Effects of Dose and Injection Site for Gummy Smile Treatment With Botulinum Type A: A Prospective Study

The smile is one of universal facial expressions of the humans. Gingival smile (GS) or gummy smile defined as any exposure of the gingiva >2 or 3 mm upon smiling, and can substantially vary from patient to patient, with patients presenting gummy exposures of up to more than 10 mm. The prevalence of GS is 10.57%, and it is more frequently seen in women. Although only an anatomical variation, it can be considered unattractive and cause significant distress and impact on one's quality of life. Moreover, most orthodontists and dentists regard GS as an important risk factors for dental treatment.

GS involves a complex interaction of facial muscles, bones and skin, specifically, it is related to the hypermobile upper lip (HUL) by the involved muscles and alterations in anatomical features such as short clinical dental crown, anterior dentoalveolar extrusion, maxillary excess and short upper lip. Therapies for GS range from botulinum toxin injections to surgical interventions according to its etiology. Whereas the outcomes of surgical procedures are long-lasting, botulinum toxin type A (BTX-A) treatment is an easy and fast outpatient procedure, requiring no downtime and with high efficacy rates. Nevertheless, there are controversies on the dosage and injection sites of BTX-A, and the efficiency of BTX-A for GS treatment shows great variation in different studies, with the improvement rate of gingival exposure (GE) ranging from 62.06% to 98%, Sucupira and Abramovitz advocate the use of an average amount of BTX-A of 2 U at bilateral levator labii superioris alaeque nasi muscles(LLSAN) for the treatment of GS, and an average satisfaction level of 9.75 on a 10-point scale was noted in their study. In their article, use of larger dosages and additional injection sites is discouraged: "Other target muscles described in the literature do not give any additional benefit to this application and could easily lead to lip ptosis, inferior lip protrusion, asymmetry, or excessive lengthening of the upper lip." Polo disagreed their argument. They believe that dosage and injection sites of BTX-A need to be individualized according to the degree of severity presented. However, no clinical study compared and verified their divergence, and the highly personal experience and uncertainty still limit the use of BTX-A for GS treatment. Some authors are of the opinion that injection with BTX-A is a safe and cosmetically effective treatment for GS only when performed by experienced practitioners. Other studies preferred to initiate the treatment with average-dose BTX-A injection to single sites initially, with retouching at a later stage, as and when required. Based on the lack of studies at the stage of creating the hypothesis for this study, the investigators compared the efficiency using the simplified method use of 2U BTX-A of at bilateral LLSAN and the individualized injection of dosage and injection sites according to the severity of anterior GS presented in patients, and also to assess safety and patients' satisfaction with the treatment.