Anat Cell Biol.  2023 Jun;56(2):161-165. 10.5115/acb.22.258.

Novel anatomical proposal for botulinum neurotoxin injection targeting depressor anguli oris for treating drooping mouth corner

• Yi KH
• Lee JH
• Hu HW
• Choi YJ
• Lee K
• Lee HJ
• Kim HJ

• KMID: 2544076
• DOI: http://doi.org/10.5115/acb.22.258

Abstract

The depressor anguli oris (DAO) muscle is a thin, superficial muscle located below the corner of the mouth. It is the target for botulinum neurotoxin (BoNT) injection therapy, aimed at treating drooping mouth corners. Hyperactivity of the DAO muscle can lead to a sad, tired, or angry appearance in some patients. However, it is difficult to inject BoNT into the DAO muscle because its medial border overlaps with the depressor labii inferioris and its lateral border is adjacent to the risorius, zygomaticus major, and platysma muscles. Moreover, a lack of knowledge of the anatomy of the DAO muscle and the properties of BoNT can lead to side effects, such as asymmetrical smiles. Anatomical-based injection sites were provided for the DAO muscle, and the proper injection technique was reviewed. We proposed optimal injection sites based on the external anatomical landmarks of the face. The aim of these guidelines is to standardize the procedure and maximize the effects of BoNT injections while minimizing adverse events, all by reducing the dose unit and injection points.

Keyword

Botulinum toxins; Depressor anguli oris; Drooping mouth corner; Dermotoxin; Anatomy

Figure

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  Fig. 1 Anatomical landmarks of soft tissue of the lower face.

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  Fig. 2 The dissected image of the lower face representing depressor levator inferioris (DLI) and depressor anguli oris (DAO). The DAO originates from the mental tubercle and converges to the narrow fasciculus, blends with the modiolus (M) and interlaces with the orbicularis oris.

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  Fig. 3 Injection points of botulinum neurotoxin for targeting depressor angulii oris muscle. The dotted line is drawn vertically at mid-pupil point, mid-pupillary line (MPL), and the transverse dotted line is drawn in middle of line crossing the cheilion and tragus and the mandibular border. The intersection point of dotted lines is injection point (orange colored dot) for the muscle with 2–3 U. This would be easily applied by placing index finger (15 mm width) for caucasions (A) and little finger (12 mm width) for Asians (B) along the lower margin of the mandible.

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  Fig. 4 The inferior labial artery runs beneath the depressor anguli oris muscle.

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  Fig. 5 Neural distribution of the face was revealed with whole mount staining method (Sihler’s method) with motor and sensory distribution. The enlarged panel with depressor anguli oris (yellow shaded) demonstrates neural distribution of the muscle. The nerve distribution seems to evenly dispersed in the muscle region.

Reference

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