Indications:

• Full Upper and Lower Dentures
• Partial Dentures

Contraindications:

• None

Checklist for Alginate Impressions

Various alginate brands may vary from this checklist. Please refer to the individual manufacturer’s instructions.

1. Select the proper tray. Ensures dimensional elastic impression materials accuracy and that all essential areas included in impression. Solid non-perforated metal rim-lock tray recommended (will force material around teeth). Rim-lock design holds impression material in place without adhesive.
   
   If tray too large: Alginate will not flow into edentulous regions and palate unless supported, reach full extent of tissue folds or may slump in palate.
   
   If tray too small or without adequate clearance: impression may be distorted due to impingement of soft tissues (will distort or tear upon removal).
2. Modify selected tray. Rim periphery wax dental compound or heavy-bodied polyvinyl siloxane impression material around entire upper and lower trays. Seat trays in mouth and muscle trim. If the patient has high vault, missing teeth or limited space in molar areas, soften modeling compound in water bath, place in tray and make impression of distal extension, edentulous areas, palate and posterior palatal seal area. Note where tooth imprints occur. Cut these out with sharp knife so compound has definite stops against the tuberosity (assures teeth will not touch tray and distort impression). Trim compound to allow for 1/8 to 1/4 inch clearance between compound and mucosa except in posterior palatal seal area. Ensure compound not loose in tray. If loose, heat wax spatula and carefully force some of compound into rim-lock borders of tray. Soften compound surface with flame. Press bulk cotton into surface for several seconds, leaving short cotton fibres embedded. Place tray in cold water to harden compound.
3. Clean teeth and prepare mouth as necessary. For regular-bodied alginates, have patient rinse with mouthwash mixture. This will cut mucin and lower surface tension helping to eliminate air bubbles. Lightly dry teeth with compressed air just prior to insertion of impression material and tray. For heavy-bodied alginates, saliva makes an excellent separating medium. Do not over dry teeth prior to insertion or heavy-bodied material will stick to teeth.
4. Place gauze in mouth to remove excess saliva, if necessary.
5. Mix pre-weighed alginate and precisely measured distilled water for 15 seconds if a vacuum mechanical mixer is employed or 60 seconds with hand spatulation (timed with a clock). Mechanical spatulation under vacuum produces the best results: a smooth, air-free mix. Distilled water is recommended as calcium and other minerals often found in tap water will contaminate mix. Setting time should be controlled by varying water temperature, not consistency of mix. Warmer water allows mix to set faster than cold water.
6. Dip tray in water to wet the cotton fibres and blow excess water away with air.
7. Load tray, being careful to force the alginate into rim-locks and cotton fibres. Smooth surface with finger dipped in cold water.
8. Remove any gauze from mouth.
9. Gently place some alginate on teeth and in palate.
10. Seat tray immediately with slight rocking motion.
11. When tray is seated, release pressure immediately and hold tray lightly in place to prevent unseating. Imperative to release pressure as soon as tray seated. Alginate materials have a directional set from tooth surface to tray. Pressure will cause impression to set under strain. On removing impression from mouth, these strains will be released, causing distortion and an inaccurate cast. Moving tray during gelation will incorporate similar strains.
12. Place small amount of alginate mix on bracket table as test sample.
13. When test sample loses tackiness, set timer for two minutes.
14. At the end of two minutes, remove impression with firm, quick snap. Do not rock or twist impression before or during removal.
15. Inspect impression carefully for defects as soon as removed and before it is washed.

Tips On Pouring the Model

1. Pour alginate impressions immediately using vacuum mixed stone and vibrator.
2. Use soft mix of stone. Thick mix apt to trap air bubbles and does not provide same strength upon setting.
3. Allow stone to set in trays with teeth down.
4. If tray is turned upside down onto base of stone, tendency for water to rise to highest point (cusp tips). Result: faulty, very soft cusps on model. Inverting tray may also “bend” alginate away from tray if excess material not trimmed away prior to pouring.
5. Remove cast immediately after adequate set or ensure alginic acid in alginate neutralized (will give the model “moth-eaten” appearance). To neutralize alginic acid at surface of impression:
1. Wash impression with “stone soup” (stone powder and water) using camel’s hair brush.
2. Thoroughly rinse impression with clean running water.
3. Dry with gentle compressed air.
4. Pour impression immediately with soft mix of vacuum mixed stone.

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