[Three-dimensional model analysis of the gingival sulcus width from different retraction time]

To explore the effect of gingival retraction time on the gingival sulcus width in different gingival areas, using three-dimensional (3D) model analysis.

Forty-six premolars from 10 volunteers were included, gingival retraction cords were applied on the buccal sulcus for three times, and the retraction time was 5, 10 and 15 minutes respectively. The least interval between two retraction procedures was 2 weeks. Impressions and stone models were made before and after gingival retraction. 3D data of the models were acquired by a 3D line laser scanner. Models were superimposed and tooth coordinate was set up with special software. Sulcus widths from different retraction time and different gingival areas were measured and compared.

Sulcus widths between retraction of 5 and 10 minutes were significantly different at midbuccal and transitional line angle (TLA) gingival areas. At TLA areas, sulcus widths between retraction of 10 and 15 minutes were also statistically different, but the difference was not significant when compared with that of 5 and 10 minutes. Sulcus widths at midbuccal areas were significantly greater than that at TLA areas for all three retraction time.

Before making impressions, gingival retraction time of single-cord mechanical technique should be at least 10 minutes. For different gingival areas, the enlargement of gingival sulcus from gingival retraction and the optimal retraction time were different. 3D model analysis could be used as a new objective method to evaluate gingival retraction effect from different retraction time.