Dental Impressions and Casts

Mouth Preparation and Primary Impression

• An impression is a negative reproduction of teeth and/or adjacent structures from which a positive replica (cast) can be made.
• The purpose of an impression is to produce a cast over which a dental restoration can be constructed.

Patient Preparation

• A denture should not be constructed unless the supporting tissues are in an acceptable condition.
• Existing dentures should be examined for fit and occlusion, and corrected temporarily with tissue conditioning material if necessary.
• Dentures should be removed from the patient's mouth for 24-48 hours before making impressions.
• Tissue preparation/conditioning involves clinical examination, correction of denture, application of tissue conditioning material, oral hygiene instructions, tissue massage, and rinse with warm water and salt.

Impressions for Complete Dentures

• Primary impressions are made using a stock tray, which is then used to construct a custom tray.
• Secondary impressions are made using the custom tray to produce a master cast.

Stock Trays

• Stock trays are ready-made, come in different sizes and forms, and can be adapted to fit the patient's mouth.
• They allow addition or removal of material and can be bent to fit the patient's mouth.
• The tray should be checked for size and adjusted by adding wax or trimming the border.

Tray Components

• A tray consists of a floor, body, flanges, and handle.
• The floor and flanges make up the body of the tray.

Tray Types

• Trays can be metal (aluminum or stainless steel) or non-metal (plastic).
• Perforated trays are used for alginate impressions, while non-perforated trays are used for impression compound.

Anatomical Landmarks

• Anatomical landmarks include peripheral, supporting, and relief areas.
• Examples of anatomical landmarks in the mandible include the labial frenum, labial vestibule, lingual frenum, buccal frenum, and buccal vestibule.

Primary Cast

• A primary cast is used to study the ridge shape, palatal vault shape, denture bearing areas, areas of undercut, relief areas, posterior palatal seal area, sharp bony edges, depth of the sulcus, inter-ridge space, and inter-ridge relations.
• It is constructed for each patient and provides more accurate information due to its customized nature.
• Types of primary cast materials include acrylic resin and shellac.