To remove the font database:
- Shut down your Mac.
- Start your Mac in Safe Mode by holding down the Shift key while starting your machine. Starting your Mac in Safe Mode removes the font database.
- Restart your Mac.
If you are using Apple's Font Book to manage your fonts you will need to manually reset the state of each font (whether they are active or not). Your font library should stay intact however.
- Open the application that was having issues.