Common signs your horse may show if they have a dental problem
Head throwing, shaking or tilting whilst riding– if the bit is pushing sharp enamel points into the side of the cheeks, the horse will react to the pain caused.
Rearing, carrying the head excessively high or backing away rapidly without being asked– Large hooks or ramps can cause immense pain to the horse with a bit in their mouth.
Smelly breath! – Bad odours coming from the horse’s mouth or one of its nostrils can indicate a variety of problems, such as retained caps (baby teeth), infection, mouth sores or tooth disease.
Long particles of food in their manure – Not the best job...but a quick glance at your horse’s manure can show if your horse is efficiently grinding their food.Frustration whilst eating or quidding– Take time to watch your horse eat, any signs of frustration, dunking mouthfuls of hay into the water bucket or dropping large clumps or chewed hay, could indicate a painful mouth. A horse that drops partially chewed food, because of age or dental problems is said to be “quidding”.
Lacking condition– This of course can be down to many things, however, it is best to ensure it is not because your horse is unable to grind its food efficiently, and therefore get the most nutritionally from it. 
It is always good to look at the whole picture when loking at how your horse behaves, however, equally as important is making sure that no one area, such as the mouth, is causing them unnecessary pain. Although it is recommended that your horse’s teeth are checked by an Equine Dentist every 6 to 12 months (e.g. dressage star versus happy hacker!), if you notice any of the above problems, it’s probably better to have them checked to make sure they are OK.