Relating The Mandible To The Maxilla InTreatment Of Class 11 MalocclusionL. W. MCIVER, D.D.S.Minneapolis, Minn.The problem of making the upperand lower teeth fit together properlyis one which has interested ortho-dontists for many years. Yet our clin-ical efforts, generally speaking, amountto little more than establishing a cuspand groove relation of the teeth. Con-sidering the fact that more anatomicparts than teeth are involved this issubstantially less than the best. In ClassI11 treatment, seeking a good cuspand groove relation is apt to result ina fairly accurate jaw relation but inClass I1 treatment (and even in ClassI) the mandible may be displacedslightly forward on one or both sides.The displacement is often too small tobe detected using lateral head x-raysand it is likely to be overlooked clin-ically because muscles adapt to the newposition. Sometimes this adaptation istemporary and the result is relapse ofmolar relation or dual bite. Other timesit is quite permanent resulting in aconvenience or protrusive bite whichmay or may not cause trouble later.There are times when these troublesare beyond the operator's control butoften they can be avoided by havinga little more respect for centric relation.If the majority of Class I1 maloc-clusions are to be thoroughly corrected,it is necessary not only to have a ratherexacting objective, but also to checkfrequently during treatment to see that.it is being attained.It is the purpose of this paper topresent what I feel should be the ob-jective in Class I1 treatments as far asRead before the Mid-Western Componentof the Angle Society, January, 1959.jaw relation is concerned, and to sug-gest several methods for attaining it.In order to achieve the best in jawrelation it is necessary to consider theposition which the mandible assumeswhen vigorous muscle forces are be-ing applied, for example, during theact of swallowing or during the finalphase of the closing stroke in mastica-tion. To illustrate this point, considerthe recent work of Paul Hayes' onsurgical correction of Class I11 maloc-clusion. Numerous investigators haveobserved that the mandibular restposition and the occlusal position doesnot always coincide (Fig. 1 A). Theremay be several millimeters differencebetween the two positions in somecases while in others there is little orno transiationai movement from restto closure. Dr. Hayes has found thisanalysis useful before surgical correc-tion of Class I11 malocclusions. It hasbeen a common observation that manypatients develop an open bite aftersuch an operation and until recentlyno satisfactory explanation has beenoffered. Hayes observed that open bitedevelops in the patients whose restposition and occlusal position differconsiderably while it does not occurin the cases where the two positionscoincide. When the teeth are wiredtogether and healing is allowed to takeplace with the condylar segments inrest position (Fig. 1B) away from thesupport of the articular eminence, anopen bite will result because, whenfixation is removed and function be-gins, the condyle seeks the support ofthe fossa1 .slope and as a result themandible assumes a more posterior218 Vol. 29. No. 4 Relating Mandible 219Fig. 1. Open bite develops after surgicalcorrection of Class I11 malocclusion whenhealing takes place with condylar segmentin rest position. From Dr. Paul Hayes.position (Fig. 1 C). Dr. Hayes isnow devising a method of securingthe condylar segment in functional pos-ition, while healing takes place, inorder to prevent open bite in suchcases.This observation illustrates anotherpoint which is important in relatingthe jaws. The condyles must have thesupport of the articular eminence ifthe mandible is to function normally.`This is not meant to imply that thetemporomandibular joint bears heavystress. Robinson' has schematicallyanalyzed the forces acting on the jointand this analysis has been expandedby Page.3 Page noted that the resultantforce of the closing muscles is approx-imately parallel to the fossal slope andbecause of this he believes that onlymoderate stress would be directedagainst the fossal bone no matter howponderous the force that operatesagainst the teeth. Many believe thatthe temporomandibular ligament as-sumes a substantial share of the stressin this area. Therefore, when we saythat condyles must have a bearingpoint, we simply mean that both con-dyles must be against the anterior slopeof the fossa when teeth are in occlusionif jaws are to be properly related.Next it is important to consider theextent to which the mandible is re-truded in normal function. There area number of observations which in-dicate that the mandible reaches max-imum retrusion, or nearly so, in nor-mal function. Consider, for example,the cinefluorographic studies of Jankel-~0x1.~ In speaking of the relationshipbetween centric relation and swallow-ing he says, "The vigorous retrusionof the tongue explains why the man-dible was inevitably carried into max-imum retrusion during involuntarydeglutition when the path of closurewas free of occlusal interference andclarifies the common observation thatin those cases where the mandible is .prevented by cuspal interference fromattaining centric occlusion, it goes tothat position after interference is re-moved."Sleichter's5 study of seventy-one dryskulls and thirty-three living persons 220 McIver October, 1959shows that the amount of retrusionfrom centric is very limited. Less thanone fourth cusp retrusion was the ruleon the living subjects while it was onlyslightly more on the dry skulls.Posselt6 has shown that if extrememovements of the mandible are re-corded graphically in the median planea characteristic figure is obtained (Fig.2). In addition, these boundary move-ments can be repeated exactly, a factorwhich would be of immense value inrelating the jaws if the centric positionwere always on the border movementpath. There is considerable controversyover this point, however. McCullumand Granger, for example, would favorpoint D while Reyron7 and Posselt andmany others would favor a positionabout 1 millimeter anteriorly. The im-portant thing to remember is that thecentric position is very close to themost retruded position.IFig. 2. Border movements of the mandible.From Beyron.Another study of interest in this con-nection was made by the author. It hasbeen observed that about eighty percent of adults can retrude slightly be-yond the intercuspal position. In aneffort to determine whether this wastrue for children, accurate records werekept on one hundred seventy childrenbetween the ages of five and fifteenyears. Seventy of the cases examinedwere untreated Class I malocclusionsand one hundred were untreated ClassI1 malocclusions. The average age ofboth groups was twelve years. In check-ing the retruded position the patientwas seated upright in the chair andinstructed to open and close as themandible was held in retrusion. Carewas taken not to have the patient ex-ceed hinge range which usually meansnot more than one half to three fourthsinch opening at the incisors. It wasfound that seventy-three per cent ofthe Class I1 malocclusions and seventy-six per cent of the Class I cases couldnot retrude beyond intercuspal posi-tion. Those cases in which retrusionwas possible could usually retrude lessthan one fourth of a cusp.Even though most studies seem toindicate that there is a preferred man-dibular position during function andthat this position is very close to themost retruded position, it is conceiv-able that a range of anteroposteriorpositions is possible if the articulareminence is favorably formed. For ex-ample, the condyle could be supportedin several positions on a fossa1 slopesuch as that illustrated in Figure 3 Awhile only one position would bepossible with the slope illustrated inFigure 3 B. But recognizing that arange of positions is possible in someindividuals, one should consider howfunction might differ in protrusion andretrusion.Perry8 has observed in an electro-myographic study of the masseter andtemporal muscles that the workingside temporal initiates the closingmovement in normal occlusions whilein some Class 11, Division I malocclu-sions the masseter was the first to giveA BFig. 3. Vol. 29, No. 4 Relating Mandible 2.2 1recordable action potentials. His ex-planation of this seems perfectly logicalwhen he states, "Perhaps the steepercurves of Spee and potentially retrog-nathic mandibles might necessitatea forward thrust of the mandible toobtain a more functional occlusion."Thus it seems probable that at leastone characteristic of a protrusive biteis that closing muscles are contractingin abnormal sequence. Very probablythe external pterygoid is overactive too.From the clinical standpoint the pro-trusive bite is generally believed to beundesirable. Joint problems are quitecommon among adults with this rela-tion. The only trouble is that this typeof relation is not very clearly definedand about the only way to diagnoseit accurately is to place flat splintsover the occlusals of the upper orlower teeth or take teeth out of oc-clusion for several hours with a biteplate. If the mandible settles back toa more posterior position, undoubtedlyit should function there.The rest position analysis is not al-ways accurate in such cases. Rest posi-tion may be stable from an electro-myographic standpoint but for clinicalpurposes it cannot always be trusted.To illustrate this, consider the case inFigure 4. This patient had a long his-tory of temporomandibular jointtrouble; she could retrude her man-dible about one half cusp but other-wise had an apparently normal occlu-sion. A rest position headplate wastaken before insertion of a removableocclusal splint which allowed her tobite in a more retruded position. Thesolid line shows this position. Aftereight hours of wearing the splint an-other rest position headplate was taken.This position is shown by the dottedline. Since the joint pain disappearedwhenever the removable splint wasworn, it seems logical to conclude thatthe more retruded rest position wasthe true one. One weakness of the restP. A.Fig. 4.position analysis is that a protrusivebite is not always detected.As previously implied, the retrudedposition may not always be reliableeither. There are some who contendthat condyles will be displaced poster-iorly if jaws are related in this man-ner. The amount of displacementpossible is said to depend on how muchspace is available posterior to the con-dyle when the mandible is in centricrelation. Others contend that retrudingthe mandible places the condyles incorrect position, that there is an up-ward and forward movement againstthe fossa1 slope because the temporo-mandibular ligament guides them tothat position.In order to help settle this argumenttemporomandibular joint x-rays weretaken of three groups of patients. Thetechnique for taking the x-rays issimilar to that described by Upde-grave9 lo except that the patient sitsupright and a head positioner of theauthor's design is used. As many assix x-rays can be obtained on one eightby ten film without moving the head.Naturally there is some distortion be-cause of the angIe at which they axetaken but, since the head does notmove, the distortion would be the samein each picture. A retruded wax bite is 222McIverOctober, 1959 Vol. 29. No. 4 Relating Mandible 223taken first. With this in place the pa-tient is positioned for the x-ray of theleft joint. The wax bite is then remov-ed and the teeth brought to naturalclosure for the next picture. This pro-cedure is repeated for the right sidemaking four pictures for each patient.The first group consisted of ten pa-tients whose mandible could not be re-truded beyond the intercuspal position.As might be expected, no differencewas observed between the retruded andclosed position (Figs. 5 and 6), butthere was often a large space posteriorto the condyle when the mandible wasin retrusion indicating that the tem-poromandibular ligament probablydoes limit the posterior movement.Naturally, the old clinical practice ofretruding the mandible is ideal for re-lating the jaws in this type of case andthe hinge axis registration is most ac-curate when the articulator is used.In the next group were ten caseswhose mandibles could be retrudedbeyond intercuspal position. All wereadults with excellent occlusions andexceptionally healthy mouths. No tend-ency for the condyles to move upwardor upward and forward against thearticular eminence was observed in anyof their x-rays. Instead, one condyleshowed no measurable change in posi-tion while the other moved away fromthe eminence (Figs. 7 and 8). The re-trusion in all of the cases was pre-dominantly unilateral and the amountthe condyle moved back averagedabout a millimeter. It seems that, whilethese patients do not function in whatis commonly regarded as the most re-truded position, the condyles are ontheir most retruded bearing pointswhen teeth are in occlusion. The factthat the condyle moves backward awayfrom the eminence rather than deeperinto the fossa indicates that this is true.In this respect they are similar to thosewhose mandibles cannot be retrudedbeyond intercuspal position.It would seem logical to regard thisretruded position as abnormal becausethe mandible is in a non-functionalposition, at least on one side. Furtherproof of this is the observation thatheavy biting force is not possible whenthe mandible is in this position. Byplacing the fingers at the angle of themandible as the patient tries to exertbiting pressure it will be observed thatthe masseter muscles do not contractvigorously until the teeth slide forwardinto occlusion. In addition to this, ifteeth are taken out of occlusion tempo-rarily with a bite plate, the mandibledoes not seek a more posterior position.This suggests that the occlusal positionis correct and that no cuspal inter-ferences are present. It seems reason-able to assume that the rest positionanalysis would be accurate for suchcases providing it is not used with anarticulator.There are two main difficulties inusing a rest position bite with thearticulator. There is no way to locatean accurate center of rotation in thecondyle and there is the possibility thatmovement from rest to closure will betranslational. On the other hand, thistype of case presents quite a problemfor those who use the hinge axis regis-tration because condyles are likely tobe displaced posteriorly away from thefossa1 slope. The split hinge articulatorseems to be a definite improvementover the rigid symmetrical types incommon use but the possibility of dis-Fig. 5. Above, Treated Class I1 malocclusion. The patient cannot retrude beyond inter-cuspal position. There is no change in condylar positions when mandible is retruded.Fig. 6, Below, normal occlusion. The patient cannot retrude beyond intercuspal position ;there ia 'no change is condylar positions xvhen the mandible is retruded. 224McIverOctober, 1959 Vol. 29. No. 4 Relating Mandible 22 5placing condyles posteriorly still exists.It seems probable that this abnormalretrusion is being obtained frequentlyin restorative dentistry by those whouse conventional articulators with re-truded wax bites and hinge axis regis-trations, but it is doubtful that such arelationship could ever be permanent-ly established by orthodontic means.There is also clinical evidence to sup-port this belief. For example, occlusalgrinding has been performed on anumber of such patients to eliminatethe forward slide and the result hasnot remained stable. Shifting of teethsoon occurs so that retrusion is onceagain possible. In addition to this, ithas been my experience that somecases cannot be treated to what is com-monly regarded as the most retrudedrelation even though mandibulargrowth is good and great care is usedin treatment.Displacing condyles posteriorly shouldbe of little concern in orthodontics,particularly in Class I1 treatment.Even in Class I11 treatment it is doubt-ful that a posterior displacement canbe permanently established. Clinicalsupport for this statement is the factthat orthodontists have been forcingthe mandible into maximum retrusionfor years in the treatment of Class I11malocclusion without harmful effects.In fact there is less joint trouble inthese patients than either the Class Ior Class 11.The third group of cases consistedof ten treated Class I1 malocclusions.A different type of retrusion was foundin most of these patients even thoughcuspal relations appeared to be similarto the normals when the mandible wasretruded. In eight of the ten cases the+-condylrs moved deeper into the fossaein an upward and backward direction.The movement was bilateral in eightcases but not always equal on eachside. An example of this type of re-trusion is shown in Figure 9. This typeof patient, unlike the normal occlu-sions, can often exert heavy bitingpressure while the mandible is retrudedand, if the teeth are taken out of oc-clusion with a bite plate, the man-dible will seek a more posterior posi-tion. It seems reasonable to conclude,therefore, that such patients do nothave a normal bite even though cuspalrelations are good. This protrusive re-lation is sometimes found in patientswho have never been treated ortho-dontically but it is doubtful that sucha relation should be considered nor-mal. This type of case is shown inFigure 4.To illustrate further that there isconsiderable variation in condylarmovement when the mandible is re-truded manually Figure 10 shows an-other case in which a considerableamount of retrusion was possible af-ter treatment. X-rays (Fig. 11) showthat both condyles move deeper intothe fossae but the left (upper rightphoto) also moves away from theeminence.When considering how far the man-dible should be retruded as teeth comeinto occlusion, it seems important toremember that the majority of normalocclusions and the majority of untreat-ed malocclusions have one thing incommon. The mandibular condyle can-not be forced upward deeper into thefossa. When retrusion beyond inter-cuspa! position is possible, the condylemerely moves backward away from theFig. 7. Above, Normal occlusion. The patient can retrude beyond intercuspal position ;left condyle moves sway from the support of the articular eminence nhen the mandibleis retruded. Fig. 8, Below, ~iorinal cteelnsion. The patient ran retrude beyond intercuspalposition; right condyle mo\e nir-ay from the support of the articular eminence whrn themandible is retruded. 226McIverOctober, I959Fig. 9. A treated Class I1 malocclusion. The patient can retrude beyond intercuspalposition; both condyles move deeper into fossae when the mandible is retruded.articular eminence, usually on one sideonly. It seems safe to say that whenteeth are in occlusion the condylesshould be supported on their most re-truded bearing points on the fossa1slope. The only difficulty is that neitherthe rest position nor manual retrusionis completely reliable in placing themandible in this position.'With this as an objective, however,it is possible to use the retruded posi-tion as a clinical guide providing itslimitations are recognized. It has theadvantage of being accurate for themajority of patients of orthodontic ageEg. 10. Treated Class I1 malocclusion. and there is also considerable merit Vol. 29, No. 4Relating Mandible227Fig. 11. The treated malocclusion shown in Fig. 10. The patient can retrude beyondintercuspal position; boh condyles move deeper into fossae and the left condyle also movesoff the articular eminence. (Upper right photo)in having teeth in contact when jawrelation is checked rather than severalmillimeters apart as they are in restposition. Another advantage is the easewith which buccolingual discrepanciesare observed. Buccolingual positions ofteeth affect the anteroposterior posi-tion of the mandible so it is importantthat they be observed. In Figure 12 isa case in which the mandible is dis-placed because of a unilateral bucco-lingual discrepancy. This type of faultyrelation is rather common but it is like-ly to be overlooked unless the retrudedposition is used.If the retruded position is to be usedas a guide, it should be realized thatonly about seventy per cent of thecases can be treated to the retrudedrelation, and this requires more thanan average amount of effort. The re-maining thirty per cent will consist ofsome cases which have normal jawrelation even though slight retrusionis possible, some which are not goodafter treatment but which may improveas a result of good mandibular growthand others which will remain less thanideal. If the mandible can be retrudedbeyond the natural closing position 228McIverOctober. 1959Fig. 12. Faulty buecolingunl relation lietween upper and lower arches is seen when themandible is retruded, lower right.and we are interested in determiningwhether or not the relation is normal,it would seem advisable to make severaladditional observations. First, theamount of retrusion possible should bevery slight. A great amount of re-trusion would lead one to suspectthat jaw relation is faulty. Second, asmall amount of midline deviation isoften normal when the mandible is re-truded but, if the deviation is greatand the posterior teeth are not relatedwell buccolingually, the relation is cer-tainly not normal. Third, if both mas-seter muscles contract vigorously whenthe mandible is retruded, chances aregood that the condyles are supportedon the articular eminence and thatthe mandible should function in thisretruded position. Fourth, it wouldseem that the direction of condyle dis-placement as seen in temporoman-dibular joint x-rays would be helpful.Kelation is probably normal if onecondyle merely moves off the eminencerather than deeper into the fossa.SUGGESTIONS FOR ATTAINING CORRECT TREATMENTThese suggestions are offered realiz-ing that there may be other methodsof obtaining the same results particular-ly in cases where patient cooperationis good. The important thing, however,is to have the objective in mind andto check at frequent intervals duringtreatment to make sure it is being at-tained. Generally speaking, these sug-gestions fall into three main categories:minimum use of Class IT elastics, sec-tional treatment rather than en massemovement of teeth and coordinationof arch widths.First consider the non-extractionClass I1 treatment. In Figure 13 arethe records of a boy eleven years ufage. Notice that second molars havealready erupted, This case was treatedwithout Class I1 elastics except forthree weeks toward the end of treat-ment when they were worn on oneside only. In Figure 14 are the castsIAW RELATION IN CLASS 11 Vol. 29, No. 4Relating Mandible229Fig. 13. Above, before treatment. Fig. 14, below, six months after retention.and photos six months out of reten-tion. This brings up the question ofwhen these cases should be started. Itis my belief that most Class I1 non-extraction cases need not be startedbefore the late mixed dentition periodwhen there are perhaps one or twodeciduous teeth remaining. Early mix-ed dentition treatment with bite plateand headgear is all right if there isno objection to four or five years ofcare. But most of these cases requirefull appliance therapy after deciduousteeth have been lost if satisfactory re-sults are to be obtained.In correcting a case of this kind,the upper first molars are banded andthe headgear is worn until a Class Imolar relation is established or untilthe headgear falls too far below the up-per incisors (Fig. 15 top). The lowerarch is also being leveled during thistime with an edgewise arch. Particularattention is given to raising the firstbicuspid in relation to the cuspid. Afterthe upper first molar is tipped back, the 2 30 McIver October, I959upper bucca! teeth are banded and an.018 or .020 arch is tied in (Fig. 15center). This uprights the molar sothat the headgear does not fall belowthe upper incisors. Figure eight ties areused to close spaces and bring the buc-7-Fig. 15. Treatment of Class I1 non-extrae-tion eases without intermaxillary elastics.Headgear is applied to the molars through-cal teeth back in Class I relation. Bythis time the lower arch is leveled andspecial attention has been given to archform (Fig. 16). Care is taken to avoidwidening across the lower cuspid areabut the arch is purposely widenedslightly in the first bicuspid area bymeans of a step-out bend. If the archis too narrow across this area, cuspalinterference will affect the anteropos-terior position of the mandible. Con-versely, care should be taken not toexpand the upper arch or torque thebicuspids and molars buccally. After thebuccal teeth are in Class I relationthe upper incisors are banded and aspace closing arch is used to bringthem lingually (Fig. 15 below). Theamount of labial torque used in thisarea varies with. .the inclination ofthese teeth. It may be advisable toband the upper incisors before they arebrought lingually in order to preventtoo much space from developing be-tween them, but they are not tied intothe arch until lingual movement isbegun.Lower archFig. 16.This type of treatment is not ad-vocated on any case which has archlength problems or too much fullnessaround the lips. The operator is at themercy of patient cooperation if thistype of treatment is to be used and hemust also be rather patient becausesome cases treated in this way will re-out Geatment.-- - quire nearly two years of care. But Vol. 29, No. 4Relating Mandible23 Ifig. 17. Above, before treatment. Fig. 18, below, after treatment,there are advantages in using thismethod of sectional tooth movementover the conventional Class I1 elasticsand second order bends. There is lessdanger of displacing the mandible for-ward and it makes non-extraction casesout of many border-line extractioncases. Even where the lower arch of-fers sufficient anchorage for the use ofClass I1 elastics, treating the buccalsegments first seems to be a good planbecause it allows the operator to feelhis way, so to speak. If a good relationcannot be established between the up-per and lower buccal teeth, it is quitecertain that incisors cannot be movedto correct position. Even though thistype of treatment may extend over alittle longer time the appointments canbe shorter so actual treatment time isnot increased.Consider next the treatment of aClass I1 four bicuspid extraction case.The records of such a case are shownin Fig. 17 and 18. Bands are placed onall teeth except the incisors at the begin-ning of treatment and space closing isstarted simultaneously in both arches 2 32 McIver October, 1959Fig. 19. Steps iu treating Class I1 extrac-tion c:tses. The headgear is applied io theupper molars throughout treatment. Molarrelation is corrected before extraction spacesaro closed.(Fig. 19 top). Upper second molarsare not banded unless a crossbite rela-tion exists. A headgear is worn fromthe beginning of treatment. Noticethe bend in both archwires at the siteof extraction; this is incorporated ineach succeeding archwire as treatmentprogresses to keep roots parallel. Whenthe lower cuspids are upright, the loweranteriors are banded and a space clos-ing arch inserted as soon as possibleFig. 19 middle. Space closing continuesin the upper arch as before. If themolar relation does not show signs ofbeing corrected, a new upper arch ismade with stops in front of the molartubes which allows the arch to standaway from the upper incisors (Fig. 19middle). Class I1 elastics are then wornduring the day and the headgear atnight until the upper first bicuspidspace is closed and the buccal teeth arein Class I relation (Fig. 19 below).After the molar relation has been cor-rected, the upper anteriors are bandedand space closing continues in botharches. When ideal arches are placed,special attention is given to coordinat-ing arch widths as in the non-extrac-tion case. Figure 18 shows the com-pleted case. Active treatment was fif-teen months. Examination of plastercasts only would indicate that this caseis not quite as nicely treated as theextraction case shown in Figure 10.The overbite is a little deeper, the cuspand groove relation is not quite as idealand the upper incisors are probablya little more upright than some wouldlike; but the jaw relation is very goodand from the functional standpoint Ibelieve it is much better off than theother one.This plan of treating the buccal seg-ments first and correcting the Class I1relation before all spaces are closedprevents the mistake of moving thelower cuspids and incisors too far back.For esthetic reasons it may be desirablesometimes to move the lower anteriorsegment as far posteriorly as possiblebut this can be accentuated in ClassI1 extraction treatment. Sometimes Ithink it is necessary to settle for a littleless in the way of esthetic improve- Vol. 29, No. 4Relating Mandible233ment to obtain a better relation ofupper and lower teeth and jaws. Clos-ing the spaces first and attempting tocorrect the Class I1 relation later ismore likely to result in failure in theform of incomplete correction of molarrelation, relapse of molar relation orprotrusive bite.Cases involving extraction of upperbicuspids only would seem to be lessof a problem than either non-extrac-tion or four bicuspid extraction casesbut convenience bites are easily pro-duced if attempts are made to movesix upper anteriors back using only thebicuspid and molar on each side as an-chorage. The headgear is important inthis type of treatment and usually it isadvisable to place a full appliance inthe lower arch. Even though Class I1elastics are not applied, the lower ap-pliance is useful in reducing the over-bite, correcting slight asymmetries andcoordinating the arches buccolingually.No matter how the Class I1 maloc-clusion is handled, it is well to remem-ber that our job in treatment is to moveteeth rather than the mandible, toguard against forward displacementrather than encourage it. With helpfrom growth our work is made easierand often a good relation will be ob-tained in spite of our lack of care.But adequate mandibular growth alonedoes not always insure good jaw rela-tion. It seems necessary to pay con-siderable attention to details and varytreatment according to the response ifsood results are to be obtained in manycases. Sometimes despite our best effortswe must settle for less than an idealrelation and in those cases we can bethankful for adaptable muscles but itdoes not seem wise to depend too muchon this kind of adjustment. It is com-forting to have the protection of theproprioceptive system but it does notgive us the right to ignore centric re-lation. If we are going to be fair withour patients we must regard functionalefficiency as highly as we do estheticimprovement.1600 West Lake St.BIULIOGKAPHP1.2.3.4.9.IO.Hayes, P. A. Hinge Axis in Open Man-dibular Resection - To be published.Robinson, Marsh. The Temporoman-dibular Joint: Theory of Reflex Con-trolled Nonlever Action of the Man-dible. J.A.D.A., October, 1946.Page, 1. L. Temporomandibular JointPhysiology and Jaw Synergy. DentalDigest. February, 1954Sankelson, B., Hoffman, G. M. andHendron, J. A. Jr. The Physiology oftho Stomatognathio System. J.A.D.A.,Vol. 46, A ril, 1953.Sleichter, (!. G. Mandibular PosteriorDisplacement. Angle Ortho. Vol. 25,July, 1955.Posselt, Ulf. Xange of Movement of theMandible. J.A.D.A. Vol. 56, No. 1,1958.Beyroil, H. L. Characteristics of Func-tiinallj Optimal Occlusion. J.A.D.A.Vol. 48, No. 6, 1954.Perry, H. T. Functional Electromvo-graphy of the Temporal and Mgs-seter Muscles. Angle Ortho. Vol. 25,KO. 1, 1955.Updegrave, W. J. Radiography of theTemporomandibular Joint in Ortho-dontics. Angle Ortho. Vol. 21, No. 4,1953.Updegrave, W. J. RoentgenographicObservations of Functioning Temporo-inandibular Joints. J.A.D.A. Vol. 54,No. 4, 1957.