CROSSBITE CORRECTION
It is important to correct posterior crossbites and mild anterior crossbites (one or two displaced teeth) in the first stage of treatment. Severe anterior crossbites (all the teeth), in contrast, are usually not corrected until the second stage of conventional treatment or might remain pending surgical correction. For both posterior and anterior crossbites, it is obviously important to make the appropriate distinctions between skeletal and dental problems and to quantitate the severity of the problem. The assumption here is that appropriate treatment has been selected, and the discussion is solely about implementing a treatment plan based on differential diagnosis.
Individual Teeth Displaced Into Anterior Crossbite :-
Anterior crossbite of one or two teeth almost always is an expression of severe crowding . This is most likely to occur when maxillary lateral incisors that are some- what lingually positioned to begin with are forced even more lingually by lack of space. Correction of the crossbite requires first opening enough space, then bringing the displaced tooth or teeth across the occlusion into proper position.
Occlusal interferences can make this difficult. The patient may tend to bite brackets off the displaced teeth, and as the teeth are moved “through the bite,” occlusal force pushes them one way while the orthodontic appliance pulls them the other. It may be necessary to use a biteplate temporarily to separate the posterior teeth and create the vertical space needed to allow the teeth to move. The older the patient, the more likely it is that a biteplate will be needed. During rapid growth in early adolescence, often incisors that were locked în anterior crossbite can be corrected without a biteplate.After that, one probably will be required.
Transverse Maxillary Expansion by Opening the Midpalatal Suture :-
It is relatively easy to widen the maxilla by opening the midpalatal suture before and during adolescence, but this becomes progressively more difficult as patients become older because of the increased interdigitation of the sutures .
Patients who are candidates for opening the midpalatal suture may have such severe crowding that even with this arch expansion, premolar extraction will be required. In these patients, however, separation of the suture should be the first step in treatment, before either extraction or alignment. The first premolar teeth are useful as anchorage for the lateral expansion and can serve for that purpose even if they are to be extracted later, and the additional space pro- vided by the lateral expansion facilitates alignment.
Sometimes, transverse maxillary expansion can provide enough additional space to make extraction unnecessary, but rarely is it wise to use sutural expansion as a means of dealing with crowding in an individual who already has normal maxillary width. Opening the midpalatal suture should be used primarily as a means of correcting a skeletal crossbite by making a narrow maxilla normal, not a normal maxilla abnormally wide.
The techniques for expansion across the midpalatal suture in the late mixed or early permanent dentition are presented. Slow expansion, with one turn 1 mm) of the screw every other day, is recommended over rapid expansion in these younger patients because it is more physiologic and equally effective. Up to about age 15 (skeletal age, it almost always is possible to open the suture . Beyond that level of maturity, it is increasingly difficult to create the microfracturing necessary to open the suture. For that reason, more rapid activation of the expansion screw initially is recommended for more mature patients. Two turns initially and two turns per day until the suture opens often the patient hears and feels it pop apart) is more likely to generate the desired sutural expansion. For these patients, slow expansion is likely to produce only dental expansion. If the suture does not open within 2 to 3 days with rapid activation of the screw, surgically assisted expansion becomes the only possibility.
In the mixed dentition, a bonded expander often is easier to place than a banded one and may be selected for that reason. For patients in the permanent dentition, the primary indication for a bonded expander is for expansion in a patient who already has excessive anterior face height.’ A bonded expander of necessity covers the occlusal surface of the posterior teeth, creating a biteplate effect, and this reduces the potential for downward-backward rotation of the mandible during expansion. A banded expander almost always creates some mandibular rotation because occlusal interferences are created as the teeth are moved, which would be ideal for a short-face patient. For patients with normal face height, either type of expander can be used without great concern for mandibular rotation.
Correction of Dental Posterior Crossbites :-
Three approaches to correction of less severe dental cross- bites are feasible: a heavy labial expansion arch; an expansion lingual arch; or cross-elastics. Removable appliances, although theoretically possible, are not compatible with comprehensive treatment and should be reserved for the mixed dentition or adjunctive treatment.
The inner bow of a facebow is also, of course, a heavy labial arch, and expansion of this inner bow is a convenient way to expand the upper molars in a patient who is wearing headgear. This expansion is nearly always needed for patients with a Class II molar relationship, whose upper arch usually is too narrow to accommodate the mandibular arch when it comes forward into the correct relationship because the upper molars are tipped lingually. The inner bow is simply adjusted at each appointment to be sure that it is slightly wider than the headgear tubes and must be compressed by the patient when inserting the facebow. If the distal force of a headgear is not desired, a heavy labial auxiliary can provide the expansion effect alone. The effect of the round wire in the headgear tubes, however, is to tip the crowns outward, and so this method should be reserved for patients whose molars are tipped lingually.
A transpalatal lingual arch for expansion must have some springiness and range of action. As a general principle, the more flexible a lingual arch is, the better it is for tooth movement but the less it adds to anchorage stability. This can be an important consideration in adolescent and adult patients.excellent choice for correction of a dental crossbite. When the lingual arch is needed for both expansion and anchorage, however, the choices are 36 mil steel wire with an adjustment loop, or the newer system that allows the use of 32 x 32 TMA or steel wire .
The third possibility for dental expansion is the use of cross-clastics, typically running from the lingual of the upper molar to the buccal of the lower molar. These elastics are effective, but their strong extrusive component must be kept in mind. As a general rule, adolescent patients can tolerate a short period of cross-elastic wear to correct a simple crossbite because any extrusion is compensated by vertical growth of the ramus, but cross-elastics should be used with great caution, if at all, in adults. As any posterior crossbite is corrected, there is a tendency to rotate the mandible downward and backward, even if cross-elastics are avoided. The elastics accentuate this tendency
If teeth are tightly locked into a posterior crossbite rela- tionship, a biteplate to separate them vertically can make the correction easier and faster. In children and young adoles cents, this is rarely needed. Use of a biteplate during trans- verse expansion indicates that elongation of the posterior teeth and downward-backward rotation of the mandible is an acceptable outcome.