If you are into oral things like gags and mouth play and you are interested in pony play, giving your pony a dental exam seems like a match made in heaven. Depending on what you like/want, it could be fun or bring discomfort to your pony, there are plenty of options here, as usual. I can give you some pointers for you to have an idea how to play dentist to your pony, but, also as usual, it’s entirely up to you create your own scene the appeals to your particular tastes.
The first thing for you to do is watch your pony. You need to observe how they are behaving and their overall attitude. Keep in mind you will need to tie your pony to something in order for you to perform the exam and you will also need a harness or trainer for them to keep their mouth open, but I assume you already knew that wink*.
When your pony is set up, use a speculum to open their mouth as big as you need. Tip: A spider or Jennings’s gag will work great for this. Alternatively, an O-ring gag as well. If your pony is not very well behaved and moves around a lot, you may need a head harness or tie halter to keep them still. You are the trainer, so you will be the judge here wink*.
Check their gums and tongue; feel the insides of their mouths for anything that may seem out of place. Look at their teeth and run your fingers through them; see the color and check for any chips they may have. When you are done thoroughly looking over at their mouths, take the gag off and loosen any ties they have. Allow them to move after being still for a while; after all you don’t want any muscle contractures on your pony.
Offer them some water to drink; maybe you’d found they need a smaller bit… or maybe you found they need to wear a ball gag for a while… and before you ask, if the ball is small enough, your pony can drink even with a ball gag on (but try it first, before it could be dangerous so be careful) Going to the dentist has ever been fun? I don’t know, you tell me wink*.