Collagen IV and MMP-9 expression in hypertrophic gingiva during orthodontic treatment.

Introduction: In the present study, we aimed to assess MMP-9 and type IV collagen in the gingival tissue in patients with gingival overgrowth (GO) after orthodontic treatment, with or without clinical signs of inflammation to appreciate the role of balance between those two markers in the onset of GO during tooth movement. Materials: Gingival tissue was harvested from 45 patients divided in three groups: 15 patients with orthodontic appliance that developed GO on at least two teeth; 15 patients with chronic gingivitis with GO; 15 patients (control group) with healthy periodontal tissues, without clinical gingival changes, in whom the first premolar was planned for extraction for orthodontic purposes (canine distalization). Methods: The tissue samples obtained by gingivectomy were fixed in 10% neutral formalin solution for 48 hours and then included in paraffin with the usual technique. The histologic examination was performed using classic Hematoxylin–Eosin technique. Double immunofluorescence was performed for anti-MMP-9 and anti-collagen IV antibodies. Results: MMP-9 / collagen IV double stainings showed an increase of fibrosis and inflammation in different degrees. Conclusions: The mechanical stress induced by the orthodontic devices, might be the key players in driving both the inflammation and the fibrotic reaction.