1 What does minor tooth movement in orthodontics mean compared with major tooth movement?

For some, there is no minor tooth movement. All tooth movement is major. One needs to understand that there is orthodontic tooth movement (and orthodontic force systems, which are lower) compared with orthopedic movement (and orthopedic force systems, which are higher).< ?xml:namespace prefix = "mbp" />¹ Lower force systems are usually related to apposition/resorption of the alveolar bone around the tooth/teeth being moved. One can compute these in ounces or in grams (28 grams = 1 ounce).

The current, preferred method for most orthodontic tooth movement is not only on the lighter side, but also in the continuous format.^1,2 One can actually have orthopedic effects (bones moved more than the teeth) with orthodontic forces. An example of this is the quadhelix appliance in the maxillary arch of preschoolers. However, most orthopedic effects are accomplished with higher, or orthopedic, force systems in which the forces applied to the anchor teeth are manifested in the bones.

A better term than minor tooth movement is probably isolated tooth movement, in which there is need for a limited amount of orthodontic movement. This also means that other teeth should not be moved; this brings up the concept of anchorage. One does not wish to move the anchor teeth or the orthodontic system is compromised. An example of an anchor unit is a canine-to-canine lingual arch that can be used in the uprighting of a mandibular permanent second molar.

The common term associated with isolated tooth movement in children is interceptive orthodontics; it is called adjunctive orthodontics when it is associated with adults. It is not associated with first-phase corrective orthodontics where too many movement objectives need to be met. Examples of first phase (usually 12 to 18 months of active therapy) are early treatment of Class II malocclusions with a headgear or a functional appliance and Class III malocclusions with a rapid palatal expander and protraction facemask therapy.²

2 When should we first consider orthodontic treatment?

The sequence of maturation of the dentofacial complex is not related to Angle’s dental classification of malocclusion, although that helps in classifying treatment problems.³ That skeletal sequence is the transverse plane (side to side), followed by the sagittal plane (anteroposterior problems), and then the vertical plane (deep bite vs. open bite, or short face syndrome vs. long face syndrome).⁴

In the primary dentition, there is usually no crowding, but there can be shifts of the lower jaw to the left or right as the teeth go into maximum intercuspation of occlusion. The maxillary primary canines can erupt into a constricted intercanine dimension about 15 to 20 months after birth that will not allow the lower arch to fit properly. This usually causes the lower jaw to shift to one side with the dental midlines becoming non-coincident.⁵

If one aligns the midlines of the two arches, it is noticeable that the lower arch cannot fit. One approach and probably the best approach to solve this problem is to expand the maxillary arch. Another approach that involves no isolated tooth movement can be achieved with an occlusal adjustment of the primary canines (i.e., facial of the lower canine and lingual of the upper canine). However, there will be little effect on the lateral overjet of the primary molars.

Expansion of the maxillary arch can be achieved in a variety of ways using either fixed or removable appliances.⁶ A removable jackscrew appliance with a biteplane has the limitations of only two turns per week or 0.5 mm of expansion as well as the issue of patient compliance in wearing the appliance. It has no orthopedic effect—only dentoalveolar tipping.

A predictable appliance for use in the preschooler is a quadhelix from the primary second molars. This appliance is an improved biomechanical one from the original “W” appliance. The quadhelix is fabricated to fit passively. Prior to insertion, the appliance is expanded approximately 10 mm in the facial-lingual dimension of the primary second molar and then cemented. By doing this, the appliance can be evaluated in 3- to 5-week intervals. Intraoral activation laterally of a cemented quadhelix is unpredictable. A 10-mm expansion usually gives 5 to 6 mm expansion within a few months. The appliance is left in place for a few months more after getting the proper lateral overjet with no quadrant in crossbite. It is not necessary to remove the appliance to place a passive Hawley for retention. The total length of the quadhelix treatment is usually about 6 to 8 months.

It is not common to have to remove, reactivate, and re-cement a properly expanded quadhelix. This is the most common active appliance in the primary dentition, and it has an orthopedic effect, which means the left and right maxillae also move. This effect is positive, since it increases the chance for the permanent molars to erupt properly.

Another appliance that can be used in the primary dentition is a two-tooth rapid palatal expander appliance (fixed appliance with a screw).^2–6 This fixed RPE can be expanded either once or twice a day. Although appreciable results can be obtained from using the two-tooth RPE, the quadhelix is also the appliance of choice for the treatment of posterior quadrant crossbites in the early to middle transitional dentition. However, upon the eruption of the maxillary first premolars and the presence of a quadrant posterior crossbite, the use of a more rigid appliance that can produce an orthopedic effect should be considered, such as a four-tooth rapid palatal expander. The mechanics related to the RPE are more complex with multiple sutural effects.⁷

The use of coordinated arch wires with light forces in the permanent dentition has been reintroduced into corrective orthodontics for adolescent treatment. The greater the expansion in the posterior portion, the more stable the results. Furthermore, the greater the effect in the middle arch, the greater the increase in arch perimeter.

3 How does one orient the lower arches with posterior crossbites?

The mandibular arch is consistently ovoid or tapered in shape with a midline suture that fuses shortly after birth. In some Class II division 2 malocclusions, the lower arch can be square. There is no orthopedic effect of the left and right mandibular bones used in orthodontics, as the midline fusion occurs so early.² However, the facial-lingual inclination of the mandibular posterior teeth (along the long axis of the tooth) helps in the understanding of the treatment of the lower arch. If the posterior permanent teeth lean inward with the crowns toward the tongue and the roots too far to the facial while the lateral overjet is minimal, then there is probably a problem with constriction of the maxillary arch. If one were to upright the lower buccal segments, the result would be a bilateral posterior quadrant crossbite. It is normal to have a mild progressive movement of the roots of the premolars/permanent molars facial to the crowns. All permanent teeth, except the maxillary incisors, are supposed to have their roots facial, or upright, compared with their tooth crowns. These incisors are supposed to have their roots lingual and crowns facial (lingual root torque). This can occur with the mandibular incisors, but it is more variable. The use in individual permanent molar crossbite is the application of cross-elastics. These elastics, usually from the lingual of the maxillary permanent molar to the facial counterpart, present problems with the collateral effect of extrusion of these teeth with the elastics with resultant worsening of the molar relationship.

4 Where does one treat most posterior crossbites?

Crossbites are usually treated in the maxilla. The maxillary arch form can vary by the type of Angle’s classification. The common maxillary arch form is ovoid; however, the Class II division 2 malocclusion can present with a square arch form whereas the Class II division 1 malocclusion can present with a tapered arch form. With this Class II division 1 middle arch constriction, as the mandible shifts forward, a bilateral posterior quadrant crossbite will be presented. Therefore, one must be aware that hidden posterior crossbites can occur when the malocclusion is not Class I.⁵

5 Is there more than one type of posterior crossbite from the classic one presented with maxilla lingual and mandible facial?

Yes. The first one, which is not common, has the lower arch completely within the maxilla. It can manifest on one side or both and is called a Brodie bite. The expansion is usually done in the lower arch with a fixed appliance plus a bite plane that helps disarticulate the occlusion. This problem needs early treatment.⁵

The second problem is usually seen later upon the eruption of the permanent second molar. The more common pattern is with the maxillary permanent second molar facial and the less common mandibular permanent second molar lingual. In the maxilla, because of the rhomboid shape of the permanent first molar and the lack of a vertical stop of the malposed permanent second molar, the second molar often needs to be moved distal first and then aligned. Cross-arch elastics are interarch elastics that can make the extrusion problem worse.

Both problems are more difficult to treat than the usual crossbite, which is due to maxillary transverse deficiency. This is due to the vertical dimension that is manifested in these problems.

6 What happens to individual tooth crossbites if left untreated?

If left long enough, abnormal wear patterns appear on the teeth. There can be adverse periodontal responses around the affected teeth. If the quadrant crossbite is left untreated, the growth of the jaw can also be affected adversely.²

From an orthodontic tooth movement point of view, the issue becomes more complex. Whatever the orthodontic intervention initially proposed, usually involving more tipping than torque movements, the problem now presents as an issue of arch perimeter and crowding in the area of crossbite. It is necessary to regain the room in the arch prior to correction of the crossbite. This might involve interproximal tooth reduction or discing and/or removal of primary teeth. One should not reduce proximal surfaces of permanent teeth in the transitional dentition in the correction of crossbite. The crossbite problem is now a two-step treatment sequence as opposed to an earlier one-step sequence.

7 If anterior and posterior crossbites exist within the same patient, which crossbite comes first in the tooth movement?

It is usually the posterior quadrant problem involving primary teeth initially. The problem of anterior crossbite of single primary teeth is as rare as a single primary molar crossbite.⁸ The anterior quadrant variety of primary incisors is usually a manifestation of a skeletal problem that necessitates a combination of intraoral and extraoral appliances.

If there is a combination of a posterior and anterior crossbite with the same patient, one treats the posterior crossbite first, then the anterior. If you treat the anterior crossbite first, you will lose its correction when the posterior crossbite is corrected.⁸ A removable appliance to assist in correction of the anterior crossbite allows retention of the corrected posterior crossbite. The anterior crossbite problem is usually associated with lingual eruption of the maxillary permanent incisors. The permanent lateral incisor is usually more common in crossbite than the permanent central incisor. It is not uncommon for the incisors to erupt lingual in a bilateral expression. The timing of treatment of the permanent incisor crossbite correction is important, and it is related to the stage of eruption and the amount of overbite. Tipping the lingually positioned incisor facially causes the overbite to become more shallow. If the overbite is very shallow initially, the tooth/teeth do not retain well in the corrected positio/>