Growth of the jaws and the etiology of malocclusion

International

Journal of

Orthodontia and Dentistry for Children (All

rights

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VOL. 21

SEPTEMBER,

1935

so.

9 -==z

Original Articles

xppliect to prelintinary du.tct, Science proceeds by a controlled use of the imagination whereby provisional hypotheses are formed; such provisional hypotheses may be of enormous value as guides to investigation, even though t,hey map subseqwntl~ prove to be inrrtleqnirtc’ or false.--Brash.

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HE practice of orthodontia has been greatlv I influenced by several extensive st,udies, the results of which were presented to the professiotr within the last decade. Each of these studies or investigations, while complete within its scope, dealt chiefly with a particular phase of the broad orthotlout,ic yroblrm. For this reason, the several conclusions arrived at stand somewbatz dissociated from the generally accepted facts; and, although a. direct relationship is recognized, the exact place of these conclusions in relation to the I’& of our knowledge has not been definitely established. Theories, which inevitably arise from such investigations, serve only in few practical instances. They remain theories, and their practical application is greatly limited. In order to justify the acceptance of theories or conelusions drawn from investigations, their usefulness in practice must be made evident ; for the ultimate aim of all scientific studies is to establish facts of practical value. The study of the growth of t,he jaws and of the etiology of malocproblem, which has many elusion is only a part, of the great orthodont,ic yamifications. Growth and etiology may be studied from diRerent, at&s. anti and special concept-s. t.lte reon account of the differences in points of view Thus oiie invrstiga,titrn may snlt,inp conclusions will correspondingly differ. *Chief

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be focused on the “normal growth processes,” which will disclose the changes Another investigation may deal with the responsible for jaw enlargement. normal physical manifestations of these changes ; while still another study may have for its object the determination of the effects of injurious influences on the growing individual. Independent endeavors in these directions are of great value, but the interpretations of the data thus obtained often contain inconsistencies, which in the light of a special concept seems logically acceptable. A proper correlation of facts from the independent studies will eliminate many such inconsistencies, and in several instances differences of opinion will disappear. The factors held responsible for the malformations of the jaws and the malocclusions of the teeth are numerous, and extensive statistical data are available. The conclusions drawn from these are not convincing, for in practically all instances they involve the presence of associated colzditions. Usually one condition, or a group of conditions, is assumed to be responsible for another. From a scientific point of view such a procedure is not permissible. It still remains to be shown that the secondary condition, which is presumably caused by the primary condition or a group of conditions, cannot exist without the presence of the primary group; and also whether the entire picture presented is not due to still a,nother cause, which in the course of investigation had not been recognized. A classic example of this is the assumption that mouth-breathing due to enlarged tonsils and adenoids is responsible for certain types of malocclusions. This assumption may or may not be true. The fact that these conditions are often associated with a particular kind of malocclusion ‘does not prove that enlarged tonsils and adenoids produce that deformity. The probability still remains that both the malocclusion and the adenoid enlargement are caused by some other influence, which we have not been able to trace. The problem of the etiology of malocclusion is intimately connected with the growth and development of the jaws. During growth, the developing individual may be subjected to injurious influences, and if malocclusions can be caused; they must necessarily be brought about by such injurious agents. But the mode of production of malocclusions and jaw deformities, is a probThe study of etiology lem separate and distinct from the problem of etiology. involves the recognition of those influences which may have an injurious effect on growth, and it is based on the assumption that malocclusions are caused by swh injuries. Without this assumption there can be no etiologic inquiry. The study of the mode of production, or genesis of malocclusions and jaw deformities, depends upon a thorough knowledge of the normal growth mechanism, and the alterations of the growt.h processes brought about by the action of injurious agents. These alterations in the processes of growth must OCCUr if malocclusions are the result of general injurious influences, and they represent a,n im%i-ftwence with growth and development, which manifests itself in relative deficiencies and excesses in the related parts of the masticatory apparatus.

Growth

of Jaws and Etiology

of Malocclusion

At presentit’is definitely established that a complex mechanism presides over the processes of growth. It is probable that alterations in the growth processes occur as a result of disturbances within the controlling mechanism itself, and that the deformities are the ultimate manifestations of these disturbances. It is equally probable, however, that malformations develop from a direct injury to the growing tissues, which may be permanent or may persist for a longer or shorter period. But whatever the mode of interference may be, the processes of growth must undergo changes under the influence of injurious agents; otherwise malformations cannot develop. The nature of these changes is not well understood, but we are in the possession of valuable ioformation regarding the behavior of tissues thus affected, which enables us to understand better the mode of production of jaw deformities and malocciusions. From the etiologic point of view it does not make any difference whether the injurious influences inflict a direct injury upon the growing tissues, or whether the resulting deformities are caused by disturbances of the growth-controlling mechanism (endocrines) . From the therapeutic standpoint it may make a great deal of difference. For our present purposes, however, it is sufficient to recognize that, apart from malformations which are primarily inherent in the individual from the time of conception, deformities are the results of injuries of a general or local character. In order to avoid speculative hypotheses regarding the mode of formation of malocclusions and malformations of the jaws, it becomes necessary to examine critically the available facts concerning growth and development. The proper correlation of these facts is the basis upon which an acceptable hypothesis will be formed which will immediately be elevat,ed to the rank of a theory by abundant evidence from investigations not primarily designed to confirm the hypothesis. An established theory will point to a better understanding of etiology and a more thorough knowledge of the factors inffuencThe hypothesis will be formulated upon facts derived from ing prognosis. generalized investigations dealing with different phases of growth. The work of Prof. James C. Brash on the Growth of the Jaws, together with Va&atians in the Form of the Jaws, by J. Sim Wallace, is adopted in this work for t?he The brilliant and convincing experimentfs of Brash study of mrwml growth. on madder fed pigs definitely establish the directions and sites of maxillary and mandibular bone growth. The observations of Wallace on the same individual for twenty-four years, enable us to estimate the lateral changes in the dental arches from childhood to adulthood. From the reinterpretations of Hellman’s measurements of the human face, the rates at which growth changes occur will be accurately determined. The most logical method of approach to a satisfactory explanation of the effect of injurious influences on the growing individual, is given by the theories of Murk Jansen on the feebleness of growth. While his theories are not generally accepted, and are regarded as highly speculative, the conohrsions of Brash and Hellman definitely confirm the fzcndamelztal laws of f&da-

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The work of Wallace will be taken up first, followed by the description of the experiments of Brash, and the measurements of Hellman. The work For a corof Jansen will be given in sufficient detail to explain his theories. rect statement of conclusions, the authors are freely quoted, and the most important part of their work is given in their own words. (To

be om.Jin.aed)