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Mandibular equilibration
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43. Bodecker, C. F. M odified dental caries index. J.A.D.A. 26:1453 Sept. 1939. 44. Henschel, C. J., and Lieber, Leon. High-urea ammoniated dentifrice: caries reduction through four years' home use. Oral Surg., O ral M ed, & O ral Path. 5:155 Feb. 1952. 45. Bruckner, R. J.; Hill, T. J., and Wollpert, B. Measurement of dental caries incidence in school chil dren usinq a sodium bicarbonate dentifrice. J. D. Res. 31:105 Feb. 1952. 46. Lefkowitz, William, and Vente, V. A . Preliminary clinical report on caries control with a high urea ammoniated dentifrice. O ral Surg., O ral M ed. & Oral Path. 4:1576 Dec. 1951. ' 47. Porter, D. R., and Dudman, J. A , Assessment of dental caries increments. I. Construction of the R.I.D. index. J. D. Res. 39:1056 Sept.-Oct. I960. 48. Boyd, J. D.; Cannon, J. J., and Leighton, R. E. Epidem ioloqic studies in dental caries. V. Placement of filling as a source of statistical error of estimate as to dental caries progression rates. J. D. Res. 31:354 June 1952.
49. Sandy, C . E., and Bulate, Lydia. Salivary lacto bacillus count as an index of caries activity. Austral. J. Den. 54:18 Feb. 1950. 50. SnydeV, M. L., and Claycom b, C . K. Simple motorized device to facilitate the spreading of inocula over agar plate surfaces. J. Bact. 67:739 June 1954. 51. Snyder, M. L., and others. Evaluation of labora tory tests for the estimation of caries activity. J. D. Res. 35:332 June 1956. 52. Claycomb, C. K.; McChesney, M . N., and Snyder, M. L. Simple rapid method for quantitative determina tion of salivary amylase. J. D. Res. 35:391 June 1956. 53. Hadiimarkos, D. M., and Sforv/ck, C. A . G e o graphic variations of dental caries in Oregon. J. D. Res. 28:415 Aug. 1949. 54. Nevitt, G. A.; Witter, D. H., and Bowman, W . D. Topical applications of sodium fluoride and stannous fluoride. Pub. Health Rep. 73:847 Sept. 1958. 55. Symposium on clinical estimation of caries inci dence and increments. O hio State University School of Dentistry, Columbus, Ohio, September, 1959.
M a n d ib u la r equilibration
V ictor H . Sears* D .D .S., Cairo, Egypt, U .A .R .
T h e essential features of mandibular equilibration are: ( 1 ) to establish occlud ing relation at an acceptable degree of jaw separation, ( 2 ) to place the load mainly in the molar regions, ( 3 ) to clear the occlusion, and ( 4 ) with artificial den tures to balance the occlusion in eccentric as well as in centric relation. Only the dentist is qualified in the mechanical phases of treatment having to do with jaw relation and tooth occlusion. Dental schools in the United States should es tablish autonomous departments to deal with tooth occlusion, as has been done by the schools in Sweden and Denmark.
T h e temporomandibular joint remains unique among its counterparts in the human body. Dentists and physicians
should be able to recognize lesions in this joint and related structures, to know the many disorders associated with such le sions, and to apply appropriate treat ments. So far as dentistry is concerned, the chief reliance should be on placing the mandible in a condition of equilibrium. Equilibrating the mandible for the re lease o f stress in the temporomandibular joint and the related structures in the body is perhaps the newest treatment used by the dentist, and one o f the most valu able. T h e present discussion is intended to bring the general concept into sharper focus. For the most part this discussion ap plies especially to the field o f complete artificial dentures, but the implications in the other fields o f dentistry will be ap parent.
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TER M IN O LO G Y
A n understanding o f the terms used is important because too many writers are causing confusion by the careless use of words. Th e term “ mandibular equilibra tion” is so new that it is not listed in the 1960 Glossary o f the Academy o f Denture Prosthetics.1 Clarity o f expression demands that each term stand for a discrete concept. Unfortunately some writers are using the terms “ equilibration,” “ occlusal adjust ment,” “ selective grinding,” “ occlusal balance,” and “ occlusal clearance” as though they were all the same thing. One writer speaks o f “ equilibrating the steep ness of the inclines,” and another even says: “ I equilibrate interproximally.” This careless use o f language only clouds our thinking and delays progress. Cer tainly it is important in this field to har monize all o f the technical words with ordinary usage, and especially with the terms used in other sciences. According to the dictionary, “ clear ance” is the condition o f being “ free of obstruction” or “ free from contact with anything that hinders.” T h e word “ balance” means “ having two scales or plates.” T h e connotation here is clearly that o f two opposing in fluences. “ Equilibrium” is defined as “ that state o f a body in which the forces acting on it are so arranged that their resultant at every point is zero.” T h e connotation of equilibrium is that o f multiple forces as in the case of a man poised on stilts. In dentistry the meanings o f “ clear ance,” “ balance,” and “ equilibrium” should be applied discretely to the three separate concepts. Producing “ clearance of the teeth” consists in causing the opposing occlusal surfaces to glide over one another without any interfering projections; producing “ balance o f the occlusion” consists in as suring simultaneous contact on right and left sides or at the front and back o f the
occlusal scheme; producing “ equilibra tion o f the mandible” consists in bringing about a condition in which all o f the forces acting on it are neutralized. Both clearing and balancing are phases o f occlusal adjustment, but they are not equilibrating. In making occlusal adjust ments, the teeth can be cleared or bal anced or both, but they cannot be equilibrated if we adhere to the logical distinctions. In this discussion the three different terms, “ clearance,” “ balance” and “ equilibrium” will be used explicitly for the three different concepts. T H E PRE S E N T S IT U A T IO N
Although temporomandibular joint clin ics are operating in some hospitals and universities, mandibular equilibration as an individual discipline has not yet been generally accepted and taught in the den tal schools o f the U nited States. However, among alert dentists and physicians there is a growing awareness o f the importance and extent o f temporo mandibular joint lesions. W ith this aware ness there comes a greater appreciation o f the value o f mandibular equilibration. H IS T O R Y
Several thousand years ago the Egyp tians wrote about the temporomandibular joint, but it was mostly concerning dis location. M ore than 200 years ago Ferrein2 made a good analysis of the m ove ments o f the mandible, and especially the condyles. In the early 1920’s W right3 and Monson4 called attention to the malrelation o f the condyles as a cause o f deafness. Th ey relied heavily on increasing the de gree o f jaw separation for the treatment o f deafness, and popularized “ bite rais ing,” which has had its resurgence with dentists from time to time since then. In the early 1930’s Costen,5 Pippin,6 and Goodfriend7 called attention to nu merous symptoms related to temporoman dibular joint dysfunction and to the
SEARS
means o f relieving these symptoms. Costen’s chief mechanical reliance was on interposed cork disks in the molar re gions with an elastic bandage pulling up on the chin to rock the condyles down. H e claimed only that this treatment “ breaks the trismus cycle.” 8 Between treatments the condyles tend to return to their displaced positions, with a return o f the symptoms. T h e writers o f this period stressed the effects o f temporo mandibular joint lesions on the fifth cranial nerve and the structures supplied by this nerve. In the early 1940’s Block and Harris9 concentrated attention on deflective cuspal prominences as the principal cause for temporomandibular joint disturb ances, and reported numerous instances o f relief after clearing o f the occlusion. Th eir writings refer to the “ upward and backward” condyle displacement as men tioned by W right and Monson, with no emphasis on the upward displacement alone. Some dentists are still content to go no further than mere clearance. In 1952 I reviewed the then-current thinking in the field and reported the re sults o f seven years’ experience with an additional therapeutic aid, the occlusal pivot. This report10 explained the ration ale o f treatment and illustrated a spe cial recording device for demonstrating changes o f the condyle positions after the use o f occlusal pivots. In 1953 before the September meeting o f the American Denture Society, there was a symposium on this subject,11 and there followed a growing number o f ar ticles in the dental journals. In the last two years, three excellent books concerned with the temporoman dibular joint have been published in this country,12-14 but unfortunately all three of them practically ignore mandibular equilibration as implemented by occlusal pivots. In 1955 the American Equilibration Society was organized for the study o f the temporomandibular joint together with
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its related structures, and has become the clearinghouse for information on the subject. Th e recent increase in the number of lectures, classes, seminars, journal articles and books on the temporomandibular joint attests to the growing interest in the subject. In the wake o f this advance, den tists and physicians are doing more for the permanent relief o f temporomandibu lar joint symptoms than previously, and are relying less on injections and surgical intervention. W ith the increased use of mandibular equilibration, the temporo mandibular joint becomes more and more a common meeting ground for medicine and dentistry. SOME CU RRENT BELIEFS
A t present, some areas o f disagreement exist. There are anatomists who maintain that certain cures reported by therapists are mechanically impossible. Physiologists and neurologists reject some of the ex planations. Y e t there continues to accum ulate an impressive amount o f evidence to show that the integrity o f the temporo mandibular joint is restored when stress is relieved. It is too early to judge the validity of all the claims; any such attempt would surely meet with objections. However, there has been a notable increase in un derstanding, and it seems appropriate to comment on 14 points about which den tal and medical writers concern them selves : 1. A few writers have tried to prove that the mandible is not a lever of the third class and that the temporomandibu lar joint is not a stress-bearing joint. However, most investigators believe that third class leverage does occur— at least sometimes. Perhaps it can be said that although the temporomandibular joint is not histologically like the hip or knee joint, nevertheless it can withstand an intermittent load o f considerable magni tude. This it does when the mandible acts
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as a third class lever during incision. However, too great a load or too con stant a load on the incisors forces the condyles pathologically upward in their sockets. 2. I t is still stated in some textbooks that the inclination o f the articular fossa determines the “ downward and forward” path o f the condyle— and so it does in the dry skull. But in the living subject a steep articular surface may be associated with a nearly horizontal path. 3. Some dentists still believe that the condyle paths for each patient are pe culiar to that patient and unchangeable. However, it can be shown that these paths become steeper when a longstanding over load on the anterior teeth is reduced. In deed, overloading on the anterior teeth is a cause o f distorting all the condyle positions, centric and eccentric. 4. “ Bite raising” has been held by some to be the chief mechanical means o f providing relief for temporomandibu lar joint lesions. This treatment still holds a place in therapy, but it occupies a less important place than formerly. Some o f the favorable results claimed for “ bite raising” now appear to be due to an in advertent pivoting o f the mandible when the posterior teeth are built up more than the anterior ones. 5. I t was once believed that a back ward displacement o f the condyle in its socket was the main cause of temporo mandibular joint dysfunction, and es pecially o f ear symptoms. Later it came to be believed that other horizontal dis placements were o f greater importance, and still later that the most important of all might be the upward displacement o f the condyles after continuous overloading o f the anterior teeth. 6. Some operators have met with suc cess in the relief of temporomandibular lesions with definitely meshing cusps set to hold the mandible in slight protrusion. Others believe that only when the man dible is unhindered by any cusps at all can it settle into its unstrained relation.
In any case it seems rational to start with flat plane teeth at the desired occluding relation, and have the patient wear the cuspless restoration until the mandible comes into its position o f equilibrium. This opinion is strengthened by the ex periences o f dentists who have been called in on consultations because the suppos edly correct treatment failed to bring about the expected improvement. In these instances it was usually found that although the pivots were located prop erly, the occlusion was locked horizontally by meshing cusps, and only after flatten ing the cusps were the symptoms relieved. 7. Some investigators have objected to the complete clearance o f the occlusion by flattening the cusps on the ground that this permits too much translatory m ove ment o f the teeth and too great excursion o f the condyles. W hatever the merit of this contention, experience shows that there is more danger from too much oc clusal restriction than from too little. 8. T h e restraining ligaments of the joint may be too lax or too taut. Either condition may require treatment. Th e most common treatments for ligaments that are too lax are rest, fixation, increas ing the circulation of blood, and the in jection o f sclerosing solutions. T h e patient is also cautioned not to open the jaws more than necessary in chewing and bit ing, and never to yawn. Common treatments for ligaments that are too taut are heat, exercise and trac tion. Whether the patient is to be treated for too little or too much tightness in the joint, it is important to maintain the major portion of the occlusal load on the posterior teeth. 9. There now remains little doubt that muscle spasm may cause pain and vice versa. Sometimes the treatment fo r one o f these conditions clears up the other. 10. Temporomandibular joint lesions may be lessened by the systemic approach, including o f course hormonal and nutri tional balance.
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11. W ith the accumulation of experi ence there is a transition from the atti tude o f “ let well enough alone” to one o f restoring normalcy where stress in the joint is discovered, whether or not the patient complains o f symptoms. It has been learned that there are many subclinical lesions which may be the pre cursors of more serious disturbances un less treated. This points to the need for prevention. 12. Conversely, any improper occlusal changes may bring on the pain-dysfunction syndrome. 13. Some dentists assert that although bilateral balance in eccentric positions may be desirable for artificial dentures, it is unnecessary and even detrimental for natural teeth. 14. Before mandibular equilibration in its several phases was developed as a treatment, there was more justification for radical measures. Meniscectomy, condylectomy,15 and the injection o f scleros ing and other solutions into the temporo mandibular joint have not lived up to expectations for permanent relief, and they are losing favor. E X A M IN A T IO N
Am ong dentists and physicians who have given attention to temporomandibular joint lesions there is considerable varia tion in the examination procedure. N o general agreement has been reached on the extent o f the examination. A t present, perhaps each practitioner should study the forms suggested by current authors and then develop his own charts. DIAGNOSIS AND T R E A T M E N T
Diagnosis o f temporomandibular joint lesions is the responsibility of both den tist and physician. Most o f the symptoms were once treated symptomatically by the physician and largely ignored by the den tist. Fortunately for the patient, more
and more dentists and physicians are co operating in diagnosis and treatment, with the dentist carrying out most o f the treatment. M any o f the pain and other symptoms associated with temporomandibular joint dysfunction are the same symptoms that are associated with other complaints in the region o f the ear. I t is important, therefore, to consider the symptoms as having possibly nothing at all to do with the joint. Neoplasms and infections should be considered. Whether or not pain is present, it is well to remember that spasm of the involuntary muscles may cause circulatory disturbances16 and may be even more disabling than spasm o f the voluntary muscles. Blood and lymph cir culation may be impeded in either case. I t is possible for the diagnostician to feel pressure in the external auditory meatus by pressing the ball o f the little finger toward the condyle as the mandible closes. This test is fairly reliable for de tecting excessive backward displacement o f the condyle. Roentgenograms can be made that will disclose any gross malpo sitions of the condyle in its socket. Displacement o f the condyle does not always cause annoyance, especially in healthy persons. I f the resistance is low ered, however, a patient may develop symptoms, especially under continuous stress such as occurs in the temporoman dibular joint from faulty occlusion. Im proper occlusal reconstruction may bring on symptoms. Also, the unfilled spaces created by tooth extractions may result in positional changes o f the remaining teeth, and the resulting malocclusion may gradually force the condyles into posi tions that result in lesions. Palpation o f the patient’ s head and neck may disclose tender areas17 when the temporomandibular joint is under stress. Tenderness in or near the joint, es pecially tenderness in the infratemporal fossa, is a possible diagnostic sign.18 Am ong the symptoms to look for are headache, nervousness, loss o f hearing,
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vertigo, nausea, tinnitis, muscle spasm, limitation o f jaw movement, and clicking joints. View ed with skepticism by some investigators as related to temporoman dibular joint dysfunction are migraine, stiff neck, general irritability, sleepless ness, fatigue, sinus congestion, mental dis turbances, and several other morbid con ditions. A ny dentist who claims success in treating any o f these disorders should accompany his reports with corroborating statements from the attending physician. A dentist or physician will report relief from symptoms after a certain treatment whereas another dentist or physician w ill report little or no success. In some in stances, failure must be attributed to im proper or incomplete treatment. Then, too, spontaneous remission o f symptoms sometimes occurs regardless o f the treat ment. Such treatments as heat, cold, vibra tion, massage, drugs, immobilization and psychotherapy should be kept in mind, but these are essentially o f temporary or limited value so long as the mandible re mains out o f equilibrium. It should also be remembered that the remedies for torn or overstretched ligaments, fluid in the capsule, inflammation, infection and arthritis are similar to those indicated in other parts o f the body. W ith all these remedies at hand, the basic therapeutic measure to be considered for the release o f stress in the temporomandibular joint is contriving the return o f the mandible to its unstrained position. T h e dentist does not need to place the mandible in any definite position; he merely removes all restrictions so that it can move by it self into its position o f equilibrium. E Q U ILIB RATIO N
O f all treatments devised recently, per haps mandibular equilibration is the most valuable, either by itself or in conjunction with other measures. As judged by clini cal results, it shows a high average of success.
Mandibular equilibration is a simple, conservative treatment. It is painless and without danger to the patient. Unlike some other treatments, it has no unfavor able side effects. Mandibular equilibra tion is valuable in differential diagnosis. It does not interfere with other measures. T h e treatment is curative as well as pre ventive. I t should be considered in prac tically all kinds o f temporomandibular joint lesions. Unfortunately some dentists with in complete understanding o f the whole problem have inflicted unnecessary suf fering on their patients by the improper application o f what has been variously called “ oral rehabilitation,” “ bite raising,” and “ occlusal reconstruction.” Beautiful looking and meticulously contrived oc clusal conformations have sometimes caused damage because the dentist neg lected the basic considerations. Patients have been subjected to costly and ex hausting “ occlusal reconstruction” only to have the entire handiwork removed because the patient could not tolerate it. Such tragic experiences can be avoided by first placing the mandible in equi librium and then devising an occlusal scheme which w ill maintain it there. Dentists who practice “ occlusal recon struction” or even “ selective grinding” should first make sure that the mandible is in equilibrium. W ith respect to complete artificial den tures, there are four mechanical consid erations in producing and maintaining mandibular equilibrium: (1 ) establishing an acceptable degree o f jaw separation with the teeth in occlusion; (2 ) pivoting the mandible; (3 ) clearing the occlusion, and (4 ) balancing the occlusion, espe cially at and near centric jaw relation. J A W SEPARATION
W ith the teeth in occlusion, there should be a degree o f jaw separation at which the muscles are comfortable and function well— neither sagging nor being over-
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Fig. I * A s dentures settle and m andible closes around intercondylar axis, lower incisor point travels upward and forw ard as indicated by do t ted line. M o v e m e n t is gre ater at incisors than at molars; this causes separation in m olar region with consequent loss of m olar support, and so load is carried b y incisors. (Artificial dentures are used in these illustrations to illustrate forces and positional changes, but the sam e principles apply with natural teeth)
stretched. In some instances the exact length of the muscles at occluding relation is not critical, whereas in others the pa tient is not comfortable unless this length is definitely fixed at occluding relation. Occasionally a patient is seen who can tolerate a rest relation with thé teeth barely out of contact, but most patients need an interocclusal space of from 1 to 3 mm. when the mandible is in rest re lation. Too great an interocclusal space per mits excessive jaw closure and produces an unesthetic facial appearance, disturbs the arrangement of the ligaments, short ens the range of the muscles too greatly, and may impair the ventilation of the eustachian tube. It may also cause ear ache and clicking joints. More serious than excessive closure is the condition in which the mandible is held by the teeth at an excessive degree of jaw separation. This condition is not well tolerated by the patient, and it causes resorption of the tooth-supporting or denture-supporting bone. Until the re
sorption of bone has progressed far enough to restore a comfortable inter occlusal gap, the destruction continues. Frequently there is pain in the joint or in the muscles even though the supporting bone may not be painful. With the elimination of all cuspal in terferences and with the occlusal load applied near the anteroposterior center of the denture foundation, finding the ac ceptable degree of jaw separation is ordi narily not at all difficult. However, it may necessitate testing the separation by hav ing the patient wear the dentures at the estimated height for several days. It should be remembered that spasm, es pecially of the temporal, masseter, or median pterygoid muscles, will interfere with finding the desired degree of jaw separation. It is therefore important to defer judgment on this point until the spasm has subsided. PIV O TIN G T H E M ANDIBLE
The occlusal pivot is a point or restricted occlusal area near the anteroposterior center of the denture foundation promi nent enough to receive the closing force applied by the mandible.19 It is used for the purpose of relieving the load from the anterior teeth and placing it in the molar region to reduce the proportion of up ward force exerted by the condyle. This redistribution of force permits the con dyle to descend in its socket toward its normal position. The need for pivoting arises when the posterior tooth support is lost or dimin ished so that the anterior teeth bear too great a load. With natural teeth the con dition develops when posterior teeth are lost and not replaced; with artificial den tures the condition develops largely be cause of settling as shown in Figure 1. When the load is carried for too long a time by the anterior teeth, one of the results is excessive upward pressure in the fossa by the condyle. The action is illustrated in Figure 2.
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ment. Despite their long-term benefits, they should be inspected from time to time by recall of the patient, or at the slightest sign of the return of the old symptoms. AD D ITIO N A L BE N E FITS OF PIVOTS
Fig. 2 • W ith contact only at incisors and with muscles pulling up between incisors and condyle, upward m ovem ent of condyle in its socket results. This causes pressure and places tem porom andibu lar joint under stress. S h ade d portion indicates, in e xaggerated degree, position of m andible b e fore displacem ent of condyle
To reverse this upward displacement of the condyle, pivots should be worn night and day until sagittal equilibrium of the mandible is achieved. This sagittal rotation of the mandible around the oc clusal pivots is demonstrated in Figure 3. The actual technic of pivoting has been described elsewhere.19 With natural teeth, the pivots may sometimes be placed on the second or third molars; with artificial dentures, the consideration of denture stability requires them to be placed farther anteriorly, usu ally on the first molars. They should glide over opposing flat surfaces so that the mandible can move horizontally without hindrance. Pivots do not “push the mandible around.” Conversely, they are used to re duce the upward force at the condyles so that the mandible can return by itself to a state of equilibrium. The results of pivoting are demonstra ble in three principal ways: relief of symptoms, “before and after” roentgeno grams, and the condyle recorder con structed for this purpose.20 Although the results of pivoting are not always permanent, they are more nearly so than most other forms of treat
Quite aside from their role in preventing or relieving temporomandibular joint le sions, occlusal pivots on dentures, by vir tue of their location, have other advan tages. Some of them are: 1. Ease of obtaining clear tracings for jaw relation records after the pivots have been worn for a short time. 2. Ease of finding an acceptable oc cluding relation. 3. Centralizing the load for making better impressions. 4. Reducing anterior ridge resorption. 5. Preventing the anterior teeth from being pushed beyond the lip line. 6. Preventing deformation of the man dible. 7. Increasing denture stability. 8. Preventing gagging.
Fig. 3 • Transferring occlusal load from incisors to molars decreases upward pressure of condyle in its socket. W ith occlusal pivot in m olar region as shown here, m andible has a limited movement around this pivot as shown by dotted lines. A s incisors move up, condyle moves down, thus re du c in g stress in tem porom andibular joint
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CLEARING T H E OCCLUSION In the several branches o f dentistry rather general agreement has developed on the desirability o f providing clearance o f the occlusion. In the complete denture field there is the further need to permit prac tically horizontal jaw movement while the opposing teeth are in occlusion. Clearance o f the occlusion is possible with cusp teeth in the sense that they can be adjusted so that no projection pre vents the other teeth from maintaining smooth gliding contact, but the flatter the cusps the less hindrance there is to the free horizontal movements o f the mandible. T h e need for horizontal free dom o f movement to protect the den ture-supporting structures was the chief reason for developing the so-called nonanatomic teeth. A t first these nonanatomic teeth were used primarily to prevent injury to the denture-supporting structures. Th ey are still used fo r this, but now are used in creasingly for the further purpose o f preventing injury to the temporoman dibular joint. In fact, many dentists have been using flat plane teeth to protect the tissues under the dentures without realiz ing that the temporomandibular joints were also being protected. T h e backward pressure caused by cusps on the lower dental ridge and on the condyle is indi cated in Figure 4. Channel teeth,20 the first teeth designed to assure anteroposterior clearance, came into use in the 1920’s. T h ey were de veloped at a time when attention was focused on preventing the posterior thrust on the lower ridge and on the condyles. However, they failed to provide for lateral freedom of movement. Another attempt to unlock the occlu sion was the motor-driven grinding at tachment to the articulator invented by U p p 21 for use with cusp teeth. This de vice provides horizontal freedom of move ment although the degree is quite limited. Th e grinding attachment still used by
Fig. 4 • Since any closure around intercondylar axis as shown in Figure I results in forward shift of mandible, slightest resorption of supporting tissues under dentures permits any deflective cusp inclines to cause backward pressure as shown here. M e sial surface of lower cusp glides on distal surface of upper cusp so that upward pull of muscles produces backward force on lower teeth and o f course on condyle, placing tem porom an dibular ¡oint under stress
some dentists was only a step toward complete clearance. Whether clearance is produced with cusp or cuspless teeth, this difference in form has little to do with chewing effi ciency. Some investigators have claimed greater efficiency for cuspless teeth than fo r cusp teeth, w hereas others have claimed just the opposite. I f there were much difference in this respect, the ques tion would have been settled long ago. Although tests show that flat plane teeth chew some foods more efficiently, other foods are chewed more efficiently with cusp teeth. W hen considering the entire range of food in the average meal, there is no significant difference in this re spect. Therefore, cuspless teeth are to be preferred not because o f their efficiency in chewing but because they make man dibular equilibration more certain and more nearly permanent. BA LAN C IN G T H E OCCLUSION
In addition to clearance, there is another occlusal adjustment— that o f assuring simultaneous contact on right and left
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sides in lateral relation and simultaneous contact front and back in protrusive rela tion. Although some dentists feel that bilateral balance in eccentric relations may be detrimental with natural teeth, few make this contention with artificial dentures. T h e essential features o f mandibular equilibration are (1 ) to establish occlud ing relation at an acceptable degree of jaw separation, (2 ) to place the load mainly in the molar regions, (3 ) to clear the occlusion, and (4 ) with artificial den tures to balance the occlusion in eccen tric as well as in centric relation. M AND IB U LAR E Q U ILIB RATIO N
T o a very great extent the temporoman dibular joint is the direct responsibility of the dental profession, and fortunately more and more dentists are accepting the responsibility. Although all practitioners o f the heal ing arts should be able to recognize tem poromandibular joint lesions, only the dentist is qualified in the mechanical phases o f treatment having to do with ja w relation and tooth occlusion. This whole subject should be given greater attention in our teaching institu tions. In the dental schools, the rational way o f covering the subject is to abandon the system o f teaching different views in the different departments and to con solidate the basic matter in a separate department on a par with the operative, prosthetic, orthodontic and other depart ments. A n arrangement of this kind per mits the other departments to build on this foundation. I t enables the school to present the subject in perspective. It largely overcomes the fragmented and conflicting instruction given under the orthodox system. T h e ultraconservatives are bound to object to this advance, but the answer to their objections lies in the fact that this system is already being fol lowed with conspicuous success. A good start has already been made in
the three dental schools in Sweden and the two in Denmark where autonomous departments have been established22 for undergraduate and postgraduate instruc tion to deal with tooth occlusion and its ramifications. M any o f us hope that all o f the schools in the U nited States and elsewhere will soon do likewise. Linking tooth occlusion with jaw relation (includ ing condyle relation) is the rational ap proach in teaching. Students in dental schools should not have to wait until after graduation to get this viewpoint. BU ILDING PU B LIC ESTEEM
From the standpoint o f the dental pro fession, two gratifying developments emerge— one in relation to the medical profession and the other in relation to the general public. T h e necessity for consultation in diag nosis and treatment brings the dentist and the physician closer together. Although only the dentist is trained in matters of tooth occlusion, the skills of the other members o f the healing arts, and espe cially the otolaryngologists, are needed in both diagnosis and treatment. T h e train ing o f the physician makes it easy for him to comprehend the role of stress in the temporomandibular joint, and for him to see the rationale of mandibular equili bration. As practitioners become more and more aware o f the importance of maintaining the integrity o f the temporomandibular joint, they will disseminate the knowledge to the public, which is becoming increas ingly aware o f the need for consultation in the healing arts. As more persons learn o f the importance o f preventing damage to the gingiva and joints o f the jaws, they will see the wisdom o f obtaining the serv ices of graduate dentists and physicians with professional training in physiology, anatomy and the related sciences. This awareness points up the stupidity o f trust ing one’s mouth to a lay technician who, with his lack of scientific training, may
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cause great damage. N o w with mandib ular equilibration we have a dramatic convincer. As more and more persons learn that there is danger to the struc tures in and near the ears from bungling treatment at the hands o f untrained per sons, the lure of bootleg dentistry becomes less attractive. This awakening is bene ficial to the public and gratifying to the dental profession. It behooves all dentists to give their patients the benefits o f advances in man dibular equilibration and in the whole field o f temporomandibular joint therapy. Dentists and physicians everywhere should render this service to their patients, or at least be sufficiently informed so that they can consult intelligently with those who are qualified to render this service. This happy development will do much to establish the professions more firmly in the minds and hearts of the general public. Presented before the American Equilibration Society February 2, 1961, and the American Denture Society February 3, 1961. *Faculty of dentistry, University of Cairo. !. Academ y of Denture Prosthetics. Glossary of prosthodontic terms. J. Pros. Den. 10:9 part 2 Nov.-Dec. I960. 2. Ferreîn, M . Sur les movements de la mâchoire inférieure. L'histoire de l'Academ ie Royale des Sciences, Paris, 1748, p. 427-448.
3. W right, W . H. Deafness as influenced by mal position of the jaws. J.N .D.A. 7:979 Dec. 1920. 4. Monson, G. S. Im paired function as a result of closed bite. J.N.D.A. 8:833 O ct. 1921. 5. Costen, J. B. N euralgias and ear symptoms asso ciated with disturbed function of the temporomandibu lar ¡oint. J.A .M .A . 107:252 Ju ly 25, 1936. 6. Pippin, B. N. Symposium on treatment of tem poro mandibular lesions caused by denture mutilations. Illi nois D. J. 12:429 Oct. 1943. 7. Goodfriend, D. J. Sym ptom atology and treatment of abnormalities of the m andibular articulation. D. Cosmos 75:844 Sept.; 1106 N o v . 1933. 8. Costen, J. B. Personal communication. 9. Block, L. S., and Harris, Elam. Approach to a rational study and treatment of temporomandibular joint problems. J.A.D.A. 29:349 March 1942. 10. Sears, V. H. M a n d ib u la r condyle migrations as influenced by tooth occlusions. J.A.D.A. 45:179 Aug. 1952. 11. Control of condyle relations in the mandibular fossa. A symposium. J. Pros. Den. 4:196 March 1954. 12. Shore, N. A. Occlusal equilibration and tem poro mandibular ¡oint dysfunction. Philadelphia, J. B. Lippincott Co., 1959. 13. Schwartz, Laszlo, and others. Disorders of the tem porom andibular joint. Philadelphia, W . B. Saunders Co., 1959. 14. Bell, W. E. Tem porom andibular joint disease. Dallas, I960. 15. Smith, A. E., and Robinson, Marsh. M andibular function after condylectomy. J.A .D .A . 46:304 March 1953. 16. Jensen, M . B. M uscular tensions and prosthetic dentistry. J. Pros. Den. 2:604 Sept. 1952. 17. Campbell, J. Paper presented at the annual con ference of the British Dental Association, Dundee, Scot land, July 10, 1958; reprinted in the 1959 Compendium of the American Equilibration Society. 18. Vaughan, H. C. Tem porom andibular joint pain. J. Pros. Den. 4:694 Sept. 1954. 19. Sears, V. H. Occlusal pivots. J. Pros. Den. 6:332 M ay 1956. 20. Sears, V. H. Channel type posterior tooth forms. J.A.D.A. 15:1111 June 1928. 21. Upp, R. W . U .S . Patent No. 1,180,745, April 25, 1916. 22. Posselt, UIf. Personal communication.
Scientific Cooperation * T he scientific method is probably the most fruitful of the human m ental disciplines, in that it allows cooperation among individuals throughout the ages and between countries, so that science is a body of knowledge drawing m ankind together in both time and place. Language is no insuperable barrier in science, for the substance of science is not peculiar to any language or any country. T he cure for cancer, w hen it is found, will be applicable internationally; and the search for the cancer cure is an international effort, whether it be recognized as one or not. The applications of scientific discovery can be m ade in all nations and in all times. Willard Frank Libby. Tomorrow in Science. Bui. M ed. Col. of Va. 41:5 Winter 1962.
43. Bodecker, C. F. M odified dental caries index. J.A.D.A. 26:1453 Sept. 1939. 44. Henschel, C. J., and Lieber, Leon. High-urea ammoniated dentifrice: caries reduction through four years' home use. Oral Surg., O ral M ed, & O ral Path. 5:155 Feb. 1952. 45. Bruckner, R. J.; Hill, T. J., and Wollpert, B. Measurement of dental caries incidence in school chil dren usinq a sodium bicarbonate dentifrice. J. D. Res. 31:105 Feb. 1952. 46. Lefkowitz, William, and Vente, V. A . Preliminary clinical report on caries control with a high urea ammoniated dentifrice. O ral Surg., O ral M ed. & Oral Path. 4:1576 Dec. 1951. ' 47. Porter, D. R., and Dudman, J. A , Assessment of dental caries increments. I. Construction of the R.I.D. index. J. D. Res. 39:1056 Sept.-Oct. I960. 48. Boyd, J. D.; Cannon, J. J., and Leighton, R. E. Epidem ioloqic studies in dental caries. V. Placement of filling as a source of statistical error of estimate as to dental caries progression rates. J. D. Res. 31:354 June 1952.
49. Sandy, C . E., and Bulate, Lydia. Salivary lacto bacillus count as an index of caries activity. Austral. J. Den. 54:18 Feb. 1950. 50. SnydeV, M. L., and Claycom b, C . K. Simple motorized device to facilitate the spreading of inocula over agar plate surfaces. J. Bact. 67:739 June 1954. 51. Snyder, M. L., and others. Evaluation of labora tory tests for the estimation of caries activity. J. D. Res. 35:332 June 1956. 52. Claycomb, C. K.; McChesney, M . N., and Snyder, M. L. Simple rapid method for quantitative determina tion of salivary amylase. J. D. Res. 35:391 June 1956. 53. Hadiimarkos, D. M., and Sforv/ck, C. A . G e o graphic variations of dental caries in Oregon. J. D. Res. 28:415 Aug. 1949. 54. Nevitt, G. A.; Witter, D. H., and Bowman, W . D. Topical applications of sodium fluoride and stannous fluoride. Pub. Health Rep. 73:847 Sept. 1958. 55. Symposium on clinical estimation of caries inci dence and increments. O hio State University School of Dentistry, Columbus, Ohio, September, 1959.
M a n d ib u la r equilibration
V ictor H . Sears* D .D .S., Cairo, Egypt, U .A .R .
T h e essential features of mandibular equilibration are: ( 1 ) to establish occlud ing relation at an acceptable degree of jaw separation, ( 2 ) to place the load mainly in the molar regions, ( 3 ) to clear the occlusion, and ( 4 ) with artificial den tures to balance the occlusion in eccentric as well as in centric relation. Only the dentist is qualified in the mechanical phases of treatment having to do with jaw relation and tooth occlusion. Dental schools in the United States should es tablish autonomous departments to deal with tooth occlusion, as has been done by the schools in Sweden and Denmark.
T h e temporomandibular joint remains unique among its counterparts in the human body. Dentists and physicians
should be able to recognize lesions in this joint and related structures, to know the many disorders associated with such le sions, and to apply appropriate treat ments. So far as dentistry is concerned, the chief reliance should be on placing the mandible in a condition of equilibrium. Equilibrating the mandible for the re lease o f stress in the temporomandibular joint and the related structures in the body is perhaps the newest treatment used by the dentist, and one o f the most valu able. T h e present discussion is intended to bring the general concept into sharper focus. For the most part this discussion ap plies especially to the field o f complete artificial dentures, but the implications in the other fields o f dentistry will be ap parent.
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TER M IN O LO G Y
A n understanding o f the terms used is important because too many writers are causing confusion by the careless use of words. Th e term “ mandibular equilibra tion” is so new that it is not listed in the 1960 Glossary o f the Academy o f Denture Prosthetics.1 Clarity o f expression demands that each term stand for a discrete concept. Unfortunately some writers are using the terms “ equilibration,” “ occlusal adjust ment,” “ selective grinding,” “ occlusal balance,” and “ occlusal clearance” as though they were all the same thing. One writer speaks o f “ equilibrating the steep ness of the inclines,” and another even says: “ I equilibrate interproximally.” This careless use o f language only clouds our thinking and delays progress. Cer tainly it is important in this field to har monize all o f the technical words with ordinary usage, and especially with the terms used in other sciences. According to the dictionary, “ clear ance” is the condition o f being “ free of obstruction” or “ free from contact with anything that hinders.” T h e word “ balance” means “ having two scales or plates.” T h e connotation here is clearly that o f two opposing in fluences. “ Equilibrium” is defined as “ that state o f a body in which the forces acting on it are so arranged that their resultant at every point is zero.” T h e connotation of equilibrium is that o f multiple forces as in the case of a man poised on stilts. In dentistry the meanings o f “ clear ance,” “ balance,” and “ equilibrium” should be applied discretely to the three separate concepts. Producing “ clearance of the teeth” consists in causing the opposing occlusal surfaces to glide over one another without any interfering projections; producing “ balance o f the occlusion” consists in as suring simultaneous contact on right and left sides or at the front and back o f the
occlusal scheme; producing “ equilibra tion o f the mandible” consists in bringing about a condition in which all o f the forces acting on it are neutralized. Both clearing and balancing are phases o f occlusal adjustment, but they are not equilibrating. In making occlusal adjust ments, the teeth can be cleared or bal anced or both, but they cannot be equilibrated if we adhere to the logical distinctions. In this discussion the three different terms, “ clearance,” “ balance” and “ equilibrium” will be used explicitly for the three different concepts. T H E PRE S E N T S IT U A T IO N
Although temporomandibular joint clin ics are operating in some hospitals and universities, mandibular equilibration as an individual discipline has not yet been generally accepted and taught in the den tal schools o f the U nited States. However, among alert dentists and physicians there is a growing awareness o f the importance and extent o f temporo mandibular joint lesions. W ith this aware ness there comes a greater appreciation o f the value o f mandibular equilibration. H IS T O R Y
Several thousand years ago the Egyp tians wrote about the temporomandibular joint, but it was mostly concerning dis location. M ore than 200 years ago Ferrein2 made a good analysis of the m ove ments o f the mandible, and especially the condyles. In the early 1920’s W right3 and Monson4 called attention to the malrelation o f the condyles as a cause o f deafness. Th ey relied heavily on increasing the de gree o f jaw separation for the treatment o f deafness, and popularized “ bite rais ing,” which has had its resurgence with dentists from time to time since then. In the early 1930’s Costen,5 Pippin,6 and Goodfriend7 called attention to nu merous symptoms related to temporoman dibular joint dysfunction and to the
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means o f relieving these symptoms. Costen’s chief mechanical reliance was on interposed cork disks in the molar re gions with an elastic bandage pulling up on the chin to rock the condyles down. H e claimed only that this treatment “ breaks the trismus cycle.” 8 Between treatments the condyles tend to return to their displaced positions, with a return o f the symptoms. T h e writers o f this period stressed the effects o f temporo mandibular joint lesions on the fifth cranial nerve and the structures supplied by this nerve. In the early 1940’s Block and Harris9 concentrated attention on deflective cuspal prominences as the principal cause for temporomandibular joint disturb ances, and reported numerous instances o f relief after clearing o f the occlusion. Th eir writings refer to the “ upward and backward” condyle displacement as men tioned by W right and Monson, with no emphasis on the upward displacement alone. Some dentists are still content to go no further than mere clearance. In 1952 I reviewed the then-current thinking in the field and reported the re sults o f seven years’ experience with an additional therapeutic aid, the occlusal pivot. This report10 explained the ration ale o f treatment and illustrated a spe cial recording device for demonstrating changes o f the condyle positions after the use o f occlusal pivots. In 1953 before the September meeting o f the American Denture Society, there was a symposium on this subject,11 and there followed a growing number o f ar ticles in the dental journals. In the last two years, three excellent books concerned with the temporoman dibular joint have been published in this country,12-14 but unfortunately all three of them practically ignore mandibular equilibration as implemented by occlusal pivots. In 1955 the American Equilibration Society was organized for the study o f the temporomandibular joint together with
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its related structures, and has become the clearinghouse for information on the subject. Th e recent increase in the number of lectures, classes, seminars, journal articles and books on the temporomandibular joint attests to the growing interest in the subject. In the wake o f this advance, den tists and physicians are doing more for the permanent relief o f temporomandibu lar joint symptoms than previously, and are relying less on injections and surgical intervention. W ith the increased use of mandibular equilibration, the temporo mandibular joint becomes more and more a common meeting ground for medicine and dentistry. SOME CU RRENT BELIEFS
A t present, some areas o f disagreement exist. There are anatomists who maintain that certain cures reported by therapists are mechanically impossible. Physiologists and neurologists reject some of the ex planations. Y e t there continues to accum ulate an impressive amount o f evidence to show that the integrity o f the temporo mandibular joint is restored when stress is relieved. It is too early to judge the validity of all the claims; any such attempt would surely meet with objections. However, there has been a notable increase in un derstanding, and it seems appropriate to comment on 14 points about which den tal and medical writers concern them selves : 1. A few writers have tried to prove that the mandible is not a lever of the third class and that the temporomandibu lar joint is not a stress-bearing joint. However, most investigators believe that third class leverage does occur— at least sometimes. Perhaps it can be said that although the temporomandibular joint is not histologically like the hip or knee joint, nevertheless it can withstand an intermittent load o f considerable magni tude. This it does when the mandible acts
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as a third class lever during incision. However, too great a load or too con stant a load on the incisors forces the condyles pathologically upward in their sockets. 2. I t is still stated in some textbooks that the inclination o f the articular fossa determines the “ downward and forward” path o f the condyle— and so it does in the dry skull. But in the living subject a steep articular surface may be associated with a nearly horizontal path. 3. Some dentists still believe that the condyle paths for each patient are pe culiar to that patient and unchangeable. However, it can be shown that these paths become steeper when a longstanding over load on the anterior teeth is reduced. In deed, overloading on the anterior teeth is a cause o f distorting all the condyle positions, centric and eccentric. 4. “ Bite raising” has been held by some to be the chief mechanical means o f providing relief for temporomandibu lar joint lesions. This treatment still holds a place in therapy, but it occupies a less important place than formerly. Some o f the favorable results claimed for “ bite raising” now appear to be due to an in advertent pivoting o f the mandible when the posterior teeth are built up more than the anterior ones. 5. I t was once believed that a back ward displacement o f the condyle in its socket was the main cause of temporo mandibular joint dysfunction, and es pecially o f ear symptoms. Later it came to be believed that other horizontal dis placements were o f greater importance, and still later that the most important of all might be the upward displacement o f the condyles after continuous overloading o f the anterior teeth. 6. Some operators have met with suc cess in the relief of temporomandibular lesions with definitely meshing cusps set to hold the mandible in slight protrusion. Others believe that only when the man dible is unhindered by any cusps at all can it settle into its unstrained relation.
In any case it seems rational to start with flat plane teeth at the desired occluding relation, and have the patient wear the cuspless restoration until the mandible comes into its position o f equilibrium. This opinion is strengthened by the ex periences o f dentists who have been called in on consultations because the suppos edly correct treatment failed to bring about the expected improvement. In these instances it was usually found that although the pivots were located prop erly, the occlusion was locked horizontally by meshing cusps, and only after flatten ing the cusps were the symptoms relieved. 7. Some investigators have objected to the complete clearance o f the occlusion by flattening the cusps on the ground that this permits too much translatory m ove ment o f the teeth and too great excursion o f the condyles. W hatever the merit of this contention, experience shows that there is more danger from too much oc clusal restriction than from too little. 8. T h e restraining ligaments of the joint may be too lax or too taut. Either condition may require treatment. Th e most common treatments for ligaments that are too lax are rest, fixation, increas ing the circulation of blood, and the in jection o f sclerosing solutions. T h e patient is also cautioned not to open the jaws more than necessary in chewing and bit ing, and never to yawn. Common treatments for ligaments that are too taut are heat, exercise and trac tion. Whether the patient is to be treated for too little or too much tightness in the joint, it is important to maintain the major portion of the occlusal load on the posterior teeth. 9. There now remains little doubt that muscle spasm may cause pain and vice versa. Sometimes the treatment fo r one o f these conditions clears up the other. 10. Temporomandibular joint lesions may be lessened by the systemic approach, including o f course hormonal and nutri tional balance.
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11. W ith the accumulation of experi ence there is a transition from the atti tude o f “ let well enough alone” to one o f restoring normalcy where stress in the joint is discovered, whether or not the patient complains o f symptoms. It has been learned that there are many subclinical lesions which may be the pre cursors of more serious disturbances un less treated. This points to the need for prevention. 12. Conversely, any improper occlusal changes may bring on the pain-dysfunction syndrome. 13. Some dentists assert that although bilateral balance in eccentric positions may be desirable for artificial dentures, it is unnecessary and even detrimental for natural teeth. 14. Before mandibular equilibration in its several phases was developed as a treatment, there was more justification for radical measures. Meniscectomy, condylectomy,15 and the injection o f scleros ing and other solutions into the temporo mandibular joint have not lived up to expectations for permanent relief, and they are losing favor. E X A M IN A T IO N
Am ong dentists and physicians who have given attention to temporomandibular joint lesions there is considerable varia tion in the examination procedure. N o general agreement has been reached on the extent o f the examination. A t present, perhaps each practitioner should study the forms suggested by current authors and then develop his own charts. DIAGNOSIS AND T R E A T M E N T
Diagnosis o f temporomandibular joint lesions is the responsibility of both den tist and physician. Most o f the symptoms were once treated symptomatically by the physician and largely ignored by the den tist. Fortunately for the patient, more
and more dentists and physicians are co operating in diagnosis and treatment, with the dentist carrying out most o f the treatment. M any o f the pain and other symptoms associated with temporomandibular joint dysfunction are the same symptoms that are associated with other complaints in the region o f the ear. I t is important, therefore, to consider the symptoms as having possibly nothing at all to do with the joint. Neoplasms and infections should be considered. Whether or not pain is present, it is well to remember that spasm of the involuntary muscles may cause circulatory disturbances16 and may be even more disabling than spasm o f the voluntary muscles. Blood and lymph cir culation may be impeded in either case. I t is possible for the diagnostician to feel pressure in the external auditory meatus by pressing the ball o f the little finger toward the condyle as the mandible closes. This test is fairly reliable for de tecting excessive backward displacement o f the condyle. Roentgenograms can be made that will disclose any gross malpo sitions of the condyle in its socket. Displacement o f the condyle does not always cause annoyance, especially in healthy persons. I f the resistance is low ered, however, a patient may develop symptoms, especially under continuous stress such as occurs in the temporoman dibular joint from faulty occlusion. Im proper occlusal reconstruction may bring on symptoms. Also, the unfilled spaces created by tooth extractions may result in positional changes o f the remaining teeth, and the resulting malocclusion may gradually force the condyles into posi tions that result in lesions. Palpation o f the patient’ s head and neck may disclose tender areas17 when the temporomandibular joint is under stress. Tenderness in or near the joint, es pecially tenderness in the infratemporal fossa, is a possible diagnostic sign.18 Am ong the symptoms to look for are headache, nervousness, loss o f hearing,
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vertigo, nausea, tinnitis, muscle spasm, limitation o f jaw movement, and clicking joints. View ed with skepticism by some investigators as related to temporoman dibular joint dysfunction are migraine, stiff neck, general irritability, sleepless ness, fatigue, sinus congestion, mental dis turbances, and several other morbid con ditions. A ny dentist who claims success in treating any o f these disorders should accompany his reports with corroborating statements from the attending physician. A dentist or physician will report relief from symptoms after a certain treatment whereas another dentist or physician w ill report little or no success. In some in stances, failure must be attributed to im proper or incomplete treatment. Then, too, spontaneous remission o f symptoms sometimes occurs regardless o f the treat ment. Such treatments as heat, cold, vibra tion, massage, drugs, immobilization and psychotherapy should be kept in mind, but these are essentially o f temporary or limited value so long as the mandible re mains out o f equilibrium. It should also be remembered that the remedies for torn or overstretched ligaments, fluid in the capsule, inflammation, infection and arthritis are similar to those indicated in other parts o f the body. W ith all these remedies at hand, the basic therapeutic measure to be considered for the release o f stress in the temporomandibular joint is contriving the return o f the mandible to its unstrained position. T h e dentist does not need to place the mandible in any definite position; he merely removes all restrictions so that it can move by it self into its position o f equilibrium. E Q U ILIB RATIO N
O f all treatments devised recently, per haps mandibular equilibration is the most valuable, either by itself or in conjunction with other measures. As judged by clini cal results, it shows a high average of success.
Mandibular equilibration is a simple, conservative treatment. It is painless and without danger to the patient. Unlike some other treatments, it has no unfavor able side effects. Mandibular equilibra tion is valuable in differential diagnosis. It does not interfere with other measures. T h e treatment is curative as well as pre ventive. I t should be considered in prac tically all kinds o f temporomandibular joint lesions. Unfortunately some dentists with in complete understanding o f the whole problem have inflicted unnecessary suf fering on their patients by the improper application o f what has been variously called “ oral rehabilitation,” “ bite raising,” and “ occlusal reconstruction.” Beautiful looking and meticulously contrived oc clusal conformations have sometimes caused damage because the dentist neg lected the basic considerations. Patients have been subjected to costly and ex hausting “ occlusal reconstruction” only to have the entire handiwork removed because the patient could not tolerate it. Such tragic experiences can be avoided by first placing the mandible in equi librium and then devising an occlusal scheme which w ill maintain it there. Dentists who practice “ occlusal recon struction” or even “ selective grinding” should first make sure that the mandible is in equilibrium. W ith respect to complete artificial den tures, there are four mechanical consid erations in producing and maintaining mandibular equilibrium: (1 ) establishing an acceptable degree o f jaw separation with the teeth in occlusion; (2 ) pivoting the mandible; (3 ) clearing the occlusion, and (4 ) balancing the occlusion, espe cially at and near centric jaw relation. J A W SEPARATION
W ith the teeth in occlusion, there should be a degree o f jaw separation at which the muscles are comfortable and function well— neither sagging nor being over-
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Fig. I * A s dentures settle and m andible closes around intercondylar axis, lower incisor point travels upward and forw ard as indicated by do t ted line. M o v e m e n t is gre ater at incisors than at molars; this causes separation in m olar region with consequent loss of m olar support, and so load is carried b y incisors. (Artificial dentures are used in these illustrations to illustrate forces and positional changes, but the sam e principles apply with natural teeth)
stretched. In some instances the exact length of the muscles at occluding relation is not critical, whereas in others the pa tient is not comfortable unless this length is definitely fixed at occluding relation. Occasionally a patient is seen who can tolerate a rest relation with thé teeth barely out of contact, but most patients need an interocclusal space of from 1 to 3 mm. when the mandible is in rest re lation. Too great an interocclusal space per mits excessive jaw closure and produces an unesthetic facial appearance, disturbs the arrangement of the ligaments, short ens the range of the muscles too greatly, and may impair the ventilation of the eustachian tube. It may also cause ear ache and clicking joints. More serious than excessive closure is the condition in which the mandible is held by the teeth at an excessive degree of jaw separation. This condition is not well tolerated by the patient, and it causes resorption of the tooth-supporting or denture-supporting bone. Until the re
sorption of bone has progressed far enough to restore a comfortable inter occlusal gap, the destruction continues. Frequently there is pain in the joint or in the muscles even though the supporting bone may not be painful. With the elimination of all cuspal in terferences and with the occlusal load applied near the anteroposterior center of the denture foundation, finding the ac ceptable degree of jaw separation is ordi narily not at all difficult. However, it may necessitate testing the separation by hav ing the patient wear the dentures at the estimated height for several days. It should be remembered that spasm, es pecially of the temporal, masseter, or median pterygoid muscles, will interfere with finding the desired degree of jaw separation. It is therefore important to defer judgment on this point until the spasm has subsided. PIV O TIN G T H E M ANDIBLE
The occlusal pivot is a point or restricted occlusal area near the anteroposterior center of the denture foundation promi nent enough to receive the closing force applied by the mandible.19 It is used for the purpose of relieving the load from the anterior teeth and placing it in the molar region to reduce the proportion of up ward force exerted by the condyle. This redistribution of force permits the con dyle to descend in its socket toward its normal position. The need for pivoting arises when the posterior tooth support is lost or dimin ished so that the anterior teeth bear too great a load. With natural teeth the con dition develops when posterior teeth are lost and not replaced; with artificial den tures the condition develops largely be cause of settling as shown in Figure 1. When the load is carried for too long a time by the anterior teeth, one of the results is excessive upward pressure in the fossa by the condyle. The action is illustrated in Figure 2.
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ment. Despite their long-term benefits, they should be inspected from time to time by recall of the patient, or at the slightest sign of the return of the old symptoms. AD D ITIO N A L BE N E FITS OF PIVOTS
Fig. 2 • W ith contact only at incisors and with muscles pulling up between incisors and condyle, upward m ovem ent of condyle in its socket results. This causes pressure and places tem porom andibu lar joint under stress. S h ade d portion indicates, in e xaggerated degree, position of m andible b e fore displacem ent of condyle
To reverse this upward displacement of the condyle, pivots should be worn night and day until sagittal equilibrium of the mandible is achieved. This sagittal rotation of the mandible around the oc clusal pivots is demonstrated in Figure 3. The actual technic of pivoting has been described elsewhere.19 With natural teeth, the pivots may sometimes be placed on the second or third molars; with artificial dentures, the consideration of denture stability requires them to be placed farther anteriorly, usu ally on the first molars. They should glide over opposing flat surfaces so that the mandible can move horizontally without hindrance. Pivots do not “push the mandible around.” Conversely, they are used to re duce the upward force at the condyles so that the mandible can return by itself to a state of equilibrium. The results of pivoting are demonstra ble in three principal ways: relief of symptoms, “before and after” roentgeno grams, and the condyle recorder con structed for this purpose.20 Although the results of pivoting are not always permanent, they are more nearly so than most other forms of treat
Quite aside from their role in preventing or relieving temporomandibular joint le sions, occlusal pivots on dentures, by vir tue of their location, have other advan tages. Some of them are: 1. Ease of obtaining clear tracings for jaw relation records after the pivots have been worn for a short time. 2. Ease of finding an acceptable oc cluding relation. 3. Centralizing the load for making better impressions. 4. Reducing anterior ridge resorption. 5. Preventing the anterior teeth from being pushed beyond the lip line. 6. Preventing deformation of the man dible. 7. Increasing denture stability. 8. Preventing gagging.
Fig. 3 • Transferring occlusal load from incisors to molars decreases upward pressure of condyle in its socket. W ith occlusal pivot in m olar region as shown here, m andible has a limited movement around this pivot as shown by dotted lines. A s incisors move up, condyle moves down, thus re du c in g stress in tem porom andibular joint
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CLEARING T H E OCCLUSION In the several branches o f dentistry rather general agreement has developed on the desirability o f providing clearance o f the occlusion. In the complete denture field there is the further need to permit prac tically horizontal jaw movement while the opposing teeth are in occlusion. Clearance o f the occlusion is possible with cusp teeth in the sense that they can be adjusted so that no projection pre vents the other teeth from maintaining smooth gliding contact, but the flatter the cusps the less hindrance there is to the free horizontal movements o f the mandible. T h e need for horizontal free dom o f movement to protect the den ture-supporting structures was the chief reason for developing the so-called nonanatomic teeth. A t first these nonanatomic teeth were used primarily to prevent injury to the denture-supporting structures. Th ey are still used fo r this, but now are used in creasingly for the further purpose o f preventing injury to the temporoman dibular joint. In fact, many dentists have been using flat plane teeth to protect the tissues under the dentures without realiz ing that the temporomandibular joints were also being protected. T h e backward pressure caused by cusps on the lower dental ridge and on the condyle is indi cated in Figure 4. Channel teeth,20 the first teeth designed to assure anteroposterior clearance, came into use in the 1920’s. T h ey were de veloped at a time when attention was focused on preventing the posterior thrust on the lower ridge and on the condyles. However, they failed to provide for lateral freedom of movement. Another attempt to unlock the occlu sion was the motor-driven grinding at tachment to the articulator invented by U p p 21 for use with cusp teeth. This de vice provides horizontal freedom of move ment although the degree is quite limited. Th e grinding attachment still used by
Fig. 4 • Since any closure around intercondylar axis as shown in Figure I results in forward shift of mandible, slightest resorption of supporting tissues under dentures permits any deflective cusp inclines to cause backward pressure as shown here. M e sial surface of lower cusp glides on distal surface of upper cusp so that upward pull of muscles produces backward force on lower teeth and o f course on condyle, placing tem porom an dibular ¡oint under stress
some dentists was only a step toward complete clearance. Whether clearance is produced with cusp or cuspless teeth, this difference in form has little to do with chewing effi ciency. Some investigators have claimed greater efficiency for cuspless teeth than fo r cusp teeth, w hereas others have claimed just the opposite. I f there were much difference in this respect, the ques tion would have been settled long ago. Although tests show that flat plane teeth chew some foods more efficiently, other foods are chewed more efficiently with cusp teeth. W hen considering the entire range of food in the average meal, there is no significant difference in this re spect. Therefore, cuspless teeth are to be preferred not because o f their efficiency in chewing but because they make man dibular equilibration more certain and more nearly permanent. BA LAN C IN G T H E OCCLUSION
In addition to clearance, there is another occlusal adjustment— that o f assuring simultaneous contact on right and left
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sides in lateral relation and simultaneous contact front and back in protrusive rela tion. Although some dentists feel that bilateral balance in eccentric relations may be detrimental with natural teeth, few make this contention with artificial dentures. T h e essential features o f mandibular equilibration are (1 ) to establish occlud ing relation at an acceptable degree of jaw separation, (2 ) to place the load mainly in the molar regions, (3 ) to clear the occlusion, and (4 ) with artificial den tures to balance the occlusion in eccen tric as well as in centric relation. M AND IB U LAR E Q U ILIB RATIO N
T o a very great extent the temporoman dibular joint is the direct responsibility of the dental profession, and fortunately more and more dentists are accepting the responsibility. Although all practitioners o f the heal ing arts should be able to recognize tem poromandibular joint lesions, only the dentist is qualified in the mechanical phases o f treatment having to do with ja w relation and tooth occlusion. This whole subject should be given greater attention in our teaching institu tions. In the dental schools, the rational way o f covering the subject is to abandon the system o f teaching different views in the different departments and to con solidate the basic matter in a separate department on a par with the operative, prosthetic, orthodontic and other depart ments. A n arrangement of this kind per mits the other departments to build on this foundation. I t enables the school to present the subject in perspective. It largely overcomes the fragmented and conflicting instruction given under the orthodox system. T h e ultraconservatives are bound to object to this advance, but the answer to their objections lies in the fact that this system is already being fol lowed with conspicuous success. A good start has already been made in
the three dental schools in Sweden and the two in Denmark where autonomous departments have been established22 for undergraduate and postgraduate instruc tion to deal with tooth occlusion and its ramifications. M any o f us hope that all o f the schools in the U nited States and elsewhere will soon do likewise. Linking tooth occlusion with jaw relation (includ ing condyle relation) is the rational ap proach in teaching. Students in dental schools should not have to wait until after graduation to get this viewpoint. BU ILDING PU B LIC ESTEEM
From the standpoint o f the dental pro fession, two gratifying developments emerge— one in relation to the medical profession and the other in relation to the general public. T h e necessity for consultation in diag nosis and treatment brings the dentist and the physician closer together. Although only the dentist is trained in matters of tooth occlusion, the skills of the other members o f the healing arts, and espe cially the otolaryngologists, are needed in both diagnosis and treatment. T h e train ing o f the physician makes it easy for him to comprehend the role of stress in the temporomandibular joint, and for him to see the rationale of mandibular equili bration. As practitioners become more and more aware o f the importance of maintaining the integrity o f the temporomandibular joint, they will disseminate the knowledge to the public, which is becoming increas ingly aware o f the need for consultation in the healing arts. As more persons learn o f the importance o f preventing damage to the gingiva and joints o f the jaws, they will see the wisdom o f obtaining the serv ices of graduate dentists and physicians with professional training in physiology, anatomy and the related sciences. This awareness points up the stupidity o f trust ing one’s mouth to a lay technician who, with his lack of scientific training, may
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cause great damage. N o w with mandib ular equilibration we have a dramatic convincer. As more and more persons learn that there is danger to the struc tures in and near the ears from bungling treatment at the hands o f untrained per sons, the lure of bootleg dentistry becomes less attractive. This awakening is bene ficial to the public and gratifying to the dental profession. It behooves all dentists to give their patients the benefits o f advances in man dibular equilibration and in the whole field o f temporomandibular joint therapy. Dentists and physicians everywhere should render this service to their patients, or at least be sufficiently informed so that they can consult intelligently with those who are qualified to render this service. This happy development will do much to establish the professions more firmly in the minds and hearts of the general public. Presented before the American Equilibration Society February 2, 1961, and the American Denture Society February 3, 1961. *Faculty of dentistry, University of Cairo. !. Academ y of Denture Prosthetics. Glossary of prosthodontic terms. J. Pros. Den. 10:9 part 2 Nov.-Dec. I960. 2. Ferreîn, M . Sur les movements de la mâchoire inférieure. L'histoire de l'Academ ie Royale des Sciences, Paris, 1748, p. 427-448.
3. W right, W . H. Deafness as influenced by mal position of the jaws. J.N .D.A. 7:979 Dec. 1920. 4. Monson, G. S. Im paired function as a result of closed bite. J.N.D.A. 8:833 O ct. 1921. 5. Costen, J. B. N euralgias and ear symptoms asso ciated with disturbed function of the temporomandibu lar ¡oint. J.A .M .A . 107:252 Ju ly 25, 1936. 6. Pippin, B. N. Symposium on treatment of tem poro mandibular lesions caused by denture mutilations. Illi nois D. J. 12:429 Oct. 1943. 7. Goodfriend, D. J. Sym ptom atology and treatment of abnormalities of the m andibular articulation. D. Cosmos 75:844 Sept.; 1106 N o v . 1933. 8. Costen, J. B. Personal communication. 9. Block, L. S., and Harris, Elam. Approach to a rational study and treatment of temporomandibular joint problems. J.A.D.A. 29:349 March 1942. 10. Sears, V. H. M a n d ib u la r condyle migrations as influenced by tooth occlusions. J.A.D.A. 45:179 Aug. 1952. 11. Control of condyle relations in the mandibular fossa. A symposium. J. Pros. Den. 4:196 March 1954. 12. Shore, N. A. Occlusal equilibration and tem poro mandibular ¡oint dysfunction. Philadelphia, J. B. Lippincott Co., 1959. 13. Schwartz, Laszlo, and others. Disorders of the tem porom andibular joint. Philadelphia, W . B. Saunders Co., 1959. 14. Bell, W. E. Tem porom andibular joint disease. Dallas, I960. 15. Smith, A. E., and Robinson, Marsh. M andibular function after condylectomy. J.A .D .A . 46:304 March 1953. 16. Jensen, M . B. M uscular tensions and prosthetic dentistry. J. Pros. Den. 2:604 Sept. 1952. 17. Campbell, J. Paper presented at the annual con ference of the British Dental Association, Dundee, Scot land, July 10, 1958; reprinted in the 1959 Compendium of the American Equilibration Society. 18. Vaughan, H. C. Tem porom andibular joint pain. J. Pros. Den. 4:694 Sept. 1954. 19. Sears, V. H. Occlusal pivots. J. Pros. Den. 6:332 M ay 1956. 20. Sears, V. H. Channel type posterior tooth forms. J.A.D.A. 15:1111 June 1928. 21. Upp, R. W . U .S . Patent No. 1,180,745, April 25, 1916. 22. Posselt, UIf. Personal communication.
Scientific Cooperation * T he scientific method is probably the most fruitful of the human m ental disciplines, in that it allows cooperation among individuals throughout the ages and between countries, so that science is a body of knowledge drawing m ankind together in both time and place. Language is no insuperable barrier in science, for the substance of science is not peculiar to any language or any country. T he cure for cancer, w hen it is found, will be applicable internationally; and the search for the cancer cure is an international effort, whether it be recognized as one or not. The applications of scientific discovery can be m ade in all nations and in all times. Willard Frank Libby. Tomorrow in Science. Bui. M ed. Col. of Va. 41:5 Winter 1962.