Spatial extent of gingival cell activation due to mechanical stimulation by toothbrushing

Background: Mechanical stimulation by toothbrushing enhances gingival fibroblast proliferation and collagen synthesis, and reduces inflammatory cell infiltration. The aim of this study was to investigate the spatial extent of proliferation of fibroblasts and endothelial cells in dog gingiva in response to mechanical stimulation by toothbrushing. Methods: All maxillary fourth premolars and mandibular first molars of 6 mongrel dogs were used. Dental plaque was removed with a curet. One of each pair of bilateral teeth (in the same jaw) was assigned to the brushing group, and the corresponding tooth (opposite side) was assigned to the control group. The Bass method was used to brush the limited mesial half of the tooth at 1.96 N for 20 seconds with a fitted plastic stent. Immediately before fixation of tissue, the surface of brushed gingiva was notched to indicate the borderline between the brushed and non-brushed areas. Histometrical analyses of the sections were performed using assays for proliferating cell nuclear antigen (PCNA) and von Willebrand factor. Results: The numbers of fibroblasts and PCNA-positive fibroblasts in the subepithelial connective tissue adjacent to oral sulcular epithelium significantly increased in brushed gingiva, not only in the brushed area but also in the non-brushed area 0 to 0.5 mm from the notch. Increased numbers of vascular endothelial cells were observed only in the brushed area. Conclusion: The effect of mechanical stimulation by toothbrushing on gingival cell proliferation was not observed more than 0.5 mm from the brushed area. These results indicate that effective activation of gingival cell proliferation requires mechanical stimulation of gingiva in all areas.