The incisors should be maintained at the proper length and angle. It can be detrimental to the proper alignment of the TMJ (temporal madibular joint) since they are the balancing point & crucial to the horses overall balance, If the incisors are maintained properly the horse is better equipped to maintain the molar tables better themselves. Horse Dentistry is about function, and performance, not just eating, if the horse can't function due to restrictions begining in the mouth, then they are not able to perform at their best.
Show me a floater that is preoccupied with the incisors and I'll show you a floater who hasn't spent enough time inside living horses mouths. It is sad but today there are many fraudulent individuals selling some new approach to caring for horses teeth. Whether it's the new power tool or some TMJ baloney it amounts to the same thing. Horses real needs get neglected, they suffer and their lives are sometimes shortened by these snake oil providers.
There are real encumbrances to proper TMJ function, but they are easy to find if you look inside the mouth beyond the incisors. These structural impediments are the lengthening areas of excess cheek teeth. When these areas are allowed to become longer they reduce the correct orbit of the mandible and instead retard it's natural and proper function. When the swing of the occlusal stroke is truncated the TMJ becomes worn into a offset placement and is harmed. Conversely when these areas are reduced and maintained the mouth regains it's proper balance and the TMJ can function comfortably
Anyone who doesn't understand the causes of incisor lengthening and the way the mouth compensates doesn't understand the most fundamental and unique aspects of the equine mouth. Of course the incisors become longer but the distance between the bars never changes because the incisor angle increases. The idea that the incisors should be kept at the same length and angle as a five year old is naive and moronic.
As to the performance of my clients horses, they have been to the Olympics and the local 4H and everywhere in between. If you work with enough living horses and not just skulls you'll understand and reject this ill conceived TMJ theory. Good Luck getting to the truth.