Alginate, Compound

Using Alginate
Alginate is probably the impression material of choice. Certainly if there are recent extractions, then use the soft alginate. (Make sure that the water you are using is not warm to the touch because if so, the alginate will set before you get it into the mouth.) Be sure to measure the powder and the water. Don't put your mixing bowl under the tap to add water. Most of the time your mix will be too loose.

It is always best to follow the manufacturer's instructions. In the preclinic if you made a loose mix of alginate to give yourself more working time, and the model was facing up then there was no problem. In the clinic the muscles will thin out the loose alginate in the vestibular area.

I am inclined to hold back a little of the measured water to see how the mix looks. If it is too viscous I add the remainder of the water.

After your tray is loaded it is a good idea to place (with your finger, or a spatula) some alginate under the lip if there is an undercut anteriorly or the ridge is high, and then take the impression.

After the tray is seated I press on the tray in the posterior ridge area (mandibular) to guide it into its final position. With the maxillary I press on the palate to hold it in place.

Using Compound
Compound is good, but you do not have much experience with it. You will need the solid (non-perforated) edentulous trays for compound. If you have a gagger, compound is better because you can take it in and out of the mouth any number of times without starting over.

Compound is useful when the patient has a large tongue. You can push the compound onto the lingual aspect of the mandibular ridge. If you used alginate the tongue would wipe it away and expose the tray. Have the patient protrude the tongue and move it from side to side to mold the lingual flange.

Remember compound sets hard so don't use it where there are severe undercuts. If you have undercuts remove the compound impression before it gets hard. Of course you never use compound when the patient has teeth.

In either case concentrate on the lingual flange. (You know we are talking about the mandibular impression.) If you are using compound, don't just load the tray but mold it to take the image of the mandibular arch. Shape the lingual flange to be longer than the buccal flange.

When taking the impression (compound or alginate), ask the patient to raise the tongue so that you can slip the lingual flange under the tongue and get an overextended impression.

Wrap the compound to the underside of the tray in four or five locations so it will lock in place.

When using compound, do not submerge the entire metal tray in the water of the compound heater. You want the compound next to the metal tray to be cooler so the compound will maintain the basic shape of the arch.

Overextension is expected for primary impressions. You want all of the available denture bearing area.

Cleaning Up
You want to make sure that your alginate doesn't end up in the sink. Why put it in the sink in the first place? Scrape the alginate from the bowl and put it on the work area next to the sink. Then put it back into the bowl and throw it in the trash.

You also don't want to clean the mixing spatula of alginate by rubbing it on the edge of the infectious waste container. Clean the spatula with a knife and then throw the material into the trash can.

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1999 by Julius Rosen, D.D.S.