comparison of recurrent rate of gingival pigmentation after treatment by liquid nitrogen and cryoprob in 18 months follows-up

background: cryosurgery is one of the simplest, most effective gingival depigmentation methods. repigmentation may happen after a while in each method. the aim of this study is to compare the recurrence rate after treatment by liquid nitrogen swap and a cryoprob in 18 months. materials and methods: a total of 26 patients with physiologic gingival pigmentation were selected. the anterior sextant was divided into left and right segments; each segment was treated randomly by swap technique or cryoprob. standard photos were evaluated with photoshop software (red, green, blue, cyan, magenta, yellow, black [rgb, cmyk]) before and at 2 week, 1, 3, 6, 9, 12, 15, 18 months after the treatment. the results were compared, by the independent t-test and repeated measure anova thereafter least signifi cant difference post-hoc. the viewpoints of patients and physicians regarding the treatment outcomes were obtained by a questionnaire and consequently evaluated qualitatively by mcnemar test (p < 0.05 was considered as signifi cant level). results: the statistical analysis showed a signifi cant difference in color change after the treatment during 18 months, in each group (p < 0.001). the mean values of rgb had signifi cantly increased after 2 weeks in both methods (p < 0.001), but the differences from 2 weeks to 18 months after treatment were not signifi cant (p > 0.05). the mean values of cmyk signifi cantly decreased after 2 weeks in both methods (p < 0.001), but the differences from 2 weeks to 18 months after treatment were not signifi cant (p > 0.05). qualitative evaluation showed the preference of the cryosurgery with swap method (p < 0.001). no signifi cant recurrence was observed during 18 months follow-up. conclusion: both methods of cryosurgery are appropriate in treatment of gingival depigmentation because no signifi cant recurrence was observed during 18 months follow-up. key words: cryosurgery, gingiva, nitrogen, nitrous oxide, pigmentation