I'm sorry he is in pain still. I think he needs his TMJs examined for TMD. The TMJs can be moved out of place in such a hit, and even a slight VERY SLIGHT amount of being out of place will cause many problems that won't go away on their own. Make sure he sees someone for TMD (TMJD) if that dentist isn't trained in it... he might need a mouth splint made just for him to help set his jaw back, allowing the tendons to return it to normal sitting.