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Commercial products such as JB Weld and super glue do not work very well in the mouth. Despite their toxicity, the moist environment tends to de-bond the adhesion and only works for a few minutes, or until you try to chew with the tooth. Go to your local pharmacy and see if they have a "tooth repair kit", which among other things, should contain a bit of temporary dental cement. Make sure the crown is dry and the tooth as much as possible. Hopefully this will hold the crown in long enough until you can see a dentist. It may come out once or twice, as it is temporary glue, but it will work better than the commercial products.
I hope this answers your question. If you would like to discuss this further or have any additional questions, please reply to my answer and I will get right back to you.
Sincerely, XXXXX XXXXX DDS