STOMATOGNATHIC SYSTEM

-Enosh Steward Nirmalkumar (20)

Submitted to department of orthodontics

Topics to be covered :-

Introduction Structures of stomatognathic systemFunctions of stomatognathic system o Masticationo Deglutition o Respiration o Speech Abnormal functions of stomatognathic system Clinical consideration Summary and conclusion.

• INTRODUCTION When we want to check occlusion of teeth, we have the patient close his mouth and we open the lips to see how upper and lower teeth meet, or we carefully articulate the plaster casts in fullest contact. This static analysis is important, but equally important is a dynamic appreciation of how these part functions. It is becoming increasingly apparent that function can influence the overall pattern and the very foundation of stomatognathic system. We must know more about function than just how mastication works. Equally important is the full appreciation of, deglutition, respiration, speech and even the maintenance of head in the constant postural position.

• STRUCTURES OF STOMATOGNATHIC SYSTEM 1) The jaw2) Teeth 3) Tongue 4) Musculature

1) Jaw The upper and lower jaws are the major part of stomatognathic system. It helps in attachment of muscles, supports the teeth.

2) Teeth Teeth are arranged in upper and lower jaw and are supported by alveolar bone and periodontium. Teeth are helpful for mastication and phonation.

3) Tongue The tongue is a highly muscular as well as adaptive organ. It is made up of intrinsic as well as extrinsic muscles.

Intrinsic muscles are - Superior longitudinal - Inferior longitudinal - Vertical - Transverse

Extrinsic muscles of tongue are - Genioglossus - Hyoglossus- Styloglossus- Palatoglossus

4) Musculature

Muscles are a potent force, whether they are in active function or at rest. As we have seen resting muscle still is performing a function that of maintaining posture and a relationship of contagious parts.

The teeth and supporting structures are constantly under the influence of the contagious musculature.

The integrity of dental arches and the relations of the teeth to each other with opposing members are the result of morphogenetic patterns, as modified by the stabilizing and active functional forces of the muscles.

During mastication and deglutition, the tongue may exert two or three times as much force on the dentition as the lips and cheeks at any one time.

Buccinator mechanism is a continuous band of muscles that encircle the dentition & is firmly anchored at the pharyngeal tubercle of the occipital bone

Starts with decussating fibres of orbicularis oris joining the right and left fibres of the lip which

constitute the anterior component of the buccinator mechanism

Runs laterally and posteriorly around corner of the mouth, joining other fibres of the buccinator muscle which gets inserted into pterygomandibular raphe.

Tongue acts opposite to buccinators mechanism exerting an outward force

Muscles of mastication

• Temporalis

• Lateral pterygoid

• Medial Pterygoid

• Masseter

Temporalis

• Origin- Bone of temporal fossa and temporal fascia

• Insertion- Coronoid process of mandible and anterior margin of ramus

• Nerve supply- Deep temporal nerves from anterior trunk of mandibular nerve

• Function- Elevation and Retraction of mandible

Lateral Pterygoid

•Origin: Upper head – infratemporal surface & crest of greater wing of sphenoid bone; Lower head – lateral pterygoid plate

• Insertion : Pterygoid fovea on the anterior surface of neck of mandible and Anterior margin of articular disc & capsule of TMJ

• Nerve Supply: Pterygoid branch of Trigeminal nerve

• Function: Depresses the mandible; Protrudes it forward for opening of the jaw; Side Movements

Medial Pterygoid

• Origin- Medial surface of lateral plate of pterygoid process and pyramidal process of palatine bone ; Superficial head- tuberosity and pyramidal process of maxilla

• Insertion- Medial surface of mandible near angle

• Nerve supply- Nerve to medial pterygoid from the mandibular nerve

• Function- Elevation and side to side movements of the mandible

Masseter

• Origin- Zygomatic arch and Maxillary process of zygomatic bone

• Insertion- Lateral surface of the ramus of the mandible

• Nerve supply-Masseteric nerve from the anterior trunk of the mandibular nerve

• Function- Elevation of the mandible

Accessory muscles of mastication :-

Suprahyoid muscles Infrahyoid muscles

Diagastric Sternohyoid

Stylohyoid Thyrohyoid

Mylohyoid Omohyoid

Geniohyoid

WOLFF’s law of transformation of bone In the year 1870, Julius Wolff gave the reason for the

arrangement of trabecular pattern He attributed that the trabecular arrangement is due

to the functional forces. “A change in the direction and magnitude of force

could produce a marked change in the intermal architecture and external form of the bone”

Increase in function leads to increase in the density of bone

Trajectories of force/Benninghoff’s lines

The trajectorial theory states that the lines of orientation of the bony trabeculae follow the pathways of maximal pressure and tension

These lines of orientation of the bony trabeculae involve not only the cancellous bone but also the compact bone

The stress trajectories respond to the demands of the functional forces collectively as a unit and not as a single bone

Head is made up of only two functional units 1) Craniofacial unit 2) Mandible

Physiologic rest position Its defined as the position of the mandible when the

muscles of mastication are in a minimum tonus of contraction

Factors influencing rest position are Body and head position, psychic factor, sleep, age,

pain, tmj disease Freeway space is the measured distance between

the occlusal surfaces of maxillary and mandibular dental arches.

Normal freeway space is 2-4mm

A large freeway space is related to excessive deep bite e.g. Class II div 2

INITIAL CONTACT:- When the patient takes the mandible from the rest position to occlusion, the position at which first tooth contact occurs is called initial contact position.

CENTRIC RELATION:- Centric relation is the unstrained neutral position of mandible in which the anteroposterior surfaces of the mandibular condyles are in contact with the concavities of the articular disc.

Bennett Movement:- Bodily side shift of the mandible towards the working side during lateral excursion is called Bennett movement

Bennett movement is necessary to permit rotation of the working condyle, because of the restraining influence of the temporomandibular ligament on the working side, the walls of the glenoid fossa

The working side condyle may either rotate, or rotate and move laterally, and also upwards or downwards.

Stages of Bennett movement : Immediate shift or progressive side shift

If the lateral component occurs early in the movement, it is termed as immediate or early side shift

A gradual lateral component is termed as progressive side shift

Bennett angle:- When the working side condyle shifts laterally, the non-working side condyle moves downwards, forwards and inwards.

Angle formed between the forward and inward movements of the non-working condyle and a straightforward movement is known as Bennett angle

Gothic arch:-The border movements of the mandible in the horizontal plane are often described as a gothic arch when observed in the incisal area

FUNCTION OF STOMATOGNATHIC SYSTEM 1) Mastication

Mastication or chewing is the process by which food is crushed and ground by teeth

In the infant food is taken in first by suckling. This is an unlearned or autonomous reflex in homo sapiens.

The classic suckle swallow position in the new born, as outlined by Bosma, shows the head extended, tongue elongated and low in the floor

of mouth, jaw apart and lips pursed around the nipple.

As the infant learns to take the solid food, the intensity of act of satisfying hunger is reduced, but most of muscles of cheek, tongue and floor of mouth are involved.

There is less activity of lips and less mandibular thrust. The infant quickly learns to use his lips primarily to keep the food from being forced out of mouth during the peristaltic like action of the tongue and cheeks as the bolus of food is forced back towards the pharynx. The ingested food is mixed with saliva by active tongue function.

In the infant, as the bolus takes up the saliva it is forced between gum pads or the occlusal surfaces of the erupting teeth.

At the same time the rhythmic action of muscles of cheek serves to force the food back toward the tongue, which mashes the bolus of food against the hard palate.

After the bolus of food is accommodated between occlusal surfaces, the mandible is forcibly closed, primarily by temporal and masseter muscle activity.

Fletcher summarizes, recent work on masticatory stroke in the adult, using the six phases outlined by Murphy.

a) The preparatory phase In which food ingested and positioned by the

tongue with in the oral cavity and the mandible is moved towards chewing side.

b) Food contact It is characterized by a momentary

hesitation in movement. This Fletcher interpreted to be a pause triggered by sensory receptors concerning the apparent viscosity of the food and probable trans-articulator pressures incident to chewing.

c) The crushing phase If starts with high velocity then slows as the

food is crushed and packed. d) Tooth contact

Accompanied by a slight change in direction but not delay. According to Murphy all reflex adjustments of the musculature for tooth contact are completed in the crushing phase before actual contact is made.

e) The grinding phase Which coincides with transgression of the

mandibular molars across there maxillary counterparts and is therefore highly constant from cycle to cycle.

Messerman termed this phase the terminal functional orbit.

Ahelgren noted that during this phase the bilateral musculature discharge becomes unequal and asynchronous indicating that the person is chewing unilaterally.

f) Centric occlusion When movement of the teeth comes to a

definite and distinct stop at a single terminal point from which the preparatory phase of next stroke begins.

Masticatory frequency is variable but appears to be one to two strokes per second with a normal bolus of food. The number of masticatory strokes before swallowing seems to be characteristic of the individual and is relatively constant.

It is defined as the mandibular position in which there is maximum intercuspation of the teeth

2) Deglutition (swallowing) a) Infantile (visceral) swallow Moyers lists the characteristics of the infantile swallow as follows:

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

2) The mandible is stabilized primarily by contraction of muscles of VII cranial nerve and the interposed tongue.

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

As stated above, the gum pads are not usually in contact during the act of swallowing. With liquid food particularly a ‘clucking’ is frequently heard.

The intrinsic and rhythmic peristaltic like muscle activity steers the liquid or bolus of food back into the pharynx by the superior, middle and the inferior

pharyngeal constrictors, past the epiglottis into the esophagus.

The glottis closes off the pharynx as the posterior peripheral portion are forced backward against the superior constrictor ring.

b) Mature (somatic) swallow

With the change in semisolid and solid food and the eruption of the teeth there is also a modification of swallowing act.

The tongue no longer is forced into the space between gum pads or incisal surfaces of teeth, which actually contact momentarily during the swallowing act.

Mandibular thrust diminishes during transitional period of 6-12 months. The mandible closing muscles take over more of the role of stabilizing the mandible as the cheek and lip muscles reduce the strength of their contraction.

The tip of the tongue is no longer moving in and out between anterior gum pads but assumes a position near the incisive foramen at the moment of deglutition.

The change to the adult swallowing pattern occurs gradually in what he has been called the transitional period.

Neuromuscular maturation, change in head posture gravitational effect on mandible are conditioning factors.

Usually by 18 months of age, the mature swallow characteristics listed by Moyers are –1) The teeth are together2) The mandible is stabilized by contraction of the mandibular elevators, which are primarily V cranial nerve muscles.3) The tongue tip is held against the palate, above and behind the incisors.4) There is minimal contraction of lips during the mature swallow.

Phases of deglutition Fletcher divides the deglutition cycle in 4 phases, highly integrated and synergistically coordinated.1) Preparatory

2) Oral phase3) Pharyngeal phase4) Esophageal phase

1) Preparatory Starts as soon as liquids are taken in, or after the bolus has been masticated. The liquid or bolus is then in a swallow – preparatory position on the dorsum of tongue. The position on the dorsum of tongue. The oral cavity is sealed by lip and tongue.

2) Oral phase During the oral phase the soft palate moves upward and tongue drops downward and backward. At the same time the larynx and hyoid bone move upward. The combined movement create a smooth path for the bolus as it is pulsed from the oral cavity by the wave-like ripping of the tongue.

While solid food is pushed by tongue, liquid food flows ahead of the lingual constrictions. The oral cavity, stabilized by the muscles of masticating maintains an anterior and lateral seal during this phase.

3) The pharyngeal phase Begins as the bolus pulses through fauces. The pharyngeal tube is raised upward and the nasopharynx is sealed off by closure the soft palate against the posterior pharyngeal wall.

The hyoid bone and the base of the tongue move forward as both the pharynx and the tongue continue these peristaltic like movement of the bolus of food.

4) The esophageal phase Swallowing commences as food passes the cricopharyngeal sphincter. While peristaltic movement carries food through the esophagus, the hyoid bone palate and tongue return to their original positions.

The average individual swallows, about once/ twice a minute between meals. Even during sleep the swallowing act is performed at infrequent intervals.

These are various estimates of the frequency of deglutition, which range as high as somatic and visceral swallows per hours period.

3) Respiration Respiration, like mastication and swallowing is an

inherent reflex activity. A wonder to behold is the fantastically efficient split second opening and closing of the epiglottis, keeping out the blood but permitting the entry of life giving air.

Bosma and his co-workers have analyzed respiration in the infants and found that quiet respiration is typically carried out through the nose, with the tongue in proximity to palate, obstructing the oral passageway.

Both the pharynx and larynx are active during respiration and it is in this area that the infant differentiates between respiration and associated activities such as the cough cry or sneeze. Posture also has a significant effect on respiration.

Respiration maintains the potency of the pharyngeal area, since there is a collapse of pharynx in the tracheotomized infant. Development of respiratory spaces and maintenance of airway are significant factor in oro-facial growth i.e. functional matrix theory.

The mechanism of crying is intimately tied up with respiration, and the laryngeal and pharyngeal coordination of muscles is seen quite early.

4) Speech Speech like breathing, also makes no gross demands in the perioral muscles. Although all mammals apparently masticate, swallow and breathe speech is limited to the human being.

Unlike mastication, deglutition and respiration, which are reflexive in nature, speech is largely a learned activity dependent on a maturation of organism.

The muscles of walls of the respiratory tract, the pharynx, the soft palate, the tongue, the lips and face and the nasal passages ways all are concerned in the production of speech sounds.

Simultaneous breathing to provide a column of air is essential to produce vibrations necessary for sound. The lips and tongue structures modify the outgoing breath stream to produce variations in the sound.

Assuming the presence of normal structure, speech production is dependent on the coordinated action and precise activity of muscles that may be performing other functions at the same time.

If the structures are not normal, as with cleft palate, normal speech sounds may not be possible, despite the compensatory muscle activity.

Even though the mechanisms for producing sounds involve at least parts of the same system used for mastication, respiration and speech, actions used in producing language differ considerably.

The speech mechanism acts on the breath streams in a number of ways, controlling the air mechanism, air direction, air flow, air release, air pressure, general air path and lingual air path.

In cleft palate, with palatal insufficiency, the inability to control the air path may elicit adaptive reaction elsewhere, e.g. greater postpharyngeal wall activity, enlargement of turbinates, mandibular postural position change, contraction of the nares, enlargement of tonsils and adenoids.

With respect to the tongue, which fills the oral cavity at birth, only the extrinsic muscles which largely control horizontal movement needed for the suckle-swallow are well developed.

Those intrinsic muscles needed for speech are poorly developed. The transition from gross movements of tongue to precise and finely controlled ones extends over the first several years of life, through the infantile and transitional swallowing periods, into the mature deglutitional pattern era.

ABNORMAL FUNCTIONS OF STOMATOGNATHIC SYSTEM

1) Mouth breathing

If the palate is high and narrow, the dorsum of tongue does not fit against the palatal vault everywhere and a potential away exist between tongue and palate.

If in addition, lips do not meet, the oral airway is complete from open lips to the oro-pharynx. So air

can be drawn in and expired just as easily through mouth cavity as through nasal cavities.

Mouth breathing is more commonly seen in children and decreases with age. Also more common during sleeping.

Classification

a) Obstructive Who have increased resistance to or a complete obstruction of the normal flow of air thorough nasal passages. Because of difficulty in inspiring and expiring air through nasal passages the child is forced by sheer necessity to breathe through his mouth. Seen in adenoid facies.

b) Habitual A child who continuously breathes through his mouth by force of habit, although the abnormal obstruction has been removed.

c) Anatomical Whose shorter upper lip does not permit closure without under efforts.

Effects of mouth breathing • Tongue position is low and forward to keep oral airway open.• Lips are flaccid, short upper lip, with lack of tonicity.• Labial flaring of maxillary anterior teeth. Hyper trophy of lower lips.• Frequently marked overbite.

• Dryness of mouth • Gingivitis and increased dental caries.• Affected gingiva is demarked from unaffected gingiva, the junction has been referred by ‘Worwick’ as tension ridge.

Etiology

1) Naso-pharyngeal obstruction Obstruction may be due to

a) Nasal deformities – DNSb) Irritation or thickening of mucosal membrane of nosec) Bone pathology d) Enlarged adenoids.

2) Mouth habits Thumb sucking lip biting, finger or nail biting, tongue thrusting

3) Abnormal development

a) Macroglossiab) Short upper lip

4) Psychosomatic problems May also show mouth breathing

Bruxism

Bruxism is a conscious or subconscious act performed by an individual which overrides the protective neurologic mechanism of masticatory system. In bruxism there is increase in tonic activity in the jaw muscles.

Emotional or nervous tension, pain or discomfort and occlusal interferences are the factors that can increase muscle tone and lead to non-functional clenching.

Effects • Tenderness of masticatory muscle• Incisal wear, occlusal facets• TMJ pain, headache or tiredness of masticatory muscles.

Etiology 1) Psychic tension Nervous children may develop bruxism

2) Occlusal discrepancies Increased muscle tonus Also seen in epilepsy, meningitis chorea.

3) Tongue Thrust

It is also known as perverted or deviated swallow, retained infantile swallow, tooth apart swallow, tongue thrust syndrome or abnormal swallow.

In the tongue thrust The tip of the tongue is placed against or between the teeth during swallowing. Then the mid portion of tongue does not contact the hard palate and does not assure 450 angulations relative to the past-pharyngeal wall as in normal swallowing.

Since in abnormal swallower the tongue is placed between the teeth. Masseter muscle activity is prevented and as a consequence these is no molar contact during deglutition. Active mentalist muscle is noted.

Fletcher has collected a grouped patterns associated with or characteristic of tongue thrust. They may include some or all of following.

1) A thrusting movement of tongue against or between anterior teeth.2) Slight or no contraction of muscles of mastication. 3) Strong contraction lip musculature 4) Movement hyoid bone in oblique or forward direction5) Distortion of speech sound

Classification

a) Anterior tongue upper and lower incision.b) Lateral or posterior – premolar and molar regionc) Combined

a) Simple tongue thrust

This is localized posturing forward, of the tongue during rest and active function with localized anterior openbite.

b) Complex tongue thrust

Forward tongue posture, tongue thrusting during swallowing, contract of perioral muscles, excessive buccinator hyperactivity. When all these symptoms present the pattern is often called as complex tongue thrust.

Incidence and duration of tongue thrust

- High incidence in school going children and patients with respiratory problem.

Fletcher associates reported following incidenceAt age 6 years - 52.3%8 years - 38.5%9 years - 49.9%10 years - 34%

Effects of tongue thrust • Anterior openbite• Lateral or posterior open bite• Proclinated upper incisors • Hypotonic upper lip which appear retracted or short• Bilateral narrowing of maxillary arch

Etiology

1) Bottle feeding due to rapid artificial with long feeding nipple which may have enlarged opening.

2) Hereditary The structure of the components of the face that is inherited, rather than habit itself.

3) Oral habits – Thumb sucking, open bite.

4) Ankyloglossia or macroglossia may cause tongue thrust.

5) Tonsillar tissue – If tonsiller tissue enlarged, can create destruction in oro-pharyngeal are a posterior

to root of tongue. As a consequence tongue may be boned to posture formed.

6) CNS disorders – Neuromuscular problems can be severe enough to prevent normal adult swallow. Recent investigations has been accumulating demonstrate that so called tongue thrust seems more likely to be the effect than the cause of malformations. The tongue is a very adoptive organ on an auxiliary function of the tongue to seal the anterior gap when the lip mastication is too weak to produce and oral seal.

Lisping and stammering These are commonly occurring speech defects.Speech defect create difficulty for the child while speaking. Social adjustment is also affected because other children laugh at his defect. The child may develop inferiority complex. He develops a sense of insecurity.

Lisping This speech defect involves change of sound of letters and wards.

Etiology

Main cause is continuity of infantile mode of speech. If the tongue is moved forward without mandible and lies on top of lower incisors lisping may result.Certain malocclusions like openbite, maxillary protrusion, mandibular retrusion and mal-aligned

tooth also cause lisping.

Stammering In stammering the child fails to produce any sound for sometime. These create emotional tension and difficulty in social adjustment.

Etiology - Hereditary - Due to emotional tension - Lack of balance among two hemispheres of the brain.- Auditory amnesia

CLINICAL CONSIDERATIONS Before any treatment is started or during diagnosis,

all functions of stomatognathic system should be checked and if not proper it can be primary etiologic factor in a malocclusion.

Many dysfunctions are acquired in the early stages of development.

Malocclusions that are acquired as a result of dysfunctions can usually be treated simply by elimination of disturbing environmental influences, which will foster normal development.

Respiration When the child is seated on dental chair, we should

check for breathing whether it is nasal or oro-nasal.

It is diagnosed by giving a sip of water to patient and ask to keep it in mouth and by placing cotton in between nose and mouth.

The etiologic factors of mouth breath is first recognized and then they are removed like correction of nasal obstruction.

Later on the restoration of oral health is done by giving proper habit breaking appliances and also different exercises like deep breathing, vigorous exercises, playing on blowing type of musical instruments and lip exercises.

Mastication The masticatory apparatus contains teeth, muscles of

mastication, TMJ movement. The functioning should be thoroughly checked.

In case of bruxism there is presence of occlusal facets, or occlusal interference, pain in TMJ or tenderness of muscles of mastication.

So the therapy includes elimination of triggering elements, mainly discrepancies between centric relation and correction by occlusal adjustment, by giving occlusal bite plate, protective mouth guard or rubber splints.

Deglutition Between 2 to 4 years of age mature swallow is seen

in normal developmental patterns. A proper diagnosis of tongue thrust should be done

on the basis of clinical features or by checking the

swallowing patterns. Circumoral tension is being used as diagnostic criteria by many clinicians.

After diagnosing a tongue thrust habit it should be properly treated.

If the tongue thrust is present at 3 to 9 years of age no appliance therapy is usually indicated only the dentist instruct the patient how to swallow correctly.

On recall appointments if the openbite improves or remains same, this approach is continued until 9 years of age.

If open bite continues to increase intraoral therapy is indicated.If the tongue thrust present after 10 years of age then dentist should consider using intraoral appliance when the malocclusion is confirmed to an anterior open bite.

If tongue thrusting is associated with lisping, only a speech therapist should be encouraged to correct the speech problem using articulation therapy.

Speech

During diagnosis attention should be given towards speech also. The etiology of speech problem should be recognized and proper treatment should be given.

The presence of speech defects in childhood is due to lack of sufficient training and maturity. As these factors are provided the speech defects disappears.

The guardians and teachers should therefore encourage children to pronounce correctly.

If defect continued till late age then they are removed by the means of surgery.

SUMMARY AND CONCLUSION

Before the orthodontist appreciates abnormal functions of the oro-facial muscles he must have a knowledge of their normal development and maturation.

Abnormal functions or habits may be considered normal for a certain stage of child’s development. The abnormal functions are particularly more at young age because of psychological requirements and emotional adjustments in that period.

In young patients, new ideas are more easily learned and more easily broken, so the treatment of habit should be started as early as possible.

Its more difficult to break habit in an adult.

REFERENCES

• Grays Anatomy for students 2nd Edition

• Wikipedia

• Friedman MH, Wusberg I. Screening procedures for temporomandibular joint dysfunction. Am Fam Phys. 1982;25:157–60.

• Janda V. Some aspects of extracranial causes of facial pain. J Prosthet Dent. 1981;56:484–7

• Orthodontics - Sridhar Premkumar