Impression-Taking Troubleshooting Guide

By Jeffrey C. Hoos, DMD, FAGD
As appeared in Collaborative Techniques, Winter 2001

Accurate Impressions The completion of an accurate impression following tooth preparation is a critical step in the long-term success of any restorative procedure. Precise impressions consistently communicate clear, detailed, and complete margins. While a variety of high-quality impression materials that provide hydrophilic and hydrophobic properties are currently available in a wide range of viscosities, meticulous care must be taken during impression taking to produce an exact replica of the patient's clinical condition.

Accurate Impressions

Exact impression capture will enable consistent, precise communication. Since the development of clear, concise margins is paramount to the transfer of critical hard and soft tissue structures, the use of high-quality impression materials will provide dimensional stability and accuracy.

Preliminary Capture

A preliminary impression of the preparations was captured without wash material. Since the material is thixotropic and does not provide sufficient contact with the tooth, the margins were inaccurate. Inadequate time between mixing and seating, rocking of the tray to achieve proper seating, and tray movement following seating will also result in inaccurate margin capture.

Definitive Impression

The final impression demonstrates clear margin detail, and the tooth structures are evenly centered within the material for accurate communication. The use of hydrophilic and hydrophobic materials may also enable fluid displacement for definitive impression capture without involved hemostasis or retraction techniques (in select instances).

Inadequate Margins

Inadequate capture of the gingival margins may occur due to:

Insufficient retraction of the sulcus around the preparation
The presence of moisture or bleeding around the dentition
Insufficient cord retraction and tissue displacement

Care must be taken not to tear the soft tissues during cord placement to avoid potential gingival recession and compromised aesthetics.

Voids

Voids can be developed within the impression due to:

Inadequate sulcus retraction
The use of incorrect syringing techniques around the preparation
A prolonged period between mixing and seating of the impression material.

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