Why do we box our final impressions for RPDs etc

[Dental916]

Why can't we just pour them up?

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[NileBDS]

Why can't we just pour them up?

If you pour the impression, you will only attain 3-4 mm of vertical height at the thinnest part of your stone model. Normally, you need 6-8 mm of thickness to prevent the stone model from breaking under flasking pressure (or something like that).

In order to compensate for the additional 3-4 mm you need in vertical height, you will need an additional mix of stone, A.K.A., THE BASE.
Those two mixes of stone will never become homogeneous, which creates a weak junction in your master model, at which it may break under flasking pressure, potentially ruining/destorting your final prosthesis.

SO, the boxing allows you to pour the impression AND the base, while maintaining that vertical height and homogeneity of your master cast stone model. It's also just a good way to create nice, flat, even land areas on your master cast model for flasking and processing purposes.

I'm sure it could have been explained using much less words too, but I'm just in a good mood.

 

[tinman831]

Wow someone asked this same exact impression not too long ago. Let me see if I can dig up that thread.

 

[tinman831]

http://forums.studentdoctor.net/showthread.php?t=556903&highlight=final+impression

 

[desert rat]

In private practice we don't use the standard wax boxes etc. We pour up the alginate and then add a base later, we trim it and write a lab slip and send to lab for framework etc.

Nothing is made as difficult as a dental school does, but still you need that base. Try sending to a lab without it and they will charge you to do that or will ask you to send work somewhere else.

You get back from the lab what you send them.