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A Simplified Approach to Botulinum Toxin Injection for the Lower Face: Concept of a 24-Hour Clock

Kim, Nam Ho M.D.; Ahn, Tae Joo M.D.; Park, Ro Hyuk M.D.; Kim, Kyun Tae M.D.; Lee, Edward Ilho M.D.

Plastic and Reconstructive Surgery: March 2017 - Volume 139 - Issue 3 - p 816e–818e
doi: 10.1097/PRS.0000000000003080

Gyalumhan Plastic Surgery, Seoul, Republic of Korea

Edward I. Lee Plastic Surgery, Houston, Texas

Correspondence to Dr. Nan Ho Kim, Gyalumhan Plastic Surgery, 21st Mijin Plaza, 390 Gangnam-daero, Gangnam-gu, Seoul 06232, Republic of Korea,

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Clinically, the purpose of botulinum toxin injection in the lower face is for smile enhancement. A well-balanced face should appear aesthetically pleasing in repose and in animation. Although the standard injection points used by most clinicians today can provide for satisfactory facial rejuvenation without a steep learning curve, this generalized approach, without respecting the balanced nature of the muscles of facial expression, can have untoward consequences. It is to this end that we believe our conceptualization of a 24-hour clock can help facilitate botulinum toxin injection and improve outcome.

Traditionally, the face is divided into upper, middle, and lower third subunits, which is useful for both description and treatment planning.1 However, we believe that dividing the face into upper and lower subunits centered around two facial expression centers is more useful for botulinum toxin treatment. Specifically, the concept of a 24-hour clock can be applied to treatment of the lower face. The vector of muscle pull on the lower face is circumferential in nature, diverging around the unpaired orbicularis oris muscle (Fig. 1). The 24 paired periorbital muscles (12 on each side) expand out from the orbicularis oris like a 24-hour clock. If one can imagine a 24-hour clock superimposed over the mouth, it becomes readily apparent which muscle groups are at play and which need to be treated to achieve the desired outcome. For example, if the 24-o’clock direction is dominant, one can expect an incisoral show (incisor smile). In contrast, if the muscles in the 21-, 22-, and 23-o’clock (and/or 1-, 2-, and 3-o’clock) direction are dominant, one can expect a canine show (canine smile).

Fig. 1

Fig. 1

Although globally described as “gummy smile,” we believe that there are numerous smile patterns depending on the location of the excessive gingival show (Table 1). In total, there are 11 types of smile patterns using the 24-hour clock concept. Table 1 lists these smile patterns along with their associated muscles and the recommended treatment location and dosage. With selective chemodenervation, one can expect to achieve more precise changes to facial expression to desired effect, even in asymmetric cases (Fig. 2).

Table 1

Table 1

Fig. 2

Fig. 2

Although a number authors have published articles suggesting the need to target specific periorbital muscles for desired effect, there remains a great variability in the injection type, location, and dosage.2–4 Moreover, there can be significant variability in muscle anatomy between individuals.5,6 As such, we do not believe that it is critical to target a specific muscle, especially given the diffusion radius of the toxin; rather, the injection should be aimed at restoring balance along the 24-hour clock. For example, if a patient presents with left Mona Lisa (zygomatic) smile because of overactive levator anguli oris and zygomaticus minor, injections are given along the 4- and 5-o’clock positions rather than aiming for the specific muscles (Table 1). Since 2006, the senior author of this article has successfully used the 24-hour clock concept to achieve favorable and predictable outcome in botulinum toxin injection to the lower face and minimize complications.

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None of the authors has a financial interest to declare in relation to the content of this article.

Nam Ho Kim, M.D.

Tae Joo Ahn, M.D.

Ro Hyuk Park, M.D.

Kyun Tae Kim, M.D.

Gyalumhan Plastic Surgery

Seoul, Republic of Korea

Edward Ilho Lee, M.D.

Edward I. Lee Plastic Surgery

Houston, Texas

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1. Janis JE, Rohrich RJThorne CHRhinoplasty.In: Grabb & Smith’s Plastic Surgery20076th edPhiladelphiaLippincott517–532
2. Sucupira E, Abramovitz AA simplified method for smile enhancement: Botulinum toxin injection for gummy smile.Plast Reconstr Surg2012130726–728
3. Suber JS, Dinh TP, Prince MD, Smith PDOnabotulinumtoxinA for the treatment of a “gummy smile”.Aesthet Surg J201434432–437
4. Hwang WS, Hur MS, Hu KS, et alSurface anatomy of the lip elevator muscles for the treatment of gummy smile using botulinum toxin.Angle Orthod20097970–77
5. Kane MAThe effect of botulinum toxin injections on the nasolabial fold.Plast Reconstr Surg200311266S–72S
6. Pessa JE, Zadoo VP, Adrian EK Jr, Yuan CH, Aydelotte J, Garza JRVariability of the midfacial muscles: Analysis of 50 hemifacial cadaver dissections.Plast Reconstr Surg19981021888–1893
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