five steps to better occlusion in class ii treatment

17
Five steps to better occlusion in Class 11 treatment L. W. McIVER, D.D.S Mimeapolis, Mim. SEVERAL months ago I sent a questionnaire to twenty-five dentists in our city, asking just one question : “If orthodontic services could be improved, what phase of it in your opinion should be improved the most I ” There were five possibilities from which they could choose : 1. Lore stable alignment 2. Better esthetic improvement 3. Better occlusion and articulation 4. Faster treatment 5. Better control of caries during treatment As might be expected, the most prevalent answer was better occlusion and articulation, with twelve of the twenty-five placing this first. Next was more stable alignment with seven who considered this most important. Perhaps twenty-five opinions do not mean very much, but I think that this does give some indication that the family dentist is concerned about the occlusions which we are producing. I am sure we agree, too, that there is room for improve- ment in this area. All of us, in our efforts to improve the patient esthetically, have created convenience bites, watched the molar relation relapse, or failed in other respects to make teeth fit together in the way they should. I believe that there are certain things which we can do in everyday practice to avoid many of these troubles and to produce better occlusions and more stable results. Therefore, I am going to offer suggestio8ns which I think will be helpful. HAKE EXACTING OBJECTIVES ‘The first suggestion is to have clearly defined goals to work for. Of course, we cannot produce the ideal occlusion for everyone, any more than we can make Presented at the annual fall meeting of the Northeastern Society of Orthodontists, Rochester, New York, Oct. 29 to 31., 1961.

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Page 1: Five steps to better occlusion in Class II treatment

Five steps to better occlusion in

Class 11 treatment L. W. McIVER, D.D.S Mimeapolis, Mim.

SEVERAL months ago I sent a questionnaire to twenty-five dentists in our city, asking just one question : “If orthodontic services could be improved, what phase of it in your opinion should be improved the most I ” There were five possibilities from which they could choose :

1. Lore stable alignment 2. Better esthetic improvement 3. Better occlusion and articulation 4. Faster treatment 5. Better control of caries during treatment

As might be expected, the most prevalent answer was better occlusion and articulation, with twelve of the twenty-five placing this first. Next was more stable alignment with seven who considered this most important.

Perhaps twenty-five opinions do not mean very much, but I think that this does give some indication that the family dentist is concerned about the occlusions which we are producing. I am sure we agree, too, that there is room for improve- ment in this area. All of us, in our efforts to improve the patient esthetically, have created convenience bites, watched the molar relation relapse, or failed in other respects to make teeth fit together in the way they should.

I believe that there are certain things which we can do in everyday practice to avoid many of these troubles and to produce better occlusions and more stable results. Therefore, I am going to offer suggestio8ns which I think will be helpful.

HAKE EXACTING OBJECTIVES

‘The first suggestion is to have clearly defined goals to work for. Of course, we cannot produce the ideal occlusion for everyone, any more than we can make

Presented at the annual fall meeting of the Northeastern Society of Orthodontists, Rochester, New York, Oct. 29 to 31., 1961.

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every patient beautiful, Unusuai growth patterns and abnorm: muscle habir,s are hazards that we al! face, but we can pay attention to the same details that guide the prosthedontist, the periodontist, and the crown and bridge expurt. For example, most of us agree that a shallow overbite is desirable, since we like to have as many teeth in contact on the working side as possible during corn- pletion of t,he chewing cycle. Shore1 describes this chewing cpclc or enveloy of motion as follows:

Trituration or mastication proper is acc.ompliahed by dropping the marl&Ho in a hinge- iike motion, then shifting to left or right functional position. In normal mastication, ~hrro there are no interfering occlusal contacts the mandible moves back into centric relation wiLLi the condyle head on the functioning side set well into the fossa to brace against the pull of the muscles as they force cuspal penetration into the bolus.

With shallow overbite we have more freedom of movement and a less vertical stroke. Head2 reported that it takes five times as much force to triturate food with a vertical stroke than with a lateral shearing action. Functioning-side contact of a11 buccal teeth is very desirable, but simultaneous cuspal contact on the nonfunetioning side is not necessary. In fact, cuspal interference on the nonfunct,ioning side is very undesirable, since it keeps the functioning side open and thus places a torque on the teeth and the mandible. I think there is little disagreement over these objectives. It is only when we talk about centric relation that our objectives seem a, little fuzzy. Therefore, this discussion will be con- cerned mainly with the most important characteristic of good occlusion-centric relation.

I would like to explain a concept of jaw relation which is rather exacting and yet quite simple to use. It is not entirely new, for it is based on information from various sources. It is sort of a middle-of-the-road concept whieh favors neither the rest position nor the retrnded position theory entirely. I believe that it is a good guide to treatment, whether the malocclusion is Class I, Class 11, or Class III.

We can start by realizing that centric occlusion is a mandible-to-skull, or bone-to-bone, relation. Teeth have nothing to do with it, except that they must be in harmony with this relation. Our job, therefore, is to place condyles in the proper position in the fossa rather Lhan to seek a cusp relation of t,he teeth. As a starting point for such a plan, we must agree that there are at least two ma,in characteristics of a proper eondyle-fossa relation. Histologic studies of joint tissues, laminagraphic studies of condyle position, cinefluorographic studies of swallowing and mastication, and all the definitions of ceritrie relation indicate that condples should be (1) deeply seated in the fossa and (2) against the anterior slope of the fossa when teeth are in occlusion. Speculat,ion as to why this is so is perhaps unncccssar;\-, but I think that the direction of muscle pull and. thr influence of the terYlpoi*omandibular ligament should not be ignored. Page3 has schematically analyzed the resultant direction of pull of the closing nnuscles and found it to be upward and backward, roughly parallei to the fossal slope. The trnlporomantli~)~~laI. ligallleut, rmurir~g at right au&s to this ~OIW, is in good position to limit, posterior movement of the coudyle and guide it to the area of bony support. TVht+hw OT not l-his explanation is cm~cct does

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Volume 48 Ntlllzbet- 3 Better occlusion in Gluss II trwhnent 177

Ilot matter \:ery ~nuch. The important thing is that tlrere is much evidence tha.t condyles need the support of the I’ossal slope to function properly and the deeply seated position in the fossa is preferred.

The next problem is to find a positive method oE placing t,he condyles in this position. For want of something better, let us consider using the posterior hinge path or centric relation arc. This is equivalent to using the retruded position at various vertical openings, since the posterior hinge path is border movement. PosseW has shown that if extreme movements of the mandible are recorded graphically in the median plane, a characteristic figure is obtained. The posterior hinge path is the pa.th which the mandible follows when pure rotation occurs. The fact that this border movement can be repeated so accurately makes it valuable in relating the jaws, but there is some argument as’ to whether or not centric relation is always on this path. This disagreement should be settled with at least, some degree of satisfaction before this method can be used with best results.

One thing tha,t would help to settle this question is to determine in what anteroposterior position we have the greatest biting force. A.s most of YOU know, Dr. Ralph Boo@ has studied the biting force of many patients in various degrees of vertical opening. Using an intraoral gnathodynamometer, he found that the greatest biting force is possible at that degree of opening which corresponds to rest position. Recently, he has also studied the biting force in various antero- posterior positions. This is what he says about mandibular position when greatest biting force was registered :

About 65 per cent of the time these power points were associated with the apex of the gothic arch tracing. The usual record was 0.5 mm. anterior to the apex. In 35 per cent of the patients the group of power points was from one to 7 mm. anterior or lateral to the apex of the needle point tracing.

As you know, the apex of the gothic arch tracing is a border position. In other words, 65 per cent of the patients had the greatest biting force within 0.5 mm. of the most retruded position.

This is strong evidence that the retruded position is accurate in at least 65 per cent of adults. But what about children of orthodontic age? A few years ago I made a rather simple study of 170 children between the ages of 5 and 15. Seventy of the children examined had untreated Class I malocclusions, and 100 had Class II malocclusions. The object was to determine how many could retrude beyond intercuspal position. For checking the retruded position, the pati.ent was seated upright in the chair and instructed to open and close the mouth islightly as the mandible was held in retrusion. It was found that 73 per cent of the children with Class II and ‘76 per cent of the children with Class I malocclusions could not retrude beyond intercuspal position. While this may not be ;absolute proof, it strongly suggests that this old clinical practice is ac- curate in about 75 per cent of the cases. Let us say, then, by way of compromise, that the retruded position or so-called centric relation arc is about 70 per cent accurate. This means that if your patient cannot retrude beyond intercuspal position you can bte reasonably sure that jaw relation is good. In such cases centric relation is on the posterior hinge path. As might be expected, the joint

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films wili silow 110 diKerem t)c~Lwcell lite ~cIl~uded a~rd oeciusw i [)oriit,iiriis ol: 1 I>(% condyle, no tna.tt.rr how mnch prt’ssurc is used to force the mandible hack. F’or ail practical pnrposes, we are placing condyles in correct posit.ion w-hen we use the posterior hinge path in such cases. What ahout the other 30 per cent-those cases in which the mandible can be retruded beyond the intercuspal position?

1’ig. I. Kor-mal occlusion. Patient can retrullc heyoul !nrarcufipal poahon. fhnrlylv :iilJr~+ an3y from support of srticular eminence on right side when mandible is rcwuded (jower films). Intercuspal or closed position ia eerrect.

To answer this, we should know- what we are doing to the eondyle-fossa relatlulk when we guide the mandible manually into retrusion in snch cases.

To study this, we made temporomandibular joint films of ten patients with excellent occlusion, all of whom could retrude beyond intercuspal position.7 The retruded-posit.ion films were taken with a thin wax bite in place. In all cases the

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Better occlusion in Class I1 treatment 179

eondyle moved straight back about 1 mm. away from the support of the fossal slope, and usually this movement was on one side only (Fig. 1). Observe that the joint gap is larger in the retruded position. The condyles did not move deeper into the fossa. Comparison of t,he two lower films discloses that the condyle is slightly farther away from the eminence: in the retruded position.

I think that this observation is important for several reasons. For one thing, it could explain why some patients have l.ess biting force in the retruded position. In about 30 per cent of the cases, retruding the mandible displaces the condyle posteriorly away from its bony support. In this position the biting force is bound to be less than when the condyle is braced a.gainst the bone. Some of you can test this on yourselves. Retrude your mandible as far as possible, place your fingers over the masseter muscles, and bite hard. You will find that this muscle will not contract as vigorously as when teeth are in occlusion.

This observation is important for another reason. It suggests that the oe- clusal position is correct for these cases and t,hat no cuspal interferences are present. Manual retrusion places the mandible in an uncomfortable, unsupported, nonfunctional position. From a functional point of view, however, these cases are no different from the 70 per cent in which the mandibles cannot be retruded beyond intercuspal position. Both types function with condyles on their most retruded bearing points. The fact that condyles merely move back away from the eminence and cannot. be forced deeper into the fossa indicates that this is true. Even though only ten such normal occlusions were studied, I think it is quite simificant that all of them showed the same thing. In view of this, we could probably estimate that at least another 20 per cent of our patients have good jaw relation before treatment is started. In other words, in about 90 per cent of t,he untreated, undisturbed occlusions of children there is a good centric relation,, no matter what the Angle classification is.

In only a small proportion of the cases do we encounter a faulty rela,tion, and I believe that these cases involve patients who have more than average mobility of the condyle in the fossa. These patients can bite in several different positions, and it is (difficult to determine which is correct. Fig. 2 shows an adult patient, for example, who was experiencing joint difficulties. The cusp-and-groove relation is shown in the upper photograph. The wear on the occlusal surfaces, however, indicates that the mandible is considerably farther back during function (lower photograph), but not in the most retruded position. Joint films show the difference between the retruded and the intercuspal positions. Let us compare the two lower films. The retruded position is not correct, for the mandible is displace’d posteriorly away from bony support. The intercuspal position is not correct either, for the mandible is t,oo far forward. The correct position is be- tween the two, and it corresponds to the most retruded position in which bony support of the condyle can be maintained during function. Thus, even in these cases, jaw relation tends to be constant and precise.

I do not mrxn to imply tha.t there is no such thing as posterior displacement. It shoul’d be remembered, however, that this type of condyle movement is pos- sible in only about 30 per cent of the general population, and even then only under c#ertain conditions. Posterior displacement could be created in denture

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Fig. 2. Patient with joint trouble. Wear m teeth indicates Thd‘c iilhW,LSp~i aositioil is ‘137,

correct. Roentgenograms show that retruded position is wt correct either, because condyles are displaced posteriorly away from eminence. This condition is not common. *

patients if the joint is similar to the one just discussed and the hinge axis reg- istration is used to mount t.he casts in the articulator. It might also he found in some adults whose posterior teeth have been lost or in whose mouths there is a bad interference, such as an extruded molar.

Patients with a full complement of teeth, however, do not easily maintain such a relation. Occlusal grinding in such patients has shown that, even shough occlusion is adjusted to a position of posterior displacement where condyles are forced away from their bony support, the mandible will not func- tion there. It will come forward until the more comforta,ble bone-to-bone rela- tion between condyle and fossa is restored. I have deliberately tried to trca,t some of these cases ort,hodontica.lly to a position of posterior displacement, only to find that the mandible comes forward amgain. Posterior displacement should be of geater concern in restorative dentistry tha,n in orthodontic treatm.ent.

All these observat,jons add up to what might be called the retruded support

concept of jaw relation. Simply st,ated, it means that our objective should be to place condples as deeply in the fossa as possible without losing contact with t-he articular eminence. Gently retruding the mandible as the paGent opens and closes the moUth will accurately position the condyles in a.bout 70 per cent of the cases. In the other 30 per cent, however, we may be displacing condyles pos- +,eriorly when this border path is used. Yet I am suggesting that the posterior hinge path be used in orthodontics to check these cases too. It is not 100 per cent, accurate, but I t,hiuk it, is the brst clinical guide that, we hnvo.

The nest suggestion for attaining better vcelusiolz is LO IIS<: i~x1 ~nai~sis

which includes at least some estimate of future growth. If QT work on the

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Fig. 3. T’reated Class II malocclusion. Patient can retrude beyond intercuspal position. Both condyles move deeper into fossa when mandible is retruded, but contact with eminence is maintained. Retruded position is correct.

theory that jaw relation is correct before treatment and that correction of Class II malocclusion is brought about only by a combination of tooth move- ment and growth and not by a change in mandibular position, then it is apparent that treatment of Class II malocclusions must be started before growth has stopped. It has been my experience that dual bite or relapse of molar relation is often the result when treatment is started too late. In the presence of insufficient ma,ndibular growth, the mandible is more likely to be displaced forward during treatment. Displacement may be temporary, resu1tin.g in relapse of molar relation, or it ma;y be more permanent, resulting in a convenience bi.te. If condyles go deeper into the fossa when the mandible is retruded but contact with the eminence is maintained, we have a convenience bite or a dual bite. Fig. 3 shows roentgenograms of such a patient taken at the

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Pig. .eaied Glass II maloeelusion.

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Better occlusion in Class II treatment 183

Fig. 6. Glass IT malocclusion before treatment and one gear out of retention slrows relapse of molar relation.

end of treatment. This boy could retrude quite far beyond intercuspal position. Notice .that both condyles move deeper into the fossa and not away from the eminence. The retruded position rather t,han the closed position is correct in this case. It is my feeling that we should be suspicious of fast corrections in Class II treatment, for there is a good chance that the mandible is being dis- placed forward like this. Of course, there is the possibility that continued con-

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t!~.lau g~~owtil a.itw t.rea.t~rlvnt wiii ~orrec:~ the jaw xia~iw. Tile ?nxndihic iit- awakes in length, bnt. instead 01: ~.Tw chin point cotuing forww rtl the cond~~!~~ gr~ows back up into the J’OXSR , gradually correelirig t.he centric relation. Two years after these s-ray pictures M-WC taken, the pa.tient was examined again and it was noted that he could no longer retrude beyond intercnspal position. (:rowth took care of onr inability to obt,ain a good centric relation. This does uot happen very often, however, so I do not believe it, is good practice to depend upon it, particularly if the patient is a girl.

Fig. 4 shows a case \shich did not. improx three years after treatment. The casts at the end of treatment look quite acceptable, but this patient has a dual Site. X-ray pictures show that condyl.es move deeper int,o the fossa when the mandible is rctruded (Fig. 3). One condyle (upper right-hand photograph) also moves slightly away from the eminence, b’ut the occlusal position is not correct. This patient was a girl whose treai.ment was started at the age of 13, too late for any help from growth.

Relapse of molar relation is another price that we pay for starting treatmeur too late. Fig. 6 shows the casts of a 13-year-old girl before treatment and about one year out of retention. In the presence of insufficient. mandibular growth, the mandible was displaced forward during treatment and then gradually settled back, resulting in relapse of molar relation. The displacement was tempora,ry, ;jrobably because joint morphology did not favor several condyle positions (Fig. 7). On one side t,hc anterior slope of the fossx was quite shallow, but on r;he other it was quite steep.

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Volume 48 Number 3 Better occlusion in Class II treatment 185

TED obtain the most stable results, I believe that Class II treatment should be started when there is enough condylar growth left to ‘move the chin point downward and forward 3 to !S mm. To be on the safe side, this means starting treatment in girls at age 10 or 11, regardless of whether or not all deciduous teeth have been lost. In boys treatment can often be delayed one or two years, or until all deciduous teeth are lost. Early mixed-dentition treatment is all right if there is no objection to two periods of treatment or four or five years of care, but it, seems doubtful that it is necessary for good stable results in most cases.

In analyzing a malocclusion we are often faced with the problem of whether to extract four teeth, two teeth, or none at all. It would be futile to attempt to reduce this problem to a set of hard and fast rules, for there are too many vari- ables. The closest thing to a simple formula that I know is a three-step process of weighing those things which help us and those things which hinder us. Since the basic plan in most treatment is to build the entire denture around properly positioned lower incisors, the first step is to analyze the position of these teeth in rel,ation to surrounding structures. Next we estimate what effect our mechanics will have on their position. Then we make an effort to predict how growth is

F’ig. 8. Many Class 11 malocclusions such as this one are treated x10x-e successfully if the treatment plan is varied according to the response.

likely to effect the incisor-APO relation. In the case shown in Fig. 8, for ex- amplIe, the lower incisors are quite crowded. Yet I would be reluctant to extract four teeth in this case, since the incisors are quite far behind the APO plane. Tf they were in front of i-his plant, I would consider ext,raction even though there was no crowding.

In est,imating the effect of our mechanics, we can be reasonably sure that expansion alone would bring the lower inci.sors forward to good position on the APO plane. The use of Class II elastics in addition, however, would be too

Page 12: Five steps to better occlusion in Class II treatment

racy. Therefore, the Class 1-P rc!ation wouid have ::u 1~ correct& entirely with headgear, or else two upper teeth would have to be removed.

The amount and direction of mandibular growth expected over the next two years could also affect the treatment plan. In this case the patient,, a boy, 1s only 11 years old; the mandible is heavy, the mandibular plane is not steep, and the occlusal plane is nearly parallel to the mandibula,r plane. Therefore, growth is likely to be of considerable help not. only in correcting the molar r‘elation but also in offsetting the effect of increasing lower arch length.

This illustrates what I think is another important point in treating Class II malocclusions. Desirable as it may be to have a definite plan before treatment and then stick to it, we must admit that growth and the patient’s cooperation

a

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Better occlusion in Class II treutment 187

are rather difficult to predict. I think, therefore, that it is often better to feel our way and vary the treatment according to the response if we are to attain the best occlusion possible.

SE’CTIONAL TOOTH MOVEMENT

My third suggestion for attaining better occlusion is to rely on sectional tooth movement rather than en masse movement of teeth. First, let us consider the nonextraction case. Fig. 9 presents records of an H-year-old boy whose second molars had already erupted. This case was t.rea.ted without Class II elasticis except for three weeks near the end of treatment when elastics were worn on one side only. Fig. 9, B shows the case six months out of retention.

In correcting a case of this kind (Fig. lo), the upper first molars are banded and the headgear is worn until a Class I molar relation is established or until the headgear falls too far below the upper incisors. The lower arch is also being

Fig. 10. Treatment of Class II nonextraction cases without intermaxillary elastics. Headgear is applied to molars throughout treatment.

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ieveled during tnis time with an &gelvwe Neil. :~ %rticulalf aitent~on is giveii LO raising the first premolar in relation to the cuspid. Sfter the upper first molar :s tipped back, the upper buccal teeth are banded and an 0.016 inch arch wire ;s tied in. This uprights the molar, SO that the headgear does not fall below the upper incisors. Figure-of-eight ties or springs are used to close spaces and bring rhe buccal teeth back into Class I relation. After the buccal teeth are in Class I :*elation, the upper incisors are banded, and a space-closing arch is used to bring them lingually as shown in the lower part of Pig. 10. It may be advisable to Sand the upper incisors before they are brought lingually in order to prevent too much space from developing, but these teeth are not tied into the arch until lingual movement is begun. Naturally, this type of treatment places the operator nt the mercy of the patient’s cooperation, but it also allows for a closer check 431 cooperation. For example, if the headgear is attached to the molar only and *lo space develops in front of the molar aft,er two or three months, the ortho- &.mt,ist. may conclude that the patient is not wearing the headgear every night. I believe that treating the buccal segments first is a. good plan, for it allows the ,Jperator to feel his way. There is less danger of displacing the mandible for- ward, because if a good relation cannot be established between upper an.d lower iuccal teeth it is quite certain that incisors cannot be moved to correct position.

In cases requiring the extraction of four premolars, a similar plan is fol- .owed. The Class II relation is corrected by means of the headgear and Cla,ss II 2astics before all spaces are closed. Care is taken not to move the lower cuspids clnd incisors too far back. In the lower a,rch cuspids and incisors can often be tnoved back as a unit, while in the upper arch the cuspids and incisors arc moved 3ack separately as shown.

it is my feeling thai closing spaces first and attempting to correct molar relation later is more likely to result in failure in the form of relapse of molar relation or convenience bite.

My fourth suggestion deals with arch 10~~ Several yearn ago f was yii~tk: itit.erested in t,he various methods of mounting casts on the articulator. T-D ztudping the detailed positioning of teeth, one cannot, help being impressed ‘?j~- the fact that interferences are very often found in th.e premolar area. This can

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often be avoided by coordina,ting a,rch widths. Fig. 12 shows what 1 consider good lower arch form a,nd poor arch form. Care should he taken to a,void widening across the cuspid area, but the arch is purposely widened slightly across the first premolar area. by means of a step-out bend, If the lower arch is too narrow or the upper arch is too wide in the premolar area, cuspal inter- ference will displace the mandible forward.

OCCLUSAL GRINDING

The final comments concern occlusal grinding. It should be our aim to pro- duce the best occlusions possible without grinding. If minor adjustments will improve our cases, however, I believe they should be made. There are precau- tions as to where and when to grind, and limitations must be observed since we do not, mount casts in the articulator.

Whenever occlusal adjustments are made, centric relation is adjusted first. Before this is done, however, we should be reasonably sure that jaw relation is not going to change as a result of condylar growth.

Suppose, for (example, that we have created a convenience bite such as the one described earlier. The condyle is downward and forward in the fossa when teeth are in occlusion, and the patient can retrude beyond intercuspal position. One year later we may observe that no retrusion is possible. The condyle has become more deeply seated in the fossa as a result of growth. The patient now has a good centric relation, indicating that it would have been a mistake to adjust the centric relation earlier by means of occlusal grinding.

cuspid6 Fig. 12. Grinding on the functioning side.

Premolars and molars

I prefer to obtain the best centric relation possible without grinding, be- cause I think that this is a dificult adjustment to make without mounting casts in the articulator. If any grinding is done for centric relation, however, we should be careful not to reduce the vertical dimension or shorten cusps which may be useful in eccentric movements. Three of the most common areas to grind Twhen centric relation is adjusted are the central fossa of the upper molar, the central fossa of the lower molar, and the lingual cusp of the upper first premolar (mesiobnccal incline of this cusp). In upper premolar extraction cases it is sometimes helpful to grind the oblique ridge of the upper first and second molars.

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~GAit~lishi~ig w~~taet :!i :t:eiil 2:~ 211~- ‘lil~CtiOIi!li~ YidC IS iic.1:. iiei’t: a#L%iH

It is best, t,o do as nluch of this as possi hle with tile aappliance i))v trtaating t,o :L ~hailow overbite or even a slight open-bite. Special attention should he given !c; placement of bands on cuspids so that these teeth a,re not elongated. The oc- clusal curve in both arches should be c,ontrolled by elevating the buccal seg- :ilents in reMion to the anterior segments. Grinding to improve functioning-side aontact should probably be postponed until we are reasonably sure that overbite IS not going to decrease as a result of growth or increase after treatment. This is one adjustment which can be made quite accurately by grinding directly in the mouth, but accepted grinding rules should be followed to avoid taking t,eeth out of occlusion in centric rela.tion (Fig. 12). Cuspids are the worst offenders, but upper teeth should not be ground at point A and lower teet,h should not be around at point B. Sometimes it is necessary to reshape premolars and molars ., tilso; in so doing the upper buceal and lower lingual cusps are ground in the u Peas shown.

Before working-side contacts can be established, however, it is necessary to remove the interference, if any, on the nonfunctioning side. This is also a difficult adjustment to make without mounting casts in the articulator, so I prefer to avoid it entirely by making every possible effort to keep upper molars and premolars upright buceolingually. By placing lingual crown t,orque in the TJpper buccal segments, it is usually possible to treat the nonfunctioning side so a no-contact relation. If any adjust,ments are attempted for these inter- ferences, however, it is usually bett,er to grind the lower teeth than the upper lingual cusps. In fact, the t.ips of the mesiolingual cusps of the upper molars ?re seldom removed, since they are important in maintaining centric occlusion.

ln summary, may I say that this has hectn simply an effort to apply clin- :~Ely what in my judgment is the best available information on occlusion.

I have made suggestions for obtaining better centric relation and more fune- tloning-side contact, as well as for treating the nonfunctioning side to a no- contact relation.

Paying attention to such details amounts to placing teeth in such positiolrs that muscles of mastication will be required to do the least amount, of work.

We do the same thing for another group of muscles when we strive for better ilsthetics, and we obtain more stable results because of it.

Let us not forget the possibility that we can also obtain more stable results through better occlusion.

REFERENCES

!. Shore, N. A.: Occlusal Equilibration and Temporomandibular Joint T~pafunction, f-‘hila delphia, 1959, J. B. Lippincott Company.

2. Head, J.: The Human Skull Used as a Bnatllodynamomcteu to Determine the Value :,i Trituration in the Mastication of Food, Dental Cosmos 49: 1189, 1901.

3. Sage, H. L.: Temporomandibular Joint Physiology and Jaw Synergy, D. Digest 60: 54,

1954.

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Better occlusions in Class II treatment 191

4. Posselt, Ulf : Ra.uge of Movemcul of the Mandible, J. Am. DonI-. ,\. 56: 10, 3958. 5. Heyron, H. L.: Characteristics of Fm~ctionnlly Optimal Occlusions, J. Am. Dent. A. 48:

6413, 1954. 6. Boos, R. H.: Vertical, Centric, anti Functional Dimeuxions Recorded by Gllathodynamics,

J. Am. Dent. A. 59: 682, 1959. 7. McIver, L. W.: Relating the Mandible to the Maxilla in Treatment of Class II Xalocclu-

sion, Angle Orthodontist 29: 218, 1959.

16(?0 West Lake St.