Impression Trays

STOCK TRAYS

Primary impressions are usually taken in stock trays. There are two types - dentulous and edentulous, both of which generally come in sizes - small, medium and large. Stock trays are made in metal (reusable) or plastic (disposable, usually made of nylon or polystyrene). The size of tray is selected so that the teeth sit centrally within the trough of the tray. Many trays were designed over 30 years ago and updating of many trays is taking place to reflect different edentulous and dentate mouths.

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1) Plastic edentulous stock trays

2) Upper and lower dentate plastic stock trays with impression handles

SPECIAL TRAYS

Special trays are made from either acrylic (light or cold cured) or shellac (a thermoplastic material). They are constructed on the primary cast which helps with adaptation of the impression material and reduces the amount required. The resulting master cast is well detailed and allows accurate construction of the denture.

A "closed" special tray (i.e. no space between the cast and special tray) is required for:

A "spaced" special tray is needed for:

Light cured composite trays are the future as they are rigid, command set and are easy to manufacture at the chairside.

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3) A selection of dentate and edentulous metal stock trays

4) A light cured upper special tray

ADHESIVES AND PERFORATIONS

It is essential that impression materials adhere firmly to the impression trays. This can be achieved by either perforations or by the use of adhesives. Adhesive solutions are needed for alginates, polysulphides and silicones. Adhesives for alginates are solutions of resins in alcohol, they are supplied in a bottle with a brush or an aerosol spray. Polysulphide adhesives are rubber solutions in acetone. Examples of silicone adhesives are isopropylalcohol or amylacetone.

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5) A light cured acrylic upper special tray

6) Tray adhesive being applied to a metal stock tray for an alginate impression