Maturation of Orofacial Musculature

Orofacial Muscles

• Location, Origin, Anatomy, Insertion, Action, Innervation, Blood Supply

• Effect of Orofacial Musculature on Growth of the Face: Cause and effect relationship

• Effects of Malrelation of Jaws and Facial Structures on Muscle Activity

Classification of Orofacial Muscles

• Cranial Nerve Innervation

  • Motor Nerve Supply: Facial nerve (5 terminal branches) ; naaguutos sa muscle

  • Motor nerve: have neurons to tell the muscle to contract thereby making new move

    1. Temporal

    2. Zygomatic

    3. Buccal

    4. Mandibular

    5. Cervical

  • Sensory Nerve Supply

    • Trigeminal nerve (5)

  • Sensory nerve

    • neurons here gather in formation of the environment and send it to the brain. responsible for sending information

• Region and Function

  • Facial muscles

  • Jaw muscles

  • Portal muscles

Facial Muscles

• Primary function: Expression of emotions (7,000 possible facial expressions according to Coleman)

• Racial and individual variability allows for variability in facial expression

Specific Facial Muscles

• Muscles of the Scalp

  1. Occipitofrontalis (ssurprised emotion)

• Muscles around the Eyelids (around the eye)

  1. Orbicularis oculi (winking)

  2. Corrugator supercilii (frowning)

  3. Levator palpebrae superioris

• Muscles of the Nose

  1. Procerus (making face)

  2. Compressor naris

  3. Dilator naris

  4. Depressor septi

• Muscles around the Mouth

  1. Orbicularis oris (kissing)

  2. Levator labii superioris alaeque nasi (angry)

  3. Levator labii superioris

  4. Levator anguli oris

  5. Zygomaticus minor (annoyed)

  6. Zygomaticus major (annoyed, laughing, smiling)

  7. Depressor anguli oris (grief)

  8. Depressor labii inferioris

  9. Mentalis (sad)

  10. Risorius (grinning)

  11. Buccinator

• Muscle of the Neck

  1. Platysma (scared/terror)

Role of Facial Muscles

• Maintenance of posture of facial structures.

• Orbicularis Oculi: Paresis leads to drooping of lower eyelid, drying of conjunctiva and inflammation.

• Orbicularis Oris: Paralysis lead to drooling and angular cheilosis (red swollen patches on the side of the mouth).

• Bells palsy both upper and lower face.

• Stroke is only lower face

• Lip and Buccinator Muscles: Opposed by the tongue, contribute to postural equilibrium of the teeth.

• Contribute to stabilization of the mandible during infantile swallowing and in chewing, and swallowing in the edentulous and occlusally compromised adult.

• Frankel's Speculation: The buccinator muscles exert a constraining force on the maxillary alveolar process and teeth; buccal shields hold the cheeks from the alveolar process and teeth, demonstrated increase in arch width with the appliance. (kulang sa maxilla so ang ginagaa is magaallow ng growth ng maxilla laterally)

• Form Dictates Function: Patients with short upper lips or excessively proclined maxillary incisors compensate by elevation of the lower lip, through action of the mentalis muscle, to establish an anterior seal during swallowing.

• Role in Communication: Important in visual and spoken communication; lip contact with opposing lip or teeth provides one-quarter of the articulations of the English language.

• Role in Mastication: Lips and cheeks are essential for bolus control in mastication; facial palsies lead to food accumulation in the labial and buccal vestibule of the affected side.

Jaw Muscles

• Postural position stabilization of the mandible

• Move the mandible during mastication and speech

• Designated as levators, depressors, protractors, and retractors

Specific Jaw Muscles

1. Lateral Pterygoid

   origin: sphenoid bone

   insertion: TMJ

2. Masseter

   origin: zyygomatic bone

   insertion: angle and ramus oof mandible

3. Temporalis

   origin: temporal fosssa

   insertion: coronoid processs

4. Medial Pterygoid

   origin: medial side of lateral pterygoid plate

   insertion: angle of mandible

Movements Produced by Jaw Muscles

• Depression: Lateral pterygoid

• Elevation: Masseter, temporalis, medial pterygoid

• Protrusion: Lateral pterygoid, medial pterygoid

• Retraction: Resisted by posterior fibers of temporalis, deep fibers of masseter, digastric, geniohyoid

• Lateral or Side to Side Movements: Lateral pterygoid

Neural Control of Mandibular Posture

• Maintained against gravity by the stretch reflex (movement in response to muscle stretching) in the mandibular elevators.

• Reflex: movement in response to stimulus without conscious thought

• Extension of the head results in an increase in freeway space.

• Flexion of the head results in a decrease in freeway space.

• Normal opening and closing of the jaw are never purely rotational; actual rotational centers are dorsal to the mandibular ramus and shift during opening and closing.

Mandibular Movement

• Perceived as that of a free body manipulated in an intricate muscular web with the teeth and joints acting as stops and guides.

• Deflective Contacts: If there are deflective contacts in the teeth (e.g., slides in functional malocclusion - displaces the condyle from its ideal positio), the mandible is shifted to the position of maximal intercuspation, displacing one or both condyles from their ideal position; this is accomplished by a complex interaction of all the muscles inserting onto the mandible.

• Mouth Breathing: Alteration of mandible, tongue, and hyoid position in mouth breathing changes the environment of both the mandible and maxilla and alters the way they grow (e.g., "long face syndrome").

• Infant Mandibular Stabilization: Before teeth arrive in the infant, mandibular stabilization is affected by synergistic activity of jaw muscles, and the facial muscles may be called upon to assist in the stabilization.

Growth and Adaptation of Orofacial Muscles

1. Structural: Jaw muscle growth may be secondary to mandibular growth.

2. Functional and Behavioral: Orofacial behavior whose development is pertinent to orthodontics includes mandibular and tongue posture, swallowing, and mastication.

Tongue Posture in Neonates

• In the neonate the postural position is the starting orientation for activities as suckling, respiration and swallowing.

• While the mandible is in its postural position, the tongue is postured forward and touches the lips while the gum pads are held slightly apart.

• Tongue posture in the neonate is more forward than later since the tongue is part of a very active sensory perceptual system.

Mature Swallow Development

• All occlusal functions are learned in stages as the nervous system and the orofacial and jaw musculature mature concomitantly with the development of the dentition.

• Most children achieve most features of the mature swallow at 12 to 15 months of age

• Arrival of the incisors cues more precise opening and closing movements of the mandible, compels a more retracted tongue posture, and initiates the learning of mastication.

• Arrival of molars causes true chewing motions to be seen to start, and learning of the mature swallow begins.

• Fifth cranial nerve muscles assume the role of mandibular stabilization during the swallow.

• Muscles of facial expression abandon suckling and the infantile swallow and begin to learn the delicate and complicated functions of speech and facial expressions.

Portal Muscles

• Upper respiratory and alimentary tract muscles

• Serve multiple functions of posture, respiration, and feeding

Muscle Groups

• Muscles of the tongue (both intrinsic and extrinsic)

• Muscles of the soft palate

• Muscles of the pharyngeal pillars

• Muscles of the pharynx proper

• Muscles of the larynx

Tongue Muscles

• Extrinsic:

  • Genioglossus M.

  • Styloglossus M.

  • Palatoglossus M.

  • Hyoglossus M.

• Intrinsic:

  • Superior longitudinal M.

  • Inferior longitudinal M.

  • Transverse M.

  • Vertical M.

*Involved in swallowing

Palate Muscles

• Tensor veli palatini

• Levator veli palatini

• Palatoglossus
  *Involved in breathing: Palatopharyngeus
  *Uvula movement: Musculus uvulae

Reflexes of the Upper Airway and Alimentary Tract

Tongue Size

• If tongue is large for the space enclosing the respiratory pharynx it can spill into the pharynx, causing risk to patient in cases of infantile syndrome of Robin and sleep apneas.

• Or tongue may be postured forward or buccally, leading to anterior or posterior open bites

Methods of Studying Orofacial Muscles

1. Anatomic

   • gross dissection: Oldest method; shape, boundaries, origin, and insertion provide insight into the possible force vectors of the muscle

   • histologic another traditional method of studying muscles

2. Functional

   • Movement

   • Force and Pressure

3. Behavioral

Types of Muscle Fibers

1. Type I muscle fibers

   • small, low-tension, slowly contracting motor units

   • very resistant to fatigue and richly supplied with capillaries

   • possess excellent endurance at low forces, which makes them well suited for maintenance of posture of the mandible

   • 75\%

     • Temporalis

     • Masseter

     • anterior medial pterygoid

     • lateral pterygoid

     • These muscles are primarily responsible for posture of the mandible

2. Type II muscle fibers

   • large, high-tension, rapidly contracting units

   • fatigue resistant (IIA) or fatigue sensitive (IIB)

   • good (IIA) or poor (IIB) capillary circulation

   • type IIA units are recruited for maximum effort of long duration

   • type IIB for maximum effort of short duration

   • 30\% type IIA: Digastric

   • Type IIB fibers: Found in all jaw muscles, highest proportion (45\%%) in the superior posterior temporalis, posterior medial pterygoid, and anterior digastric muscle

Functional Methods

1. Movement: Kinesiology; study of movement resulting from muscle action. Movement of facial structures studied via recording on moving film and holography.

2. Force and Pressure: Measured by strain gauges, pressure transducers. Masticatory, swallowing, and maximal biting forces have been recorded on the teeth. Pressure transducers study pressure gradients in the upper alimentary tract during swallowing.

3. Electromyography: Instrument most often used for evaluating the activity of orofacial muscles; can give useful information on whether a muscle is active and define when the activity begins and ends in the muscle fibers sampled.

Behavioral Methods

• Noninvasive and examines total muscle activity in the natural state

• Congenital behavior are less easily altered by training than are those which are learned during development or throughout life (e.g., myofunctional therapy directed at the role of the tongue in bolus handling is likely to be unsuccessful)

• Some behavior is predetermined and unlearned (e.g., nest building of birds is predetermined while singing is learned from birds of the same species)

• Swallowing: Bolus propelling component appears to be predetermined while the anterior seal and stabilization components are learned

Pharyngeal Pillars

• Anterior pillar by palatoglossus muscles.

• Posterior pillar is formed by palatopharyngeus muscles.

Pharynx Muscles

• Outer circular layer

  • Inferior constrictor muscle

  • Middle constrictor muscle

  • Superior constrictor muscle
    *During swallowing, these muscles constrict to propel bolus downwards (an involuntary process)

• Inner longitudinal layer

  • Stylopharyngeus muscle

  • Salpingopharyngeus muscle

  • Palatopharyngeus muscle
    *During swallowing, these muscles act to shorten and widen the pharynx.

Larynx Muscles

1. Cricothyroid

2. Posterior cricoarytenoid

3. Lateral cricoarytenoid

4. Transverse arytenoid

5. Oblique arytenoid

6. Thyroarytenoid and thyroepiglottic

Portal Reflexes

• Reflexes of the oropharynx must support a patent airway during respiration and provide a pressure gradient during swallowing

• Two portal reflexes of greatest significance to orthodontics are: pharyngeal airway maintenance and Swallowing

Airway Maintenance During Swallowing

• Soft palate blocks the nasal cavity

• Tongue blocks the oral cavity

• Epiglottis blocks the larynx

Infantile vs. Mature Swallow

Infantile or Immature Swallow Characteristics:

1. The jaws are apart, with the tongue between the gum pads.

2. The mandible is stabilized mainly by contraction of the muscles innervated by the VII (seventh) cranial nerve and the interposed tongue

3. The swallow is guided and to a great extent controlled by sensory interchange between the lips and the tongue

• Closely associated with suckling, and both are well developed by about the thirty-second week of intrauterine life

• During the infantile swallow: the tongue is between the gum pads in close apposition the with lips

• Its contraction plus those of the facial muscles help to stabilize the mandible

• Mandibular elevators, which play a prominent role in normal mature swallows, show minimal activity

• Many oral functions in the neonate are guided primarily by tactile stimuli from the lips and tongue. When the incisors erupt the tongue posture changes to mature position. Alveolar process growth vertically during eruption aids in the normal change in the tongue's posture during the first year of life

Mature Swallow Characteristics:

Usually, by 18 months of age

1. The teeth are together.

2. The mandible is stabilized by contraction of the mandibular elevators, these being primarily innervated by the trigeminal nerve.

3. The tongue tip is held against the palate above and behind the incisors.

4. There are minimal contractions of the lips during the mature swallow.

*An unconscious swallow of saliva during sleep (infantile swallow): Note the dominance of the facial muscles and the minimal activity in the only mandibular elevator sampled.
*Mature swallow: Note the strong contractions in the temporal muscle which is a jaw muscle.