Jaw Bone Diseases: Fibrous Dysplasia, Paget's, Osteomyelitis

The jaws suffer the skeleton's bone diseases plus some peculiar to the mouth. Three essentials for a dental student: fibrous dysplasia (bone replaced by fibrous tissue), Paget's disease (chaotic, excessive remodelling), and osteomyelitis (bacterial infection of the bone itself).

They change how teeth can be moved, extracted, or implanted. Mistaking fibrous dysplasia for a tumour invites unnecessary resection; missing osteomyelitis lets infection spread through the mandible.

Key Concepts

• Fibrous dysplasia: a developmental disorder where normal bone is replaced by fibro-osseous tissue due to a GNAS gene mutation. It may involve one bone (monostotic, often the maxilla) or many (polyostotic). The jaw swells painlessly in childhood or adolescence, and growth stops after puberty.
• Paget's disease (osteitis deformans): a disorder of older adults where bone remodelling goes into overdrive — excessive resorption followed by disorganized formation of bulky but weak bone. The maxilla is affected more than the mandible; patients notice dentures no longer fit. Serum alkaline phosphatase is markedly raised.
• Osteomyelitis of the jaws: bacterial infection of bone and marrow entering through an infected tooth, socket, or fracture. The mandible suffers more than the maxilla due to poorer blood supply. Pus, pain, swelling, loose teeth, and discharging sinuses are typical.

How It Works

• Step 1 — fibrous dysplasia pathogenesis. The GNAS mutation makes bone cells produce a fibrous stroma with irregular woven-bone trabeculae instead of lamellar bone — the classic "ground-glass" X-ray appearance with borders blending into normal bone.
• Step 2 — Paget's disease pathogenesis. Overactive osteoclasts resorb bone rapidly; osteoblasts replace it with weak, mosaic-patterned woven bone — the "cotton-wool" radiographic pattern with thickened cortices.
• Step 3 — osteomyelitis pathogenesis. Bacteria invade the marrow; pressure rises inside the rigid bone, blood vessels compress, bone dies into a sequestrum, and pus drains through sinuses.
• Step 4 — diagnosis. Combine history, radiographs (ground-glass vs cotton-wool vs sequestrum), and blood tests (alkaline phosphatase in Paget's; ESR and white cells in osteomyelitis). Biopsy confirms fibrous dysplasia.
• Step 5 — management. Fibrous dysplasia: observe mild cases, recontour after growth stops. Paget's: bisphosphonates. Osteomyelitis: remove the cause, drain pus, give antibiotics, and remove sequestra surgically.

Worked Example

A 58-year-old patient reports that his upper denture, comfortable for years, no longer fits, and his maxilla looks enlarged. Blood tests show serum alkaline phosphatase of 440 IU/L. Interpret the finding.

1. The adult reference range is about 44–147 IU/L; the enzyme rises when osteoblasts are very active.
2. The patient's value of 440 IU/L is about 3 times the upper limit of normal (440 ÷ 147 ≈ 3.0), indicating greatly increased bone formation activity.
3. Maxillary enlargement over 50 plus very high alkaline phosphatase points to Paget's disease — not fibrous dysplasia or osteomyelitis.
4. Next steps: skull and jaw radiographs looking for the cotton-wool pattern, and referral for bisphosphonate therapy to control the abnormal remodelling. Note that Paget's bone, though bulky, is weak — extractions and implants need cautious planning.

Common Misconceptions

• Fibrous dysplasia is a true tumour needing wide resection. Wrong. It is developmental, not neoplastic; aggressive resection in a growing child does more harm than the disease.
• Paget's disease only affects the spine and pelvis. Wrong. The jaws — especially the maxilla — are commonly involved, and the first sign is often dental: a loose denture or widening gaps between teeth.
• Osteomyelitis needs antibiotics alone. Wrong. Antibiotics cannot penetrate dead bone; the infected tooth or sequestrum must be removed surgically.

Real-World Applications

Fibrous dysplasia replaces bone with fibrous tissue in the young, Paget's rebuilds it chaotically in the old, osteomyelitis infects it at any age. Telling the three apart keeps dental treatment safe.