Polyvinyl siloxane impression material — also referred to as addition silicone or vinyl polysiloxane (VPS) — is a two-component elastomeric impression material used to capture highly accurate replicas of prepared teeth, soft tissue, and surrounding dental anatomy. It is among the most widely used materials in restorative and prosthetic dentistry for fabricating crowns, bridges, inlays, onlays, and implant-supported prostheses.
How It Works
Polyvinyl siloxane sets through an addition polymerization reaction when a base paste and a catalyst paste are mixed together. Unlike condensation silicones, the addition reaction releases no chemical by-products, meaning the material undergoes virtually no shrinkage during or after setting. Once polymerized, the impression is dimensionally stable for an extended period, allowing laboratory fabrication of dental stone or die stone models at the clinician’s convenience rather than requiring immediate pouring.
Clinical Advantages
The material’s combination of precision, flexibility, and stability makes it a preferred choice across a wide range of clinical scenarios. Key benefits include:
- Exceptional dimensional accuracy — captures fine margin detail critical for well-fitting indirect restorations
- High tear resistance — minimizes distortion when removing the tray from undercut areas near the gingival margin
- Long-term stability — permits multiple pours of dental stone from a single impression
- Hydrophilic formulations — modern surfactant-enhanced materials improve flow in the presence of moisture
- Range of viscosities — available as heavy-body, light-body, monophase, and putty to suit different tray and syringe techniques
Clinical Considerations
Despite its advantages, polyvinyl siloxane is sensitive to contamination. Latex gloves, certain hemostatic agents, and sulfur-containing compounds can inhibit polymerization, leaving a tacky or unset surface — a problem known as set inhibition. Clinicians should use vinyl or nitrile gloves when handling unset material. Adequate retraction of the gingival tissue and a clean, dry field remain essential for capturing accurate subgingival margins. When used with a stock or custom impression tray, an appropriate adhesive is required to prevent tray separation and distortion.
Attention to moisture control, correct viscosity selection, and sufficient setting time directly determines the accuracy of the final impression and, ultimately, the fit of the definitive restoration.