Oronasal Fistula in a Daschund Dog is common and due to bone destruction from periodontal disease adjacent to the teeth in the upper jaw.
In this case the teeth were extracted but the surgery sites were not closed. This caused an open communication between the oral cavity and the nasal cavity. Patients experience sneezing and snorting and sometimes aspiration of food and water while eating and drinking. It is critical to close these surgically to prevent chronic nasal infection and complications from aspiration.
In order to repair a defect this large, extensive oral surgery skill and experience is needed. Most cases fail due to tension on the sutures caused by a tentative approach to dissection. A board certified veterinary dentist is the best option although some veterinarians have undergone additional training and can repair minor defects.