Pouring a dental model after taking an impresson.
What is a dental model?
A dental model is used in dentistry so the dentist can have an exact replica of the patient’s teeth, gingiva, and surrounding tissues in the mouth. It can be used for studying purposes to determine the patients course of treatment. They can also be used for the fabrication of appliances like whitening trays, mouthguards and more.
Why pour a model?
Pouring a model in dental stone is a vital component of fabricating an accurate, well-fitting dental appliance.
It is the only way to make a cast or ‘positive’ model of the patient’s dentition out of the alginate dental impression or ‘negative’ mould.
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How to pour a dental model:
Unwrap paper towel from alginate impression.
Disinfect before pouring either with a spray or immersion in solution.
The impressions should be slightly moist. If needed run impression under water shake off excess this reduces surface tension and allows stone to flow over impression much easier. There is also a surfactant spray that does the same.
Check the impressions for distortions. Cut excess impression material from the back areas of the tray, leaving at least 2-3mm of material behind the last tooth on each side of the arch.
It is a judgment call how much stone and water to use for pouring a model.
Put large scoop of stone in a green mixing bowl and add water get powder wet start mixing slowly so powder does not get all over.
Keep adding water and mixing until stone is creamy like cake batter and holds its own weight on the spatula.
Turn on the vibrator place the mixing bowl on a vibrator to remove any remaining bubbles, then place a small amount of stone at the corner of the tray with the spatula, watch it flow into the teeth making sure there are no bubbles in the mix.
Once all teeth are filled you can start to add stone more rapidly to impression without worrying about voids. Some stone may run out the back of tray on to vibrator. Pile more stone on top to build up height.
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Base stone should be a little thicker than what goes in the impression, you can add more powder to bowl to make it thicker if needed. Put base on a paper towel on the counter.
Do not place poured model on the counter with the vibrator or your base will not hold up.
Using a spatula, form the solid base of the model thick enough to hold impression, about 1/2 inch. Set impression on top take away excess.
If base is a runny mix wait 2-3 minutes and trim off excess. Do not let stone lock edge of tray or you will not be able to break impression out without breaking teeth.
The stone mixture should set for approximately 1 hour to obtain maximum strength. Remove the impressions carefully to prevent breakage.
If for some reason you can not break the impression out, place the whole model including tray into a hot water bath for five minutes, this will melt the tray adhesive and you should be able to break the tray away from impression material then remove impression material from the stone.
This should keep model and teeth intact.
Models are now ready to be trimmed.
For more Information:
References: Elements of Dental Materials for Dental Hygienist and Assistants by Phillips, Fourth Edition
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