Tumors that grow teeth are called teratomas, and they can do this because they arise from cells that retain the ability to become any tissue in the human body. These pluripotent cells, most often found in the ovaries and testes, can differentiate into skin, bone, muscle, fat, hair, and yes, fully formed teeth. About 56% of mature teratomas contain teeth or other calcifications, making this phenomenon surprisingly common in a tumor type that accounts for the majority of ovarian growths.
How One Cell Builds an Entire Tooth
In the first few weeks of embryonic development, a process called gastrulation creates three foundational cell layers. The outer layer (ectoderm) eventually forms skin, hair, and tooth enamel. The middle layer (mesoderm) builds bone, muscle, and cartilage. The inner layer (endoderm) lines the gut and other organs. Every tissue in your body traces back to one of these three layers.
Teratomas grow from germ cells, the same cells that would normally become eggs or sperm. These germ cells are pluripotent, meaning they carry the blueprint to produce any cell type from all three layers. When something goes wrong and these cells begin dividing on their own, they don’t just multiply into a uniform mass the way most tumors do. Instead, they follow fragments of the body’s developmental program, producing a chaotic mix of tissues that can include hair follicles, fat, cartilage, bone, gut lining, thyroid tissue, and teeth. A single teratoma can contain anywhere from one to seven individual teeth, each with recognizable enamel and root structures.
Why Ovaries Are the Most Common Location
Ovarian dermoid cysts, which are mature teratomas, are the most common ovarian tumor. The ovary is packed with germ cells waiting to develop into eggs, so it makes sense that this is where pluripotent cells most frequently go rogue. These cysts can grow for years without symptoms, often discovered incidentally during imaging for something else. When doctors spot a mass with fat and toothlike calcifications on an X-ray or CT scan, that combination is essentially diagnostic for a mature teratoma.
Fat shows up in about 93% of these tumors on imaging, and teeth or other calcified structures appear in more than half. A standard abdominal X-ray can reveal them clearly: a large mass with distinct toothlike shapes visible in the pelvis. CT and MRI make the diagnosis even more straightforward because they’re highly sensitive to fat, which is almost always present.
Teratomas in Men and Children
Teratomas also occur in the testes, though less frequently. They account for roughly 3 to 7% of certain testicular cancers as a pure form, but appear in about half of mixed germ cell tumors. On the cut surface, testicular teratomas look strikingly heterogeneous: hairs, teeth, fat, cysts filled with waxy material, and solid chunks of cartilage or bone can all be visible to the naked eye.
The behavior of these tumors depends heavily on age. In children, testicular teratomas typically appear in the first two years of life and are generally indolent, with no potential to spread. In adults who develop them after puberty, the picture changes dramatically. Postpubertal testicular teratomas carry a metastasis rate of 22 to 37%, and pure mature teratomas in adults have been reported to spread in over 40% of cases. They’re also resistant to chemotherapy, which makes complete surgical removal critical.
Mature vs. Immature Teratomas
About 95% of all teratomas are the mature type, also called dermoid cysts. These contain fully differentiated, adult-looking tissues and are benign. The teeth inside them are recognizable as teeth. The hair looks like hair. The fat looks like fat. These tumors are typically slow-growing and can sit quietly in the body for years.
Immature teratomas are the malignant counterpart. They contain tissue that resembles what you’d see in an embryo rather than in a fully developed body. Despite being classified as malignant, their prognosis is generally good. Five-year survival rates range from about 98% for early-stage disease down to 72% for the most advanced cases, with an overall five-year survival around 90%. A rare variant called struma ovarii, making up about 3% of ovarian teratomas, consists almost entirely of thyroid tissue and can occasionally cause hyperthyroid symptoms.
What Removal Looks Like
Surgery is the standard treatment. For ovarian teratomas, laparoscopic (minimally invasive) surgery is considered the gold standard, offering less blood loss, shorter hospital stays, less pain, and fewer adhesions compared to open surgery. In younger women who want to preserve fertility, surgeons typically remove just the cyst while leaving the ovary intact. In other cases, removing the entire ovary is the standard approach.
One concern during surgery is spillage of the cyst’s contents into the abdominal cavity, which could theoretically cause a chemical irritation of the abdominal lining. In practice, this complication is extremely rare and can be managed with thorough rinsing during the procedure. For some small, asymptomatic teratomas, doctors may recommend monitoring with periodic imaging rather than immediate surgery.
Why Teeth Specifically
Of all the strange tissues teratomas produce, teeth get the most attention because they’re so visually jarring. But teeth aren’t actually unusual for these tumors. Enamel comes from the ectoderm, the same layer that produces skin and hair, both of which are extremely common in teratomas. The tooth’s inner structure, dentin and pulp, comes from cells that originate near the boundary between ectoderm and mesoderm. Since teratomas routinely produce tissues from all three germ layers, they have all the raw ingredients for tooth formation. The cells just need to end up in close enough proximity to trigger the signaling cascade that normally builds teeth in your jaw. When that happens inside a tumor, you get a fully formed tooth growing in someone’s pelvis, chest, or abdomen, complete with enamel, roots, and sometimes even the beginning of a socket-like bone structure around it.