Mandibular conditions in puppies present unique diagnostic and therapeutic challenges, particularly in large breeds during rapid skeletal growth. Several proliferative or inflammatory diseases can mimic each other clinically and radiographically, making recognition and differentiation essential for prognosis and treatment.

Mandibular Periostitis Ossificans (MPO)
MPO has been documented in immature large breed dogs between 3–5 months of age, including Labradors, Great Danes, and Great Pyrenees. Clinical presentation involves unilateral mandibular swelling, firm ventrally and fluctuant intraorally. Histopathology reveals necrotic bone, sterile fluid, fibrin, immature granulation tissue, and vascular proliferation with acute inflammation. Most cases involve male dogs, with left-sided swelling in 80%. The proposed mechanism parallels human periostitis ossificans: odontogenic infection elevates the periosteum, which responds by laying down new bone. Repeated cycles periosteal elevation produce the classic “onion-skin” radiographic appearance. Over time, the layers consolidate, and normal bone remodeling may occur. These lesions are often self-limiting, though some enlargement may persist.

Craniomandibular Osteopathy (CMO)
CMO, colloquially known as “lion jaw” or “Westie jaw,” is a developmental orthopedic disease of terrier breeds aged 3-8 months. Clinical signs include pain on opening the mouth, palpation discomfort, bilateral firm mandibular swellings, reduced jaw motion, excessive salivation, and intermittent fever. Atrophy of the masticatory muscles may develop. Radiographically, CMO shows spiculated, mineralized hyperostotic cortical bone, usually bilaterally. Histology demonstrates exuberant new bone formation. While self-limiting, supportive care-nutritional support, fluids, analgesia, and corticosteroids-may be required. Relapses are common if treatment stops prematurely, and in some cases, progress to malnutrition due to the inability to open the mouth. A genetic basis is implicated, particularly involving the SLC7A2 gene, a glucose-phosphate transporter in osteoclasts. In West Highland White Terriers, 36% were carriers, highlighting incomplete penetrance and variable expression.

Idiopathic Canine Juvenile Cranial Hyperostosis (ICH)
ICH affects dogs 3–8 months of age across multiple breeds, including Boston Terriers, Pit Bulls, Dobermans, Great Danes, and others . Predilection sites vary but often include the parietal and occipital bones, tympanic bullae, mandibular rami, and temporomandibular joints. This condition is non-neoplastic, with proliferative periosteal thickening. The etiology remains unclear but may involve trauma or inflammation.

Hypertrophic Osteodystrophy (HOD)
HOD (the CMO of the long bones) primarily affects large breed puppies aged 2-6 months. It presents with painful, usually bilateral swelling of the metaphyses, often accompanied by fever. The disease is self-limiting but may recur, and nutritional support and analgesia are essential.

Hypertrophic Osteopathy (HO)
Though less common in puppies, HO manifests as distal periosteal new bone proliferation, usually secondary to thoracic disease. Proposed mechanisms include vagal stimulation from pulmonary pathology, altered vascular dynamics, or systemic hormonal influences. Puppy mandibular diseases range from self-limiting developmental conditions to proliferative inflammatory diseases, including MPO. Accurate diagnosis requires the integration of a patient’s history, clinical examination, imaging, and, in some cases, histopathology. Awareness of breed predispositions and genetic influences is critical. While many conditions resolve spontaneously, supportive care and careful monitoring are essential to minimize pain, prevent malnutrition, and preserve mandibular function.