Focus On: Mandibular Fractures

Focus On: new textbook on Oral and Maxillofacial Surgery editied by Frank Verstaete Mandibular coming soon (I hope – I submitted my Fractures chapter almost two years ago!). Fracture of the mandibles is a common When managing a mandibular injury in dogs and cats and can arise fracture, the first step is to get good, from a variety of situations. How to intra-oral dental radiographs. I know I manage these fractures will be the sound like a broken-record on this subject of this article. I will use subject, but I have never seen a skull examples drawn from my own case files radiograph on standard film that gave as to show you both the wrong ways and good information as can be obtained the right ways. In showing failed cases with intra-oral film. We need to find all managed by others, it is not my intent to of the fractures (bone and dental) and embarrass anyone. I just want all of my assess their significance in both the short readers to have the benefit of learning term and the long term. from the experience (positive and negative) of others. We are supposed to Priorities in managing mandibular learn from our mistakes, but life is too fractures include excellent anatomical short for you to make all the mistakes reduction of the fracture to ensure proper you could learn from. It will be faster if occlusal and TMJ relationships, rigid you can also learn from other people’s stabilization of the fracture site to allow mistakes experiences. bone healing, minimizing iatrogenic damage to dental and oral tissues and a This is going to be a very brief rapid return to function of the oral cavity discussion, as a detailed one would take to allow the animal to eat and drink hundreds of pages. There is an excellent immediately after surgery. chapter on this in the Vet Clinics issue mentioned on page 1 and watch for a Sometimes the fracture is such that use of the oral cavity post-op will not be a Radiograph of the left mandible of a dog (ignore the restorations in the molar. I had been practicing on this skeleton years ago). Note the large lucent canal ventral to the tooth roots. This space is This was a maxillary fracture that was occupied by the mandibular vein, artery poorly managed. The occlusal and nerve. The only substantial area of relationships were ignored and so after dense cortical bone is ventral to the canal healing, the dog could not close its mouth. – not much to work with. Dorsal to the Several teeth required extraction to allow canal is the cancellous alveolar bone and comfortable function. a lot of tooth roots. From The CUSP, October 2005 Fraser A. Hale, DVM, FAVD, Dipl AVDC mandible behind the last molar and ends at the mental foramina in the region of the chin. In small dogs, the roots of the teeth are proportionally longer so that the apices may be beside the mandibular canal and may even extend down into the ventral cortex. The blood supply to the mandibular bone and all of the mandibular teeth comes from the mandibular artery which travels through the mandibular canal. There is Radiograph of the fractured left mandible no significant vascular cross-over at the in a Shih Tzu. The fracture involves the symphysis and so no collateral periodontal ligament space of the mesial circulation to the mandible. Therefore, root of the first molar. Note how in this preserving the integrity of the small dog, the roots of the first molar mandibular artery is crucial to ensuring extend beside the mandibular canal and adequate blood supply to the bone to into the ventral cortex. These large holes support healing. In some seriously (alveoli) running through the majority of displaced fractures, the artery is severed, the mandible leave it rather weak, predisposing these small dogs to but if the fracture is reduced and mandibular fractures. Notice also how stabilized shortly after injury, the artery much more of the total height of the can re-anastomose on its own (give the mandible the mandibular canal takes up body half a chance and it will try to and so how little solid bone there is to heal). work with. feasible goal and in these cases, Wire Alone = Bad placement of an esophagostomy feeding There are a few specific inter-dental tube will allow enteral nutrition and wiring patterns, which if well executed hydration, but the other objectives must with proper case selection, can provide be met. quite good fracture reduction (Ivy Loop, Now let’s look at some of the anatomical Stout’s Multiple Loop, Essig’s and features and physics of the mandible as Risdon’s patterns). In general, however, they pertain to repair options. wire on its own is a poor choice. Wire tends to develop small kinks during The mandible is full of tooth roots. If the handling. The wires may seem tight and patient enjoys good periodontal health, the fracture stable at discharge, but in a the roots are surrounded by a thin layer few days, the wire stretches, the kinks of bone on the lingual and buccal sides straighten and the wire becomes loose. and then there is cancellous bone Now the fracture is free to fall out of between the roots. Between each root alignment and the wire is just an and the surrounding bone is the annoying foreign body. Wire alone is periodontal ligament. bad news. In mid to large size dogs, the ends of the tooth roots (apices) are dorsal to the Plates = Bad mandibular canal, a hollow chamber that The ventral cortex is the compression begins on the lingual aspect of the side of the fracture and the dorsal From The CUSP, October 2005 Fraser A. Hale, DVM, FAVD, Dipl AVDC (alveolar) ridge is the tension side. fracture or the other, then the splint may Therefore, a plate or wire placed in the have to be wired to the mandible in some solid bone ventrally will have a hard fashion. time holding the dorsal edges together – Intra-oral splints can often be fashioned it is in the wrong place mechanically. to avoid iatrogenic damage to teeth and Ventral appliances tend to become hinge bones, they give good stability in all points. dimensions and allow immediate return Putting a plate on a mandible further to ailementation. They put the stability dorsally runs an extreme risk of along the tension side of the fracture, seriously damaging the mandibular which is where you want it and they are artery, thus compromising the blood custom made to re-establish and supply rostral to the screws. Going maintain proper anatomic alignment. dorsal to the mandibular canal runs a Now let’s look at some examples. very real risk of drilling through tooth roots, causing lots of iatrogenic damage The Shih tzu whose film appears on necessitating extraction of the teeth. page 3 had a fracture through the Plates are flat and rigid and so cause the alveolus of the mesial root of the first mandible to adapt to the shape of the molar. This gave us lots of crown and plate, making preservation of proper root surface area on both sides of the occlusion next to impossible. Plates are fracture to hold a splint. bad news. Treatment began with careful lavaging Pins = Bad of the fracture site with saline. I did not curette the wound, as I wanted to Another idea that has been tried is to run preserve the periodontal ligament fibers an IM pin up the mandibular canal to on the root surface to get periodontal stabilize the fracture. This will destroy healing rather than ankylosis of the root the mandibular vein, artery and nerve, to the bone. I then sutured the soft killing the pulp in each of the teeth and tissues with absorbable material. A likely devascularizing the fracture site. wire/composite splint was constructed in Again, pins are straight and the mandible the mouth to hold the fracture stable as is not, so an IM pin pulls the jaws out of shown in the radiograph at the top of this proper occlusion. Pins also offer no page. rotational stability. Pins are bad news. The dog was sent home with instructions Intra-Oral Splints = Good to feed only very soft food and to avoid all rough play and activities. An Whenever possible, the first choice for antiseptic solution was dispensed for mandibular fracture repair is the use of rinsing around the appliance to reduce an intra-oral splint. Typically these will irritation to the soft tissues. have a wire base and then be reinforced with dental composite or acrylic to hold them rigid in 3-dimensions. If there are enough teeth on either side of the fracture, then the splint is anchored (bonded) to the tooth crowns. If there is insufficient coronal surface-area to support the splint on one side of the From The CUSP, October 2005 Fraser A. Hale, DVM, FAVD, Dipl AVDC Treatment again involved flushing the wound, closing of the soft tissue and creation of an intra-oral splint. The distal portion of the first molar had good coronal surface area but the root was about to fall into the fracture gap. The Due to geography, it was 2.5 months second molar had good root stability, but before we saw the dog again at which not much coronal surface area to bond point, the mandible looked like this: to. So, I wired the distal root of the first molar to the second molar to create one functional unit.

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