Video courtesy of Dr. Ulf Temnitzer and UOP PRD
- Alginate packages with water measure
- Stock edentulous/dentate trays
- Ortho or red rope wax
- Cotton forceps
- Ziploc baggies
- Alginate adhesive
- Alginate bowl and spatula
- Mouth mirror
- 2x2 gauze
- Select appropriate tray size for each arch: edentulous trays for minimal ridges, dentate trays for robust ridges.
- The trays should be outlined with red or white rope wax, and then the empty trays are inserted in the mouth and held in position. If there is difficulty placing the trays in the mouth because of restricted opening of the lips, use a mouth mirror instead of a finger for initial lip retraction.
- Remove the tray from the mouth and chill the wax in cold water. Dry the tray without deforming the wax.
- Place adhesive on the tray with brush (light coat) and wait 5 mins.
- Mix alginate powder with slightly less water, to make a thicker-than-ordinary mass (improves vestibular displacement). Overload the tray and smooth the surface with a wet finger.
- Place in the mouth and press to position over the ridge. For maxillary impressions, make sure to place a finger-load of material in the palatal vault, then seat the tray front-to-back, making sure that the labial flange of the tray is completely seated behind the upper lip first, before the posterior aspect of the tray is positioned. This will result in more posterior flow of material (toward the palate), but will result in an impression with the ridge more nearly centered in the tray, with full capture of vestibules and without large voids in the palate.
- When the alginate has set (100% rebound from fingernail indentation), remove impression from the mouth by a snap motion. Rinse the impression with copious water.
- Be critical about what you accept for a preliminary impression. Severe tissue displacement, large voids, and short vestibules all create recurring errors for the rest of your diagnosis and treatment.
- Alginate impressions are straightforward to repeat until the result is optimal; over-extension is preferred to under-extension.
- When the impression is judged to be acceptable, spray with disinfectant, label, and seal in a zip-lock baggie for transportation to the lab.
- Place correct amount of water in bowl. (Make sure water is not warm.)
- Add power to water and mix while bowl is situated on vibrator.
- Hold impression tray on vibrator.
- Add small increments to the most distal tooth of one side of the impression tray.
- Allow stone to slowly flow from tooth to tooth around the arch until adequate stone for first pour.
- Add retention spikes onto first pour.
- Allow stone to set for 20 minutes.
- Trim spikes (if too large) to proper even lengths.
- Add water and powder to bowl and mix.
- Pour a base on model base plate and invert model onto plate.
- Place models down so that they seat parallel to the counter.
- Push stone up towards the impression tray to fill in space between two layers. DO NOT LOCK IMPRESSION TRAY INTO STONE.
- Use a green handled knife or spatula to smooth lingual portion of mandibular tray.
- Let stone set to a slightly thicker consistency and remove excess base from the sides of the impression tray.
- Allow stone to set for 45 minutes.
- Remove alginate from stone.
- Trim excess off models.
- Ensure that the model trimmer plate is perpendicular to the wheel.
- When trimming the base, be sure that the occlusal surface of the molars and bicuspids are parallel to the wheel so that when the cast is set on table, the occlusal surfaces of the molars are parallel to the table.
- You may have to trim more on one side of the base until it is even or the entire base is parallel to occlusal surfaces.
- Base should be 10-15mm thick to allow space to mount the case on the articulator.
- Remove blebs from occlusal surfaces and fill in voids.
- Label with patient name.