How many muscles are involved in making a smile?

How Many Muscles Are Used to Make a Smile

A smile involves approximately 17 muscles, with the primary smile muscles being the zygomaticus major, zygomaticus minor, levator labii superioris, levator labii superioris alaeque nasi, and orbicularis oculi. While the face consists of a total of 30 different muscles divided across three muscle planes (superficial, middle, and deep) 1, not all of these are activated during smiling.

Primary Smile Muscles and Their Functions

The smile is produced by a coordinated action of several facial muscles, primarily:

1. Zygomaticus Major:

   • Primary muscle responsible for lifting the corners of the mouth upward and laterally
   • Has a line of pull at approximately 55.5° angle 2
   • Creates the characteristic upward curve of the smile

2. Zygomaticus Minor:

   • Present in only about 53% of people (found in 10 of 19 hemifaces in anatomical studies) 2
   • Has the most transverse line of pull at 31.6° 2
   • Elevates the upper lip

3. Levator Labii Superioris:

   • Elevates the upper lip
   • Has a nearly vertical orientation with an angle of 74.7° 2
   • Works in coordination with other elevators

4. Levator Labii Superioris Alaeque Nasi:

   • Elevates the upper lip and dilates the nostrils
   • Most vertical orientation at 79.0° 2
   • Contributes to the nasolabial fold appearance during smiling

5. Orbicularis Oculi:

   • Creates the characteristic "crow's feet" at the corners of the eyes
   • Significantly improves smile attractiveness 3
   • In about 22.7% of people, some fibers of this muscle connect directly or indirectly to the zygomaticus major 4

Additional Muscles Involved in Smiling

Other muscles that contribute to various types of smiles include:

• Risorius: Creates a more horizontal smile
• Buccinator: Controls the cheek during smiling
• Orbicularis Oris: The sphincter muscle around the mouth that modifies the smile
• Depressor Anguli Oris: Can be relaxed during smiling to allow upward movement
• Mentalis: Affects the chin appearance during some smiles

Smile Complexity and Muscle Coordination

Research shows that smile esthetics increase with increased recruitment of muscles involved in smile production 3. A smile that uses four labial muscles is rated significantly more attractive than a smile involving only the risorius muscle 3.

The quality of a smile is affected by:

1. Muscle Coordination: The synchronized activation of multiple facial muscles
2. Muscle Vector Direction: The various angles of pull create the characteristic smile shape
3. Neural Control: Complex neurological processes control the timing and intensity of muscle activation 5

Clinical Implications

Understanding smile anatomy has important clinical applications:

• In facial reanimation surgery, the mimetic muscle vector is quite vertical compared to traditional reconstruction approaches 2
• Botulinum toxin injections for "gummy smile" treatment target the convergence point of the three lip elevator muscles (LLS, LLSAN, and ZMi) at what has been termed the "Yonsei point" 6
• Smile training exercises can improve smile quality through neurologic and muscular training 5

The human smile is a complex coordinated activity that primarily involves 17 muscles working in harmony, with the zygomaticus major being the principal muscle that creates the characteristic upward curve of the smile corners.