An approach to prosthodontics through speech science

THE PHENOMENON COMPLETE DENTURE

AN APPROACH Part

Norfolk,

L.

FUNCTION IN PROSTHODONTICS

TO PROSTHODONTICS

IV. Physiology

ALEXANDER

OF

THROUGH

SPEECH

SCIENCE

of Speech*

MARTONE,

D.D.S., M.Sc.,**

Vu., and Columbus,

AND JOHN

W.

BLACK,

PH.D."**

Ohio

are multipurpose, being at least, first, a part of the digestive system, second, an esthetic appliance, and, third, a part of the speech mechanism. The making of dentures, however, has not been characterized by the team approach. Typically, the prosthodontist is his own phonetician, and the professional literature shows that he is gradually becoming aware of this role. It remains a secondary role, however, and not one that is supported by his professional curriculum. Consequently, the physiology of mastication is well known to the dentist whereas the physiology of speech is infrequently considered. A brief review of the physiology of speech here is intended to provide a background for the practical application of the principles of speech science to prosthodontic problems. Speech is ordinarily taken for granted. There are no primary organs of speech, since each organ involved in the production of speech serves other basic requirements. The speech mechanism, then, may be considered a usurper, modifying from moment to moment each of several tracts to suit the particular needs of speech, The speech mechanism consists essentially of the upper digestive tracts and of the respiratory tracts (Fig. l), modified to form and control valves,

C

OMPLETE

DENTURES by definition

BREATHING

At the beginning of inhalation, the nostrils dilate to facilitate the intake of air. This air passes through the nares, nasal cavity, nasal and oral pharynx, and larynx. The soft palate is relaxed to provide a free passageway, and the pharynx is widely opened. The air passes through the open rima glottidis of the larynx into the *Part I, J. PROS. DEN. 11:1009-1018, 1961; Part II, J. PROS, DEN. 12:4-27, 1962; Part III, J. PROS, DEN. 12:206-219,

1962.

**Associate, Departments of Anatomy and Prosthodontics, Medical College of Virginia, ***Director, Speech and Hearing Science, The Department of Speech, The Ohio State University. 409

410

MARTONE AND BiACK

J. Pros. Den.

May-June,

1962

trachea and bronchi and then into the lungs. In general, this process is reversed in exhalation. A few observations about the power supply for speech are in order. Speech, at least loud speech, involves hyperventilation or excessive breathing. Quite simply, as the pressure level of speech is increased, more air is utilized in producing voice, and this amount of air exceeds the needs for physiologic wellbeing. The outward flow of air results from the coordination of contraction of the ventrolateral muscles of the abdomen, relaxation of the diaphragm, and “collapse” of the rib cage, forced in some measure by the internal intercostal muscles. This collapse is orderly to the extreme point that the physiologic accompaniment of the syllable, according to Stetson1 is a “stroke” of the internal intercostal muscles. Speech is directly related causally to exhalation, not inhalation. The sound is characterized by phonation or articulation, or both, plus resonance. The primary physiologic functions of the respiratory and digestive tracts in relation to their secondary function of producing and modifying sounds may be understood by recognizing that the speech mechanism includes three principal physiologic valves (Fig. 2) : valve I, the glottis; valve II, the palatopharyngeal region; and valve III, the orifice of the mouth. Physiologic Valve I: True Vocal Folds of the Larynx.-The vibrating mechanism produces vocal tones, and the true vocal folds serve as a valve only in con-

Fig. l.-Hemisection and point of crossing

of the head and neck showing the upper digestive of air and food (valve II: pharyngeal isthmus).

and respiratory

tracts

“,;lLILleer

;2

PHENOMENON

OF

I?LNCTION

Fig. 2.-Hemisection of the head and gions: (I) true vocal fold; (II) palatopharyngeal oral pharynx; (LP) laryngeal pharynx.

IN

neck

COMPLETE

showing region;

DENTURE

physiologic (Ill) mouth;

PROSTHODONTICS

valves (NP)

and nasal

pharyngeal p’harynx;

411

re. COP)

nection with speech sounds that have tone, i.e., the voiced sounds. Otherwise, the outgoing stream of air passes through the region of the vocal folds without interference, as in normal breathing. The valve mechanism serves to modulate the outgoing breath stream in the instance of voiced sounds only. It is a generator of sound waves which enables man to communicate at a distance as contrasted to the short distance through which one might communicate by whispering. The larynx, containing the vocal folds that serve intermittently as valve I during speech, is composed of three single cartilages and three pairs of cartilages. These are connected by ligaments and moved by muscles (Fig. 3, A). The larynx has a mucous membrane lining that is continuous superiorly with the pharynx and inferiorly with the trachea. The cartilages and muscles offer the means for adducting (approximating) and abducting (separating) the true vocal folds and for tensing them (shortening anteroposteriorly ) and relaxing them (elongating anteroposteriorly) (Fig. 2). The true vocal folds are causally related to voice, as opposed to whisper. The folds are attached anteriorly to the thyroid cartilage and posteriorly to the arytenoid muscles. When in a position of rest, as in quiet breathing, the free edges of the folds form a triangular opening which has its apex located anteriorly and its base posteriorly. The opening or aperture between them when they are not approximated is called the rima glottidis (Fig. 3, B). When voice is desired, the folds are approximated, and air is pushed against them from below with sufficient force to blow the edges of these elastic folds apart. The overload of air pressure is momentarily

412

MARTONE

AND

BLACK

Fig. 3.-Intrinsic muscles and cartilages of the larynx and the true vocal folds. A, Posterooblique view (portion of thyroid oartilage and cricothyroid muscle removed): (TA) transverse arytenoid; (OA) oblique arytenoid; (PC%) posterior cricoarytenoid; (Ct) cricothyroid; (Ae) aryepiglottic; (LCa) lateral cricoarytenoid;
spent. Tension restores the folds to a closed position. This cycle is repeated and becomes quasivibratory. The acoustic output is called voice. The muscles that control the vocal folds are divided into two classes, those within the organ itself (intrinsic) and those which act upon it from without (extrinsic). The intrinsic muscles have two main functions : (1) to adduct and abduct the folds and (2) to regulate the degree of their tension and length. The muscIes that open the rima glottidis are the posterior cricoarytenoids. They are attached to the posterior surfaces of the arytenoid and cricoid cartilages. Thus, they may rotate the arytenoid cartilages laterally and separate the true vocal folds. Closure of the rima glottidis is effected by the arytenoid and lateral cricoarytenoid muscles. They rotate the arytenoid cartilages medially and cause the true vocal folds to be approximated. The arytenoid muscles extend from the posterior and lateral surfaces of one arytenoid cartilage to the corresponding surface of the other. These bring the arytenoid cartilages together, consequently narrowing the rima glottidis. The most important muscle used in lengthening and tensing the true vocal folds is the cricothyroid. The vocal folds are relaxed and shortened by the thyroarytenoid muscles. The extrinsic (accessory) muscles act upon the larynx as a whole, connecting

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PHENOMENON

OF FCNCTIOK

IN

CObIPLETE

DEKTURI’

I’ROSTIIODONTICS

413

the larynx with the hpoid belle, the sterntmi, the toiigur, atid the pharynx (Fig. 4). By means of these muscles, the larynx nlay be elevated, tlepressed, and tilted. Physioloyic Valve II: Palatoplzary~~yeal Regiolz.-The pharynx is made up primarily of a constrictor band of broad, flat musclesinserting into a median raphe

Fig.

4.

Fig.

5.

Fig. 4.-Extrinsic laryngeal muscles with the sternohyoid and omohyoid muscles retracted: sternohyoid; (Oh) omohyoid; (Th) thyrohyoid; (Stt) sternothyroid. Fig. 5.-Posterior wall of pharynx: (LVP) levator veli palatini muscle; (LPP) lateral pterygoid plate; (WC) superior pharyngeal constrictor; (MPG’) middle pharyngeal constrictor; (IPC) inferior pharyngeal constrictor; (Sph) stylopharyngeus muscle; (Dp) posterior belly of digastric muscle; (PP) pharyngopalatinus muscle; (IP) internal pterygoid muscle; (SG) styloglossus muscle; (Sh) stylohyoid muscle; (La) lingual artery. (Sth)

414

MARTONE

AND

BLACK

J. Pros. May-June,

Den. 1962

along its posterior wall (Fig. 5). The pharynx may be divided arbitrarily into three parts (Fig. 2) : (1) The nasal pharynx is a continuation of the nasal cavity posteriorly; it is bounded inferiorly by the soft palate and terminates along the posterior pharyngeal wall near the atlas (1st cervical vertebra). Its only function is respiratory. (2) The oral pharynx is a continuation, inferiorly, of the nasal pharynx to the laryngeal pharynx, i.e., about the level of the hyoid bone. Its functions are respiratory and digestive. (3) The laryngeal pharynx is the inferior portion of the pharynx. It extends inferiorly from the oral pharynx and terminates in the esophagus at about the level of the VIth cervical vertebra. Its function is strictly digestive. The palatopharyngeal valve is located in the region in which the respiratory and digestive tracts cross each other (pharyngeal isthmus). Both in the act of swallowing and in speech, this valve divides the pharynx into the nasopharyngeal and oropharyngeal cavities (Fig. 2). The principal closure is effected by movement of the soft palate into contact with the posterior wall of the pharynx. Physiologic Valve III: The Mouth.-The mouth is a complicated valve, capable of making many changes, both in capacity and in size of the orifices. It is modified by many articulators, the chief one being the tongue (Fig. 2). The three physiologic valves serve to form a number of more specific articulatory valves, such as (1) the mandibular lip against the maxillary lip, (2) the mandibular lip against the maxillary teeth, and (3) the tip of the tongue against the alveolar ridge, etc. These valves are formed by momentary intrusions of some segment of the physiologic valves into the path of the outgoing airstream. Attention will now be focused upon the mechanism of speech as it depends upon the physiologic valves. PRODUCTION

OF

SPEECH

SOUNDS

Modulating the Airstream: The Consonants.-The kind of physical event that has been described as happening at the vocal folds can occur in somewhat the same manner at the lips or at the teeth. The successive events that give rise to speech sounds are ( 1) pent-up pressure, (2) overriding pressure, (3) momentary release of the pressure, and (4) forming again the obstacle to the breath stream. The trilled r, “vibrated” lips, or the s result from such sequences, but each is unique in the frequency of the “main events” (the series of quasiexplosions) and in the higher orders of frequencies that are superimposed on the little explosions. The dentist may remove, repair, or restore one of the two portions of a blocking obstacle that the patient habitually puts in the path of the airstream. The breath stream may be modulated more than one time for a single speech sound. For example, the airstream may be turned into a voiced sound at the vocal folds, This, in turn, can be reshaped or remodulated into z at the teeth or d at the alveolar ridge. In addition to sounds that are only voiced, only modulated one time, such as vowels, the ones that are both voiced and given an added character through a second modulation (for example, z) may result from blocking the airstream either completely or partially. The ones that are blocked completely, either voiced or voiceless, are called plosives and include p, t, g, k, b, and d. In forming these sounds, the

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PHENOXENON

OF

TABLE

FUiYCTIOK

I.

PRESSURE

IX

COMPLETE

BEHIND

DENTURE

THE

LIE

PROSTHODOI’iTICS

(P.S.I.)

INITIAL SOUND IN A WORD

FINAL SOUND 1N A WORD

Plosive Continuant

33.5 39.3

24.0 30.6

Voiced Voiceless

30.2 42.2

23.7 31.9

SOPND

‘l-ABLE

11.

I’KESSURES

OF hITIAL

AND

INITIAL SOUND IN A WORD

SOUND

--

E‘IIt4L

415

SOUNDS

FINAL IN A

SOUND

worn

-__

Plosive Voiced \Toiceless

0.08 0.09

0.26 0.28

Con tinuant Voiced Voiceless

0.16 0.17

0.28 0.30

air pressure builds up, probably not to a point of breaking through the obstruction but to an amount that “seems right” kinesthetically, and then is released or allowed to break through the obstruction as the muscles that control the blocking agents are relaxed. Individuals who experience reduced muscular tonicity through a loss of strength lose proper coordination for making these sounds. The air pressure over-, rides the blocking agents and results in a “sputtering.” Long habits may be disturbed by the dentist who “moves” the fixed articulator against which the talker presses a mobile one. For example, the maxillary teeth, gingivae and rugae are fixed and are pressed by the tongue tip for t. The amounts and distributions of the intraoral pressure that attend the plosive consonant sounds and other consonant sounds differ. In one instance, eight sounds were selected for comparison : h, d, t, p, v, u”, f, and s. The first four are plosive; the second four are fricative or continuant sounds (Fig. 6). Four of the eight are voiced ; four are voiceless. The pressure behind the lips in ounces per square inch in two different comparisons2 is shown in Table I. In yet another comparison of the same sounds, an interesting set of apparently contradictory values emerged.3 Note ab ove that initial sounds have more pressure than final so~~nds. Thus, the first t in “taught” would carry a greater pressure than the final sound of the word. Yet the pressure of the final consonants, when integrated throughout the duration of the sound, exceeded the values of the initial consonants in the ratio of 2 and 3 to 1. These results are shown in Table II. The

416

MARTONE

AND

BLACK

J. Pros. May-June,

Den. 1962

Fig. 6.--A, Profile view of a subject producing speech sounds: a plosive t with related oral structures outlined B, A fricative S; compare the relative positions of the oral structures with A.

of this outcome is apparent if the time over which the sounds occur is taken into account. In other words, initial sounds are brief and carry a relatively high charge of pressure. Final sounds are longer and do not have as high a charge of pressure as initial ones. However, when the pressure of the sounds is accumulated throughout their duration, the total pressure of final sounds exceeds that of initial ones. The differences in intraoral pressure, shown above, are acoustically differentiating. The dentist who alters the “fixed” portion of the block to the airflow risks giving his patient an articulatory disorder (Fig. 7). The ultimate outcome will reasonableness

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PHENOMENON

OF FUNCTION

IN

COMPLETE

DENTURE

I’ROSTIIODONTICS

417

B.

Fig. 7.-A, Profile view of a subject producing speech sound s. The natural teeth with proper oral pressure maintained. B, The drawing shows when the alveolar ridge is altered by loss of teeth and insertion of dentures.

drawing shows the the loss of pressure

depend (1) upon the extent of the alteration, (2) upon the auditory acuity of the patient, and (3) upon the patient’s facility in changing and shaping motor habits. The Vowels.-The pipe or tube that extends upward and forward from the vocal folds and particularly forward from the pharynx can be “divided” by humping the tongue. The hump may be far in front as in saying e or far back as in oo (toot j . The pipe or its divisions can be altered further in size through raising and lowering the mandible. These changes in the vocal tract represent the physiologic causal factors in the differentiation of vowels.

M.4RTOKE

AKD

HI.ACK

3. Pros. Den. May-June, 1962

Fig. %-The innervation of muscles of speech: (A) mesencephalic nucleus; (B) motor nucleus of mandibular nerve; (C) motor nucleus of facial nerve; (D) motor nucleus (ambiguus) of glossopharyngeal and vagus nerves; (E) hypoglossal nucleus; IF) sensory nucleus of trigeminal nerve; (G) sensory (solitary) nucleus of facial, glossopharyngeal, and vagus nerves; (DP) corticobulbarcortlcospinal tract; (EP) extrapyramidal tract; (Hns. gang.) basal ganglia. Ih-NERVATION

OF SPEECH

The principal motor nerves for the muscles of speech are the trigeminal (\‘th cranial), facial (VIIth cranial), glossopharyngeal ( IXth cranial), vagus (Xth cranial), and hypoglossal (XIIth cranial). These innervate the laryngeal muscles (vagus), muscles of the soft palate (mandibular division of the trigemitial and vagus), pharyngeal muscles (glossopharyngeal and vagus), muscles of the tongue (hypoglossal), and muscles of the periphery of the mouth (facial) in order to obtain motility, to control tonus, and, in turn, to generate and withstand pressure. The speech mechanism is characterized by motility, by the capacity to exert pressure, by the capacity to resist pressure, and by the ability of the talker to identify through habitual pressures against familiar structures the conditions for a particular sound. The muscles and the structures of the head and neck have been detailed previously in this series .4 The motor innervation involved derives from three pathways : the corticobulbar pathway, extrapyramidal paths, and cerebellar

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PHENOMENON

OF

FUNCTION

IN

COMPLETE

DENTURE

PROSTHODONTICS

41’)

paths (Fig. 8). The first of these, the corticobulbar-corticospinal, or pyramidal, tract permits the conscious control of precise movements required, e.g., in the arin the relearning of ticulation of speech sounds. This tract becomes important speech habits to accommodate new intraoral structures. The extrapyramidal tract also conveys some voluntary impulses as well as the control of muscle tonus, the regulation and inhibition of opposing sets of muscles, and the coordination of depth of breathing, tension of vocal folds, the lips, the cheeks, the tongue, and the pha-ryngeal walls. The third pathway, from the cortex to the speech muscles, is the cere-

bellar one, the route of the automatic coordination. This one takes over much of speech after childhood until violent changes in the speech mechanism or the functioning SUM

of the mechanism

are introduced.

RlARY

Some aspects of the physiology

of speech have been discussed

to provide

a basis

for a scientific approach to the phonetic factor in denture construction. In the next article of this series, current research in the field of speech science which has prosthodontic significance will be considered. REFERENCES

1. Stetson, R. H. : Motor Phonetics, Amsterdam! 1951, North Holland Publishing Co. 2. Black, J. W.: The Pressure in the Oral Cavity in the Production of Consonants, Pensacola, 1950, The Ohio State University Research Foundation and U. S. Naval School of Aviation Medicine, The Bureau of Medicine and Surgery, Project NM 001 064 01 Report No. 4. 3. Black, J. W.: Some Physiological Accompaniments of Speaking, Pensacola, 1952, The Ohio State University Research Foundation and U. S. Naval School of Aviation Medicine, The Bureau of Medicine and Surgery, Project NM 001 064 01 Report No. 10. 4. Martone, A. L., and Edwards, L. F.: The Phenomenon of Function in Complete Denture Prosthodontics. Anatomy of the Mouth and Related Structures. I. The Face, J. PROS. DEN. 11:1006-1018, 1961; II. Musculature of Expression, J. PROS. DEN. 12:4-27, 1962; III. Functional Anatomic Considerations J. PROS. DEN. 12:206-219, 1962. 909 NORFOLK MEDICAL NORFOLK 7, VA. DEPARTMENT THE OHIO COLURIBUS

TOWER

OF SPEECH STATE UNIVERSITY 10, OHIO