The Steps to Alginate Impression

Alginate is an irreversible impression material made with agar-agar, a gelatinous derivative of seaweed. Alginate impressions are a vital part of dental procedures such as creating dentures, braces, crowns and bleaching trays. It is a powder that when mixed with water sets quickly, giving a negative impression of a patient's teeth. Once filled with dental stone or plaster it makes a positive model. Prodedures such as alginate impressions should only be done by trained dental assistants, hygienists or dentists.

Explain the Procedure to the Patient

• Alginate impression material is a mouthful. Most brands taste like mint, but have a gritty aftertaste. Placing the filled impression tray in the mouth may cause the patient to feel the alginate is flowing down the throat, especially on the upper teeth. This causes patients anxiety and the need to gag. Explaining the procedure to the patient in a positive way can allay any fears they may have, making the procedure easier.

Select the Proper Impression Tray

• Using the correct size impression tray is essential to a useable impression. The upper hard palate and areas along the gums under the tongue should be inspected for protruding bone, called "tori." The extra bone could cause the impression to be painful if an ill-fitting tray rubs on them. The tray should have a rim-lock edge, or be perforated, preventing the alginate from separating from the tray once set. Place a tray, starting with the upper jaw in the patient's mouth, seating it from the back of the teeth to the front. A proper fitting tray will cover all of the teeth and gums without impinging on any tissue or tori. There may be a need to consider numerous trays to get to the correct size.

Preparing the Alginate

• Shake the canister of alginate to fluff the powder, prior to opening. Measure out the number of scoops of alginate powder needed, according to manufacturer directions. Level off each scoop with the spatula edge, before emptying the powder into the rubber bowl. For most alginates, two scoops are enough for an impression. Fill the water vial, to the second line with cool water, pouring it onto the powder. Using the flat sides of the spatula, mix the alginate, holding the rubber bowl with one hand while pressing the alginate against the side of the bowl with the spatula and mixing it in a figure eight motion. This provides the alginate a smooth, uniform consistency without bubbles.

Taking the Impression

• Scoop all of the alginate into the impression tray, spreading it evenly, without overfilling, as it can cause the patient to gag. Place the tray in the mouth -- seating the back of the tray first, with the front of the mouth seating last. Taking the impression like this forces extra alginate to the front and out of the tray, rather than down the patient's throat. Fast setting alginate usually sets within 1/2 to 1 1/2 minutes. Regular set can take up to 3 minutes. Once set, remove the tray by pressing down on the handle to release the suction created by the alginate, and carefully remove the tray from the mouth.

Inspect the Impression

• A usable alginate impression should have complete detail showing not just teeth, but the surrounding tissues along with the muscle attachments, called frenums, as well. The roof of the mouth will be entirely filled in with no gaps or bubbles visible. If the impression is correct, allow the patient to rinse out the chalky taste of the alginate and any remnants that may be caught in folds of tissue. Wrap the impression in damp paper towels and set it aside while taking the next impression of the opposing arch or teeth. To prevent distortion, pour the impressions with dental stone or plaster as soon as possible.