immediate effects of rapid maxillary expansion with haas-type and hyrax-type expanders

Immediate effects of rapid maxillary expansionwith Haas-type and hyrax-type expanders:A randomized clinical trialAndr!e Weissheimer,a Luciane Macedo de Menezes,b Mauricio Mezomo,a Daniela Marchiori Dias,a

Eduardo Martinelli Santayana de Lima,b and Susana Maria Deon Rizzattoc

Porto Alegre, Rio Grande do Sul, Brazil

Introduction: The purposes of this study were to evaluate and compare the immediate effects of rapid maxillaryexpansion (RME) in the transverse plane with Haas-type and hyrax-type expanders by using cone-beamcomputed tomography. Methods: A sample of 33 subjects (mean age, 10.7 years; range, 7.2-14.5 years)with transverse maxillary deficiency were randomly divided into 2 groups: Haas (n 5 18) and hyrax (n 5 15).All patients had RME with an initial activation of 4 quarter turns followed by 2 quarter turns per day until theexpansion reached 8 mm. Cone-beam computed tomography scans were taken before expansion and at theend of the RME phase. Maxillary transversal measurements were compared by using the mixed analysis ofvariance (ANOVA) model and the Tukey-Kramer method. Results: RME increased all maxillary transversedimensions (P\0.0001). There was less expansion at skeletal than dental levels. The hyrax group had greaterstatistically significant orthopedic effects and less tipping tendency of the maxillary first molars compared withthe Haas group. Conclusions: Both appliances were efficient in correcting a transverse maxillary deficiency.The pure skeletal expansion was greater than actual dental expansion. The hyrax-type expander producedgreater orthopedic effects than did the Haas-type expander, but this effect was less than 0.5 mm per side andmight not be clinically significant. (Am J Orthod Dentofacial Orthop 2011;140:366-76)

Rapid maxillary expansion (RME) is an importantmethod used to correct a transverse maxillary de-ficiency. It was first described in the literature over

a century ago by Angell,1 and it has been disseminatedand made widely popular by Haas since 1961.2 InRME, rigid and fixed expanders are used to produceheavy forces to obtain the maximum skeletal responseby opening the midpalatal suture, with minimumorthodontic movement.2-5

Among the appliances used for RME, the tooth-tissue–borne (Haas-type) and the tooth-borne (hyrax-type) expanders are the most recognized in the literature.The main difference between them is the acrylic pad thatleans on the lateral walls of the palatal vault (Haas-type)

to reinforce the anchorage for greater orthopedicresponse and better force distribution during RME.2,4

In the hyrax-type expander, there is no acrylic pad;therefore, it is more hygienic and prevents soft-tissueirritation caused by food impaction under the acrylicplate.6 Although a cephalometric investigation has notdemonstrated any differences between Haas-type andhyrax-type expanders,7 there is no consensus in the lit-erature regarding the differences in the immediateRME effects produced by these appliances.

Several investigations have analyzed the effects ofRME through 2-dimensional cephalometric radiographs,which do not allow accurate identification of dentoske-letal structures because of the superimposition of manybones in the different planes of space.2,7-9 To overcomethese limitations, computed tomography (CT) for theassessment of the transverse dimensions of themaxilla was introduced by Timms et al10 in the1980s. However, the use of conventional CT scans inorthodontics has been limited because of cost and ra-diation concerns.11 Cone-beam CT (CBCT) has usheredin a new era in dental diagnostics. This technology wasdesigned for imaging hard tissues of the maxillofacialregion with minimum distortion at a lower cost andwith lower radiation emissions compared with

From the Department of Orthodontics, Pontifical Catholic University of RioGrande Do Sul, Porto Alegre, Rio Grande do Sul, Brazil.aPostgraduate student (Ph.D.).bProfessor.cAssistant professor.The authors report no commercial, proprietary, or financial interest in the prod-ucts or companies described in this article.Reprint requests to: Andr!e Weissheimer, Pontif!ıcia Universidade Cat!olica do RioGrande do Sul, Faculdade de Odontologia, Pr!edio 6, Avenida Ipiranga, 6681, sala209, Porto Alegre, RS, Brazil, CEP 90619-900; e-mail, [email protected], March 2010; revised and accepted, July 2010.0889-5406/$36.00Copyright ! 2011 by the American Association of Orthodontists.doi:10.1016/j.ajodo.2010.07.025

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ORIGINAL ARTICLE

mailto:[email protected]

conventional CT. The high resolution of CBCT imagesis due to the isotropic voxel (equal in all 3 dimensions),which produces submillimeter resolutions ranging from0.4 mm to as low as 0.125 mm.11 Several investigationshave shown the high accuracy of CBCT images forquantitative and qualitative analyses.12-15 Its use isrecommended in orthodontics for several purposessuch as evaluation of impacted teeth,16,17 evaluation

of bone grafts in cleft regions,18 analysis of alveolarbone before placement of orthodontic temporary an-chorage devices,19 and evaluation of RME effects onnasomaxillary structures.20

The purposes of this study were to evaluate and com-pare the immediate effects of RME on the transverseplane with Haas-type and hyrax-type expanders byusing high-resolution CBCT.

Fig 1. A, Haas-type expander and B, hyrax-type expander at the end of the active phase of RME.

Fig 2. Transverse maxillary posterior region evaluation:A andB, preexpansion;C andD, at the end ofthe active phase of expansion.

Weissheimer et al 367

American Journal of Orthodontics and Dentofacial Orthopedics September 2011 ! Vol 140 ! Issue 3

MATERIAL AND METHODS

This study was approved by the ethical committee ofthe Pontifical Catholic University of Rio Grande do Sul inBrazil. Informed consent was obtained from the parentsof all patients who agreed to participate in this study. Thesample was selected by examining subjects in need of or-thodontic treatment at the Department of Orthodonticsof the School of Dentistry. The inclusion criteria forthis study were transverse maxillary deficiency, mixeddentition or early permanent dentition, and no surgicalor other treatment that might affect the RME effectsduring the expansion period. Patients with congenitalmalformations or periodontal diseases, or above 15 yearsof age were excluded from the study sample.

In this prospective study, the sample comprised 33healthy white children (11 boys, 22 girls) with a meanchronologic age of 10.7 years (range, 7.2-14.5 years)and a mean skeletal age of 10.9 years (range, 6.8-15years). These patients were randomly divided into 2groups: Haas (n 5 18) and hyrax (n 5 15). In the Haasgroup, the Haas-type expander, with 4 bands (first perma-nent molars and first premolars or first deciduous molars)and buccal and lingual stainless steel bars of 1.0-mmdiameter was used (Fig 1, A). In the hyrax group, thehyrax-type expander, with 4 bands, buccal and lingualstainless steel bars of 1.0-mm diameter and a jackscrew

with 1.4-mm stainless steel extensions soldered to the lin-gual surfaces of each pair of bands, was used (Fig 1, B).

Both appliances had expansion jackscrews with acti-vations of a quarter turn equivalent to a 0.2-mm expan-sion. All patients in the Haas and hyrax groups had RME,with initial activations of 4 quarter turns (0.8 mm)followed by 2 quarter turns per day (0.4 mm) until theexpansion screw reached 8 mm.

The i-CAT (Imaging Sciences International, Hatfield,Pa) was used to obtain CBCT images before RME (T1)and at the end of the active expansion phase (T2). TheCBCT scans were performed at 120 kV, 8 mA, scantime of 40 seconds, and 0.3-mm voxel dimension. Thedata for each patient were reconstructed with 0.3-mmslice thickness, and the digital imaging and communica-tions in medicine (DICOM) images were assessed by us-ing the EFILM workstation software program (version2.1.2, Merge Healthcare, Milwaukee, Wis). All linearand angular measurements were made by a blinded ex-aminer (M.M.), who had no access to the data or the clin-ical consultations of the patients in this sample.

For transverse maxillary posterior region evaluation,the DICOM files with CBCT images at T1 and T2 were im-ported into EFILM and visualized as axial imagesarranged side by side. To obtain standardized axial andcoronal slices and thus allow the comparisons betweenT1 and T2, the following references were used. In the

Fig 3. Landmarks used in the evaluation of the maxillary posterior region.

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axial slices, the images that displayed the root canal inthe most apical region of the palatal root of maxillaryfirst permanent molars were selected. By using the Mul-tiPlanar Reformation tool, the MultiPlanar Reformationline was positioned at the root canal in the most apicalregion of the palatal root of the maxillary first perma-nent molars on the right and left sides. From these ref-erences, standardized coronal images were produced,and the measurements were made (Fig 2). The landmarksused for evaluation of the maxillary posterior region areshown in Figure 3 and described in Table I.

The analyses of the transversal changes in the maxil-lary anterior region were performed in a similar way tothose of the posterior region. In the axial slices, imagesat T1 and T2 were selected with the root canals in themost apical region of the roots of the maxillary perma-nent canines visualized. After that, the MultiPlanar

Reformation line was positioned at the root canal inthe most apical region of the maxillary permanentcanine root on the right and left sides. From theses ref-erences, standardized coronal images were produced,and the measurements were made (Fig 4). The landmarksused to evaluate the RME effects in the anterior region ofmaxilla are shown in Figure 5 and described in Table I.

Statistical analysis

Intraexaminer reliability of the measurements wasdetermined by intraclass correlation coefficients. Doubleassessments of each parameter at T1 and T2 (10 daysapart) of 15 randomly selected patients from bothgroups were compared (Table II). The data obtainedfrom all measurements were processed with SAS soft-ware (version 9.0.2, SAS, Cary, NC). Means and standarderrors for each parameter were calculated, and data at T1

Table I. Landmarks for transverse maxillary evaluationSkeletalLine 1-2 Posterior baseline Line formed by the 2 lower points at the inferior inner contour of the

posterior nasal cavity on the right and left sides, respectively.Line 13-14 Anterior baseline Line formed by the 2 lower points at the inferior inner contour of the anterior

nasal cavity on the right and left sides, respectively.Distance 5-6 Posterior apical base width Distance between points 5 and 6 (points formed by the intersection of the

line 1-2 with buccal contour of maxilla on the right and left sides,respectively).

Distance 11-12 Posterior midpalatal suture width Distance between points 11 and 12 (lower points at medial limits of maxillarypalatine processes, on the right and left sides, respectively), representingthe midpalatal suture.

Distance 15-16 Anterior apical base width (inferior) Distance between points 15 and 16 (points formed by the intersection of line13-14 with buccal contour of maxilla on the right and left sides,respectively).

Distance 17-18 Anterior apical base width (superior) Distance between points 17 and 18 (intersection of the straight line, which isparallel and 5 mm superior to line 13-14, with buccal contour of maxillaon the right and left sides, respectively).

Distance 21-22 Anterior mid-palatal suture width Distance between points 21 and 22 (lower points at medial limits of maxillarypalatine processes, on the right and left sides, respectively), representingthe midpalatal suture in the anterior region.

AlveolarDistance 3-4 Posterior width at the alveolar crest level Distance between points 3 and 4 (coronal-most points of the maxillary

buccal alveolar processes, on the right and left sides, respectively).Distance 19-20 Anterior width at midalveolar level Distance between points 19 and 20 (intersection of the straight line, which is

parallel and 5 mm inferior to line 13-14, with buccal contour of maxilla onthe right and left sides, respectively).

DentalDistance 7-8 Intermolar width at occlusal surface Distance between points 7 and 8 (points formed by the intersection of

a straight line, that superimpose the long axis of the root canal of firstpermanent molar palatine root, with the occlusal surface on the right andleft sides, respectively).

Distance 9-10 Intermolar width at palatal root apices Distance between points 9 and 10 (apices of palatine root of permanent firstmolars, on the right and left sides, respectively).

Angle 1MD Right first molar angulation Angle formed by the straight line from point 7 and that superimposes thelong axis of the root canal of permanent first molar palatine root, on theright side, with line 1-2.

Angle 1ME Left first molar angulation Angle formed by the straight line from point 8 and that superimposes thelong axis of the root canal of permanent first molar palatine root, on theleft side, with the line 1-2.



and T2 were compared by using the mixed analysis ofvariance (ANOVA) model and the Tukey-Kramer methodat a significance level of 5%.

RESULTS

The overall immediate effects of RME on the trans-verse plane are shown in Table III. There were signifi-cant increases in maxillary width at the skeletal,alveolar, and dental levels for both the Haas (TableIV) and the hyrax (Table V) groups in all parameters(P \0.05). There was less expansion at the skeletalthan at the dental level, just as the increase in the max-illary apical base was smaller in the posterior region(distances 5-6 and 11-12) compared with the anterior(distances 15-16, 21-22) (Tables III-V). The hyraxgroup had greater statistically significant increases inthe maxillary transverse dimensions at the skeletallevel than did the Haas group in both posterior(distances 5-6 and 11-12) and anterior (distance 21-22) regions (Table VI). There was no significant differ-ence between the groups for the buccal inclination ofthe maxillary first permanent molars, except for the

linear measure (distance 9-10), which indicated greaterinclination of these teeth in the Haas group than in thehyrax group (Table VI).

DISCUSSION

After Broadbent21 introduced the cephalostat in1931, several investigations have analyzed the effectsof RME through cephalometry in 2-dimensional radio-graphs.3,8,22 The major problem associated withcephalometry is projection errors, which have an effecton linear and angular measurements, caused bymagnification and distortion and are compounded byincorrect patient positioning.23,24 To overcome theselimitations, we evaluated and compared, using high-resolution CBCT, the immediate effects of RME on thetransverse planes with Haas-type and hyrax-type ex-panders. CBCT was used because it is a suitable exami-nation for imaging craniofacial areas, with minimumdistortion, at a lower cost and with lower radiation dos-ages than conventional CT.11,25,26 In addition, CBCT isan accurate and reliable method for assessing changesassociated with RME on nasomaxillary structures.20

Fig 4. Transverse maxillary anterior region evaluation: A and B, preexpansion; C and D, at the end ofthe active phase of expansion.



Regarding previous reports that used CT images toevaluate RME, our study had an adequate sample size(33 subjects).10,20,27-33 Furthermore, this study designhad some important features: (1) it was a prospectivestudy; (2) the patients were randomly divided betweenthe groups; (3) the methodology was highlystandardized in terms of appliance fabrication, and rateand amount of expansion; and (4) it used high-resolution CBCT. In this study, since the active expansionphase lasted only 19 days, there was no need to usea control group without treatment since normal growthwas not an influencing factor in this short time. In this

study, the overall effects of RME produced a significantskeletal increase in the transverse maxillary dimension,confirming previous reports.2-5,20,28,30,34,35 The skeletalexpansion amounts were greater in the anteriorregion—2.82 mm (distance 17-18), 3.48 mm (distance15-16), and 4 mm (distance 21-22)—compared withthe posterior—2.64 mm (distance 5-6) and 2.88 mm(distance 11-12) (Table III). In agreement with previousauthors, the expansion pattern was triangular witha wider base at the anterior portion of maxilla.20,29,35

The greater expansion in the anterior region could beexplained by the resistance of the medial and lateralpterygoid plates of the sphenoid bone to the maxillarytip movement during the RME.35 Another feasible expla-nation would be through maxillary expansion biome-chanics: ie, the direction of the expansion forceproduced by the expanders would be located anteriorto the center of resistance of each maxillary half.36

The hyrax-type expander produced greater skeletalexpansion—3.14 mm (distance 11-12) and 4.37 mm(distance 21-22)—than did the Haas-type expander—2.62 mm (distance 11-12) and 3.63 mm (distance21-22) (Table VI). The skeletal gain in the hyrax groupaccounted for 38.5% to 39.2% (posterior region) and37.5% to 54.7% (anterior region) of the total expansion(8 mm). In the Haas group, the increases were smaller,ranging from 27.2% to 32.7% in the posterior region

Fig 5. Landmarks used in the evaluation of the maxillary anterior region.

Table II. Intraclass correlation coefficients of the mea-surements

Measurement ICCDistance 5-6 0.98Distance 11-12 0.94Distance 15-16 0.96Distance 17-18 0.95Distance 21-22 0.61Distance 3-4 0.98Distance 19-20 0.96Distance 7-8 0.95Distance 9-10 0.97Angle 1MD 0.93Angle 1ME 0.74



and 32.7% to 45.2% in the anterior region. Thesecomparison results between the appliances differ fromprevious reports.7,28,37 Siqueira et al7 compared theHaas-type and hyrax-type expanders through frontalcephalometric radiographs and found no differencesbetween them. Garib et al28 also found no differencesbetween these 2 expanders using spiral CT. This phe-nomenon could be explained by the small study sample(n 5 8), which reduced the power of the t test to showstatistically significant differences. When significantdifferences are demonstrated in such situations, theyclearly exist and most likely have clinical importance.However, the absence of significant differences doesnot necessarily indicate that they do not exist. In addi-tion, the RME changes were analyzed 3 months afterthe active expansion phase, unlike our study, with theimmediate effects of RME on 33 patients evaluated. Indisagreement with the present study, Oliveira et al37

found that the Haas-type expander achieved expansionwith a greater component of orthopedic movementthan the hyrax-type expander. However, the comparisonbetween the 2 kinds of expanders was performed onstudy models and anteroposterior cephalograms.

The main difference between Haas-type and hyrax-type expanders is the acrylic pad close to the palate in

the Haas-type appliance. According to Haas,4 a purposeof the acrylic pad is to reinforce the anchorage forgreater orthopedic response during RME. However,the results of our study did not support this theory,at least regarding the immediate effects of expansion.Better results in the immediate skeletal response wereobtained by the hyrax-type expander vs the Haas-type. This fact can be explained by differences in appli-ance design: more specifically, in the connection mech-anism of the jackscrew to the bands of the anchorageteeth. In the hyrax-type appliance design, the jackscrewwas directly connected to the bands by a rigid stainlesssteel framework (1.4 mm), unlike the Haas-type appli-ance design, where the acrylic was responsible for con-necting the stainless steel framework (1.0 mm) to thejackscrew. According to a previous study about the bio-mechanics of RME, appliance designs that use anacrylic interface with the teeth are far less stiff thanthose constructed solely of soldered stainless steelwire, as in the case of the hyrax-type expander.36 How-ever, the acrylic pad against the palate would be impor-tant, especially during the retention period, when itwould prevent the bone from moving through theteeth, thus averting an orthopedic relapse of the ex-panded maxilla.4,5,20

Table III. Immediate changes in the maxillary transverse plane with RME

Variable

T1 T2 Change

PMean SE Mean SE Mean SESkeletalDistance 5-6 (mm)

Posterior apical base width 60.29 0.64 62.93 0.64 2.64 0.11 \0.0001*Distance 11-12 (mm)

Posterior midpalatal suture width 00.00 0.08 02.86 0.08 2.88 0.09 \0.0001*Distance 15-16 (mm)

Anterior apical base width (inferior) 38.37 0.61 41.85 0.61 3.48 0.23 \0.0001*Distance 17-18 (mm)

Anterior apical base width (superior) 38.96 0.83 41.78 0.83 2.82 0.23 \0.0001*Distance 21-22 (mm)

Anterior midpalatal suture width 00.00 0.10 04.00 0.11 4.00 0.13 \0.0001*AlveolarDistance 3-4 (mm)

Posterior width at alveolar crest level 51.65 0.51 57.28 0.51 5.63 0.16 \0.0001*Distance 19-20 (mm)

Anterior width at midalveolar level 40.06 0.58 44.46 0.58 4.40 0.22 \0.0001*DentalDistance 7-8 (mm)

Intermolar width at occlusal surface 43.51 0.44 51.31 0.44 7.80 0.15 \0.0001*Distance 9-10 (mm)

Intermolar width at palatal root apices 29.90 0.52 32.55 0.52 2.65 0.14 \0.0001*Angle 1MD (")

Right first molar angulation 110.6 1.4 118.1 1.4 7.53 0.74 \0.0001*Angle 1ME (")

Left first molar angulation 117.7 1.2 123.8 1.2 6.17 0.68 \0.0001*

*Statistically significant (P\0.05).



In the hyrax group, the transverse expansion at thesuture gradually decreased from the anterior, by 4.37mm (distance 21-22), to the posterior, by 3.14 mm

(distance 11-12) (Table V). This sutural orthopedic sep-aration accounted for 54.7% and 39.2% of the totalexpansion (8 mm) at distances 21-22 and 11-12,

Table IV. Immediate changes in the maxillary transverse plane with RME in the Haas group

Variable

T1 T2 Change

PMean (mm) SE (mm) Mean (mm) SE (mm) Mean (mm) SE (mm)SkeletalDistance 5-6

Posterior apical base width 61.10 0.87 63.29 0.87 2.19 0.15 \0.0001*Distance 11-12

Posterior midpalatal suture width 00.00 0.11 02.61 0.11 2.62 0.12 \0.0001*Distance 15-16

Anterior apical base width (inferior) 38.98 0.82 42.28 0.82 3.29 0.30 \0.0001*Distance 17-18

Anterior apical base width (superior) 39.70 1.12 42.33 1.12 2.62 0.31 \0.0001*Distance 21-22

Anterior midpalatal suture width 00.00 0.15 03.63 0.15 3.63 0.17 \0.0001*AlveolarDistance 3-4

Posterior width at alveolar crest level 51.96 0.69 57.41 0.69 5.44 0.25 \0.0001*Distance 19-20

Anterior width at midalveolar level 40.56 0.79 44.59 0.79 4.03 0.30 \0.0001*DentalDistance 7-8

Intermolar width at occlusal surface 43.42 0.59 51.12 0.59 7.70 0.20 \0.0001*Distance 9-10

Intermolar width at palatal root apices 30.57 0.71 32.72 0.71 2.15 0.18 \0.0001*


Table V. Immediate changes in the maxillary transverse plane with RME in the hyrax group

Variable

T1 T2 Change

PMean (mm) SE (mm) Mean (mm) SE (mm) Mean (mm) SE (mm)SkeletalDistance 5-6

Posterior apical base width 59.48 0.92 62.58 0.92 3.10 0.17 \0.0001*Distance 11-12

Posterior midpalatal suture width 00.00 0.12 03.14 0.12 3.14 0.14 \0.0001*Distance 15-16

Anterior apical base width (inferior) 37.75 0.87 41.42 0.87 3.66 0.34 \0.0001*Distance 17-18

Anterior apical base width (superior) 38.22 1.19 41.22 1.19 3.00 0.35 \0.0001*Distance 21-22

Anterior midpalatal suture width 00.00 0.16 04.37 0.16 4.37 0.20 \0.0001*AlveolarDistance 3-4

Posterior width at alveolar crest level 51.34 0.73 57.15 0.73 5.80 0.28 \0.0001*Distance 19-20

Anterior width at midalveolar level 39.58 0.83 44.34 0.83 4.76 0.34 \0.0001*DentalDistance 7-8

Intermolar width at occlusal surface 43.60 0.62 51.50 0.62 7.90 0.23 \0.0001*Distance 9-10

Intermolar width at palatal root apices 29.24 0.75 32.38 0.75 3.14 0.21 \0.0001*




respectively. These findings endorse a previous report inwhich, of the total expansion achieved, the hyrax-typeexpander produced 55% of the suture expansion in theanterior and 38% in the posterior regions.20 However,the RME changes were analyzed 3 months after theactive expansion phase, unlike our study, where theimmediate effects of RME were evaluated.

This investigation showed a more significant skele-tal response compared with other studies.29,30 Ina study by Lione et al,29 the RME was performedwith a modified hyrax-type expander (bands on thefirst permanent molars only), and less sutural expan-sion was obtained in both the anterior (2.17 mm)and the posterior (1.15 mm) regions. This small ortho-pedic effect could be explained by (1) the use of a mod-ified hyrax-type expander, which had less anchorage;(2) less total expansion (7 mm); and (3) the sutural ex-pansion evaluated in a more posterior region (posteriornasal spine) than in our study (in the first molar re-gion). In our investigation, the amounts of suturalexpansion (2.88 mm in the posterior and 4 mm inthe anterior regions) were greater than the amounts

reported by Podesser et al30 (1.6 mm in the posteriorand 1.5 mm in the anterior regions). This differencecould be explained by less total expansion (7 mm)and the relapse that might have occurred because ofappliance removal and replacement at the end of theactive phase of RME for CT scan acquisition in theirstudy. In our investigations, there was no need to re-move the appliances before the CBCT examination atT2 because of the lower level of metal artifacts pro-duced by CBCT compared with conventional CT.11,38

The greater amounts of expansion at the alveolarlevel (distances 3-4 and 19-20) than the sutural expan-sion (distances 11-12 and 21-22) (Table III) show thebending of the alveolar processes of the maxilla; this re-sult agrees with previous reports.20,28,30 The expansionat the alveolar level (distance 3-4) accounted for 70%of the total expansion, 36% of which representssutural expansion and 34% is purely alveolar bendingtoward the buccal aspect.

The great changes in maxillary transverse dimensionsoccurred at the dental level, where the expansion ac-counted for 97% (distance 7-8) of the total expansion

Table VI. Comparison between the changes in the maxillary transverse planes in the groups

Variable

Haas group Hyrax group

P

T2-T1 T2-T1

Mean SE Mean SESkeletalDistance 5-6 (mm)

Posterior apical base width 2.19 0.15 3.10 0.17 0.0002*Distance 11-12 (mm)

Posterior midpalatal suture width 2.62 0.12 3.14 0.14 0.010*Distance 15-16 (mm)

Anterior apical base width (inferior) 3.29 0.30 3.66 0.34 0.427Distance 17-18 (mm)

Anterior apical base width (superior) 2.62 0.31 3.00 0.35 0.438Distance 21-22 (mm)

Anterior midpalatal suture width 3.63 0.17 4.37 0.20 0.007*AlveolarDistance 3-4 (mm)

Posterior width at alveolar crest level 5.44 0.25 5.80 0.28 0.342Distance 19-20 (mm)

Anterior width at midalveolar level 4.03 0.30 4.76 0.34 0.119DentalDistance 7-8 (mm)

Intermolar width at occlusal surface 7.70 0.20 7.90 0.23 0.526Distance 9-10 (mm)

Intermolar width at palatal root apices 2.15 0.18 3.14 0.21 0.0008*Angle 1MD (")Right first molar angulation 8.25 0.98 6.80 1.11 0.334

Angle 1ME (")Left first molar angulation 6.14 0.90 6.19 1.02 0.975

*Statistically significant difference (P\0.05).



(8 mm) (Table III). This greater expansion at the dentallevel compared with the skeletal level agrees with previ-ous reports.3,4,20,28,30,34,37 However, the actual dentalexpansion can be found by subtracting the totalexpansion at the dental level (distance 7-8) from thesuture and alveolar expansions (distance 3-4). Thus,from 97% (7.8 mm) of the total expansion at thedental level (distance 7-8), only 27% (2.17 mm)represents actual dental expansion, which was smallercompared with 36% (2.88 mm) of pure skeletalexpansion (distance 11-12) and with 34% (2.75 mm)of pure alveolar bending. RME produced significantbuccal tipping of the first permanent molars,accounting for 7.53" (angle 1MD) on the right sideand 6.17" (angle 1ME) on the left side (Table III). Therewere no statistically significant differences between the2 groups in angular measurements. The amounts of buc-cal tipping of the first permanent molars for the Haasgroup were 8.25" on the right side (angle 1MD) and6.14" on the left side (angle 1ME), whereas, in the hyraxgroup, the tipping amounts were 6.80" on the right and6.19" on the left sides. However, there was a statisticallysignificant difference between the Haas and hyraxgroups in the linear measurement (distance 9-10), whichrepresents the distance between the apices of the palatalroots of the first permanent molars. The higher values fordistance 9-10 (nearly 8 mm of expansion) reflecteda small buccal tipping of the first molars. In the hyraxgroup, distance 9-10 increased by 3.14 mm, whereas,in the Haas group, there was an increase of 2.15 mm,showing greater tipping of the first permanent molarswith that expander (Table VI). Similar results were re-ported in other investigations.28-37 In the study ofGarib et al,28 the Haas-type expander produced greaterbuccal tipping of the first permanent molars (3.5")than did the hyrax-type expander (1.6"). Oliveiraet al37 found that the Haas-type expander producedgreater buccal tipping of the first permanent molars(7.12" right side, 6.64" left side) compared with theHyrax-type expander (6.94" right side, 1.21" left side).However, these differences were not considered statisti-cally significant in either study.

We assessed the immediate effects of RME; therefore,long-term evaluation is necessary for a better under-standing of the differences between Haas-type andhyrax-type expanders, especially during the retentionand postretention phases of RME.

CONCLUSIONS

Based on this clinical trial with CBCT to assess theimmediate effects of RME on the transverse plane with2 kinds of palatal expanders, the following conclusionscan be drawn:

1. RME produced significant increases in all maxil-lary transverse dimensions. The expansion patternwas triangular, with smaller effects at the skeletallevel than at the dental level. However, the pureskeletal expansion was greater than actual dentalexpansion. The sutural expansion showed a wedgeshape with the wide base in the anterior maxilla.

2. The opening of the midpalatal suture accountedfor 50% of the total expansion (8 mm) in theanterior region and 36% in the posterior region(there was a decrease from anterior to posterior).

3. The hyrax-type expander produced greater orthope-dic effects in 3 of the 5 skeletal points measuredcompared with the Haas-type expander. However,the effects were less than 0.5 mm per side and mightnot be clinically significant.

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