SPECIAL ARTICLES

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SPECIAL ARTICLE

THUMBSUCKING:

A

LEARNED

RESPONSE

By David S. Palermo

Child Welfare Research Stat#{252}nm, State Uniccrsity of iowa

ADDRESS: l)epartment of Psychology, Southern Illinois University. Carhondm,le, Illios.

392

Ped

#{237}a!

rics

VOLUME 17 MARCH 1956 NUMBER 3

T

HE1IE was a day not so long ago when

the habitual tllumbsucking baby was

looked upon as being a happy baby. Today, however, the ignorance of the people who

held this 1)oillt of view is sometimes looked

impon as imi indicatiomi of the progress of

modern blues. It is the purpose of this paper

to attemnpt to show briefly how the modern

point of view has come about, to indicate

that the ignorance of the past is largely still with us, and finally to put forth a theory

to account for the arousal of the

thumb-sticking response in terms of general

learn-ing theory principles.

There were 3 main reasons for the fail of the Old! theory. First came the rise of

moi-em medicimie amid the discovery of the germ.

There need be little said here about the

en-suing rapid! awareness of the public as vell as the better informed of the necessity for

cleanliness, especially with respect to things which miiight go into the body. Thus, it naturally follower! that babies shoimidi not

1)ut their fingers in their miloutils for fear

that germs would enter their defetiseless

i)Odlies. It iiiight be nientiomiedi before leav-imig the subject that today there seems to be

gemieral agreement ill the medical

profes-sion that there are humidreds of sources of

germs which enter the 1)ody in many himmi-dreds of ways, one of the least importamlt of which is

by

thumbsucking; Ofld! further,

that disease itsitally does not directly fol-low the entrance of germs into the body

bitt often occurs in a period of lowered resistance during which time germs

at-ready iii the 1)ody are emiable :1 to miaultiplv and caimse sYflhI)toms.

The second! group decrying the thimmi)-sticking child! was the dentists, particimlarlv the orthodomitists who spoke imp becaimse of the great harm they felt was being (lone to

tile jaws, palate, and the occlusion of the

teeth. This group in particimlar recorn-mended devices including niorlified strait

jackets, and bar! tasting stmbstances to pitt on the tliimmb, iii order to prevent any

in-jury to future mastication.

The third force diriving out the old theory

calile vitli the rise of Freudian theory. Freud believed!, “. . . that the associatiomi

of the manifestations into which we have gained au insight through psychoanalytic

investigation justifies us in claiming

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essential features of infantile sexual activi-ties.” Freimd stresses the point that this sexual imptmlse is not directed to other per-sons but that the child gratifies himself on his own body, i.e., he is autoerotic. The child’s most important activity and greatest pleasure is the sucking associated with

eat-ing and he therefore sucks his thumb to

satisfy a pleasure which he has already perienced and now remembers. The lips

come to behave like an erogenous zone.

“The child does not make use of a strange

object for sucking but prefers his own skin, because it is more convenient, because it thus makes himself independent of the otmter world which he cannot control, and

because in this way he creates for himself,

as it were, a second, even if an inferior,

erogenous zone.” Freud than goes on to say that, “In thumbsucking or pleasure-sucking, we are already able to observe the three essential characters of an infantile sexual manifestation. It has its origin in an

aria-clitic relation to a physical function which

is very important for life; it does not yet

know any sexual object, that is, it is auto-erotic, and its sexual aim is under control of an erogenous zone.”

Since open expression of sexual impulses is taboo in our cimlture it became clear, as

Freud became more and more popular, that

a baby certainly should not suck his thumb. However, if this theory was not enough to indicate that thumbsimcking is not what a

happy child does, the numerous theories

which arose from the Freudian beginning made the sins of thumbsucking quite clear.

Various theories pointed out that if the child sucked his thumb he was bottle not

breast fed, or he was not getting enough sucking experience which is very important, or he was weaned too abruptly; in any case

the parent was not iiandling the child in

the proper psychological fashion. Thus, the parents of today have been whipped into an emotional turmoil over the thumbsucking of

tileir children to the extent that, “Often

parents who have such intense emotional reactions over the habit of thumbsucking that it becomes an all-absorbing worry, are

(luite UIlcoIlsCiOuS about the thoughts and

feelings of their children.

We shall now take a look at what little experimental evidence exists on the subject

to determine if any conclusions may be

drawn from the data. One of the most strik-ing aspects of reviewing the literature is the fact that there has been so little work

done in the area. The concern about the

1)rOblem of thutmbsucking as expressed by many writers in child psychology would

lead one to expect more than 3 experimental studies during the last 8 years in the psy-chological literature. True there are another

3 in the journals of the pediatrician but 6

experiments in 8 years on a problem so grave as some would lead us to believe per-haps reflects the opinion of this author, and at least one other, that as far as thumb-sucking and nail biting are concerned they

“both have been regarded as far more

serious than they really are.”#{176}

In the first study of this form of behavior Levy’3 concluded that some thuml)sucking

was congenital but that more often its origin was closely associated with the infant’s

original feeding methods, i.e., “that babies who sucked a long time for their meals, hardly ever developed the habit, that babies “ ho worked a very little time for their

meals . . . almost invariably developed

sucking iiabits.” Subsequently v’ felt that an experiment with puppies in which sucking time could be controlled woimld con-stitute “a final test of the theory.” Using 6 puppies from the same litter, he let 2 re-main with the mother amid on the tenth day of life 4 were takemi and fed by a bottle.

The quantity of milk was controlled so that

all dogs maintained approximately the same

weight. One pair of dogs sucked from

bottles with small-holed nipples and after

feeding was given supplementary sucking

on the examiner’s finger. The other pair

sucked very rapidly from bottles having large-holed nipples. The siiort-time feeders,

exclusively, developed suckimig movements after meals, simcking noises during sleep,

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At about this same time Lewis published

several studies”’7 on the effects of

thumb-sucking on the teeth. His results indicated

that children who sucked their thumbs did have significantly more malocclusion of the

deciditous teeth bitt if the child stopped the habit by 6 years of age the malocclusion corrected itself. A few years later Johnson7

studied the effects of thumbsucking on

nialocclusion. He concluded that

thumb-sucking may be an etiological factor in Inalocclusion ill either the deciduous or the

permanent denture but that malocclusion

of the deciduous dentition may correct it-self after the thumbsucking habit is broken

if normal function of the lips exists.

Heering3 ill an observational study of 25

hal)ies between 2 and 17 weeks of age con-eluded that “sucking can be considered

habitual for the early period of infancy.”

In addition, she notes that the most common

position for the baby’s arms is either such

that the hands rest between the waist and chin with the arms close to the body or on it, or with the arms heid close to the body and the hands lying between the chin and

the top of the head.

In 1938 Bakwin and Bakwin’ noted that “there is no evidence to indicate that thumb-suckers are more susceptible than other children to gastrointestinal disturbances, in-fection, or stomatitis.”

In 1937 Gesell and Ilg4 published a book

on the feeding behavior of infants in which

they proposed, on the basis of their work, that thumbsucking was not due to sucking

want nor to a reduction in the duration of the

feeding time due to abnormal rapidity of mniik flow because there are so many excep-tions to this relationship. They note that

finger sucking is most prominent when the

postural development is most facilitative and that the behavior seems to wax and vane with the teething periods, i.e., each successive teething episode seems to

exacer-I)ate this hand to mouth response. These aimthors conclude: “In considering the pos-sible underlying factors in thumb-stmcking.

OtiC is strimck by a sex difference and by

cer-tam

associated personality characteristics.

A greater number of boys than girls suck

their thumbs. The thumb suckers are good sleepers from an early age. They omit a night bottle at 3 or 4 months because they do not awaken for it. They play contentedly

alone but are usimally sociable when

ap-proached. They are fairly amenable in variety of situations. They are inclined to be more rather than less active and given to sudden fatigue. Generally they show no special attachment either toward bottle or

breast. Their feedings are usually at 4- or

even 5-hour intervals. This schedimle has the effect of reducing their simcking, but they (10 not insist on bottle feeding. Tue bottle

is readily relinquished when withdrawn, or it may even be refused.

“It is apparemit, therefore, that a large

variety

of

factors must be considered in the

interpretation of any given case of thumb sticking.”

Regarding the seximal significance

attrib-uted to thumbsucking these authors have

the following to say: “In the neonatal period

vigorous sucking by male infants is often

accompanied by erection of the penis. The erection may continue for a short time

be-yond the nursing bitt tends to disappear

with satiety. It does not follow that thumb sucking has a specific seximal significance.

Erection occurs also imi association with

other types of activity. The phenomenon,

therefore, may be explained on the basis of autonomic overflow, and may have neither more nor less significance than

other associated evidences of autonomic

activity.”

Thus it may be seen that by 1938 there

was evidence that all 3 of the main factors

which had brought aboitt the taboo on thumbsucking had been indicated to he

false by some sort of experimental research.

Bakwin and Bakwin had spoken out against

the medical argument, Lewis had shown the dental argument to be largely false, and

Gesell and hg argued against the professed

psychological aspects involved.

That

the question was not settled,

how-ever, even as late as 1944, is seen in the

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about the sucking opportunities of babies and although she does not concern herself quite so much with the bad effects of

thumbsucking she is : “. . . thoroughly

con-vinced that a favorable sucking experience for the first three months contributes

con-siderably to the development of several

aspects of structure and of behavior. The evidence indicates that sucking experience

is important for the structural development

of the face and jaws, for digestion, for the

general well-being of the child, for the de-velopment of alertness toward factors

out-side the child’s own body, for the age at which speech appears, and for the facility

of the speech function.

“These findings and the fact that babies

whose sucking experience is favorable show

a distinctly pleased expression lead me to

believe that sucking plays an important part

in the structural development of the face

and jaws and of the sections of the brain

connected with facial expression.”

More recent literature has viewed thumb-sucking as evidence, “which indicates an emotional disturbance or in other words a distimrbance in interpersonal relations”;’#{176} that “One of the primary determinant fac-tors in the arousal of the habit, as far as can be judged, is the degree of satiation in

infants of the simcking activity”;hl and an

activity which seems to affect the oral

struc-tures of children with poor bites but has little effect on good bites;21 amid that

“what-ever tile cause or cure of thumb sucking,

self-regulated feedings without limitation in nursing time are no complete panacea.”22

Ruttle et al.’ in a recent dental study of

thumbsucking children found elongation of the anterior segment of the maxillary arch

producing spacing, labial inclination, and protrusion of the maxillary incisors. In

addi-tion, true and apparent overjet were

in-creased strongly by the thumbsucking habit. In this study, however, most of the children

sucked their thumbs long after 6 years of

age so that the results are not contradictory

to those found earlier by Lewis.

Kunst” found, in a rather careful

obser-vational study, that thumb and finger

suck-ing

frequency increased as time elapsed

after feeding, and that the amount of this

sucking correlated positively with the liquid

volume of the formula taken by the infant

and negatively with the caloric value of the formula consumed. Also there was a fairly consistent trend toward more thumb and finger sucking by teething infants, and from birth to 5 months there was more thumb and finger sucking in the prone than in the supine position.

In a study by Davis et al.2 60 babies were divided into 3 groups of 20 each, 1 group fed by cup, 1 by bottle, and 1 by breast during the first 10 days of life. They found that breast fed babies developed a stronger sucking reflex than either of the other 2 groups which did not differ from one another. There were no statistically signifi-cant differences between the groups with

respect to amount of spontaneous oral

ac-tivity or amount of crying.

Yarrow,’4 in a recent study of the relation-ship between feeding in infancy and thumb-sucking, reports no significant relationship between duration of breastfeeding and thumbsucking, nor between age of weaning to the cup and thumbsucking although there was a definite trend in the latter case for children weaned late to engage in more thumbsucking. A significant relationship was found indicating that the shorter the feeding time in infancy the greater the amount of thumbsucking exhibited by the children. The author, however, gives no indication whether the short time feeders had more feedings per day.

Approaching the problem from a some-what different point of view, Sears and Wise’#{176}used a technique in which mothers were interviewed concerning the feeding be-havior of their children after the children

were somewhat older. Their results indicate

that the oral drive is strengthened by longer

retention of the sucking method of feeding.

According to their theory, once the sucking

(Irive is stremigthened by 1ractie amid the

accompanyimig reinforcement, the amount of

substitutive sucking would be expected to

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suck-ing. The data temldled to indicate that it is the strength of the oral drive and not the amount of frustration involved in weaning that determined the occurrence of

thumb-sucking. They show how Levy’s results are not contradictory, as might be thought on first glance, but rather are in accord Witil

their resimlts.

In summarizimig the literature it would

seen-i clear that the medical claims against thumbsucking, and those of the dental group were highly exaggerated if not false.

The psychological problems are not quite so clear, but, these too, seem to have been rather exaggerated or at least not backed

imp with any amount of convincing

experi-mental data. The data are sparse,

contra-dictory, imnsystematically gathered in many cases, and by no means conclusive as far as the psychological causes or implications

of this behavioral manifestation are

con-cerne(!. Kanner8 gives what seems a

broad-minded practical approach to the problem

on the i)asis of what we know today: “No therapeutic measures are needed when

in-fants suck their fingers in the first 2 or 3 years of life. Treatment is to be directed to I)aremital attititdes. Anxieties based on any of the above-mentioned cultural implica-tions (damage to physiognomy, suscepti-bility to pathogenic germs, future alcoholism and oscimlatory perversions) should he dis-pelled; this can be done by the creation, on the part of dentists and pediatricians, of a less fear-ridden attitude with regard to the performance.”

At this point the aimthor will advance a theory, somewhat in the same framework

as the one in which Sears and Wise worked, in an attempt to show that thumbsucking is a response which may be learned during infancy in accordance with the laws of learning as developed by such investigators

as Pavlov, Thorndike, and most recently by

Hull.6

For purposes of analyzing this response

let us assiimiie that hunger arouses certain disturbimig internal stiiiiuli to which the

OrgamiiSni iiiay respomid. Further, let its

assunie that if the responses made to these

imiternal stilliuli result in the reductioti or elimination of them, then on future

occa-sions when these stimuli are aroused there

will be an increased probability that the

same response or response sequence will

occur. In addition, let us assume that stimuli similar to those which arouse the response or response pattern involved may also

aroimse the same response or response

se-quence. The more similar these stimuli are to the original ones, the greater is the

prob-ability that they may arouse the same re-s1)Onses. This latter is tile familiar concept of stimulus generalization. Finally, let us assume that as the intensity of the stimuli increases there will be ami increased! 1)r01)-ability of the occurrence of some response.

(It follows from the second assumption that

ill this case the response most likely to occur

is the one which has previously reduced

tue

dlisturbing stimulation now present.) %Vith

these assumptions in mind we may now turn to the specific analysis of the tiiumbsimcking

response and the manner in which it iiay

he learned.

The infant at birth has several dloniinant

needs which he cannot satisfy and one of

these is hunger. As a result of being

en-tirely dependent on others for the

satisfac-tion or reduction of this drive the infant cannot reduce the drive as it arises and, therefore, must wait on an adimit to help him. As a result of this dependency the drive and the resultant stimulation becomes quite great, at times, before anything is done about them. It seems only natural, if

it may be assumed that this is one of the few sources of intense stimulation not

im-mediately removed as soon as it arises, that

the first learning of the infant will occimr in connection with the reduction of this stimu-lation. Thus, the child learns to suck the nipple of the breast or bottle, as the case may be, and is rewarded by the reduction

of the iiimnger pains. This one soimrce of

stimulation then is responsible for at least

a large part of the child’s first learning.

The stimulus is the nipple, the response the sucking, and the disturbing stimuli

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:397

It would seem that the situation is

ex-additiomi to these t)asic aspects of tile feed-ing process, there are a number of other

incidental stimuli and responses which are associated with this sequence. The stimuli

include the warmth associated with being

held during this act, and obtained from the

food itself, the presence of the mother, the tactual stimulation of the nipple and the

srmcking movements, the swallowing of the food, the vocalizations of the parent, and a

number of less tangible factors which may or may not be involved, such as the sup-posed security, pleasure, and comfort which, from an adult point of view, seem to be as-sociated with this sequence of behavior. In addition to the response of sucking and the

subsequent reduction of the hunger

stimu-lation there is also closely associated with feeding the sleeping response which

ally follows the period of sucking.

Thus it may be seen that the sequence,

for the infant, involves the arousal of a

strong hunger drive (so strong that the child cries as a result of the internal stimu-lation involved) followed by the mother’s picking up the child and presenting the

nipple, whereupon tile child sucks until full, and usually falls asleep.

Before going any further with this analy-sis it should be pointed out that if it may

be assumed that the child develops in a

ce1)halo-caimdlal amid I)roximo-c!istal manner,

one of the most sensitive parts of its body

is the head and most particularly the lips.

Thus, the sucking associated with eating is a highly stimulating response. In addi-tion, the only things the infant is capable of playing with are his own hands. This is

largely because he cannot handle any other

objects and due to poor sensory apparatus his hands are some of the few available things that stimulate him. Due to the child’s postural development the hands are quite close to one of his most sensitive receptors, the lips, and as a result, at times, come in contact with these receptors. Further, the thumb, in particular, is similar in size and

shape to the nipple b’ which the child is

fed.

cellent for the development of a thumb-sucking response. The first time the response occurs it is probably jimst a ramidona move-ment whereby the hand comes in contact with the face and the finger or thumb be-comes lodged in the mouth. At first it is probably an anticipatory response to tile

first internal stimuli aroused by himnger as evidenced in the Kimnst study where it was foimnd that between 2 and 17 weeks the sucking response begins as soon as hunger contractions begin to gain momentum.

Combining the physiological aspects with learning principles it would appear quite

Plausible that tile tiiimmnbsucking response might be expected to occur qimite often imi

the young infant. During his random

move-ments it is quite conceivable that the hand of the child should come in contact with

the face and one of the fingers become lodged in the mouth. The thumb, or finger, once in the mouth, acts as an

imncondi-tioned stimulus evoking the sucking re-sponse which in turn brings about the flow of saliva which is swallowed, and in part, completing the cycle of the imsual feeding procedure. Considering the fact that the infant when actually eating takes 20 to 30 minutes to reduce the hunger stimulation completely it is not surprising that thumb-sucking does not extinguish easily just be-cause the hunger stimuli are not immedi-ately reduced.

Since the stimulation from hunger in-creases as a function of time since last feed-ing it follows from the assumptions made earlier that one would expect thumbsuck-ing to increase with time of food depriva-tion. The hypothesis is borne out to some extent by Kunst’s data where she found that the thumbsucking in infants up to 17 weeks begins when hunger contractions begin to gain momentum and increases in frequency until the feeding time.

Thus it appears that thumbsucking has

all the necessary components to make it

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stimulus reduction is actually so far re-Ilioved from the beginning of the food suck-ing response that thumbsucking is not

easily extinguished. In this manner we are

able to account for the behavior of

thumb-sucking before meal time.

The fact that thumbsucking is next most often observed when the child is tired may

be explained in a similar manner. It will be remembered that the infant as a rule falls asleep upon the completion of the feeding process. Thus, the sucking response

and the stimuli which it produces act to produce the sleep response. As a result, a

stimulus-response connection is set up in such a manner that when the child becomes tired the internal stimuli associated with

tiredness arouse the sucking response and

the ensuing sleep reinforces the response.

It would follow from the above

hy-potheses that children fed on a schedule of frequent feedings should exhibit less thumb-sucking since there is less possibility that

the amplitude of the hunger contractions

will cause enough stimulation to produce a simcking response. In Levy’s study” we

find confirmation of this deduction for he foimnd that children fed 011 a 3-hour schedule exhibited less thumbsucking than those on

a 4-hour schedimle. It would also be expected

that children who did not fall asleep upon completion of the feeding process as infants,

would suck their thumbs less when tired

than those who fell asleep during the time

they were fed. There are no experimental

data on this deduction, however, to this writer’s knowledge.

In line with the Sears data, it follows

from this development that infants fed by cup from birth should exhibit less

thumb-sucking behavior than those fed by nipple.

Fimrther, the Sears data indicate that the

more sucking the child has (i.e., the more

tiiorough the conditioning or learning of

the sucking response) the greater the amount of sucking when the child is weaned. This finding again is in line with the theory here put forth.

As far as the differential incidence of

thuimhsucking in breast- or bottle-fed babies

is concerned it would appear from this

tileory tilat there should be no difference

between the 2 groups except in so far as perhaps the nipple of the bottle is closer on

a similarity continuum to that of the thumb

of the child. Thus, there might be expected

slightly more thumbsucking on the part of

the bottle-fed babies.

There is one otiier occasion on which

tiiitnibsucking is noted! quite often in

chit-dren; at times \viletl the child seems to be insecitre for some reason. It would seem

that the dlevelopment of the response in this sitimation would be a result of later learning than occurs in infancy. As the child grows to the stage where he meets some of the social barriers for the first time, lie begins to be punished for dloing things

which iiis parents amid! others wish him not

to (10. If we assume tiiat omie of the times

the chilc! may he sure lie is doing the right

thing is when he is eating, then eating, or specifically the simcking response in this case, becomes associated with a feeling of security and lack of anxiety. When the

child is simcking on his bottle usually every-omie is quite happy, there are few umipleasant eyents, and the child is reinforced! in

numerous ways by the parents and others for being a good child. If we may assimme

this to be the case, like other occasions

when the thumbsucking response is learned,

the response will occur at times when it will reduce internal stimulation, in this case when anxiety or insecurity arouse internal stimulation of a disturbing nature. It would follow from this that in children from homes

where the feeding situation is a pleasant

one between mother and child, i.e., where the mother is neither anxious nor punitive about the feeding situation, thumbsucking would be more common at times of

in-security on the part of the child. Again. there are no data on this hypothesis to the writer’s knowledge.

In summarizing, it would appear that thumbsucking is one of the earlier examples of learning in the infant. It seems to follow all the general laws of learning as far as

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hypoth-SPECIAL ARTICLE 399

eses otmtlined here. It appears plausible in

this case to assume that if the response is considered undesirable, the parent should remove the reinforcement which the

re-sponse brings about, or remove the stimuli

involved before the thumbsucking response

has a chance to be aroused. With the

ac-quisition of verbal facility on the part of the child one would expect that the re-sponse should drop out by itself as the ap-propriate cause and effect relationships are learned. This, of coimrse, presumes that the response has not, in the meantime, taken on other rewarding characteristics such as the manipimlation of adult behavior as a result of constant parental concern over the child’s

behavior.

ACKNOWLEDGMENT

The author is greatly indebted to Dr. Alfred Castaneda, Dr. Ernest Hixon and Dr. Winifred Shepard for their helpful

suggestions about parts of this paper and

to Dr. Boyd McCandless for his critical

readings and encouragement during the

preparation of the manuscript.

REFERENCES

1. Bakwin, R. M., and Bakvin, H.:

Psycho-logic care during infancy.

J.

Pediat.,

12:71, 1938.

2. Davis, H. V., Sears, R. R., Miller, H. C., and Brodbeck, A.

J.

: Effects of cup, bottle and breast feeding on oral

activi-ties of newbormi infants. PEDIATRICS, 2:

549, 1948.

:3. Freud, S. : Three contributions to the theory of sex. In Brill, A. A., editor: The Basic Writings of Sigmund Freud. New York, Random, Inc., 1938, book III, pp. 553-629.

4. Gesell, A., and JIg, F. L. : Feeding Be-havior of Imifants. Philadelphia, Lip-pincott, 1937.

5. Heering, G. A. : A study of thumb-sucking in infants from two to seventeen weeks of age. Child Development, 3:273,

1932.

6. Hull, C. L. : Principles of Behavior. New York, Appleton, 1943.

7. Johmison, L. R.: The status of

thumb-suckimig and finger-sucking.

J.

Am. Dent.

A., 26:1245, 1939.

8. Kanner, L. : Child Psychiatry. Sprimigfield, Thomas, 1950.

9. Kanner, L. : Behavior disorders in

child-hood. In Hunt,

J.

1cV., editor: Per-sonality and the Behavior Disorders,

Vol. II. New York, Ronald, 1944, pp.

761-793.

10. Kaplan, M. : A note omi the psychological implications of thumb-sucking.

J.

Pediat. 37:555, 1950.

1 1. Klackenberg, G. : Thumbsucking;

fre-quency and etiology. PEDIATRICS, 4:418, 1949.

12. Kunst, NI. S. : A stimdv of thumb- amid! finger-sucking ill infants. Psychol. Monogr., 62:1, 1948.

13. Levy, D. M. : Fingersucking amid acces-sory movements in early’ infancy. Am.

1

Psvchiat., 7:881, 1928.

14. Levy, D. M. : Experiments on sucking reflex amid social behavior of dogs. Am.

J.

Orthopsychiat., 4:203, 1934.

15. Lewis, S.

J.

: Thumb-sucking; Cause of malocclusion in (leciduoims teeth.

J.

Am. Dent. A., 17:1060, 1930.

16. Lewis, S.

J.

: Undesirable habits

influenc-ing the deciduous dentitiomi.

J.

Am.

Dent. A., 18:1766, 1931.

17. Lewis S.

J.

: The effect of thumb and

finger sucking on the primary teeth and dental arches. Child Development, 8:

93, 1937.

18. Ribble, M. A.: Infantile experience in

relation to personality development. In Hunt,

J.

McV., editor: Personality and the Behavior Disorders, Vol. II. New

York, Ronald, 1944, pp. 621-651. 19. Ruttle, A. T., Qimigley, W., Crouch,

J.

T.,

and Ewan, C. E. : A serial study of the

effects of fimiger-simcking.

J.

Dent. Res.,

32:739, 1953.

20. Sears, R. R., and Wise, G. W. : Relation

Of cup feeding ill infancy to thumb-sucking and the oral drive. Am.

J.

Orthopsychiat., 20: 123, 1950.

21. Sillman,

J.

H. : Thumb-sucking and the oral

structures.

J.

Pediat. 39:424, 1951.

22. Simsarian, F. P. : Case histories of five thumb-sucking children breast fed on

unscheduled regimes, without limitation of nursing time. Child Development,

18:180, 1947.

23. Thom, D. A. : Everyday Problems of the

Everyday Child. New York, Appleton,

1927.

24. Yarrow, L.

J.

: The relationship between nutritive sucking experiences iii infancy

and non-nutritive sucking in childhood.

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1956;17;392

Pediatrics

David S. Palermo