How to Size Dental Impression Trays

Anyone who has ever had a precision dental appliance, such as; braces, crowns, bridges, partial or complete dentures; likely remembers the impressions taken to make it. Dental impressions are usually the least enjoyable part of dental treatment. Having the consistency of chalk, jelly or putty, depending on what the impressions are for, they often have the added displeasure of causing patients to gag. Unfortunately, dental impressions are an essential part of restorative dentistry. As a result, impressions and sizing of impression trays, should only be done by a dentist or dental assistant.

Things You'll Need

• Impression trays
• Mouth mirror
• Cuspidor or high speed suction

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Instructions

• 1

  Select trays for the dental impression to be taken, such as, perforated trays for alginate, water-cooled for hydrocolloid or rimmed for polyvinyl siloxane. Alginate is gritty and used for study models, initial denture and opposing impressions. Hydrocolloid is hot and jelly-like, for use in crowns, bridges and inlays. Putty-like polyvinyl siloxane is for the same procedures as hydrocolloid.

• 2

  Inspect the patient's mouth to estimate the correct tray size. Dentists and assistants who have a lot of experience can often tell what size just by looking at the jaw.

• 3

  Choose an impression tray and place it in the patient's mouth, seating it from back to front.

• 4

  Retract the lips with a mouth mirror, to see how well the tray covers the arch. Ensure that no parts of the tray pinch the patient's gums or soft-palate. A tray that is too large will likely cause the patient to gag, occasionally uncontrollably.

  Lower impression trays are less likely to cause irritation of the patient's gag reflex. A tray that is too small will not get a true impression of the entire arch. The tray should fit loosely, covering every surface of every tooth. It should also fit under the lips into the vestibules -- the area between gums and lips -- all the way to the frenum -- the muscle attachment of the lip to the gums).

• 5

  Repeat these steps, until the proper impression tray size is determined.