Dr. Pauline Hayes Garrett

Dr. Karen Faraone

Department of Endodontics, Prosthodontics and Operative DentistryUniversity of Maryland, Baltimore

The purpose of this lecture is to visulize the manipulation of alginate as a duplicating impression material on a simulated patient with a typodont model and a clinical edentulous patient so that the resulting impression records every detail of the teeth and mucosa found on the patient.

Advantages:Simple to useEase of manipulationMinimum equipment

requiredEconomical

Disadvantages:Displaces soft tissueInability to capture fine

tissue detail

*Clinical Significance:

Alginate is an adequate material for treatment planning and preliminary impressions, but is not suitable for final impressions.

rubber mixing bowlbeaver tail mixing spatulaRim Lock impression trays (#11-upper, & #12-

lower)can of alginate impression material (Jeltrate,

irreversible hydrocolloid-normal set)measuring scoop (specifically for Jeltrate

powder)water measure (specifically for Jeltrate

powder)Simulation patient with typodont (Operative,

with all 32 teeth present)

**Important: Read directions on the can of Jeltrate.

Impression trays should be tried on the Maxillary and mandibular arches of the patient to check for proper fit. A well fitting tray should be

centered on the teeth, should not impinge on any

structures in the mouth, should have enough room for 6

mm or 1\4 inch of alginate, should extend to cover all the

teeth in the arch and should be easy to place into and remove from the typodont or mouth.

In some instances the tray may need to be modified to achieve a proper fit (e.g. by adding soft rope wax to the ends or borders or palate).

For the purpose of this preclinical lecture, one size of maxillary and one size of mandibular impression trays are demonstrated.

The #11 tray is a maxillary tray and should only be used for a maxillary impression, and the #12 tray is a mandibular tray and can only be used for mandibular impressions.

If the maxillary tray is slightly “short” in the posterior region, wax can be added to the end of the tray to ensure that the third molars are included in the impression. This may also be true for the mandibular tray.

If the patient has a high palate, you may apply rope wax to the palatal area of the try to provide a uniform amount of material to minimize distortion.

For additional length of flange or posterior border

To provide uniform ¼” of material

Only when necessary

“Fluff the Alginate Container for consistency

Fluff the alginate powder by gently tumbling the canister. Typically, you measure three level scoops of powder and place each in the bowl for a maxillary impression and 2 level scoops for a mandibular impression.

water/powder ratio alters strength/ flow properties in addition to effects on working time and surface quality

For three scoops of powder, the water should be even with the third line of the water measure.

Room temperature water works best. (Cold water slows down the setting time while warm water speeds up the setting time of the alginate.)

One impression will be made at a time.

Normally, the mandibular impression is made first to allow the patient to become familiar with the material on the easier of the two arches.

Measure Water

Pour the water over the powder and gently stir together with the beaver tail spatula.

Once all the powder is wet, thoroughly mix the alginate by spreading it against the sides of the bowl while rotating the bowl in your hand for 15-20 seconds.

Pressing the alginate against the sides of the bowl helps eliminate air bubbles created by the mixing process.

This technique is best learned by demonstration and practice.

The alginate is correctly spatulated when it becomes a wet, thick, creamy paste, and all the powder is incorporated into the mix.

Load the tray to fill the interior and cover all the borders with alginate in several large increments with the spatula.

Maxillary trays should not be overloaded in the posterior area to prevent excess material from sliding down the patient’s throat.

Mandibular trays should be

loaded to the top. Use a wet finger to smooth the

top of the alginate and move it around if necessary.

To eliminate bubbles and achieve better surface detail, wipe the occlusal surfaces of the posterior teeth and all of the interdental areas with some of the extra alginate on your finger prior to incerting the loaded tray.

Finger load into difficult areas

Maxillary arch, the tray should be seated from the posterior to anterior,

Mandibular arch the tray should be seated from anterior to posterior.

The tray is correctly seated when:

Handle is aligned with the patient’s midline,

Tray is centered over the arch and is pressed enough to allow the borders to extend to vestibular areas.

Do not press too hard. The inside of the tray should not come in contact with the teeth or ridges in the case of an edentulous impression. Alginate must do this!

Stabilize the tray while the alginate is setting by holding it in place without movement or pressure. (Check the directions for the setting time.) Feeling the alginate that is remaining in the rubber bowl is another way to confirm it is set. It will be firm and rubbery.

Stabilize the Trays during Setting

After the alginate is set, attempt to remove the tray with a single, quick movement. By “snapping” the impression from the arch, less distortion is introduced than if the tray is slowly pried off the arch.

The teeth or ridge in the opposing arch should be protected by your fingers during tray removal.

After Tray Removal:Check the patient’s mouth

for residual alginate and remove it.

Rinse the impression with water for about 1 minute, and inspect it to see that it is accurate and free of voids.

Wrap the impression in a damp (not soaking wet!)paper towel and place it in a plastic bag while making the next impression. Alginate is best stored in

100% humidity until stone is poured into the impression.

Rinse thoroughly

Disinfect

Trim excess

Eliminate excess moisture

Store suspended in 100% humidity

In all cases, the objective in mixing gypsum products is to wet all powder with water totally to achieve a homogeneous mix with few air bubbles (produces porosities in the final casts). For this exercise, we discuss two methods of Spatulation of stone. We discuss the use of a motor-driven spatula with a vacuum which achieves the best possible result; as well as hand spatulation of stone.

small spatula (#7 wax spatula) for dentate impressions

mixing spatula (also called a plaster spatula)graduated cylinder (to measure volume of water)scale (to measure weight of stone)type of gypsum product desired (in this case,

Denstone)vacuum assisted mixing bowl and hose (Whip Mix

power mixer)table vibrator

Read the directions from the box of Denstone.

Weigh 100 grams of Denstone on a piece of paper on top of the scale.

100 grams of stone mixes with 30 ml of water to optimize the physical properties of the stone

This will be different for different manufacturers and different types of stone.

So…. BE SURE TO READ THE DIRECTIONS.

Then weigh the Denstone!!!

Shake your impression to remove excess water, if present. If dry, moisten the impression and shake to remove excess water.

NEVER TRY TO POUR SONE INTO A DRY IMPRESSION. AIR WILL BE TRAPPED AND VOIDS WILL APPEAR ON THE CAST.

Measure 30 ml of water in the

graduated cylinder. (Water temperature will affect working and setting time of the stone. Room temperature water works best.)

There are two methods of mixing gypsum products. They can be hand-spatulated in a

rubber bowl. Power-mixed with a motor-driven

bowl and spatula. A vacuum hose attached to

some of the motor-driven spatulas to minimizes the air trapped in the mix.

Motor-driven mixing produces a faster setting gypsum product with slightly better physical properties.

Motor-driven mixing under a vacuum produces a gypsum product with less porosity and increases the wear-resistance and compressive strength of the set stone.

Wet the vacuum mixing bowl with water and shake it out.

Pour 30 ml of water into the bowl. Add measured powder to the bowl.

Always add powder to water to achieve the most bubble free mix when working with gypsum products.

“Wet” the powder by stirring gently with a spatula

1. Spatulate for 20 seconds, under vacuum, with the Whip Mix power mixer.

2. Vibrate the bowl for 5-10 seconds.

3. Spatulate for 20 more seconds, under vacuum.

4. Remove the hose from the

bowl and vibrate the bowl another 5-10 seconds with the spatula on the side to allow stone to vibrate from it into the bowl.

5. Immediately wash the spatula under running water to keep stone from setting on it.

6. Allow the vacuum to run for

one minute before turning the machine off.

Cover the table vibrator with paper or a plastic bag to protect it from wet stone.

While gently vibrating the alginate

impression with one hand, introduce stone into the last tooth on the right or left side in small increments with the small wax spatula.

As the stone moves throughout the

impression, continue adding small amounts while rotating the impression tray until the impression is completely filled.

When finished the stone should be slightly

above the borders of the impression. The purpose of placing the stone in small

increments while vibrating the impression is to avoid trapping air bubbles in the confined spaces of the impression.

Single pour- complete denture diagnostic castsBase made Before stone in impression is set.

Double pour- all other castsImpression is poured and retentive dollops are

added.Base is made After stone in impression is set.

To make the base: make a second mix of new stone that has a thicker consistency than used for pouring the cast

Approximately 190 grams of powder to 60 ml of water.

Place this stone on a ceramic tile and shape it into a square about the size of the impression tray.

Approximately 1 inch in thickness. Invert the impression tray with the almost set dental stone onto this square and gently seat it.

The tray should be level with the tile.

The plaster spatula is used to remove gross excess of the stone from the sides forming the cast base and to smooth the base and impression together.

Allow to set for approximately 45 minutes.

1. Suspend the impressions by their handles to let set prior to placing on base. This will help prevent distortion of final cast from pressure.

2. Form base.3. Vibrate stone into retention

nodules.4. Invert impression tray and blend

base onto the set stone impression.

As soon as the impression is poured and while it is setting, clean up the laboratory area and equipment used.

It is easier to clean dental stone from the spatula, bowl and vibrator before it has set.

Large excesses of stone should be placed in a trash receptacle.

Any stone washed down the drain should be followed by copious amounts of water to avoid having it set in the drains.

As soon as the stone is set in the impression, the cast should be separated from the impression in the tray.

Use a laboratory knife to remove excess dental stone beyond the peripheral borders of the tray.

Gently rock the cast out of the impression in small anterior to posterior movements to avoid breaking off a tooth. The cast is now ready to be trimmed.

The alginate should be removed from the tray and discarded.

Produces a symmetrical base

Professional appearance for discussing treatment with your patient and colleagues.

No sharp angles

Edentulous cast needs to provides access to the vestibule

½” base parallel to teeth or ridge.Base for an Adult cast should measure approximately 1/2

inches, IF YOU ARE NOT SURE ABOUT THE QUALITY OF YOUR CASTS, ASK YOUR LABORATORY INSTRUCTOR TO EVALUATE THEM BEFORE YOU TRIM THEM.

The cast base should be ~1/2” thick!

The electric powered cast trimmer is a revolving abrasive wheel that must be kept lubricated and clean during use by a constant stream of water bathing the wheel.

If operated dry, it will become clogged with particles of stone.

Place the cast on its base, and trim away excess at the posterior aspect of the cast.

Base of the cast should be parallel to the occlusal (biting) surfaces of the posterior teeth or edentulous rim.

Place the cast on the posterior end trimmed in Step 1, and press the base against the wheel to parallel it to the teeth.

Place the cast back on its base and trim the remaining periphery to the proper area on the cast.

The casts should be rinsed with clean water and left to dry for at least 12 hours. Do not store the casts in an occluded position, as the teeth may wear or fracture especially when the casts are wet.

After drying, small blebs or imperfections in the surfaces of the stone may be scraped away with a laboratory knife or wax spatula.

Large blebs or imperfections usually require making a new set of impressions and casts.

Dentate Cast

Edentulous Cast