Introduction
An oronasal fistula (ONF) is a communication between the oral and nasal cavity. An oroantral fistula is communication with the oral cavity and the maxillary recess. The epithelial surfaces of the nasal and oral cavity communicate via the fistula. The nasal cavity is normally separated from the oral cavity by the incisive, maxilla, and palatine bones and overlying mucosa as well as the soft palate tissues caudally. In the caudal region of the canine nasal cavity a maxillary recess is present and communication of the distal root of the third premolar, 4th premolar, and molar result in an oroantral fistula. Causes of ONF include periodontal disease, trauma, traumatic malocclusion (i.e., linguoversed mandibular canine teeth), electrocution, cleft palates, neoplasia, severe eosinophilic granulomas, and surgical dehiscence secondary too inappropriate, or lack of, closure of surgical extraction sites, and/or maxillofacial surgery. Commonly, and for the purpose of the following discussion, oronasal fistulas secondary to severe periodontal disease, and particularly, loss of the maxillary canine teeth will be discussed.

Commonly the loss of the maxillary canine teeth and/or periodontal disease associated with the maxillary canine teeth in small breed dogs’ result in oronasal fistulas or inapparent oronasal fistulas, respectively. The palatal aspects of the maxillary canine teeth are separated from the nasal cavity by several millimeters of bone depending on the size of the patient. Intrabony pockets (vertical bone loss) on the palatal aspects of teeth 104 and 204 provide a good environment for periodontal pathogens to proliferate with resulting loss of periodontium. The teeth may, or may not, be mobile and it is not uncommon to have normal or slightly increased to moderate buccal periodontal probing measurements with very large probing depths palatally. Occasionally, a trickle of blood may be seen exiting from the ipsilateral nares when the probing depths are measured palatally, confirming an ONF. Occasionally, the periodontal probe is inhibited from reaching true probing depths by large accumulations of subgingival calculus and inflammatory tissue.

Oral stratified keratinized squamous epithelium and the nasal stratified cuboidal to non-ciliated pseudostratified columnar and ciliated pseudostratified columnar epithelium line the maxillary and nasal sides of the defect, respectively. An ONF allows connection of these epithelialized surfaces thereby oral bacteria, food, fluid, debris, etc. communicate with the nasal epithelium. The nasal cavity is not designed to withstand the insults of products from the oral cavity, acute and chronic inflammatory rhinitis, infection, and morbidity results. Clinical signs may include chronic nasal discharge (serous, mucopurulent, and/or epistaxis). Sneezing may or may not be present. Oronasal fistulas may be obvious upon clinical examination or may be a pinpoint lesion that requires anesthesia and a thorough oral exam to identify.

ONF Repair Techniques
There are various techniques to repair defects between the oral and nasal cavity. Repair techniques for oronasal fistula and cleft palate defects have been reported and include single buccal mucoperiosteal sliding flap, palatal inverted and buccal sliding flaps, palatal and labial buccal pedicle flaps, split U-flap, rotational palatal flaps, auricular cartilage grafts, laminar bone membranes, advancement flaps, and obturators. Advanced surgical techniques for complicated cleft palates (acquire or congenital) are discussed elsewhere. For oronasal defects secondary to periodontal disease of teeth 104 and 204 a single buccal mucoperiosteal flap is adequate for primary repair.
It is the author’s experience that the majority of oronasal fistulas secondary to periodontal disease in the maxillary teeth can be easily closed with a single buccal mucoperiosteal flap if surgical principles are followed. With very large defects or failures, an inverted double palatal and buccal sliding flap may be utilized to close the defect. With 25+ years of dentistry and oral surgery experience a single buccal mucoperiosteal flap has all that has been required, in my hands, for repair of maxillary canine tooth oronasal fistula defects secondary to periodontal disease even with previous failed referring veterinarian repairs.

Surgical Principles for Successful Flap Repair
1. The surgical flap should be larger than the defect to be repaired (1.5-2.0 times the width of the bone defect)
2. Suture lines should be planned to be placed over bone
3. The epithelial margins of the defect must be debrided
4. Denude palatal epithelium along margins
5. There must be no tension on the flap
6. The sutures should be placed 2 mm apart with 2 mm bites of tissue
7. 25-Polyglecaprone is used as the appropriate suture material
8. Gentle tissue handling
9. Appropriate home care instructions
10. Client and patient compliance

Single Buccal Full Thickness Mucoperiosteal Flap
The keys to surgical success, whether closing a defect or following extraction of a canine tooth with an oronasal fistula include, a large broad-based full thickness (soft tissue and mucoperiosteum) mucoperiosteal flap maintaining blood supply, absolutely no tension, suture lines placed over bone, and simple interrupted sutures placed 2 mm apart with adequate 2-3 mm “bites” into healthy palatal tissue and mucoperiosteal flap tissue. The periodontal flap also creates visibility of the underlying bone and root surface by surgically separating gingiva or mucosa from the underlying tissues. Visualization of the bone defect into the nasal cavity is necessary to debride any necrotic bone margins, remove the inflammatory tissue, infected material, and remove the communicating epithelium. The goal of surgical intervention is to provide an epithelial surface on the nasal and oral sides of the flap. Nasal epithelial cells will migrate over the nasal side of the flap during the healing process.

The dorsal and ventral labial arteries and the angular artery provide vascularization to the buccal mucosa and preservation of blood supply is important. Long, narrow, skinny flaps may have inadequate blood supply and lead to necrosis of a portion of the flap with subsequent failure.
The epithelial margins of the flap are removed with a sharp #15 scalpel blade, La Grange scissors, Goldman Fox Scissors, etc. Following elevation of the mucoperiosteal flap, the author likes to further “freshen the margins” of the palatal mucosa with a medium diamond bur to ensure removal of all the epithelial tissues and perform on osteoplasty on any irregular, rough bone margins. Fresh vascularized margins will allow first intention healing to occur following apposition and suturing. The mucoperiosteal flap is elevated using a periosteal elevator directed toward the bone and moving in an apical direction. Care is taken not to perforate the mucosa, which will diminish the success of the procedure. Perforated flaps leave mucoperiosteal defects and suture lines over bone defects and not over underlying bone greatly increasing chance of flap failure.

Closure of the mucoperiosteal flap without tension and harvesting a large broad-based flap with appropriate releasing incisions are requirements. Additionally, releasing the oral mucosa and connective tissue from the periosteum with a careful scalpel incision or blunt surgical scissor dissection allows the flap to be released and easily moved to cover the defect without tension.

A broad based mucoperiosteal flap can be created to cover an oral nasal fistula from a maxillary canine tooth by incising from distal aspect of 103/203 to distal 105/205 (being certain to return gingiva around 105/205 with the flap closure if those teeth are present) or equivalent, depending on the presence and absence of adjacent teeth. Alternatively, a distal divergent incision can be created leaving gingiva with teeth 105/205. Following release of the flap, removal of epithelialized tissue margins, and osteoplasty of the bone defects, the flaps are initially apposed and sutured at the vertical release corner margins to the palatal mucosa. After the flap is anchored, the fresh margins of the palatal mucosa and free margin of the mucoperiosteal flap are sutured. Finally, the vertical releasing incisions are sutured in apposition. The simple interrupted sutures are placed approximately 2-3 mm apart and no less than 2-3 mm from the incision. Suture choices for surgical flap closure include poliglecaprone-25, polyglactin 910. Polydioxanone is NOT an appropriate suture for the oral cavity due to its long degradation time and potential to cause foreign body reactions. Chromic gut is NOT an appropriate suture as it is degraded too quickly.

Inverted Palatal Mucosal Flap with Buccal Mucoperiosteal Flap (Double-Flap Technique)
The author never has had to utilize this technique in clinical practice over 25+ years. With this technique, an immediate epithelial surface adjacent to the nasal cavity is created. A full thickness palatal flap is created by incising the palatal mucosa parallel to the mesial and distal margins of the defect near or past the midline of the palate. Hemorrhage is anticipated from the vascular palatal mucosa and the major palatine arteries and its terminal branches. The palatal artery may need to be ligated and digital pressure applied to the region to temporarily control bleeding. The palatal mucosa, adjacent to the defect, acts as a hinge as the palatal flap is inverted to cover the oronasal defect.
A second flap as described previously (single buccal mucoperiosteal flap) is created and sutured over the inverted palatal flap. The palatal defect is allowed to heal by second intention. A potential troublesome consequence with this technique is exposure of the nasopalatine foramen. Therefore, the flap may need to be made split thickness in that location. Additional more complicated palatal surgery would then be necessary to close the defect created by the surgeon. This can be prevented with knowledge of anatomy and using a split-thickness flap, if necessary.

Additional Techniques
There are publications demonstrating the use of inverted palatal mucosal flap with buccal mucoperiosteal flap (Double-Flap Technique), autogenous auricular cartilage to cover the defect and support the mucoperiosteal flap. This requires a second surgical site, sterility, and may result in disfigurement of the patient’s ear. The use of OssiflexTM membrane or other types have been reported to be used in a similar fashion. Essentially these autogenous and allogenic materials are used to support a single buccal mucoperiosteal flap. Nevertheless, If the flap is not created correctly, the surgical site will still fail! The author has never had to utilize those additional materials.

Post-Operative Recommendations
1. Soft food only for 10-14 days
2. No chews or toys for 10-14 days
3. +/- 0.12% chlorhexidine gluconate rinses every 12 hours for 10-14 days, if tolerated.
4. Minimal client handling of the flap and lip
5. Leash control when outside to urinate and defecate to prevent foreign objects being picked up in mouth for 10-14 days.
6. Elizabethan collar to prevent patient from rubbing or pawing at the incision, if indicated. Very often not used with my surgical cases.
7. Post-operative pain medication (NSAIDS, Gabapentin, etc. as indicated based on underlying metabolic/systemic disease and concurrent medications)
8. Antibiotics, if indicated, for 5-7 days.
9. Written discharges to ensure client compliance
10. Recheck in 14-28 days