Effect and longevity of botulinum toxin in the treatment of gummy smile: a meta-analysis and meta-regression

Objective: The aim of this systematic review is to synthesize the evidence on the effectiveness and longevity of the botulinum toxin in the treatment of individuals with excessive gingival exposure. Methods: The search was adapted to six electronic databases and gray literature. The risk of bias was assessed using the Cochrane Risk of Bias Assessment Tool for Non-Randomized and Randomized Studies of Interventions. Meta-analyses and meta-regression were performed using random effects models. Results: A total of 5247 articles were collected during the final search in the database, resulting in 17 articles included. There was a mean decrease of 3.42 mm [95% CI = −4.50 to −2.34; I2 = 97%] in the level of gingival exposure 2 weeks after the application of botulinum toxin. The application time explained 29.58% of the observed variance (p < 0.001), with a tendency for the effect size to decrease from the second week of application onwards, with values returning close to baseline levels in 24 weeks. Conclusion: Botulinum toxin is an alternative technique considered effective for reducing gummy smile, especially for gummy smiles up to 4 mm, with a longevity of at least 12 weeks, returning close to initial values within 24 weeks after application. Clinical relevance: The knowledge about the longevity and effectiveness of botulinum toxin in the treatment of gummy smile allows for a more adequate clinical planning for these cases, as well as for clinical decisions, as for prognostic factors.