's greater hydroactivity in the very first phases after mixing can be a practical advantage, provided stricter pouring times are respected (generally within an hour) compared to silicones.

Polyethers, due to their high rigidity once set, are traditionally considered among the best-suited materials for multiple implant impressions, because they better stabilize transfer copings, reducing their micro-movement during removal; this same rigidity, however, makes them less suited than PVS when material resilience matters more than absolute stiffness, as in impressions with marked undercuts or deep subgingival margins.

On Oralzon you'll find polyvinylsiloxane and polyether impression materials in all the viscosities needed, from light body for marginal detail to putty for the tray, along with the related mixing accessories.