Frontalis muscle:

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  Sole brow elevator and upper forehead depressor that originates from the galea aponeurotica and inserts into the superciliary ridge of the frontal bone.

Glabellar muscles:

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  Procerus: The muscle originates from the inferoanterior surface of the paired nasal bones and inserts into the skin of the nasal root.

  
  
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  Corrugator supercilii: They lie deep to the frontalis and procerus muscles. The oblique head originates at the superciliary arch, and the transverse head inserts into the skin right above the brow-lash line, which is approximated by a vertical extension from the medial corneoscleral limbus.

  
  
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  Depressor supercilii: This muscle immediately inferior and superficial to the corrugator is, by some, considered as a component of the orbicularis oculi complex and part of a functional group together with the corrugators, which also depress the medial/central brow. This muscle originates at the medial orbital rim and extends to the medial aspect of the bony orbit.

The upper face should be evaluated by a general assessment that considers deficiencies that might benefit by treatment from both a surgical, filler, and neuromodulator approach.

The temple should be flat or slightly convex, without any significant concavity, depression, or hollowing (see Chapter 53 Filler Finesse: Forehead).

The aesthetically desirable female eyebrow should be over the supraorbital margin with the medial aspect slightly lower than lateral aspect.

In the central aspect, the brow ideally peaks in a vertical line along the lateral limbus of the iris.

The upper eyelid should have fullness that follows the natural arc of the eyebrow and upper eyelid margin, and there should be no hooding.

The upper face should be assessed for volume loss in the temples and forehead, position of the eyebrow, and the presence of excess skin in the upper and lower eyelids.

Presence of static lines at rest and dynamic lines during animation should be evaluated in the forehead, glabella, lateral canthus, and eyebrows.

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  The frontalis muscle elevates the eyebrow and is the only elevator muscle in the upper face.

  
  
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  Contraction of the frontalis muscle leads to the development of horizontal forehead lines and can also act as a hairline depressor.

  
  
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  Frown lines may develop because of natural aging and ongoing contraction of the procerus, corrugator, and orbicularis oculi muscles.

  
  
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  Contraction of the procerus muscle lowers the medial aspect of the eyebrow and is the main contributor to the horizontal lines in this region.

  
  
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  Contraction of the corrugator muscle mostly draws down the medial aspect and can centralize the medial brow head of the eyebrow and is primarily responsible for vertical lines.

  
  
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  Repeated contraction of numerous facial muscles involved in smiling and squinting, notably the lateral orbicularis oculi muscles, leads to formation of lateral canthal lines, also known as crow’s feet lines. These lines start as dynamic only (not present at rest) and eventually become static (present at rest).

  
  
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  The orbital part of the lateral orbicularis oculi can affect the position of the eyebrows and primary functions for voluntary eyelid closure.

The neurotoxin agent is available in powder form and reconstitution is performed in 0.9% sterile saline. Most injectors prefer to use bacteriostatic saline to reduce injection discomfort but this is considered “off-label.”

Manufacturers recommend using the toxin within 4 hours of reconstitution and storing it at 2 to 8 °C. Experience indicates that the toxin maintains integrity and potency beyond this recommendation.

Individual preferences regarding reconstitution vary from 1 to 5 mL and were originally felt to have little effect on results, but this concept has been recently challenged and may vary in optimization depending on which neurotoxin is considered and which muscle groups are targeted. Injectors also have varied preferences on syringe and needle types, but most commonly use 1-mL syringes to allow for precise injection of volume with fine tip needles of 30 to 32 gauge.