Ameloblastoma

Excerpt

The word ameloblastoma derives from the early English word “amel,” meaning enamel and the Greek word “blastos,” meaning germ. They are rare, odontogenic tumors, thought to be composed of the epithelium of ectodermal origin, which means they are tumors arising from the cells around the tooth root, or in close approximation, derived from the ectoderm germ layer. Ameloblastomas represent about 1% of all jaw tumors, but they are the second-most common odontogenic tumor. They are much more common in the lower jaw than in the upper jaw, and more common in the posterior mandible as compared to the anterior. The vast majority of the time, they are a benign tumor with aggressive behavior; however, rarely they can develop into, or be associated with, a malignancy (malignant ameloblastoma or ameloblastic carcinoma). It is extremely rare to find ameloblastomas outside the maxilla and mandible due to the association with teeth and their structures.

Anatomy: There are 20 deciduous teeth (“baby teeth”) and 32 permanent teeth (generally depending on third molar development or wisdom teeth) that start to appear in the mouth around 6 years of age. The last four permanent teeth to erupt are third molars or "wisdom teeth," each of which may or may not grow in. Among deciduous teeth, ten usually are found in the maxilla (upper jaw), and ten are in the mandible (lower jaw). For permanent teeth, 16 are in the maxilla, and 16 are in the mandible.

There are specific anatomic landmarks unique to each type of tooth which define them as incisors, molars, canines, etc. The anatomy of the tooth itself consists of the root which is hidden in the gums, and the crown, or visible part. The root of the tooth is anchored to the bone to which it is associated and allows for blood flow and nerve supply to the tooth to maintain viability. This system of ligamentous attachment connecting the tooth to the surrounding socket is called the periodontium. The hard tissue covering the crown is the enamel. The root is covered by cementum, a substance that is a hardy mineral but softer than enamel.

Natural History: The vast majority of ameloblastomas are benign and slow-growing, with locally aggressive behavior, which can lead to significant pathology and require extensive surgical treatment. The abnormal cell growth easily infiltrates local tissue, typically bone. Surgical excision is usually needed to treat this disorder. It has a high propensity for local recurrence even with proper surgical management and requires lifelong follow up for surveillance.

Patterns of spread: Amelomlastomas spread locally, invading surrounding tissues. They spread through bone and can invade soft tissues as well if given enough time to do so. However, this is a benign tumor so metastasis to lymph nodes, distant sites, etc., is rare and changes the staging to malignant. The thinking is that malignant ameloblastomas comprise less than 1% of all ameloblastomas.