What are the signs of an infection or abscess following a temporary crown?

1) Warm salt water rinses are fantastic for gums.  
2) Can you take Ibuprofen?  Research states taking Ibuprofen (Advil/Motrin) may help reduce inflammation, therefore reduce pain.  Called "Ibuprofen Therapy", you want to take at least 400mg (2 tabs -- but no more than 4 tabs) every 4-6hrs for 3 days. 
Hopefully these suggestions will help prior to seeing your dentist.  
If you have a zit-like pimple or swelling form on the cheek-side of your gums, that is an abscess and you should go to immediate care.  Good luck!