The depressor anguli oris muscle is a facial muscle responsible for shaping the angle of your mouth downward and laterally. It connects to the platysma muscle, and innervated by its marginal mandibular branch of the facial nerve.
As we age, this muscle becomes weaker, which may restrict smiling. To strengthen it, here is an exercise to strengthen the DAO muscle.
Stretching
Depressor anguli oris is a buccolabial facial muscle that works to frown and pull the angle of the mouth downward, as well as contribute to depth and contour of nasolabial fold depth and contour. Neuromodulation often targets this muscle due to fusion with other treated muscles requiring injection; for this reason it’s essential to understand how to stretch this muscle correctly in order to maximize results from treatment.
For optimal stretching of this muscle, start by holding your head in a neutral position and placing your fingertips underneath your chin. Slowly move them in an arc above and beneath your chin until they reach the corner of your mouth – repeat this several times to relax this muscle and reduce its tension. Also try doing this exercise with eyes closed as this provides even further relaxation for all facial structures.
One way to stretch the depressor anguli oris (DAO) is to place your finger on the marionette line and ask your patient to smile, which will reveal co-contraction between DAO and the zygomatic major muscle, which could obstruct DAO function and limit smiles from happening. This technique can also be used to identify hyperactivity in DAO muscles as well as determine safe injection sites for botulinum toxin type A injections.
Depressor anguli oris (DAO), also known as depressor anguli oris muscle of buccolabial group, is a large superficial muscle of buccolabial group. It originates from oblique line and mental tubercle of mandible on its anterior aspect to form buccolabial group. Fibers from its muscles converge into a narrow fascicle that extends superiorly towards the angle of the mouth and then blends with other muscle insertions into lips. The DAO muscle has the shape of an inverted fan; its medial edge overlaps with that of the depressor labii inferioris muscle while its lateral border lies near to both risorius and zygomaticus major muscles. Its attachment is at the oral commissure and may interdigitate with the platysma muscle for further depressor action on this commissure. All three structures are under regulation by the mandibular branch of facial nerve.
Contracting
Depressor Anguli Oris Muscle (DAO) is a triangular muscle found lateral to the chin that serves to draw downward on the angle of mouth when expressing sadness or asking questions, as well as opening mouth. Multiple muscles of face work together in this movement including corrugator Supercilii Muscle and Procerus Muscle.
The DAO is supplied by facial nerve CN VII and receives its blood supply through inferior labial artery. With Bell’s palsy, however, the DAO may become paralyzed leading to co-contraction with zygomatic muscles which restrict smile. Neuromodulation techniques may help relax this area and restore freedom in smile.
Bell’s palsy, Ramsay Hunt syndrome, acoustic neuroma surgery or trauma are among several conditions which may cause facial paralysis in which facial muscles become paralyzed, leading to excess activity from depressor anguli oris (DAO) muscles that contract uncontrollably and lead to marionette area creases forming that cause DAO contraction and permanent contracture leading to facial frowning expressions and even facial asymmetry.
To identify whether a patient has an overactive depressor anguli oris muscle, place your finger just superior to the corner of their lower lip and slightly laterally. This area is where DAO muscles are most active. They should be able to drop and move the lower lip/corner of mouth laterally without encountering resistance; otherwise they could be overactive.
An effective way of assessing whether a depressor anguli oris muscle is overactive is by palpating it with both index finger and middle finger and asking your patient to open their mouth. When opening their mouth, palpating should cause the DAO muscle to contract while not making tight vertical movements that occur too often – otherwise the muscle would be classified as overactive and require treatment. Neuromodulation treatments like Botox or Xeomin may help relax this muscle by blocking neurotransmitters that tell it when to move – improving dynamic wrinkles while correcting asymmetrical smiling.
Remaining neutral
Depressor anguli oris muscle is one of the smallest muscles in the face and when overactive can create a sad, tired or angry appearance that makes smiling difficult for some patients. Neuromodulation offers hope in this situation by restoring natural smiles through neurostimulators.
The depressor anguli oris muscle attaches to the modiolus of the oral commissure, which serves as a fibrous hub between multiple muscles at the corner of the mouth. It is an integral component of buccolabial muscles and contributes to facial expression nuances and variations. Depressor anguli oris muscles exert downward forces while platysma pulls upward, depressing angle of mouth and impeding smile. Furthermore, its lateral border often co-contracts with zygomatic muscles for co-contraction that causes twisting.
Researchers conducted a study at an academic tertiary referral hospital that revealed how DAO could be inhibited with local anesthetic injection, measuring its effects on smile dynamics and perceived emotional state. Participants were divided into extraverted and introverted groups and their EMG responses were recorded after viewing images depicting pictures with positive, negative, neutral valence; results revealed that both major muscles increased with positive valence whereas depressor anguli oris activity decreased with negative ones.
This research suggests that the lateral margin of depressor anguli makes an excellent site for botulinum toxin type A injections, although its medial border may be difficult to identify due to overlapping with levator labii superioris muscle and m. risorius muscles. Therefore, to safely and efficiently administer botulinum toxin type A treatments it is vitally important to possess a thorough knowledge of its topography as well as any surrounding muscles to locate safest and most effective botulinum toxin type A injection sites.
Variations
Depressor Anguli Oris Muscle (LAT) is an essential facial muscle for expressing emotions such as sadness and anger, and also plays an integral role in smiling. Innervated by both marginal mandibular and buccal branches of Cranial Nerve VII, its attachment into the angle of mouth places it between lower lip and mandibular border with an extension lateral towards mental foramen; continuous with platysma muscle which serves to pull corner down for further expression; extend and deepen mentolabial Sulcus as well.
The modiolus muscle arises from the oblique line and mental tubercle of the mandible located on its anterior surface. Its fibers converge to form a narrow fasciculus that runs superiorly towards the angle of mouth where other muscles insert. At their point of intersection is known as the modiolus; one of the key defining features of facial anatomy, described by some as being either muscular or tendinous node located somewhere within cheek area.
Reports have surfaced of congenital hypoplasia of the left depressor anguli oris muscle in a newborn, leading to atypical crying facies, death, or disability in certain cases. As this rare condition requires close observation from physicians as well as possible special treatments, close monitoring may be required and possible special interventions.
Drooping nasal tips were once treated by manipulating the depressor anguli oris muscle; however, this procedure can lead to co-contraction of zygomatic muscles and block your smile. A simple lidocaine injection test can be conducted to identify where this muscle lies beneath.
The study involved 36 hemifaces from Korean adult cadavers. Results demonstrated that the median width of DAO’s periosteal insertion was less than that of pterygopalatine fossa, as well as being wider among males than other muscle examined. Additionally, its thicker and stronger periosteal insertion made up for any deficiencies observed elsewhere in this muscle group.
