Your database backups must be consistent and accurate, especially for master. If you back up a database that contains internal errors, the errors persist in a restored version of the database.
Use the dbcc commands to check a database for errors before backing it up. Always use dbcc commands to verify the integrity of a database before dumping it. If dbcc detects errors, correct them before dumping the database.
Over time, if you discover few or no errors while running dbcc, you may decide that the risk of database corruption is small and that you need to run dbcc only occasionally. If the consequences of losing data are too high, continue to run dbcc commands each time you back up a database.
See System Administration Guide: Volume 2 > Checking Database Consistency.