Can a temporary crown cause dry mouth, nasty coating on teeth around it & bad breath?

Hi:It is highly unlikely that the temporary crown is causing the problem but never the less possible.  I recommend to also use a mouthwash while you have the temporary crown in your mouth.Best,Dr. Maddahi

It is best to visit your dentist to check the fit of the temporary and the health of the gums surrounding your temporary crown. Gum inflammation is due to excess cement or  gum pockets that needed to be treated PRIOR to having a dental crown. Bad breath stemming from the tooth, could be many factors such as a bad root canal failing ( if you had one), or decays and many other factors....
See you dentist as soon as you can!