CATEGORY 68 AUSTRALASIAN DENTIST The transverse dimension has been a focus of controversy among orthodontists. A key issue debated has been the possibility of altering the skeletal width of the maxilla or the mandible through either orthodontic or orthopaedic treatment. Nearly 15% of adolescents and adults have severely or extremely irregular incisors that would require major arch expansion or extraction of some teeth in order to align them. It is appropriate to address maxillary transverse deficiency at the beginning of skeletal problems because this is the first dentofacial dimension to cease growing. Like all craniofacial sutures, the midpalatal suture becomes more tortuous and interdigitated with increasing age. If the maxilla is narrow relative to the rest of the face, a diagnosis of transverse maxillary deficiency is justified by: u a comparison of both the width of the maxillary premolar teeth and the width of the palate with population norms. This has been advocated as one of the methods to diagnose maxillary deficiency. u another appropriate comparison of maxillary width to other transverse proportions in the same patient (e.g., bizygomatic width), not to population averages. Seemingly, a narrow maxilla accompanied by a narrow mandible and normal occlusion should not be considered a problem just because the jaw widths are below the population mean. Therefore, transverse deficiencies can be mistakenly diagnosed because there is really an anteroposterior maxillary deficiency and not really a transverse deficiency. Accurate diagnoses can avoid unnecessary treatment. The arch expansion potential for each individual case depends on: u biological limits of what is actually possible for the individual, based on their arch configuration, u gingival biotype, that is the thickness of the gingiva and how much they protect and support the teeth, u physiological response to the treatment, being how the teeth actually respond to the treatment. Expansion in the Primary and Early Mixed Dentition For most children with crowding and inadequate space in the early mixed dentition, some facial movement of the incisors and expansion can be accommodated. Skeletal expansion is easiest when the midpalatal suture has not fused or has only minor initial bridging, so that heavy force and extensive microfracturing are not needed to separate the palatal halves. Almost any expansion device will tend to separate the midpalatal suture in addition to moving the molar teeth in a child up to age 9 or 10. Methods used for palatal expansion in children: u a split removable plate with a jackscrew or heavy midline spring, u a lingual arch, for example, the W-arch or quad-helix design, u a fixed palatal expander with a jackscrew, which can be either attached to bands or incorporated into a bonded appliance. A key question is whether early expansion of the arches gives more stable results than later expansion (in the early permanent dentition). This early expansion can involve any combination of several possibilities: u Maxillary dental or skeletal expansion, moving the teeth facially and/or opening the midpalatal suture. u Mandibular buccal segment expansion by facial movement of the teeth. u Advancement of the incisors and distal movement of the molars in either arch. The most aggressive approach to early expansion uses maxillary and mandibular lingual arches in the complete primary dentition. This produces an increase in both arch perimeter and width, which must be maintained for variable periods during the mixed dentition years. CLINICAL Fallacies of purely arch expansion Dr Geoff Hall By Dr Geoffrey Hall Fig 1 Bilateral skeletal landmarks on a PA cephalogram. Maxillare (Mx) or J point, located at the depth of the concavity of the lateral maxillae contours, where the maxilla intersects the zygomatic buttress; Antegonion (Ag) or antegonial notch of the mandible, defined as the innermost height of the contour along the curved outline of the inferior mandibular border, low and medial to the gonial angle. The skeletal measurements were: Mx-Mx, the distance between the left and right Mx (in mm), which represents the skeletal width of the maxilla; Ag-Ag, the distance between the left and right Ag (in mm), which represents the skeletal width of the mandible. Fig 2 Methods for palatal expansion Fig 3 Lingual arch
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