[souffle]

He sounds to be grooming due to pain from the affected area. The root cause of this issue needs treated before you will be able to stop the scratching at the skin as this is introducing another issue. It could be that there is an infection in a tooth root or tear duct that is causing the problem and this is very painful for them. He may need some painkillers to get him to stop annoying at it so I'd suggest another vet visit for a recheck of this. Unkempt fur is a sign of generally feeling unwell. Give plenty clean tissue and clean sand to bathe in.
I hope he improves soon