Ask the Vet: Equine Dentistry

Answered by, Cindy Allen, DVM, Bit O’ Magic Equine, Aluchua, Fla.

Question: My dental question is in regards to EOTRH in a severe parrot mouthed horse. In your research or clinic, do you have knowledge of a horse(s) with severe parrot mouth, where there is complete loss of incisor contact, to be off feed due to EOTRH? 

Answer: In my understanding of where we are in current research, the pathology of EORTH is now thought to be caused by pressure necrosis of the alveolar ligament. With constant pressure on any single or multiple incisor/s or the first premolar the tooth structure below the alveolar rim places pressure on portions of the thin living alveolar ligament. This ligament is a living tissue requiring circulation to remain as a viable connection between the cement layer of the tooth and the alveolar bone. The bone can remodel under pressure but the tooth is an already mature and solidified structure that does not allow for significant remodeling in the healthy tooth. Thus the living ligament selectively dies and becomes necrotic within the socket. This produces one or more of several clinical clues upon examination such as:

  1. necrotic draining pustules breaking through the gum at level of the alveolar rim margin above the gingival attachment, these “bumps” drain pus when gently opened.
  2. The affected tooth starts loosening- with resulting food packing due to motion seen between teeth and significant discomfort during grinding of the tooth or hand rasping.
  3. With prolonged infections, eventual sclerosis and a direct bony attachment may form between portions of the tooth and the alveolar bone.
  4. With a loosening ligamentous attachment the root sometimes becomes prolific, with layers of bulbous cementation (an attempt by the body to solidify a moving tooth in the bony socket or an inflammatory reaction to the process) and subsequent remodeling and enlargement of the visible shape of the bone surrounding that root.So this would infer that any tooth that has severe unnatural pressure can develop the disease, and secondarily if it is present EORTH is almost always painful to the horse in my experience.

Clinically, I have not personally seen a case of either maxillary or mandibular prognathism with diagnosed EORTH present, but our knowledge of the pathology would infer that if pressure contact with the bony palate is severe on the lower incisors, or bio-mechanical pressure during mastication caused by the lower incisors trapped behind the upper incisors severe, then over time ligament necrosis is possible.

In any case, start by clinical examination of the length and positioning of the teeth and the surrounding gums and bone and a thorough whole mouth exam and balancing if indicated to rule out other possible obstruction and imbalance issues causing discomfort (horses with conformational malocclusion of the incisors may or may not have properly conformed and opposing upper and lower cheek teeth). If the restriction due to trapped teeth or large hooks or waves is severe, I have seen horses lose a normal interest in food due to pain without disease present yet. Secondly, if EORTH is suspected, obtain a set of radiographic views of each arcade with good resolution and delineating the alveolar ligaments, or lack thereof.  Separate radiographic views of each of the arcades can be readily obtained by open mouth DV and VD views, utilizing a protective tunnel for the digital plate or a set of two 3” long plastic wedges placed in each side of the cheek arcades and in a sedated horse. (It is important to know that teeth are fairly well smoothed and do not have large waves present to preclude damage if imbedding hooks or pressuring high cheek teeth when the horse chews against the wedges.) Adding a slightly oblique view can sometimes allow visualizing the root in a different plane if pathology is questionable in the lower corner incisor teeth.

If EORTH is diagnosed, or an unresolvable obstruction by offending teeth is present, it should likely proceed to a discussion between your equine dental specialist and yourself to weigh the benefits vs. the  problems presented by surgically removing diseased incisor teeth to resolve the EORTH discomfort and prevent damage to the palate. If palatal trauma or entrapment of the arcades is severe enough then extraction to correct mechanically induced pain may be warranted, keeping in mind that if only some of the lower teeth are removed it may increase palate trauma or mechanical pressure by or on the remaining teeth.

A few of my cases have involved stoic horses whose problems were not noticeable to their owners, but who showed extreme sensitivity to dental prophylaxis on incisors. These were diagnosed using radiographs and subsequently after extractions made a noticeable improvement in mastication and attitude per their owners. So the signs of EORTH in behavior changes is not always clear in EORTH cases, especially if the horses attitude has changed slowly.  As you are likely already aware, a complete turn around in patient wellness becomes apparent in most cases after extraction of all the painful teeth, with horses happily eating all their  grain and hay shortly after the teeth are out. Nipping short grass is, of course, not possible for horses without any front teeth opposing, but for a severe overbite as you describe, there may already be an inability to graze normally. I have noticed that most horses do hang their tongue out a small amount when relaxed if all of the upper teeth are removed.

As a general note;

In managing my cases of non contacting incisor arcades due to maxillary prognathism; regular (2-4 times) yearly grinding of the incisors combined with careful balancing of the cheek teeth may aid in reduction of the palatal trauma over time, and may check rampant caudally curving overgrowth of the upper incisors for some horses, particularly if started early in life. Of course, caution must be practiced at each prophylaxis to protect the vital pulp of the incisors, while doing as much shortening as possible. I have also found that preservation of the height of the lower rostral cheek teeth arcades; the proximal to distal rise of the 300 and 400 arcades to the 306 and 406 teeth and the same of the maxillary teeth, (within normal functional TMJ balance, i.e. not too drastic of a rise), is helpful in providing distance under the palate and managing the incidence of palatal trauma over the long term.