IRCT2013091012487N3 IRCT 2013-10-22 vice chancellor for research of Islamic Azad University Khorasgan Branch Comparison of two Cryotherapy techniques in gums color Comparison of gingival depigmentation by open and closed cryosurgery in an Iranian population: A clinical trial 2011-02-04 anticipated 32 Complete https://irct.ir/trial/12565 interventional Randomization: Randomized, Blinding: Single blinded, Placebo: Not used, Assignment: Parallel, Purpose: Treatment, Other design features: Randomization: Each patient was given a number from 1 to 16. The anterior sextant was divided into left and right segments from mid-line, after isolating of the location by cotton rolls, each segment was treated randomly by either swap technique or cryoprob, based on even or odd number of the patients. Blindness: All pre and postoperative photographs were traced and measured by another examiner who is expert in using photoshop software and was blind to the utilized technique in each segment. 3 Gingival Pigmentation. Intervention 1: Case2: Cryoprob model C505T, Danesh Company, Iran. The prob was applied to pigmented areas (4 mm in diameter) for 10-15 second. This procedure was repeated 4 or 5 times for each segment. Intervention 2: Case1: Liquid Nitrogen, Iran Liquid nitrogen100% ,Zeitun Company,Iran, was applied to pigmented areas by a cotton swab (4 mm in diameter) with a forward and backward rolling technique. This procedure was repeated 4 or 5 times for each area.