Gummy smile has traditionally been treated with invasive or demanding surgical and orthodontic techniques. Several studies have shown that targeted injection of the upper lip elevator muscles with botulinum toxin is an effective treatment for this condition. However, no standardized injection protocol with reproducible results has yet been published. A systematic review of the literature has been performed using Medline, Scopus, and Embase. All articles relevant to the research question were analyzed. After removing duplicates, 162 articles were selected, of which 9 were included in the analysis after applying exclusion and inclusion criteria, for a total of 269 patients. Onabotulinum toxin type A (ONA-BoNTA) was used in 7 studies and abobotulinum toxin type A (ABO- BoNTA) in 2 studies, at various dilutions. The number of sites injected varied from 1 to 3 per side, with variable targeting of the Levator labii superioris alaeque nasalis, Levator labii superioris, Zygomaticus minor, Zygomaticus major and Orbicularis oris. The dose used per side varied from 1.25 to 6 U of ONA-BoNTA and from 2.5 to 7.5 U of ABO- BoNTA. The injection protocol was tailored to the type of gingival smile in one study only, another study compared results of targeting two different muscles, and one study evaluated different dosages of toxin for the same injection site. The average improvement ranged from 24.85% to 99.65% and the effect persisted from 12 to 36 weeks. Very good patient satisfaction was reported in 6 studies. Fourteen adverse events were reported, all of them mild and transient. The treatment of gummy smile by botulinum toxin injection is effective, safe, rapid, minimally invasive and reversible. Protocols vary widely in the literature and no standardized procedure emerges. A patient-specific approach, adapted to their anatomy, type of gummy smile and the severity of the exposure seems to be the most appropriate. Randomized controlled studies are needed to make this approach more systematic.
Keywords: Botulinum toxin; Excessive gingival display; Gingival exposure; Gummy smile; Hyperfunctional lip elevator; Smile esthetics.
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