Incisor reductions are still a contentious debate item outside of the veterinary world. Let’s start with a little history.
In the early 1900’s there are reports of rasping the incisors but it was short lived. Then one morning in the mid 1990’s a non-veterinary equine dentist in a parking lot of the Saratoga harness track in NY climbed into the cab of another non-veterinary equine dentist (a personal friend). He said to my friend, “Hey guess what? I’ve developed a new profit center!” He then proceeded to describe the filing of the incisors “because the customer can see that.”
In a short time, this process was introduced into the veterinary world and called “incisor reductions.” The main veterinary spokesman for this developed the idea of “lateral excursion” of the mandibular incisors against the maxillary incisors. He published a paper where he used a marker to show that this excursion was often not equal in distance and that filing the incisors would alleviate this inequality and thus “balance” the mouth. There was an assumption that these horses were sedated which may have altered the results of the measurement.
In the late 1990’s I was asked to present to the alumni of the Cornell vet school my technique of floating horses along with another vet from Texas. I watched him mark the incisors with a Sharpie ink marker and then cut off the excess incisors in the heavily sedated horse with a Dremal tool. Many of us “older” vets at the time looked in amazement and then conferred with each other. We all thought that this was just a gimmick because the instructor never revealed to us the real purpose behind the reduction other than to “balance” the mouth. In other words, he never explained what this procedure solved other than balance, which no animal or human really is. Just look in the mirror to see your own asymmetry.
In 2002 I attended the British Equine Veterinary Association’s meeting in Glasgow Scotland. This is the equivalent of our AAEP (American Association of Equine Practitioners). I was one of 6 Americans attending and only myself and one other vet from the US were there for the dentistry component which was a major section of this meeting. Dr Paddy Dixon was the lead of the section and he is currently the head of surgery at Edinburgh Veterinary College, co-author of “Equine Dentistry” and the author or co-author of hundreds of papers on dentistry in horses.
The BEVA program director found out that I was in attendance from the USA and so she set up a lunch meeting for me with Dr Dixon – just the 2 of us.
Dr Dixon asked me then what I thought of incisor reductions. I answered that I thought it was unethical and unjustified in equine dentistry and that all the “problems” our eyes see in the incisors (uneven bite alignment) are a secondary effect from altered movement of the jaw and tongue caused by oral pain. I concluded that if we correct the cheek teeth and remove the pain causing points then the incisors will take care of themselves.
Dr Dixon popped up his eyebrows and looked at me for a minute. Then he said, “We are now finding this same conclusion and here in the United Kingdom and we are rapidly moving away from incisor reductions.” He further explained that through electron microscopy, the prisms that make the enamel of the incisors are different and softer than the prisms of the cheek teeth enamel. This goes with the idea that an unbalanced incisor occlusion would be secondary to something else.
Two months later in December 2002 I attended the AAEP meeting with a special wet lab for dentistry in Ocala FL. Here Dr Lowder from the Georgia vet school also said at his station that we were “rapidly moving away from incisor reductions.” I thought it was odd that they both used the same phrasing, but I also felt that I had been validated. Incisor reductions had no valid place in routine equine dentistry.
Since 2002, there has been little said for the performing of incisor reductions in the veterinary literature or at meetings other than the occasional reports (as well as personal communications to me) of horses losing their lives after an incisor reduction had opened a pulp chamber creating a life ending infection in the jaw.
The Temporomandibular Joint
The only group still promoting the reduction of incisors is Advanced Whole Horse Dentistry. They believe that there needs to be a 3 point balance between the incisors and the temporomandibular joints (TMJ’s) before any cheek tooth work can be done. Simultaneously, veterinarians from the vet school at Saskatchewan Canada have performed extensive research (both active experiments as well as retrospective studies) determining that horses do not suffer from primary temporomandibular joint disease or dysfunction. These studies are very interesting. This statement comes from one study: “Horses with degenerative joint disease (DJD) of the temporomandibular joint (TMJ) have been reported infrequently, with the majority of cases describing the disease as a consequence of an earlier traumatic event. A case of clinically significant TMJ-DJD due to a non-traumatic event has not been published.”
This aligns with a personal communication from Bill Bradley, DVM from NY who purchased a nuclear scintigraphy machine for his new equine hospital. He told me that every horse that came in for a specific joint bone scan was actually given a full body scan so he could learn the details of his new diagnostic machine. He told me that in every horse scanned, “the TM joints lit up like a Christmas tree.” He further said that he would never scan these joints in the future because it would be pointless. I reminded him that these amazing joints move on average 25,000 times a day (range is 10,000 to 40,000 according to Dr Katherine Houpt, professor emeritus at Cornell vet school in behavior). Because they are the most active joint in the horse, it would make sense they would always scan positively due to activity and the associated blood flow.
The Teeth And A Boat
The debate still goes on whether to file the incisors. In my experience I have not seen a reason but this is because of a paradigm I would like to explain here. Imagine a boat moored to a thick wood piling in the water. As it gently rocks over time from wind and waves it wears a notch in the wood. Does the notch in the piling prevent the boat from moving? No. It is a result of the movement of the boat which continues unimpeded. With this paradigm, couldn’t the incisors be worn due to the movement of the jaw and tongue? Does this uneven wear impede the movement of the jaw? I say it doesn’t just like in the boat example.
This brings about another point. What causes the incisors to wear? In the 300 horses I photographed for my aging project I noticed several things. For at least half of the horses, when the lips are raised and the incisors are photographed straight on, there is a relaxed space between the occlusal surfaces with the tongue present between them (see the image at the top of this post). In fact, I’ll bet that your incisors (really all of your teeth) right now are not together. So where is this idea that horses need a 3 point balance when in the normal state the incisors don’t come together? If a chew takes 1 second to perform and there are 86,400 seconds in a day, then on average the horse is NOT chewing for about 2⁄3’s of a day.
In addition, with slow motion videography it is seen that the tongue exits and enters for every bite of food and every harvested parcel of grass when grazing. More evidence that the incisors don’t really serve any purpose in horses other than defense is that all ruminants have no upper incisors. And horses that have lost their incisors (trauma, EOTRH) still harvest grass with ease. Have you ever seen a skinny parrot mouthed or sow mouthed horse where the incisors don’t even meet?
Where Is The Proof?
Finally, if we really want to put the need for incisor reductions to rest then there needs to be a study where only the incisors are reduced in a horse with a bit or chewing issue. After this we need to determine if the issue has been resolved. This then would suggest that there are certain issues in a horse’s life that can be resolved with only an incisor reduction. In my practice I have done enough horses where the cheek teeth are addressed without incisor work that resolve bit and chewing issues so I don’t think we need to perform that experiment. But there have been no studies to show that incisor reductions alone actually give an improvement in these issues because all equine dentists who perform an incisor reduction also perform point removal at the same time.
As a veterinarian with over 70,000 observations I look forward to learning new things but I also look backwards for patterns to learn from. So far I have found no evidence for incisor reductions and will not be adding that to my techniques.