Hi Dear !! Thanks for your query to HCM .
Read and reviewed your query and health concerns. 
You seems to suffer from a risk of -Adrenal Crisis due to the 
stress of surgical resection for Crohn's and due to stress of 
dental extraction.
This adrenal crises-is due to the long 
steroid reducing the body response by adrenal gland,in case of stress during both these  procedures.
Hence  added covering dose of long acting steroids-like Dexamethasone(
Dexona ) is needed to tide over the surgical stress during these 2 procedures which you will be undergoing soon.
So nothing to worry, but disclosure to anaesthetist about the steroid exposure and dose of it would reduce the risks during surgery,especially under GA, where the body responses are to be kept under meticulous monitoring during these procedure.
Hope this would help you to plan further care of this complex illness of yours. 
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Good Day!!
Wishing Good Healthy Life in time to come!!
Dr.Savaskar M.N.
Senior Surgical Specialist
M.S.Genl-CVTS