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TECH NOTES Edited by: Larry W. White, DDS, MSD ([email protected]) A RATIONALE FOR EXPANSION Michael Owen Williams, DDS Larry W. White, DMD, MSD Orthodontic researchers and clinicians have traditionally considered the mandibular arch as the ultimate limitation for diagnosis, treatment planning, and therapy for nonextraction cases; ie, the size of the mandible and positions of the teeth could not assume dimensions that differed greatly from those of the malocclusion.1,2 These researchers simply confirmed what successors to Angle have presumed about expansion—that it remains unstable. Orthodontists have habitually evaluated malocclusions as though they were an effect of mandibular development alone and that the maxilla should and could adapt around this somewhat immutable feature of the oral defect. Nevertheless, researchers suggested some time ago that the position of the maxilla might have an important effect on the position of mandibular incisors.3 Tweed popularized the use of the mandible and, in particular, the mandibular incisors as the a priori diagnostic and treatment planning paradigm after his unhappy experience with Angle arch expansion techniques.4,5 He received early and enthusiastic endorsement from respected clinicians such as Steiner, 6,7 Williams,8 and Ricketts9 and the mandibular incisor remained the mainstay of orthodontic diagnosis for several decades until Holdaway,10,11 Creekmore,12 and Alvarez13 suggested the maxilla and the maxillary incisors as determinates of the soft-tissue profile. Future studies of arch stability should probably consider both maxillae and mandibles when assessing the perimeter and arch width changes during treatment and postretention. The successful use of orthopedic appliances alerted orthodontists to the possibility of increasing arch widths and arch perimeters with minimum forces.14,15 Although mandibular canines show singular resistance to significant expansion, mandibular premolars and first molars often experience substantial and stable expansion. Brader’s work with the trifocal ellipse arch form hinted at this expansion possibility,16 but he failed to suggest how this might result in wider and more accommodating arch patterns. The exploitation of this expansive capability offers orthodontists additional opportunities to accommodate crowded denti- CORRESPONDENCE Dr Michael O. Williams 424 Courthouse Road Gulfport, MS 39507, USA www.gulfcoast orthodontics.com tions and to treat patients with a nonextraction regimen. Weinberg and Sadowsky17 explained how orthodontic clinicians have three options for increasing the arch perimeters of patients with crowded Class I relationships: 1. Distal retraction of molars 2. Advancement of incisors 3. Expansion of arches distal to the canines Effective retraction of first molars requires the removal of second molars, and even this approach gains little space.18 The simple placement of brackets and archwires will ordinarily advance incisors, which will sometimes exceed acceptable positions. Of these 3 strategies, expansion distal to the canines probably offers the most benefits with the fewest liabilities. However, clinicians can avoid excessive incisor advancement by combining brackets and wires with a specially designed compressed titanium coil expander. The MSX 2000 appliance [AU: mfr?] allows lateral arch development in the premolar and first molar regions, without subsequent incisor displacement (Fig 1). The MSX 2000 Appliance The MSX 2000 offers clinicians a low profile, continuous lightforce fixed apparatus that mimics the expansion Frankel and others achieved with passive appliances. The MSX 2000 presents an assembly of tubes and rods soldered to either bands or crowns, and it receives its expansive energy from compressed titanium coil springs (Fig 2). Clinicians can adapt the appliance for use in either the maxilla or mandible to achieve lateral arch development. Many orthodontists have trouble understanding the rationale for expansion in the maxilla in the absence of a crossbite. However, waiting until maxillary canines erupt with insufficient space offers a less desirable strategy than providing for their entrance while the patient undergoes growth and development. Clinicians need to make a habit of evaluating the maxillary width, as measured between the 2 first permanent molars, to assess the need and potential for lateral arch development. It almost seems counterintuitive to view the maxillary arch as the limiting feature for the alignment of crowded mandibular incisors, but the maxillary expansion must accommodate the mandibular development. 189 WORLD JOURNAL OF ORTHODONTICS Tech Notes Fig 1 Fig 2 Fig 3 MSX 2000. MSX 2000 compressed titanium coil springs. DMAX 2000 Fig 4 Pretreatment facial views. Fig 5 Pretreatment intraoral views. Bishara suggests that a lingual arch in the mixed dentition will increase the potential for a terminal plane shift into a Class II malocclusion without distal retraction of the maxilla or the maxillary molars.19,20 When clinicians need maxillary molar retraction and expansion simultaneously, a variation of the MSX 2000 can achieve those aspects without benefit of an extraoral retractor (Fig 3). Clinical Application Providing extra arch perimeter represents a major feature of the MSX 2000, and this makes it valuable in treating borderline extraction patients. Profitt21 has suggested that 3 mm or less of arch-length discrepancy usually calls for nonextraction therapy. Ten millimeters or more of arch-length discrepancy almost certainly requires an extraction treatment plan. The patients with 4 to 9 mm of discrepancy represent a group that can justifiably receive either extraction or nonextraction therapy. A nonextraction treatment plan ordinarily offers clinicians an attractive alternative to extractions, with less patient trauma, simpler mechanics, and the requirement of less patient compliance. A dependable arch development therapy can often achieve such treatment. The following treatment features an Asian female of 13 years 4 months with Class I molars and Class II canines (Figs 4 and 5). She had excessive overbite and overjet and considerable maxillary and mandibular arch-length discrepancies. A cephalometric evaluation revealed a midface deficiency anteroposteriorly and 190 transversely (Fig 6). Therapy consisted of dual arch development with MSX 2000 appliances, in conjunction with a fully bonded 0.018-inch preadjusted appliance (Fig 7). The expansion devices continue until the maxilla expands to a minimum of 36 mm, as measured transpalatally from first molar to first molar at the lingual cementoenamel junction.22 The expansion occurred distal to the canines in both arches, along with improvements in facial dimensions (Figs 8 and 9). As orthodontists diagnose and plan treatment for young patients, they need to anticipate what those adolescent faces may look like at maturity. By starting with the eventual end in mind, orthodontic clinicians can often select alternatives to extraction therapies for patients with nonprotrusive profiles. Summary Over the past 100 years, orthodontists have vacillated between extremes of nonextraction and extraction therapies. Injudicious selection of therapies despite facial dimensions has probably contributed to the major clinical disappointments within each style of therapy. The belief that expansion distal to the canines would not stabilize after the cessation of active treatment has contributed to the reluctance to use such therapy. However, experience has shown that this type of expansive, nonextraction therapy can have success without relapse and merits more attention from the specialty. VOLUME 6, NUMBER 4, 2005 Tech Notes Analysis (Ricketts) Frontal analysis Initial Norm Clinical deviation Cranial relationships Cranial structure Anterior cranial base (mm) 51.7 58.8 -2.9 Posterior facial height (mm) 68.5 65.2 1.0 Cranial deflect (degrees) 22.0 28.0 -2.0 Porion location (mm) -41.3 -41.0 -0.1 Ramus Position (degrees) 69.8 75.0 -1.7 Maxillary position Maxillary depth (degrees) 85.6 89.0 -1.1 Maxillary height (degrees) 52.2 60.9 -2.9 SN-palatinal plane (degrees) 2.7 7.3 -1.3 Mandibular position Facial depth (degrees) 81.1 87.6 -2.2 Facial axis (degrees) 86.9 86.0 0.3 Mandibular plane (degrees) 29.6 28.4 0.3 Total facial height (degrees) 57.7 60.0 -0.8 Facial taper (degrees) 69.3 65.0 1.2 Maxillary/mandibular relationships Maxilla Convexity (mm) 3.9 2.0 0.9 Mandible Corpus length (mm) 65.0 70.7 -1.3 Mandibular arc (degrees) 34.2 27.4 1.7 Maxilla/mandible Lower facial height (degrees) 45.2 47.0 -0.5 Dental relationships Maxillary dentition Mx 1, to APo (mm) 6.8 6.2 0.3 Mx 1, to FH (degrees) 103.1 111.0 -1.3 Mx 6, to PTV (mm) 7.1 16.4 -3.1 Mandibular dentition Md 1, to APo (mm) 2.7 3.0 -0.1 Md 1, inclination (degrees) 29.8 25.0 1.2 Md 1, extrusion (mm) 2.3 2.2 0.1 Hinge axis angle (degrees) 104.6 90.0 3.6 Maxillary/mandibular dentition Interincisor angle (degrees) 123.8 124.0 -0.0 Molar relationship (mm) -1.7 -1.8 0.1 Incisor overjet (mm) 4.9 3.2 0.7 Incisor overbite (mm) 4.5 2.3 1.1 Esthetic relationships Lower lip E-plane (mm) 1.1 2.0 -0.4 Summary description Facial type: Mesiofacial, brachyfacial tendency (0.0) Skeletal: Class II tendency Dental: Class I Maxilla (anteroposterior): Mild retrognathia Mandible (anteroposterior): Moderate retrognathia Maxillary incisors: Normal Mandibular incisors: Normal Lower lip: Normal Overjet: 4.9 mm Overbite: 4.5 mm [AU: WHAT DO ASTERISKS STAND FOR?] ** ** * * ** * ** * Facial width (mm) Nasal width (mm) Maxillary width (mm) Mx-Md width right (mm) Mx-Md width left (mm) Molar relation right (mm) Molar relation left (mm) Intermolar width (mm) Molar to jaw right (mm) Molar to jaw left (mm) Mandibular width (mm) Intercanine width (mm) Denture midline (mm) Mx-Md midline (degrees) J distance right (mm) J Distance left (mm) AG distance right (mm) AG distance left (mm) AG menton right (mm) AG menton left (mm) Initial Norm 133.0 32.8 66.6 13.6 10.6 2.8 -0.2 52.7 12.5 11.2 87.9 20.7 0.4 2.3 32.5 34.1 45.2 42.7 51.8 45.9 134.6 30.4 65.6 11.0 11.0 1.5 1.5 57.0 6.7 6.7 88.2 27.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Clinical deviation -0.5 1.2 * 0.3 1.7 * -0.3 0.9 -1.1 * -2.1 ** 3.4 *** 2.6 ** -0.1 -2.2 ** 0.2 1.1 * 0.3 0.3 0.5 0.4 0.5 0.5 [AU: WHAT DO ASTERISKS STAND FOR?] * * * *** * *** * Fig 6 Pretreatment cephalometric tracing and analysis (Quick Ceph 2000) 191 Tech Notes Fig 7 Expansion views. Fig 8 Posttreatment cephalometric tracings and superimpositions. 96 WORLD JOURNAL OF ORTHODONTICS VOLUME 6, NUMBER 4, 2005 Tech Notes Fig 9 Posttreatment views. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Dugoni S, Lee J, Varela J, Dugoni A. Early mixed dentition treatment: Postretention evaluation of stability and relapse. Angle Orthod 1995;65:311–320. Little RM, Riedel RA, Stein A. Mandibular arch length increase during the mixed dentition: Postretention evaluation of stability and relapse. Am J Orthod Dentofacial Orthop 1990;97:393–404. Schulhof R, Allen R, Walters R, Dreskin M. The mandibular dental arch. Part 1: Lower incisor position. Angle Orthod 1977;47:280–287. Tweed CH. The Frankfort mandibular incisor angle (FMIA) in orthodontic diagnosis, treatment planning and prognosis. Angle Orthod 1954;24:121–169. Tweed CH. The diagnostic facial triangle in the control of treatment objectives. Am J Orthod 1969;55:105–121. Steiner CC. 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