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ORIGINAL ARTICLE

Three-dimensional assessment of buccal alveolarbone after rapid and slow maxillary expansion:A clinical trial study

Mauricio Brunetto,a Juliana da Silva Pereira Andriani,b Gerson Luiz UlemaRibeiro,c Arno Locks,c Marcio Correa,d

and Let�ıcia Ruhland Correab

Curitiba, Paran�a, and Florian�opolis, Santa Catarina, Brazil

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Introduction: The purposes of this study were to analyze and compare the immediate effects of rapid and slowmaxillary expansion protocols, accomplished by Haas-type palatal expanders activated in different frequenciesof activation on the positioning of the maxillary first permanent molars and on the buccal alveolar bones of theseteeth with cone-beam computerized tomography. Methods: The sample consisted of 33 children (18 girls, 15boys; mean age, 9 years) randomly distributed into 2 groups: rapid maxillary expansion (n5 17) and slow max-illary expansion (n5 16). Patients in the rapid maxillary expansion group received 2 turns of activation (0.4 mm)per day, and those in the slow maxillary expansion group received 2 turns of activation (0.4 mm) per week until 8mm of expansion was achieved in both groups. Cone-beam computerized tomography images were takenbefore treatment and after stabilization of the jackscrews. Data were gathered through a standardizedanalysis of cone-beam computerized tomography images. Intragroup statistical analysis was accomplishedwith the Wilcoxon matched-pairs test, and intergroup statistical analysis was accomplished with analysis ofvariance. Linear relationships, among all variables, were determined by Spearman correlation. Results andConclusions: Both protocols caused buccal displacement of the maxillary first permanent molars, which hadmore bodily displacement in the slow maxillary expansion group, whereas more inclination was observed inthe rapid maxillary expansion group. Vertical and horizontal bone losses were found in both groups; however,the slow maxillary expansion group had major bone loss. Periodontal modifications in both groups should becarefully considered because of the reduction of spatial resolution in the cone-beam computerizedtomography examinations after stabilization of the jackscrews. Modifications in the frequency of activation ofthe palatal expander might influence the dental and periodontal effects of palatal expansion. (Am J OrthodDentofacial Orthop 2013;143:633-44)

Correction of the maxillary transverse discrepancyis essential for treatment of various types ofmalocclusions. Palatal expansion is the most

common method used to improve the transverse dimen-sions of the maxilla. Three types of protocol for palatalexpansion are shown in the literature: rapid maxillary ex-pansion,1-3 slow maxillary expansion,4-17 and semirapid

te practice, Curitiba, Paran�a, Brazil.te practice, Florian�opolis, Santa Catarina, Brazil.ssor, Department of Orthodontics, Federal University of Santa Catarina,n�opolis, Santa Catarina, Brazil.ssor, Department of Radiology, Federal University of Santa Catarina,n�opolis, Santa Catarina, Brazil.uthors report no commercial, proprietary, or financial interest in the prod-r companies described in this article.t requests to: Mauricio Brunetto, Rua Francisco Rocha, 62 T�erreo, Curitiba,�a, Brazil 80420-130; e-mail, [email protected], May 2012; revised and accepted, December 2012.5406/$36.00ight � 2013 by the American Association of Orthodontists./dx.doi.org/10.1016/j.ajodo.2012.12.008

maxillary expansion.15,18 The latter and its variations19

have generated less interest in orthodontics comparedwith the first 2 types, which are evaluated and citedmore frequently.

Rapid maxillary expansion is associated with inter-mittent high-force systems20 and tooth-tissue-borneappliances (Haas type).1-3 Slow maxillary expansion isoften associated with continuous low-force systemsand quad-helix appliances or coil springs.4,5,8-11,15

Interestingly, the combination of Haas-type palatal ex-panders and slow maxillary expansion (ie, reduction inthe frequency of activation of the jackscrew) exists buthas been rarely studied.12,16,17 The advantages anddisadvantages of each protocol have been analyzed formany years, yet the issue remains unclear andcontroversial, since different devices andmethodologies interfere with the comparisons.6 Despitethe polemic, the literature indicates that both protocolsprovide maxillary expansion, although slow maxillary

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http://dx.doi.org/10.1016/j.ajodo.2012.12.008

Fig 1. Palatal expander.

634 Brunetto et al

expansion has been related to more physiologic effectson sutural tissues,6,20 greater tooth movement, andlower orthopedic effects compared with rapid maxillaryexpansion.7,8,15,21 Additionally, both rapid and slowmaxillary expansion cause lateral flexion of thealveolar processes and buccal displacement of theanchorage teeth with varying degrees ofinclination.1,3,7,10-13,22-30

Displacement of the teeth outside the alveolaranatomic limits can damage the periodontium,31,32

compromising tooth longevity.10 Few studies concern-ing a quantitative analysis of periodontal modificationsresulting from maxillary expansion have been devel-oped, possibly because of the difficulty of observationof the height and thickness of the alveolar bone ona conventional radiographic examination.33-36

Recently, and because of its numerous advantagesover conventional radiography and conventionalcomputerized tomography,37-40 cone-beam computer-ized tomography (CBCT) has been used for quantitativeanalysis of skeletal,41,42 dentoalveolar,8,35,36,41,42 andperiodontal8,35,36 changes from rapid and slow maxillaryexpansion. These latter studies indicate that both rapidmaxillary expansion34-36 and slow maxillary expansion8

cause buccal bone loss in varying degrees; however,they used different types of appliances and analyzed indi-vidually each protocol. The literature lacks simultaneouscomparative studies between the 2 protocols, especiallycomparisons with the same type of appliance and CBCT.

Therefore, the purposes of this study were to quantita-tively analyze and compare the immediate effects of rapidand slow maxillary expansion with Haas-type palatal ex-panders activated at different frequencies on the positionsof the maxillary first permanent molars, as well asthemodificationsof thebuccal alveolar boneof these teeth,byusingCBCT. Thenull hypothesiswas that the 2protocolscause similar dental movements and periodontal effects.

MATERIAL AND METHODS

The sample was selected in a public school and fromorthodontic patients who sought treatment at theFederal University of Santa Catarina in Brazil. All parentsor guardians signed the informed consent form, whichwas duly approved by the ethics committee in humanresearch of the university.

The inclusion criteria were a clinical maxillary transversedeficiency and age between 7 and 10 years (intertransitoryperiod of the mixed dentition). Patients with physical orpsychological limitations or metallic restorations in the firstpermanent molars were excluded. A sample of 59 subjectswas selected and randomly divided into 2 groups: rapidmaxillary expansion and slow maxillary expansion. All pa-tients used the tooth-tissue-borne palatal expander

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recommended by Haas (Fig 1).1 Each appliance includeda screw expander with a maximum aperture of 11.0 mm(Dentaurum, Inspringen, Germany) and bands in the firstdeciduous and first permanent molars. The subjects inboth groups had an 8-mm opening of the screw, for a totalof 40 activations. With a digital caliper (Ortho-pli, Philadel-phia, Pa), we monitored all expansion procedures every 15days to check the activation protocol. At the end ofactivation, thedeviceswere stabilizedwith0.12-mmligaturewires (Morelli, Sorocaba, Brazil) and maintained as retainersfor 5months in the rapidmaxillary expansion group and for1 month in the slow maxillary expansion group.43

Patients who did not correctly follow the protocol ofactivation, who did not return for control dental ap-pointments, who did not have their final examinationwithin 7 days after screw stabilization, whose cementa-tion of appliance failed, whose molars were exfoliatedduring treatment, or whose dental structures were diffi-cult to visualize on the CBCT scans as a result of artifactsfrom the palatal expander were excluded.

The rapid maxillary expansion group initiallycomprised 28 subjects, but only 17 remained in the study(10 girls, 7 boys). Their mean age was 8.9 years, and theywere treated with the rapidmaxillary expansion protocol:a half turn (0.4 mm) per day.1 The palatal disjunctor wasactivated a full turn on the first day. Of the 31 subjects inthe slow maxillary expansion group, only 16 were evalu-ated in the final sample (8 girls, 8 boys). Their mean agewas 9 years, and they were treated with the slow maxil-lary expansion protocol: a half turn (0.4 mm) weekly.Upon cementation of the appliance, activation consistedof a half turn. The patients received a CBCT examinationbefore orthodontic treatment (T1) and between 1 and 7days after stabilization of the screw (T2). The applianceswere not removed for the T2 examinations.

The CBCT examinations were performed with ani-CAT device (Imaging Sciences International, Hatfield,Pa) at 120 kV, 20 mA, and 14.7-second scan time. Theimages had a 0.25-mm thickness with 0.25-mm

Journal of Orthodontics and Dentofacial Orthopedics

Fig 2. General overview of the multi-planar reconstruction mode of the software.

Brunetto et al 635

isotropic voxels. After acquisition, the images were savedin digital imaging and communications in medicine(DICOM) format and were built and manipulated inlayers of 0.5 mm with OsiriX Medical Imaging 32-bitsoftware (open source; Pixmeo, Geneva, Switzerland;www.osirix-viewer.com). The same operator (M.B.)made all measurements; he was unaware of the groupto which each patient belonged.

The tomographic analysis performed was similar tothat proposed by Bernd.36 The long axis of themesiobuc-cal root of the maxillary first permanent molar served asa reference for the standardization of CBCT slices madeat T1 and T2. For this purpose, the images were initiallyviewed in the multiplanar reconstruction mode of thesoftware. In this mode, there are 3 sections in 3 differentwindows (each corresponding to each plane of space) and3 color lines (Fig 2). Each color line relates to the scrollingof the tomographic cuts in a specific plane of space; eg,orange lines refer to the sagittal plane, purple lines referto the axial plane, and blue lines refer to the coronalplane. To scroll for tomographic cuts in the sagittal plane,the orange line must bemoved into the coronal or the ax-ial section. The same process is valid for the other 2 lines.

The first step of the method was the identification ofthe furcation region of the maxillary right first perma-nent molar in the axial section, where the buccal rootswere slightly separated. In this image, the intersection

American Journal of Orthodontics and Dentofacial Orthoped

of the orange and blue axes was positioned over thecenter of the mesiobuccal root, and the blue line waspositioned following the direction of the buccolinguallong axis of the root (Fig 3, A). In the next step, theinclination of the blue line was adjusted in the sagittalsection so that it passed through the center of the mesio-buccal root about its long axis (Fig 3, B). Finally, in thecoronal section, the position of this tooth was adjustedso that the buccal surface of the root was parallel tothe tomographic vertical plane (Fig 3, C). The samepatterning process was also performed for the maxillaryleft first permanent molar. According to these criteria,a standard image was derived in the coronal section(Fig 3, D): orthogonal to the axial and vertical plane de-scribed by the buccolingual axis of the mesiobuccal root.

From the standard image in the coronal section,variables related to the height of the buccal alveolarbone (NOVC and NOV; Fig 4, Table I) were determinedin full-screen mode. For measurements related to thethickness of the buccal bone plate, a vertical line 10mm long was drawn parallel to the tomographic verticalplane (Fig 5). The most inferior point of this line wassuperimposed on the buccal cementoenamel junction(CEJ). At this time, a horizontal line was traced perpen-dicular to and passing through the highest point of thevertical 10-mm line, determining the measurement ofthe CEJ 10 (Fig 6, A; Table I).

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http://www.osirix-viewer.com

Fig 3. A, Positioning of the blue line on the axial section following the direction of the buccolingual longaxis of the root;B, adjustment of the inclination of the blue line following the long axis of themesiobuccalroot by the sagittal section; C, positioning of the buccal surface of the root parallel to the tomographicvertical plane by the coronal section; D, the standard image derived in the coronal section.

Fig 4. NOV and NOVC measurements.

636 Brunetto et al

The vertical line was reduced to 5 mm and then 3 mmin length, each kept parallel to the vertical tomographicplane. Then, 2 new horizontal lines were outlined foreach vertical line, determining the measurements CEJ5 and CEJ 3, respectively (Fig 6, B and C, respectively;Table I).

In this evaluative study, we also used quantitativeanalysis of the inclination of the first permanent molars.For this purpose, in the axial section, the furcation areasof the maxillary right and left molars, when both buccalroots were slightly separated, were determined. In caseof unevenness between the teeth, the furcation area ofthe right molar was determined (Fig 7, A), and levelingwas accomplished by moving the purple line in thecoronal section (Fig 7, B). The resulting image in theaxial section (Fig 7, C and D) was used for determinationof the DR measurement (Fig 8, A; Table I). Also, in thesame axial image, the blue line was moved so that itpassed between the mesiobuccal and distobuccal roots

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Table I. Definitions of variables in the tomographic analysis

Variable Definition PurposeNOV (mm) Distance between the buccal CEJ and the most occlusal point of the buccal

alveolar crestAlveolar bone height

NOVC (mm) Distance between the buccal cusp tip and the most occlusal point of thebuccal alveolar crest

Alveolar bone height

CEJ 3 (mm) Distance between the outer surface of the buccal alveolar plate and the outerwall of the buccal root 3 mm above the CEJ

Alveolar bone thickness


Alveolar bone thickness


Tooth inclination

DC (mm) Distance between the mesiobuccal cusp tips of the maxillary first permanentmolars

Tooth displacement and inclination

DR (mm) Distance between the most buccal points of the root canals of themesiobuccal roots of the maxillary first permanent molars

Tooth displacement and inclination

AI (�) Angle formed by the intersection of 2 lines traced toward the midline andtangent to both mesial cusp tips of each maxillary first permanent molar

Tooth inclination

Fig 5. Tracing of the 10-mm line parallel to the tomo-graphic vertical plane.

Brunetto et al 637

of the maxillary right and left first molars (Fig 7, E). Thederived image in the coronal section (Fig 7, F) was usedto determine the angle AI andmeasurement DC (Fig 8, B;Table I).

Statistical analysis

Statistical calculations were performed by using IBMSPSS software (version 20; SPSS, Chicago, Ill), with a Pvalue less than 0.05 indicating statistical significance.The Wilcoxon matched-pairs test determined the intra-group statistical analysis between T1 and T2. Intergroupstatistical analysis was determined by analysis ofvariance (ANOVA) of the differences of means betweenT1 and T2. Mean values between sides were consideredfor bilateral variables (NOV, NOVC, CEJ 3, CEJ 5, and CEJ10). The power of the ANOVA test was also calculated,since the exclusion criteria reduced the sample size to33 patients. The Spearman correlation test was used todetect any linear relationships between the variables.


For the systematic error investigation, 10 examina-tions of each group were randomly chosen, measuredagain after a minimum of 15 days, and analyzed byusing an intraclass correlation coefficient (ICC).

RESULTS

Means, standard deviations, ranges, and statisticalanalyses for each group at T1 and T2 are shown inTables II and III. The differences of means andstatistical analyses between groups are presented inTable IV.

The results demonstrated buccal displacement of thefirst permanent molars in both groups. The rapid maxil-lary expansion group showed significant increases in themeans of DC, DR, and AI (Table II). The slowmaxillary ex-pansion group showed similarly significant modificationin the same variables, reported in Table III.Whenwe com-pared the results of the 2 groups (Table IV), differences intooth inclinationswereminor in the region of the crowns,as shown by the small variation in DC. However, changesin the furcation area, represented by the variableDR,werelower in the rapid maxillary expansion group.

A significant increase in the means related to boneheight was detected in both groups, as demonstratedby measurements NOV and NOVC (Tables II and III).Furthermore, these changes had greater intensity inthe slow maxillary expansion group (Table IV).

The means of CEJ 3 and CEJ 5 decreased between T1and T2 in both groups (Tables II and III). CEJ 10 showeda significant reduction in the slow maxillary expansiongroup (Table III) and an increase in the rapid maxillaryexpansion group (Table II). Statistical analysis betweengroups (Table IV) indicated significant differencesbetween CEJ 3 (�0.88 mm in rapid maxillary expansionvs �1.36 mm in slow maxillary expansion) and CEJ


Fig 6. Determination of A, CEJ 10; B, CEJ 5; and C, CEJ 3 measurements.

638 Brunetto et al

5 (�0.60 mm in rapid maxillary expansion vs�1.49 mmin slow maxillary expansion).

All variables had values higher than 76% after calcu-lation of the power of the ANOVA test for intergroupcomparison. Measure CEJ 10 showed the lowest value(76.59%). All other measurements had values higherthan 98% when rejecting the null hypothesis.

A negative linear relationship was detected betweenbone thickness (CEJ 3) at T1 and height of the buccalbone plate (NOV) at T2 (r5�0.65 in the rapid maxillaryexpansion group and r 5 �0.77 in the slow maxillaryexpansion group). Likewise, but only for the slowmaxillary expansion group, there was a negative correla-tion between variables CEJ 5 at T1, and NOVC and NOVat T2 (r 5 �0.70 and r 5 �0.72, respectively).

Regarding systematic error, all variables showedhigh levels of reliability, as determined by ICC values(Table V).


DISCUSSION

The inclusion of a control group in this study witha similar skeletal pattern as the treated sample was notpossible because of ethical concerns. The observationof untreated patients would be important to differenti-ate natural skeletal growth from changes derived fromtreatment, especially in the slow maxillary expansiongroup, where the opening of the screw extended over5 months.

Standardization of the activation of palatal ex-panders (8 mm) and the CBCT slices (long axis of themesiobuccal root of the maxillary first permanent molar)was necessary to reduce possible bias from varyingdegrees of inclination of the anchorage teeth that couldbe a result of palatal expansion.33

Most studies comparing rapid and slow maxillaryexpansion contrast the type of force delivered by eachprotocol: eg, high intermittent forces applied with


Fig 7. Determination of the furcation area of the maxillary first permanent molars: A, note theunevenness between both furcation areas; B, the purple line in the coronal section is moved toaccomplish leveling of the furcation areas; C and D, the resulting image in the axial section, used fordetermination of the DR measurement; E, the blue line positioned in the axial image to pass betweenthe mesiobuccal and distobuccal roots of the maxillary right and left permanent molars; F, the derivedcoronal image, used for determination of the AI angle and the DC measurement.

Brunetto et al 639

a jackscrew for rapid maxillary expansion20 and lowcontinuous forces applied with springs or wires forslow maxillary expansion.4,5,8-11,15 The association oftooth-tissue-borne appliances and slow maxillary ex-pansion has been rarely evaluated; the result is that thereis no standard protocol of activation for this procedure.The expansion rate of 0.4 mm per week has been appliedto the slow maxillary expansion group according to therationale that slower rates of expansion allow morephysiologic changes on tissues6,17,20 as well as theformation of sufficiently mature bone to maintainpalatal separation.9,14 Furthermore, Proffit et al17


suggested that approximately 0.5 mm of expansionper week is the maximum rate at which the tissues ofthe midpalatal suture can adapt.

Small samples might increase the standard error of themean, tending to accept the null hypothesis even whenthere is a clinically relevant difference. Hence,when apply-ing the ANOVA test for intergroup comparisons, the powerof the analysis was calculated. The results indicated thatthe remaining sample was sufficient to not reject the hy-pothesis of difference between treatments for the variablesanalyzed, since the smallest value found (CEJ 10) wasgreater than 76%.


Fig 8. A, DR measurement; B, measurement of DC and AI angle.

Table II. Means, standard deviations, ranges, and statistical significance at T1 and T2 for the rapid maxillary expan-sion group

Variable

T1 T2

PMean SD Minimum-maximum Mean SD Minimum-maximumNOV (mm) 0.93 0.25 0.60-1.56 1.68 0.84 0.97-4.12 \0.001*NOVC (mm) 7.85 0.52 6.85-8.81 8.64 0.92 7.13-10.67 \0.001*CEJ 3 (mm) 1.98 0.59 0.89-3.16 1.10 0.56 0.00-2.37 \0.001*CEJ 5 (mm) 2.42 0.88 1.01-4.19 1.82 0.87 0.48-3.54 \0.001*CEJ 10 (mm) 5.18 2.05 2.23-8.86 5.95 2.13 2.5-10.02 \0.001*DR (mm) 47.14 2.19 44.58-53.65 52.00 2.49 47.58-57.36 \0.001*DC (mm) 49.92 1.84 47.51-53.79 59.19 2.70 55.21-63.96 \0.001*AI (�) 158.17 9.80 138.91-178.18 145.29 8.93 117.22-155.26 \0.001*

*P\0.05.

640 Brunetto et al

Concerning the movement of the maxillary firstpermanent molars, variations of DR, DC, and AI (TablesII-IV) confirm previous findings of displacement andbuccal inclination of these teeth as a result ofrapid maxillary expansion27,33,35,41,42,44,45 and slowmaxillary expansion.8,12,15,16 Although indicating thesame trend, the values presented here are discrepantwith most of the literature. Such variations could beattributed to differences in samples (size and age),6

type of appliance,6 amount of activation of thescrew,6,36 methodology,6 type of computerized tomog-raphy,42 settings of the computerized tomographydevice,45 and methodologies of tomographic analyses.8

Rungcharassaeng et al35 achieved increases of lessmagnitude (6.66 mm) in the distance and inclination(6.64�) of the maxillary right and left first permanentmolars, possibly due to the smaller amount of openingof the expansion screw, on average 4.96 mm, againstthe standardized 8 mm in this study. Investigating thedental effects of slow maxillary expansion with CBCT,Corbridge et al8 observed an increase of only 6.5 mm,probably because they used a different appliance(quad-helix), and measurements were made between


the palatal grooves of the maxillary right and left firstpermanent molars. The few studies that combinedHaas-type expanders with slow maxillary expansionprotocols found lower values than we did for bothdistance and intermolar inclination12,16; however,these studies used plaster models. On the other hand,Bernd36 reported values of DC (9.26 mm), DR (4.86mm), and AI (�12�) that were close to those achievedin the rapid maxillary expansion group, possibly becauseof similarities with our study, including the use ofa Haas-type palatal expander, the frequency of activa-tion in the rapid maxillary expansion procedure, theamount of screw activation (8 mm), and the method ofanalysis of the CBCT images.

The variable DC demonstrated significant and similarincreases in both groups (Tables II and III). DR showeda larger increase and the AI angle had less reduction inthe slow maxillary expansion group (Tables III and IV).DR and AI variations denoted greater displacements ofthe vestibular region of root furcation and a lowerinclination of teeth, indicating the predominance ofbodily movement of the first permanent molars in theslow maxillary expansion group. It is probable that in


Table IV. Differences of means between T1 and T2 forboth groups and statistical analysis

Variable

Rapid maxillaryexpansion group

(n 5 17)

Slow maxillaryexpansion group

(n 5 16)

PT2-T1 SD T2-T1 SDNOV (mm) 0.75 0.72 2.94 1.74 0.0004*NOVC (mm) 0.78 0.72 3.28 1.68 0.0000*CEJ 3 (mm) �0.88 0.28 �1.36 0.44 0.0082*CEJ 5 (mm) �0.60 0.25 �1.49 0.39 0.0000*CEJ 10 (mm) 0.77 0.76 �1.81 0.74 0.0000*DR (mm) 4.85 1.31 6.39 1.12 0.0011*DC (mm) 9.26 2.05 9.02 1.70 0.7194AI (�) �12.88 9.35 �7.87 6.80 0.9050

*P\0.05.

Table V. Systematic error analysis (ICC)

Variable ICC 95% CINOV 0.99 0.98-0.99NOVC 0.96 0.93-0.98CEJ 3 0.96 0.93-0.98CEJ 5 0.96 0.93-0.98CEJ 10 0.95 0.90-0.97DR 0.97 0.91-0.98DC 0.95 0.91-0.98AI 0.99 0.97-0.99

Table III. Means, standard deviations, ranges, and statistical significance at T1 and T2 for the slow maxillary expan-sion group

Variable

T1 T2

PMean SD Minimum-maximum Mean SD Minimum-maximumNOV (mm) 1.43 0.53 0.89-3.01 4.37 1.86 1.17-7.08 \0.001*NOVC (mm) 7.87 0.81 6.80-9.98 11.15 2.17 7.52-14.66 \0.001*CEJ 3 (mm) 1.68 0.58 0.43-2.75 0.31 0.45 0.00-1.33 \0.001*CEJ 5 (mm) 2.18 0.71 1.05-3.65 0.69 0.59 0.00-1.90 \0.001*CEJ 10 (mm) 5.65 1.73 4.16-10.33 3.84 1.96 1.72-9.62 \0.001*DR (mm) 45.82 2.68 41.39-51.01 52.22 2.66 48.04-57.57 \0.001*DC (mm) 48.75 3.16 44.08-53.59 57.78 3.27 51.80-62.68 \0.001*AI (�) 155.62 13.52 127.24-179.69 147.75 14.34 116.98-167.33 \0.001*

*P\0.05.

Brunetto et al 641

the rapid maxillary expansion group, the large amount offorce generated and suddenly directed to the crowns ofthe first molars caused greater inclination of the teeth,whereas in the slow maxillary expansion group, a slowerrate of activation associated with the anchorage set bythe structural rigidity of the palatal expander resulted inlower tooth inclination. Nevertheless, the higherinclination of the alveolar process in the rapid maxillaryexpansion group compared with the slow maxillaryexpansion group, observed in another study,46 mightalso have contributed to the amount of inclination ofthe maxillary first permanent molars.

In the rapid maxillary expansion group, the T2examinations were taken at 21 to 28 days into treat-ment, whereas for the slow maxillary expansion group,the examinations were obtained between 141 and 148days. This difference of 120 days might be enough topermit dental movement through the alveolar housingin the slow maxillary expansion group. Therefore,higher variations of the DR measurement in the slowmaxillary expansion group might also be related toa major degree of orthodontic movement. This


interpretation can invalidate the use of DR for themeasurement of the pattern of buccal displacementof the root. However, variations of AI and CEJ 10 stillsupport different types of movement of anchor teethbetween the groups.

The type of movement of the first molars resultingfrom palatal expansion was also investigated byRungcharassaeng et al.35 The absence of correlationbetween their weekly mean rate of activation for thejackscrew (0.83 mm, compatible with the values ofrapid and slow maxillary expansion described in litera-ture) and the variable related to dental inclination (DIA)associated with the higher values of dental tippingfrom studies with continuous low-force systems(quad-helix or coil springs) led those authors to specu-late that the type of movement of the first molarsmight be more affected by the force delivery system(spring or jackscrew) rather than the activation proto-col. In contrast, we detected differences in the inclina-tion of the first molars as a result of the activationprotocol. These conflicting data possibly relate to thefact that the slow maxillary expansion group followeda specific protocol, with 2 weekly activations, whereasRungcharassaeng et al evaluated the mean rate of ex-pansion of a rapid maxillary expansion procedure,which although compatible does not represent a specificslow maxillary expansion protocol.


642 Brunetto et al

Measurements CEJ 3 and CEJ 5 are located near theocclusal edge of the alveolar bone crest; therefore, theseare more directly influenced by changes in the verticalalveolar bone. CEJ 10, on the other hand, is located inan apical area thatmost likely experienced little influencefrom vertical alveolar bone changes as a result of treat-ment. Hence, the mean variation of CEJ 10 was associ-ated with the measurement of inclination of the rootregions of the maxillary right and left first permanentmolars. The significant increase in CEJ 10 in the rapidmaxillary expansion group (Tables II and IV) can beinterpreted as a greater inclination in the region of theroots of the maxillary first permanent molars, whereasthe significant decrease in the slow maxillary expansiongroup (Tables III and IV) might represent greater bodilymovement of those teeth, confirming the variations inDR and AI.

Rapid maxillary expansion33-36,47 and slow maxillaryexpansion8 procedures have been shown to be related tothe loss of buccal alveolar bone height and thickness ofthe anchorage teeth. The same changes represented byvariations in NOV, NOVC, CEJ 3, and CEJ 5 wereobserved in both groups of this study (Tables II-IV).However, there are considerable variations whencomparing the literature with the rapid maxillaryexpansion group. Differences between samples,6 meth-odologies,6 types of computerized tomography,42 tomo-graphic device settings,45 and evaluated tomographicslices8 might have contributed to such variations. Astudy using conventional computerized tomographyfound greater reductions in bone height (3.8 mm) inthe first molars,34 and another study found smallerreductions in alveolar bone thickness (0.3-0.5 mm) ofthe same teeth in subjects treated with rapid maxillaryexpansion and hyrax-type expanders.33 Other investiga-tions with different tomographic analysis methodologiesobserved more pronounced vertical (2.92 and 3.3 mm,respectively)35,47 and horizontal (1.24 mm)35 bone loss.Nevertheless, 1 study evaluated adults treated withhyrax-type expanders and surgically assisted rapid max-illary expansion.47 Bernd36 observed bone loss of 0.5mm in thickness. Despite the similarities betweenBernd's study and ours, the individual characteristicsof the samples represented by differences in the initialranges andmeans of measurements possibly contributedto the discrepancies.

The slow maxillary expansion protocol was tested inanimals,9,14 and,when tested in patients, a quad-helix ap-pliance8,10,15 or coil springs4,11,13 were commonly used.Only 2 investigations related slow maxillary expansionprocedures to Haas-type palatal expanders, althoughwithout anyperiodontal or radiographic examination.12,16

Ours is the first study to quantitatively assess by means of


CBCT the dental and periodontal effects of slowmaxillaryexpansion in patients treated with Haas-type expanders.Therefore, direct comparisons between the slow maxillaryexpansion group and the literature were not possible.

All measurements were correlated to examine possi-ble linear relationships. The negative correlationsbetween measurements CEJ 3 at T1 and NOV at T2 inboth groups, as well as between CEJ 5 at T1 and NOVand NOVC at T2 for the slow maxillary expansion group,indicate that the greater the bone thickness at the begin-ning of treatment, the lower the vertical bone loss at theend of therapy. Importantly, these results agree with theresults of Garib et al.34

Patients in the slow maxillary expansion groupsuffered major periodontal consequences (Table IV); 9patients had signs of dehiscence. Of this total, 6 hadCEJ 3 reduced to zero, and 3 had both CEJ 3 and CEJ5 reduced to zero. The full effect of orthodontic treat-ment on the periodontium might not be readily notice-able10; however, changes of such magnitude wouldprobably be discernable clinically, but that was notobserved in our sample. The highest rates of periodontalbone loss, which occurred in the slow maxillary expan-sion group, can be attributed to the greater bodily move-ment of the first permanent molars combined with lowerflexion of the alveolar processes and the possibility ofmajor orthodontic movement in the slow maxillaryexpansion group. All of these 3 factors facilitate theapproximation of the roots to the buccal alveolarbone, allowing the onset of periodontal changes.

CBCT technology has many advantages comparedwith conventional radiographic imaging38 and comput-erized tomography.39,48,49 A recent study showed thatperiodontal bone height and thickness can bemeasured quantitatively with great precision by usingCBCT images.49 Despite this, certain characteristics andlimitations of CBCT technology, particularly in the eval-uation of the alveolar bone, are neither fully establishednor understood.45,49,50 The ability to differentiatebetween 2 distinct objects close to each other definesthe spatial resolution of CBCT images; this becomesimportant in small measurements, such as thealveolar buccal bone.8,50,51 Spatial resolution hasa multifactorial nature and can be affected by variationsin shading, signal-to-noise ratio, field of view, and voxelsize.45,50,51 Voxels smaller than 0.3 mm can providebetter average spatial resolution for adequatevisualization of the buccal bone.50 Another importantfactor that directly influences spatial resolution is metalartifacts. Surrounding structures of metal orthodonticbraces and bands can be misrecognized or not correctlyreconstructed by CBCT units; thus, spatial resolution canbe compromised in this area.50


Brunetto et al 643

Images acquired in this study used voxels of 0.25mm; however, the palatal expanders were not removedat the T2 examinations. This implies a reduction ofspatial resolution influencing the display of imagesand resulting in a much more limited ability to distin-guish between the root portions of the teeth and thebuccal bone plates. Hence, in patients of the slowmaxillary expansion group with suggestive images ofdehiscence, a thin buccal alveolar bone layer probablyremained; however, its correct visualization might nothave been achievable because of variations in spatialresolution. This might be related to the absence ofclinical signs of periodontal alterations in the patientsof this group. In any case, these subjects probably had,to some extent, periodontal sequelae to the anchorageteeth of the palatal expander that can make themmore susceptible to periodontal problems in the longterm, as a result of traumatic brushing, periodontal dis-ease, or occlusion trauma.10

The buccal displacement of the maxillary first perma-nent molars, with a consequent increase of inclinationand alveolar bone loss, should be regarded as a constitu-ent of the palatal expansion procedure.22,35 Froma periodontal point of view, maxillary expansionshould preferably be performed in the deciduous orearly mixed dentition, because the eruption ofpermanent teeth can minimize the periodontal effectsproduced by rapid or slow maxillary expansion.34

As previously mentioned, there is no standard proto-col for slow maxillary expansion with Haas-type palatalexpanders. Mew18 and Proffit et al17 recommended slowmaxillary expansion with 1 mm of weekly activation.More specifically, Proffit et al suggested that activationsof 0.25 mm on alternate days provide a satisfactoryskeletal-to-dental ratio gain (50% each) and a morephysiologic response. The recommendations of Proffitet al have recently been evaluated by Huyhn et al12

and Wong et al,16 who tested slow maxillary expansionprocedures with Haas-type palatal expanders. However,as previously cited, these authors collected no radio-graphic data regarding periodontal changes. Activationsof 0.4 mm, used in our study, represent a unique situa-tion in the current literature but from a periodontalstandpoint do not seem to be the best alternative.Thus, further studies for evaluating the periodontal ef-fects of slow maxillary expansion should be developedby testing its association with tooth-tissue-borne ex-panders and other frequencies of jackscrew activation.

CONCLUSIONS

After a quantitative analysis and comparison of theimmediate effects of rapid and slow maxillary expansionprotocols on the positioning of the maxillary first


permanent molars and on themodifications of the buccalalveolar bones of these teeth, it can be concluded that thenull hypothesis was rejected for the following reasons.

1. The tested rapid and slow maxillary expansionprocedures caused significant buccal displacementof the maxillary first permanent molars, witha significant difference in the degree of inclinationbetween the groups. The rapid maxillary expansiongroup had higher inclinations, and the resultssuggest greater bodily movement of the teeth inthe slow maxillary expansion group.

2. Loss and reduction of height and thickness of bonewere detected in both groups, with greater intensityand significance in the slow maxillary expansiongroup. These modifications should be carefullyconsidered because of the reduction of the spatialresolution in CBCT examinations at T2.

3. Changes in the frequency of activation of the palatalexpander might influence the dental and periodon-tal effects of maxillary expansion treatment.

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