Figure 1: Oronasal fistula associated with a missing left maxillary canine tooth (tooth 204). The dotted lines indicate the releasing incisions, and the rectangular box indicates the area where epithelium should be removed to create an appropriate recipient bed. Last month, I discussed clinical signs and physical examination findings associated with oronasal fistulas that arise secondary to severe periodontal disease. This month’s column discusses the surgical approach to treatment of the most common manifestation of oronasal fistulas: those that occur in the area of the maxillary canine tooth in dogs (Figure 1). The technique that I will describe below may be used in treatment of either preexisting oronasal fistulas or in fistulas discovered at the time of extraction of the maxillary canine tooth. First things first There are two important concepts to grasp prior to embarking on successful oronasal fistula repair. First and most important is understanding what a fistula is: an abnormal connection between two hollow spaces. In the context of oronasal fistulas, this is an epithelized communication. If no attempt is made to de-epithelialize the recipient bed, the mucoperiosteal flap will absolutely not heal, even if the perfect flap is raised. Freshening the recipient bed by removing tissue with either a scalpel blade or a diamond bur is essential for a successful outcome (Figure 2). Figure 2: A No. 23 diamond bur is used to de-epithelialize the recipient bed (ventral and palatal to the defect) prior to raising a mucoperiosteal flap. The second important concept is this: large flaps are necessary for successful repair of small defects, and very large flaps are necessary for successful repair of large defects. It is essential that these flaps are tension free. Therefore, the periosteum must be released from the underlying mucosa (Figure 3) and broad-based mucosal releasing incisions are extended dorsally as needed to ensure a tension-free closure. To release the periosteum, I use a pair of tenotomy, iris, or LaGrange scissors. Getting to work Dentistry, much like life, is more often about finesse than strength. This comes to mind when repairing an oronasal fistula. Rather than using a larger gauge suture, I like to use 5-0 monofilament absorbable sutures in a simple interrupted pattern on a tapered needle. The tapered needle takes a bit of getting used to, but it is less likely to tear through friable tissues. The smaller suture size allows me to more closely space the sutures so that each suture hopefully will serve the purpose of a spot weld of the flap to its recipient bed. Closely spaced simple interrupted sutures are key. I’ve found it helpful to place an initial submucosal horizontal mattress suture that decreases tension on the mucosal layer of sutures and may decrease the chance of dehiscence (Figure 4). Other methods Figure 3: Tenotomy scissors are used to bluntly and sharply dissect the periosteum from the dorsal aspect of the underside of the flap. What about the use of membranes beneath mucoperiosteal flaps used to close oronasal fistulas? One such membrane is a bone allograft membrane that holds sutures. Membranes can be considered in an effort to provide some support over a bony defect if it can be sutured across the defect prior to closure of the mucoperiosteal flap. Similarly, use of ear cartilage has been described for repair of oronasal communications by acting as a scaffold for epithelium to traverse the site in smaller defects.1-3 I find these to be rarely necessary. You may have heard of a double flap technique. This method is viable, though I find that I rarely need to consider anything more than a single flap technique for defects associated with a diseased or missing maxillary canine tooth. The double flap technique involves not only a mucoperiosteal flap raised on the buccal aspect of the defect, but also an initial flap of palatal mucosa and submucosa raised with a hinged attachment palatal to the defect. Prior to closure, try this test to determine if the flap is tension-free. Lay the flap over the defect and see if it recoils to its original position or if it stays where placed, even without any suture. This will tell you if tension will play a role in possible dehiscence. If the flap recoils, more release of the periosteum is necessary or releasing incisions should be lengthened. Postoperatively, alert pet owners to not put tension on the sutured flap by avoiding lifting the upper lip on the side of the oronasal fistula. Hopefully these tips will help with your next oronasal fistula repair. Similar to congenital palatal defect surgeries, the first chance of obtaining closure is the best chance, so raise a large, tension-free flap and place your simple interrupted sutures close together (Figure 5) for optimal results. Figure 4: Initial submucosal mattress suture. A bite is taken of the palatal submucosa (yellow arrows) and of the submucosal soft tissue of the mucoperiosteal flap (black arrows). This suture helps to decrease tension on the mucosal layer of sutures Figure 5: Postoperative appearance of single flap technique to close the oronasal fistula seen in Figure 1. References 1 Cox CL, Hunt GB, Cadier MM. Repair of oronasal fistulae using auricular cartilage grafts in five cats. Vet Surg. 2007;36(2):164-9. 2 Soukup JW, Snyder CJ, Gengler WR. Free auricular cartilage autograft for repair of an oronasal fistula in a dog. J Vet Dent. 2009;26(2):86-95. 3 Lorrain RP, Legendre LF. Oronasal fistula repair using auricular cartilage. J Vet Dent. 2012;29(3):172-5. Dr. John Lewis practices veterinary dentistry and oral surgery at NorthStar Vets in Robbinsville, N.J.
