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THE RELATION OF DEGLUTITION TO THE

MASTICATORY MECHANISM

JOSEPH

S.

LANDA,

D.D.S.

New York, N. Y.

T

HE PHARYNX

is one of the most complex organs of the human body. Its per-

formance in deglutition, respiration, and phonation is one of the most deli-

cate neurophysiologic phenomena. This article describes the salient points of an-

atomy and physiology of the pharynx and their relation to the masticatory mech-

anism and function of complete dentures and obturators.

ANATOMIC CONSIDERATIONS

The pharynx is a tubular passage approximately 12.5 cm. long which com-

mences at the base of the cranium and extends vertically to the esophagus. An-

teriorly, in its uppermost part, the pharynx communicates with the nasal cavity and

is called the nasopharynx. This part has a strictly respiratory function. Below, the

pharynx communicates with the oral cavity and is called the oropharynx. This

serves as a passage for both food and air. The lowest part of the pharynx is the

the laryngopharynx, which communicates with the opening of the larynx and also

serves both alimentary and respiratory purposes.

The pharyngeal tube is widest anteroposteriorly as well as laterally in the

area of the nasopharynx and becomes constricted as it descends to the oral and

laryngeal openings, respectively. The lateral or transverse diameter is broader than

the anteroposterior diameter. Anteriorly, the pharyngeal tube is incomplete and

is attached successively to the base of the cranium, the medial pterygoid plate, the

pterygomandibular raphe, the posterior part of the mylohyoid ridge, the tongue, the

stylohyoid ligament, the hyoid bone, and the thyroid cartilage.

Posteriorly, the pharynx is connected to the cervical vertebral column by

a layer of loose areolar tissue. The tissue connects the thin tunica fibrosa in front

to the prevertebral fascia behind.

Laterally, the pharynx is attached to the styloid processes and their muscles.

The pharynx is made up of three layers: mucous, fibrous, and muscular.

The pharyngeal aponeurosis, or fibrous layer, is situated between the mucous and

the muscular layers. In dissecting the posterior wall of the pharynx from the ven-

tral surface to the cervical vertebral column, the following structures are observed:

the mucous membrane, the pharyngeal aponeurosis, the muscular layer, the thin

tunica fibrosa, the layer of areolar tissue, and the prevertebral fascia which covers the

longus colli and longus capitis muscles.

Read before the Greater New York Academy of Prosthodontics, New York, N. Y.

820

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The mucosa is attached to the base of the cranium, where it is of thick

consistency and dark in color. As the mucosa descends to the auditory tubes and

the choanae, it becomes thinner; still lower it becomes more pale and is formed

into longitudinal fo1ds.l

The interval between the upper free border of the superior constrictor

muscle and the base of the skull is known as the sinus of Morgagni. The sinus is

closed by the pharyngeal aponeurosis which is well marked in front of the pharyn-

geal spine of the basilar process of the occipital bone. The aponeurosis extends

from the occipital bone to the undersurface of the apex and adjacent petrous

portion of the temporal bone. It descends to the auditory tubes and to the medial

plates of the pterygoid process. From there, the aponeurosis runs along the ptery-

gomandibular raphe to the posterior segment of the mylohyoid ridge of the

mandible and passes then along the side of the tongue to the stylohyoid ligament,

the hyoid bone, and the thyroid cartilage. The farther the aponeurosis is from

its origin, the thinner it becomes, and gradually it becomes lost. The aponeurosis is

reinforced posteriorly by a st.rong fibrous band which is attached above to the

pharyngeal spine of the occipital bone and descends forming a median raphe

which gives attachment to the pharyngeal constrictor muscle. Externally to the

pharyngeal aponeurosis is situated the thick muscular layer of various cross-striated

muscles arranged so they can respond instantaneously to any forthcoming demands.

The pharynx is the organ in which mastication, deglutition, respiration, and

phonation are not only correlated but harmoniously integrated with extreme rapid-

ity. The muscles capable of achieving this remarkable work are chiefly sphincter-

like constrictors in function. They include the glossopalatine muscles which con-

strict the faucial isthmus, the pharyngopalatinus muscles which constrict the

pharyngeal isthmus, and the superior, middle, and inferior pharyngeal constrictors.

The stylopharyngeus, pharyngopalatinus, and salpingopharyngeus muscles represent

a ring of incomplete vertical layers of muscles enclosing the circularly arranged

constrictors of the pharynx.

In instances of advanced specialization of the pharynx, the longitudinal and

circularly positioned muscles are so interwoven and intertwined that it is difficult

to determine whether the circular muscles enclose the longitudinal or the longi-

tudinal enclose the circular ones. The extreme elasticity and flexibility and the

rich texture in the interrelatedness of all the structures composing the pharynx

constitute the secret of its extraordinary and exceptional speed of mobility.

MECHANISM OF DEGLUTITION

The physiology of deglutition may be divided into four stages in accordance

with the course the bolus pursues from the mouth into the esophagus : (1) mastica-

tion, trituration, and insalivation of the bolus within the oral cavity, (2) propulsion

of the bolus from the oral cavity proper into the pharynx, (3) conveyance of the

bolus through the pharynx, and (4) propulsion of the bolus through the laryngo-

pharyngeal sphincter into the esophagus.

These four stages are closely interdependent. Thus, the more thorough the

mastication, trituration, and insalivation of the bolus within the oral cavity, the

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J. Pros. Den.

Sept.-Oct., 1961

easier is its propulsion into the pharynx. Similarly, the less the bolus irritates

and tickles the pharyngeal mucosa, the quicker and smoother are its conveyance

through the pharynx into the laryngopharynx. And finally, the more uneventful the

passage of the bolus up to the laryngopharynx, the easier is its penetration through

the laryngopharyngeal sphincter.

There are many theories and conflicting statements concerning the elaborate

functions of the musculature of the pharynx. One contributing factor to these

conflicting views may be that the studies of the anatomy and physiology of the

maxillofacial structures are not correlated with those of the head and neck.

A second reason may be the complicated convergence of the suprahyoid and

infrahyoid muscles to the hyoid bone and the simultaneous participation in func-

tion of all the muscles of deglutition with those involved in mastication. All this

is further complicated because certain other muscles (the sternomastoid, trapezius,

longus colli, and longus capitis) which are concerned with various head postures

are frequently invoked to assist in the deglutitive process.

Further difficulty derives from the inability to reach some of the muscle

groups or individual muscles for study purposes by either cinefluography or elec-

tromyography. However, most of the theories extant on the subject of de-

glutition are based on studies with the aid of fluoroscopy, cinefluoroscopy, and

electromyography.

THEORIES AND HYPOTHESES

About 1880, the theory was proposed that fluids and semifluids are propelled

directly into the stomach by the contraction of the tongue and mylohyoid muscles

effecting a syringelike action to pressure the liquids downward. The muscles of the

pharynx proper came into play only for propulsion of solid food substances.

Another concept of the mechanism of deglutition was advanced as the result

of the use of fluoroscopy. A radiolucent area in the laryngopharyngeal cavity

was observed just prior to the propulsion of the bolus into the pharynx. The

radiolucent area disappeared immediately to provide space for the bolus. This

concept gave rise to the theory of an instant negative pressure within the laryngo-

pharyngeal cavity that pulled the bolus in by suction.

The concept that the process of deglutition is performed successively by

contraction of the oral, pharyngeal, and esophageal muscles has been confirmed

by the roentgenographic studies of Bosma .2 He also announced a new theory

based on his roentgenographic studies which he calls motion in anticipation of

the approaching bolus.3 Bosma was impressed by a particular position or posture

assumed by the upper part of the pharynx and the consecutive elevation of the

larynx and laryngopharyngeal area an instant prior to penetration by the bolus.

All theorists agree that the pharynx is endowed with extreme rapidity

of motion and, therefore, that all structures involved in deglutition must be ex-

ceedingly flexible and elastic. Correspondingly, these structures, while favoring

the mobility of the pharynx, make it more vulnerable to impairment by various

pathologic conditions such as peritonsilar, parapharyngeal, and postpharyngeal

absecesses as well as by abscess in the thyroglossal duct of the tongue.

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Structures of the anterior boundary of the pharynx, that is, the tongue, hyoid

bone, and larynx, may be displaced posteriorly to the vertebral column. This condi-

tion is characteristic of individuals with weakness of the cervical muscles, as in in-

stances of poliomyelitis. Similar tongue displacement may occur in individuals who

have had an excessively insufficient vertical dimension of occlusion for a long time

and in persons who wear complete dentures or even a single upper denture de-

ficient in retention. All these deficiencies lead to difficulty in deglutition.

TRAUMATIC OCCLUSION AND 1 MPAIRMENT IN DEGLUTITION

Lack of occlusal harmony between the upper and lower occlusal surfaces

of the teeth in centric occlusion is a frequent cause of a disturbance in degluti-

tion. Every time the bolus of food is ready to be propelled into the pharynx, de-

flective occlusal contacts of the opposing masticatory surfaces upset the delicate re-

flex interaction between the mechanisms of mastication and deglutition. The pa-

tients register vague complaints of severe discomfort, a sensation of almost

choking while swallowing. These complaints are frequently disregarded and sus-

pected of being emotional in nature. The patient hardly has any other way to

describe the symptoms except to characterize them as a sensation of choking.

The dentist must command a good working knowledge of anatomy and

physiology before he is able to proceed with a scientific clinical study of this

symptomatology. These clinical symptoms must be analyzed on an adequate number

of patients, correlated, and, if possible, integrated with well-established data on

anatomy and physiology. The synthesis of all the factors participating in the in-

teraction and interplay of the masticatory mechanism with the mechanisms of de-

glutition and respiration provides a clue to an etiologic diagnosis of the sensation

of choking.

I conducted a study of the time interval between mastication and deglutition

and found the interval to be characterized by a static contact between the

mandibular and maxillary teeth associated with centric relation. This can be

utilized as one of the tests in establishing and checking the correctness of the

centric relation record.

Preceding this centric occlusal contact of the teeth in the deglutitive process,

the anterior third of the tongue presses against the lingual surface of the upper

anterior teeth and the anterior third of the palatal vault. Then, the middle part

of the dorsum of the tongue presses against the palatal vault for the propulsion

of the bolus into the pharynx.

INADEQUATE DENTURE RETENTION AND THE SWALLOWING MECHANISM

The swallowing mechanism deteriorates when the upper denture is lacking in

retention and stability, particularly from a faulty posterior palatal seal. The pressure

of the tongue against the lingual inclined planes of the upper anterior teeth loosens

the upper denture by leverage,

and it drops posteriorly. The space between

the posterior border of the denture and the dorsum of the tongue becomes markedly

reduced, and this renders the propulsion of the bolus through the faucial isthmus

into the pharynx rather embarrassing for the patient.

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Some of these patients complain that their difficulty in swallowing is caused

by the lower denture swimming around.

They do not realize that while the

tongue is unconsciously raised to prevent the upper denture from dropping, the

mylohyoid muscles are displacing the lower denture upward. The real culprit is

the upper denture. The patient is suffering from a choking sensation that does

not reside in the pharynx but in the ill-fitting, loose upper denture. This is not

globus hystericus but a typical physical condition misdiagnosed at times as of emo-

tional origin.

SOFT PALATE AND POSTERIOR WALL OF PHARYNX VIEWED

CINEFLUOROGRAPHICALLY

For a long time, it was believed that when the bolus penetrated the pharynx,

the soft palate was pulled upward and backward to effect contact with the ventral

surface of the posterior wall of the pharynx at Passavants cushion to prevent

penetration of liquids into the nasopharynx. 4 I have made many cinefluorographic

exposures of deglutition which show that the contact of the uvula with the pos-

terior pharyngeal wall is effected at a much higher level than has been recognized.

Cinefluorographic studies indicate it to be so.

This new finding is of great practical significance in cleft palate rehabilitation

whether surgical or prosthetic procedures are employed. The contact at the higher

level is by far more effective in preventing the liquids and solid substances from

penetrating into the nasopharynx. The raised position of the tongue and the con-

traction of the constrictors of the faucial isthmus (glossopalatine muscles) and

the constrictors of the pharyngeal isthmus (pharyngopalatinus muscles) prevent the

bolus from returning into the oral cavity.

Simultaneously with the teeth effecting contact in deglutition, the stylopharyn-

geus muscles contract to dilate the pharynx because their origins at the styloid proc-

esses are farther apart than their insertions on the sides of the pharynx. Thus,

the contraction of these muscles draws the pharynx upward and laterally. The

diameter of the pharyngeal tubular passage also increases in breadth in an antero-

posterior direction by elevation and forward protraction of the tongue, larynx, and

hyoid bone.

The pharyngopalatine muscle which inserts into the posterior and lateral

walls of the pharynx and the areolar tissue that fills the retropharyngeal space

contribute to effective and rapid mobility of the pharynx. The elevation and

forward protraction of these structures also place the larynx under the shelter of

the base of the tongue ; in this way, food is prevented from entering the larynx.

MANDIBULAR OVERCLOSURE AND POSITION OF HYOID BONE

I conducted a series of experiments upon myself utilizing cineroentgenography

(image intensification). These experiments were conducted with solid foods

coated with barium and also while drinking and gargling liquid barium. Careful

study and observation of the film made of these cineroentgenographic exposures

tended to indicate that the hyoid bone moved forward perceptibly more when the

jaws were brought into occlusion for swallowing than it had when cinefluorographic

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tests were made on myself 6 years previously. The hyoid bone descends slightly

downward and backward when the mandible assumes a position of rest.

The difference in the position of the hyoid bone in these experiments might be

explained by the clostire of the vertical dimension of occlusion that took place during

the elapsed period of 6 years. This in turn suggests the hypothesis that with a

marked decrease in the vertical dimension of occlusion, the tongue, hyoid bone, and

larynx tend to be displaced (gradual and small as the displacement may be) in the

direction of a closer approximation with the cervical vertebral column. If there

is inadequate time for readaptation to new environmental conditions, such displace-

ment will impair somewhat the physiologic state of deglutition and respiration.

CONCLUSION

The interrelationship and intimate interdependence between mastication, deglu-

tition, respiration, and phonation are, from a neurophysiologic standpoint, over-

whelmingly intricate and extremely fascinating. The instantaneous interaction and

smooth performance of these vital functions require a complex integration of the

cranial somatic innervation in coordination with the autonomic nervous system.

The heightened awareness that the oral cavity with its adjacent and associated

structures (the area of the dentist) plays such a vital and distinctive role in human

physiology is certainly most gratifying and encouraging. Even our most mechan-

ically minded colleagues are beginning to realize that biologic values are basic 2:~

dental practice and dental resenrch. Total acceptance and complete recognition that

biologic values form the very -foundation of denture prosthesis will greatly reduce

the number of elusive factors that lead to failures in this specialty of dentistry.

A serious attempt to correlate and integrate structure and function in the

oronasopharyngolaryngeal structures still must wait upon a great deal more study

and research. Not only are senility and disease etiologically multifactorial, but all

physiologic processes in living organisms in various stages of their development are

the resultants of a constellation of many factors. Some of these factors are the

genetic characteristics of the cells, tissues, and structures involved, their ability to

re-establish and maintain homeostasis, the influence of the endocrine systems, nu-

trition, metabolism, and the influence of various mechanical phenomena.

Clinical observations and cinefluorographic investigations indicate that none

of the extant theories on the conveyance of the bolus through the pharynx can be

accepted as definitive. The answer will probably come from a synthesis of concepts

of various investigators after study of this subject

new and original approaches.

REFERENCES

under different spectra and from

Complete Systematic Treatise, ed. 11,. Schaeffer, J. P., editor: Morris Human Anatomy: A

New York, 1953,Blakiston Comoany.

2. Bosma, J. F.: Studies of the Pharynx.* I. Poliomyelitic DisabilitiesJ. Pediat. ?e On l -lC,

L7ioo1-7,, Ijr.J,.

of the Upper Pharynx,

,lutition : Pharynaeal Stage. Phvsiol. Rev. 37:275-300. 1957.. Bosma,J. F. : Deg

4. Best, C. H., and Taylor, N. B.:

- Plhysiolo&l Basis of Medical Practice, ed. 5, Baltimore

1950,Williams & Wilkins Company,p. 560.

136 EAST 54~~ ST.

NEW YORK

22, N. Y.