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; I 2 = 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.