Objectives: The aim was to investigate the efficacy of single injections of two different hyaluronic acid products, Flex Barrier and Revident, in reducing the size of black triangles to treat Nordland-Tarnow Class I and II recessions. Material and Methods:Forty adult patients were recruited with at least two upper and two lower interdental papilla defects in the front region between canine teeth. According to the Nordland-Tarnow classification of papillary defects, both Class I and Class II recessions were included in the investigation. Patients were randomly assigned to experimental groups to receive single injections of two different hyaluronic acid products, either Flex Barrier or Revident. The untreat-ed sites served as controls. Photographs were taken before and immediately after the treatment, and again after one week and one month. To determine the size of the black triangles, Image J software was used. For statistical analysis, a mixed-design ANOVA was applied. Results:Both Flex Barrier and Revident significantly decreased the size of the treated defects immediately after the treatment and also one week later (p<0.001). The beneficial effect of Revident lasted longer than Flex Barrier as it remained significant even after one month in Revident-treated patients, however, not in the Flex Barrier-treated group. Furthermore, Nordland-Tarnow Class I lesions generally showed a greater improve-ment than Class II lesions. Conclusion: In this proof-of-concept, randomized clinical trial we have demonstrated the clinical applicability of both Flex Barrier and Revident, although Revident gave longer-lasting improvements than Flex Barrier. Further trials are needed to optimize multiple-application protocols for treating gingival black triangles.