Interstitial fluid drainage from rat apical area takes place via vessels in the mandibular canal

Abstract

Interstitial fluid drainage from rat apical area takes place via vessels in the mandibular canal Virtej A, Tenstad O, Wiig H, Berggreen E. Interstitial fluid drainage from rat apical area takes place via vessels in the mandibular canal. Eur J Oral Sci 2020; 128: 190-195.We sought to investigate the transport route for protein-rich fluid from the apical area towards the draining lymph nodes. The first mandibular molar root canals in 24 female Wistar rats were instrumented and filled with radioactive-labelled human serum albumin. The rats were sacrificed at different intervals beginning after 10 min (time 0) and continuing up to 72 h. Three jaw segments, gingiva around the first molar, blood samples, submandibular and cervical lymph nodes were collected and analyzed for radioactivity. The starting volume of tracer (control) for all experiments was calculated from measurements at time 0. At time 0, radioactivity was only detected in the jaw segments. Within lymph nodes and serum, the tracer was found after 4 h, with the highest amount recorded in serum up to 24 h. Lymphatics were found within the mandibular canal along blood vessels and nerves and exiting via foramen mandibularis, after immunohistochemical staining in four untreated rats. Our results show tracer distribution from the apical area towards the mandibular canal in a posterior direction. The tracer washout rate was low, and the fluid was mainly absorbed into blood vessels. The lymphatics in the mandibular canal may be more important for immune cell transport than for fluid drainage.

Fluid transport from the dental pulp revisited

“…Lymphatic vessels were also found in the bone just below the apical periodontal ligament of molars (Fig. 2) and above the molar roots in the rat upper jaw (20).…”

“…Another remaining question is where the uptake of macromolecules from the pulp into the lymph takes place. We have recently shown that there are no lymphatic vessels in human granuloma tissue or in rat apical periodontal ligament (19, 20). We know that patients with acute apical periodontitis can develop lymphadenitis, meaning that the infectious material is spread via the lymph to the draining lymph nodes.…”

“…However, the afferent lymphatic vessels that were responsible for the transport were not localized. We have recently demonstrated lymphatic vessels in close proximity to blood vessels and nerves in canalis mandibularis in rats (20). Lymphatic vessels were also found in the bone just below the apical periodontal ligament of molars (Fig.…”

“…Podoplanin + lymphatic vessel localized below the apical periodontal ligament (PDL) in the mandibular canal (arrow) in a rat jaw (partly modified from (20)). [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…Furthermore, injection of a depot of radioactive tracer bound to the plasma protein human albumin into the rat pulp chamber, after the tissue removal and apical foramen widening, resulted in an immediate transport of tracer within the whole mandibular canal (20), which is most likely due to a high hydraulic conductivity within this loose connective tissue. No tracer was found in gingiva surrounding the rat molar.…”