Problems in the transverse dimension can be challenging to manage, especially in adult patients. The purpose of this article is to provide a review of normal transverse jaw development, the etiology and diagnosis of transverse discrepancies, goals of adult transverse treatment, and treatment options for adult transverse discrepancies. Mirroring a seminar from your orthodontic residency, this article is written in question and answer format. We ask that you think through answers to the questions we present very carefully and make the best decisions you can, before you refer to the answers we provide. Like your orthodontic residency, you will find that certain principles are emphasized and applied time and time again to a spectrum of patients in this case-based article. These are the principles which have served us well over many years of teaching and treating adults in the transverse dimension.
Q: Our knowledge of the transverse morphologic changes which occur during growth and development is far greater than our understanding of the biology underlying those changes. That said, can you describe the pattern of transverse bone changes which occur during maxillary and mandibular growth and development?
A: A pattern of bony width change occurs as a gradient in the vertical dimension. As illustrated in Fig.1 , the greatest width change occurs more superiorly (Jugal point), and the least width change occurs inferiorly (mid-alveolar point of the mandible). Divorced from this pattern are the transverse mandibular basal bone changes, measured as bi-gonion and bi-antegonion.
Q: Can you describe the transverse dental (permanent molar) movements which occur during growth and development.
A: Maxillary molars erupt with buccal crown torque and upright with age as the maxilla widens. Mandibular molars erupt with lingual crown torque and upright with age. These molar crown torque changes are accompanied by concurrent increases in maxillary and mandibular intermolar widths ( Fig.2 ). On average, the basal bone of the maxilla increases in width by 5.4 mm; maxillary intermolar width increases by 3.0 mm; mandibular intermolar width increases by 2.0 mm; and mandibular cross arch crest level alveolar width increases by 1.6 mm.
Q: What does the above finding mean in terms of dental treatment goals?
A: The finding provides support for the American Board of Orthodontics’ requirement that ideal finishing treatment include upright posterior teeth.
Q: Can you list at least four etiologic factors that cause adult transverse discrepancies?
A: Etiologic factors include :
Ectopic tooth eruption. Fig.3 A illustrates a developing (left to right) buccal cross bite resulting from ectopic first permanent molar eruption.
Soft tissue imbalance (example: prolonged digit sucking). Fig.3 B shows the posterior cross bite (and anterior open bite) resulting from three decades of heavy thumb sucking.
prolonged retention of primary teeth
Asymmetric mandibular growth ( Fig.3 C andD) – note the right posterior cross bite (and right chin deviation) that has resulted from excess left mandibular growth.
Excess or deficient anteroposterior growth of the maxilla or mandible. Fig.3 F–H illustrates a 19-year-old male with complete lingual cross bite of the entire dentition due to maxillary anteroposterior deficiency/mandibular anteroposterior excess.
Some TMD issues. Temporomandibular joint dysfunction has been associated with skeletal asymmetries and cross bite occlusion.
Excess or deficient maxillary or mandibular transverse growth. Fig.3 I–K illustrate a left posterior cross bite developed in a cleft lip and palate patient due to deficient maxillary transverse growth.
Q: Can you discuss five factors that should be considered when formulating a diagnosis and treatment plan for adult patients with transverse discrepancies?
A: The following factors must be considered:
Magnitude of transverse discrepancy: This is the single most important factor in your transverse treatment planning decision. The magnitude of the transverse apical base discrepancy will determine the degree to which a posterior cross bite is characterized as dental or skeletal; it will, in most instances, dictate whether a skeletal cross bite can be corrected by masking or must be corrected by surgery; and in cases of surgical treatment, it may lead you to choose a specific surgical modality.
As illustrated in Fig.4 , transverse dental compensations (usually maxillary posterior buccal crown torque and mandibular posterior lingual crown torque) must be taken into consideration when determining the magnitude of the transverse discrepancy. Buccally-tipped maxillary molars will tend to move lingually as they are uprighted (unless a trans-palatal arch is used to apply torque to upright their roots while maintaining the intermolar distance). Likewise, lingually-tipped mandibular molars will tend to move buccally as they are uprighted (unless a lower lingual holding arch is used to apply torque to upright their roots while maintaining the intermolar distance). Removal of these compensations by uprighting the molars can dramatically increase the transverse occlusal discrepancy and worsen the cross bite relationship.
Finally, always remember that changes in the sagittal and vertical relationships of the maxillary and mandibular apical bases can affect transverse occlusal relationships. If one plans to move the maxilla or mandible relative to each other either by orthopedics during growth or surgery after completion of growth, then one must check how the movements will affect the resulting posterior transverse relationships (e.g. see absolute vs. relative transverse discrepancy below).
Facial symmetry or asymmetry :
The first thing to do when compiling a problem list in the transverse dimension is to examine the patient’s face in the frontal view. Unlike problems in either the anteroposterior or vertical dimensions, problems in the transverse dimension are frequently camouflaged by the overlying soft tissue. However, asymmetries can usually be spotted during clinical examination. The use of CBCT scan can also be of value in assessing skeletal asymmetries and transverse skeletal discrepancies between the maxilla and mandible.
We do not recommend using 2-D posteroanterior cephalometric radiographs to determine transverse skeletal discrepancies between the maxilla and mandible because the alveolar process bone of the jaws, the bone that houses the roots of the teeth and is the bone of interest in diagnosing transverse skeletal discrepancies, is obscured in posteroanterior cephalometric films.
Presence of a lateral CR-CO shift:
One should always check for a CR-CO shift in every patient at every appointment . If one detects an asymmetry, especially a deviation of the chin in the presence of a unilateral cross bite, one should try to establish whether the asymmetry is a result of the shift. In addition, one should check for lateral deviation upon opening. One should ask the patient to touch their tongue to the roof or back of their mouth while they open and close slowly until their teeth just touch to help seat the condyles. Then, ask the patient to close into maximal intercuspation to check for a CR-CO shift. If there is any doubt on the presence of a functional shift, one can place the patient on a flat-plane bite plate for a week or two to disarticulate the occlusion and deprogram them. However, compliance with a removable appliance is not always forthcoming. We prefer to deprogram using either a fixed expansion appliance (in the presence of a constricted maxilla while attempting orthopedics, masking, or SARME) or leveling and aligning with fixed orthodontic appliances. Whenever possible, remove the need for compliance.
Principle of CR-CO shifts and treatment planning: if you detect a sizable CR-CO shift, then inform the patient that you cannot establish your final treatment plan until the shift has been eliminated. It is only when the shift is eliminated that one can understand the true relationship between the jaws and develop a rational treatment plan.
Whether the transverse discrepancy is relative or absolute :
Haas introduced the terms relative and absolute transverse discrepancy. A relative transverse discrepancy exists when the posterior teeth do not coordinate in centric relation, but do coordinate when the canines of the models are placed in Class I occlusion. For instance, Fig.5 A shows the models of an adult patient with a severe Class II malocclusion. Note the significant transverse discrepancy in CR. The patient was treatment planned for mandibular advancement. Fig.5 B shows the same models advanced to a Class I canine relationship. Note that the transverse discrepancy has disappeared. This patient had a relative transverse discrepancy.
On the other hand, an absolute discrepancy exists when the posterior teeth still do not coordinate even when the canines are placed into a Class I relationship. For instance, Fig.5 C shows the models of a patient with a severe Class III malocclusion in centric relationship. Note the significant transverse discrepancy. The patient was treatment planned for a mandibular setback. Fig.5 D shows the same models setback to Class I canines. Note that the transverse discrepancy is still present. In fact, the discrepancy will be even worse when the mandibular molars are uprighted ( Fig.5 E, dental compensations removed). This patient had, therefore, an absolute transverse discrepancy.
Magnitude of buccal corridors:
In terms of esthetics, the transverse dimension is probably the least studied. When a patient smiles, the buccal corridors are spaces existing between the lateral surfaces of the posterior teeth and the inner commissures of the lips or cheeks. Usually, a patient with a constricted maxilla and narrow maxillary arch will have large buccal corridors. Conversely, a patient with a wide maxilla, and a broad maxillary arch, will have small buccal corridors. Moore and colleagues studied the effect of buccal corridor size on smile esthetics and found that large buccal corridors are considered unaesthetic ( Fig.6 ).
When examining a patient, we recommend recording the presence and magnitude of buccal corridors during a natural smile.
Whether the posterior cross bite (transverse discrepancy) is dental or skeletal : this factor will be considered in detail in the following series of questions.
Q: Let’s assume that a patient presents to you with a posterior cross bite ( Fig.7 ). Further, assume that the patient is Class I without a functional shift. Is the cross bite of dental or skeletal origin? Can dental cross bites be differentiated from skeletal cross bites simply by counting the number of teeth in cross bite?
A: No. We cannot conclude that when only 1–2 posterior teeth are in cross bite that it is a dental cross bite, and we cannot conclude that when more teeth are in cross bite that it is a s keletal cross bite.
Q: Why not?
A: Differentiation between dental and skeletal cross bites is not that simple. As recently reported, there is a large variation in transverse skeletal widths (and transverse compensations) in the absence of cross bites ranging from:
Small maxillary skeletal width compared to a large mandibular skeletal width ( Fig.8 A), to
Comparable maxillary and mandibular skeletal widths ( Fig.8 B), to
Large maxillary skeletal width compared to a small mandibular skeletal width ( Fig.8 C).
In other words, a large transverse skeletal discrepancy can exist in the absence of a cross bite, in the presence of only a few teeth in cross bite, or in the presence of a large number of teeth in cross bite. Counting teeth to determine the presence or absence of a transverse skeletal discrepancy is ill advised . You must consider the presence and magnitude of dental compensations in order to determine whether a transverse skeletal apical base discrepancy exists.
Q: How do transverse dental compensations develop?
A: Transverse dental compensations develop in the same way, and for the same reasons, that anteroposterior dental compensations develop. Teeth tend to erupt throughout life until sufficient occlusal, or soft tissue, load prevents further eruption. They erupt along their long axes, but their buccal-lingual direction is influenced by the soft tissue envelope (tongue-cheeks-lips) in order to bring them into occlusion with teeth from the opposing jaw. In the presence of a hypoplastic maxilla, the tongue will tend to tip the maxillary incisors forward, and the mandibular lip will tend to tip the mandibular incisors lingually (anteroposterior compensations). In that way, the incisors will be brought into occlusion. In a similar fashion, in the presence of a hypoplastic maxilla, the tongue will tend to tip the maxillary molars buccally, and the cheeks will tend to tip the mandibular molars lingually (transverse compensations). In that way, the molars will erupt into occlusion.
Q: So, if we cannot simply count the number of posterior teeth in cross bite, then how do we differentiate between a dental and skeletal cross bite?
A: By visualizing what happens in the transverse dimension when we upright the molars (eliminate transverse compensations). For instance, since maxillary and mandibular skeletal bases relate well in a dental cross bite, uprighting molars will improve (eliminate) a dental cross bite ( Fig.9 A). On the other hand, since maxillary and mandibular skeletal bases do not relate well in a skeletal cross bite, then uprighting molars will worsen a skeletal cross bite ( Fig.9 B).
Q: List the goals of adult transverse treatment.
A: Goals of adult transverse treatment include:
Correcting posterior cross bites, lateral CR- CO shifts, and skeletal asymmetries
Uprighting posterior teeth (eliminating transverse dental compensations)
Creating a stable and coordinated posterior occlusion
Reducing large buccal corridors
Maintaining a healthy periodontium
Increasing chewing efficiency (for example, in patients with scissor or Brodie bites)
Q: An adult presents to you with a posterior lingual cross bite. Can you list the options for dealing with this problem?
A: The options may include:
No treatment – leave the patient in posterior cross bite
Dental cross bite – upright the involved teeth, thus improving/correcting the cross bite
Skeletal cross bite – the same three general options are available for dealing with transverse skeletal discrepancies as for dealing with anteroposteriorly, or vertical, skeletal discrepancies:
Orthopedics ( attempt maxillary skeletal expansion)
Masking (camouflage, increasing transverse compensations)
The challenge is deciding which the best option is. You must consider all the factors discussed earlier: magnitude of the transverse discrepancy, presence of an asymmetry and/or CR-CO shift, whether the cross bite is of dental or skeletal origin, whether the transverse discrepancy is relative or absolute, the presence and degree of dental compensations (torques), which jaw is at fault, the presence of large buccal corridors, the patient’s age, the condition of the periodontal tissues, and the patient’s desires.
Q: When is the option of no transverse treatment reasonable?
A: When we treat children, we almost always correct cross bites, eliminate posterior transverse compensations (upright posterior teeth), and correct lateral CR-CO shifts. However, in adults we may choose to leave these problems. As the presence of posterior cross bite is not thought to increase the incidence of TMD, the decision to improve posterior crossbite will depending upon the patient’s desires, transverse discrepancy magnitude, absence of a CR-CO shift, and periodontal biotype.
For example, the Class III patient in Fig.10 A–C stated that he wanted the “easiest, fastest, treatment without surgery.” Since he currently had no problems with his posterior cross bite, and since his posterior teeth were relatively upright, we chose to treat him with mandibular first premolar extractions but to leave him in cross bite ( Fig.10 D–F). This option was appealing because we were at least able to provide him with canine rise disclusion ( Fig.10 G–H).
Q: A 35-year-old female presents with a right posterior buccal cross bite of her first and second molars ( Fig.11 ). CR = CO. Does the patient have a skeletal, or dental, posterior cross bite and Why?
A: The patient’s right posterior cross bite is a dental cross bite. Why? Clearly, the mandibular right molars have erupted with significant lingual crown torque ( Fig.11 E). The maxillary right second molar exhibits buccal crown torque ( Fig.11 F). Since uprighting these teeth will improve, or correct the cross bite, we can conclude that the patient has a dental cross bite.
Q: In general terms, how would you correct the cross bite?
A: Since uprighting posterior teeth improves a dental cross bite and the skeletal bases relate well, one can move the right maxillary second molar crown lingually and the mandibular right molar crowns buccally ( Fig.12 ).
Q: What specific problems would you anticipate when uprighting the right molars?
A: One major problem is the amount of right molar overbite . In other words, the right molars have erupted so far past each other ( Fig.11 H and I) that the vertical dimension may be significantly opened as the right molars are uprighted and brought into occlusion. The patient’s right molars may become the only teeth in contact, and the patient may not be able to tolerate this increase in vertical dimension. Furthermore, the patient may require significant occlusal adjustment (enameloplasty), molar endodontics, or even molar crowns on her right side to finish with a reasonable occlusion. The patient must be informed of these possibilities.
Q: How would you proceed?
A: We placed comprehensive fixed orthodontic appliances, and asked the patient to wear cross bite elastics from right mandibular molar lingual buttons to right maxillary molar buccal brackets. Surprisingly, no other treatment was necessary, not even an anterior biteplate to allow the right molars to pass across each other. The post-treatment deband photographs are shown in Fig.13 .
Q: A 19-year-old woman presents ( Fig.14 ) with a chief complaint of “I want my top teeth straightend.” The patient has a straight profile, but dentally the premolars appeared to have a Class II relationship by about 2 mm. The incisors contacted edge-to-edge. The patient has a bilateral posterior lingual cross bite and large buccal corridors. Does this patient have a posterior dental or skeletal cross bite?
A: There are no intra-oral frontal views of the maxillary and mandibular arches (teeth separated) to clearly ascertain posterior crown torques (compensations). However, in Fig.14 E it appears that the maxillary premolars and first molars have lingual crown torque, and the mandibular molars have lingual crown torque.
Therefore, if the patient’s maxillary posterior teeth are upright, they will tend to move buccally, and the cross bite should improve. This would suggest that the patient has a dental cross bite. On the other hand, if the mandibular posterior teeth are upright, they should also tend to move buccally, and her cross bite would worsen. This would suggest that the patient has a skeletal cross bite. Fig.14 B shows that the patient has large buccal corridors, suggesting that a relatively small maxilla. In summary, the patient’s posterior cross bite has features of both a dental and skeletal cross bite.
Q: How can this 19-year-old patient have an edge-to-edge incisor relationship when the patient only has a mild Class II malocclusion? In other words, most patients with edge-to-edge incisors have a Class III malocclusion.
A: Although we are speculating, the patient’s maxillary premolars may have erupted, or drifted forward from the ideal position leaving the maxillary canines with inadequate room to erupt. Conversely, her maxillary incisors may have drifted posteriorly into an edge-to-edge relationship with her mandiublar incisors.
Q: What are the options for dealing with her bilateral posterior cross bite? Why would, or why would you not choose the following options?
A: The options include:
No treatment – leaving the patient in posterior cross bite. This option is not recommended. If comprehensive treatment is to be pursued, then it would be negligent to leave the patient in posterior cross bite.
Attempting orthopedic treatment with a rapid maxillary expansion appliance (RME). If the maxillary mid-palatal suture were to separate, and if one were to get significant maxillary skeletal widening, then this could be an ideal option.
Attempt to mask or camouflage the malocclusion by increasing transverse compensations – may be a viable option since, as we previously stated, uprighting the maxillary posterior teeth will bring them buccally – improving the cross bites. We would then only need to increase the mandibular posterior teeth lingual crown torque to correct the cross bites.
Surgically-Assisted RME (SARME) – would guarantee correction of the bilateral posterior cross bites, skeletally. The drawbacks of this option are the surgical risks.
Multiple Piece Maxillary Osteotomy (MPMO) to widen the maxillary skeleton – would not be a better choice than SARME since the surgery would be more complex (requiring a maxillary down fracture) and the amount of expansion achievable with MPMO would be limited compared to SARME.
Q: What are the potential problems in attempting RME expansion in a 19-year-old woman?
A: The maturity of the maxillary sutures at the patient’s age. Sutural separation can be obtained most effectively before/during pubertal growth spurt. Maxillary expansion after the pubertal growth spurt results in mainly dentoalveolar (not orthopedic/skeletal) effects. At 19years of age, this young woman’s facial skeleton may be too mature, and offer too much skeletal resistance, to permit separation of her mid-palatal suture. However, one could attempt RME at the rate of 0.25 mm per day, or 0.25 mm every other day, and monitor patient to see if the mid-palatal suture separates.
Q: Is the mid-palatal suture the major site of skeletal resistance to RME?
A: No. If the mid-palatal suture was the major site of skeletal resistance to RME, then once the suture was opened, the skeletal resistance would drop dramatically. However, Isaacson and Ingram reported no significant change in the RME opening force during the time the mid-palatal suture opened. Instead, it has been suggested that the zygomatic buttress is the major site of skeletal resistance to RME.
Q: If you attempt to treat this patient with RME, how would you know if the mid-palatal suture has separated or has not separated?
A: The most obvious sign of mid-palatal suture separation is the development of a maxillary midline diastema. However, if a midline diastema does not form, then look for other signs that indicate the suture is not separating such as:
The absence of a clear bony radiographic mid-palatal split on an occlusal radiograph.
The impingement of the RME appliance’s metal arms on the palatal soft tissue (indicating lateral dental movement and not lateral hemi-maxillae bone movement).
A sensation of expansion pressure from the screw more than 5 or 10 min beyond expansion screw activation.
Patient complaints of pain.
Q: What is the first principle of attempting maxillary skeletal expansion (maxillary transverse orthopedics) in an adult? How does this principle apply to this patient?
A: First principle: when attempting maxillary skeletal expansion (orthopedics) in an adult patient, you must have a “fallback” plan if the mid-palatal suture does not split .
With this 19-year-old woman, we recommend first activating the RME appliance screw once a day, or once every other day, for 1 or 2 weeks. If the mid-palatal suture does not separate, you are achieving only dental movement.
If the dental expansion achieved is large compared to what you need to correct the cross bites, if the maxillary posterior buccal periodontium is robust (thick buccal bone, thick keratinized attached tissue, thick biotype), and if you believe you can correct her cross bites by increasing posterior compensations, then your fallback plan could be continuing dental expansion slowly with the RME appliance (at the rate of 0.25 mm or 0.5 mm per week.)
If the dental expansion achieved is small compared to what you need to correct the cross bites, or if the posterior buccal periodontium is a thin biotype, then your fallback plan could be either surgical intervention (i.e. SARME) or leaving her in cross bite.
Q: Which of the above options have you decided to use and treat this patient?
A: Following discussions with the patient, we decided to attempt orthopedics using RME (0.25 mm expansion per day, patient returning to clinic for a follow-up in 1 week). Our fallback plan, if a mid-palatal split was not achieved, would be a referral for SARME.
Fortunately, a mid-palatal split was achieved ( Fig.15 A and B). Following spontaneous maxillary midline diastema closure, fixed orthodontic appliances were placed, arches were leveled and aligned, Class II elastics were worn to correct molars and canines to Class I, and Fig.15 C shows the post-treatment facial photograph of the patient. Note the reduction in buccal corridors.