Ethical orthodontics (Proceedings)
Although human orthodontics can be traced back to 1000 B.C., veterinary orthodontics has just recently evolved. Attempts to correct malaligned teeth in animals have been attempted principally by owners and breeders of animals since the 19th century and possibly before. Indiscriminate tooth extraction to relieve crowding, rubber ligatures, finger pressure and wires were used on horses, dogs, and occasionally cats to relocate teeth thought to be out of alignment. It wasn't until the last 20 years that veterinarians began to use orthodontic appliances and surgery to correct malocclusions and address dental occlusion rather than tooth alignment alone. Proper occlusion was finally seen as the basis for orthodontics to ensure function and to resist dental disease.
Crowded malaligned teeth and jaw size discrepancies are the most common contributors to malocclusion. Posterior crossbite occurs when the line of occlusion is incorrect buccolingually. Usually, the upper teeth are positioned lingually to the lower teeth. This is called lingual crossbite or just posterior crossbite. In buccal crossbite, which occurs rarely, if the upper teeth are too far buccally, there is no or little occlusal contact. This is a common finding in line bred pocket pets and in some equine lines. The premolars and molars of some rodents can be seen to rotate 360 degrees extending into the orbit or turbinates in advance cases. Anterior cross bites are common in domestic canines. One or more upper incisors are displaced lingual to the lower incisors when the teeth are in occlusion.
A severe malocclusion may compromise all aspects of oral function. There may be difficulty in mastication if only a few teeth meet, and jaw discrepancies may force adaptive alterations in swallowing. Malocclusion contributes to both dental decay and periodontal disease. Plaque and food is retained in areas that are out of normal function making it harder to care for the teeth leading to pathology.Congenital absence of teeth in dogs and cats can be the result of disturbances during the initial stages of formation of a tooth. Anodontia, the total absence of teeth, is the extreme form. The term oligodontia refers to congenital absence of many but not all teeth, whereas hypodontia implies the absence of only a few teeth. Since the primary teeth give rise to the permanent tooth buds, there will be no permanent tooth if its primary predecessor was missing. It is possible; however, for a primary tooth to be present and for the permanent counterpart to be absent. Anodontia or oligodontia in man is usually associated with an unusual but mild systemic abnormality, ectodermal dysplasia. Occasionally, oligodontia occurs in a patient with no apparent systemic problem or congenital syndrome.
Anodontia and oligodontia are rare, but hypodontia is a relatively common finding in dogs, especially pure bred and line bred dogs where the genetic fault has been perpetuated. As a general rule, the premolar teeth are the most commonly missing - usually the second premolar. Rarely are the carnassial or canine teeth missing. Malformed teeth are not as prevalent as supernumerary teeth. These abnormalities in tooth size or shape result from disturbances during the morph differentiation stage of development.
Supernumerary teeth also result from disturbances during the initiation and proliferation stages of dental development. Supernumery teeth may disrupt normal occlusal development and can contribute to periodontal disease. Supernumerary teeth, sclerotic bone, and heavy fibrous gingiva can also interfere with eruption. Extract only those supernumerary teeth that may contribute to malocclusion or crowding. If there is room for an extra tooth and its position does not present problems, it is not extracted. Dolicocephalic head types can accommodate extra premolars without crowding or occlusal disturbances.
Dental trauma can lead to the development of malocclusion. Damage to permanent tooth buds from an injury to primary teeth, drift of permanent teeth after premature loss of primary teeth, and direct injury to permanent teeth are primary causes. Trauma to a primary tooth can displace the developing permanent tooth bud or disrupt enamel formation with resultant coronal and or root defects. This root form is call dilaceration, defined as a distorted root form. Dilaceration can occur from any distortion of the crown relative to the root, and so may result from mechanical interference with eruption, but its usual cause is trauma to primary teeth, which also displaced the permanent buds.
It may be necessary to extract a severely dilacerated tooth. A relationship between anatomic form and physiologic function is apparent in all animals. Over evolutionary time, adaptations in the jaws and dental apparatus are prominent in the fossil record.