Muscles of facial expression and mastication

muscles of mastication and facial expression and their role in prosthodontics

1. MUSCLES OF FACIAL EXPRESSION AND MASTICATION Muscles around the lips Muscles around the lips Muscles around the lips Ajay yerramsetti

2. CONTENTS Introduction Muscles of the facial expression Origin and insertion Functions Applied anatomy Muscles of mastication Origin and insertion Functions Prosthodontic Considerations Clinical relevance References

3. Face is the most prominent part of the body. Facial muscles help in showing a wide range of emotions. The face, therefore is an index of the mind.  INTRODUCTION

4. DEVELOPMENT OF FACIAL MUSCLES EMBRYOLOGICALLY : They develop from the mesoderm of the second branchial arch. MORPHOLOGICALLY : They represent the best remnants of Panniculus Carnosus , which is a continuous subcutaneous muscle sheet seen in some animals.

5. FACIAL MUSCLES :

6. CORRUGATOR SUPERCILLI Muscle   Origin Insertion Action Corrugator supercilli .   Medial end of superciliary arch. Skin of mid-eyebrow. Vertical wrinkling of forehead, frowning. Muscles of the eye

7.   Muscle Origin Insertion Action ORBICULARIS OCULI Orbital part Palpebral part Lacrimal part       Medial part of medial palpebral ligament & adjoining bone. Lateral part of medial palpebral ligament. Lacrimal fascia & lacrimal bone.     Concentric rings return to the point of origin. Lateral palpebral raphae . Upper& lower tarsi.     Closes lids tightly, wrinkling, protects eye from bright light. Closes lids gently, blinking. Dilates lacrimal sac, directs lac. Puncta into lacus lacrimalis , supports the lower lid.

8.   Muscle Origin Insertion Action Procerus Nasal bone and upper part of lateral nasal cartilage Skin of forehead between eyebrows and on bridge of the nose Causes transverse wrinkling

9.  Muscle Origin Insertion Action Compressor naris Maxilla just lateral to nose Aponeurosis across dorsum of nose Nasal aperture compressed Dilator naris Maxilla over the lateral incisor Alar cartilage of nose Nasal aperture dilated Depressor septi Maxilla over the central incisor Lower mobile part of nasal septum Nose pulled inferiorly

10. Muscle Origin Insertion Action ORBICULARIS ORIS Intrinsic part   Superior incisivus , from maxilla, inferior incisivus , from mandible   Angle of mouth   Closes lips and protrudes lips, numerous extrinsic muscles make it most versatile for various types of grimaces Extrinsic part Thickest middle stratum, derived from buccinator,thick superficial stratum, derived from elevators and depressors of lips and their angles  Lips and the angle of the mouth

11. BUCCINATOR Pierced by Parotid duct Buccal branch of mandibular nerve Upper fibers , from maxilla, opposite molar teeth.   Lower fibers , from mandible, opposite molar teeth.   Middle fibers , from pterygomandibular raphae Straight to upper lip. Straight to lower lip. Decussate before passing to lips.   Flattens cheek against gums & teeth, prevents accumulation of food in vestibule. Whistling Muscle. Muscle Origin Insertion Action

12. Muscle Origin Insertion Action Levator labii superioris Infraorbital margin of maxilla Skin of upper lateral half of the upper lip Elevates the upper lip, forms nasolabial groove Zygomaticus Major Posterior aspect of lateral surface of zygomatic bone Skin at the angle of the mouth Pulls the angle upwards and laterally as in smiling Levator anguli oris Maxilla just below infraorbital foramen Skin of angle of the mouth Elevates the upper lip, forms nasolabial groove

13. Muscle Origin Insertion Action Zygomaticus Minor Anterior aspect of lateral surface of zygomatic bone Upper lip medial to its angle Elevation of the upper lip Depressor anguli oris Oblique line of mandible below the first molar, premolar and canine teeth Skin at the angle of the mouth and fuses with orbicularis oris Draws angle of mouth downwards and laterally

14. Muscle Origin Insertion Action Mentalis Mandible inferior to incisor teeth Skin of chin Elevates and protrudes lower lip Risorius Fascia on the masseter muscle Skin at the angle of the mouth Retracts angle of the mouth

15. Platysma Upper parts of pectoral and deltoid fasciae. Fibres run upwards and medially Anterior fibres, to the base of the mandible and posterior fibres to the skin of the lower face Releases pressure of skin on the subjacent veins; depresses mandible; pulls the angle of the mouth downwards as in horror or fright. Muscle Origin Insertion Action

16. A few of the common facial expressions & the muscles producing them are given below: Smiling & laughing: Zygomaticus major. Sadness: Levator labii superioris & Levator anguli oris . Grief: Depressor anguli oris . Anger: Dilator naris & Depressor septii . Frowning: Corrugator supercilii & procerus. Horror, terror& fright: Platysma. Surprise: Frontalis

17. Doubt: Mentalis. Grinning: Risorius. Contempt: Zygomaticus minor. Whistling: Buccinator Snarl: Levator labii superioris alaeque nasi Blinking: Orbicularis oculi Grimace: Orbicularis oris

18. NERVE SUPPLY The facial nerve is the motor nerve of the face. Emerge from the parotid gland and diverge to supply the various facial muscles. Temporal - frontalis, auricular muscles, orbicularis oculi Zygomatic - orbicularis oculi (lower eyelid) Buccal - muscles of cheek and upper lip Marginal mandibular- muscles of lower lip Cervical - platysma

19. Ophthalmic division of trigeminal nerve Supratrochlear nerve Supraorbital nerve Lacrimal nerve Infratrochlear nerve External nasal nerve Upper eyelid and forehead Upper eyelid, frontal air sinus, scalp Lateral part of upper eyelid Medial parts of both eyelids Lower part of dorsum and tip of the nose. Maxillary division of trigeminal nerve Infraorbital nerve Zygomaticofacial nerve Zygomaticotemporal nerve Lower eyelid, side of the nose and upper lip Upper part of cheek Anterior part of temporal region Mandibular division of trigeminal nerve Auriculotemporal nerve Buccal nerve Mental nerve Upper 2/3 rd of lateral side of auricle, temporal region Skin of lower part of cheek Skin over chin Sensory nerve supply The trigeminal nerve with its three branches is the chief sensory nerve of the face Trigeminal neuralgia may involve one or more of the three divisions of the trigeminal nerve. It causes attacks of very severe burning and scalding pain along the distribution of the affected nerve.

20. Applied anatomy: INFRANUCLEAR LESION Injury to the facial nerve at the stylomastoid foramen is known as Bell’s palsy, upper and lower quarters of the face on the same side get paralyzed. During mastication, food accumulates between the cheek and the teeth. Articulation of labials is impaired.

21. Lagophthalmos It is the inability to close the eyelid. It may be the result of the residual effect of 7 th cranial nerve damage secondary to Bell’s palsy, tumour, cancer removal. Failure to provide protection to the eye may lead to exposure keratitis, corneal abrasion, or blindness. The treat includes ointments, eye drops, taping, tarsorraphy , or an eyelid implant.

22. SUPRANUCLEAR LESION: u sually a part of hemiplegia with injury of corticonuclear fibres, Only the lower quarter of the opposite side of the face is paralyzed. The upper quarter with the frontalis and orbicularis oculi escapes due to its bilateral representation in the cerebral cortex. Only voluntary movements are affected and the emotional expressions remain normal as there are separate pathways for voluntary and emotional movements.

23. Prosthodontic Considerations Aging Wrinkles start appearing when layers of fat are lost. Age reduces the concavity and “pout” of the upper lip, and it flattens the philtrum. The nasolabial grooves deepen, which produces a sagging look to the middle third of the face, whereas atrophy of the subcutaneous and buccal pads of fat dissapears , and the upper lip droops( chelioptosis ) over the maxillary teeth. These canges are accentuated even more dramatically when teeth are lost or there is loss of occlusal vertical dimension.

24. Treatment of patients with facial paralysis. In cases of unilateral facial paralysis- cheek plumper can be used. They are also known as the cheek lifting appliance and are basically prosthesis for supporting and lifting the cheek to provide required support and esthetic that will increase the self-esteem of the patient. A conventional cheek plumper is a single unit prosthesis with extensions on either side in the region of the polished buccal surfaces of the denture and are continuous with the rest of the denture.

25. Demerits of such a design are: Excessive weight which could hamper retention of the maxillary complete denture Can result in muscle fatigue. Can destabilize the maxillary denture Could interfere with masseter muscle and coronoid process of the mandible Difficult to insert the denture due to excessive weight. Can’t be used in patients with limited mouth opening. This problem can be solved with the fabrication of denture with detachable cheek plumper creating dentures that are in harmony and dignity with the aging individual, which will not eradicate but compliment the stigma of aging in them.

26. Modifications of cheek plumper:   

27. MUSCLES OF MASTICATION  

28. DEVELOPMENT The muscular system develops from intra embryonic mesoderm Muscles of mastication are derived from first or mandibular arch. Therefore all muscles are supplied by the mandibular nerve .

29. FUNCTIONS: Control all movements of the mandible. There is a wide area of origin of some of the muscles compared with the area of insertion, making it possible to have a wide range of movement. The muscles of mastication occur bilaterally in pairs. Each muscle runs in a different direction and at a different level. This also helps in the range of movement.

30. Activities- divided into 2 types- FUNCTIONAL- chewing, speaking, swallowing PARAFUNCTIONAL - grinding, clenching, and bruxing

31. MUSCLES Masseter Temporalis Lateral pterygoid Medial pterygoid Accessory muscles : Buccinator Suprahyoid muscles Infrahyoid muscles

32. Muscle Origin Insertion Function Masseter -Quadrilateral muscle Superficial layer from the anterior 2/3 of the lower border of zygomatic arch& from the zygomatic process of maxilla. The superficial fibers pass downwards& backwards at an angle of 45 degrees. They are inserted into the lower part of lateral surface of ramus of mandible. The muscle elevates the mandible to close the mouth & clenches the teeth.   - Fibers are arranged in three layers. Middle layer from anterior 2/3 of deep surface& posterior 1/3 of lower border of zygomatic arch. The middle fibers are inserted into the middle part of ramus Deep layer from the deep surface of the zygomatic arch. the deep fibers into the upper part of ramus & into the coronoid process.

33. Muscle Origin Insertion Function Temporalis This muscle fills the temporal fossa -Temporal fossa, excluding the zygomatic bone. -Temporal fascia.   -The margins & deep surface of coronoid process & - The anterior border of ramus of mandible. -Elevates the mandible. -Posterior fibers retract the protruded mandible. - Side to side grinding movements of mandible

34. Muscle Origin Insertion Function LATERAL PTERYGOID Short,conical and has muscle has upper & lower heads Both heads arises from the sphenoid bone. a) The upper head is small. It arises from the infratemporal surface & crest of greater wing of sphenoid bone. b) The lower head is large. It arises from the lateral pterygoid plate The fibers runs forwards & laterally & converge to be inserted into: a) The pterygoid fovea on the anterior surface of neck of mandible. b) The anterior margin of articular disc & capsule of TMJ.   Depresses the mandible to open the mouth, (with suprahyoid muscles) . The lateral & medial pterygoid muscles of both sides acting together protrude the mandible. The medial & lateral pterygoid muscles of the two sides contract alternatively to produce side to side movements of mandible (as in chewing).

35. Muscle Origin Insertion Function MEDIAL PTERYGOID This is a quadrilateral muscle. It has a small superficial head & a large deep head which forms the major part of muscle. a) Superficial head from the tuberosity of maxilla & adjoining bone. b) Deep head from the medial surface of the lateral pterygoid plate & adjoining part of palatine bone.   The fibers run downwards, backwards & laterally - inserted into the roughened area on the medial surface of angle & the adjoining part of ramus of mandible, below & behind the mandibular foramen & the mylohyoid groove.   -Elevates the mandible. -Helps to protrude the mandible.  

36. Nerve supply Masseter- Masseteric nerve, a branch of anterior division of the mandibular nerve. Temporalis- Deep temporal branches from the anterior division of mandibular nerve. Lateral pterygoid- A branch from the anterior division of mandibular nerve. Medial pterygoid- Nerve to the medial pterygoid, which is a branch of the main trunk of mandibular nerve.

37. Blood supply: Masseter: maxillary artery which is a branch of external carotid artery. Temporalis : middle and deep temporal arteries Medial Pterygoid : Pterygoid branch of maxillary artery Lateral Pterygoid : Pterygoid branch of maxillary artery.  

38. ACCESSORY MUSCLES SUPRAHYOID MUSCLES -    

39. Muscle Origin Insertion Function DIGASTRIC Anterior belly : from digastric fossa of mandible, supplied by nerve to mylohyoid Posterior belly: from mastoid notch of temporal bone, supplied by facial nerve Hyoid bone - It depresses the mandible when mouth is opened wide,it is secondary to lateral pterygoid. -Elevates hyoid bone

40. Muscle Origin Insertion Nerve supply Function MYLOHYOID Flat, triangular muscles forming the floor of the mouth and lies deep to anterior belly of digastric. mylohyoid line of mandible hyoid bone nerve to mylohyoid - Elevates the floor of the mouth in first stage of deglutition. - depresses the mandible

41. Muscle Origin Insertion Nerve supply Function GENIOHYOID inferior mental spine (genial tubercle) Hyoid bone Hypoglossal nerve. Elevates the hyoid bone and depresses the mandible when hyoid is fixed

42. Infrahyoid muscles: Function: They have no direct significance. Their action is to fix or depress the hyoid bone so that suprahyoid muscles can act

43. Relevance in prosthodontics: MASSETER: It will responsible for formation of masseteric notch (distobuccal to the pad i.e. outline of distobuccal border) it forms due to the action of masseter over buccinator. This area of denture must be carefully recorded because overextension causes soreness. Under extension, may result in a loss of support and resistance, to distal displacement . ACTIVATION - Hold the tray with index finger and thumb at lower border of mandible. Instruct the patient to close his mouth against the pressure exerted by the finger of operator. This will result masticatory muscle contract against buccinator muscle .

44. Buccinator Superior fibres of buccinator- seat the denture. Inferior fibres of buccinator- control denture stability and relaxes to form a pouch to store food. A clinical study involving electromyography analysis of the function of the buccinator muscle by Lundquist’ showed that the nature of buccinator muscle contraction was not able to adapt to changes in the contours of the denture base. Because learning and adaptation appear to be limited, the denture contours should be designed to harmonize with existing buccinators muscle function

45. Mylohyoid It is very important to achieve stability of lower denture by acquiring adequate peripheral seal in that area. It can be determined by:- Skillful border moulding and impression procedures. BOUCHER says that the denture flange must be parallel to the mylohyoid muscle when it is contracted. ACTIVATION: - During borer moulding or impression making procedure, ask the patient to swallow or move the tongue RT and Lt Side.

46. In maxilla: Buccal frenum : Levator anguli oris - attaches beneath the frenum Orbicularis oris - pulls frenum in forward direction Buccinator – pulls frenum in backward direction Inadequate provision for the buccal frenum of excess thickness of the flange distal to the buccal notch can cause dislodgement of the denture when the cheeks are moved posteriorly as in a broad smile. Recording: the cheek is elevated and then pulled outward, downward and inward and moved backward and forward.

47. Buccal vestibule: Varies with the contraction of the buccinators Contraction of the masseter muscle under heavy closing forces reduces the space available for the distal end of buccal flange. Recording : the cheek is elevated and then pulled outward, downward and inward.

48. IN THE MANDIBLE Buccal frenum: overlies the depressor anguli oris and buccinator is attached to it. Denture should be extended less in this region and the impression should be functionally trimmed to have the maximum seal. Buccal vestibule : This space is influenced by the masseter. When the masseter contracts, it pushes inward against the buccinator, producing a bulge in the mouth, which is reproduced as a notch in the denture flange.

49. Neutral zone The neutral zone has been defined as the area in the mouth where during function, the forces of the tongue pressing outwards are neutralised by the forces of the cheeks and lips pressing inwards. The aim of the neutral zone is to construct a denture in muscle balance. That is a denture which is in harmony with its surroundings to provide optimum stability, retention and comfort. A denture shaped by the neutral zone technique will ensure that the muscular forces are working more effectively. So the area is reduced in bulk, but concavity should not be made too pronounced because it can lead to food accumulation and the buccinators is unable to clean out this hollow

50. When the posterior fibres of temporal muscle contract they tend to move the mandible posteriorly in CR or to hold it in its most post position during terminal hinge movement. Thus when a patient is instructed to “ Pull your lower jaw back and close on your back teeth” to make a CR record or to locate the post terminal hinge axis the temporal muscles and the inframandibular muscles retrude the mandible and maintain it in this most posterior position. The lateral pterygoid muscle are also responsible for the lateral and protrusive movements of the mandible that are necessary to make eccentric interocclusal records or pantographic tracings used when one is adjusting the horizontal condylar guidances and the lateral condylar guidances of the articulator.

51. Muscle involvement in horizontal jaw relation The temporal, masseter and Medial pterygoid muscles elevate the mandible to a particular vertical relation with the maxillae. The lateral pterygoid muscle show little activity when mandible is in centric relation. Muscle involvement in vertical jaw relation The elevator muscle, temporalis, masseter and the medial pterygoid are involved in stablishing vertical jaw relations. The depressor muscles are the inframandibular and suprahyoid muscles including the mylohyoid, geniohyoid, digastric and platysma muscles. These muscles plus gravity help to control the tonic balance that maintains physiologic rest position.

52. Clinical Considerations Trismus : Limited jaw mobility can result from trauma, surgery, radiation treatment, or even TMJ problems. The limitation in opening may be a result of muscle damage, joint damage, rapid growth of connective tissue (i.e. scarring) or a combination of these factors. Treatment: Externally activated appliances: Inflatable bite opener, Dynamic bite opener, threaded tapered screw, Shell-shaped mouth opener, Screw type mouth gag, Tongue blades, Fingers, Therabite jaw motion Rehabilitation system. Internally activated appliances: tongue blades, plastic tapered cylinders.

53. Bruxism Bruxism is excessive teeth grinding and jaw clenching. It is an oral parafunctional activity. Muscles involved: masseter,temporalis,pterygoids,digastric and stylohyoid SYMPTOMS and SIGNS: Indentations of the teeth in the tongue ( crenated tongue) Hypertrophy of the muscles of mastication, particularly the masseter muscle. Tenderness, pain or fatigue of the muscles of mastication, which may get worse during chewing or other jaw movement. Excessive tooth wear, particularly attrition and abfraction, tooth fractures, and repeated failure of dental restorations Treatment : mouth gaurds

54. Effects of bruxism on dentures Complete dentures : Textbooks on complete denture fabrication often mention that clinical experience indicates that bruxism is a frequent cause of complaint of soreness of the denture-bearing mucosa. Parafunctions can be a possible factor related to the magnitude of ridge reduction. Removable partial dentures : The question of restoring lost posterior support by means of mandibular distal extension removable partial dentures (RPDs) in moderately shortened dental arches remains controversial. However, systematic reviews have concluded that shortened dental arches comprising anterior and premolar teeth generally fulfill the requirements of a functional dentition without the need for prosthodontic extension, especially in older patients.

55. Myasthenia gravis It is an autoimmune neuromuscular disease that leads to fluctuating muscle weakness and fatigue. Muscle weakness first appear in the muscles of face,neck and jaw. Symptoms Partial paralysis of eye movements,droopy eyelids Weakness and fatigue in neck and jaw with problems like chewing ,swallowing and holding up the neck TREATMENT Medication - acetylcholinesterase inhibitors to directly improve muscle function and immunosuppressant drugs to reduce the autoimmune process. Thymectomy is a surgical method

56. MPDS- myofascial pain dysfunction syndrome Medial pterygoid muscle is most commonly involved. Also spasm of elevator and lateral pterygoid muscles are seen. SIGNS AND SYMPTOMS : Facial pain, restricted jaw function and joint noise. Jaw movements increase the pain. Patients may describe a generally tight feeling, or a sensation of the jaw "catching" or "getting stuck“. TREATMENT: Physiotherapy and myotherapeutic excercises TENS (Transcutaneous electronic nerve stimulation) Muscle relaxants and Surgery Botulinum toxin A ( BtA ) injections.

57. Conclusion Masticatory and facial muscles include the most vital parts of oro -facial structure both structurally and functionally. Thus the success of prosthodontic treatment is in direct proportion to the dentist's knowledge of functioning anatomy and the application of this knowledge to denture construction

58. References: 1.B D Chaurasia’s Human Anatomy. Vol 3 Head, Neck and Brain. 11 th edition. 2.Boucher. Prosthodontic treatment for edentulous patients. 9 th edition Mosby 1985. 3.McCracken. Removable Partial Prosthodontics. 11 th edition. 2005 4.Extended buccal flange technique to manage bells palsy patient with complete denture. International Journal of Dental Clinics; Vol 4, No 3 (2012) 5.Larsen SJ, Carter JF, Abrahamian HA. Prosthetic support for unilateral facial paralysis. The Journal of Prosthetic Dentistry. 1976; 35(2):192-201.

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