When we are referring to the contact between individual opposing teeth or groups of teeth, we use the word dental occlusion. For example, we would refer to occlusion when describing how an upper molar meets a lower molar. In a normal horse’s mouth, the upper and lower molar arcades will slope slightly upwards from front to back, but will have each molar matched to the level of adjacent teeth quite evenly. The crowns, being the erupted part of the tooth will all have a very similar height. This is how nature intended it and this allows the jaw to sweep from side to side, grinding the feed effectively whilst it is being transported towards the back of the mouth. Molar malocclusion refers to any occlusion that is dysfunctional. When this is the case the horse has greater difficulty grinding the feed properly. Molar malocclusions can be extremely destructive to your horse’s mouth and health. The condition can require years of corrective treatment in younger horses, or the case of old horses, cannot be corrected at all without destroying vital grinding structures.
The wave mouth (pictured above) is a malocclusion that can cause significant detriment to the horse and is a major cause of periodontal disease. Wave mouth refers to the vertical misalignment of the molars when the jaws close together. If you were able to see the molar arcades from the side, the grinding surfaces would present like a wave formation. In a wave mouth some molar crowns become longer than adjacent teeth in an arcade. These dominant molars wear down the opposing tooth excessively, sometimes even down to gum level.
The teeth do not align as they should and the jaw is less able to effect an efficient grinding motion. Transport of the feed towards the back of the mouth is affected causing slower eating. This means such horses are less able to efficiently process and digest their feed. Colic, choke and weight loss can result. We frequently observe slow eating, feed packing, feed spillage and excessive salivation.
Wave mouth has been attributed to many different causes such as deciduous teeth (baby teeth) not shedding correctly or improper filing of the teeth in the past. In some cases such as in miniature horses genetics also play a role. Although we cannot clearly identify why wear is so significantly altered as to lead to wave mouth, by far the most significant conditions that appear to contribute to wave mouth are:
- Overbite (brachygnatia)
- Underbite (prognathia)
- Incorrect dental correction over a long time
- Premature removal of deciduous teeth
Some equine dental practices report that 30% of mature race thoroughbred race horses over 5 years of age have wave mouth in combination with overbite. It has also been reported that in horses over 15 years of age at least 40% have some degree of wave mouth. Of that figure, about 15% have extremely severe forms. It is clear that the incidence relates to raised feeder positioning, breed, diet and the standard of equine dental care.
The most common abnormal conditions found in horses with wave mouth are:
- Lateral displacement of teeth
- Linear tooth drift
- Periodontal disease
- Loss of occlusal enamel contours
- Trauma to opposing gingival or bone tissue
Treatment objectives and frequency
Horses’ teeth erupt for much of their life so are not static like ours. They only have a certain amount of tooth root to erupt to replace tooth crowns over their lifetime. Horses have enamel ridges on their molars to grind effectively, and when reducing a wave mouth a dentist must grind some of this surface away. This is because a dentist can only do so much each visit without adversely affecting the horse. By filing too much tooth, a dentist can make the horse sensitive while eating and can reduce the grinding capabilities of the tooth by filing the enamel surface excessively. The tooth pulp may also be exposed and cause infection of the tooth. A wave mouth can range from mild to extreme and if your horse has had a wave mouth for his or her entire life, most likely the teeth opposite the dominant teeth will have been eroded almost entirely, leaving no grinding surface and no crown. This leaves no more reserve tooth to grow back into place to assist with the correction of the wave mouth. In these cases your dentist will explain the situation and then will discuss diet options for horses that can no longer chew effectively so the horse can still live a well-fed life.
Unlike regular sharp points, which form on the edges of the teeth, reducing a wave mouth requires some filing of the grinding (occlusal) surface. To make sure your horse doesn’t go off its feed, or get impaction colic due to ineffective grinding of feed, your dentist will file small amounts from the prominent crowns over an extended period of time yet minimise the amount of filing of shorter crowns. If the horse is young, then completely correcting the wave mouth over a period of time can be achieved by an equine dental practitioner. However, if the wave mouth is extreme or occurs in an older horse, the tooth structures cannot be corrected adequately without causing ecxcessive collateral damage. To correct a wave mouth or keep the condition in check, your equine dental practitioner will plan visit your horse more often. This is the only safe and effective way to treat a wave mouth. Once the equine dental practitioner is satisfied the wave mouth has been remedied or is able to be kept in check, then he or she will prescribe a new treatment interval between treatments.