Following are differential diagnoses, listed in order of likeliness, for dogs presented with oral ulceration.
Mechanical trauma from malpositioned dental hard tissue (dental malocclusion)
Mechanical trauma from foreign body
Hyperimmune mucositis reaction to adjacent plaque
Mucocutaneous pyoderma
Mechanical injury or trauma (eg, chewing on an electric cord)
Thermal injury
Chemical injury
Drug reaction (eg, methotrexate [shown to cause oral ulceration in humans])
Breed predisposition (eg, Cavalier King Charles spaniel)
Viral infection (canine distemper virus)
Erythema multiforme
Malignancy (eg, amelanotic melanoma, squamous cell carcinoma, fibrosarcoma, epitheliotropic lymphoma, melanoma, osteosarcoma)
Uremia
Eosinophilic granuloma
Lupus erythematosus (discoid, mucocutaneous)
Pemphigus vulgaris or pemphigus foliaceus
Bullous pemphigoid or mucous membrane pemphigoid
Candidiasis
Leptospira spp infection
Chemotherapy or radiation therapy