Balanced Occlusion–Its Practical Application in Partial Denture Construction*

Balanced Occlusion–Its Practical Application in Partial Denture Construction*

BALANCED OCCLUSION-ITS PRACTICAL APPLICA' TION IN PARTIAL DENTURE CONSTRUCTION* By A RTH UR PAUL LITTLE, D.D .S., St. Paul, Minnesota H E term balanc...

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BALANCED OCCLUSION-ITS PRACTICAL APPLICA' TION IN PARTIAL DENTURE CONSTRUCTION* By A RTH UR PAUL LITTLE, D.D .S., St. Paul, Minnesota

H E term balanced occlusion has to do, not merely with tooth inter­ digitation, but with a perfect re­ lationship and coordination o f a ll parts dependent on or controlled by the teeth themselves. T o have perfect relationship and perfect coordination o f all parts would be to have an ideal. T h e ideal is that which exists only in imagination. H ow ­ ever, in many o f the sciences, it is necessary that we use the ideal as a standard o f measure in making our de­ ductions. In the study o f balanced oc­ clusion, we lay our foundation or basis on the ideal human denture. T his means that every part o f the base o f the cranium on which the oc­ clusion exerts an influence must be given consideration, and a knowledge o f the physiologic functions o f these parts is essential for the fullest appreciation o f their importance. A t no period in life does the relative significance o f this guiding factor in the maintenance o f health and efficiency in the dental ap­ paratus decrease. In infancy and child­ hood and throughout adult life , the condition o f the occlusion denotes the state o f health o f the mouth and its tributary parts. W ith a hope that the knowledge gained w ill act as a guiding

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♦Read before the Section on Paxtial Den­ ture Prosthesis o f the American Dental Association, Louisville, Ky., Sept. 22, 1925.

Jour. A .D .A ., May, 1926

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influence in our restorative work, let us briefly analyze the points in the ideal human denture that are o f interest in a consideration o f balanced occlusion. Every part o f the human body reaches a certain height o f development as a result o f the physical forces to which it is subjected. T he anatomic structures o f the head and neck are de­ veloped to their maximum functional efficiency largely through the develop­ mental influence o f the natural teeth. When this process goes on undisturbed, the result is a perfect coordination o f all parts. This means that there w ill be established a certain definite relation­ ship between the mandible and maxillae. As long as this relationship remains un­ disturbed, the mandible and maxillae serve as proper support for the attached anatomic structures. It is obvious, then, that one o f the chief functions o f the teeth is to preserve this condition. Physiology teaches that, in order to have muscles function properly, the distance between the origin and insertion must remain constant. A common ex­ ample o f the failure to obey this law is seen in the limbs when, from injury or disease, the linear dimension is lessened, and only partial function remains. W e see not only a diminution in the normal activities but also atrophy, in proportion to the interference. T he maximum efficiency in the functions o f mastication, deglutition,

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respiration, drainage o f the oral cavity and posterior part o f the pharynx, equal­ ization o f air pressure in the middle ear

Figure 1 shows a w ell developed skull in which it is clearly evident not only that the teeth bear a definite relationship to each other, but also that they are the sole means o f maintaining a definite balance between the mandible and maxillae. In Figure 2, your attention is directed to the space occupied by the meniscus or

Fig'. 1.— Skull showing that the teeth are the sole means of maintaining a definite bal­ ance between the mandible and maxillae.

through the eustachian tube, and supply o f blood to these parts are directly or indirectly dependent on the maintenance o f the occlusion. T he accompanying group o f illus-

Fig. 3.— Muscles of expression.

Fig. 2.— Skull showing space occupied by the meniscus or fibrocartilage.

trations w ill be an aid in visualizing the responsibility that good occlusion has toward the proper functioning o f the human dental apparatus.

fibrocartilage. It is one o f the functions o f the occlusion to preserve this space and avoid traumatism that may arise in the temporomandibular joint.1 When the occlusion is disturbed the condyle produces pressure on the meniscus. This sometimes goes as far as to cause an ir­ reparable injury. 1. Prentiss, H. J. : A Prelim inary Report upon the Temporom andibular Articulation in the Human Type, Dent. Cosmos, 60: 505 (June) 1918.

Little—Balanced Occlusion Figure 3 shows the superficial structures o f the head, face and neck. In this group w ill be found the muscles o f expression. T o avoid that atrophic appearance so often seen in the face and commonly accepted as due to old age, it w ill be necessary that the origin and in­ sertion o f these muscles remain constant. As these muscles are directly or in­ directly attached to the mandible and maxillae, it is apparent that, if their de-

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Dr. Lischer, through the sagittal plane o f the head, shows the correct position o f the tongue and the relationship it bears to the surrounding structures. Note the amount o f space in the naso­ pharynx. In event o f a closure o f the bite, it is easy to see how the tongue will be crowded back into the throat space and act to diminish its functions and those o f the tributary parts. I f the only means o f maintaining a

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Fig. 4.-—Muscles of neck and throat.

velopmental dimension is to be main­ tained, it is necessary to maintain the proper distance between the mandible and maxillae. Figure 4 shows the muscles o f the neck and throat. As many o f these structures are directly attached to the mandible, their functional efficiency w ill be at its best when there is no rel­ ative change from its original position. T he natural teeth, or satisfactory sub­ stitutes, are the only means o f maintain­ ing this original position o f the mandible. Figure 5, a cross-section prepared by

Fig. 5.— Cross-section through the saggital plane showing the correct position of the tongue and the relationship it bears to sur­ rounding structures. (Lischer.)

balance is the teeth, it becomes necessary, when restoring balance to the broken down arches, to have some knowledge both individually and collectively of Nature’s method o f arranging them in the ideal human denture. A study of this arrangement gives an explanation o f what is necessary for efficiency, and a better understanding o f the dis­ advantages under which teeth are forced to operate when there is not a correlation o f all the parts and the adjacent structures.

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It is now an established fact that the human mandible in its various move­ ments from central occlusion with the teeth in occlusal contact describes a series o f arcs. T his was one o f the con­ tributions made by Dr. Monson in his early research work. Hence the term spherical occlusion arose.2 He found that, in the higher types o f development, the occlusal surfaces o f the teeth and the center o f the condyles conform to the surfaces o f a sphere whose diameter is

Figure 7, the posterior view o f the sphere applied to the mandible, shows the center o f the condyles conforming to the surface o f the sphere. T he radial dimension from the center o f the sphere is common to the condyle and all o f the teeth. Thus, we see that the radial cen­ ter is the center o f applied force in our mechanism o f mastication. It is true that the ideal human den­ ture is somewhat visionary; but the knowledge gained in studying the high-

Fig. 6.— Anterior view of 8-inch sphere applied directly to mandible. (M onson.)

Fig. 7.— Posterior view of sphere applied to mandible. (M onson.)

approximately 8 inches; also, that the long axis o f the teeth when projected passed through the center o f this sphere. For the purpose o f explaining the spherical theory in a simple manner, Dr. Monson made use o f the 8 inch sphere applied directly to the mandible. W e see here (F ig. 6 ) , the application o f the sphere from a front view. Note the conformity o f the teeth to the surface; also that lines drawn from the center pass through the long axis o f the teeth.

est types o f development better enables us to analyze the specific needs in each individual case that we meet in practice. D o not get the impression that every human dental apparatus can be brought back to the high type o f efficiency found in the ideal. W e do, however, recognizc in each individual a certain height o f development that becomes the goal toward which w e strive when attempt­ ing to restore. W hat has been said regarding the ideal has been mentioned merely to 2. Monson, G. S.: Occlusion as Applied reestablish in our minds a broader con­ to Crown and Bridgework, J.N .D.A ., 7: 399 (M ay) 1920. ception o f our responsibilities, before

Little— Balanced Occlusion taking up the management o f cases in which there has arisen serious impair­ ment to the physiologic functions for which w e should be responsible. In the life o f every individual there comes a time when various agencies act to destroy the human occlusion, and, owing to these retrogressive changes, little o f the original is le ft. Functional efficiency has suffered to a considerable extent. In fact, the mere presence of retrogression may be taken as a definite expression o f the lack o f harmony in all coordinating parts, usually in a direct ratio to the amount o f retrogression. In considering any loss o f teeth, our first thought should be as to the seriousness o f the condition, at no time losing sight o f the fact that Nature has made some provision for taking care o f the minor losses. On each operator falls the responsi­ bility o f deciding at just what period in the patient’s life these losses reach a point where it is advisable to cease bas­ ing our considerations on the individual tooth. He must recognize when such procedure has reached the limits o f its usefulness and be able, at the proper time, to visualize the problem in its en­ tirety. T h e incorporation o f balanced occlusion into our restorative work means little change in our methods. W hat it does mean is that we must change our point o f view. W e must be able to make a mental picture that reaches beyond the individual unit— a picture that includes all the units work­ ing as one. It makes little difference in our routine mechanical procedure whether we build with our minds on the dental apparatus and its various functions in correlation or whether we

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build to perpetuate the existing deformi­ ties. However, our restorations must be designed in such a way that, when completed, they w ill function and main­ tain health, instead o f representing something entirely out o f harmony with Nature’s plan. It is w ell to remember that as long as any natural teeth remain on which some degree o f function is possible, there w ill be exerted considerable muscle action and reaction. T h e result o f these forces we have all seen clini­ cally. For example, what happens when the posterior teeth are lost, and all function takes place on the anterior? In a short time, we find that owing to the muscular forces exerted over the un­ supported bone the two opposing alveolar ridges are drawn together. In some instances, these actually come in contact. Another very common abnormality is the deflection o f the mandible from one side to the other o f the median line, due, as a rule, to long continued uni­ lateral function, the teeth on the op­ posite side being lost or worn to the extent that they no longer counteract the forces applied on the functioning side. As a result o f these disharmonies, there are presented many o f the worst types o f deformities that we are called on to treat with restorative dentistry. T he various agencies that act to destroy the human occlusion are distributing their forces in such a manner that changes and destruction are going on very rapidly. Muscle pull is being diverted in wrong directions. T he remaining teeth are drifting out o f position, and, in many instances, they cease to take the applied stress parallel to their long axis.

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In any closure, from the original height o f development, we have a re­ duction o f the cubic contents o f the oral cavity. T his reduces the normal tongue space, with a result that this organ is forced back into the throat.3 A ll related and interrelated function, such as de­ glutition, respiration and drainage, as w ell as the circulation in this region, suffers from this interference. In overbite cases, the class which pre­ dominates, this change is the greatest. In the prognathic and the end-to-end types, the closure may not be so marked, and, as a rule, the disturbance o f this vertical relationship does not take place so rapidly. Dr. Prentice has called our attention to the traumatic conditions that arise in the glenoid fossae, when, as a result o f the breaking down o f the occlusion, this member becomes a weight sustaining joint.4 In this connection, Dr. Monson gives us a thought worthy o f consider­ ation when he draws a comparison be­ tween the temporomandibular joint and the knee. T he latter joint is primarily designed, both in size and shape, to sus­ tain the weight o f the body. T he pounds o f pressure exerted by the muscles o f mastication in many instances is greater than the bodily weight. W e can readily see that Nature, in designing the tempo­ romandibular joint, made no provision for this tremendous force other than to distribute it over the occlusal surfaces.

In all periods in life, it is w ell to re­ member that the existing conditions in the glenoid fossae are the result o f the transmission o f those forces that have been active on the occlusal surfaces. In other words, the condition o f the tem­ poromandibular joint is always second­ ary to and governed by the teeth themselves. It is Nature’s intent that the natural teeth serve as a guiding in­ fluence to prevent the condyle from coming in actual osseous contact with the glenoid fossae. T his prevents injury to the meniscus and the joint. T he ob­ servance o f this natural law is one of the principle objects in view when build­ ing our restorations, so that, when com­ pleted, they w ill present an occlusal arrangement which, during mandibular movement, gives proper guidance to the condyle. Do not lose sight o f the fact that, as the occlusion ceases to counteract the muscular force in maintaining a proper relationship o f the mandible to the maxillae, the direction o f muscle pull is changed and the mandible and its sus­ pended structures are carried backward and upward.3 This condition is greatly pronounced in the overbite types, for, as the closure becomes greater, the over­ bite acts as an added influence in the creation o f this distal relationship. T he result is that an overbite is established, which interferes with oc­ clusal balance in the posterior region during all excursion o f the mandible. 3. Monson, G. S.: Impaired Function as T he central occlusion relationship o f the a Result o f Closed Bite, J.N .D.A ., 8: 833 mandible to the maxillae w ill, in these (O ct.) 1921. cases, be distal from its original position.

+. Prentiss, H. J . : Regional Anatomy, Emphasizing M andibular Movements with Specific Reference to F u ll Denture Construc­ tion, J.A.D.A., 10: 1085 (Dec.) 1923.

5. Monson, G. S.: Some Im portant Fac­ tors Which Influence Occlusion, J.N .D.A ., 9: +98 (June) 1922.

Little—Balanced Occlusion T he prognathic and end-to-end types, which form only a small percentage of the cases we treat, generally acquire a central occlusion relationship anterior to the original. It is obvious that the utilization o f this central occlusion re­ lationship as a guide in building partial denture restorations w ill result merely in a perpetuation o f the existing malrelations. Follow ing all this disharmony in the dental apparatus, we find mandibular movement restricted to whatever free­ dom the remaining natural teeth w ill permit. In many o f the severe cases, the interference with this function is so great that the mandible is limited to little more than an open and shut movement. However, no matter how great this interference may have been, except in cases in which injury or disease has caused the impairment, I have never handled a case that was not capable o f accepting all the ranges o f otclusion, when the existing interferences were wiped out and a new occlusion es­ tablished which embodied the spherical principles. T he basis o f every scientific pro­ cedure is made up by combining all of the natural laws involved. In the case o f partial denture construction, the present deplorable state is due, I believe, in some measure, to our failure to ob­ serve the existing natural laws. In the past, much o f this service has consisted merely o f filling space in the dental arches with teeth and vulcanite.6 Many times, as an extra feature, we would exercise the opportunity to make use of

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some favorite mechanical appliance, trusting that its use would overcome all the problems that came up. Strict observance o f the principles of balanced occlusion teaches us that, coupled with the mechanical phases, there are other vital considerations and possi­ bilities. T he dental profession today is realizing the fact that we have been paying too much attention to the mechanics involved and too little at­ tention to the functional side o f our restorations. A summary o f the reasons for the use o f balanced occlusion in partial denture work shows that they are both physio­ logic and mechanical. Among the phys­ iologic reasons, we have a betterment o f all the functions directly or indircctly related to the occlusion. W e may get some correction o f the deformities that exist in the osseous parts. Generally, there is some improvement in the exist­ ing conditions in the temporomandibular joint when the load is taken off the condyle, and thrown back on the alveo­ lar ridges, where Nature has made pro­ vision for its reception. This is accomplished by opening the bite and ob­ taining a better relationship between the mandible and the maxillae, then con­ structing restorations to maintain this relationship which have embodied in them the spherical principles o f oc­ clusion, to receive and distribute the ap­ plied stresses. Does it not seem logical that, if many o f the acquired deformities with which we are confronted are the result o f a breaking down o f the occlusion and a diversion o f the stress to other parts in 6. Little, A. P .: F illing Spaces or Build­ whose mechanical design Nature has ing fo r Efficiency, Dent. Digest, 28: 777 (Dec.) 1922. made little or no provision for its re­

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ception, with a proper correction and the reestablishment o f occlusal balance any change would be for the better? T his is but in accord with the natural laws that govern bone change. W ith any correction that might come in the mandible itself from a redistribu­ tion o f the applied stresses or from any improvement in the relationship o f the mandible to the maxillae, gained by a bodily shifting, when possible, to a position nearer that which originally existed at the height o f development, we w ill have the suspended soft structures working to a better advantage. As all function is more or less dependent on correct occlusion, it is only natural that, follow ing correction, we find an im­ provement in the functional activities o f the soft structures. Balancing the occlusion aifords an opportunity to improve the condition under which the remaining natural teeth receive the applied stress. In nearly all closures, the teeth receive the crushing force in other directions than those parallel to their long axis.7 W e all know this is contrary to the physiologic laws that govern the proper functioning of the pericemental membrane. A disregard o f this factor in handling our cases w ill result in no improvement o f the health o f the investing tissue, and, as time goes on, tends to aggravate the already un­ favorable conditions under which these teeth are functioning. Among the chief mechanical advan­ tages gained are: ( 1 ) we have more room for our restorations; ( 2 ) we can improve the shape and design; (3 ) the retention problem is materially modi­ fied; for we have the maximum occlusal contact in the various ranges o f the

mandible, a factor in tissue bearing restorations that has a tendency to keep them seated at all times, causing much less strain on the abutment teeth. Follow ing this review o f the basic principles o f balanced occlusion, we shall give some consideration to their practical application in partial denture construction. Naturally, if we are go­ ing to build our restorations to supply that which has been lost from the human occlusion, it w ill be necessary to make a careful mouth survey to analyze the conditions that the loss o f the teeth have brought about. Here, too, our point o f view must change: we must consider the physiologic as w ell as the mechanical problems that exist.8 Primarily, our thoughts, in the past, in making a mouth survey, were on the mechanical problems. W hile I do not wish to belittle the mechanics involved, they become merely the medicine with which w e treat the disease. Where would medicine be today if physicians featured the selling o f drugs as a prime factor in the service they rendered? Dentistry w ill make a great step forward when we cease to hold mechanical den­ tistry out to our patients as our main contribution to the healing art. A fter our analytic deductions there w ill be ample time to work out the best possible mechanical program to fit the special needs at hand; and I assure you that, with such a logical procedure, the num­ ber o f our mechanical failures w ill be greatly reduced. T h e patients that come in for partial denture service, generally speaking, show an oral functional efficiency greatly lowered because o f loss o f the

8. Aldrich, H. D .: M outh Survey with 7. Smith, T om : T raum atic Occlusion and Special Reference to Malocclusion and Lost Its Correction in the Treatm ent o f Pyorrhea Facial Dimensions, read before Iowa State Alveolaris, J.N .D.A ., 8 :9 7 1 (D ec.) 1921. Dental Association, December, 1920.

Little— Balanced Occlusion teeth. T hey generally have had dental service rendered on individual teeth here and there, with no consideration o f the mouth in its entirety. Their ideas and knowledge o f dentistry are largely the result o f these experiences. Our first problem, then, is one o f changing their point o f view from that o f unit den­ tistry to a consideration o f the dental apparatus in its entirety; in other words, an educational talk is necessary, covering all functional responsibilities directly or indirectly related to the occlusion. This should serve a tw o-fold purpose: that certain knowledge may be imparted to

Fig. 8.— G raft’s base plates, with modeling compound occlusal rims.

the patient relative to the changes that have taken place in his own mouth, and that the operator may gain some valuable information as to the type o f patient he is dealing with. I f such an educational talk, based on the physiologic points in­ volved, makes no appeal to the patient, further procedure w ill bring forth little gain. It is necessary, in carrying out a program o f balanced occlusion, to have the patients interested enough in their own welfare to give at all times their fullest cooperation. It is advisable at the end o f this inter­ view to ask the patient a few simple well-directed questions, with the idea o f seeing just how much o f the talk is understood. W e may have been too

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technical, and we must not lose sight o f the fact that such educational talks, while they may seem somewhat rudi­ mentary to us, are entirely foreign to our patients. This fact applies as well to the better educated patients. In order not to get the patient’s mind away from the physiologic trend o f thought, it is w ell, at this time, to make no mention o f mechanics or o f fees. As all this is a new line o f thought to most patients, they may take some time to think things over before showing any real interest. T he patient who is too

Fig. 9.— Registering the relation o f the condyle to the occlusal surface o f the teeth by the use o f the transfer bow.

easily enthused is generally as quickly discouraged. A fter we have created in our patients an interest and a desire to go farther, two plaster casts should be made, in­ cluding all the detail necessary for a clinical study o f the case. By means o f a transfer bow technic, these should be mounted on an instrument that is cap­ able o f reproducing the movements o f the mandible, and on which provision has been made for determining the indi­ vidual problems presented that may be due to developmental deficiencies or to the loss o f teeth. W hen transferring and mounting casts, in cases in which the posterior

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teeth are missing, it is necessary to con­ struct base plates and occlusal rims to hold the casts in position while going through the various steps. (F ig. 8.) These base plates should be o f a non­ yielding type, and the occlusal rims are most satisfactory when formed o f modeling compound. It w ill be noted that the occlusal rims are notched. This is done for a definite purpose. W hile being attached to the instrument, the upper cast must be held in position by means o f a check-bite wax, which will

accurate as possible, for the better the transfer technic, the less the adjustment o f the instrument necessary later on. Figure 10 shows the location o f the

Fig. 11 .— Adjusting the ends o f the trans­ fer bow to the markings on the patient.

condyle. In the average patient, it w ill be found that a position one-half inch anterior to the center of the tragus of the ear and on a line with the tip o f the nose w ill be very close. In some cases, through palpating, we may see fit to change our markings for a better location o f the center o f the condyles. Fig. 10.— M arking the location of the condyle on the patient.

facilitate in assembling and maintain the correct position o f the casts. Figure 9 visualizes the theory o f just what we endeavor to accomplish by the transfer; that is, to register the exact distance from the center o f the condyle to the occlusal surfaces o f the teeth, in order that we may have a like relation­ ship between the occlusion o f our casts and the axis o f movement on the in­ strument. W hen put in practice, this operation becomes merely an approxi­ mation; for it is absolutely impossible to arrive at that degree o f accuracy shown in the picture when trying to locate the center o f the condyles in the living. However, we attempt to be as

Fig. 12.— Anterior view of the transfer bow in position and adjusted.

A piece o f check-bite wax to both sides o f the transfer inserted in the mouth, and wax is warm, the patient is

is secured plate and while the asked to

Little— Balanced Occlusion close. (F ig. 11.) T he ends o f the trans­ fer bow are adjusted to the markings on the face, and both friction screws are tightened on the transfer bow. »

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mounting the lower cast to the dividers at 4 inches. T he incisal edge o f the lower teeth should be 4 inches from the top o f the instrument. T he posterior part o f the cast is taken care o f by hav­ ing the ends o f the transfer bow inter­ sect the condyle rods equidistant from the ends o f the rods. T his being accomplished, the lower cast is secured to the instrument. In Figure 14, the upper cast is also secured to the instrument. In order to do this, the check-bite wax, which was

Fig. 13.— M ounting lower cast on instru­ ment.

Fig. 15.— Cast mounted showing amount of closure (rig h t side).

Fig. 14.-—Securing upper cast to instrument.

Figure 12 shows an anterior view of the transfer bow in position and ad­ justed. Figure 13 shows the method o f

the

made at the time o f the transfer, is placed on the lower cast and base plate; and the upper cast and base plate is placed on the check-bite, which will maintain the correct position o f the upper cast while it is being attached to the upper cast carrying plate o f the instrument. Figure 15 is a view o f the right side o f the mounted case, occlusal rims being removed to show the amount o f closure. Figure 16 is a le ft view o f the mounted case. In making our clinical deductions to determine the amount o f restoration re­ quired, it is necessary to divide the

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mouth survey into two parts: the exami­ nation o f the patient, and the study of the mounted casts. In the examination o f the patient, the oral, facial and con­ dyle conditions should be noted, and a complete set o f radiograms should be taken not only o f the remaining natural teeth but also o f the ridges.

Fig. side).

16.— Same as Figure fifteen

which they are receiving these applied stresses. Whether the existing deformi­ ties are congenital or acquired, or a com­ bination, is determined. W e must make certain that the ridges are free from in­ fected areas, and we should not accept the responsibility involved in the pres-

(left

T he oral examination consists o f a study o f the entire mouth with ob­ servation o f the remaining natural teeth, the relation they bear to each other and their state o f health. W e should note how the remaining teeth are receiving their applied stress, ruling out any teeth whose inclination would make it im­ possible to improve the conditions under

Fig. 17.— Casts opened and in position of new central occlusion.

ence o f oversized maxillary tuberosities and other osseous projections that would mean too much o f a compromise or in­ terfere with the mechanics involved. T he operator should try to detect any tongue or lip habits that might be troublesome during and after treatment. T he facial examination often reveals external evidences o f closure, such as

Little— Balanced Occlusion shortening o f the low er third o f the face, w ith the accompanying thick lips and receding chin, and the deep lines extending over the low er third o f the face and especially from the corners o f the nose to the corners o f the mouth. T h e condyle examination is made for the purpose o f testing any condyle en­ croachm ent that m ight occur as a result o f closure. T h e test fo r condyle en-

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done, all the control screws on the instrum ent are locked. T h e casts are now in a position o f new central oc­ clusion.

Fig. 19.— Testing fo r condyle encroach­ ment.

Fig. 18.— Positioning guide.

croachment w ill be shown in detail later. A ll these clinical observations are made while examining the patient, and any conclusions arrived at are valuable aids in studying the mounted case, to which we w ill now turn our attention. T he casts are opened to slightly plus clearance in the forward range, the in­ cisors being brought to an end to end relationship which is a general guide in this type o f case to the amount the bite must be opened to relieve condyle en­ croachment and abnormal stress on an­ terior teeth. (F ig. 17.) W hen this is

Figure 18 illustrates what is termed the “ positioning guide.” Its object is to duplicate the same relative position of the mandible to the maxillae in verify­ ing in the patient’s mouth our diagnosis that was made on the instrument.9 It is made by placing a small piece o f soft

Fig. 20.— Balanced occlusion guide.

modeling compound between the upper and lower anterior teeth and closing the 9. Bird, C. K .: Reasons and Technic for Obtaining Balanced Occlusion in Fixed Re­ construction, Dent. Summary, 45: 291 (A p ril) 1925.

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upper cast in the new locked central oc­ clusion. T h e cast is then chilled and removed. It is now ready for the patient’s mouth. Figure 19 illustrates the method o f making the test for condyle encroach­ ment. T o make this test, the tips o f the little fingers are inserted in the external auditory meatus and the patient is asked

w ill now be materially decreased if not entirely absent, which demonstrates that this condition can be relieved only by opening the bite. Observance has re­ vealed the fact that, in certain types o f cases, reducing this condyle trust or en-

Fig. 21.— Balanced occlusion guide. Tech­ nic fo r correcting the occlusal rims.

to open and close to central occlusion. As the patient opens, the operator pulls for­ ward. T he tips o f the fingers w ill fo l­ low the advancing condyles. As the patient closes, there w ill be a decided thrust o f the condyle heads fe lt against the tips o f the little fingers if the bite is appreciably closed. N ow the position­ ing guide is taken to the patient’s mouth and the same test is made. W e are now making this test to our newly established central occlusion. T he condyle trust

Fig. 22.— Adjusting the upper cast to the corrected lower by the use of the balanced occlusion guide.

croachment by opening the bite is a valuable guide in determ ining the cor­ rect relationship o f the m andible to the maxillae. W e have now determ ined the amount to open the bite, which is approximately the am ount this case has retrogressed from its original height o f development.

Little— Balanced Occlusion T he next step is to design restorations whose occlusion presents an arc that is the same as the arc o f mandible move­ ment.10 For facilitating this procedure, Dr. C. K. Bird o f St. Paul conceived the balanced occlusion guide. (F ig. 20.) T he balanced occlusion guide is a plate o f german silver stamped to conform to the surface o f a sphere and perforated for a definite purpose. Its use makes it possible to know in advance whether the arc chosen w ill, when incorporated into our restoration, give us a balanced oc­ clusion. T he essential technical steps in making this test are illustrated. The base plate and occlusal rims used in making the transfer are placed on the lower cast. (F ig. 2 1 .) Now, by measurement, we determine to what ex­ tent the occlusal rims w ill have to be altered in order that all edges o f the balanced occlusion guide shall be equi­ distant from the radial center o f the in­ strument. T his is done by building up the occlusal rims with soft modeling compound and forcing the balanced oc­ clusion guide to the correct radius, as determined by the dividers, care being taken to maintain the same radius on the guide all the way around. W hen this is accomplished, the next step is to add compound to the concave or palatal side o f the guide. T o do this, the upper cast is moistened. (F ig. 2 2 .) Soft compound is placed on the balanced occlusion guide, a small amount being forced through the per­ forations in the center, which w ill act in retention. N ow the upper cast is placed on the corrected occlusal rims o f the lower, and is closed until the longest re­ 10. Little, A. P. : Occlusion and Its Sig­ nificance in P artial Denture Construction, read before the New Jersey State Dental So­ ciety, A pril, 1923.

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maining natural teeth come in contact with the guide, which is adapted to the cast and chilled. In using the balanced occlusal guide in partial denture cases, it is very important that the result of this step shall give us an accurate im­ pression o f the ridges and palate, for in the absence o f natural teeth, the guide, when taken to the mouth, must be firmly supported by the ridges and palate. It is now ready for the test in the mouth. (F ig 2 3 .) T he corrected lower occlusal rims are removed from the lower cast and placed in position in the

Fig. 23.— Testing the occlusal rims in the mouth fo r the various ranges of mandibular movement.

mouth, the balanced occlusion guide is inserted and the patient is asked to close and go through the various ranges of mandibular movement. During these excursions o f the mandible, the guide should remain in continuous occlusal contact with the lower occlusal rims. A fter such a test, it is obvious that the utilization o f this newly established arc as a guide to build the occlusion w ill give a balance in all the ranges. T he lower restoration is made first. (F ig. 2 4 .) T he balanced occlusion guide is placed back on the mounted casts. T h e occlusal rim is removed from the base plate on one side, the oc­ clusal rim on the opposite side being left intact to maintain the proper height for

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the lower teeth. T h e teeth are now set up to the guide, with both the buccal and lingual cusps in contact. W hen this is accomplished, the occlusal rim is re­ moved on the opposite side. These teeth are set up to make con­ tact with the balanced occlusion guide. (F ig. 2 5 .) T he lower teeth now pre­ sent the same arc and same height as did the occlusal rims which were used in the test.

Fig. 24-.— Setting lower teeth on right side to balanced occlusion guide.

W e are now ready to construct our upper restorations. (F ig. 2 6 .) T he positioning guide, which was used in the diagnosis to determine the amount o f opening, is placed between the casts, and the instrument is locked to maintain this position. This gives the same relative position to the casts that the mandible had to the maxillae during the diagnosis. W ith the instrument in this relation­ ship, the positioning guide is removed. (F ig. 2 7 .) A base is adapted to the

upper cast and the teeth are set to oc­ clude with the lowers in central oc­ clusion. N ow the friction screws are released on the instrument. The oc­ clusion is noted when the various move­ ments such as forward and lateral are made. A ll the teeth should be in maximum balanced occlusion. W e should bear in mind that the mandible travels slightly forward as it moves laterally, and be

Fig. 25.—-Lower set-up showing teeth in contact with balanced occlusion guide.

sure that provision is made for this in the arrangement o f the teeth. A fter the teeth are arranged in a balanced occlusion on the instrument, the case is tried in the mouth, and checkbites are made in the forward and both lateral ranges. T his step is very im­ portant in so far as it is the means whereby we prove or disprove the ac­ curacy o f the mounted case. Great care should be exercised to avoid distortion during the making and subsequent handling o f the check-bite waxes. The method employed in making a check-

L ittle— Balanced Occlusion bite wax is as follow s: T he check-bite wax is softened in warm water, and is placed in the mouth, and the patient is

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with cusp influence, we w ill have un­ equal pressure, not only on the under­ lying tissue but also in the compressible portion o f the temporomandibular joint. As each check-bite is made, it should be removed from the mouth and chilled, then reinserted in the mouth, and the patient made to close in the same position in the chilled wax. This w ill tend to correct any distortion that may be

Fig. 26.— Adjusting- casts on the instrument by the use of the positioning guide.

Fig. 28.— Use of check-bite wax to verify the correct mounting o f casts on the instru­ ment.

Fig. 27.— Upper teeth set to the new cen­ tral occlusion relationship.

asked to close gently in the desired range, care being observed that the teeth do not pass entirely through the wax in any place, the reason for this being that,

present. O w ing to the physical changes which wax undergoes when le ft lying around, it is advisable to take the case to the instrument and make the test at once. A ll the control screws on the instru­ ment are released. (F ig. 2 8 .) One o f the check-bite waxes is placed on the lower occlusal surface and the upper is adjusted into its respective impression in the wax, the same test being made with the other two check-bite waxes. Assuming that the teeth set up in wax

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have not become distorted, it would seem logical that a failure to make the casts fit properly into the check-bite waxes means that, during the transfer or in mounting casts on the instrument, we have failed to get the casts in the same relationship to the mechanical axis o f movement on the instrument that the natural teeth bear to the condyles. I f such is the case we adjust the instrument

range, and Figure 31, balanced oc­ clusion in the right lateral range. Figure 32 illustrates balanced oc­ clusion in the forward range. Note that the anterior teeth are not in contact. This is done for a definite purpose. A fter the case is inserted in the mouth,

Fig. 29.— Finished case in central occlusion.

by means o f the jackscrews underneath the lower cast carrying plate until the casts fit in all three check-bites. T he teeth are then rearranged to a balanced occlusion in this corrected relationship. N ow , with the corrected occlusion as a guiding factor to control the move­ ments o f the instrument, the occlusion o f any individual teeth that need res­ toration is waxed up and the case finished. Figure 29 shows the finished case in central occlusion; Figure 30, the balanced occlusion in the le ft lateral

Fig. 30.— Balanced occlusion in le ft lateral range.

certain changes take place, consisting of a rearrangement o f the gum tissue when continued pressure is applied and farther resorption o f the alveolar process when work is placed on it. W ith these changes, which vary in different parts o f the mouth, we find it necessary to ad­ just the base or regrind the occlusal surfaces. Each or all o f the foregoing are factors in bringing the mandible in

Little— Balanced Occlusion closer apposition to the maxillae. This naturally acts to close the space between the anterior teeth. Our ultimate aim is to have the teeth in maximum con­ tinuous occlusal contact during all ranges. I f tissue-bearing restorations are constructed so that the occlusion is

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ern it here. In many cases, after analytic study, it may be found that the correction is too great to be ac­ complished in one restoration. In some cases, the retrogression may be so great that it w ill be necessary to carry them over a period o f time as treatment cases before reaching the ultimate goal. In reality, compromise, which we all know at times is necessary, becomes a personal

Fig. 32.— Balanced occlusion in the fo r­ w ard range.

Fig. 31.— Balanced lateral range.

occlusion

in

right

continuous at the time o f insertion, we w ill have created, follow ing these changes, an overbite that w ill throw the posterior teeth out o f balance during the various excursions o f the mandible. It cannot be denied that the element o f compromise enters into this work, just as in all other dental operations. The factors which govern compromise in other dental operations w ill also gov­

matter between the dentist and the patient, determined by the case at hand. One very important thing to consider when incorporating balanced occlusion into tissue-bearing partial denture con­ struction is the matter o f proper bases to receive the stress. This work varies somewhat from the ordinary partial denture, which is generally built to the existing central occlusion, no matter how bad it may be. Many o f these cases present malocclusion, which acts to limit mandibular movement. Any inter­ ference in the movements o f the mandi­

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ble results in a diminution o f the muscular efficiency. T he construction o f a new occlusion built to conform to the spherical principles permits the mandible to move freely in its various ranges. This freedom o f movement results in a return o f muscular tone. As a result, the muscles become capable o f exerting great pressure. T o counteract this pres­ sure, the bases upon which the occlusion is constructed must be as large and ex­ tensive as possible. In many cases, the entire load is thrown on the restoration; as, for example, when the restoration involves a case with a big over-bite, the posterior teeth having been lost. In such cases, small saddles commonly em­ ployed in partial denture work do not present sufficient seating area to with­ stand the muscular force exerted. Before commencing the construction o f tissue-bearing partial denture re­ storations, the patient should be in­ formed as to the transitory nature of this work. He should be educated to ex­ pect that maintenance o f the restoration w ill be necessary for proper function. T his is important. W ithout such an explanation, the patient generally judges this work in the same light as fixed den­ tistry. W hen these cases are rendered useless owing to the changes that take place, the blame is generally placed on the dentist. Failure to impart this in­ formation regarding the upkeep gener­ ally results in the patient becoming disappointed in this type o f work. A fter a review o f the principles which underlie the practical application of balanced occlusion to partial denture construction, it becomes very evident that the dentist who can see only the problem in terms o f gold, vulcanite and teeth can never succeed in this branch o f restorative dentistry. Unless he has a proper conception o f the anatomy and

physiology o f the parts involved, it will be very difficult to differentiate between deformity and the ideal. T o build our restoration to the existing deformity w ill never solve the problems that surround this work today. However, to be able to recognize what retrogressive changes have taken place after the loss of the' oc­ clusion w ill be a material aid in the solution. DISCUSSION

M ark E. Vance, Lincoln, Nebr.: Quoting from Dr. Little’s paper: “T o have perfect relationship and perfect coordination o f all parts would be to have an ideal. T he ideal is that which exists only in imagination. In many of the sciences it is necessary, however, that we use the ideal as a standard o f meas­ ure in making our deductions. For that rea­ son, in the study o f balanced occlusion we lay our foundation or basis in the ideal hu­ man denture.” T he ideal we must keep in mind at all times. While in dental college, I learned the making of gold fo il restorations; an almost lost art in dentistry today, I regret to say, owing largely to the invention o f the gold inlay and the development o f porcelain. In the m aking o f every gold fo il operation, I have constantly before me the ideal. I have had a mental picture always before me o f the foil restoration which D r. C. N. John­ son tried to teach me. I have never attained the ideal by any means, but I often see some of the foil operations which I made fifteen and twenty years ago or more, and they are preserving the tooth structure, while some of my later w ork in inlays and porcelain has failed. There is fortunately a tendency today in some parts o f the country tow ard a return to gold foil, which in my estimation is the nearest to the ideal fo r tooth preservation T his does not apply directly to what Dr. Little has tried to give us in his paper, but what I am pointing out is the necessity of striving fo r the ideal not only in balanced occlusion in partial denture construction but in all we do in dentistry. T he man whose principal aim in the profession is, “ to make a lot o f money quick,” as expressed by a young man who graduated in my class, will have no ideal nor ideas o f any ideal. Money does not reward one’s effort in dentistry. It is the satisfaction of having rendered an

Little— Balanced Occlusion honest service conscientiously performed. T he financial remuneration w ill come to such a man. The opening o f the bite in construct­ ing partial dentures, fu ll dentures or fixed bridgework is a procedure overlooked by most men, judging from my observation. I have been somewhat in touch with the work which D r. Little is doing, and since studying the principles o f balanced occlusion, I have had a fa r greater understanding of what the effect on the supporting tissues of the oral cavity is when the occlusal balance has been dis­ turbed either by loss of teeth, occlusal wear or improperly constructed restorations. The scientific w ork which D r. Little has given us in his paper has brought the profession to a realization o f how much proper occlusion o f the teeth, be they natural or artificial, has to do with the “functions of mastication, deglu­ tition, respiration, the drainage of the oral cavity and posterior part of the pharynx, the equalization o f air pressure in the middle ear through the eustachian tube, and the supply of blood to these parts are dependent.” R eferring to Figure 5, it takes no stretch of the imagination to see what happens to the oral tissues if they are compressed and forced out o f their normal position. And yet, until someone like D r. Little points these things out to us, little thought is given to it. I wish I could throw on the screen this same illustra­ tion with the oral tissues compressed and forced out o f position as they must be when proper occlusion is disturbed. Illustrations may speak louder than discussions. I have opened the bite in mouths fo r many years and have been criticized by other den­

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tists fo r doing so, but while I hardly knew what effect it was having on the oral tissue, I rarely found a patient that did not seem benefited by having more space fo r these tis­ sues. In most partial denture cases, the sad­ dles are entirely too small. T he seating area should be as large as possible. T h is I noted in D r. Little’s practical cases which I have seen in his office. I was quite surprised at first at the weight o f materials which Dr. Little used in all such cases, but I am satisfied that many cases are failures because of the lack o f rigidity which the added bulk of material gives. Education of the patient in what we are endeavoring to do is an essential thing. W ithout it, many cases are doomed to failure from the beginning. T his same thing applies to all kinds of fixed or remov­ able restorations, fillings, inlays and all work done in the mouth. Changes in the oral tis­ sue, which will occur in every mouth after res­ torations are made and worn, are absolutely beyond the control of the dentist. This the patient should thoroughly understand in order that he may give to the dentist the thorough cooperation necessary to the success o f any restoration. Most dentists are general prac­ titioners, and comparatively few specialize in any one branch o f dentistry. T herefore, if the suggestions made by D r. Little, and his procedures, are not applicable to the every­ day work o f the general practitioner, they are o f comparatively little value. Likewise, if the general practitioner does not understand the application o f these procedures to his everyday operations, they are o f little value to his patients. I speak on this subject from the standpoint o f the general practitioner.