Congenital oligodontia of the deciduous teeth and anodontia of the permanent teeth in a cat

Abstract

This report describes a rare case of congenital oligodontia of the deciduous teeth and anodontia of the permanent teeth in a cat. According to cat's veterinarian, the patient had only two deciduous upper canines and no permanent teeth had ever erupted. Post-mortem evaluation showed a complete absence of teeth in the oral cavity and inflammatory lesions were not found on the gums. Histopathological analysis of serial sections of maxilla and mandible revealed absence of odontogenic epithelium, inflammatory cells and odontoclastic resorptive lesions. Diagnosis was confirmed after both the establishment that there were no remaining dental structures and the exclusion of other relevant diseases that lead to tooth loss, such as periodontal disease, renal fibrous osteodystrophy, odontoclastic resorptive lesions, ectodermal dysplasia and trauma.

Congenital tooth diseases are characterized by agenesis, a condition in which teeth no develop. ¹ These diseases are defined by the number of teeth: hypodontia refers to an absence of less than six teeth, ¹ oligodontia is an absence of more than six teeth ² and anodontia is the complete absence of teeth. ³

The partial absence of teeth (oligodontia and hypodontia) is slightly more common than anodontia and has been reported in many species. ^4–8 Non-syndromic forms of tooth absence in humans are well described and are the result of defects in two genes, MSX1 and PAX9. In humans with defective MSX1 and PAX9 genes, the permanent teeth are most frequently affected rather than the deciduous teeth. ¹ In dogs, hypodontia and oligodontia mostly occur in the small breeds and usually involves the molars. ⁶ Hypodontia and oligodontia are infrequent in felines, but are generally characterized by the absence of the upper second premolar. ^5,8

Anodontia is a rare condition in all species, including humans. In cats, there are few documented reports. ^3,9 The objective of this report is to describe a rare case of congenital oligodontia of the deciduous teeth and anodontia of the permanent teeth in a cat.

A 2-year-old neutered male domestic shorthair cat was presented to the Veterinary Teaching Hospital with a suspected case of feline lower urinary tract disease (LUTD). According to cat's original veterinarian, the patient had only two deciduous upper canines and no permanent teeth had ever erupted. The cat was fed a diet of commercially available dry cat food.

After clinical examination, the diagnosis of LUTD was confirmed. During treatment, the cat died. Post-mortem examination revealed a total absence of teeth with no signs of trauma or inflammatory lesions in the oral cavity, such as gingivitis, stomatitis, calculus and tooth fracture (Fig 1a). The body was in good condition overall, except for the lesions related to the LUTD (hemorrhagic cystitis and hemorrhagic urethritis with an obstruction caused by a blood clot). Lesions in other organs were not found.

Fig 1.

(A) Oral cavity showing a total absence of teeth with no signs of trauma or inflammatory lesions, such as gingivitis, stomatitis, calculus and tooth fracture. (B) Radiograph showing no evidence of teeth or unerupted teeth from the mandible and maxilla. (C) Intraoral radiograph of the rostral mandible showing no evidence of residual teeth. (D) Intraoral radiograph of the rostral maxilla showing no evidence of residual teeth. (E) Photomicrograph of a mandibular segment showing the crestal bone of the alveolar process covered by hyperplasic oral mucosa with no evidence of odontogenic epithelium. Hematoxylin–eosin, Bar=400 μm. (F) Photomicrograph of a maxillary segment showing the bone covered by hyperplasic oral mucosa with no evidence of odontogenic epithelium. Hematoxylin–eosin, Bar=400 μm.

After necropsy, the skull was sawed in two half to avoid put upon images to the radiological examination. Lateral radiographs of the each half of skull were taken. Additionally, intraoral periapical radiographic exam was performed (Spectro 70×, Dabi Atlante) by bisecting angle technique. Radiographically, there was no evidence of any residual teeth or unerupted teeth from the mandible and maxilla (Fig 1b-d). Tissue samples were collected from the mandible, maxilla, kidneys, liver, bladder, heart, lung, spleen, central nervous system and skin from three different sites (neck, thorax and abdomen) for histological evaluation. The bones were demineralized in a formic acid solution for 20 days. All the tissue samples, including the soft tissues, were fixed in 10% neutral-buffered formalin, routinely processed and embedded in paraffin. Serial histological sections, 5 μm thick, of the whole maxilla and mandible were obtained in the transversal plane. Sections of all organs (kidneys, liver, bladder, heart, lung, spleen, central nervous system and skin) were stained with hematoxylin and eosin.

Histopathological examination of the mandible and maxilla revealed that the crestal bone of the alveolar process was covered by hyperplasic oral mucosa, with no evidence of odontogenic epithelium (Fig 1e and f). The alveolar nerve was present, but there were no impacted or unerupted teeth. There was no evidence of osteoclastic bone resorption, osteopenia, inflammatory cells or any other lesion. Skin samples had a normal morphology, including the hair follicles and adnexal glands. Bladder had hemorrhagic cystitis. Kidneys, heart, lung, spleen and central nervous system were normally histologically.

In this case, diagnosis is a congenital oligodontia of the deciduous teeth, given that this cat was born with only two deciduous teeth. Furthermore, diagnosis of a congenital anodontia of the permanent teeth was confirmed after both the establishment that there were no remaining dental structures by intraoral radiographic examination and by serial histological sections of maxilla and mandible and the exclusion of other relevant diseases such as periodontal disease, renal fibrous osteodystrophy, odontoclastic resorptive lesions, ectodermal dysplasia and trauma. A different diagnosis must be made in cases with a loss of teeth resulting from periodontal disease and odontoclastic resorptive lesions. Given that these are the most common diseases of oral cavity in cats, predominantly occurring in older cats due to problems such as plaque, gingivitis, stomatitis and resorptive lesions, ⁸ cats presenting with few teeth should be thoroughly examined before diagnosing as congenital hypodontia, oligodontia or anodontia. In spite of the absence of serum concentrations of urea and creatinine, the diagnostic of renal fibrous osteodystrophy was moved away by the fact of the kidney did not present any histological lesion. Besides, the fibrous osteodystrophy due to renal secondary hyperparathyroidism is characterized by substitution of the bone tissue for fibrous tissue and intense osteoclasia. ¹⁰ Those alterations were not found in the cat.

Ectodermal dysplasia is a syndrome that occurs in cattle and humans and is characterized by hypodontia, oligodontia and seldom anodontia, skin anomalies, such as hypotrichosis and missing or reduced adnexal gland numbers and reduced respiratory tract mucous gland numbers. ^7,11,12 Ectodermal dysplasia is a diagnosis that should be considered in cases of anodontia; however, in this case, ectodermal dysplasia was ruled out as there was no evidence of abnormal skin or respiratory tract mucous gland development. ¹¹

Dentition development is a process that requires a complex series of epithelial-mesenchymal genetic interactions involving growth factors, transcription factors, signaling receptors and other morphogens. Disturbances in this process may result in tooth agenesis. ¹ In calves, anodontia is a sex-linked characteristic and can affect male calves descended from the same mother. ⁷ Unfortunately, the cat's owner was unable to provide any information about the cat's family. Regardless, there are no known reports on the genetics of tooth development in cats.

One consequence of anodontia is an impaired body condition due to the difficulty of chewing hard food without teeth. ⁷ However, considering that this cat received dry food and had a body in good condition, this type of feeding was not a problem for it. Another possible consequence of anodontia is a reproductive challenge. According to Elzay and Hughes, ³ it was reported that breeding was difficult for male cat with anodontia, possibly because the cat could not grasp the female during the sexual act.

Congenital dental diseases are rare and must be differentiated from inflammatory processes such as periodontal disease. This case report stresses the importance of a detailed examination of the oral cavity before diagnosing congenital hypodontia, oligodontia or anodontia.