Periodontal ligament on pulp-free root slices – an in vitro model for early tooth (re)integration. An exploratory...

Reintegration of freshly extracted healthy teeth is very successful, most likely due to the regenerative capacity of their roots’ residual periodontal ligament (PDL). We hypothesised that in vitro cultures of the consecutive slices of a sectioned root will represent the entity of PDL cell types engaged in tooth-sided reintegration. For confirmation, apex and pulp from human premolars were removed and roots cut into 6 to 9 about 1 mm thick slices. These were immobilised to separate wells and cultured for 20 days, under daily inspection for the initiation of cell outgrowth (ICO). ICO and the distribution of vital slices along, the cell growth around as well as the expansion of outgrown cells off the root axes after 20 days were displayed for each tooth as 3D-like profiles. Of the 81 slices from 11 teeth, 55 showed ICO; 64% within one week and 96% within two weeks. Such dynamics compare to the early (day 2–5) and the intermediate (day 9–14) integration phase reported for PDL cells in vivo. Experimental phase contrast images of a single slice showed at ICO few fibroblast- and stem/progenitor- like cells. Four and five days later at the same site cells had grown in number and changed in shape and space over time. This exploratory study indicates that in root slice cultures PDL cells behave similarly to those during reintegration in vivo. It favours our hypothesis, which is now to be adequately verified. Eventually, the model may facilitate the identification of outgrowing cells and cellular changes over time, as triggered by tissue rupture. It may further allow for emulating cellular interactions between the root surface and alveolar bone or engineered constructs, natural or engineered scaffolds, or other tissue, in an in vivo-like situation.