Take a look in his mouth to see if there are any teeth that look dark or might be cracked as you are right a dental problem can be one cause of this.
Look under his tongue to see if there are any lumps there too if you can.
If you happen to have a female in heat nearby he may be vibrating his jaw in response to the pheromones. Dogs have an organ on the roof of the mouth that helps them 'taste' pheromones and will chatter their jaws to get the scent up to the organ.
The nerves that work the muscles in the head including the jaw are run from the neck around the head. Any pinching of those nerves can cause muscle tremoring and may lead to a problem such as mascitory myositis which you can read about here
A splinter from the mouth that is driven up into the roof of the mouth or the eye area can lead to infection behind the eye and tremoring like you see.
And there is also the possibility that this is a seizure as focal or partial seizures, unlike the grand mal type episode, can show as a twitching in the face area and the dog stays totally alert as it happens.
You can read about seizures here
I'd plan a vet visit for an exam and if you can get a video of the episodes to show to your vet this may help in diagnosis.