Higher Doses of Botulinum Toxin in the Treatment of Gummy Smile

The smile is one of the universal facial expressions of humans. Gingival smile is characterized by gingival exposure of >3 mm upon smiling. The degree of gingival exposure can vary substantially between patients, with patients presenting gingival exposure of up to more than 10 mm. The prevalence of gingival smile is 10.57%, and it is more frequently observed in females. Although gingival smile is merely an anatomical variation, it can be considered unattractive, causing significant distress and impacting one's quality of life. Moreover, most orthodontists and dentists regard gingival smile as an important risk factor for dental treatment.

Gingival smile involves a complex interaction between the facial muscles, bone, and skin; specifically, it is related to hypermobility of the upper lip with muscle involvement and alterations in anatomical features, such as a short clinical dental crown, anterior dentoalveolar extrusion, maxillary excess, and a short upper lip. Therapies for gingival smile range from botulinum toxin injections to surgical interventions according to its etiology. Although the outcomes of surgical procedures are long-lasting, botulinum toxin type A treatment is an easy and fast outpatient procedure that requires no downtime and has high efficacy rates. Nevertheless, there are controversies around the optimal dose and injection site of botulinum toxin type A. Moreover, the efficiency of botulinum toxin type A for gingival smile varies markedly between studies, with the improvement rate of gingival exposure ranging from 62.06% to 98%. Sucupira and Abramovitz advocate the use of a low amount of botulinum toxin type A of 1.95 U per side for the treatment of gingival smile. They noted an average satisfaction level of 9.75 on a 10-point scale with this approach. They claimed that higher doses does not provide further benefit, and, in fact, could lead to lip ptosis, asymmetry, and excessive upper lip length. However, Polo disagreed with their argument, claiming 2-5 U injection of botulinum toxin type A according to the severity of gingival smile. In this regard, Garcia and Fulton showed that low-dose injection of botulinum toxin per muscle (2-5 IU) was as effective as higher doses. Though prior studies have demonstrated a correlation between higher doses of botulinum toxin and intensity and duration of muscle paralyses, no conclusion can be drawn regarding duration and intensity of doses used in the recent studies. A safe approach advocated by some authors consists of starting with low toxin doses initially, with retouching at a later stage if required. In this study, the investigators compared botulinum toxin type A efficiency using the average-dose method (2-5 U botulinum toxin type A per side determined according to the severity of anterior gingival smile) and , the higher-dose method (3-10 U botulinum toxin type A per side determined according to the severity of anterior gingival smile). The investigators aimed to assess the efficiency and duration of these approaches, as well as side effects and patients' satisfaction with treatment.

Inclusion criteria

• ≥ 3.0-mm anterior gingival exposure upon unrestricted, "full-blown" smiling
• healthy adults

Exclusion criteria

• contraindication of BTX-A
• previous diseases or treatments affecting the position of the gingiva or upper lips
• history of BTX-A injections to the head or neck region
• facial paralysis
• having received and/or receiving active orthodontic treatment that includes vertical dimension treatment, such as extrusion and intrusion, and presence of
• periodontal disease
• subject's refusal to participate