CATEGORY 70 AUSTRALASIAN DENTIST the midpalatal suture begins, not at final complete fusion. This means that for most children, palatal width increase would normally end by early adolescence, and to alter this later with appliance therapy would require heavier force to open the midpalatal suture. Transverse maxillary expansion therefore is more physiologic if done before adolescence. Finally, to expand or extract? Substantial hereditary tooth-size/archlength discrepancy is a frequent finding in early childhood, and the crucial question for orthodontists is whether the appropriate treatment plan is to change the form of the basal bone or the arch form by either expansion, distalization, or proclination, or to perform a serial-extraction treatment approach instead. A narrow maxillary arch is related to the extraction/non-extraction decision in that a child with crowded teeth and deficient maxillary width can have transverse expansion to provide space to align the teeth. Many of these patients have some distortion of the arches, tooth abrasion from interferences of anterior teeth, and either anterior or lateral mandibular shifts that can lead to the possibility of mandibular skeletal asymmetry. Palatal expansion can be done at any time before the end of the adolescent growth spurt, but the technique varies with the patient’s age, with different procedures for preadolescents, early and late adolescents, and adults. However, the existing sagittal, vertical, transverse, and skeletal relationships, as well as the patient’s soft tissue profile are to be included in the final treatment plan. It is “…often stated confidently that extraction leads to incisor retraction and narrower arches and that expansion leads to incisor protrusion and wider arches.” Some recent studies that compared patients with malocclusions who were treated either with expansion or extraction, showed little or no difference. However, for both frontal and profile appearance, the amount of change in both scenarios would be related to the amount of crowding and protrusion that was present initially, and to the clinician’s decision as to how to manage arch expansion or closure of extraction spaces. A final set of guidelines is as follows: u From the perspective of both aesthetics and stability: • The more we can expand without moving the incisors forward, the more patients we can treat satisfactorily without extraction. • The more we can close extraction spaces without over-retracting the incisors, the more patients we can treat satisfactorily with extraction. u For oral health, excessive expansion increases the risk of mucogingival problems. u For masticatory function, expansion or extraction makes no difference. u References • Flavia Artese, To expand or not to expand? Dental Press J Orthod. 2020 Jan-Feb;25(1):7-8. • Robert H. W. Strang, The Fallacy of Denture Expansion as a Treatment Procedure, Angle Orthod (1949) 19 (1): 12–22. • Robert T. Lee, Arch width and form: A review, Am J Orthod Dentofacial Orthop 1999;115:30513 • William. R. Profitt, Contemporary Orthodontics (6th edition). Dr Geoff Hall, Specialist orthodontist Founder and Director of OrthoED, Smilefast, CAPS and Clear Aligner Excellence Tel: 03 9108 0475 geoff@orthoed.com.au CLINICAL Fig 8 Midpalatal suture In Mandible: As the lower arch is more constrained, the limits of expansion for stability seem to be tighter for it than the maxillary arch. According to various studies, moving lower incisors forward more than 2 mm is problematic for stability, probably because lip pressure seems to increase sharply at about that point. Expansion across the canines is not stable, even if the canines are retracted when they are expanded. Expansion across the premolars and molars, in contrast, can be stable if it is not overdone. Basal bone and apical base are synonymous terms for the bone that supports the teeth and is continuous with the alveolar process as well as with the maxillary and mandibular bodies. Therefore, according to R.H.W. Strang, (AO 1949), after measuring a large number of cases, a conclusion could be drawn about the fallacy of expansion as a treatment procedure: Fig 9 Mandibular expansion limits Strang Conclusions u Every malocclusion represents an apical base under the influence of, and stabilised by, balanced muscular forces. u These balanced muscular forces are inherent to the individual and cannot be changed by any known method of treatment. u These muscular forces are present in two forms – muscular tonus and muscular contractions. u Successful treatment must aim to preserve this muscular balance, rather than alter or upset it. u The key teeth in designating the tooth positioning that is harmonious with the muscular forces constantly in action upon the apical base, are the mandibular canine and mandibular first molar dental units. u Therefore, stabilised results can only be gained when the width of the mandibular base in the canine and molar areas is maintained inviolate. u The form of the maxillary denture and positioning of the maxillary teeth are governed by the mandibular base form and tooth positioning established by adhering to the dictates of muscular balance. u When it is impossible to rearrange the mandibular dental units in the desired alignment with the incisors re-established in locations overlying their basal supporting bone, without moving the canine teeth labially and the molar teeth buccally, extraction of dental units is definitely indicated. u If muscular balance is preserved in treatment, it should be possible to eliminate mechanical retention at the end of active treatment and have a result that would remain stable.
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