At 14 months this behavior is a bit of testing boundaries and over-exhuberence. It's also quite annoying and as you are seeing dangerous.
Since the "thumping under the chin" isn't really working anymore, you should probably try something different. If this is happening during play, yourdog is getting too wild and loosing his manners. Play needs to stop and your dog needs to settle down before it resumes. If your dog refuses to stop, then you can bring him to another room and make him wait in the room for about 3 or 4 minutes to calm down.
In my home teeth are never allowed to touch human skin- ever. But I have young children in my home so it's a safety thing. Some people allow their dog to mouth them, but when the pressure gets applied, then the playing stops. I tend to use a toy to play with my dogs and they can direct their exhuberance onto that toy. Figure out what you want and be consistent. If I feel a tooth on me when we play, the toy goes away, the game stops, and we have to settle down. I don't reprimand. I just become very neutral and calm. I don't want to heighten the excitement and escalate a behavior. I certainly don't want them to try harder to get my attention to the point of pulling out new behaviors. Once things have settled a bit, I can assess the sitaution and either find a different toy, a new game, take them on a walk, redirect, etc.
See if that will work for you. If not, try something else. Also, there is no substitute for a good obedience class. A dog wit ha tried mind is a wonderful animal to be around.
-----
Chelle and the rest of the crew including, but not limited to Kita and Taiko (the shiba inu wrestle maniacs), Adi (reserved and dignified tabby cat), and all 28 reptiles
