Gingival reactions after experimentally induced extrusion of the upper incisors in monkeys

To evaluate the gingival movement with orthodontic tooth extrusion, the four upper incisors of monkeys were vertically extruded. The teeth were extruded (maximum 10.9 mm, minimum 2.6 mm) in five experimental subjects with three controls. The following parameters were measured before and after the experiments: (1) the movement of the free gingiva; (2) the movement of the mucogingival junction; (3) the clinical sulcus depth; and (4) the clinical crown height. The reaction of the gingival tissues attached to the extruded teeth was also examined histologically. The results were as follows: (1) The gingiva moved in the same direction in which the teeth were extruded. The free gingiva moved about 90% and the attached gingiva moved about 80% as far as the teeth were extruded. (2) The width of the attached gingiva on the labial surface increased as the teeth were extruded. (3) The sulcus depth decreased about 20% of the distance that the teeth were extruded; the clinical crown height was increased about 20%. (4) The mucogingival junction before the experiment was positioned the same after the experiment. (5) The epithelial attachment originated at the cementoenamel junction of the experimental teeth after the tooth extrusion. There was no gingival migration, gingival pocket formation, or inflammation on the labial surface. No clinical nor histologic problems were encountered in the gingival tissues if the teeth were extruded properly.