Proliferative response of cells of the dentogingival junction to mechanical stimulation

The aim of this research was to study the proliferative response of junctional epithelium (JE) and gingival connective tissue (GCT) to mechanical stimulation in vivo with regard to the potential occurrence of apical migration of JE and loss of GCT attachment during orthodontic tooth movement. Elastic bands were inserted between the maxillary first and second molars of male rats aged 8 weeks, which were pulse-labelled with 3H-thymidine and subsequently killed in groups, together with labelled control animals (a total of 98 rats) after periods of 1-168 hours. Autoradiographs were prepared from plastic mesiodistal sections, and parameters of cell proliferation for JE and GCT of the papilla between the second and third molars were determined. Although the distance between the apical limit of JE and the most coronal periodontal ligament (PDL) fibres decreased on the pressure and increased on the tension sides of mechanically stimulated animals, the total cross-sectional area of JE remained unchanged compared with controls. In the basal and suprabasal layers of JE, cell proliferation was reduced on the pressure side and showed no change on the tension side. In the apical JE compartments on both sides, mechanical stressing resulted in lower proliferative activity. Cell proliferation in GCT adjacent to JE in stimulated animals did not differ from the corresponding controls. JE rapidly adapted to mechanical stimulation by means of differential local adjustments of cell proliferation without an occurrence of apical migration or hyperplasia. GCT cells in the vicinity of JE maintained their steady-state proliferative activity. These results do not support the concept that orthodontic tooth movement might per se have detrimental effects on the stability of the dentogingival junction.