Rat calvaria cells (RC cells) and monkey periodontal ligament fibroblasts (MPL cells) were cultured for 4–6 days with demineralized dentine, acid-washed glass particles or untreated glass particles to determine whether the presence of these particles can affect the orientation of the cells. Encapsulation of dentine particles began as early as the first day in culture and occasional cells were attached to, and oriented between adjacent particles. Multilayers of cells formed along the periphery of the dentine particles and the more superficial of these cells projected outwards in a radial fashion. Oriented cell sheets were evident between dentine particles after 3 days in culture. Finally, the cell sheets tore away from the surface of the culture fish to give rise to thick multilayered cellular bridges between dentine particles. The nuclear orientation index (ratio of L/W) for each RC cell lying between 15 randomly selected pairs of each particle type in 4-day cultures was measured along 2 axes; the length represented by the shortest distance between the 2 particles and the width perpendicular to this axis. The nuclear orientation index was 1.52 for cells between dentine, 1.13 between acid-washed glass and 1.06 between untreated glass. Control measurements of cells associated with single particles were 1.06, 1.09 and 1.06 respectively. The frequency of cellular orientation occurring between dentine particles was significantly greater than that occurring between acid-washed glass particles (chi 2 > 0.001) which in turn was significantly greater than that for untreated glass particles (chi 2 > 0.001). The observations and results suggest that the development and maintenance of the observed cell orientation depends upon development and maintenance in the cell sheet of tensional forces oriented parallel to the axis between the dentine particles, and that this is related directly to the capacity of the cells to attach to the particles.

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