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Impression Techniques and Armamentarium

Besides choosing the correct impression material for a specific restoration, the technique and armamentarium also influence the accuracy of an impression.

Tray Selection

Rigid vs non-rigid: the rationale for using a rigid tray is to avoid distortion by controlling dimensional stability and minimising polymerisation shrinkage. Conversely, plastic or non-rigid trays cause distortion, even if using light-bodied materials. As a general rule, plastic trays are suitable for single units, but metal trays are preferable for multiple units.

Stock vs custom: stock trays offer convenience and disposability (plastic variety). Most fixed prosthodontic impressions are feasible on metal stock trays with modifications using dental compound material. However, well-adapted, uniformly spaced (4 mm) custom trays fabricated from autopolymerising or light-cured resins are an ideal choice for removable prostheses, complex cases involving a combination of teeth and implant-supported restorations, or if voids and drags are persistent in a stock tray impression. Also, care is necessary when using rigid materials, e.g. polyethers or putty-wash techniques, especially in the presence of undercuts, which may prevent removal of the custom tray after the material has set.

Perforated vs closed: the reasoning for using a perforated tray is that the holes act as vents for excess material. However, the drawback is that material seepage may elicit a gagging reflex.

Inter-arch vs intra-arch: Full or intra-arch trays are essential for removable, and preferred for fixed, prosthodontics. In some countries, there is a penchant for using inter-arch trays, which simultaneously act as a bite registration. While this may be useful for single u/>

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