Once the mysqld server listens to the external interface, any cooleader armed with a port scanner can detect it. Then he can charge the brute force picking up passwords from the root, bombarding it with attempts to login. If the root password is simple, it will be picked up sooner or later.
Those. Formally, the answer is “yes” : an extra open port, service accepting connections from the outside - the risk of hacking increases.
How to prevent - read about the security of MySQL and the OS of your dedicated server. It is necessary to cut off all the possibilities, except for those foreseen: if you expect connections to MySQL only from a certain server, whose IP is known, you must disable connections from all others. Well, change the password in MySQL root.