My boerboel shows pain (discomfort) while opening his mouth widely

[Antonis Milou]

It's been a few days now since I realised that my almost 3year old male Boerboel has pain in his mouth.
I tried to open his mouth but he screamed like a baby, then I realised that something is causing him pain. He eats very carefully and avoid eating hard food. I took him to the vet who gave me some antibiotics, which made him feel better after a couple of days but still he refuses opening his mouth more than a couple of inches. He is very alert and willing to play, nothing have changed to his behaviour, but I can see him being very careful while eating.
Last night I was looking on the Internet and came across a post where the dog owner was describing almost identical symptoms to my dog, his vet mentioned "Masticatory myositis". I don't know how bad this is and how should I take care of! Anyone who has experienced something similar please share your thoughts. Also what else could it be?
I would do anything to treat my boy, please help me.

Regards
Antonis

[Jennifer]

Any updates?