Can’t open mouth

2 year old dog, suddenly unable to open his mouth, can eat and drink by sucking food in, won’t bark or pick up toys.   Vet has seen and given pain killers,  made no difference, teeth appear ok

Hello - what happened after the pain killers didn't work?  Usually this would be the time to contact or revisit your vet for further advice, because being unable to open the mouth properly is a serious problem which may deteriorate quickly if not solved or resolved - and this may require proper investigation, for example x-rays or other tests.  Possible problems include cancer, dental pain, arthritis, tongue problems or even, depending where you are, Tetanus.  Please contact your vet or their emergency cover to triage the situation and arrange appropriate help from here.

Important Note on Tetanus - this is actually uncommon in dogs but it does occur, following the infection of a wound with the Tetanus toxin, which is common.  Its occurrence does not depend on geography as I may have implied in my last answer but on exposure to the Toxin, which can be found in soil and manure.