【Objective】 To choose the best retraction material with biocompatibility for the clinic by evaluating the gingival inflammation related to different retraction materials. 【Methods】 A total of 50 maxillary premolars of 25 students were divided into five groups according to the randomized block design. Group A was ferric sulfate group, group B was epinephrine hydrochloride group, group C was Oxymetazoline hydrochloride group, group D was normal saline control group and group E was paste-like material(Expasyl)...