You may think there is not a lot to do with the mouth until you need to check the capillary refill time of your horse's gums when he is sick or your horse gets a kick in the face and you need to check its teeth and treat wounds.
How about bridling, do you use a hackamore because your horse will not let you touch his mouth? There will come a time when you need to see inside your horses' mouth, do not wait until for an emergency to address the problem, start today with these lessons to build a more relaxed and accepting partner.
Place a halter on your horse and start by stroking the horses' face in area he is comfortable.
One stroke at a time, work your way to his mouth always taking your hand off before the horse reacts.
Praise the horse with a rub on the neck or with your voice each time he accepts your touch no matter how quick it was.
Be gentle when you get to the mouth area, as it is very sensitive.
If the horse pulls away and your hand is still on his mouth, your hand got too slow too fast.
Go back to a place on the horse's face where the horse is comfortable and get to the spot slower but speed up your hand so your hand is off his mouth before he reacts.
When the horse accepts your hand strokes on his mouth, begin to slow your hand down until the horse accepts your hand resting on his mouth.
Now you can start messing with his face a little at a time, always praise any improvements from the horse.
Give him breaks, switch sides, and practice the same lessons on the other side.
Rub all around the muzzle staying a little longer each time.
Be careful not to get irritating to the horse by staying on the mouth too long.
When he is comfortable with you rubbing all around his muzzle, start rubbing the outside of his lips and between the lips.
Place your right arm under the horses' head and bring your right hand to the bridge of the horses' nose where the halter strap lies.
Now with your left hand carefully rub the insides of the lips.
Next, while lifting the lip out of the way with your right had, rub the outsides of his bars and gums with one finger until he is comfortable.
Take small steps and if you meet a lot of resistance go back to a point the horse is comfortable, stay shorter and move forward slower.
When the horse is comfortable with the outside of his bars, start rubbing the tops of his bars, where the bit will lay and then his tongue.
Many horses learn to love having their gums rubbed, so do not be surprised if your horse is enjoying that part of the lesson.
Use extreme caution when working around the horses' mouth that you do not place your fingers where they could be easily bitten.
There is a gap between the incisors and molars that has no teeth.
It is also where the bit rests.
This is the only place you should put your fingers actually into their horses' mouth.
If you choose to do so, the horse will try to spit your finger/hand out with his tongue.
Use extreme caution that you do not allow him to draw your finger/hand into his teeth where he could mistakenly bite them.
When the horse is comfortable with one finger in his mouth at the bars, add more until the horse will allow you to place your entire hand in his mouth at his bars while staying relaxed and calm.
Your horse should also allow you to hold his tongue to the side of his mouth as well for checking his teeth or administering medications.
When you place your hand, at the bars, into his mouth, he will try to spit it out, gently take his tongue, pull it out to the side, and let the horse have it back.
Praise the horse and work these exercises for the next week or so, going over them each time the horse is groomed, until the horse accepts them as everyday tasks.