CHAPTER 50 Dental Radiography in Relation to Sinus Disease
In evaluating a horse with sinus disease, consideration of a dental origin is of paramount importance, and diagnosis necessitates quality radiographic and clinical examination. Survey films narrow the possible field of diagnosis. Intraoral radiographs reveal detailed information that can lead to more specific diagnosis. Understanding and appreciation of disease processes and early recognition and early intervention can arrest or reverse the disease process, thus resolving the problem while maintaining dental longevity.
Common dental lesions resulting in sinusitis include pulpitis of the dental apices of young horses, fractures or dental decay in any age horse, and periodontal disease especially in older horses. Not all root tips (dental apices) are in the sinuses. As a general rule, the apices of the first two cheek teeth, the 6’s and 7’s of the Triadan system, are not located in the sinus; the next two cheek teeth, the 8’s and 9’s, are almost always located in the rostral maxillary sinus; and the last two cheek teeth, the 10’s and 11’s, are located in the caudal maxillary sinus. The rule of thumb, therefore, is “2, 2, and 2,” meaning that the root tips of the first two are not in the sinus, the root tips of the next two are usually in the rostral maxillary sinus, and the root tips of the last two are in the caudal maxillary sinus.
In young horses, apical pulpitis develops most commonly in the 4th premolar, or 08 in the Triadan system, as it erupts between two previously erupted adult teeth. The so-called tooth bumps seen in young horses are a result of the eruption process. The apices may or may not be inflamed. When inflamed, they produce chemotactic agents that attract blood-borne infectious organisms, a process known as anachoresis. These organisms occasionally cause pulpitis, which occurs in varying degrees of severity. Some cases resolve spontaneously; others develop sufficient pulp response to wall off or otherwise resolve infection, and horses with more severe cases develop disease that results in pulp death. Any of these processes can result in sinusitis, diagnosis of which requires quality intraoral radiographs. Treatment varies with the condition.
Tooth fractures can directly or indirectly expose the pulp canal or result in instability of the tooth or some part thereof. Indirect pulp-canal exposure occurs via dentinal tubule communication with the pulp. Not all direct pulp exposures result in pulp death. The pulp of young teeth is highly immunocompetent and mounts a vigorous immunologic response to insult by creating secondary and tertiary dentin in the form of a dentin bridge, which can wall off the damage and maintain viable pulp tissue apical to the injury. This capability decreases with age because the pulp canal of geriatric teeth is smaller, less cellular, and has reduced vascularity. As a consequence, the teeth of geriatric horses more commonly die when the pulp canal is exposed.
Tooth fractures may lead to periodontal disease. The fracture causes an uneven mastication surface topography with spaces in which food material accumulates and decays. The decay process breaks down periodontal structures and can lead to disease that ascends into the apex. The result is loss of attachment of the tooth to the alveolus. In some instances the infectious process ascends into the sinus. Diagnosis requires intraoral radiographs.
Dental decay occurs most commonly as infundibular disease. Indirect pulp exposure can ensue as decay breaks down enamel and dentin. Infectious agents thereby gain access to the pulp via dentinal tubules, and this can be followed by apical disease and sinusitis. Although unusual, this disease process generally results in tooth loss. Early recognition of infundibular disease and appropriate treatment can prevent this sequence of events.
An understanding of dental anatomy facilitates recognition and appropriate treatment of infundibular cavities. The occlusal surface of the equine tooth is composed of cementum, dentin, and enamel. The peripheral enamel is coated by cementum. Each upper cheek tooth has a pair of crescent-shaped infundibula variably filled by cementum. During development, the cementum fills the enamel-lined infundibulum from the occlusal surface apically. It is common for the infundibulum to be incompletely filled with cementum during the process of embryologic development. In many horses the apical portion of the infundibulum remains void of cementum throughout the horse’s life.
Infundibular disease begins when there is cemental hypoplasia. Decay begins within the cementum and progresses peripherally (apically) as cemental canaliculi fill with food residue and microorganisms. Continual decay involves the surrounding enamel and later the dentin.
Infundibular disease can be staged. In stage I teeth, the decay process, if present, is confined to the cementum and is restricted from expansion by the enamel border. In the vast majority of teeth, the disease remains limited to this stage. Few of these cases progress to stage II, which is defined as involving enamel. In some cases (stage III) the lesions extend to involve both the enamel and the dentin surrounding the infundibulum. In such cases, the dentin and enamel separating the two infundibula may be lost either by fracture or by further decay. The resulting coalescence of the two infundibula creates a large defect in the occlusal surface. As the grinding process of mastication occurs, the lower arcade moves across the upper arcade with both shearing and crushing forces. If any defects are present in the occlusal surface of either arcade, there is an increased risk of tooth fracture and an increased rate of attrition.
Degradation progresses peripherally from the infundibulum. It may progress apically but not necessarily. No measurement of the depth of involvement is used in this system of classification because it is complicated by the uneven nature of cemental hypoplasia and decay within the infundibulum and the variable depth of the enamel lining. Intraoral radiographs most effectively demonstrate the extent of decay. The general recommendation is to perform restorations on stage II and III cavities, but not stage I problems. Other decay processes can be restored to protect the pulp and prevent further decay and potential tooth fracture, all of which may result in premature tooth loss.
Periodontal disease can extend apically and result in sinusitis. It is rare in young horses, but in geriatric horses periodontal disease is a common cause of tooth-related sinusitis. The primary contributing factor is the ever-shortening crown length, leaving a short distance from the oral cavity to the tooth apex. An additional predisposing factor is the thin maxillary bone and its correspondingly reduced ability to serve as an impediment to extension of disease. Whereas most teeth with periodontal disease that is causing sinusitis are treated by extraction, some can be saved by first treating the underlying periodontal disease first and then flushing the sinus.
Some primary sinus problems can result in dental disease. Tumors can displace teeth and bone, resulting in malocclusions, and in some cases these malocclusions can further displace teeth as orthodontic forces from mastication push teeth in abnormal directions.
Facial flat-bone fractures can also result in dental disease by displacement or by damage to the tooth itself. If tooth displacement is minimal and if the tooth is young, the pulp may be able to repair a fractured tooth. Close inspection of good-quality radiographs is necessary in order to make this determination.
Most horses with tooth-related sinus disease will be presented with a specific owner complaint. Examples include nasal discharge, quidding, dropping feed, slowed eating, and occasionally behavior change, such as depression or problems with the bit.
All horses should receive a physical examination, especially geriatric horses. Some will have additional or complicating problems. Many will have multiple dental problems. In such cases, staging treatment is appropriate. Treatment of one problem at a time, beginning with the most severe, reduces stress, sedation time and dosage, and allows recovery time for the horse before further treatment. Also, it is less likely to cause inappetence in geriatric horses, which can be disastrous in some individuals. Some horses that lose their appetite do not regain it easily. In such cases, owners may choose euthanasia rather than asking a favored old friend to endure further treatment.