impression

what are impression trays?

a device used to carry, confine and control impression material while making an impression

what is an impression?

a negative reproduction of an object which a positive likeness or cast can be made

what is an impression considered to be in dental prosthesis?

a negative registration of the entire denture bearing area

what is a cast?

a positive reproduction of the form of tissues of the upper or lower arch

what is a primary or preliminary impression?

an impression made in a stock tray for making a study cast on which a custom or special tray is constructed on

what is a secondary or final impression?

an impression made in a custom / special tray and is used to make the master (working) cast on which the denture is constructed on

what are the parts of the tray?

• body

• handle

body of tray

consists of a floor and flanges

what does the upper tray consist of?

a vault to cover the palatal area in patient

what does the lower tray consist of?

lingual flanges to allow free movement of the tongue

handle of the tray

used to facilitate insertion and removal of the tray

characteristics of trays for dentulous patients

flat floor and vertical high flanges to cover teeth

characteristics of trays for edentulous patients

oval floor and short flanges to cover the shape of the alveolar ridge

how are trays classified according to their use?

1. stock trays

2. custom (special or individual) tray

what are factors that affect the selection of stock trays?

1. presence of teeth (dentulous, edentulous or partially edentulous)

2. arch form (tapered, square or ovoid)

3. size of arch (1,2,3,4 or S,M,L,XL,XXL)

4. impression material used

what is the purpose of perforated stock trays?

allows for mechanical retention of alginate impression material

what is the purpose of nonperforated stock trays?

allows for easy applying and removing of modeling compound impressions

what is the purpose of rim lock with cooling system stock trays?

allows for the circulation of a cooling system for agar-agar impressions

what are stock trays made out of?

1. metal, and they are either stainless steel or aluminum. autoclavable / can be sterilized

2. plastic, and they can be either autoclavable or non-autoclavable (disposable)

what is a special tray?

also known as a custom tray, it is a device prepared for a particular patient, and it is constructed and fitted on a primary cast

how are special trays classified?

1. thermoplastic

2. plastics

3. metal

what does thermoplastic special trays consist of?

• shellac base plate

• modeling compound

what does plastic special trays consist of?

• acrylic resin and can be self, heat or light cured

• old dentures

what does metal special trays consist of?

• cast low-fusing metal

• modified stock tray

what are the ideal requirements of a special tray?

1. well fitted and accurately adapted to the supporting tissues

2. dimensionally stable

3. free of voids and projections

4. sufficiently thick enough to be rigid (2-3 mm)

5. has a handle

how can acrylic resin custom trays be classified according to the tissue relation?

1. close fit tray

2. open fit (spaced) tray

close fit tray

directly adapted to the cast and is close to the tissues. it is used to record definite pressure impression

open fit (spaced) tray

constructed on a 2mm wax spacer and is adapted to the cast and is kept away from the tissues by an even 2mm wax spacer

what impression materials are used by a special tray?

1. zinc oxide eugenol paste

2. alginate

3. silicone

4. plaster