Lymphatic Transport Route From the Dental Pulp

Objectives: The lymphatic vessels are important for drainage of protein-rich interstitial fluid and for transport of immune cells to the draining lymph nodes. The existence of lymphatic vessels in the pulp has long been debated, but new evidence shows that the dental pulp and the apical area lack lymphatic vessels. After pulpitis, a normal fluid balance can be re-established and immune cells travel from the pulp to local lymph nodes for antigen presentation. The objective was to investigate the transport route of protein-rich fluid from the apical area of molars toward the cervical draining lymph nodes and identify lymphatic vessels in the jaws.
Methods: Lower 1. molars in rats were exposed and the pulps removed with files (S1, Protaper). The pulp chambers were filled with 3-5 µl ¹²⁵I labelled human serum albumin and sealed with Cavit. The rats were kept awake for 4, 6, 8 or 24 hours and the jaws, lymph nodes and blood samples were collected. The jaws were separated in parts: 1. molar, 2+3.molar and the posterior part of ramus including the foramen mandibularis. All samples were counted in a γ-counter.
Jaws from separate rats were sectioned and immunoreacted with podoplanin antibody.
Results: After 4, 6 and 8 hours, a substantial part of the radioactive tracer was located in the 2. + 3. molar and the posterior part of the jaw. At 8 hours an increase in tracer was found in the lymph nodes, but a decline was found after 24 hours parallel with an increase in plasma. Podoplanin⁺ lymph vessels were found in the mandibular canal close to nerve bundles and blood vessels.
Conclusions: The transport route for protein-rich fluid from the apical area is within the mandibular canal where it is taken up by lymphatic vessels and transported to the lymph nodes.