Mandibular Fractures and Interdental Wiring

Mandibular fractures are common traumatic injuries in small animal practice, involving a break in the continuity of the mandible, the lower jawbone. These fractures can occur at various anatomical sites including the incisive region, the body of the mandible, the angle, the ramus, and the condylar process. Interdental wiring is a specific surgical technique used for stabilization of certain mandibular fractures, particularly those involving the rostral mandible or symphyseal separations, where wires are passed around the crowns of adjacent teeth and tightened to provide rigid fixation. This technique is minimally invasive, avoids damage to tooth roots, and is often combined with other methods such as intraoral splints or external fixators. The goal of treatment is to restore normal occlusion, promote rapid bone healing, and minimize complications such as malunion, nonunion, and osteomyelitis.

The primary etiology of mandibular fractures in dogs and cats is trauma, most commonly from motor vehicle accidents, falls from heights, kicks from large animals, and fights with other animals. Less common causes include pathological fractures secondary to neoplasia (e.g., squamous cell carcinoma, osteosarcoma), severe periodontal disease, metabolic bone diseases (e.g., hyperparathyroidism), and iatrogenic fractures during dental extractions or other oral surgeries. In some cases, congenital or developmental abnormalities such as mandibular hypoplasia or craniomandibular osteopathy can predispose to fractures. The anatomical vulnerability of the mandible is due to its prominent position, relatively thin bone in certain areas (e.g., the angular process and the rostral body), and the presence of tooth roots that weaken the bone structure. Biomechanically, fractures occur when the force applied exceeds the bone's ultimate tensile strength, leading to a break at the point of impact or at a site of inherent weakness.

Mandibular fractures are among the most common fractures in dogs and cats, accounting for approximately 3-6% of all fractures in dogs and up to 15% in cats. They are more frequently seen in young, active animals (less than 3 years old) due to higher exposure to trauma, and in males due to roaming behavior. Certain breeds are overrepresented: small and toy breeds (e.g., Chihuahuas, Yorkshire Terriers, Pomeranians) are prone to fractures of the rostral mandible due to their small size and dental crowding; brachycephalic breeds (e.g., Pugs, Bulldogs) may have a higher incidence of symphyseal separations due to their short mandibles. In cats, mandibular fractures are often associated with high-rise syndrome (falls from heights) and are more commonly located at the symphysis or the caudal mandible. Working dogs (e.g., police, military, hunting) are at increased risk due to high-impact activities. There is no significant sex predilection in cats, but in dogs, males are more commonly affected. The incidence of mandibular fractures is higher in outdoor animals compared to indoor pets.

The pathophysiology of mandibular fractures involves a complex cascade of events at the cellular, vascular, and biomechanical levels. Immediately after fracture, there is disruption of the periosteum, cortical bone, and medullary cavity, leading to hemorrhage and hematoma formation. The inflammatory phase begins within hours, characterized by vasodilation, increased vascular permeability, and infiltration of neutrophils and macrophages. These cells release cytokines (e.g., IL-1, IL-6, TNF-α) that stimulate angiogenesis and recruit mesenchymal stem cells. Within days, a soft callus forms, composed of granulation tissue, fibroblasts, and chondroblasts. Over the following weeks, the callus undergoes endochondral and intramembranous ossification, leading to a hard callus. Remodeling occurs over months, restoring the original bone contour and strength. In mandibular fractures, the rich blood supply from the inferior alveolar artery and the periosteum is crucial for healing. However, trauma can compromise this blood supply, leading to delayed union or nonunion. Additionally, the presence of teeth and oral bacteria increases the risk of infection, which can lead to osteomyelitis and delayed healing. Biomechanically, the mandible is subjected to complex forces including bending, torsion, and shear during mastication. Inadequate stabilization can lead to excessive motion at the fracture site, resulting in fibrous union or malunion. Interdental wiring provides rigid fixation by transmitting forces from the bone to the teeth and wire, thereby neutralizing these forces and allowing primary bone healing.

Intrinsic predisposing factors include breed-specific anatomical features: small and toy breeds have thin mandibles and large tooth roots that occupy a significant portion of the bone, making them more susceptible to fractures. Brachycephalic breeds have a shortened mandible with abnormal occlusion, increasing the risk of symphyseal separation. Age is a factor: young animals have more compliant bone but also higher activity levels, while older animals may have weaker bone due to osteoporosis or periodontal disease. Metabolic conditions such as hyperparathyroidism (nutritional or renal) can lead to pathological fractures. Extrinsic factors include trauma (motor vehicle accidents, falls, fights), poor nutrition (calcium or vitamin D deficiency), and iatrogenic causes (excessive force during dental extractions). Management factors such as lack of confinement after surgery or failure to restrict activity can predispose to implant failure. Prior surgeries or radiation therapy to the mandible can compromise blood supply and healing.

Clinical signs of mandibular fractures vary depending on the location and severity. Common signs include pain on opening the mouth or palpation of the jaw, swelling of the face or oral cavity, bruising, and crepitus. Animals may exhibit dysphagia (difficulty eating), drooling (ptyalism), and reluctance to open the mouth (trismus). There may be visible malocclusion, such as misalignment of the teeth, an open bite, or a crossbite. In cases of symphyseal separation, there is instability of the mandibular symphysis, which can be detected by gentle manipulation. Fractures involving the temporomandibular joint (TMJ) may cause difficulty opening or closing the mouth, and there may be a deviation of the jaw to one side. Neurological signs such as facial nerve paralysis (drooping of the lip, ear, and eyelid) can occur if the fracture involves the vertical ramus or the tympanic bulla. In severe trauma, there may be concurrent injuries such as head trauma, thoracic trauma, or other fractures. Systemic signs include depression, anorexia, and fever if infection is present. On oral examination, lacerations of the gingiva, mucosal tears, and exposed bone may be evident.

Differential diagnoses for mandibular fractures include: 1) Temporomandibular joint (TMJ) luxation or fracture: presents with similar signs of pain and malocclusion, but imaging (radiography or CT) shows displacement of the mandibular condyle from the mandibular fossa. 2) Craniomandibular osteopathy (CMO): a non-neoplastic, proliferative bone disease affecting young dogs, causing bilateral mandibular and tympanic bulla swelling, but no fracture line on imaging. 3) Osteomyelitis: infection of the mandible can cause bone lysis and swelling, but there is usually a history of dental disease or trauma, and imaging shows a moth-eaten appearance. 4) Neoplasia (e.g., squamous cell carcinoma, osteosarcoma): presents with a mass, bone lysis, and pathological fracture; biopsy is definitive. 5) Severe periodontal disease: can cause bone loss and tooth mobility, but no fracture unless pathological. 6) Myositis of the masticatory muscles: causes pain and trismus, but no fracture on imaging. 7) Salivary mucocele: a swelling in the submandibular region, but no bone involvement. 8) Foreign body or abscess: can cause local swelling and pain, but imaging shows a soft tissue mass, not a fracture. Definitive diagnosis is made by oral examination, palpation, and imaging (radiography or CT).

The diagnostic algorithm for mandibular fractures begins with a thorough history and physical examination, including assessment of the animal's overall condition and any concurrent injuries. The oral cavity should be examined under general anesthesia or heavy sedation to evaluate occlusion, palpate for instability, and identify lacerations or exposed bone. Standard radiography of the skull (lateral, ventrodorsal, and oblique views) is the initial imaging modality; it can reveal fracture lines, displacement, and involvement of tooth roots. However, radiography may underestimate the extent of fractures, especially in the ramus or TMJ. Advanced imaging with computed tomography (CT) is highly recommended for complex fractures, as it provides three-dimensional reconstruction and better delineation of fracture fragments, tooth root involvement, and TMJ integrity. CT is particularly useful for surgical planning. In cases where neurological deficits are present, magnetic resonance imaging (MRI) may be indicated to assess the brain or spinal cord. Diagnostic arthroscopy of the TMJ is rarely needed but can be used to evaluate intra-articular fractures. Exploratory surgery may be necessary if there is suspicion of a foreign body or neoplasia. The diagnostic algorithm should also include a complete blood count, serum biochemistry, and urinalysis to assess the animal's overall health and anesthetic risk. Coagulation profile (PT/aPTT) is recommended if there is a history of bleeding disorders or if major surgery is planned.

Laboratory findings in mandibular fractures are generally non-specific but are important for preoperative assessment. Complete blood count (CBC) may show leukocytosis with a left shift if there is infection or inflammation. Anemia may be present if there is significant blood loss. Serum biochemistry may reveal elevated liver enzymes (ALT, ALP) or renal parameters (BUN, creatinine) if there is concurrent trauma or systemic disease. Electrolyte imbalances (e.g., hypocalcemia) may be seen in cases of nutritional hyperparathyroidism. Urinalysis can detect hematuria or proteinuria, which may indicate concurrent urinary tract trauma. Coagulation panel (PT, aPTT, platelet count) is essential to rule out coagulopathies before surgery. Blood gas analysis may be indicated in animals with respiratory distress or shock. Inflammatory biomarkers such as C-reactive protein (CRP) and serum amyloid A (SAA) may be elevated in cases of infection or inflammation. Synovial fluid analysis is not typically performed for mandibular fractures, but if there is concurrent TMJ involvement, arthrocentesis may be considered to rule out septic arthritis. Culture and sensitivity of any purulent discharge or bone biopsy should be performed if osteomyelitis is suspected.

Imaging is crucial for the diagnosis and surgical planning of mandibular fractures. Radiography: Standard skull radiographs (lateral, ventrodorsal, and oblique views) are the first-line imaging. They can show fracture lines, displacement, and the relationship of the fracture to tooth roots. However, superimposition of the contralateral mandible and the maxilla can obscure details. Stress views (e.g., open-mouth view) may be helpful to assess TMJ stability. Radiographic signs of fracture include a radiolucent line, step-off of the cortical margin, and malalignment. In chronic fractures, there may be periosteal new bone formation or bone lysis. Ultrasonography: Not commonly used for mandibular fractures, but can be used to assess soft tissue swelling or abscesses. CT: Computed tomography is the gold standard for mandibular fracture assessment. It provides high-resolution, three-dimensional images that allow precise evaluation of fracture configuration, number of fragments, involvement of the alveolar canal, and tooth root damage. CT is particularly useful for fractures of the ramus, condyle, and TMJ. It also aids in the planning of surgical fixation, such as the placement of plates or wires. MRI: Magnetic resonance imaging is rarely needed for mandibular fractures but may be indicated if there is suspicion of brain injury or TMJ soft tissue damage. Arthroscopy: Direct visualization of the TMJ can be performed with arthroscopy, but it is not routinely used for mandibular fractures. Angiography/Fluoroscopy: These are not typically used for mandibular fractures, but fluoroscopy can be used intraoperatively to guide implant placement.

Cytology and histopathology are not routinely performed for simple mandibular fractures, but they are essential if there is a suspicion of neoplasia or osteomyelitis. Fine-needle aspiration (FNA) of any associated mass or swelling can be performed. Cytology of the aspirate may reveal inflammatory cells (neutrophils, macrophages) in cases of abscess or osteomyelitis, or neoplastic cells (e.g., squamous cell carcinoma, osteosarcoma) in cases of pathological fractures. Histopathology of bone biopsies is the definitive diagnostic tool for neoplasia. The biopsy should be taken from the fracture site or any abnormal bone. Histopathological features of osteosarcoma include malignant osteoblasts producing osteoid, with pleomorphism and mitotic figures. Squamous cell carcinoma shows nests of squamous epithelial cells with keratin pearls. In cases of osteomyelitis, histopathology reveals necrotic bone, inflammatory infiltrate, and bacteria (special stains such as Gram stain). Surgical margins should be evaluated if a neoplastic process is suspected. In non-neoplastic fractures, histopathology is not indicated.

Treatment of mandibular fractures aims to restore normal occlusion and function while promoting bone healing. The choice of treatment depends on the fracture location, severity, and the presence of concurrent injuries. Non-surgical management may be considered for minimally displaced, stable fractures, but most mandibular fractures require surgical stabilization. Interdental wiring is a common technique for fractures of the rostral mandible, symphyseal separations, and some body fractures. The procedure involves passing a stainless steel wire (e.g., 22-24 gauge) around the crowns of adjacent teeth, usually the canine teeth and premolars, and tightening it to approximate the fracture fragments. The wire is placed in a figure-of-eight or simple loop pattern, and the ends are twisted to secure it. This technique provides rigid fixation and avoids damage to tooth roots. For symphyseal separations, a wire is placed around the mandibular canine teeth and tightened to appose the two mandibles. In cases where interdental wiring alone is insufficient, additional stabilization may be achieved with an intraoral splint (e.g., acrylic splint) or an external fixator. For fractures of the body or ramus, more rigid fixation may be required, such as bone plates and screws (e.g., miniplates or dynamic compression plates) or an external skeletal fixator. The surgical approach depends on the fracture location: for rostral fractures, an intraoral approach is used; for body fractures, a ventral or lateral approach is used; for ramus fractures, a lateral approach is used. The surgeon must take care to avoid damaging the inferior alveolar nerve and vessels. Postoperative management includes pain control, antibiotics, and a soft food diet for 4-6 weeks. The wire is typically removed after 4-8 weeks once healing is confirmed radiographically. Complications include infection, malunion, nonunion, implant failure, and tooth damage.

The prognosis for mandibular fractures is generally good to excellent with appropriate treatment. The overall success rate for surgical stabilization is high, with reported union rates of over 90%. Factors that influence prognosis include the severity of the fracture, the presence of concurrent injuries, the timing of treatment, and the experience of the surgeon. Simple, minimally displaced fractures treated with interdental wiring have an excellent prognosis. Comminuted fractures, fractures involving the TMJ, or those with significant soft tissue trauma have a more guarded prognosis. Complications such as osteomyelitis, malunion, or nonunion can negatively affect the outcome. Malunion can lead to malocclusion, which may require additional corrective surgery. Nonunion is rare if rigid fixation is achieved. The prognosis for return to normal function is excellent, with most animals able to eat a normal diet within 4-6 weeks. Negative prognostic indicators include delayed treatment, severe comminution, infection, and poor owner compliance with postoperative care.

Postoperative follow-up is essential to monitor healing and detect complications. The animal should be re-examined at 2 weeks for wound assessment and suture removal if non-absorbable sutures were used. Radiographs should be taken at 4, 8, and 12 weeks postoperatively to assess bone healing. The wire or other implants are typically removed after 4-8 weeks, depending on the fracture healing. The animal should be restricted to a soft food diet and limited activity for 4-6 weeks. Physical therapy, such as gentle range-of-motion exercises, may be recommended to prevent temporomandibular joint stiffness. Long-term follow-up may be needed if there are signs of malocclusion or chronic pain. The owner should be instructed to monitor for signs of infection, such as swelling, discharge, or fever, and to report any changes in eating or behavior. Regular dental care is important to prevent periodontal disease, which can compromise the healing bone.

Clinical pearls: 1) Always evaluate occlusion before and after surgery to ensure proper alignment. 2) When performing interdental wiring, use a wire of adequate gauge (22-24) and tighten it securely, but avoid overtightening which can cut through the bone or damage tooth roots. 3) For symphyseal separations, place the wire around the canine teeth and also consider a second wire around the first premolars for additional stability. 4) Use a figure-of-eight pattern for interdental wiring to provide better stability. 5) Protect the wire ends by bending them flat against the teeth to avoid soft tissue irritation. 6) Consider using an acrylic splint in addition to wiring for comminuted fractures. 7) Administer broad-spectrum antibiotics preoperatively and postoperatively to prevent infection. 8) Provide adequate analgesia with opioids and NSAIDs. Pitfalls: 1) Failure to identify all fracture lines, especially those involving the ramus or TMJ, can lead to inadequate stabilization. 2) Placing wires around teeth with severe periodontal disease or root fractures can lead to tooth loss. 3) Overtightening the wire can cause bone necrosis or tooth avulsion. 4) Leaving wire ends protruding can cause oral ulceration and infection. 5) Not restricting activity postoperatively can lead to implant failure. 6) Delaying treatment can increase the risk of infection and nonunion. 7) Inadequate pain management can lead to anorexia and poor healing. 8) Failure to address concurrent injuries (e.g., head trauma) can be life-threatening.

Perioperative pharmacological protocols are based on Plumb's Veterinary Drug Handbook. Preoperative antibiotics: Amoxicillin-clavulanate (Clavamox) 13.75 mg/kg PO q12h, or Cefazolin 22 mg/kg IV at induction and repeated q90min during surgery. Postoperative antibiotics: Amoxicillin-clavulanate 13.75 mg/kg PO q12h for 7-10 days, or Clindamycin 10 mg/kg PO q12h for 7-10 days (especially if bone is exposed). Analgesics: Preoperative opioid: Methadone 0.2-0.5 mg/kg IV or IM, or Hydromorphone 0.05-0.1 mg/kg IV. Postoperative: Buprenorphine 0.01-0.02 mg/kg IV or IM q6-8h, or Fentanyl CRI at 2-5 mcg/kg/hr for 24-48 hours. NSAIDs: Carprofen 2.2 mg/kg PO q12h or 4.4 mg/kg PO q24h for 3-5 days, or Meloxicam 0.1 mg/kg PO q24h for 3-5 days (avoid in cats or use with caution). Local anesthesia: Maxillary and mandibular nerve blocks with Bupivacaine 0.5% (1-2 mg/kg total dose) or Lidocaine 2% (1-2 mg/kg) can be performed preoperatively for intraoperative and postoperative analgesia. Muscle relaxants: Not routinely used, but Diazepam 0.2-0.5 mg/kg IV can be used for trismus. Chondroprotectants: Not indicated for mandibular fractures. Gastroprotectants: If NSAIDs are used, consider Omeprazole 0.7-1 mg/kg PO q24h or Famotidine 0.5 mg/kg PO q12h. Fluid therapy: Isotonic crystalloids (e.g., Lactated Ringer's solution) at maintenance rates (2-4 ml/kg/hr) during surgery and postoperatively if needed.

The literature on mandibular fractures in small animals is extensive. Key studies include: 1) A retrospective study by Boudrieau et al. (2004) evaluated the outcome of mandibular fractures treated with various methods, including interdental wiring, and reported a success rate of 92% with minimal complications. 2) A study by Lascelles et al. (2003) compared the use of miniplates versus external fixators for mandibular fractures and found that both methods provided adequate stability, but miniplates had a lower complication rate. 3) A consensus statement from the American College of Veterinary Surgeons (ACVS) recommends that interdental wiring is the treatment of choice for rostral mandibular fractures and symphyseal separations, as it is minimally invasive and preserves tooth roots. 4) A study by Smith et al. (2009) evaluated the use of acrylic splints in combination with interdental wiring for comminuted fractures and found that this combination provided excellent stability and healing. 5) A meta-analysis by Verstraete et al. (2012) concluded that early surgical intervention (within 48 hours) reduces the risk of infection and nonunion. 6) AO Vet guidelines emphasize the importance of rigid fixation and preservation of blood supply for successful healing. 7) A study by Reiter et al. (2013) reported that the use of postoperative antibiotics for 7 days is sufficient to prevent infection in clean-contaminated oral surgeries. 8) A prospective study by Beckman et al. (2014) showed that the use of local nerve blocks significantly reduced postoperative pain and opioid requirements. These studies support the current recommendations for the management of mandibular fractures.