(This is a verbatim copy of a topic from an article entitled The Control of Vertical Overbite in Clinical Orthodontics, presented at the 1967 Annual Meeting of the American Association of Orthodontics and published in the Angle Orthodontist in 1968. It was republished in a book by Fred Schudy and George Schudy in 1992. It was also translated into French and will be published in the year 2000.)

The principles of treatment to be described here have been used very successfully for the past twenty years; it had been assumed that most orthodontists also used them. In recent years it has been observed that they are not well understood and that there is a definite need for their discussion.

It is well known why teeth shift laterally within the respective jaws in which they are situated. Why do mandibles shift laterally? I think that it can be said that mandibles shift laterally because of at least five reasons: (1) the maxillary arch is too wide either bilaterally or unilaterally, (2) the mandibular arch is too narrow either bilaterally or unilaterally, (3) the maxillary arch is too narrow, (4) the mandibular arch is too wide, and (5) a combination of these situations. We could have a constriction, for example, on the left side of the maxilla and constriction of the right side of the mandible. The mandible shifts to the right or the left for the sake of convenience and comfort. It shifts laterally to bring enough teeth into occlusion to masticate efficiently.

Frequently during treatment we will note that the midline deviation becomes greater as we go along. In the beginning, the midline may be slightly off, but near the end of treatment it may become worse. Why does this happen? It seems logical to assume that since teeth become loose as treatment proceeds, they are subject to the pressures of mastication. If the patient does all of the mastication on one side, greater asymmetry may be produced. The maxillary posterior segment on the side of mastication tends to shift buccally. Also, if our treatment procedures are faulty and we expand an arch through poor arch construction, say on the maxillary left side, then the mandible will shift in that direction to keep pace with the expanded arch so that mastication can be performed. Also, if due to poor arch manipulation and poor treatment procedures, we allow the mandibular arch to become more narrow on one side, then the mandible must shift toward that side in order to masticate efficiently. If both sides have been constricted equally, the individual must choose whether to use the left or the right side.

We will not discuss the correction of lateral shifts of teeth within the arches. We all know how to move teeth laterally, with coil springs, vertical loops, rubber bands, elastic threads, etc. We will deal only with correcting a mandible that is displaced laterally. The first thing to do, of course, is to note it on the model and note the extent of the deviation and the possible cause. The cause may or may not be apparent from examination of the models. Then, we go to the patient and have him move the mandible to where the midline of the maxillary teeth is directly over the midline of the mandibular teeth. This usually entails moving the mandible forward and, of course, to the right or to the left. We must be careful to have the patient move the teeth into an end-to-end position, or almost to such a position, as we make this examination. When the mandible is in the right position, we study the tooth movements that will be necessary to place the posterior segments of teeth into apposition. In nearly all cases, if not all, it will be apparent that one side of the maxilla must be moved laterally, buccally or lingually. We may note also that a posterior segment of the mandibular teeth must be moved laterally, either on one side or both sides.

As we see the lateral discrepancy of the posterior segments of both maxilla and mandible, we should at the same time note the amount of vertical movement of the posterior teeth that is going to be necessary to bring them into occlusion when the anterior teeth are also in occlusion.

Figure 1 This illustrates the use of intermaxillary elastics in the correction of a midline asymmetry. A. The midline of the mandibular arch is to the patient's left of the center of the maxillary arch, when the teeth are in natural occlusion. There is also an anteroposterior discrepancy, especially on the left side, which does not show in this diagram. B. The relationship of the molare when the patient places the mandible forware and to the right until the midlines are directly over each other. A Class II elastic o the left side and a crossbite elastic on the right will be required to correct the asymmetry. Torque force may also be indicated in one or both arches.

If we have a condition in which the mandible is shifted toward the left side, the teeth in the mandible are in the proper positions on the bone but the entire jaw is shifted toward the left side due to a combination of some of the aforementioned causes (Fig. 1). When the patient moves the mandible, which is to the left, to where the midlines are correct, we note that the maxillary arch is too narrow on the right side. We see a cross-bite condition on the right side, meaning that the maxillary arch is either too narrow on the right side or that the mandibular arch is too wide on the same side, or a combination of both. At any rate, the correction requires a Class II elastic on the left side and a cross-bite elastic on the right, running from the lingual of the maxillary right molars to the buccal of the lower right molars. The Class II elastic together with the cross-bite elastic will have the effect of rotating the mandible toward the right side and shifting the left condyle forward. The cross-bite elastic will also constrict the right mandibular posterior segment and expand the maxillary right posterior segment. This will usually correct most midlines; however, there are many varieties of midline deviations which require different procedures (Figs. 2 and 3). The time to apply these elastics is certainly not at the beginning of treatment. It will usually be after the leveling procedures, very frequently after all space closures if there have been extractions, after the bite has been opened and after good arch form has been attained. In other words, we must so arrange the teeth in the individual arches to occlude correctly when the midline is correct.

Figure 2 A. Shows the existing asymmetry of the midlines, when the teeth are in natural occlusion. B. The relationship of the molars when the patient places the midlines in harmony; a Class II and a crossbite elastic on the left side will be required to correct the midline asymmetry. Torque may also be needed to aid the elastics.

Figure 3 A. The existing midline asymmetry when the teeth are in natural occlusion. B. The relationship of the molars when the patient moves the mandible to bring about harmony of the midlines. The arrangement of elastics necessary to correct the problem is indicated. Note that both crossbite elastics are pulling the mandible to the left but we expect it to move toward the right.

In order to accomplish the correction of asymmetry of arches, in most instances it is necessary to think in terms of the correction of segments of teeth. When it is necessary to extract four premolars, we must consider the mesiodistal shifting of the buccal segments before our spaces are closed. This greatly facilitates the correction of the midline. If we extract teeth and close the spaces, leaving the midline discrepancy as it was in the beginning, then we have a major job to accomplish.

Occasionally a malocclusion may be found in which there is a lateral shift of the anterior teeth within one or both of the arches in addition to a lateral shift of the mandible. In such cases it may not be necessary to place the intercentral embrasures directly over one another at the oral examination, but instead allow for the tooth shift by having the patient move the mandible only part of the way.

Now let us consider a case in which the midline of the mandible is deviated toward the left side approximately one half the width of a lower incisor (Fig. 2). The first thing to do is to have the patient move the mandible toward the right until the two midlines are together.

We note that, when the mandible is in this position, the buccal segments on the right side are directly over one another, while on the left side the mandible is constricted, or the maxilla is too wide, or both. For correction place a Class II elastic on the left side and a cross-bite elastic on the same side running from the lingual of the mandible to the buccal of the maxilla. This will have the effect of moving the mandible forward, rotating it toward the right side, and at the same time moving teeth in both arches occlusally. We are also moving the maxillary left posterior teeth lingually, and the mandibular left posterior teeth buccally. This should bring about the correction of the midline of the two arches. While the operation of the two elastics prescribed will in most cases correct the asymmetry, yet it is possible that in addition to these it will be necessary to use a Class III elastic on the right side for a short time. That will have the effect of rotating the mandible from left to right while bringing the posterior segments into apposition laterally.

Let us use an example a Class II, Division 1 extraction case in the last three to four months of treatment. Rotations and leveling have been accomplished, all spaces are closed and the Class II is corrected, but the mandibular midline is one mm to the right. The first molars and second premolars are in good occlusion on both sides. The first bicuspids have been extracted; we note that the cuspids are occluding reasonably well, especially on the left side. When we place the mandible so that the midline of the maxillary arch is directly over the midline of the mandibular arch, we see that the laterals are occluding quite differently on the two sides. On the left, the mandibular and maxillary laterals are in contact; on the right side the laterals are one mm apart. They occlude on the left side when the midlines are correct, and on the right they do not. This immediately tells us that the mandibular left lateral incisor is forward on the mandible and that the mandibular right lateral incisor is too far distally on the mandible; or, the maxillary left lateral incisor is too far posteriorly, or the right lateral incisor is anteriorly. The four halves of the arches are not anteroposteriorly harmonized, and we must check treatment arches for symmetry. It is obvious we must place a Class III elastic on the left side and a Class II elastic on the right. This will have the effect of rotating the mandible while moving the maxillary left posterior segment anteriorly and the maxillary right posterior segment posteriorly. We may need a cross-bite elastic from the lingual of the mandibular right to the buccal of the maxillary right. The bite must have been opened to an end-to-end relationship before we can expect to correct this asymmetry. These elastics should be worn in this manner until there is an overcorrection, that is, until the midline of the mandible is toward the left side.

What is the rationale for this method of correction of midline asymmetries? Elastics must be strong to overpower muscle pull and overcome a deeply ingrained neuromuscular functional pattern. Elastics do not affect mandibular position per se. They only affect tooth position, which in turn influences mandibular position. In other words, a mandible will only adjust to an altered tooth position, and not be directly affected by elastic pull, however strong this may be. In many instances the vertical dimension plays an important part in the etiology of asymmetries of the teeth. A differential in the vertical growth of the alveolar process can be quite important in producing a horizontal asymmetry. The correction of this by the vertical pull of the elastics is an integral part of the over-all correction. Thus, both the vertical and horizontal disharmony must be corrected.

In Figure 3 it can be seen that both cross-bite elastics are pulling the mandible toward the patient's left and we want it to move to the right. Quite a paradox! The mandible will move to the right only after the teeth have moved on their bases, after the maxillary teeth have moved in the direction we want the mandible to move and/or the mandibular teeth have moved in the opposite direction.

Elastics must be very strong (up to 16 oz.). It is best to use weaker elastics for about three days leading up to the strong ones. The patient and parents must be informed carefully about the purpose of the elastics. They must be told that in order to break a habit of many years standing we must use strong forces to shock, disturb and confound the existing neuromuscular balance. They must also be told, with emphasis, that the elastics are not to be removed from the mouth under any circumstances-not even to brush the teeth. But, they can be promised that only three to six weeks will be required to correct the asymmetry. The reader must be reminded that such a system of elastics must not be applied unless both arches are completely leveled.

Many men have expressed concern about the possible reaction of the temporomandibular joint to such drastic and forceful changes in the position of the mandible. They have wondered if such therapeutic measures would lead to malfunction and discomfort at the time of the treatment or in the future. The author can truthfully say that in twenty years of application exactly as described here he has never noted any discomfort at the time or later. Quite to the contrary, on numerous occasions discomfort and clicking have been eliminated by these procedures.

About the only exceptions to rapid correction that have been observed are deep-seated anatomical asymmetries. These are usually in the form of gross differential in growth of the two rami; however, the abnormality may be located in the temporal bone or the maxilla. In such instances the recommended principles still apply; however, the effect is different. In these cases the mandible will not change its position appreciably and only the teeth will move. Since anteroposterior movement of teeth on their bases is usually necessary, considerable time will be required. In order to bring the two midlines in harmony it will be necessary to continue elastics until both maxillary and mandibular teeth are moved off the center of their respective bases. The maxillary incisors will be off center in one direction and the mandibular incisors will be off in the opposite. This, of course, is not desirable but is the only alternative other than surgery to equalize ramus length.

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