Periodontal disease in the horse

Up to 34 percent of horses of all ages experience some level of perio-dontal disease, but up to 60 percent of horses 13 years of age and older suffer from severe periodontal disease.

Photo 1: A 7-mm pocket in a 19-year-old paint mare.

These animals may present with mouth pain, tooth loss and dysmasti-cation. Exfoliated teeth may sit atop a healed alveolus held in position by mastication forces and gravity. Chewing may be painful and inefficient, and some teeth may be so loose they literally can be removed by hand.

Periodontal disease is "a general term referring to the altered state of the perio-dontium," including both the resting and active states of the disease process, according to David Klugh, DVM, fellow, Academy of Veterinary Dentistry/Equine in Newberg, Ore. Periodontitis, he says, refers to "the active state of the disease with inflammation of the periodontium, while gingivitis refers to inflammation of the gingiva only."

Pathophysiology

The normal oral flora consists of populations of different bacteria. When disease begins, there is a shift to a "greater number of pathogenic organisms, producing an inflammatory response and subsequent degradation of host tissues," Klugh explains.

Photo 2: After a year, the pocket size is reduced with healing of the soft ­tissue and reattachment of the gingiva.

The initial clinical sign of the pathological process is gingivitis, with tissue becoming edematous and reddened. The sulcular epithelium is inflamed, and gingival collagen support is lost. Further inflammation leads to involvement of deeper periodontal tissues.

Periodontal pocket formation occurs as the junctional epithelium proliferates apically in an attempt to maintain tooth contact, while detachment occurs at the coronal margin. Bacterial invasion results in inflammation and thickening of the sulcular epithelium, which eventually becomes necrotic. If uninterrupted, the cycle continues until the tooth is exfoliated.

Equine dental anatomy is unique in that the cementum of the clinical and reserve crown is involved in perio-dontal disease. Supragingival and subgingival cementum can become necrotic.

Unlike animals with brachydont teeth, equine hypsodont teeth rarely build up enough plaque and calculus to cause attachment loss. "In most cases of equine periodontal disease, no calculus or plaque is present," says Klugh. "The triggering event in horses is stasis of feed material and its resulting decomposition."

Feed stasis and putrefaction result from several factors, including alteration of the normal range of motion in mastication, direct gingival abrasion and orthodontic tooth movement by malocclusion.

Disease progression

The pathological endpoint of perio-dontal disease is tooth exfoliation. Affected teeth eventually become loose with excessive attachment loss and succumb to mastication forces. Tooth mobility can be measured, ranging from no movement to movement of greater than 3 mm for severe disease.

Stage 1 of periodontal disease is characterized by gingivitis, the gingiva being swollen and reddened. The gingival sulcus is of normal depth, but might bleed when probed. No attachment loss is present. The cementum may be normal or decayed.

Feed material is present in the depressions of the periodontal topography of Stage 2 disease, just as in Stage 1. Further disease progression presents with pocketed food debris.

During early periodontal disease there is less than 25 percent attachment loss and/or crestal bone loss around teeth. Gingival sulcus depth is > 5 mm. The gingiva has receded and is ulcerated. Supragingival cementum is decayed. Sulcular epithelium varies from mild to severe inflammation and necrosis. Subgingival cementum is decayed. Tooth mobility is slight.

In Stage 3, pockets appear similar to Stage 2, and the condition of the gingival, cementum and sulcular epithelium are similar. But during this moderate stage there is 25 percent to 50 percent attachment loss or a bone loss of up to 50 percent around teeth roots.

At Stage 4, prior to tooth exfoliation, the disease is widespread and severe, including gingival recession, ulceration and edema, with excessive bleeding. Cementum is decayed supra- and subgingivally. Sulcular epithelium is necrotic, with purulent discharge. Tooth mobility may be severe. Radiographic changes will show loss of alveolar bone, blunting of apices and lytic changes in the subgingival crown and roots. This advanced periodontal disease is exhibited by greater than 50 percent attachment loss or bone loss greater than 50 percent.

Examination

"All parts of the periodontium must be examined for accurate determination of attachment loss," Klugh says. "This includes characteristics and measurement of the gingiva, cementum, alveolar bone and periodontal ligament.

"Oral examination begins with removal of feed debris. The condition of the tooth and periodontium is examined for gingival inflammation, ulceration and recession, condition of the sulcular epithelium, pocket depth and mesial/distal length, condition of the cementum and tooth mobility," Klugh explains.

"Determination of the degree of advancement of the disease is critical in treatment and prognosis."

Treatment

Occlusal equilibration is the first step in treatment of mild to moderate periodontal disease. Upon noting disease of an affected tooth with accumulation of debris or orthodontic movement, the opposite arcade is examined for an overlong tooth located in an opposite position to it, which is then reduced. "Many cases of Stage 1 or Stage 2 disease are quickly resolved by reducing overlong occlusal surfaces on the opposing arcade," Klugh says.

After resolving the occlusal problem, food debris should be removed, and once the periodontium is clinically characterized further treatment may be undertaken.

Debridement of the infected space is critical. Diseased epithelium and underlying connective tissue are removed by scraping the lining of the peridontial pocket to eliminate all necrotic tissue. There will be some bleeding of healthy tissue. "Debridement of necrotic cementum prevents extension of the decay process in an apical and peripheral direction, thus arresting the condition," Klugh explains.

Stage 1 mobile teeth usually are found in aging equine patients with periodontal disease. "These teeth usually require only removal of sharp enamel points that may abrade oral soft tissues," Klugh says.

Stage 2 mobile teeth are treated by reducing the opposing tooth such that the pair are not in occlusion. "By resting the mobile tooth from the forces of mastication, the inflammation of the damaged periodontal ligament resolves," Klugh explains.

Stage 3 mobile teeth, those with occlusal movement greater than 3 mm, are extracted. In addition, the alveolar socket may be patched if necessary.

The use of perioceutic agents should be considered as secondary treatment, but not relied on exclusively. These can provide antibacterial benefit and have other therapeutic advantages.

Citric acid-containing products demineralize the cementum, thereby exposing cementum collagen and promoting formation of new attachment.

"Doxycycline inhibits collagen breakdown by the enzyme collagenase, which is elaborated from bacteria and polymorphoneuclear cells during the inflammatory process," Klugh says.

Ascorbic acid aids in collagen formation, and zinc-containing products have antibacterial effects. Chlorhexadine has antibacterial effects that last for several hours after oral rinse, due to its absorption by oral epithelial cells. Products containing disinfectants are very effective in treating periodontal disease.

With understanding of the causes of periodontal disease and proper treatment, prognosis for a successful outcome is excellent.

Risk of systemic disease

A study of more than 59,000 dogs with a history of Stage 1, 2 and 3 periodontal disease "revealed a significant relationship between periodontal disease and an increased risk of endocarditis and cardiomyopathy in pet dogs," according to Lawrence Glickman, VMD, DrPH, and colleagues at Purdue University's Department of Comparative Biology, School of Veterinary Medicine. Though there is no similar research data in horses, most equine dentistry experts agree that the potential risk of systemic disease in horses warrants research.

Case example

An example of periodontal disease in a 19-year-old paint mare demonstrates a few important principles. One is that initial basic wound treatment proved to be important, along with reduction of the opposing arcade's excessive transverse ridge. A second principle is the ability of the periodontium to repair its own soft tissue.

The mare presented with a 7-mm pocket that extended well into the interproximal space (Photo 1, p. 2E). The opposing arcade's excessive transverse ridges were reduced and the pocket debrided.

The next year, the pocket was smaller, at 5 mm in depth, and new soft tissue attachment on the palatal side had formed. The underlying bone loss remained, thus preventing complete healing of the pocket (Photo 2, p. 2E), but the underlying concept of limitation of disease extension was demonstrated.

Kane is a Seattle-based writer.