Osteonecrosis of the jaw typically appears as an area of yellowish-white or grayish exposed bone in the mouth that refuses to heal, often surrounded by red, swollen, or infected-looking soft tissue. The exposed bone can range from a small patch the size of a pencil eraser to a large stretch spanning several teeth, and it may be accompanied by loose teeth, pus drainage, or a foul taste. The condition progresses through distinct stages with very different visual presentations, and what you see with the naked eye often tells only part of the story compared to what imaging reveals underneath.
The Hallmark Sign: Bone That Will Not Stay Covered
The defining feature of osteonecrosis of the jaw (ONJ) is nonhealing exposed bone in the mouth or face area. In a healthy mouth, bone is always covered by gum tissue. When ONJ develops, that covering breaks down or never forms after a procedure like a tooth extraction, leaving bare bone visible inside the mouth.1PubMed. Bisphosphonate-related osteonecrosis of the jaw: a pictorial review The exposed bone itself can look dull white, pale yellow, or grayish, and its texture is rough or irregular rather than smooth. Sometimes the bone takes on a brownish tint as it becomes further necrotic and contaminated by oral bacteria.
Surrounding the exposed bone, the gum tissue is often inflamed: red, puffy, and tender to touch. In more advanced cases, you may see pus oozing from the margin where gum meets bone, or a small tunnel-like opening in the tissue called a fistula. A fistula may look like a pimple or blister on the gum, and when probed by a dentist, the instrument passes through the soft tissue and hits bone underneath, confirming that necrotic bone is present even when it is not immediately visible to the eye.2PubMed Central. Medication-Related Osteonecrosis of the Jaws: A Comparison of SICMF–SIPMO and AAOMS Guidelines
What the Earliest Stage Looks Like, Before Bone Shows
One of the trickiest aspects of ONJ is that its earliest stage has no visible bone exposure at all. Clinicians refer to this as Stage 0, and it can easily be mistaken for ordinary dental problems. At this point, you might notice dull, aching pain in the jaw or teeth that does not match any obvious cavity or infection. Teeth in the affected area may start to feel loose. The gums may look mildly swollen or inflamed, and you might experience a heavy or numb feeling in part of your lower lip or chin.
Research from a Japanese clinical trial found that tooth looseness accompanied by signs resembling periodontal disease may be one of the most useful early warnings of Stage 0 ONJ.3PubMed. Reliability of early stage symptoms/clinical findings of osteonecrosis of the jaw: Japanese Osteoporosis Intervention Trial-05 (JOINT-05) The catch is that millions of people have gum disease and loose teeth for other reasons, so this early stage is genuinely difficult to spot. Other Stage 0 symptoms include unexplained sinus pain, bone pain that seems out of proportion, and altered sensation in the face. On X-rays at this stage, a dentist might see thickening of the space around tooth roots or unusual bone density changes, but the mouth itself can look deceptively normal.2PubMed Central. Medication-Related Osteonecrosis of the Jaws: A Comparison of SICMF–SIPMO and AAOMS Guidelines
How ONJ Looks at Each Stage
Once past Stage 0, the condition is classified into three progressively more severe stages, each with a distinct visual profile.
In Stage 1, you can see exposed bone or a fistula that probes to bone, but the area is not actively infected. The bone is visible but the surrounding gums are not particularly red or swollen, there is no pus, and the patient may have no pain at all. Someone with Stage 1 ONJ might notice the exposed patch only because it feels rough against their tongue or because a dentist spots it during a routine exam.2PubMed Central. Medication-Related Osteonecrosis of the Jaws: A Comparison of SICMF–SIPMO and AAOMS Guidelines
Stage 2 adds infection and inflammation to the picture. The exposed bone is now surrounded by angry red gum tissue, and there may be swelling of the cheek or jaw visible from outside the mouth. Pus may drain from the exposed site or from a fistula. Pain becomes a significant feature, and the area is tender when chewing or even at rest. Many people first seek care at this stage because the pain and bad taste from the infection become impossible to ignore.
Stage 3 is the most severe and visually dramatic. The exposed necrotic bone extends beyond the immediate tooth-bearing area, and complications pile up. These can include a pathologic fracture of the jawbone itself, a fistula that breaks through to the outside of the face, or a communication between the mouth and the sinus cavity or nasal passage. In one documented case, a patient presented with a large area of bone exposure spanning the entire left upper jaw arch, with the dead bone becoming loose as the body tried to push it away. The necrosis had extended into the sinus, causing sinusitis, while a separate area of exposed bone appeared on the opposite side of the jaw.4PubMed Central. Medication-Related Osteonecrosis of the Jaw: Successful Medical Management of Complex Maxillary Alveolus with Sinus Involvement At this level, surrounding teeth are often highly mobile, and the facial swelling can be substantial.
Upper Jaw Versus Lower Jaw: Different Patterns
ONJ does not look identical depending on whether it affects the upper jaw (maxilla) or the lower jaw (mandible), and the lower jaw is the more common site. A case-control study comparing the two locations found distinct patterns on imaging. In the upper jaw, bone destruction (osteolysis) was the dominant finding, appearing in over 90% of cases. In the lower jaw, the bone was more likely to show a periosteal reaction, where new bone forms in uneven layers along the outer surface, giving the jaw a thickened or lumpy appearance on scans. Sequestration, where a fragment of dead bone separates from the surrounding living bone, was also far more common in the lower jaw, appearing in about 80% of mandibular cases compared to roughly a third of upper jaw cases.5Clinical Oral Investigations. Uncovering jaw-specific radiographic differences in medication related osteonecrosis of the jaws (MRONJ): a case-control study
These differences are thought to reflect the distinct anatomy and blood supply of each jaw. The lower jaw is denser and has less blood flow per unit of bone, which may explain why dead bone tends to linger as sequestra rather than dissolving away. The upper jaw has thinner bone and richer blood supply from multiple arteries, so bone tends to erode rather than form thick necrotic chunks. For a patient, this means upper jaw ONJ may present more as a progressively deepening hole in the bone, while lower jaw ONJ is more likely to produce visible or palpable lumps of dead bone that the body is trying to expel.
What ONJ Looks Like on X-Rays and CT Scans
The mouth exam tells you what is happening at the surface, but imaging reveals the full extent of the problem underneath. On a standard dental panoramic X-ray, ONJ can show up as areas of abnormally dense (sclerotic) bone, ragged or irregular bone margins, dark spots indicating bone destruction, and persistent tooth sockets that never filled in with new bone after extractions.6PubMed. Radiographic findings of bisphosphonate-related osteonecrosis of the jaws: Comparison with cone-beam computed tomography and panoramic radiography A sequestrum shows up as a bright fragment of bone surrounded by a dark halo where it has separated from the living jaw.
Cone-beam CT scanning, a three-dimensional imaging technique commonly available in oral surgery offices, consistently shows more extensive disease than panoramic X-rays. One study comparing the two found that cone-beam CT demonstrated a greater extent and quality of bony changes in nearly all cases, picking up sclerosis, bone fragmentation, sinus involvement, and cortical bone irregularity that flat X-rays missed entirely.7Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology. Use of cone-beam computerized tomography for evaluation of bisphosphonate-associated osteonecrosis of the jaws This is clinically important because the visible bone exposure in the mouth may represent only the tip of the iceberg; the disease underneath often extends well beyond what you can see or probe.
MRI and Advanced Imaging Clues
MRI adds a different layer of information, especially for soft tissue involvement and early detection. In healthy bone, marrow gives off a characteristic bright signal on certain MRI sequences. When bone becomes necrotic, it loses this signal and appears dark. Specifically, early-stage ONJ shows decreased marrow signal on one type of MRI weighting while showing increased signal on sequences sensitive to fluid and inflammation, reflecting the swelling within and around the dying bone.8Japanese Dental Science Review. Role of imaging in drug-related osteonecrosis of the jaw: An up-to-date review When contrast dye is injected, affected bone and surrounding tissue light up, indicating active inflammation even before the bone breaks through the gum surface.
In a study comparing MRI with other imaging methods, all confirmed sites of ONJ showed the same pattern: dark on one sequence, bright on another, with contrast dye uptake throughout the affected area and surrounding tissue.9American Journal of Neuroradiology. Bisphosphonate-Induced Osteonecrosis of the Jaw: Comparison of Disease Extent on Contrast-Enhanced MR Imaging, [18F] Fluoride PET/CT, and Conebeam CT imaging MRI’s strength is that it can reveal inflammation in the soft tissue and bone marrow before the bone surface breaks down, making it potentially useful for catching the disease at Stage 0 when the mouth still looks relatively normal.10PubMed Central. Do various imaging modalities provide potential early detection and diagnosis of medication-related osteonecrosis of the jaw? A review
Conditions That Look Like ONJ but Are Not
Several other jaw conditions can mimic the appearance of ONJ, which makes diagnosis tricky in some situations. Osteoradionecrosis, which happens after radiation therapy to the head and neck rather than from medications, produces nearly identical-looking exposed bone in the jaw. Both conditions feature nonhealing bone, sequestra, and infection. However, there are subtle differences. Periosteal reaction, that layered buildup of new bone along the jaw surface, has been found only in medication-related ONJ and not in radiation-induced cases.11PubMed. Differences between osteoradionecrosis and medication-related osteonecrosis of the jaw The patient populations also differ: radiation-induced cases skew heavily male and tend to occur in older patients, while medication-related cases are more often female, reflecting the demographics of osteoporosis treatment.12PubMed Central. Resemblances and differences between osteoradionecrosis of the jaw and medication-related osteonecrosis of the jaw
An even more concerning look-alike is cancer that has spread to the jaw. In one reported case, a breast cancer patient developed a jaw lesion that was initially presumed to be metastatic disease spreading to the bone. It was treated with palliative radiation before follow-up imaging revealed the lesion was actually ONJ caused by bisphosphonate therapy.13PubMed Central. Bisphosphonate-related osteonecrosis of the jaw mimicking bone metastasis This kind of misidentification matters enormously because the treatment for metastatic cancer in the jaw is completely different from the treatment for ONJ. The lesson for patients is that any new jaw lesion in someone with a cancer history and bisphosphonate use warrants careful investigation rather than assumptions.
Ordinary dental infections, advanced gum disease, and even some benign bone tumors can also produce areas that superficially resemble early ONJ. The key distinguishing factor is usually the combination of exposed bone that does not heal over weeks and a history of medication use or radiation therapy. Without that medication or radiation history, the same-looking exposed bone would likely receive a different diagnosis.
What Healing Looks Like After Treatment
If you have been looking at exposed bone in your mouth for weeks or months, you probably want to know what successful treatment looks like. The goal of surgery for ONJ is to remove the dead bone and get healthy gum tissue to close over the site, restoring the normal state where no bone is visible. A large study tracking outcomes found that complete coverage of the surgical site by intact mucosa was achieved in about 78% of all cases, with the median time to healing around five weeks after surgery.14PubMed Central. Postoperative healing and recurrence in osteonecrosis of the jaw: influence of risk factors and surgical approach
The healing process is not always smooth. About 44% of patients in that study experienced a temporary wound breakdown during the early recovery period, typically noticed at the first follow-up visit about two weeks after surgery. This can look alarming: the surgical site may partially reopen, exposing a small area of bone again. But in roughly half of those cases, the opening closed on its own with conservative care, meaning rinses and close monitoring rather than another operation.
Surgical technique makes a noticeable difference in what healing looks like. In advanced cases, surgeons use tissue flaps, where a section of well-vascularized tissue from nearby is repositioned to cover the bone defect. Studies comparing different flap techniques report that over 90% of patients treated with various local flap approaches achieved intact mucosal coverage at their last follow-up.15PubMed. The efficacy of different local flaps for wound closure of defects after removal of necrotic bone in advanced medication-related osteonecrosis of the jaw: A single-center cohort study A newer technique using a double-layer closure achieved intact tissue coverage in about 68% of patients at eight weeks, compared to roughly 26% with the conventional single-layer approach.16PubMed. Double-layer versus conventional mucoperiosteal flap closure in the surgical treatment of medication-related osteonecrosis of the jaw: A combined Retrospective-Prospective cohort study Successful healing looks like smooth, pink, intact gum tissue with no exposed bone, no draining fistula, and no pain on probing.
What Surgeons See During the Operation
During surgery, clinicians need to determine exactly where healthy bone ends and dead bone begins, and the boundary is not always obvious to the naked eye. A technology called autofluorescence-guided surgery has emerged to help. Under a specialized light, living bone fluoresces, glowing a bright green, while necrotic bone shows no fluorescence or only a pale, washed-out glow. This makes the boundary between viable and nonviable tissue much more visible than it would be under normal operating-room lights, where dead and living bone can look surprisingly similar once the soft tissue is peeled back.17PubMed Central. Autofluorescence-Guided Surgery in the Management of Osteonecrosis of the Jaw: Correlation Between Bone Autofluorescence and Histopathological Findings in 56 Samples
When examined under a microscope after removal, ONJ bone tells a more detailed story. Histological analysis shows heavy infiltration by inflammatory cells, widened bone structural elements with reduced space between them (meaning the bone has become abnormally dense and compact), and significantly fewer living bone cells compared to healthy samples. Infection-related findings are common, and bacteria from the Actinomyces family appear frequently in removed bone specimens from both medication-related and radiation-induced ONJ.18Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology. Histologic analysis of medication-related osteonecrosis of the jaw compared with antiresorptive-exposed bone and other infectious, inflammatory, and necrotic jaw diseases These bacterial colonies form characteristic yellow granules called “sulfur granules” within the tissue, though this is a detail visible only under magnification.
The Historical Echo of “Phossy Jaw”
The appearance of modern ONJ has an eerie historical parallel. In the 19th century, workers in match factories who were exposed to white phosphorus developed a condition called “phossy jaw” that looked strikingly similar: nonhealing extraction sockets, exposed dead bone, sequestra separating from the jaw, and devastating facial disfigurement in advanced cases. Early comparisons between the two conditions noted that the clinical presentations of nonhealing sockets and bone sequestra are shared by both.19PubMed Central. A historical review of ‘phossy jaw’ The modern condition has even been nicknamed “bis-phossy jaw” by some researchers, referencing the bisphosphonate drugs most commonly associated with it.20PubMed. Bisphosphonate osteochemonecrosis (bis-phossy jaw): is this phossy jaw of the 21st century?
There is one important visual difference, though. Diffuse osteosclerosis, the widespread abnormal bone density seen on modern ONJ imaging, is characteristic of medication-related ONJ and was not associated with the phosphorus-induced version.19PubMed Central. A historical review of ‘phossy jaw’ This makes sense given the mechanism: bisphosphonates work by making bone resist breakdown, so the bone becomes excessively dense in a way that phosphorus poisoning, which killed bone cells through direct toxicity, did not produce. Despite their shared surface appearance, the two conditions leave different fingerprints on imaging, and recognizing that distinction matters for understanding what is happening beneath the visible wound.