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| case report is lateral to the wing of the nose.3, 4, 8–10 After being injected into the predetermined locations, the toxin decreases the contraction of the muscles responsible for the elevation of the upper lip, and this reduces gingival exposure.3–11 Each muscle involved in the elevation of the upper lip has a function during the action of smiling. The points of the injections are determined by the contraction of spe- cific muscle groups that results in different areas of gin- gival display. Several classifications have been proposed for gummy smile: anterior, posterior, mixed and asym- metric, depending on the muscle groups involved.4, 10 The anterior gummy smile should be treated with the conventional technique, with the applications lateral to the wing of the nose. In patients with posterior gummy smile, the application of the toxin must involve the zygo- maticus major and minor muscles, with the injection of the toxin at two different points: the point of greatest con- traction of nasolabial folds during the action of smiling and the second point 2 cm lateral to the first, at the level of the ala-tragal line. In the case of patients who have mixed gummy smile, the application of the toxin should be performed at all the points mentioned above. How- ever, the dose should be reduced to 50% at the point lat- eral to the wing of the nose.5 In cases of labial asymme- try, which occurs owing to differences in muscle activity,4 patients receive injections of different doses on either side of the face.5, 10 Botulinum toxin A is a hydrophilic powder, stored under vacuum, that is sterile and stable.3, 6, 8 The reconstitu- tion occurs with the smooth injection of the diluent (0.9% sodium chloride) into the bottle. The solution should be stored at 2–8 °C and used within 4–8 hours in order to ensure its effectiveness.3, 9 At the beginning of the treatment, extra-oral photo- graphs, including a close-up of the smile, were taken. Several authors note the importance of recording the smile before and after the application of the toxin.6, 10, 11 It has been suggested that the photographing of the smile should be performed with the muscles individu- ally stimulated with electrical current in order to ensure that the muscle contraction is controlled, precise and repeatable, as a spontaneous smile is extremely difficult to replicate. Patients know that the treatment is carried out to produce a different smile, so from this perspective, unconsciously, there is a tendency to smile differently in photographs after the treatment.11 The injection of botulinum toxin, despite being a simple and safe procedure, may be associated with some adverse events, such as pain at the injection site, bruis- ing, infection, oedema, dysphonia, dysphagia, ptosis or lengthening of the upper lip and asymmetry of the smile. The dentist should be attentive to dosage, precision of technique and location of the injection sites.3, 5, 6, 9, 11 In this case, no complaints or changes arising from the application were reported. Contra-indications to the use of botulinum toxin are pregnancy, lactation, hypersen- sitivity(allergy) to botulinum toxin, lactose and albumin, muscle and neurodegenerative diseases (myasthenia gravis and Charcot-Marie-Tooth disease), and concur- rent use of aminoglycoside antibiotic, which enhances the action of the toxin.3, 9 In this case, the result was satisfactory regarding the harmony of the smile of the patient by the combination of treatments, resective gingival surgery and application of botulinum toxin A. The use of isolated treatments would not have achieved the excellence of the results obtained. Initially, the creation of the new dental zenith during the course of resective gingival surgery promoted the new dental architecture, favouring gingival-dental-facial har- mony for the patient. Subsequently, the application of botulinum toxin A softened the gummy smile, by the uni- form dehiscence of the upper lip, promoting smooth- ness of the facial lines of the smile, as can be seen in the nasolabial folds adjacent to the nostrils by compar- ing Figures 1 and 5. Conclusion In summary, the application of botulinum toxin is an alternative treatment that is less invasive, faster, safer and more effective, and it produces harmonious and pleas- ing results when applied to target muscles, respecting the appropriate dose and type of smile. Therefore, it is a useful adjunct in the aesthetic improvement of the smile and provides better results when combined with resec- tive gingival surgery. Editorial note: A list of references is available from the publisher. about Dr Irineu Gregnanin Pedron is a specialist in periodontics and im- plan tology. He is an independent researcher at the College of Dentistry of the University of São Paulo, Brazil, and Professor of Periodontology and Multidisciplinary Clinic at the College of Dentistry of the University Brasil, São Paulo, Brazil. He teaches botu- linum toxin course in Dentistry at Bottoxindent Institute, São Paulo, Brazil. He is the author of the book Toxina Botulínica: Aplicações em Odontologia (Editora Ponto, 2016; Portuguese). Pedron works in a private practice in São Paulo, Brazil. He can be contacted at igpedron@alumni.usp.br. 12 ortho 1 2018