title: Comparison of recurrent rate of gingival pigmentation after treatment by liquid nitrogen and cryoprob in 18 months follows-up.
abstract: 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.
  
  
  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 significant 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 significant level).
  
  
  RESULTS
  The statistical analysis showed a significant difference in color change after the treatment during 18 months, in each group (P < 0.001). The mean values of RGB had significantly increased after 2 weeks in both methods (P < 0.001), but the differences from 2 weeks to 18 months after treatment were not significant (P > 0.05). The mean values of CMYK significantly decreased after 2 weeks in both methods (P < 0.001), but the differences from 2 weeks to 18 months after treatment were not significant (P > 0.05). Qualitative evaluation showed the preference of the cryosurgery with swap method (P < 0.001). No significant recurrence was observed during 18 months follow-up.
  
  
  CONCLUSIONS
  Both methods of cryosurgery are appropriate in treatment of gingival depigmentation because no significant recurrence was observed during 18 months follow-up.
authors.affiliation: Department of Periodontology, Dental School, Khorasgan (Isfahan) Branch, Islamic Azad University, Isfahan, Iran.
authors.forename: Shirin Amini
authors.initials: SA
authors.lastname: Sedeh
authors.affiliation: Department of Community Dentistry, Dental School, Khorasgan (Isfahan) Branch, Islamic Azad University, Isfahan, Iran.
authors.forename: Saba
authors.initials: S
authors.lastname: Badihi
authors.affiliation: Department of Periodontology, Dental School, Khorasgan (Isfahan) Branch, Islamic Azad University, Isfahan, Iran.
authors.forename: Vahid
authors.initials: V
authors.lastname: Esfahaniyan
keywords: Cryosurgery; gingiva; nitrogen; nitrous oxide; pigmentation