Abstract
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 10min (time 0) and continuing up to 72h. 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 4h, with the highest amount recorded in serum up to 24h. 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.
Highlights
The dental pulp is frequently challenged by pathogens, which can result in pulpitis and, if left untreated, the infection can spread outside the pulpal compartment and promote apical periodontitis
Several recent studies have shown that lymphatic vessels are not found in the dental pulp or in the apical periodontal ligament [3,4,5,6], whereas gingiva is well supplied with lymphatic vessels [7]
When we extended the working length and opened the apical constriction, part of the applied 125I-HSA tracer left the canal through the apical foramen and was immediately distributed to the two posterior parts of the jaw (M2 + 3 and posterior tissue) within the mandibular canal
Summary
Lymphatic vessels drain excess protein-rich fluid from the interstitial space and transport immune cells for antigen presentation in regional lymph nodes. As uptake of fluid containing larger proteins rarely takes place in blood vessels, protein-rich fluid transport from the inflamed area must occur in lymphatic vessels. Several recent studies have shown that lymphatic vessels are not found in the dental pulp or in the apical periodontal ligament [3,4,5,6], whereas gingiva is well supplied with lymphatic vessels [7]. The questions we seek to answer here are how protein-rich fluid is transported from the apical area and where the lymphatics that drain excess fluid from the pulp and apical periodontal ligament are located. We aim to measure the washout rate of fluid from the apical area and test the hypothesis that drainage, at least in part, takes place via gingival lymphatics
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