What can cause a malocclusion? A malocclusion is a misalignment of teeth (mal = bad, occlusion = alignment of teeth). Malocclusions can also be due to misalignment of the jaw. What causes these situations? The horse of today has an upper and lower jaw that are of unequal size and even different shapes. This can cause no opposing surface for a tooth to wear. This is the reason for enamel points that need to be removed. Some of the other malocclusions seen are hooks, ramps, step mouth, wave mouth, shear mouth, missing and overpowering teeth (taller than its neighbors).
What things can these issues cause? Some examples are problems with biting, lesions in the gums, cheek injury, jaw restriction, loss of feed when eating (as the horse has to open wider to chew to get past the restriction) and quidding (the wading or balling of food) is also very common and a constant with certain malocclusions.
Molar Malocclusions:
Hooks – The molar arcades lie slightly different from each other letting part of the front molar or the rear molars to not wear evenly. This is because it is unopposed and has nothing to wear against. This creates a pointed section of tooth that will overlap the opposite tooth.
Ramps – The ramp is different from a hook as it is a more gradual rising of the molar and the whole tooth is involved vs. just part of the tooth. They are similar in the fact that they usually involve the first and last molars. Ramps can also cause the opposing tooth to be more worn down and it remains short as it can?t erupt any further than the opposing tooth will allow.
Step Mouth – Step mouth is usually the result of the loss of an opposing tooth/teeth, or slow eruption of the tooth/teeth. The unopposed tooth than erupts faster than usual and becomes overpowering. Less severe cases can lead to or go hand in hand with wave mouth.
Wave Mouth – Wave mouth usually involves more than one tooth and is an up and down curve of the molars. Wave mouth is not always the base problem in the mouth, but the result of other issues. This malocclusion can be improved, but usually takes more than one session depending on the height and number of teeth involved.
Shear Mouth – In shear mouth the nature angle of the molars are steeper than what is considered average. This can create sharper enamel points than a horse with normal angles. This is due to the lack of opposing pressure that would normally wear down those points. Horses with condition tend to chew more up and down vs. in the normal orbital fashion.
Excessive Transverse Ridges – The natural design of the chewing surface includes ridges that help to grind and break down food. These ridges sound relatively unimportant to movement, but this is not the case. If the ridges are excessively high, it can restrict front to back movement of the jaw. This also restricts and adds pressure to the TMJ joint. These ridges can be reduced to a more natural height with floats easily.
Overpowering & Missing Teeth – Missing and overpowering teeth go hand in hand. If there is a missing tooth, the opposing tooth can then become overpowering since it does not have any pressure to wear it down. This means it becomes taller than its neighbors and will cause a lot of restricted or locking of the jaw movement.
Incisor Malocclusions:
What things can these types of malocclusions cause? Incisors are very important to the comfort and function of the TMJ. When the incisors are unevenly worn or are overly long, they can cause uneven pressure and wear on the joint. This then causes soreness and headaches for the horse. It can also contribute to imbalances throughout the body as the TMJ is a huge information center. Incisor malocclusions should always be addressed and the incisors balanced along with the molars to insure the mouth is working as a whole unit.
Slant – This is when the incisors are worn in a diagonal pattern vs. being in a horizontal line. Long incisors meet up with short ones and reverses on the other side. This can cause the molars to separate too early as the horse has to open wider sooner to accommodate the difference in lengths. The TMJ joint movement is also changed as they open wider and can cause soreness in the joint.
Ventral Curve or “Smile” – Incisors curve upward at both sides creating a smile appearance. The lower corner incisors and the upper central incisors are too long. This can cause the molars to separate too early as the horse has to open wider to accommodate the difference in lengths. It can also result in the molar tables having steeper angles as there isn’t proper opposing pressure to wear them normally. The TMJ movement is also changed as they open wider to chew.
Dorsal Curve or “Frown” – Incisors curve downward at both sides creating a frown type appearance. The upper corner incisors and the lower central incisors are too long. This can cause the molars to separate too early as the horse has to open wider to accommodate the difference in lengths. It can also result in the molar tables having steeper angles as there isn’t proper opposing pressure to wear them normally. The TMJ movement is also changed as they open wider to chew.
Overly Long Incisors – Incisors are longer than average due to reduced grazing time, improper wear and no change to eruption rate. This creates incorrect pressure on the angle of the TMJ and will cause soreness in the joint. Incisors must be reduced to a more proper length and should be done in multiple visits depending on how long they are.
Overbite or “Parrot Mouth” – This is where the upper incisors protrude over the lower incisors. Along with this incisor malocclusion there will also be hooks present on the upper first molars and lower rear molars. This is due to how the jaw lines up and that there are no opposing teeth to wear against in these places. If the lower incisors are too long this may cause irritation or lesions on the soft palette as the horse chews.
Underbite or “Sow Mouth” – This is where the lower incisors protrude from under the upper incisors. Along with this incisor malocclusion there will also be hooks present on the lower first molars and upper rear molars. This is due to how the jaw lines up and that there are no opposing teeth to wear against in these places. If the upper incisors are too long this may cause irritation or lesions on the soft gums as the horse chews.
Missing or Overpowering Incisors – Missing and overpowering teeth go hand in hand. If there is a missing tooth, the opposing tooth can then become overpowering since it does not have any pressure to wear it down. This means it becomes taller than its neighbors and will cause a lot of restricted or locking of the jaw movement.