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Orbicularis Oris
Orbicularis oris is a complex circular muscle that surrounds the orifice of the mouth and forms the majority of the lips. It belongs to a large group of muscles of facial expression called the buccolabial group.
- This muscle may be regarded as a single muscle anatomically, but functionally it appears to consist of different parts that act either independently or together with other facial muscles.
- It has neither a bony or tendinous origin.
EMBRYOLOGY
- The muscle is a derivative of the mesoderm of the second branchial arch.
- Between the 3rd and 8th week, mesoderm of the second arch starts thickening.
- Between 6 and 8 weeks, premyloblasts and myeloblasts which appear as sheet-like collection begin to extend to form five different laminae.
- The orbicularis oris muscle develops from two embryonic laminae, the mandibular lamina and the infraorbital lamina.
STRUCTURE
Consists of two parts;
- A larger peripheral part,
- Smaller marginal part.
ORIGIN AND INSERTION
| Origin | Medial aspects of maxilla and mandible, perioral skin and muscles, modiolus |
| Insertion | Skin and mucous membrane of lips |
MUSCLES
The orbicularis muscle consists of two well-defined parts, namely a deep and a superficial part. These two parts have different names from different authors, such as
- Deep part and superficial part
- Pars marginalis and pars superficialis
- Marginal part and peripheral part
- Intrinsic and extrinsic bundle
FUNCTION
- The cheek muscles to create contact between the teeth and lips by pressurizing the dental arches.
- Mainly account for facial expression.
- Collaborating in the production of speech sounds.
- Marginal portions of orbicularis oris muscle are also referred to as the labial cords, as by changing their length and tension similarly to the vocal cords, they produce some consonantal (labial) sounds.
- These consonants include /p/ of peas, the /b/ of basket that are produced by bringing the lips together; /f/ of feet or /v/ of valley are produced by pressing the lower lip against the upper teeth and others.
- In addition, the labial cords can act as vibrating strings and enable whistling or playing a wind instrument.
- It is also crucial for swallowing, mastication, and sucking.
- This muscle also helps in puckering the lips due to which it is sometimes known as the “kissing muscle.”
- The musicians also use this muscle when they play brass or woodwind instruments.
RELATIONS
| MEDIAL | levator anguli oris, depressor anguli oris, buccinator, risorius and zygomaticus major muscles |
| LATERAL | buccinator |
| SUPERFICIAL | risorius muscle |
NOTE
Relation with superior and inferior peripheral portion
| SUPERIOR PERIPHERAL PORTION | Blends with levator labii superioris, zygomaticus major, zygomaticus minor and levator anguli oris |
| INFERIOR PERIPHERAL PORTION | Blends with depressor labii inferioris, depressor anguli oris, mentalis, and platysma |
INNERVATION
Buccal branch of facial nerve (CN VII)
BLOOD SUPPLY
Facial artery - Superior and inferior labial arteries
Maxillary artery - Mental and infraorbital arteries
Superficial temporal artery - Transverse facial artery
APPLIED CLINICAL ASPECT
- Facial palsy : As the muscle receives nerve supply from the seventh cranial nerve, thus, injury to this nerve can result in paralysis of the muscle. In Bell palsy, sagging of the orbicularis oris results in drooling.
- Loss of tone : Loss of tone of this muscle to the muscles leads to drooping of the commissure as it controls the oral sphincter, which can cause drooling and difficulty in eating.
- Clinical implication in prosthodontics : The orbicularis oris muscle due to its fiber orientation has a positive action in maintaining the stability of the denture.
