Incisors – A Question From An Owner

A YouTube visitor left me the following comment (verbatim). The red numbers in his question correspond to my answer below.

His question:

I have found some of your videos interesting but I wanted to discuss this incisor bit with you, purely for curiosity.

If a horse doesn’t need “proper grinding” how is it that a horse who is over-floated can “starve” from lack of nutrition? (1)
Do you really believe proper mastication doesn’t increase digestion efficiency? (2)

Also, I just wanted to point out that though “back teeth grind and your front teeth never touch” is it not also true that a horse’s front teeth are always in occlusion?? (3)

What have your results been with a horse who has incisor malocclusions? (4)

Have you looked into “camming?” (5)

When the lateral movement of the mandible takes place, and the horse’s incisors are in occlusion, BUT there is a slant or a curvature, this HAS to separate the back teeth, and hence you would notice a larger temporal muscle on one side. (6)

This is PROOF of excessive use on one side due to incisors and so I am curious as to your results/thoughts.

My answers:

1) Overfloating can remove all points preventing the horse from getting a grip on the food causing him to not form a swallowable bolus. This is why some horses have difficulty chewing after floating with quid formation. In the worst case, the horse is unable to swallow anything causing starvation.

2) The purpose of chewing is to form a swallowable bolus. Other results of chewing include increasing the exposed surface area for digestive enzymes and bacteria to do their work. Adding saliva lubricates as well as starts the breakdown of sugar. There is no study to prove that increased chewing causes improved digestion. Rather, a study of 17 horses with various teeth conditions was given the same feed. Sampling digestive contents showed that digestion occurs in the digestive tract and that chewing was not a factor. As every horseman knows, most of the manure in one barn all looks the same. Condition of the colon has the most factor of manure consistency with horses on high grain diets having colonic ulcers causing loose and watery manure and whole grains passing undigested. To answer your question, no, “proper mastication” doesn’t increase digestion efficiency.

3) Incisor occlusion – the only time incisors occlude (and again there is no study, only assumptions) is when they are biting something. They are used as weapons in fighting. They are used to bite grass. But all ruminants (cows, deer, sheep, goats) have no upper incisors. With that in mind, what causes teeth to wear? Specifically incisors? Their enamel is of a different type and it is softer than the cheek teeth enamel. My theory is that the tongue moving over the teeth causes the most wear. I also believe it is the constant pressure of the tongue behind the incisors that move them forward in older horses. Do they come into occlusion? Yes and anywhere there is no opposition an overgrowth occurs such as the upper 3’s forming the seven-year hook. My statement was WHEN CHEWING the incisors do not come into occlusion because the bolus of food prevents full closure of the mouth. Again, for chewing, the incisors are not required. Why then are the incisors looked upon with such interest by horse dentists? Because it is a “profit center” as expressed by the man who invented it in the 1980s. There is no science behind it and several horses have actually died from the process as secondary osteomyelitis caused the horse to stop chewing from pain which lead to starvation.

4) My results with horses with incisor malocclusions – Any variance to a perfect horizontal occlusion is secondary to something causing the horse to chew in an uneven way. The number one reason I have seen for this is sharp points on the cheek teeth causing buccal ulcers and chronic pain. The horse chews in a way to avoid the pain much like a man walks lopsided if one leg hurts. The second reason to cause uneven chewing is an over-erupted tooth such as 311 and 411 hooks. In every horse, I have seen with uneven incisors each has been in good body condition. One of my expressions is, “I have never seen a skinny parrot-mouthed horse.” The same is true for uneven incisors. Smoothing all sharp points of the cheek teeth always improves their chewing. Again, no study has been done involving just reducing the points, reducing just the over-erupted incisors, or both.

5) No, I have not looked into “camming” as my belief in its’ theory is doubtful.

6) “When the lateral movement of the mandible takes place, and the horse’s incisors are in occlusion, BUT there is a slant or a curvature, this HAS to separate the back teeth, and hence you would notice a larger temporal muscle on one side.” – This is classic “cart and horse” argument. Which came first. Your statement requires that the over-eruption of the incisors which is causing the uneven bite is an active event that forces the jaw out of position. My view is that the over-eruption is a passive event secondary to the horse’s chewing movement. Removing incisor growth doesn’t cause the teeth to become re-balanced. However, removing the pain being caused by the cheek teeth will allow it to close correctly and over time the incisors can self-correct. Nobody though has taken the time to prove this. As far as the asymmetry of the muscle, that again can be caused by an altered chewing pattern caused by pain, not by incisor obstruction.

Finally, I want to thank you for asking me my opinion on incisors in horses. I believe that horses have survived for many years without our interference. I also believe in doing what is in the best interest of the horse. Reducing incisors and balancing them is something I have looked at for two decades and I am not convinced that it is the right thing to do. In a personal conversation with Dr. Paddy Dixon in Scotland (co-author of Equine Dentistry) in 2003, he said that the United Kingdom is moving away from recommending incisor reductions as they are secondary to a primary event in the cheek teeth area. In addition, they have caused the death of several horses. Later that year the same thing was said at the AAEP equine dentistry wet lab. That was enough for me to end the discussion on the subject.

In summary, after over 50,000 floats and 30 years of floating as a veterinarian, I look at the theories of incisor reduction, balancing, and equilibration with suspicion. As Sherlock Holmes said, “I never guess. It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts (Sir Arthur Conan Doyle, Adventures Of Sherlock Holmes, A Scandal in Bohemia). Until these theories are proven, I will continue to believe that the abnormal wear of incisors is secondary to improper movement of the jaw and not a primary obstruction to jaw movement. There are too many fat horses with disfigured incisors to make me think otherwise.

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