SHORT COMMUNICATION

Maxillary arch changes during levelingand aligning with fixed appliancesand low-friction ligaturesLorenzo Franchi,a Tiziano Baccetti,b Matteo Camporesi,c and Massimo Lupolic

Florence, Italy

Introduction: The aim of this study was to evaluate the changes in the transverse dimension and theperimeter of the maxillary arch produced by a low-friction system during the leveling and aligning phases offixed appliance therapy. Methods: The low-friction protocol consisted of a combination of preadjustedbrackets, superelastic nickel-titanium archwires, and nonconventional elastomeric ligatures; it was used in20 consecutively treated patients with mild crowding. Results: Statistically significant increases wererecorded for all dentoalveolar widths (with the exception of intermolar width measured lingually) and archperimeter (3.5 mm on average). The increase in arch perimeter showed a significant negative relationship withthe individual perimeter of the maxillary arch before treatment. No significant change was found for archdepth. Conclusions: The low-friction system produced statistically significant increases in the transversedentoalveolar width and the perimeter of the maxillary arch during the leveling and aligning phases of

treatment with an average duration of 6 months. (Am J Orthod Dentofacial Orthop 2006;130:88-91)

Arch development is a therapeutic effect of fixedappliances in nonextraction treatment protocols.Dentoalveolar expansion leading to changes in

arch form and size has been documented in studies onthe effectiveness of fixed appliances in orthodonticpatients.1-5 Changes in the transverse measures of themaxillary arch include increases in intercanine widthfrom 0.55 mm1 to 2.13 mm2, interpremolar width (atthe second premolars) from 2.10 mm1 to 4.94 mm,2 andintermolar width from 1.53 mm1 to 2.96 mm.2 Thesemodifications have an impact on arch perimeter withthe consequent production of space to accommodateteeth. The reported increases in arch perimeter or archlength range from 0.2 mm3 to 1.8 mm.5

Classically, with straight-wire appliances, changesin arch form occur mostly during the final phases ofcomprehensive treatment when thick round or rectan-gular stainless steel archwires are used.6 The advent of

From the Department of Orthodontics, University of Florence, Florence, Italy.aLecturer; Thomas M. Graber Visiting Scholar, Department of Orthodonticsand Pediatric Dentistry, School of Dentistry, University of Michigan, AnnArbor, Mich.bAssistant professor; Thomas M. Graber Visiting Scholar, Department ofOrthodontics and Pediatric Dentistry, School of Dentistry, University ofMichigan, Ann Arbor, Mich.cLecturer.Reprint requests to: Lorenzo Franchi, Dipartimento di Odontostomatologia,Universitá degli Studi di Firenze, Via del Ponte di Mezzo, 46-48, 50127,Firenze, Italy; e-mail, l.franchi@odonto.unifi.it.Submitted and accepted, January 2006.0889-5406/$32.00Copyright © 2006 by the American Association of Orthodontists.

doi:10.1016/j.ajodo.2006.01.017

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low-friction techniques has introduced new perspec-tives in the clinical management of fixed applianceswith preadjusted brackets. For instance, self-ligatingappliances and other low-friction systems have beenreported to induce arch development and dentoalveolarexpansion of the maxillary arch during the initialphases of therapy with superelastic nickel-titaniumarchwires.7,8 An alternative method to generate lowfriction at the bracket/archwire unit is nonconventionalelastomeric ligatures (Slide, Leone Orthodontic Prod-ucts, Sesto Fiorentino, Firenze, Italy) that can be usedon conventional brackets.8-10

The aim of this study was to analyze the changes inthe transverse dimension and the perimeter of themaxillary arch produced by a low-friction systemconsisting of preadjusted brackets and nonconventionalligatures during the leveling and aligning phases offixed appliance therapy.

SUBJECTS AND METHODS

The sample consisted of 20 consecutively treatednonextraction patients (13 female, 7 male) with a meanage of 15 years 6 months. All subjects had mildamounts of crowding in the maxillary arch that did notrequire extractions. The treatment protocol comprisedpreadjusted brackets (STEP brackets, Leone Orthodon-tic Products) with nonconventional low-friction liga-tures (Slide and superelastic nickel-titanium archwires[.014-in archwires followed by .016-in archwires]) of

Tru-Arch medium form (Ormco, Sybron Dental Spe-

molar angulation.

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Franchi et al 89

cialties, Orange, Calif). All subjects gave their in-formed consent to participate in the study.

The duration of the aligning and leveling phase wason average 6 months � 2 months. Dental casts of themaxillary arch were taken at T1 (immediately beforetreatment) and T2 (at the end of leveling and aligningphase).

The following measurements were made on themaxillary dental casts at T1 and T2 (Fig).

● Intercanine width (lingual): distance between themost lingual points on the lingual surface of themaxillary canines.

● Intercanine width (cusp): distance between the tips ofthe cusps of the maxillary canines.

● First interpremolar width (lingual): distance betweenthe most lingual point on the lingual surface of themaxillary first premolars.

● First interpremolar width (fossa): distance betweenthe central fossae on the occlusal surface of themaxillary first premolars.

● Second interpremolar width (lingual): distance be-tween the most lingual point on the lingual surface ofthe maxillary second premolars.

● Second interpremolar width (fossa): distance be-tween the central fossae on the occlusal surface of themaxillary second premolars.

● Intermolar width (lingual): distance between thelingual fissure locations on the lingual surface of themaxillary first molars.

● Intermolar width (fossa): distance between the mesialfossae on the occlusal surface of the maxillary firstmolars.

● Arch depth: distance from a point midway betweenthe facial surfaces of the central incisors to a linetangent to the mesial surfaces of the first permanentmolars.

● Arch perimeter: sum of the segments between con-tact points from the mesial surface of the firstpermanent molar to the mesial surface of the oppositefirst permanent molar.

● Molar angulation: angle of intersecting lines drawntangent to the mesiofacial and mesiolingual cusp tipsof the right and left maxillary and mandibular firstpermanent molars.

The coordinates of all points on the dental castswere digitized by using a 3-dimensional electromag-netic digitizer (Microscribe-3DX, Immersion, San Jose,Calif) interfaced with a computer. The data were stored,and measurements were made with software (Rhinoc-eros NURBS modeling for Windows, Robert McNeel &

Associates, Seattle, Wash).

Fig. Measurements. A, transverse maxillary widths(continuous lines, distances between cusps or fos-sae; dotted lines, distances between lingual points);B, maxillary arch depth and perimeter; C, maxillary

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90 Franchi et al

Statistical analysis

Descriptive statistics were calculated for all maxil-lary dental cast measurements at T1 and T2, and for theT2-T1 changes. The Shapiro-Wilks test showed normaldistribution of the values at T1 and T2 for all measure-ments. Paired Student t tests were used to analyzestatistical differences between T1 and T2 values(P �.05). Linear regression analysis analyzed thedependence of T2-T1 changes in arch perimeter on thebasis of the T1 values for arch perimeter. All statisticalcomputations were performed with software (version12.0, SPSS, Chicago, Ill). The method error for thedental cast measurements ranged from 0.02 mm for firstinterpremolar width (lingual) to 0.16 mm for interca-nine width.

A control group is not required when investigatingdentoalveolar changes during a short observation pe-riod as described here (6 months). Transverse andsagittal arch changes in untreated subjects in the per-manent dentition at an average age of 15 years 6months are expected to be minimal.11

RESULTS

Descriptive statistics are reported in the Table.Intercanine widths (lingual and cusp) showed sig-

nificant increases from T1 to T2: 1.96 and 2.30 mm,respectively. The first interpremolar widths (lingual andcusp) had significant increases of 2.98 and 3.65 mm,respectively, similar to the second interpremolar widths(lingual and cusp), with significant increases of 2.30and 3.03 mm, respectively. The change in intermolarwidth at the lingual points was not statistically signif-icant (�0.04 mm), whereas the measurement at the

Table I. Descriptive statistics and comparison of maxil

T1

Measurement (mm) Mean SD

Maxillary arch width (fossae)Intercanine (cusps) 31.71 2.36Interpremolar (first) 32.49 2.49Interpremolar (second) 37.50 2.45Intermolar 42.65 1.94

Maxillary arch width (lingual)Intercanine 22.64 2.20Interpremolar (first) 24.18 1.83Interpremolar (second) 28.81 1.94Intermolar 31.59 1.45Maxillary arch depth 24.60 2.80Maxillary arch perimeter 71.22 4.79Maxillary molar angulation 165.65 9.59

*P � .05; †P � .01; NS, not significant.

fossa showed a significant increase (1.71 mm). A

significant reduction in molar angulation (�4.33°) wasfound; it indicated significant buccal inclinations of thecrowns of the first molars.

The change in arch depth was not significant fromT1 to T2 (0.57 mm). Arch perimeter had a statisticallysignificant T2-T1 increase (3.50 mm) that was signifi-cantly dependent on the pretreatment value for archperimeter (R � 0.58, P �.01).

DISCUSSION

In this study, we attempted for the first time toevaluate the changes in the transverse dimension andthe perimeter of the maxillary arch produced by alow-friction system during the leveling and aligningphases of fixed appliance therapy. The low-frictionprotocol consisted of a combination of preadjustedbrackets and nonconventional ligatures (Slide). Anin-vitro study compared the frictional forces generatedby nonconventional and conventional elastomeric liga-tures with .014-in superelastic nickel-titanium wire.9

The amount of both static and kinetic friction wasminimal (�10 g) with nonconventional ligatures withboth aligned and misaligned brackets. Another studyconfirmed the low-friction characteristics of the non-conventional ligatures combined with preadjustedbrackets during the leveling and aligning phases oforthodontic treatment.10

Arch form development and posterior expansion ofthe dental arches have been indicated as effects oflow-friction mechanics with self-ligating brackets dur-ing the initial phases of treatment with superelasticnickel-titanium .014-in wires.7 Our findings showedstatistically significant increases in maxillary arch

easurements at T1 and T2

T2 T2-T1 Paired t test

SD Mean SD Significance

1 2.18 2.30 2.32 †

3 2.14 3.65 2.67 †

4 2.37 3.04 2.50 †

6 2.63 1.71 2.92 *

0 1.79 1.96 1.63 †

7 1.86 2.98 2.29 †

2 2.17 2.30 2.11 †

4 2.31 �0.04 2.20 NS7 2.20 0.57 1.44 NS2 3.94 3.50 3.25 †

1 12.58 �4.33 6.14 †

lary m

Mean

34.036.140.544.3

24.627.131.131.525.174.7

161.3

widths and perimeter with low-friction ligatures and

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Franchi et al 91

preadjusted brackets during the leveling and aligningphase of treatment (average duration, 6 months). Sta-tistically significant increases were found for all widthmeasurements between the posterior teeth, with theexception of the first molars measured lingually. In-creases in arch width that used lingual points formeasurement were consistently smaller than the in-creases recorded by using points located at cusps orocclusal fossae. This indicates that expansion of themaxillary arch was achieved with a component ofbuccal inclination of the posterior teeth. The firstmolars also showed an increase in the angle of theirreciprocal inclination, thus confirming a significanttendency to buccal tipping of the crowns.

When contrasted with the data in the literature, theincreases in arch widths measured in this study werewithin the range described for transverse changes of themaxillary arch induced by comprehensive treatmentwith fixed appliances.1-5 The greatest transverse in-creases were recorded at the level of the premolars andthe canines, whereas smaller increases were found atthe level of the molars. A possible reason for thisdifferential effect might be the shape of the archwiresused for alignment of the maxillary teeth (Tru-Archform); these have an accentuated width in the canine-first premolar region.

The significant increases in the transverse widths ofthe maxillary arch led to a statistically significantincrease in maxillary arch perimeter (on average 3.5mm), a clinically favorable result for nonextractiontreatments. Linear regression analysis indicated that theamount of increase in arch perimeter depended signif-icantly on the pretreatment arch perimeter. Smallerpretreatment perimeters experienced greater increasesin arch length. The shape of the archwires used for theorthodontic treatment in our sample probably played an

important role for the attainment of this clinical result.

CONCLUSIONS

Our findings indicate that a low-friction systemconsisting of nonconventional elastomeric ligaturescombined with preadjusted brackets and superelasticnickel-titanium wires can produce statistically signifi-cant increases in the transverse dentoalveolar width andthe perimeter of the maxillary arch during the levelingand aligning phases of treatment with an averageduration of 6 months.

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