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Eyebrows are maintained by the dynamic balance of frontalis, corrugator supercilii, and orbicularis oculi muscles, and various combinations of motor recruitment of these muscles determine the eyebrow position and shape. For youthful eyebrows, attenuation of the depressor muscle may restore the muscle balance in treatments for eyebrow rejuvenation.
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Yun et al. (2014) studied this question.
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