Answer: Dental papilla

Histology: At low power, the tissue has a triangular shape with a smooth rounded surface. The surface is only focally lined by a single layer of epithelial cells, but these cells are highly degenerated. The tissue is primarily composed of spindled to stellate cells that are evenly dispersed in a fibromyxoid stroma.

Discussion: The dental papilla may become separated from the corresponding developing tooth during surgery and may be included with a surgical specimen separate from any formed tooth elements. Like odontogenic myxomas, the dental papilla is characterized by the presence of bipolar and stellate stromal cells set in a loose and slightly fibrous myxoid stroma. Due to this significant morphologic overlap, the myxomatous dental papilla is very frequently misdiagnosed as an odontogenic myxomas.

There are a few features that can be helpful in recognizing the myxomatous dental papilla and distinguishing it from odontogenic myxomas. First, the dental papilla is a triangular structure with a smooth rounded border. It lacks the ill-defined and infiltrative borders the shapeless odontogenic myxoma. Second, the dental papilla is often lined a layer of reduced enamel epithelium. Because this epithelium is in the state of degeneration prior to tooth rupture, it may be a very focal finding. A third clinical clue is that most dental papilla are associated with impacted 3rd molars.