Authors | Topics | Forthcoming
(Read before the annual meeting of the New Jersey State Dental Society, at Newark, April 8 to 11, 1925.)
So much has been written about anatomical articulation within the last few years, and so many theories have been presented, with as many instruments designed to bear out these theories, that to many of us it may seem a well earned rest is needed, and that the subject should be laid aside until we have digested thoroughly what has already been presented. The intention of this paper, therefore, is not to burden you with anything new, but to present to you merely a summary of the results obtained from a series of experiments carried out over a period of several months of reaserch, with a word or two by the way of interpretation. Up to the present time, the solution of this problem has been attempted either by men outside the prosthetic field, who have made extensive studies in the development and functioning of the temporomandibular joint from the anthropological standpoint, or by men within the prosthetic field, who, by virtue of the skill they have attained over a long period of years of pracice and experience, have logically enough formulated certain theories, and have devoted years of time and huge sums of money to the construction of instruments especially designed to bear out these theories. It is frankly surprising to note that the results aimed at, such as the construction of serviceable dentures or other prosthetic appliances, have been obtained in spite of the diametrically opposed lines of reasoning followed. The fact that the results obtained by these men have been consistently uniform, although their theories differed, suggests the inference that the uniformity of these results may be traced, not to the working out of these very diverse theories, but very probably to the application of an intuitive diagnostic sense which they have gradually acquired over their long period of years of experience in this particular branch of dentistry. Let us then approach the subject from a diagnostic point of view; that is, first attempt to diagnose a case, and then perscribe the remedy, rather than to invert the logical mode of procedure as has apparently heretofore been the practice,
Which would seem more logical, to attempt to construct a set of dentures or partial appliances for a patient without first knowing or having at least an idea of the condition to which his masticatory apparatus has been reduced, or to find some means of the first diagnosing the case by ascertaining whether or not any apparent abnormaility exists before the construction of the appliance attempted? The answer is obvious. To the prosthodontist this reasoning may seem ridiculous, but we must bear in mind that, as a specialist in his field, either by virtue of genius or long experience, he has acquired that intuitive diagnostic sense which may lack and some perhaps never acquire. Take the dental student, for example. He is taught dental anatomy in which
the relation of the occlusal planes of the upper teeth to those of the lower is emphasized. He is give instruction in anatomical articulation and denture construction. The progressive changes in the condyles and glenoid fossae of persons past middle life and the variance in the condyle-path inclinations of such persons are demonstrated and indicated on human skulls. But when no means of detecting and meeting these conditions in his practical work is afforded, he senses the inadequacy of the means at his disposal, and concludes that the continual reference to anatomical articulation is simply the result of an obsession of his instructors or of various clinicians, and something which has no practical value other than to prolong the course, or perhaps to dignify it with a formidable array of meaningless scientific terms. However this may be, it is nowise intended that the foregoing statement as to the present attitude of the dental student should minimize the value of the several theories which have been advanced, and which, indeed, form the nucleus of our present conception of anatomical articulation; but rather to reflect with impartiability the point of view of the student himself in his endeavor to visualized the practical applicability of these various hypotheses. The underlying motive which has promted this line of research was of a purely educational nature, and the result of an urgent need felt in attempting to meet the problems of the present-day dental student. Owing to the higher standard of the entrance requirements of the dental schools, our modern student is of a type reluctant to accept things for granted. He is very quick to ovserve the weakness of the involved generalizations with which we are forced at times to answer some of his questions.
It is on the subject of the so-called anatomical articulation and its exact value in dentistry that some of the student's searching questions are asked. What happens is this: The instructors know and realize the imprtance of the subject of anatomical articulation, and also realize that it should be carefully taught and that its importance should be impressed upon the student's mind. But when it comes to answering what the student supposes to be as simple and specific question regarding its nature, functioning, etc., his instructors are driven to the necessity of referring him to the various printed explanations and hypotheses which have thus far been advanced; and there the matter ends. The object of this paper is not to adopt a radical or iconclastic attitude toward all previous work in this field. On the contrary, its purpose is merely to reverse the processes now in vogue, to attack the problem from an experimental rather than theoretical point of view, and to proceed from a practical study of the temporomandibular joint to a possible resultant theory.
It seemed logical to suppose that once a method for the pracitcal study of tis joint was evolved and its fundamentals tried and understood, the hard and perplexing question as to the nature of the principles involved in the execution of the mandibular movements and their relative importance to prosthetic dentsitry would automatically take care of itself. And, in fact, in the method which has been evolved the capital point is the application of the principle of a mechanical tracing device already extensively used in other fields of activity aside from dentistry. Before going into the details of the basic reasoning on which a diagnostic method is to be built, we may say that a short, comparative study of the various similarly funcitoning hinge joints of the human body will not disclose any fundamental structural variationsl but it is a fact that, although the temporomandibular joint studied anatomically will present a picture no different from any other hinge joint, if taken functionally, on account of the ever-changing factors entering into its development and the variety of the duties it has to perform, it will assume the aspect of a complex mechanism, of which the precise manner of a operation can be ascertained only by a
close study of the movements it produces. We are all aware of the complexity of the vital processes which are constantly in operation durring embyronic life, and also durring the varios stages of life from birth to senility. And although these vital processes are essentially an uninterrupted succession of extremely complex causes and effects, we cannot fail to discern a certain predominating purpose, which its outstanding elements maintained and prevailing throughout the whole cycle.
Such being the case, our purpose in the study and better understanding of the why and the how of matters pertaining to the temporomandibular joint as one of the component parts of the human body becomes clearer.
To be more specific, its purpose is to afford various movements, such as masticatory movements, movements to assist the making of sounds, and movements aiding in the exhibition of various emotions. Its develoment, true to the laws governing life, follows the course necessary for the ultimate execution of certain indispensable specific movements. As we are at this time interested only in its masticatory movements, we shall in part disregard the others, and in our endeavor to disover and define its outstanding elements, we shall briefly follow its develpoment from birth through its various stages. At birth, the mandible is capable, in a more or less rudimentary way, of the various movements necessary in mastication, simply by birtue of the construction of its hard tissue components, that is, the mandible itself with its various parts either calicifeid or not, its soft tissue components, the ligaments and muscles and its controlling element, the nerves. These persist throughout life, constantly undergoing changes as other factors begin to creep in, which control and limit its movements. The most important factor, which we may safely say controls and limits its movements, makes its appearance in the eruption of the deciduous teeth, soon after followed by the first permanent molars, and in the subsequent displacement of the dciduous by the permanent teeth. Another factor of a constantly varying nature and largely dependent on the one previously mentioned, is the condyle path, composed of its floor and lateral walls. The floor of the condyle path, taht is, its horizontal plane, has either been overemphasized or completely ignored in previous studies, while the lateral walls of the gleniod fossa, which are also a part of the condyle path, have almost wholly been avoided as too variable to attempt to define or their importance to vague to note. The condyle path normally owes its existance and constantly varying nature to the coordinate action of the muscles and ligaments of the jaw with the occlusal planes of the teeth; is subject to the laws governing cartilage and bone calcification, and incidentally to aquired habits and other interferences. In short, it is the result of the functional coordination existing between the muscles ans the propelling force and the teeth as the guides.
In all, there are three prime elements or factors entering into the development of the temporomandibular joint. They are as follows:
I. The muscles and ligaments.
II. The inclined planes of the teeth.
III. The condyle path.
Of these three factors, the first, namely, the action of the ligaments and muscles, being progressively consiteant thoughout life. With the partial or total loss of teeth, the second and most important factor with which we are primarily concerned gradually becomes eliminated and, with it, all specific masticatory control of the movements of the mandible lost.
As our mission in all dental reconstruction work is to restore this lost factor, that is, the teeth, the problem as to how it should be done so completely to fufill its purpose at once becomes apparent.
In our every-day work we are striving to reestablish the harmonious coordination which existed between all three factors between the loss of teeth, and have thus far ascertained the existing relationship between all the contributing factors responsible for the functioning of the temporomandibular joint as related to mastication, assuming all factors to be present.
Now, with the loss of the teeth, the occlusal planes becoming an unknown quantity, teh two known and existing factors bearing the same analogous relation to each other as to the unknown, our problem becomes a purely mathematical one, that is, to restore, in a definite and conclusive manner, this unknown facto with the aid adn diagnostic value of the two known factors.
The finding, determining and recording of all these factors cannot be done in a hapahzard, abstract fashion, as no one factor alone can be of any great value without the others.
All these factors have been so correlated as the result of years of reciprocal coordinating action that, unlsee they are recognized as a unite and taken as such, they mean nothing. In any case of diagnosis for tany purpose whatsoever, it is imperative that all the contributing factors be known; else a complete diagnosis is not possible.
A unit of parts intended to perform a unit of movements cannot be governed by anything else but a unit of factors working in an endless succession of causes and effects. This very condition exists in the temporomandibular joint. It contains of a unit wholly interdependent parts, with the purpose of execiuting a unit of indispensable movements, and its governed in its entirety by a group of factors, which group itself constitutes a unit. ANy sudden or gradual change in any of its factors will bring about either a sudden or gradual interference in the fufillment of its purpose, and and will induce a corresponding change in one or more of its constituent parts. THis is an undeniable fact, tand the imprtance we give it subconciousy governs our daily activities in this field. Were these movement to be reproduced with some degree of accuracy, they would undoubtedly reveal the factors responsible for their execution, and incidentally would help to diagnose the condtion to which the temporomandibular joint has been reduced. Assuming that ewe are all interested in restoring the masticatory apparatus of a patient to soemthing like its original condtition, any treatment based on any other reasoning or theory will fall short of its objective.
Definitions of such terms, as "the ideal occlusion," "normal occlusion," "average normal occlusion," etc., naturally have their educational value from a purely academic standpoint, as in the case of the compling or grouping of various types of statistics; but they can mean nothing, and should not be made the goal of our actitivies in teh treatment of individual cases. They help only in the grouping and classifying of the results, after the reuslts have been obtained, but not before.
Individual cases can be properly diagnosed on the basisi of the following facts:
With the cusps of the teeth in contact, both extreme right and left and forward excursions of the mandible, starting from central occlusion, must necessarily pass thorugh all the planes or directions of movement which the mandible will describe during all its masticatory or other movements,. In other words, the range of the jaw movements of any individual is contained within its extreme lateral and forward postitions. All these movements are simultaneously compund movements in various planes or directions. Thus an extreme lateral movement is executed in three definite planes: a forward plane, a lateral plane and an inclined plane. The muscles propelling the mandible are responsible for the forward and lateral planes. THe inclined planes of the teeth when present , and the condyle path when the teeth are absent, are responsible for the inclined plane. the extreme forward movement, however, is executed only in two planes, the direct forward and the inclined plane. By employing a tracing instrument
very similar to a pantograph, constructed so it can be brough back iether automatically or at will into a central position, these movemnts can be traced, recorded, and reproduced.
Starting from central occlusion and donoting it as zero, the mandible, placed in an extreme lateral position without undue efford, will diagrammatically travel in three planes, radiating as three lines from a common center.
Guiding the course of these movemnts or excursions are certain limitations or interferences, which we can easily determine, record and reproduce at will.
Owing to the inherent limitations of all mechanical devices, the apparatus employed for the recording fo the various mandibular movements will record accurately the angle of the horizontal plane of the condyle path, but noth the curvature of the path. In other words, the correct position of the condyle at the two extremes will be accurately reproduced atnd described as a straight plane, but any intermediate variation from a straight plane will not be recorded. However, the lateral interference of these movements, that is, the interference caused by the depth and curature of the lateral walls of the condyle path, can be reproduced with a greater degree of accuracy, as it was made possible to record and reproduce quite accurately the lateral curvature of the condyle path. After examining and recording a large number of cases, the following observations were made:
A more detailed discussion of each one of these observations will not be out of order at this point.
(1) The phrase propelling action is used because it can best explain what is shown actually to take place in some cases durin gthe lateral excursions of the mandible. The mandible is seen being thrust bodily onto a lateral and forward position. For example, if we were to register the readings traced by the right lateral excursion, we would see in most cases both the right and left condyles sliding forward and laterally. Th eleft, however, would be seen covering a greater distance than the right, giving the appearance of the whole mandible being pushed forward and laterally to the right. The same would happen, perhaps in a varying degree, if we were to repeat this for the tracings of the left lateral excursion.
(2) In making these record, we would notice that the distance traveled by the mandible during the right excursion would not be the same as the one travled durring the left, and vice versa. This indicates that during lateral movements a limiting action is brought to bear on either side independently, due undoubtedly to the structure of the ligaments and the hard tissues, such as the shape of the condyle or the varying depth of the lateral walls of the glenoid fossa, or again, to an injury. (3) It will be found that no apparent absolute pivoting action of either of the condyles takes place when the opposite condyle is in excursion, but, on the contrary, both of the condyles are in motion. (4) In practically all of the cases of edentulous mouth examined, there was no apparent indication of a center or centers of rotaition. The mandible appeared to be moving in a groove or trough. (5) Records of the condyle path registered during the lateral movemnts were found to vary considerably. Readings, such as positive for the right and negative for the left, or vice versa, were not uncommon.
(6) If we were to check up the readings of the lateral tracings, we would be apt to find a different inclination registered when the mandible is thrust forward from the one registered with the mandible moving laterally. This condition has been found in persons who at some time or other have injured either the condyle or the glenoid fossa on one or both sides; so that, when the mandible is moved into a lateral postion, the condyle, traveling over the injured path of the glenoid process, will register a certain inclination and, when moved into forward position over the uninjured part, will register an entirely different inclination. It is therefore possible to have two different condyle-path readings on the same side of the mandible -- that is, a negative reading for the lateral movement and a positive reading for the forward movement. (7) The degree of protrusion during the lateral excursions of the mandible will be found to vary considerable for either side -- from a few millimeters to half an inch or more.
(8) In recording the lateral inclination of the condyle path, it will be found that it varies from an almost straight olane to a decidedly curved one. Now, in trying to arrive at some conclusion from the records obtained from these various cases, we are immediately confronted with the fact that tehre is enough variation in each case, and even in the most closely similar ones, to make it imperative that each case be taken independently and treated differently. And it also becomes apparent that when we are about to restore the lost second factor responsible for its development, the behavior of the tempromandibular joint in its enterety must be taken into serious consideration. It seems, therefore, logical to assume that only though an accurate diagnosis of its condition shall we be able to restore it to the degree of efficiency neccesary to carry out the work for which it is intended.
Aside from the considerations of its prosthetic value, let us suppose that we were interested in establishing an efficient occlusion for a child having all its teeth, but presenting an asymmetrical occlusion or, in other words, maloocclusion. Would it not be of some value to know the condition of the temporomandibular joint of that child when the work is begun, noting its functioning, adn watching not only the changes that are taking place in the position of the teeth and the form of the arches as the treatment progress, but also the relative changes which are being induced in the temporomandibular joint itself by the treatment? And, again, would not the vivid picture of the concrete and actual happenings in the whole masticatory apparatus of the child suggest a more specific treatment than one based wholly on general principles? In some prosthetic cases and in dealing with easily adaptable patients, we might attempt a correction of some outstanding asymmetries, if they could be readily corrected, and if the patients were willing to submit to corrective treatment. Most generally, however, we must maintain the conditions as we find them, bearing in mind that we are engaged in a mission, the object of which is to bring about relief and to replace lost organs having a direct and immediate bearing on the patients health, and that we must not subject our patients to any additional hardship by attempting to mold their temporomandibular joint to a different condition or shape other than the one the possess, in order to make it conform to a presupposed ideal form. It is not fair to assume that nay additional hardship, added to the inevitable one caused by the mere presence of even the most comfortable appliance or denture in the patient's mouth, will detract from the efficiency and usefulness of that appliance or denture? Whether we are occupied with the teaching of dental students or with our own private work, we must bear in mind that, being aware of the existing conditions in a patient's mouth, treatments, wheter corrective or otherwise, must be consistent with those condtitions, else we are groping in the dark.
To regard any existing condition of the temporomandibular joint as merely incidental to the masticatory movements, and to lay undue stress on the form and position of the teeth, or this or that factor alone, would mean deliberately to disregard all of the important factors which entered into its development and which act as a unit, and treat it as a mechanism to be abused and changed at will, forgetting that the condition in which we find it is the result of an uninterrupted succession of causes and effects functioning coordinately with the progressive or retrogressive physiological processes which have been going on for a long period of years.
The value of diagnosing the condition of the temporomandibular joint, when any restorative or corrective work is to be attempted, has exactly the same bearing on the success of the treatment as the radiogram has in the treatment of a pulpless tooth. How many of us today would attempt to treat any morbid condition in the mouth without an x-ray, in instances where the x-ray has been proved to be of value as a diagnostic measure? Shall we have to prove that dentures must be judiciously constructed in order to fit and function?
It goes without sayin gthat we shall encounter difficulties at times while attempting to make tracings and to record conditions, but while the readings of the tracings in such cases may not be exact, they will, however, point in the right direction. Once a dental student is familiar with the various elementary factors entering into the development of the temporomandibular joint, he will easily carry out any rational method of diagnosis, and will intelligently operate any instrument of precision constructed for the purpose. If he proves incapable of learning to do so, he will be unfit to perform any operation in his profession that requires care and precision, for scientific methods leave nothing to conjecture. Another important reason for an accurate diagnosis lies in the fact that it is impossible to apply the laws of physics and mechanics entering into the construction of dental appliances in any other than a general way, if we deliberately ignore certain factors which alone can predetermine the manner in which these laws can be fully applied. We have laws governing the application of certain mechanical principles. In carrying out these principles shall we adhere to the established laws, or shall we apply theories or simply expedient methods? In closing, it may perhaps be of value to repeat some of the important points which have a direct bearing on this subject. The practical study of the temporomandibular joint can be accomplished only by a close scrutiny of its movements, and not by any one theory, because none of the existing hypotheses can be applied to all cases alike.
The movements studied must be reproduced as closely as possible in the manner in which they are executed by the patient. Taking central occlusion as the starting point of these movements, the person whose temporomandibular joint is to be studied is instructed to place his mandible in an extreme right or left position without undue effort; then with the aid of locking molds and a recording instrument, these extremes are recorded in a most simple way. Another important point, which is of great value in the construction of dentures or appliances, narrowing the lattitude for the arranging of the teeth within a more or less small and definite range, is the ability to determine the range within which the mandible is capable of moving.
Finally, being able to ascertain, record and reproduce all of these movements, their value becomes apparent, inasmuch as we are enabled to construct our applicances intelligently within the existing limitations of each person's individual jaw movements, fashioning our appliances to function consistently and in harmony with the existing conditions. The purpose of this paper is, and has been throughout, to show clearly the diagnostic value of the practical study of
the temporomandibular joint, adn not to enter into an academic discussion of the subject from an anatomical or physiological standpoint. However, it seems not wholly undesireable to make at least passing mention, in concluding, of a logical conclusion at which we can indidentally arrive as a consequence of this, namely, that the mandible is a floating member, suspended and propelled by ligaments and muscles; that it is guided by the occlusal planes of the teeth when the teeth are present, and that the various planes of the condyle path when the teeth are absent; and that the various planes of the condyle path, together with the muscles and ligaments, provide a groove-like control which guides and limits its movements.
483 BEACON ST.
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