Giving your pony a dental exam can be fun for you and your pony (or just for you). As with everything else in ponyplay, a dental exam will not appeal to all ponies or their owners/trainers/vets. However, for those to whom this does appeal, I encourage you to give it try. I am a very oral pony and like all sorts of gags and mouth type play, so the idea of dental play appeals to me. But again, it is not for everyone. Just like all veterinary play, none of this is intended to diagnose or treat any real pathology. That is why it is veterinary play.
Similar to the general physical exam, the dental exam will begin by observing the pony from a couple feet away while he is being held by his owner or handler. Note how the pony is holding his head. Note the pony's attitude and general demeanor. Have the pony's owner/handler lead him over to an area where he can be tied. Since you will be examining the pony's mouth, you will need to restrain him using a halter or a harness. Alternatively, you can make use of stocks (used during many veterinary procedures) if they are available to you.
With the pony secured open his mouth and put a full mouth speculum on him. Use this to open his mouth as wide as you require, but do be careful not to overdo it. An open mouth gag such as a "Jennings" or a "spider" mouth gag will work best here, but O-ring gags and other are also fine. Check to make sure the pony is ok. You may need to secure to pony's head to a greater or lesser degree (e.g. tie halter, head harness, hair, etc. securely to prevent head motion) depending on how well behaved the pony is.
After you have applied an appropriate gag to keep the pony's mouth open, and confirmed the pony is properly secured to prevent head movement, take an initial look in the pony's mouth. Start by looking at the mucous membranes. They should be pinkish and not pale. Feel the inside of the pony's cheek to check for ulceration or signs of injury. Examine the pony's tongue for ulceration as well. Carefully grasp the pony's tongue and pull it out towards you. Look for any discolorations, abrasions, etc. When finished with the tongue, move on to the gum lining. The gum lining should be a nice pink color where they meet the teeth.
Finally, check each of the pony's teeth for sharp edges by running your finger along them. Be sure the check the teeth on which the pony's bit will sit. Examine these teeth carefully for chips.
Remove the gag from the pony's mouth and loosen any bonds securing the pony's head so that he can move his head before it gets too stiff. Offer the pony some water and then take him back to his stall. Depending on your findings, the pony may need a larger or smaller bit. Perhaps the pony would benefit from wearing a ball gag for a while. Maybe you want to teach the pony to drink around a ball gag (definitely possible even with 2.5" ball - know this from experience) to help the pony learn to drink around a bit.
Many possibilities exist to adapt a dental exam into a more involved scene. Use your imagination here...