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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.
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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.
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WORLD JOURNAL OF ORTHODONTICS
VOLUME 6, NUMBER 4, 2005
Tech Notes
Fig 9
Posttreatment views.
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2.
3.
4.
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7.
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