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Diagnosis and treatment planning ofpatients with asymmetries
Diagnosis and Treatment Planning of Patients With Asymmetries CharlesJ. Burstone The diagnosis, treatment planning, and design of mechanics for the asymmetric patient requires the differentiation between problems of dental and skeletal origin. Although much information can be gleaned from a cephalometric analysis, the clinical examination and study models offer important clues in establishing the diagnosis of skeletal discrepancy. Abnormal and asymmetric axial inclinations can either produce a dental asymmetry or, if compensatory in nature, may mask an underlying skeletal problem. The role of axial inclination in diagnosis is applied to the following situations: subdivision cases, unilateral crossbites, midline discrepancies, arch form deviations, and frontal cants to the occlusal plane. The management of axial inclination asymmetries depends on the treatment plan. Nonextraction patients may require maintenance of asymmetric compensatory axial inclinations. Surgical and extraction patients can be treated to a more ideal symmetry. (Semin Orthod 1998;4:153-164.) Copyright© 1998
by W,B. Saunders Company
t is c o m m o n to find asymmetric occlusal relationships in patients requiring o r t h o d o n t i c treatment. Examples include a Class II occlusion on one side of the arch with a Class I or Class III occlusion on the other. T h e r e may be lack of midline c o r r e s p o n d e n c e between the u p p e r and lower arches or both midlines may n o t be symmetrically placed in the face. Unilateral crossbites can exist and arch f o r m may n o t be symmetric, or u p p e r and lower arches may n o t be congruent. T h e cause of these asymmetries can be multivariate. In some patients, the p r o b l e m originated with a b n o r m a l dental eruption, p r e m a t u r e loss of primary teeth, or loss of p e r m a n e n t teeth; however, in o t h e r patients, the origin may be primarily skeletal in nature in which an asymmetric maxilla or, m o r e likely, an asymmetric m a n d i b l e is present. T h e first step in the diagnosis and t r e a t m e n t p l a n n i n g of all patients is to identify these asymmetries and to differentiate be-
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From the Department of Orthodontics, School of Dental Medicine, University of Connecticut Health CentG Farmington, CT. Address correspondence to Charles J. Burstone, DDS, MS, Professor, Department of' Orthodontics, School of Dental Medicine, University of Connecticut Health Cent~ Farmington, CT 06030. Copyright © 1998 by W.B. Saunders Company 1073-8746/98/0403-000558. 00/0
tween those that are of a dental or a skeletal cause. It is only t h e n that the clinician can make a valid decision c o n c e r n i n g the n e e d for surgery or a nonsurgical a p p r o a c h and, if the a p p r o a c h is nonsurgical, if extraction or n o n e x t r a c t i o n is the t r e a t m e n t of choice. The diagnosis of skeletal or dental asymmetry can be accomplished by an overall evaluation of the patient's skeletal and soft-tissue facial pattern. Radiographs, such as the posteroanterior (PA) and submental views, are particularly useful in making this type of diagnosis. T h e submental vertex view helps to m o r e precisely diagnose the nature of the asymmetry, particularly if it is a m a n d i b u l a r problem. Specialized radiographs, such as c o m p u t e d t o m o g r a p h i c scans and the use of stereometry with or without implants, offer m u c h i n f o r m a t i o n but are too d e m a n d i n g for the average patient. T h e soft tissues of the face also offer a clue to any existing skeletal problem. Close observation during the clinical examination, both f r o m a frontal and inferior aspect, along with o r i e n t e d facial photographs, is a necessary r e q u i r e m e n t for p r o p e r diagnosis. T h e cephalometric a p p r o a c h to the differentiation of skeletal asymmetries regarding both their nature and m a g n i t u d e is b e y o n d the scope of this article. The emphasis here is on the use of teeth as markers to make this determination. By evaluating parameters such as axial inclinations of teeth and the a m o u n t of space available, valid j u d g m e n t s can be m a d e to assist in developing an appropiate t r e a t m e n t plan.
Seminars in Orthodontics, Vol 4, No 3 (September), 1998: pp 153-164
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Differential Diagnosis Based on Tooth Position: The Posterior Teeth T h e starting position of any evaluation of asymmetric occlusion is centric relation. A l t h o u g h there may be some a r g u m e n t about what is the correct position of the m a n d i b l e and the condyle in occlusion, a g o o d reference is centric relation rather than centric occlusion. Centric occlusion can be confusing because many patients show m a n d i b u l a r shifts that can make the asymmetry appear either m o r e or less severe. A patient with asymmetric occlusion in centric occlusion is shown in Figure 1, in which the right side is in Class II and the left side is in Class I occlusion. During the initial stages of treatment, in which simple leveling occurred, the occlusion c h a n g e d to a m o r e symmetric Class II occlusion as the m a n d i b l e was repositioned close to centric relation. If the t r e a t m e n t plan was based on the original improperly t r i m m e d models in centric occlusion, subsequent t r e a u n e n t could lead to significant errors in t r e a t m e n t planning, such as asymmetric extraction and the use of asymmetric mechanics. For this reason, it is r e c o m m e n d e d that all models be t r i m m e d in centric relation. Centric relation can be established by manipulation of the mandible, the use of splints where tight musculature
prevents easy m a n d i b u l a r manipulation, or, as in the case shown, therapeutic diagnosis can be helpful. In therapeutic diagnosis, some tooth m o v e m e n t is accomplished, such as crossbite correction by expansion dentally or by skeletal expansion with rapid maxillary expansion or o t h e r m i n o r tooth m o v e m e n t before the final treatment plan is established. After this initial m i n o r t r e a t m e n t stage, it is usually easier to establish a correct centric relation. An occlusal plane should be established that is the t r e a t m e n t plane of occlusion. T h e emphasis is on the word " p l a n e , " which is three-dimensional in nature so an occlusal line can be evaluated either as a lateral or a frontal line. T h e occlusal plane and dental axial inclinations m e a s u r e d to this plane can t h e n be used to establish the presence of either a dental or skeletal asymmetry. This supplements the previous database of the facial bones that was established from the clinical examination, photographs, and radiographs. Figure 2 shows a Class I occlusion on the right side and Class II occlusion on the left. The u p p e r left first molar is mesially inclined. Simulation of what a simple single force could accomplish can be p e r f o r m e d by mentally uprighting the tooth a r o u n d a p o i n t a little below the center of resistance (near the center of the
Figure 1. Pseudoasymmetry. Centric occlusion. (A) Right-side Class II. (B) Left-side Class I. After initial leveling, the m o l a r relationship is m o r e symmetric (C, D). Mandible repositioned to centric relation.
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root). A couple would also a p p r o a c h rotating the tooth a r o u n d this point. With single forces, there is little d e m a n d on a n c h o r a g e and, because teeth migrate usually by tipping, visualization of u p r i g h t i n g can help differentiate a dental p r o b l e m from a skeletal problem. In Figure 2, it can be seen that such u p r i g h t i n g of the u p p e r first m o l a r would place the left side into Class I; hence, the diagnosis is a dental asymmetry. C o m p a r e this asymmetry to Figure 3, in which the axial inclinations of the u p p e r molars are n o r m a l and a skeletal Class II is present. If the u p p e r left molar had a distal axial crown inclination, equalizing axial inclinations so that both sides are identical would make the Class II left side even m o r e asymmetric. Observation of mesiodistal axial inclinations of posterior teeth c a n n o t always differentiate dental from skeletal origins of asymmetry because migration of a tooth may have o c c u r r e d early in its eruption, p r o d u c i n g little tipping. O t h e r dental guides m i g h t be helpful, including the rotation (mesial-in) of the u p p e r m o l a r and the a m o u n t of r o o m posteriorly either in the tuberosity or the ramus. In c o m p a r i n g the differences of axial inclination between the right and left sides, it is i m p o r t a n t to maintain a constant plane o f occlusion. T h e relevant differentiation to make is the difference in axial inclination between the right and left sides and, only secondarily, which axial inclinations m i g h t be m o r e correct for the patient. T h e same a p p r o a c h can be used to evaluate unilateral posterior crossbites. In Figure 4, a dental crossbite is shown. Mentally u p r i g h t i n g the u p p e r left m o l a r would correct the crossbite. Conversely, in Figure 5, uprighting the u p p e r left m o l a r so that its axial inclination would be the same as the right side would make the crossbite worse; hence, this is a skeletal crossbite.
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Figure 3. Class II subdivision. Skeletal asymmetry. All molars have n o r m a l axial inclinations. Asymmetric Class I occlusion is shown in Figure 6 where the axial inclinations are not symmetric and the u p p e r left m o l a r is compensating. U p r i g h t i n g the tooth a r o u n d the center of the root would p r o d u c e Class II occlusion o f the left side; indicating a skeletal discrepancy that is masked. In some patient.s, there may be a difference in buccolingual axial inclinations f r o m right to left with no crossbite. In Figure 7, the teeth have c o m p e n s a t e d for a skeletal discrepancy, and equalizing the axial inclinations on the left side with the right would p r o d u c e a crossbite. T h e clinician should carefully evaluate the mesiodistal and buccolingual axial inclinations o f all the posterior teeth, and n o t only the molar teeth, because this allows for differentiation of skeletal f r o m dental problems. This a p p r o a c h provides the
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Figure 2. Class II subdivision. Dental asymmetry. Left u p p e r molar is tipped mesially.
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Figure 4. Unilateral crossbite of dental origin. U p p e r left molar leans toward the lingual.
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Figure 5. Unilateral crossbite of skeletal origin. Molars have n o r m a l axial inclinations. U p p e r left m o l a r leans slightly toward the buccal. p r o p e r b a c k g r o u n d to d e t e r m i n e later, during treatm e n t planning, w h e t h e r c o m p e n s a t o r y axial inclinations should be m a i n t a i n e d or produced.
Differential Diagnosis of Midline Discrepancies O n e of the challenges in treatment p l a n n i n g and t r e a t m e n t is the correct p l a c e m e n t of the u p p e r and lower dental midlines. Not only must the dental midlines correspond, but they must be in a p r o p e r relationship to the face. A n u m b e r of criteria have b e e n used to establish the positioning of the u p p e r and lower dental midlines. S o m e of these are some-
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Figure 7. C o m p e n s a t o r y axial inclination on the left side. Potential unilateral crossbite. what arbitrary and can lead to i m p r o p e r diagnosis and treatment. A skeletal midline can be established using the PA head film. F r o m horizontal planes in cranial base, perpendiculars are drawn through crista galli or some o t h e r midline point. T h e fallacy o f establishing a midsagittal plane in this m a n n e r lies in the fact that the horizontal planes may n o t be parallel to each o t h e r and are often difficult to establish. Also, any
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Figure 6. C o m p e n s a t o r y axial inclination gives Class I occlusion. Potential unilateral Class II occlusion on the left side.
Figure 8. Facial midline is d e t e r m i n e d by soft-tissue factors: the p h i h r u m and distance of the canine to the corners of the mouth.
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Figure 11. Upper dental ntidline to the right of the lower midline. Skeletal problem with apical base discrepancy.
Figure 9. Incisor apical base discrepancy between upper and lower arches. Arbitrary skeletal midsagittal plane passes through the lower apical base midline.
Figure 10, Upper midline to the right without an apical base discrepancy. Upper incisors are tipped toward the right.
deviation in the horizontal plane and the perpendicular drawn to it can lead to large errors in establishing a dental midline. Others have tried to establish a midline by bisecting the distance between bilateral points on the greater wing of sphenoid or the orbits or other lateral points on the outside of the skull. Even in the most symmetric individuals, there are differences in width between right and left sides; hence, bisecting the distance between two corresponding points can lead to an erroneous midline. Sometimes the median palatal raphe is used as a guide. The raphe may be misleading because of error in establishing a perpen-
Figure 12. Dental midlines correspond. Apical base discrepancy is masked by compensatory tipping of the upper incisors to the left side.
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Figure 13. Dental midline discrepancy without apical base discrepancy. Lower incisors are easily tipped to the left with a single force. Before (A) After (B).
Figure 14. U p p e r dental midline to right. No apical base discrepancy. Only simple tipping of the u p p e r incisors is required. Before (A) After (B). dicular to the raphe and because many raphes are not linear, but display curvature. T h e arbitrary planes that have b e e n discussed are n o t based on realities that can benefit the patient. Two o t h e r concepts can be used that are m o r e realistic for establishing a plane on which the dental midlines should be placed; namely, the facial midline and the apical base midlines. A c o m m o n p r o c e d u r e to establish the facial midline is to take a piece of dental floss and c o n n e c t points at glabella or nasion, subnasale and p o g o n i o n . This can lead to e r r o n e o u s results because of inaccuracy in identifying the points and the parallax required in visualizing the points. In addition, if there is any type of m a n d i b u l a r asymmetry, the three points would not correspond. The facial midline is an aesthetic midline; and a midline that the patient can easily identify as the correct midline for the tace. Patients do n o t take dental floss and place it in front of their face to evaluate the midline. They look at o t h e r factors, and it is these factors that will now be discussed as a better guide to midline placement. T h e center of the p h i l t r u m is a g o o d guide to the placem e n t of the maxillary dental midline. T h e "V" at the
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Figure 15. Greater condylar growth on the right side should p r o d u c e buccal crossbite of the mandibular arch on the left side.
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Figure 16. Severe skeletal asymmetry Class III right (A), Class II left (B). Lower dental midline to left (C). Good arch harmony with little crossbite. Other details in Figures 17 and 18.
Figure 17. Compensatory axial inclinations. Canine leans buccally on left side, frontal view (A). Upper left molar leans toward buccal more than the right molar, viewed from posterior (B). Lower left molar leans toward lingual, viewed from posterior (C).
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vermillion b o r d e r forms a g o o d landmark that is easily identified by orthodontists and patients (Fig 8). Ano t h e r guide is to look at the distance between the canine or first p r e m o l a r and the c o r n e r of the mouth. If the midline is properly positioned, the patient will see the same a m o u n t of tooth exposure on the right and left side. T h e patient is m o r e apt to look at soft-tissue guides, such as the p h i l t r u m and the corners of the mouth, in evaluating the dental midline, than any arbitrary string that is placed in front of the face. In addition to the facial midline, skeletal asymmetry as viewed from the front of the patient should be
studied carefully. A tracing is m a d e of the PA head film. A t r e a t m e n t occlusal plane is established, and to that occlusal plane, the midlines of the maxilla and m a n d i b l e are evaluated. Unfortunately, there are no g o o d landmarks to accurately p i n p o i n t these midlines. A g o o d c o m p r o m i s e is to use the teeth as markers, as was previously d o n e to evaluate the posterior occlusion. Points are identified approximately at the center of the roots of the u p p e r incisors and the lower incisors. This m e d i a n p o i n t of the roots is called the apical base point. Perpendiculars are drawn to the occlusal plane f r o m these points to evaluate if an apical base midline discrepency exists. Apical base
Figure 18. Occlusal view of models. The wider u p p e r arch (A) and the narrower lower arch (B) on the left side compensating for the crossbite tendency. PA tracing showing the skeletal asymmetry and dental compensations (C).
Diagnosis and TreatmentPlanning
discrepancies imply some type of skeletal asymmetry with either an asymmetric maxilla or, most likely, an asymmetric mandible. It is possible, however, to have early drift of teeth, particularly with a unilaterally missing lateral incisor where an apical base discrepancy exists without any skeletal asymmetry showing on the face. In Figure 9, a patient with an apical base midline discrepancy is shown. T h e lower incisor midline lies on an arbitrary skeletal midline t h r o u g h m e d i a n structures. The lower apical base also lies on this line, and the u p p e r apical base p o i n t is to the patient's right. W h e n there is an apical base discrepancy, t r e a t m e n t becomes m o r e difficult because translation of teeth across the midline may be required. With translation, a n c h o r a g e loss can p r o d u c e skewing or rotation of the arches with undesirable side effects. F r o m the clinical examination or the study casts, axial inclinations can be used to d e t e r m i n e if an apical base discrepancy exists. This can be accomplished by mentally uprighting teeth so the axial inclinations on the right and left side are equalized, or visualizing where the centers of the roots might be so that a p e r p e n d i c u l a r can be d r o p p e d to the occlusal plane. Figure 10 shows a midline discrepancy with the u p p e r incisors to the right of the lowers. By mentally uprighting the incisors to equalize their axial inclinations, midlines would c o r r e s p o n d and a dental midline discrepancy therefore exists. In contrast, in Figure 11, a skeletal discrepancy is shown. Equalizing axial inclinations would not help the midline. The midlines b e c o m e further apart as the teeth are uprighted. This is an example of a skeletal or apical base discrepancy. T h e r e are patients who may have no discrepancy between the u p p e r and lower dental midlines, and yet a skeletal apical base discrepancy could exist. Such a situation is shown in Figure 12, in which the u p p e r teeth have tipped to the left. U p r i g h t i n g these teeth would p r o d u c e a midline discrepancy with the u p p e r midline to the patient's right. In many t r e a t m e n t plans, compensatory axial inclinations should be mainrained at least in part to ensure p r o p e r correction in apical base discrepancies for which no surgery is planned. If a midline discrepancy between the u p p e r and lower is present and no apical base discrepancy is observed, t r e a t m e n t is simplified because simple single forces can be used to tip teeth to correct the midlines so they properly correspond. The mechanics are simple, and they usually will n o t p r o d u c e major side effects if p e r f o r m e d appropriately. Conversely, where there is a true apical base discrepancy, the translatory mechanics r e q u i r e d b e c o m e m o r e difficult and are a limitation to the a m o u n t of mesiodistal m o v e m e n t possible. In Figure 13A, the lower dental midline is to the right of the facial midline, and no apical base discrepancy exists. Even without a head film, the lower
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Figure 19. C o r r e c t i o n of right and left mesiodistal occlusal differences requires m o v e m e n t a r o u n d the arch. Arrows show possible direction of tooth movement. incisors can be mentally u p r i g h t e d to see the midlines correspond. T h e finished case is shown in Figure 13B, in which simple tooth m o v e m e n t by tipping allowed the midlines to correspond. In Figure 14, the u p p e r midline is to the patient's right. No apical base discrepancy exists, so the incisors very easily tipped to the left after extraction therapy. No wires or appli-
Figure 20. Crisscross elastics and or c o m b i n e d Class II and Class IIl elastics can p r o d u c e rotation of the entire arch, which is n o t usually desirable,
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ance's were used on the incisors because the incisors followed the canines and were self-correcting by means of the transeptal fibers.
Arch Form Symmetry and Arch Correspondence Because skeletal asymmetries are common, it is important to review the role of compensations in the dental arch that occur naturally. If a skeletal asymmetry is produced by a mandible that has grown more horizontally on one side than the otheL a crossbite would normally be expected. In the diagram shown in Figure 15, the added mandibular growth on the right side is responsible not only for Class III occlusion on the right side and Class II occlusion on the left, but a dental midline shift with the mandibular midline moving to the left. Also, a crossbite would be expected with mandibular buccal overjet appearing on the patient's left side. Although crossbites can be observed, usually the magnitude of the crossbite is minimized by compensatory movement and axial inclinations of the teeth. A patient with this asymmetric relationship is shown in Figure 16. The right side is Class III and the left side approaches Class II. The lower midline is to the left of the upper midline. Nevertheless, the amount of overjet and crossbite tendency is relatively small. It is important to look in greater detail to see why dental compensations have minimized this crossbite tendency. Looking from the frontal view, it is noted that the left canine leans more toward the buccal than the right canine (Fig 17A). Looking from the posterior, the upper left molar leans more toward the buccal than the upper fight molar (Fig 17B). In the lower
arch, the left molar leans toward the lingual more than the right molar (Fig 17C). These compensations are produced by muscle forces that have effectively eliminated most of the crossbite that would have been expected. The occlusal view of both the upper and lower arches shows that, relative to the median palatal raphe, arch width is not symmetric right to left. In the upper, the left side is wider (Fig 18A) and, in the lower arch, the width relative to the median palatal raphe is smaller on the left side (Fig 18B). The tracing of the PA head film confirms the skeletal asymmetry and the compensatory migration of the teeth that minimized the crossbite (Fig 18C). What is the significance of these buccolingual axial inclination compensations? The patient shown has an extreme skeletal discrepancy that requires orthognathic surgery. In preparation for tile surgery, for the bones to be positioned correctly, the axial inclinations should be equalized so that no asymmetry will be present at the end of treatment. There are many patients who have skeletal problems that are not so extreme or in whom the treatment of choice or preference would be nonsurgical. In these patients, it is necessary to maintain the asymmetry of the axial inclinations. It would be an error to correct the axial inclinations by placing symmetric brackets with straight wires that produce torque on the individual teeth. Such mechanics, of course, would lead to the production of a crossbite. It should be recognized that compensation in the form of changes in the axial inclinations of teeth as in arch width has resulted from muscular activity. Idealistically, orthodontists have been taught that the most desirable arch form is symmetric. In some patients this may be true; however, in nonskel-
OP FH
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Figure 21. Some skeletal asymmetries may have one ramus longer with a cant to the occlusal plane (OP). Axial inclinations that are compensatory will appear more symmetric to OP than to Frankfort horizontal (FH).
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etal t r e a t m e n t of a patient with skeletal asymmetry, these compensations should be m a i n t a i n e d to treat to an asymmetric arch. T h e malocclusion of a patient who presents with Class II occlusion on one side and Class III or Class I occlusion on the o t h e r side can either be of skeletal or dental origin or of both. If the origin is dental, it is clear that the tooth m o v e m e n t r e q u i r e d is m o v e m e n t a r o u n d the arch. This is n o t an en masse m o v e m e n t of the entire arch but, rather, m o v e m e n t of the teeth a r o u n d the arch like pearls on a chain. To reach this goal, distal m o v e m e n t or extraction may be required. As previously discussed, if the discrepancy is skeletal in origin and no crossbite exists, the m o v e m e n t is still a r o u n d the arch if no orthognathic surgery is p l a n n e d (Fig 19). Sometimes orthodontists will try to correct an asymmetric posterior occlusion by the use of Class II elastics on o n e side, Class III elastics on the othm, a n d / o r anterior crisscross elastics. T h e effects of Class II and Class Ill elastics are shown in Figure 20. T h e m o v e m e n t is an en masse m o v e m e n t in which the entire arch is rotated a r o u n d its center o f resistance. Not only is this m o v e m e n t difficult to achieve, but it can lead to crossbite and lack of arch harmony.
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Occlusal Plane Considerations T h e patient who is treated surgically should have the occlusal plane, as evaluated f r o m the frontal view, parallel to facial structures, such as the eyes. In the nonsurgical patient with a skeletal asymmetry, there may be a cant to the plane of occlusion relative to the face. This cant is not easily altered f r o m a line c o n n e c t i n g posterior teeth because of m e c h a n i c a l difficulties in i n t r u d i n g entire posterior segments. F u r t h e r m o r e , the lips may also be angled so that a m o r e aesthetic relationship of the canted occlusion and the lips is observed. Figure 21 shows compensatory differences between molar axial inclinations. T h e u p p e r left molar is leaning toward the buccal and the right m o l a r is leaning toward the lingual. Relative to the entire occlusal plane based on the face (such as a line c o n n e c t i n g the pupils of the eyes), there is a marked difference. In some patients, a vertical asymmetry may be present in which the right side of the m a n d i b l e has grown vertically m o r e than the left, p r o d u c i n g a cant in the occlusal plane. Notice that this plane, which would be a t r e a t m e n t plane of occlusion for a nonsurgical patient, minimizes the axial inclination difference. Study casts that are t r i m m e d to the canted occlusal plane may n o t show as m u c h variation in axial inclination between the right and the left sides as would be observed f r o m the PA h e a d film, in which a truer horizontal plane is used for orientation (Fig 21).
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Figure 22.
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An anterior crisscross elastic produces the undesirable side effect of canting the occlusal plane (A). Patient showing unaesthetic canting p r o d u c e d by anterior crisscross elastics. Mechanics to move the incisors a r o u n d the arch should have b e e n used (B).
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It may be desirable to treat to a canted occlusal plane if a skeletal asymmetry is present and very undesirable in a skeletally symmetric patient. O n e of the undesirable effects of the use of an anterior cFisscross elastic is that it can cant the plane of occlusion. T h e patient in Figure 22 had an anterior crisscross elastic attached f r o m the u p p e r right to the lower left. Note that the occlusal plane has canted down to the patient's right side.
Summary T h e r e are many t r e a t m e n t options for patients who show asymmetries in occlusion. These include orthog-
nathic surgery, orthopedics and orthodontics employing extraction or n o n e x t r a c t i o n therapy. Part of the decision in t r e a t m e n t selection and the detailed treatm e n t plan that d e t e r m i n e s tooth position in threedimensional space is based on differentiating skeletal from dental problems. This article has c o n c e n t r a t e d on the utility of using tooth position, mainly axial inclinations, as a diagnostic tool. Such i n f o r m a t i o n can be gleaned from the study casts and can serve as a guide to help in developing a c o m p r e h e n s i v e and valid t r e a t m e n t plan for the patient. This is n o t to suggest that an overall evaluation be ignored, because the clinical examination and the use of p r o p e r cephalometric techniques are equally important.
by W,B. Saunders Company
t is c o m m o n to find asymmetric occlusal relationships in patients requiring o r t h o d o n t i c treatment. Examples include a Class II occlusion on one side of the arch with a Class I or Class III occlusion on the other. T h e r e may be lack of midline c o r r e s p o n d e n c e between the u p p e r and lower arches or both midlines may n o t be symmetrically placed in the face. Unilateral crossbites can exist and arch f o r m may n o t be symmetric, or u p p e r and lower arches may n o t be congruent. T h e cause of these asymmetries can be multivariate. In some patients, the p r o b l e m originated with a b n o r m a l dental eruption, p r e m a t u r e loss of primary teeth, or loss of p e r m a n e n t teeth; however, in o t h e r patients, the origin may be primarily skeletal in nature in which an asymmetric maxilla or, m o r e likely, an asymmetric m a n d i b l e is present. T h e first step in the diagnosis and t r e a t m e n t p l a n n i n g of all patients is to identify these asymmetries and to differentiate be-
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From the Department of Orthodontics, School of Dental Medicine, University of Connecticut Health CentG Farmington, CT. Address correspondence to Charles J. Burstone, DDS, MS, Professor, Department of' Orthodontics, School of Dental Medicine, University of Connecticut Health Cent~ Farmington, CT 06030. Copyright © 1998 by W.B. Saunders Company 1073-8746/98/0403-000558. 00/0
tween those that are of a dental or a skeletal cause. It is only t h e n that the clinician can make a valid decision c o n c e r n i n g the n e e d for surgery or a nonsurgical a p p r o a c h and, if the a p p r o a c h is nonsurgical, if extraction or n o n e x t r a c t i o n is the t r e a t m e n t of choice. The diagnosis of skeletal or dental asymmetry can be accomplished by an overall evaluation of the patient's skeletal and soft-tissue facial pattern. Radiographs, such as the posteroanterior (PA) and submental views, are particularly useful in making this type of diagnosis. T h e submental vertex view helps to m o r e precisely diagnose the nature of the asymmetry, particularly if it is a m a n d i b u l a r problem. Specialized radiographs, such as c o m p u t e d t o m o g r a p h i c scans and the use of stereometry with or without implants, offer m u c h i n f o r m a t i o n but are too d e m a n d i n g for the average patient. T h e soft tissues of the face also offer a clue to any existing skeletal problem. Close observation during the clinical examination, both f r o m a frontal and inferior aspect, along with o r i e n t e d facial photographs, is a necessary r e q u i r e m e n t for p r o p e r diagnosis. T h e cephalometric a p p r o a c h to the differentiation of skeletal asymmetries regarding both their nature and m a g n i t u d e is b e y o n d the scope of this article. The emphasis here is on the use of teeth as markers to make this determination. By evaluating parameters such as axial inclinations of teeth and the a m o u n t of space available, valid j u d g m e n t s can be m a d e to assist in developing an appropiate t r e a t m e n t plan.
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Differential Diagnosis Based on Tooth Position: The Posterior Teeth T h e starting position of any evaluation of asymmetric occlusion is centric relation. A l t h o u g h there may be some a r g u m e n t about what is the correct position of the m a n d i b l e and the condyle in occlusion, a g o o d reference is centric relation rather than centric occlusion. Centric occlusion can be confusing because many patients show m a n d i b u l a r shifts that can make the asymmetry appear either m o r e or less severe. A patient with asymmetric occlusion in centric occlusion is shown in Figure 1, in which the right side is in Class II and the left side is in Class I occlusion. During the initial stages of treatment, in which simple leveling occurred, the occlusion c h a n g e d to a m o r e symmetric Class II occlusion as the m a n d i b l e was repositioned close to centric relation. If the t r e a t m e n t plan was based on the original improperly t r i m m e d models in centric occlusion, subsequent t r e a u n e n t could lead to significant errors in t r e a t m e n t planning, such as asymmetric extraction and the use of asymmetric mechanics. For this reason, it is r e c o m m e n d e d that all models be t r i m m e d in centric relation. Centric relation can be established by manipulation of the mandible, the use of splints where tight musculature
prevents easy m a n d i b u l a r manipulation, or, as in the case shown, therapeutic diagnosis can be helpful. In therapeutic diagnosis, some tooth m o v e m e n t is accomplished, such as crossbite correction by expansion dentally or by skeletal expansion with rapid maxillary expansion or o t h e r m i n o r tooth m o v e m e n t before the final treatment plan is established. After this initial m i n o r t r e a t m e n t stage, it is usually easier to establish a correct centric relation. An occlusal plane should be established that is the t r e a t m e n t plane of occlusion. T h e emphasis is on the word " p l a n e , " which is three-dimensional in nature so an occlusal line can be evaluated either as a lateral or a frontal line. T h e occlusal plane and dental axial inclinations m e a s u r e d to this plane can t h e n be used to establish the presence of either a dental or skeletal asymmetry. This supplements the previous database of the facial bones that was established from the clinical examination, photographs, and radiographs. Figure 2 shows a Class I occlusion on the right side and Class II occlusion on the left. The u p p e r left first molar is mesially inclined. Simulation of what a simple single force could accomplish can be p e r f o r m e d by mentally uprighting the tooth a r o u n d a p o i n t a little below the center of resistance (near the center of the
Figure 1. Pseudoasymmetry. Centric occlusion. (A) Right-side Class II. (B) Left-side Class I. After initial leveling, the m o l a r relationship is m o r e symmetric (C, D). Mandible repositioned to centric relation.
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root). A couple would also a p p r o a c h rotating the tooth a r o u n d this point. With single forces, there is little d e m a n d on a n c h o r a g e and, because teeth migrate usually by tipping, visualization of u p r i g h t i n g can help differentiate a dental p r o b l e m from a skeletal problem. In Figure 2, it can be seen that such u p r i g h t i n g of the u p p e r first m o l a r would place the left side into Class I; hence, the diagnosis is a dental asymmetry. C o m p a r e this asymmetry to Figure 3, in which the axial inclinations of the u p p e r molars are n o r m a l and a skeletal Class II is present. If the u p p e r left molar had a distal axial crown inclination, equalizing axial inclinations so that both sides are identical would make the Class II left side even m o r e asymmetric. Observation of mesiodistal axial inclinations of posterior teeth c a n n o t always differentiate dental from skeletal origins of asymmetry because migration of a tooth may have o c c u r r e d early in its eruption, p r o d u c i n g little tipping. O t h e r dental guides m i g h t be helpful, including the rotation (mesial-in) of the u p p e r m o l a r and the a m o u n t of r o o m posteriorly either in the tuberosity or the ramus. In c o m p a r i n g the differences of axial inclination between the right and left sides, it is i m p o r t a n t to maintain a constant plane o f occlusion. T h e relevant differentiation to make is the difference in axial inclination between the right and left sides and, only secondarily, which axial inclinations m i g h t be m o r e correct for the patient. T h e same a p p r o a c h can be used to evaluate unilateral posterior crossbites. In Figure 4, a dental crossbite is shown. Mentally u p r i g h t i n g the u p p e r left m o l a r would correct the crossbite. Conversely, in Figure 5, uprighting the u p p e r left m o l a r so that its axial inclination would be the same as the right side would make the crossbite worse; hence, this is a skeletal crossbite.
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Figure 3. Class II subdivision. Skeletal asymmetry. All molars have n o r m a l axial inclinations. Asymmetric Class I occlusion is shown in Figure 6 where the axial inclinations are not symmetric and the u p p e r left m o l a r is compensating. U p r i g h t i n g the tooth a r o u n d the center of the root would p r o d u c e Class II occlusion o f the left side; indicating a skeletal discrepancy that is masked. In some patient.s, there may be a difference in buccolingual axial inclinations f r o m right to left with no crossbite. In Figure 7, the teeth have c o m p e n s a t e d for a skeletal discrepancy, and equalizing the axial inclinations on the left side with the right would p r o d u c e a crossbite. T h e clinician should carefully evaluate the mesiodistal and buccolingual axial inclinations o f all the posterior teeth, and n o t only the molar teeth, because this allows for differentiation of skeletal f r o m dental problems. This a p p r o a c h provides the
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Figure 2. Class II subdivision. Dental asymmetry. Left u p p e r molar is tipped mesially.
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Figure 4. Unilateral crossbite of dental origin. U p p e r left molar leans toward the lingual.
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Figure 5. Unilateral crossbite of skeletal origin. Molars have n o r m a l axial inclinations. U p p e r left m o l a r leans slightly toward the buccal. p r o p e r b a c k g r o u n d to d e t e r m i n e later, during treatm e n t planning, w h e t h e r c o m p e n s a t o r y axial inclinations should be m a i n t a i n e d or produced.
Differential Diagnosis of Midline Discrepancies O n e of the challenges in treatment p l a n n i n g and t r e a t m e n t is the correct p l a c e m e n t of the u p p e r and lower dental midlines. Not only must the dental midlines correspond, but they must be in a p r o p e r relationship to the face. A n u m b e r of criteria have b e e n used to establish the positioning of the u p p e r and lower dental midlines. S o m e of these are some-
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Figure 7. C o m p e n s a t o r y axial inclination on the left side. Potential unilateral crossbite. what arbitrary and can lead to i m p r o p e r diagnosis and treatment. A skeletal midline can be established using the PA head film. F r o m horizontal planes in cranial base, perpendiculars are drawn through crista galli or some o t h e r midline point. T h e fallacy o f establishing a midsagittal plane in this m a n n e r lies in the fact that the horizontal planes may n o t be parallel to each o t h e r and are often difficult to establish. Also, any
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Figure 6. C o m p e n s a t o r y axial inclination gives Class I occlusion. Potential unilateral Class II occlusion on the left side.
Figure 8. Facial midline is d e t e r m i n e d by soft-tissue factors: the p h i h r u m and distance of the canine to the corners of the mouth.
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Figure 11. Upper dental ntidline to the right of the lower midline. Skeletal problem with apical base discrepancy.
Figure 9. Incisor apical base discrepancy between upper and lower arches. Arbitrary skeletal midsagittal plane passes through the lower apical base midline.
Figure 10, Upper midline to the right without an apical base discrepancy. Upper incisors are tipped toward the right.
deviation in the horizontal plane and the perpendicular drawn to it can lead to large errors in establishing a dental midline. Others have tried to establish a midline by bisecting the distance between bilateral points on the greater wing of sphenoid or the orbits or other lateral points on the outside of the skull. Even in the most symmetric individuals, there are differences in width between right and left sides; hence, bisecting the distance between two corresponding points can lead to an erroneous midline. Sometimes the median palatal raphe is used as a guide. The raphe may be misleading because of error in establishing a perpen-
Figure 12. Dental midlines correspond. Apical base discrepancy is masked by compensatory tipping of the upper incisors to the left side.
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Figure 13. Dental midline discrepancy without apical base discrepancy. Lower incisors are easily tipped to the left with a single force. Before (A) After (B).
Figure 14. U p p e r dental midline to right. No apical base discrepancy. Only simple tipping of the u p p e r incisors is required. Before (A) After (B). dicular to the raphe and because many raphes are not linear, but display curvature. T h e arbitrary planes that have b e e n discussed are n o t based on realities that can benefit the patient. Two o t h e r concepts can be used that are m o r e realistic for establishing a plane on which the dental midlines should be placed; namely, the facial midline and the apical base midlines. A c o m m o n p r o c e d u r e to establish the facial midline is to take a piece of dental floss and c o n n e c t points at glabella or nasion, subnasale and p o g o n i o n . This can lead to e r r o n e o u s results because of inaccuracy in identifying the points and the parallax required in visualizing the points. In addition, if there is any type of m a n d i b u l a r asymmetry, the three points would not correspond. The facial midline is an aesthetic midline; and a midline that the patient can easily identify as the correct midline for the tace. Patients do n o t take dental floss and place it in front of their face to evaluate the midline. They look at o t h e r factors, and it is these factors that will now be discussed as a better guide to midline placement. T h e center of the p h i l t r u m is a g o o d guide to the placem e n t of the maxillary dental midline. T h e "V" at the
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Figure 15. Greater condylar growth on the right side should p r o d u c e buccal crossbite of the mandibular arch on the left side.
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Figure 16. Severe skeletal asymmetry Class III right (A), Class II left (B). Lower dental midline to left (C). Good arch harmony with little crossbite. Other details in Figures 17 and 18.
Figure 17. Compensatory axial inclinations. Canine leans buccally on left side, frontal view (A). Upper left molar leans toward buccal more than the right molar, viewed from posterior (B). Lower left molar leans toward lingual, viewed from posterior (C).
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vermillion b o r d e r forms a g o o d landmark that is easily identified by orthodontists and patients (Fig 8). Ano t h e r guide is to look at the distance between the canine or first p r e m o l a r and the c o r n e r of the mouth. If the midline is properly positioned, the patient will see the same a m o u n t of tooth exposure on the right and left side. T h e patient is m o r e apt to look at soft-tissue guides, such as the p h i l t r u m and the corners of the mouth, in evaluating the dental midline, than any arbitrary string that is placed in front of the face. In addition to the facial midline, skeletal asymmetry as viewed from the front of the patient should be
studied carefully. A tracing is m a d e of the PA head film. A t r e a t m e n t occlusal plane is established, and to that occlusal plane, the midlines of the maxilla and m a n d i b l e are evaluated. Unfortunately, there are no g o o d landmarks to accurately p i n p o i n t these midlines. A g o o d c o m p r o m i s e is to use the teeth as markers, as was previously d o n e to evaluate the posterior occlusion. Points are identified approximately at the center of the roots of the u p p e r incisors and the lower incisors. This m e d i a n p o i n t of the roots is called the apical base point. Perpendiculars are drawn to the occlusal plane f r o m these points to evaluate if an apical base midline discrepency exists. Apical base
Figure 18. Occlusal view of models. The wider u p p e r arch (A) and the narrower lower arch (B) on the left side compensating for the crossbite tendency. PA tracing showing the skeletal asymmetry and dental compensations (C).
Diagnosis and TreatmentPlanning
discrepancies imply some type of skeletal asymmetry with either an asymmetric maxilla or, most likely, an asymmetric mandible. It is possible, however, to have early drift of teeth, particularly with a unilaterally missing lateral incisor where an apical base discrepancy exists without any skeletal asymmetry showing on the face. In Figure 9, a patient with an apical base midline discrepancy is shown. T h e lower incisor midline lies on an arbitrary skeletal midline t h r o u g h m e d i a n structures. The lower apical base also lies on this line, and the u p p e r apical base p o i n t is to the patient's right. W h e n there is an apical base discrepancy, t r e a t m e n t becomes m o r e difficult because translation of teeth across the midline may be required. With translation, a n c h o r a g e loss can p r o d u c e skewing or rotation of the arches with undesirable side effects. F r o m the clinical examination or the study casts, axial inclinations can be used to d e t e r m i n e if an apical base discrepancy exists. This can be accomplished by mentally uprighting teeth so the axial inclinations on the right and left side are equalized, or visualizing where the centers of the roots might be so that a p e r p e n d i c u l a r can be d r o p p e d to the occlusal plane. Figure 10 shows a midline discrepancy with the u p p e r incisors to the right of the lowers. By mentally uprighting the incisors to equalize their axial inclinations, midlines would c o r r e s p o n d and a dental midline discrepancy therefore exists. In contrast, in Figure 11, a skeletal discrepancy is shown. Equalizing axial inclinations would not help the midline. The midlines b e c o m e further apart as the teeth are uprighted. This is an example of a skeletal or apical base discrepancy. T h e r e are patients who may have no discrepancy between the u p p e r and lower dental midlines, and yet a skeletal apical base discrepancy could exist. Such a situation is shown in Figure 12, in which the u p p e r teeth have tipped to the left. U p r i g h t i n g these teeth would p r o d u c e a midline discrepancy with the u p p e r midline to the patient's right. In many t r e a t m e n t plans, compensatory axial inclinations should be mainrained at least in part to ensure p r o p e r correction in apical base discrepancies for which no surgery is planned. If a midline discrepancy between the u p p e r and lower is present and no apical base discrepancy is observed, t r e a t m e n t is simplified because simple single forces can be used to tip teeth to correct the midlines so they properly correspond. The mechanics are simple, and they usually will n o t p r o d u c e major side effects if p e r f o r m e d appropriately. Conversely, where there is a true apical base discrepancy, the translatory mechanics r e q u i r e d b e c o m e m o r e difficult and are a limitation to the a m o u n t of mesiodistal m o v e m e n t possible. In Figure 13A, the lower dental midline is to the right of the facial midline, and no apical base discrepancy exists. Even without a head film, the lower
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Figure 19. C o r r e c t i o n of right and left mesiodistal occlusal differences requires m o v e m e n t a r o u n d the arch. Arrows show possible direction of tooth movement. incisors can be mentally u p r i g h t e d to see the midlines correspond. T h e finished case is shown in Figure 13B, in which simple tooth m o v e m e n t by tipping allowed the midlines to correspond. In Figure 14, the u p p e r midline is to the patient's right. No apical base discrepancy exists, so the incisors very easily tipped to the left after extraction therapy. No wires or appli-
Figure 20. Crisscross elastics and or c o m b i n e d Class II and Class IIl elastics can p r o d u c e rotation of the entire arch, which is n o t usually desirable,
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ance's were used on the incisors because the incisors followed the canines and were self-correcting by means of the transeptal fibers.
Arch Form Symmetry and Arch Correspondence Because skeletal asymmetries are common, it is important to review the role of compensations in the dental arch that occur naturally. If a skeletal asymmetry is produced by a mandible that has grown more horizontally on one side than the otheL a crossbite would normally be expected. In the diagram shown in Figure 15, the added mandibular growth on the right side is responsible not only for Class III occlusion on the right side and Class II occlusion on the left, but a dental midline shift with the mandibular midline moving to the left. Also, a crossbite would be expected with mandibular buccal overjet appearing on the patient's left side. Although crossbites can be observed, usually the magnitude of the crossbite is minimized by compensatory movement and axial inclinations of the teeth. A patient with this asymmetric relationship is shown in Figure 16. The right side is Class III and the left side approaches Class II. The lower midline is to the left of the upper midline. Nevertheless, the amount of overjet and crossbite tendency is relatively small. It is important to look in greater detail to see why dental compensations have minimized this crossbite tendency. Looking from the frontal view, it is noted that the left canine leans more toward the buccal than the right canine (Fig 17A). Looking from the posterior, the upper left molar leans more toward the buccal than the upper fight molar (Fig 17B). In the lower
arch, the left molar leans toward the lingual more than the right molar (Fig 17C). These compensations are produced by muscle forces that have effectively eliminated most of the crossbite that would have been expected. The occlusal view of both the upper and lower arches shows that, relative to the median palatal raphe, arch width is not symmetric right to left. In the upper, the left side is wider (Fig 18A) and, in the lower arch, the width relative to the median palatal raphe is smaller on the left side (Fig 18B). The tracing of the PA head film confirms the skeletal asymmetry and the compensatory migration of the teeth that minimized the crossbite (Fig 18C). What is the significance of these buccolingual axial inclination compensations? The patient shown has an extreme skeletal discrepancy that requires orthognathic surgery. In preparation for tile surgery, for the bones to be positioned correctly, the axial inclinations should be equalized so that no asymmetry will be present at the end of treatment. There are many patients who have skeletal problems that are not so extreme or in whom the treatment of choice or preference would be nonsurgical. In these patients, it is necessary to maintain the asymmetry of the axial inclinations. It would be an error to correct the axial inclinations by placing symmetric brackets with straight wires that produce torque on the individual teeth. Such mechanics, of course, would lead to the production of a crossbite. It should be recognized that compensation in the form of changes in the axial inclinations of teeth as in arch width has resulted from muscular activity. Idealistically, orthodontists have been taught that the most desirable arch form is symmetric. In some patients this may be true; however, in nonskel-
OP FH
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Figure 21. Some skeletal asymmetries may have one ramus longer with a cant to the occlusal plane (OP). Axial inclinations that are compensatory will appear more symmetric to OP than to Frankfort horizontal (FH).
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etal t r e a t m e n t of a patient with skeletal asymmetry, these compensations should be m a i n t a i n e d to treat to an asymmetric arch. T h e malocclusion of a patient who presents with Class II occlusion on one side and Class III or Class I occlusion on the o t h e r side can either be of skeletal or dental origin or of both. If the origin is dental, it is clear that the tooth m o v e m e n t r e q u i r e d is m o v e m e n t a r o u n d the arch. This is n o t an en masse m o v e m e n t of the entire arch but, rather, m o v e m e n t of the teeth a r o u n d the arch like pearls on a chain. To reach this goal, distal m o v e m e n t or extraction may be required. As previously discussed, if the discrepancy is skeletal in origin and no crossbite exists, the m o v e m e n t is still a r o u n d the arch if no orthognathic surgery is p l a n n e d (Fig 19). Sometimes orthodontists will try to correct an asymmetric posterior occlusion by the use of Class II elastics on o n e side, Class III elastics on the othm, a n d / o r anterior crisscross elastics. T h e effects of Class II and Class Ill elastics are shown in Figure 20. T h e m o v e m e n t is an en masse m o v e m e n t in which the entire arch is rotated a r o u n d its center o f resistance. Not only is this m o v e m e n t difficult to achieve, but it can lead to crossbite and lack of arch harmony.
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A
Occlusal Plane Considerations T h e patient who is treated surgically should have the occlusal plane, as evaluated f r o m the frontal view, parallel to facial structures, such as the eyes. In the nonsurgical patient with a skeletal asymmetry, there may be a cant to the plane of occlusion relative to the face. This cant is not easily altered f r o m a line c o n n e c t i n g posterior teeth because of m e c h a n i c a l difficulties in i n t r u d i n g entire posterior segments. F u r t h e r m o r e , the lips may also be angled so that a m o r e aesthetic relationship of the canted occlusion and the lips is observed. Figure 21 shows compensatory differences between molar axial inclinations. T h e u p p e r left molar is leaning toward the buccal and the right m o l a r is leaning toward the lingual. Relative to the entire occlusal plane based on the face (such as a line c o n n e c t i n g the pupils of the eyes), there is a marked difference. In some patients, a vertical asymmetry may be present in which the right side of the m a n d i b l e has grown vertically m o r e than the left, p r o d u c i n g a cant in the occlusal plane. Notice that this plane, which would be a t r e a t m e n t plane of occlusion for a nonsurgical patient, minimizes the axial inclination difference. Study casts that are t r i m m e d to the canted occlusal plane may n o t show as m u c h variation in axial inclination between the right and the left sides as would be observed f r o m the PA h e a d film, in which a truer horizontal plane is used for orientation (Fig 21).
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Figure 22.
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An anterior crisscross elastic produces the undesirable side effect of canting the occlusal plane (A). Patient showing unaesthetic canting p r o d u c e d by anterior crisscross elastics. Mechanics to move the incisors a r o u n d the arch should have b e e n used (B).
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It may be desirable to treat to a canted occlusal plane if a skeletal asymmetry is present and very undesirable in a skeletally symmetric patient. O n e of the undesirable effects of the use of an anterior cFisscross elastic is that it can cant the plane of occlusion. T h e patient in Figure 22 had an anterior crisscross elastic attached f r o m the u p p e r right to the lower left. Note that the occlusal plane has canted down to the patient's right side.
Summary T h e r e are many t r e a t m e n t options for patients who show asymmetries in occlusion. These include orthog-
nathic surgery, orthopedics and orthodontics employing extraction or n o n e x t r a c t i o n therapy. Part of the decision in t r e a t m e n t selection and the detailed treatm e n t plan that d e t e r m i n e s tooth position in threedimensional space is based on differentiating skeletal from dental problems. This article has c o n c e n t r a t e d on the utility of using tooth position, mainly axial inclinations, as a diagnostic tool. Such i n f o r m a t i o n can be gleaned from the study casts and can serve as a guide to help in developing a c o m p r e h e n s i v e and valid t r e a t m e n t plan for the patient. This is n o t to suggest that an overall evaluation be ignored, because the clinical examination and the use of p r o p e r cephalometric techniques are equally important.