Why don't your muscles fully relax when given general anesthesia? the dr said he had a hard time opening my mouth for the tube for last surgery

Depends: Depends on he anesthesia. One component simply puts you to sleep, a different medicine paralyzed you. They were probably simply light on the paralyzingly portion of the medicine. This is normal practice for lightvanesthesia.

Several Possibilitie: Muscle relaxants used for general anesthesia are effective at relaxing voluntary muscles, including those that you use to open and close your mouth. Other tissues, such as tight ligaments or scar tissue, would not relax. Some patients have tm joints that "lock" when the jaw is opened. Find out if you had "succinylcholine induced masseter spasm" which is an adverse reaction to relaxants.

Usually they do.: It often depends on the medications and patient characteristics as to how they perform during anesthesia. If you had truisms, where the jaw muscle lock up under anesthesia, this could be one cause of the problem. If a patient has TMJ disease they might be unable to open their jaw normally. Talk to your anesthesia provider and get specifics, so next time you have an operation they can be prepared.