CATEGORY AUSTRALASIAN DENTIST 69 Palatal Expansion in Preadolescents (Late Mixed Dentition) With increasing age, the midpalatal suture becomes more and more tightly interdigitated. By the late mixed dentition period, sutural expansion often necessitates placement of a relatively heavy force directed across the suture, which microfractures the interdigitated bone spicules so that the halves of the maxilla can be moved apart. A fixed jackscrew appliance (either banded or bonded) is necessary. As many teeth as possible should be included in the anchorage unit. A modern view would be that for patients of this type, tooth-supported expansion should not be attempted. Instead, micro-implant assisted palatal expansion (MARPE) should be used, with one activation of the screw (0.25 mm) per day, rather than using heavy force against the teeth. This approach along with surgically assisted palatal expansion (SARPE) and segmental osteotomy of the maxilla are the possibilities for the more mature patients in whom tooth-supported expanders will not work. Transverse expansion of the maxillary arch, which decreases buccal corridor width, improves the appearance of the smile if the buccal corridor width was excessive before treatment. u Should this be done only with dental expansion or by opening the midpalatal suture? That depends on the amount of expansion that is needed to meet the other goals of proper occlusion and long-term stability. An important consideration in widening a narrow arch form, particularly in an adult, is the axial inclination of the buccal segments. Patients in whom the posterior teeth are already flared laterally are not good candidates for dental expansion. Arch Expansion for Alignment Alignment in non-extraction cases requires increasing the arch length, moving the incisors farther from the molars. The important factor to consider is the amount of arch expansion that a given patient can tolerate without the creation of major aesthetic and post-treatment stability problems. In the context of this factor, a decision should be made at the treatment planning stage, and the focus on how to efficiently accomplish an appropriate amount of arch expansion in different situations as illustrated in Figure 7 below. Stability Considerations Clinical applications reflect extreme optimism about arch expansion and growth modification. Expansion of the arches moves the patient in the direction of more prominent teeth, but extraction tends to reduce the prominence of the teeth. Facial aesthetics can become unacceptable on either the too-protrusive or too-retrusive side. An individual with thick, full lips looks good with incisor prominence that would not be acceptable in someone with thin, tight lips. It is quite challenging to determine the aesthetic limit of expansion from toothbone relationships on a cephalometric radiograph. The key criterion for arch expansion is the amount of lip support from the anterior teeth needed for a satisfactory facial appearance. The timing of maturation and the potential to effect a change in the different facial planes of space are not uniform. In Maxilla: Maxillary growth in the transverse plane of space, the first to cease growing, stops when the first bridging of CLINICAL Fig 4 Jackscrew appliance Fig 5 MARPE In the late mixed dentition, root resorption of primary molars may have reached the point at which these teeth offer little resistance, and it may be wise to wait for eruption of the first premolars before beginning expansion. Expansion in Adolescents (Early Permanent Dentition) In mid-adolescence, there is a near 100% probability of opening the midpalatal suture with a banded or bonded expansion device, but as the adolescent growth spurt ends, interdigitation of the suture reaches the point that opening it may no longer be possible. Guidance for decision-making regarding the state of the midpalatal suture could be gained from chronologic age or dental developmental age. It can also be provided by one of several developmental staging methods such as the cervical vertebra maturation staging (CVMS), which is used to estimate mandibular growth potential and also to evaluate midpalatal suture maturation. This extension, however, has not been evaluated for validity. Skeletal anchorage for expansion is more likely to be successful in adolescents because retention of bone screws and plates requires a level of bone maturation that is not reached until mid-adolescence. The later years of adolescence are when decisions regarding maxillary expansion become most difficult. For these late adolescents, rapid expansion does make some sense, because force builds up rapidly to the point at which either the suture fractures or the treatment is discontinued. Slow expansion would be likely to just move the teeth, not open the suture. Fig 6 Buccal Corridor Fig 7 Arch expansion purpose, method, debate
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