Congenital and Inherited Anomalies of the Mouth
Congenital oronasal fistulas are the result of failure of fusion of the palatine shelves during gestation (which occurs at 25–28 days of gestation in dogs). Clefts can be either of the primary palate (involving the lip and incisive bone) causing cleft lip (harelip), or of the secondary palate (involving the hard and soft palate) causing cleft palate. The conditions can occur singly or together. In dogs, CT studies have shown association of cleft palate with other craniofacial abnormalities, including hypoplastic tympanic bullae, hypoplastic nasal turbinates, and maxillary malocclusions, mostly of the incisors. Neurologic examination should be performed in affected animals, because concurrent hydrocephalus has also been described. Animals are typically diagnosed at, or shortly after, birth by oral examination, by observation of dysphagia or milk from the nares after nursing, and/or by respiratory compromise and aspiration pneumonia. Many affected neonates are euthanized or die early in life.
Cleft palate and cleft lip have been described in most domesticated animal species, including dogs, cats, ruminants, horses, and camelids. In dogs, brachycephalic breeds are overrepresented, with up to 30% risk factor. Other breeds with higher incidence include Beagles, Cocker Spaniels, Dachshunds, German Shepherds, Labrador Retrievers, Schnauzers, Old Spanish Pointers, and Shetland Sheepdogs. The most commonly affected cat breed is the Siamese. Etiologies include genetic, teratogenic, and nutritional causes. Modes of inheritance are monogenic autosomal recessive or incomplete dominant in several breeds. In Brittany Spaniels, Pyrenean Shepherds, Beagles, Old Spanish Pointers, and Boxers, it is believed to be an autosomal recessive trait, whereas in Bulldogs (French and English) and Shih Tzus, an autosomal dominant with incomplete penetrance mode of inheritance is suspected. Autosomal recessive inheritance patterns are seen in Angus cattle with arthrogryposis multiplex, in Charolais cattle with cleft palate and arthrogryposis, and in Texel sheep with cleft lip. Teratogens and nutritional causes during pregnancy include high levels of vitamin A in the diet, administration of griseofulvin, folic acid deficiency, and ingestion of toxic plants. In cattle, ingestion of lupine during days 40–100 of gestation results in arthrygryposis and cleft palate, due to the effects of anagyrine found in Lupinus sericeus and L caudatus. Ingestion of poison hemlock (Conium maculatum), which contains the toxic principle coniine, results in similar signs in both cattle and goats, whereas ingestion of Veratrum californicum in sheep, goats, and cattle all result in cleft lip and/or palate in the fetus.
For puppies and kittens in which euthanasia is not elected, medical management is required until surgical options are explored. Animals are fed via orogastric intubation until dry food can be tolerated. Water can be offered by overhead dispenser. A custom-molded palate guard has been described in experimental settings to allow adult dogs to eat and drink normally. Aspiration pneumonia should be quickly identified and treated. Surgical correction is recommended after at least 12 wk of age, although some studies have shown higher success when performed at >20 wk, or as adults. Surgical correction has a high failure rate because of continued growth of puppies or kittens postoperatively, the size of the patient, and irritation of the surgery site by the tongue and feed material. Surgical techniques depend on the location and size of the cleft defect. For secondary palate defects, sliding mucoperiosteal flaps or overlapping flaps are most commonly used.
Extensive involvement of the soft palate carries a poor prognosis, even with surgical intervention. Surgical repair should be attempted only after ethical questions have been addressed, and the affected animal should be surgically sterilized or removed from breeding stock to prevent reproducing the anomaly in future offspring.
Occlusal abnormalities due to abnormal lengths of the maxilla and mandible are common in animals. Brachygnathia, also called overbite, overshot, overjet, short lower jaw, or parrot mouth in horses, is manifest when the mandible is shorter than the maxilla. It can be found, with varying severity and incidence, in all species of animals and is diagnosed by oral examination. In Red Angus cattle, it is inherited in a recessive manner through a deletion mutation on chromosome 4, which results in stillborn calves with osteopetrosis (see Osteopetrosis), brachygnathism, and impacted molars. In Simmental cattle, brachygnathism can be seen in calves as an autosomal recessive trait, or in combination with trisomy 17, a lethal condition. A lethal, autosomal recessive disorder of Merino sheep results in brachygnathism, cardiomegaly, and renal hypoplasia. Brachygnathism is common in horses, due to either a lengthened maxilla or shortened mandible. Modes of inheritance are unknown. It may occur in utero due to treatment of the mare with griseofulvin. Most horses do not experience dysphagia; however, cheek teeth malocclusions are common, and regular dental care is required. Correction can be attempted in foals via surgical placement of tension band wires around the maxillary incisors to inhibit maxillary growth.
In small animals, mild forms may be of no clinical significance; however, more severe forms may result in trauma to the hard palate or the restriction of normal mandibular growth secondary to erupting adult mandibular canine teeth. Treatment varies from none to various orthodontic or endodontic procedures, depending on severity. The mandibular canine teeth are often removed or a crown reduction procedure performed, with concurrent pulpotomy or root canal. Intervention early in life is recommended and improves both short- and longterm outcomes.
Prognathia, also called undershot, underjet, or monkey or sow mouth in horses, is identified when the mandible is longer than the maxilla. It is diagnosed by oral examination. In brachycephalic dogs and Persian cats, it is considered a normal breed characteristic. In horses, it is more commonly seen in miniature and Arabian breeds. The degree of severity is variable and may not require treatment. In severe cases in foals, surgical placement of tension band wires can allow for continued maxillary growth. The most severe consequences are the result of malocclusions. Affected foals may have difficulty nursing, and older animals may experience difficulty grazing. Cheek teeth malocclusions should be addressed with regular dental care.
Chondrodysplasia, a simple dominant trait of Dexter cattle, is a lethal defect that can result in “bulldog calves,” with severe skeletal malformation and craniofacial dysplasia that has the appearance of prognathism.
Ankyloglossia, also called “tongue-tie,” is a disorder of Anatolian Shepherd dogs characterized by a short, thickened lingual frenulum that inhibits normal movements of the tongue. By unknown mechanism, the normal fetal apoptosis of the cranial ⅔ of the frenulum does not occur. Clinically, the tongue appears notched or with a “W” shape. Animals may experience dysphagia; difficulty suckling, drinking, or licking; trouble vocalizing; and impedence of panting and therefore thermoregulation. Frenuloplasty is corrective. Breeding of affected animals is not recommended.
Microglossia is a congenital defect characterized by missing or underdeveloped lateral and rostral thin portions of the tongue that result in prehensile and motility disturbances. It is often referred to as “bird tongue” in dogs and may be a component of the fading puppy syndrome, because affected puppies have difficulty nursing and swallowing and can aspirate or quickly become dehydrated. In cattle, excessive salivation has been seen. Even with supportive dietary measures, the prognosis is poor.
Macroglossia, or large tongue, has been described in association with nasopharyngeal dysgenesis in Dachshunds. It has also been seen in double-muscled cattle breeds, such as the Belgian Blue, and can inhibit nursing of calves.
Epitheliogenesis imperfecta is a disorder of the skin in which the epithelium is absent, revealing the dermis. Commonly affected areas include the limbs, back, and oral mucosa and tongue. It is inherited by a simple recessive manner and is well described in cattle and horses, particularly Saddlebreds. Euthanasia is typically elected.
A small or absent lower anterior lip vestibule is a congenital defect of some Shar-Pei dogs. The lower lip covers the mandibular incisors and canines, disrupting normal occlusion, inhibiting mandibular growth, and leading to the dog biting on the lip (which presents welfare issues). In extreme cases, the mandibular incisors become lingually directed. Surgical correction by chelioplasty has been described using several different mucosal flap techniques. Any animals that have undergone surgical correction should not be presented for conformation showing and should not be bred.