I have replaced my own dental crowns with superglue (cyanoacrylate) on 3 occasions. The main practical problem is that of being able to put the crown in exactly the right place quickly, so I practised placing it several times without the glue until I was certain I would be able to do it fast. Superglue sets very quickly and I would suggest that if you are not certain of getting the crown seated perfectly in less than 5 seconds - then don't try it.
I suspect it is also important that the crown itself is dry before applying glue - I think the glue setting is catalysed by moisture? The last time I reglued a crown the join failed after about 9 months, before that about 4 months. I think it may be important to completely fill the space under the crown with glue.
As far as I can ascertain, cyanoacrylate adhesives are not toxic, and indeed have medical applications.