Mechanical stretching increases the number of epithelial cells synthesizing DNA in culture.

The influence of mechanical stretching on epithelial (E) cells was examined by culturing E cells derived from the epithelial cell rests of Malassez on a flexible plastic substrate and stretching the substrate by means of an orthodontic screw. A significant increase in the number of E cells synthesizing DNA was observed after just 30 min of stretching. In 17 experiments the ratio of cells labelled with tritiated thymidine in cultures stretched for 2 h to the number of labelled cells in unstretched controls was 1.92 +/- 0.34. An increase in labelling as a result of stretching was found for E cells cultured at either high or low cell-population densities but the effect was most pronounced for E cells cultured at higher concentrations of foetal bovine serum. Morphometric analysis of electron micrographs of stretched and unstretched cultures indicated that the stretched cultures had a higher volume fraction of filamentous structures and more desmosomes per unit length of cell membrane than unstretched cultures. The behaviour of E cells in response to stretching in vitro appears to be similar to the response of the epithelial rests in vivo when the latter are exposed to tension as a result of forces produced by orthodontic techniques.