[dentveran]

Hello,

I bought this silicone material to make a silicone part that goes into a person's mouth. I couldn't find any information regarding toxicity.

Any idea if it's safe to use in a person's mouth?

Thanks

[Borek]

You need to ask the manufacturer.

[DrCMS]

Hei-Cast 8400 is not a silicone it is a three component polyurethane for vacuum casting/molding. 

One of those components is an isocyanate and that is likely to be toxic. 
One of the other components is a polyol which is harmless.
The third component is probably a plastisier as adding more of it reduces the hardness of the finished article.  Some plastisiers can be a health issue.

I would not put a product made by you using this in my mouth.