Midpalatalminiscrewsandhigh-pullheadgearfor ...lingually during the en-masse retraction. When the extraction space measured 2 to 3 mm, a 0.018 3 0.025-in stainless steel archwire with

ORIGINAL ARTICLE

Midpalatal miniscrews and high-pull headgear foranteroposterior and vertical anchorage control:Cephalometric comparisons of treatment changes

Jungkil Lee,a Ken Miyazawa,b Masako Tabuchi,c Misuzu Kawaguchi,c Momoko Shibata,c and Shigemi Gotod

Nagoya, Japan

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238

Introduction:Our aimwas to evaluate which anchorage system is better suited for both anteroposterior and ver-tical anchorage control of maxillary posterior teeth.Methods: Fifty-one subjects requiring maximum anchoragewere divided into 2 groups according to maxillary posterior anchorage reinforcement: high-pull headgear,conventional transpalatal arch, and interarch elastics (n 5 28); or modified transpalatal arch supported by 2midpalatal miniscrews (n 5 23). Bilateral maxillary first premolars were extracted in all patients. Pretreatmentand posttreatment lateral cephalometric radiographs were superimposed to compare skeletal and dentalchanges between the groups. Results: (1) The miniscrew group had less mesial movement of the maxillary firstmolars (0.85 vs 3.63 mm) and greater maxillary incisor retraction (6.87 vs 4.50 mm) than did the headgear groupwith the same treatment duration. (2) The maxillary molars were significantly intruded in the miniscrew group(1.30 mm), whereas they were extruded in the headgear group (0.71 mm). In the miniscrew group, intrusionof the maxillary molars resulted in a statistically significant decrease in the mandibular plane angle (0.80�).Patients using high-pull headgear showed no significant decrease in these measurements. Conclusions: Inboth the anteroposterior and vertical directions, a modified transpalatal arch supported by 2 midpalatal mini-screws provided more stable anchorage. (Am J Orthod Dentofacial Orthop 2013;144:238-50)

It is no exaggeration to state that anchorage controlin edgewise treatment is the most important factorthat affects the treatment plan and the results, espe-

cially for high-angle patients whose chief complaint isupper lip protrusion. In adults, such major orthodontictreatment plans require premolar extractions andmaximum anchorage.1

Traditionally, extraoral or intraoral appliances suchas high-pull headgear and interarch elastics were usedto help maintain the anchorage of the maxillary poste-rior teeth.2 However, high-pull headgear has inherent

the Department of Orthodontics, School of Dentistry, Aichi-Gakuin Univer-agoya, Japan.ent.ssor.uctor.ssor and chairman.tudy was partially supported by a Grant-in-Aid for Scientific Research froministry of Education, Science and Culture of Japan (24593115).thors have completed and submitted the ICMJE Form for Disclosure of Po-l Conflicts of Interest and none were reported.t requests to: Jungkil Lee, Department of Orthodontics, School ofstry, Aichi-Gakuin University, 2-11, Suemori-Dori, Chikusa-Ku, Nagoya,651, Japan; e-mail, [email protected], November 2012; revised and accepted, March 2013.5406/$36.00ight � 2013 by the American Association of Orthodontists./dx.doi.org/10.1016/j.ajodo.2013.03.020

disadvantages associated with patient noncompliance,duration of wear, unacceptability by many adults, andpotential risk of injury. Furthermore, although interarchelastics are effective in correcting the anteroposterior re-lationships of the dentition, some undesirable sideeffects can occur. Many authors have noted adverse re-sults because of the vertical force vector that is inherentwith interarch elastics.3,4 This vertical force can causeteeth to extrude and lead to an opening rotation ofthe mandible.

Since the advent of temporary anchorage devices orskeletal anchorage devices, miniplates and miniscrewshave been used to obtain skeletal anchorage withoutpatient cooperation, with promising results.5,6 Manycase studies have reported that buccal miniscrews,used as direct anchorage, allow the anterior teeth tobe retracted effectively without anchorage loss.7,8

However, root contact of buccal miniscrews isconsidered a primary reason for their failure whenplaced in interdental areas.9-11 Interdental miniscrewscan also act as a mechanical interference that limitsadjacent tooth movement. Therefore, the removal andreplantation of miniscrews are required in certain cases.

Sites for miniscrews should be carefully selected tominimize root movement interference and the number

mailto:[email protected]

http://dx.doi.org/10.1016/j.ajodo.2013.03.020

Lee et al 239

of replantation procedures. To prevent root contact ofminiscrews and to decrease failure rates, nondental-bearing areas such as the midpalatal area of the maxillahave been reported to be good sites for miniscrewimplantation.12-14 Moreover, the midpalatal suture is ahighly dense structure with sufficient bone height upto the cresta nasalis, ensuring biomechanical stabilityof the midpalatal miniscrews.12,15 In addition, thecovering soft tissue is keratinized; this is beneficial inminimizing inflammation in the midpalatal area. Itsthickness is consistent at 1 mm, enough to supportmidpalatal miniscrews.15 However, other mediatingappliances are required because the midpalatal suturearea is far from the teeth that the clinician aims to con-trol. Various attempts have been made to use miniscrewsas skeletal anchorage in the midpalatal suture area.16,17

In this study, the combination of 2 midpalatalminiscrews with a modified transpalatal arch was usedas a skeletal anchorage system to reinforce anchorageof the maxillary posterior teeth both anteroposteriorlyand vertically.

The null hypothesis was that there would be no sig-nificant differences in anchorage losses of the maxillaryposterior teeth between the miniscrew group (skeletalanchorage system) and the high-pull headgear group(traditional anchorage system) when treating patientswith maxillary dentoalveolar protrusion and a hyperdi-vergent facial type. The purposes of this retrospectivestudy were to compare the skeletal and dental changesin subjects treated with 2 anchorage systems with thesame orthodontic mechanics and to evaluate whichanchorage system is better suited for both anteroposte-rior and vertical anchorage control of the maxillary pos-terior teeth.

MATERIAL AND METHODS

The clinical records of consecutively treated patientsfrom 2008 to 2011 were searched to identify appropriatesubjects. The patients had undergone level anchoragesystem treatment at Aichi-Gakuin University Dental Hos-pital in Nagoya, Japan. A total of 51 subjects met thefollowing inclusion criteria: (1) Angle Class II Division 1or Class I malocclusion with bimaxillary protrusion, (2)hyperdivergent skeletal pattern, (3) well-aligned maxil-lary incisors with minimal crowding (#3.5 mm), (4) fullpermanent dentition (except for the third molars), and(5) extraction of bilateral maxillary first premolars (withvarious strategies for the mandibular arch, includingnonextraction or extraction of the first or second premo-lars). All subjects were successfully treated (ie, Class I orfull-cusp Class II molar relationship, Class I caninerelationship, and adequate overbite and overjet were

American Journal of Orthodontics and Dentofacial Orthoped

obtained). The exclusion criteria were (1) poor film qual-ity or incomplete records, (2) patients who received skel-etal anchorage in the mandible and midpalatal areas, (3)patients with major rotations or a posterior crossbite, (4)prolonged use of vertical seating elastics during the fin-ishing stage, and (5) patients with congenital malforma-tions, systemic diseases, or syndromic conditions.

The subjects were characterized by maxillary den-toalveolar protrusion and a hyperdivergent skeletalpattern. The treatment plan involved maximum maxil-lary incisor retraction in addition to vertical dimensioncontrol. In these patients, both the anteroposterior andvertical control of the maxillary posterior anchorageswere of major importance. The subjects were dividedinto 2 groups according to the type of maxillary poste-rior anchorage reinforcement (Table I).

The high-pull headgear group included 28 subjectswho received traditional anchorage reinforcement withhigh-pull headgear, conventional transpalatal arch,and interarch elastics. After the initial leveling and align-ing in the maxillary arch, maxillary posterior anchoragewas reinforced with high-pull headgear, and Class IIIelastics were used for anchorage preparation to uprightthe mandibular molars. After stabilization of themandibular arch, high-pull headgear and Class II elasticswere used during the maxillary en-masse retraction. Allsubjects were instructed to wear the high-pull headgearfor 10 to 12 hours per day throughout the treatmentperiod and to record their headgear wear time on dailycharts. A force of approximately 250 g on each sidewas applied at the level of the buccal trifurcation (centerof resistance) of the maxillary first molars. The impor-tance of wearing the extraoral appliance as anchoragewas explained at the initial stage and reiteratedthroughout active treatment.

The miniscrew group consisted of 23 subjects whoreceived implantation of 2 self-drilling miniscrews(Induce MS-II; GC Ortholy, Tokyo, Japan; diameter,1.8 mm; length, 6.0 mm; and Dual-Top Anchor; JeilMedical, Seoul, Korea; diameter, 2.0 mm; length, 6.0mm) in the midpalatal suture. The miniscrews were in-serted under local anesthesia between the mesiolingualcusps (center of the occlusal surface) of the maxillaryfirst molars and those of the maxillary second molars.To reduce soft-tissue inflammation around the mini-screws, strict instructions regarding oral hygiene weregiven to the subjects. After 2 weeks of healing, the 2midpalatal miniscrews were connected with a horizontal0.030-in stainless steel ligature wire (Fig 1). The hori-zontal ligature wire provided support where the verticalligature wires were firmly tied, enabling them to fasten amodified transpalatal arch (Figs 2 and 3). Intrusion wasperformed with either elastomeric chains or ligature

ics August 2013 � Vol 144 � Issue 2

Fig 1. Two midpalatal miniscrews were placed approxi-mately 5 to 8 mm apart in the midpalatal suture and con-nected with a horizontal 0.030-in stainless steel ligaturewire.

Fig 2. Anchorage reinforcing appliances in theminiscrewgroup:A, amodified transpalatal arch with distally extend-ing arms to control the posterior teeth (a, 1 stabilizationhook; b, 2 anchorage hooks); B, the maxillary molarswere controlled both anteroposteriorly and verticallywith the modified transpalatal arch, which was supportedby 2 midpalatal miniscrews.

Table I. Demographic information for the 51 subjectsin this study

Headgeargroup

Miniscrewgroup

Pvalue Significance

Subjects (n) 28 23Sex (male/female)

6/22 0/23

Initial age (y) 19.61 6 7.43 21.50 6 6.19 0.334 NSTreatmentduration (mo)

36.89 6 10.12 34.75 6 7.48 0.404 NS

Independent-samples t test.NS, Not significant.

240 Lee et al

wires from the horizontal ligature wire to the stabiliza-tion hook of the modified transpalatal arch. The stabili-zation hook was used to prevent mesial tipping of theposterior teeth and to apply intrusive force to the poste-rior teeth. Ideally, the modified transpalatal arch shouldbe positioned 5 to 7 mm from the depth of the palate toprevent impingement of the arch on the tissues when anintrusive force is applied to the maxillary molars. When along action range of the intrusion action componentswas needed, the horizontal ligature wire and lingualsheathes of the molar bands were connected with longerelastomeric chains. While the maxillary molars were be-ing intruded, the modified transpalatal arch was alsoused to prevent palatal tipping of the maxillary molars.

All midpalatal miniscrews achieved primary stability.However, 3 (1 in each of 3 subjects) of the 46 total mid-palatal miniscrews became mobile during the en-masseretraction, for a success rate of 93.48%. In the failedcases, a hairpin-shaped wire was bent to fit the headpart of the remaining sound miniscrew passively; thisprovided support instead of a horizontal ligature wire.Treatment was continued with 1 remaining sound

August 2013 � Vol 144 � Issue 2 American

miniscrew. Therefore, the failed cases can be consideredto have had a limited influence on the results.

All subjects were treated with preadjusted edgewiseappliances, 0.018 3 0.025-in slot, level anchorage sys-tem prescription brackets (3M Unitek, Monrovia,Calif).18 We applied the same treatment protocol inboth groups with 1 exception: the method of anchoragereinforcement. After the initial leveling and aligning inthe maxillary arch, stabilizing transpalatal arches wereneeded to control the posterior segments. Therefore,we added stabilizing (conventional or modified) transpa-latal arches in both groups. Maxillary posterioranchorage was reinforced with high-pull headgear orminiscrew-supported modified transpalatal arches ineach group. Once the clinicians were satisfied that theanchorage reinforcement was secure, the bilateral maxil-lary first premolars were extracted. In both groups, 6maxillary anterior teeth were retracted on a 0.017 30.025-in nickel-titanium archwire with 0.010 30.036-in stainless steel closed-coil springs that werestretched two-thirds of the distance from the maxillary

Journal of Orthodontics and Dentofacial Orthopedics

Fig 3. A, Lateral cephalometric radiograph;B, schematicdiagram (a, 1 stabilization hook; b, 2 anchorage hooks;red line, horizontal ligature wire; blue lines, vertical liga-ture wires): the modified transpalatal arch was ligated at2 anterior anchorage hooks and at 1 posterior stabiliza-tion hook with the vertical ligature wires.

Lee et al 241

first molars to the crimpable hooks located mesial to thecanines. Gable bends of 45� were placed in the extrac-tion sites to prevent tipping of the maxillary incisorslingually during the en-masse retraction. When theextraction space measured 2 to 3 mm, a 0.018 30.025-in stainless steel archwire with keyhole loopswas used for root control in the extraction sites, torquecontrol of the maxillary anterior teeth, and final spaceclosure.18 The keyhole loops were activated 1 mm at atime. Anchorage reinforcement was continued untilthe extraction space was closed. When the mandibulararch was stabilized and the maxillary canines were in aClass I relationship with the mandibular canines, the pa-tients were instructed to stop wearing the high-pullheadgear, or the midpalatal miniscrews were discon-nected from the modified transpalatal arch. Stabilizing(conventional or modified) transpalatal arches werealso removed in both groups. In the finishing phase, afterremoving only the posterior segments of the 0.018 30.025-in stainless steel finishing archwires, laced poste-rior vertical elastics were applied for better interdigita-tion of the occlusion; these remained in place for 2 to3 weeks at the most.


Lateral cephalometric radiographs, obtained routinelywithin 1 month before treatment and immediately afterremoval of the fixed appliances, were taken in centric oc-clusion. The images were then hand-traced on mattecephalometric acetate tracing film by the orthodontistsin charge (M.T.,M.S.,M.K.) and verifiedby another ortho-dontist (K.M.). Tracings were made through the mid-points between the right and left structures, and themeasurements were adjusted to eliminate radiographicmagnification. All radiographs were taken anonymouslyby obscuring any patient data.

To evaluate changes between the pretreatment andposttreatment data and to compare treatment changesbetween the 2 groups, skeletal and dental changeswere calculated according to the method described byPancherz.19,20 In several recent studies, the dentofacialmorphology of subjects with maxillary dentoalveolarprotrusion was compared using the Pancherzcephalometric analyses.21,22 The Pancherz approachcomprises sagittal occlusal analysis19 and verticalocclusal analysis20; the use of these 2 methods enablesdifferentiation between sagittal and vertical dentofacialproblems, as well as associated changes. The cephalo-metric landmarks and reference lines for Pancherz'ssagittal, vertical, and angular analyses are shown inTable II and Figures 4 through 6.

Statistical analyses

All statistical analyses were performedwith SPSS soft-ware (version 15.0; SPSS, Chicago, Ill). For each variable,the mean and standard deviation values were calculated,and the levels of statistical significance were P\0.05,P \0.01, and P \0.001. The Kolmogorov-Smirnovmethod was used to confirm the normal distribution ofthe measurements. The distribution of the data wasfound to be normal; therefore, parametric statisticswere applied.

For both groups, the pretreatment measurements ofthe radiographs from each group were assessed using anindependent-samples t test to check for pretreatmentequivalence.A paired-samples t testwasused todeterminethe significance of the treatment changes in both skeletaland dental positions from the pretreatment and posttreat-ment radiographs in eachgroup. Treatment changes in theskeletal and dental positions between the 2 groups werecompared with an independent-samples t test.

All cephalometric measurements were repeated bythe same examiner (J.L.) 4 weeks later. The repeatedmeasurements were assessed with a paired-samples ttest for systematic errors. No variable had statisticallysignificant systematic errors (P .0.05). The greatestmean differences between the first and second readings


Table II. Definitions of landmarks, reference planes, and measurements for the Pancherz analysis

Ii (incison inferius) The incisal tip of the most prominent mandibular incisorIs (incison superius) The incisal tip of the most prominent maxillary incisorMi (molar inferius) The mesial contact point of the mandibular first permanent molar by a tangent parallel to OLpMic The mesiobuccal cusp tip of the mandibular first molarMs (molar superius) The mesial contact point of the maxillary first permanent molar by a tangent parallel to OLpMsc The mesiobuccal cusp tip of the maxillary first molarPg (pogonion) The most anterior part of the bony chin determined by a tangent parallel to OLpA The deepest point on the anterior contour of the maxillary aleveolar projection determined by a tangent parallel to OLpN NasionS SellaANS Anterior nasal spinePNS Posterior nasal spineMe MentonGo GonionIs-OLp–Ii-OLp OverjetMs-OLp–Mi-OLp Molar relationshipA-OLp Maxillary base positionPg-OLp Mandibular base positionA-OLp–Pg-OLp Jaw-base relationshipIs-OLp Maxillary central incisor positionIi-OLp Mandibular central incisor positionIs-OLp–A-OLp Maxillary central incisor relationship to A-pointIi-OLp–Pg-OLp Mandibular central incisor relationship to PgMs-OLp Maxillary first permanent molar positionMi-OLp Mandibular first permanent molar positionOLp Occlusal plane perpendicular, reference line perpendicular to OLs through SIi-OLs Overbite, the distance Ii perpendicular to OLsANS-Me Lower face heightIs-NL Maxillary central incisor position, the distance Is perpendicular to NLIi-ML Mandibular central incisor position, the distance Ii perpendicular to MLMsc-NL Maxillary first permanent molar position, the distance of Msc perpendicular to NLMic-ML Mandibular first permanent molar position, the distance of Mic perpendicular to MLNL/NSL Nasal plane angle, the angle between the maxillary plane (ANS-PNS) and the N-S plane (NSL)ML/NSL Mandibular plane angle, the angle between the mandibular plane (Me-Go) and the N-S plane (NSL)OLs/NSL Maxillary occlusal plane angle, the angle between the maxillary occlusal plane and the N-S plane (NSL)OLi/NSL Mandibular occlusal plane angle, the angle between the mandibular occlusal plane and the N-S plane (NSL)NL Nasal line (maxillary plane)ML Mandibular line (mandibular plane)NSL Nasal sella lineOLs Maxillary occlusal planeOLi Mandibular occlusal plane

When double projections gave rise to 2 points, the midpoint was used.

242 Lee et al

for all linear and angular measurements did not exceed0.5 mm and 0.5�, respectively. The mean values wereused in the statistical analysis. An intrarater reliabilityanalysis with the weighted kappa statistic was performedto determine consistency. The weighted kappa statisticfor the repeated readings showed the highest value of0.96 for Is-OLp and the lowest value of 0.87 for theSNB angle. There was almost perfect agreement betweenall measurements.

RESULTS

There were no statistically significant differences ininitial ages and treatment durations between the 2


groups (P .0.05) (Table I). The effect of any residualgrowth and treatment periods on treatment changescould be expected to be similar.

Pretreatment differences in the variables for thegroups are shown in Table III. For the sagittal measure-ments, A-OLp, Is-OLp, and Ms-OLp were used tocompare the anteroposterior amounts of skeletal anddental changes according to maxillary posterioranchorage. These parameters represented the antero-posterior position of the maxillary base, the maxillarycentral incisor, and the maxillary first permanent molar,respectively. The pretreatment anteroposterior positionshowed no significant differences between the 2 groups(P .0.05). The pretreatment axial inclination of the


Fig 4. Cephalometric landmarks and reference lines forthe sagittal measurements. The sagittal skeletal anddental changes were analyzed by constructing a refer-ence grid based on 2 reference planes: the maxillaryocclusal line (OLs) and the occlusal line perpendicular(OLp), obtained from the pretreatment lateral cephalo-gram. This reference grid was used for all sagittal mea-surements between the OLp and the cephalometriclandmarks. The reference grid from pretreatment wastransferred to the posttreatment radiographs by superim-position on the SN line with the sella as the registeringpoint.

Fig 5. Cephalometric landmarks and reference lines forthe vertical measurements. The vertical measurementsincluded OLs, NL, and ML. OLs was obtained from thepretreatment radiograph and transferred by superimposi-tion on the anterior cranial base to the posttreatment ra-diographs. The vertical movements of the maxillarymolars and incisors were determined by measuring thedistance to the NL.

Lee et al 243

maxillary incisor showed no significant difference(P .0.05). However, overjet, molar relationship, jawrelationship, and ANB angle were significantly greaterin the miniscrew group. These results suggested thatthis group would have greater anteroposterior discrep-ancies in skeletal and dental relationships. For the verti-cal measurements, an independent t test showed nosignificant differences for any variable between thegroups.

Table IV shows the skeletal and dental changes ineach group and compares the changes between thegroups. For each cephalometric parameter, changes be-tween pretreatment and posttreatment in each group arelisted and compared with the associated P values, asdetermined by the paired-samples t test. An increase inthe measurement was expressed as a positive value; adecrease was expressed as a negative value. Positivevalues indicated extrusion, mesial movement, or crownanterior and root posterior angular changes; negative


values indicated intrusion, distal movement, or crownposterior and root anterior angular changes.

For the anteroposterior treatment changes, signifi-cant differences between the groups were apparent forthe following 6 sagittal variables: A-OLp, Is-OLp,Ms-OLp, overjet, Is-OLp-A-OLp, and Mi-OLp. We notedsignificant posterior movement of Point A (A-OLp) in theminiscrew group, but little anterior movement in theheadgear group (�0.61 vs 0.02 mm, respectively). Thisdifference was statistically significant (P \0.05). Inboth groups, the maxillary incisors (Is-OLp) exhibitedsignificant retraction (�4.50 vs �6.87 mm, respec-tively); this was significantly greater in the miniscrewgroup (P\0.01). The variable Ms-OLp suggested signif-icant mesial movement of the maxillary molars in bothgroups (3.63 vs 0.85 mm). However, the change in theheadgear group was significantly greater than that inthe miniscrew group (P\0.001).

Significant differences in the vertical parametersbetween the 2 groups were found in variables Is-NL,Msc-NL, and ANS-Me. Statistically significant differ-ences between the groups were noted in the vertical po-sitional change of the maxillary incisors (Is-NL) and firstmolars (Msc-NL). The maxillary incisors and molars were


Fig 6. Cephalometric landmarks and reference lines forthe angular measurements. Angular measurementswere used to identify angular changes in the dentofacialcomplex.

244 Lee et al

intruded by 1.54 and 1.30 mm, respectively, in the mini-screw group. However, in the headgear group, the maxil-lary incisors did not change in their vertical positions,although the first molars were significantly extrudedby 0.71 mm in relation to the nasal line.

The rotational changes in the maxillary occlusalplane were 2.23� 6 3.04� in the headgear group and3.13� 6 5.62� in the miniscrew group. Changes in themaxillary occlusal plane were greater in the miniscrewgroup than in the headgear group, although thesechanges were not significantly different between thegroups. In relation to the mandibular line, the mandib-ular molars showed significant extrusion–measuring1.79 mm in the headgear group and 1.52 mm in theminiscrew group, indicating similar amounts of extru-sion. The rotational changes in the mandibular occlusalplane were 2.50� 6 4.76� in the headgear group and4.43� 6 5.32� in the miniscrew group, with no statisti-cally significant difference between the groups.

These differences in vertical tooth displacementsmight explain the changes in the mandibular planeangle. In the headgear group, in spite of the tendency to-ward reduction (�0.36� 6 0.34�) in the mandibularplane angle (ML/NSL), the treatment change showedno significant difference (P .0.05). In contrast to thelack of significant changes in the headgear group, themandibular plane angle decreased (�0.80� 6 0.02�)significantly in the miniscrew group (P\0.05).


DISCUSSION

Our main concern in this study was whether theminiscrew-supported modified transpalatal arch wouldreinforce the maxillary posterior anchorage both antero-posteriorly and vertically. At the start of treatment, sta-tistically significant differences were not found in thesagittal measurements that determined the anteroposte-rior position of the maxillary base, central incisor, andfirst molar (A-OLp, Is-OLp, and Ms-OLp). For lip protru-sion improvement, maximum maxillary incisor retrac-tion was indispensable for both groups. The maxillaryanterior teeth were to be moved as distally as possible.For comparison of treatment changes, evaluation ofthe subjects was thought to be helpful in assessing theclinical benefits of a skeletal anchorage system.

For a comparison study, the ideal experimental setupwould involve a randomized controlled trial. Becausethis was a feasible and clinical retrospective study, wetook measures to minimize bias and tried to achieve anacceptable level of evidence. However, the 2 groupsshowed significant differences in anteroposterior rela-tionships (overjet, molar relationship, jaw relationship,and ANB) before treatment. An unequal distribution ofClass II severity between the groups might have influ-enced these results, but this was not the case. These dif-ferences were not considered to have a significantinfluence on our results.

In other studies, midpalatal miniscrews were usedindependently for either en-masse retraction ofmaxillaryanterior teeth or intrusion of maxillary molars. However,although we used 2 midpalatal miniscrews for indirectanchorage, using them with the modified transpalatalarch, we could control themaxillarymolars anteroposter-iorly and vertically at the same time. The modified trans-palatal arch appliance was designed to be an effectivealternative for the conventional transpalatal arch. Wewere able to treat the patients without changing thetreatment mechanics such as the direction and magni-tude of the applied force.

The modified transpalatal arch was useful to main-tain symmetry and arch widths, as well as to preventmesial rotation of the maxillary molars during theen-masse retraction. The appliance was also useful inpreventing palatal tipping while the intrusive force wasapplied to the molars. The intrusive force could bemore effectively applied because the midpalatal mini-screws were higher in the vertical position than theapex of the maxillary molars. The midpalatal miniscrewsalso allowed light, constant intrusive force application tothe posterior maxillary molars. The palatal application ofthe intrusive force prevented buccal tipping and hangingpalatal cusps of the maxillary molars, which were often


Table III. Comparison of pretreatment measurements between the groups

Parameter

Headgear group Miniscrew group

P value SignificanceMean SD Mean SDSagittal measurementsOverjet (mm) 4.86 3.52 6.85 3.06 0.038 *Molar relationship (mm) �2.54 2.38 �0.04 1.88 0.000 y

Position of maxillary base (mm) 79.13 4.05 79.80 4.16 0.559 NSPosition of mandibular base (mm) 82.11 5.27 79.70 7.74 0.212 NSJaw relationship (mm) �2.98 3.84 0.11 4.60 0.012 *Position of maxillary central incisor (mm) 92.02 4.52 92.98 3.77 0.421 NSPosition of mandibular central incisor (mm) 87.16 5.83 86.13 4.77 0.499 NSMaxillary central incisor relationship to A-point (mm) 12.89 2.95 13.17 2.37 0.714 NSMandibular central incisor relationship to Pg (mm) 5.05 3.70 6.43 5.64 0.299 NSPosition of maxillary first permanent molar (mm) 58.75 3.88 60.57 4.54 0.130 NSPosition of mandibular first permanent molar (mm) 61.29 5.14 60.61 4.96 0.637 NSSNA (�) 81.36 2.74 82.63 3.11 0.127 NSSNB (�) 77.55 3.98 75.54 3.36 0.060 NSANB (�) 3.80 2.11 7.09 2.26 0.000 y

Angulation of maxillary central incisor (�) 108.32 11.58 105.61 12.44 0.425 NSAngulation of mandibular central incisor (�) 98.93 6.67 102.41 7.07 0.077 NSInterincisal angle (�) 114.18 9.57 111.65 13.03 0.429 NS

Vertical measurementsOverbite (mm) 1.93 2.15 2.39 3.80 0.607 NSLower facial height (mm) 73.77 4.39 75.76 7.08 0.247 NSPosition of maxillary central incisor (mm) 31.34 2.72 32.85 3.05 0.068 NSPosition of maxillary first permanent molar (mm) 25.48 2.12 25.22 2.60 0.690 NSPosition of mandibular central incisor (mm) 46.68 2.60 48.00 3.36 0.120 NSPosition of mandibular first permanent molar (mm) 37.11 2.60 37.54 3.05 0.584 NSNasal plane angle (�) 10.25 3.07 8.83 3.24 0.114 NSMandibular plane angle (�) 37.41 6.27 39.46 8.11 0.315 NSMaxillary occlusal plane angle (�) 20.39 4.55 22.39 5.59 0.165 NSMandibular occlusal plane angle (�) 16.55 5.60 17.59 7.08 0.563 NS

Independent samples t test.NS, Not significant.*P\0.05; yP\0.001.

Lee et al 245

observed when the intrusive force was delivered from thebuccal side.

Two miniscrews were connected with a horizontalligature, which helped them to resist forces that couldloosen them. Therefore, it was possible to perform 2 ormore dimensional tooth movements simultaneously:eg, en-masse retraction and intrusion. By adjusting themodified transpalatal arch and ligature wires, the forceapplication points were optimized for various toothmovement options without placing additional mini-screws or relocating them. The procedure for the adjust-ment was easily performed because the modifiedtranspalatal arch was removable.

Anchorage preservation is a key factor in treating pa-tients with bialveolar dental protrusion.23 The maxillaryextraction spaces were closed with closed-coil springsfrom the maxillary first molars to the crimpable hookson the archwires in both groups, resulting in retractionforces on the maxillary molars in the mesial direction.The mesial movement of the maxillary molars can be


considered to represent the mean anchorage loss inthis study because all subjects had maxillary dentoalveo-lar protrusion requiring maximum anchorage. In theminiscrew group, the maxillary first molars moved mesi-ally by only 0.85 mm. This finding was statistically sig-nificant when compared with the headgear group, inwhich mesial movement was 3.63 mm. Although 1 to2 mm of anchorage loss is clinically acceptable, higheramounts can be detrimental to the overall efficiency ofthe treatment, especially when anchorage is critical.23

In previous studies by Upadhyay et al,23 Park et al,5

and Park and Kwon,7 buccal miniscrews were used asthe first step in en-masse retraction of maxillary anteriorteeth. As a result, distal movement of the maxillary mo-lars followed. Contrary to these studies, we found signif-icant anchorage losses in patients treated withmidpalatal miniscrews. Two reasons might partiallyexplain the average of 0.85 mm of mesial movementof the maxillary molars that was still noted in the mini-screw group. First, anchorage loss in the miniscrew


Table IV. Comparison of treatment changes between the groups

Parameter

Headgear group

Pretreatment Posttreatment

Difference P value Significance*Mean SD Mean SDSagittal measurementsOverjet (mm) 4.86 3.52 3.07 0.66 �1.79 0.012 z

Molar relationship (mm) �2.54 2.38 �2.23 2.64 0.30 0.371 NSPosition of maxillary base (mm) 79.13 4.05 79.14 4.11 0.02 0.935 NSPosition of mandibular base (mm) 82.11 5.27 82.98 5.52 0.88 0.105 NSJaw relationship (mm) �2.98 3.84 �3.84 4.42 �0.86 0.083 NSPosition of maxillary central incisor (mm) 92.02 4.52 87.52 4.33 �4.50 0.000 §

Position of mandibular central incisor (mm) 87.16 5.83 84.45 4.35 �2.71 0.000 {

Maxillary central incisor relationship to A-point (mm) 12.89 2.95 8.38 2.77 �4.52 0.000 {

Mandibular central incisor relationship to Pg (mm) 5.05 3.70 1.46 3.61 �3.59 0.000 {

Position of maxillary first permanent molar (mm) 58.75 3.88 62.38 4.16 3.63 0.000 {

Position of mandibular first permanent molar (mm) 61.29 5.14 64.61 5.41 3.32 0.000 {

SNA (�) 81.36 2.74 81.02 2.73 �0.34 0.004 §

SNB (�) 77.55 3.98 77.36 3.98 �0.20 0.407 NSANB (�) 3.80 2.11 3.66 2.17 �0.14 0.565 NSAngulation of maxillary central incisor (�) 108.32 11.58 100.32 10.05 �8.00 0.001 {

Angulation of mandibular central incisor (�) 98.93 6.67 95.55 8.71 �3.38 0.030 z

Interincisal angle (�) 114.18 9.57 127.43 8.54 13.25 0.000 {

Vertical measurementsOverbite (mm) 1.93 2.15 1.57 0.49 �0.36 0.386 NSLower facial height (mm) 73.77 4.39 74.46 4.74 0.70 0.123 NSPosition of maxillary central incisor (mm) 31.34 2.72 31.89 3.38 0.55 0.072 NSPosition of maxillary first permanent molar (mm) 25.48 2.12 26.20 2.02 0.71 0.001 {

Position of mandibular central incisor (mm) 46.68 2.60 44.86 3.19 �1.82 0.000 {

Position of mandibular first permanent molar (mm) 37.11 2.60 38.89 2.58 1.79 0.000 {

Nasal plane angle (�) 10.25 3.07 10.34 3.09 0.09 0.259 NSMandibular plane angle (�) 37.41 6.27 37.05 7.06 �0.36 0.337 NSMaxillary occlusal plane angle (�) 20.39 4.55 22.63 5.30 2.23 0.001 {

Mandibular occlusal plane angle (�) 16.55 5.60 19.05 5.24 2.50 0.010 §

NS, Not significant.*Paired-samples t test; yIndependent-samples t test; zP\0.05; §P\0.01; {P\0.001.

246 Lee et al

group might be attributed to bending or loosening ofthe modified transpalatal arch used to connect the an-chor teeth to the midpalatal miniscrews; this mighthave been because the miniscrews were used as indirectanchorage instead of direct anchorage.24 Second,anchorage loss in the miniscrew group might havebeen due to the early loss of the connection betweenthe modified transpalatal arch and the midpalatal mini-screws.25 In the finishing stages, the early disconnectionwas clinically required to establish a stable Class I occlu-sion. Our subjects had hyperdivergent facial types. Themaxillary anterior teeth were to be moved as distally aspossible, but without distal displacement of the maxil-lary molars and consequently clockwise rotation of themandible. The treatment goal was to prevent mesialdrifting of the maxillary molars.

In addition to this anchorage capacity, the otherproblem with the use of headgear involves the relianceon patient compliance. Unlike miniscrews with their


continuous action, the headgear might not be worn allthe time for social and esthetic reasons. Thus, intermit-tent force applications from the headgear could haveaccounted for part of the anchorage loss. Compliancewith headgear wear was assessed by experienced clini-cians treating these patients and reinforced with chartscompleted at home. The clinical records showed thatall subjects had good cooperation. However, clinical indi-cators of compliance with headgear wear can bemisleading.26 Consequently, miniscrew-supportedmodi-fied transpalatal arches might be a compliance-free, pre-dictable method of producing more powerful anchorage.

Maximum maxillary posterior anchorage wasrequired to fully close the first premolar extractionspaces by retracting the protruding incisors. The maxil-lary base (Point A) and central incisors in both groupswere anteroposteriorly placed in the same positionbefore treatment (Table III). We noted significant poste-rior movement of Point A in the miniscrew group but


Miniscrew group Headgear group vs miniscrew group

Pretreatment Posttreatment

Difference P value Significance* P value SignificanceyMean SD Mean SDSagittal measurements

6.85 3.06 3.04 1.83 �3.80 0.000 { 0.047 z

�0.04 1.88 �0.28 3.34 �0.24 0.645 NS 0.364 NS79.80 4.16 79.20 3.89 �0.61 0.002 § 0.033 z

79.70 7.74 79.78 8.07 0.09 0.831 NS 0.254 NS0.11 4.60 �0.59 5.38 �0.79 0.118 NS 0.806 NS

92.98 3.77 86.11 4.52 �6.87 0.000 { 0.003 §

86.13 4.77 83.07 4.64 �3.07 0.000 { 0.697 NS13.17 2.37 6.91 2.22 �6.26 0.000 { 0.016 z

6.43 5.64 3.28 4.76 �3.15 0.000 { 0.606 NS60.57 4.54 61.41 4.80 0.85 0.034 z 0.000 {

60.61 4.96 61.70 5.48 1.09 0.073 NS 0.004 §

82.63 3.11 82.02 2.79 �0.61 0.012 z 0.253 NS75.54 3.36 75.26 3.65 �0.28 0.212 NS 0.792 NS7.09 2.26 6.76 2.18 �0.33 0.214 NS 0.609 NS

105.61 12.44 96.30 9.31 �9.30 0.001 { 0.683 NS102.41 7.07 100.39 9.41 �2.02 0.235 NS 0.543 NS111.65 13.03 124.33 9.12 12.67 0.001 { 0.880 NS

2.39 3.80 1.65 0.57 �0.74 0.373 NS 0.677 NS75.76 7.08 75.26 7.13 �0.5 0.188 NS 0.047 z

32.85 3.05 31.30 3.53 �1.54 0.023 z 0.005 §

25.22 2.60 23.91 2.60 �1.30 0.000 { 0.000 {

48.00 3.36 45.39 4.47 �2.61 0.000 { 0.181 NS37.54 3.05 39.07 3.23 1.52 0.000 { 0.466 NS8.83 3.24 8.89 3.05 0.07 0.328 NS 0.818 NS

39.46 8.11 38.65 8.28 �0.80 0.021 z 0.374 NS22.39 5.59 25.52 6.47 3.13 0.014 z 0.496 NS17.59 7.08 22.02 6.60 4.43 0.001 { 0.177 NS

Table IV. Continued

Lee et al 247

little anterior movement in the headgear group (�0.61vs 0.02 mm, respectively) (P \0.05). The retraction ofthe maxillary incisors in the miniscrew group (6.87mm) was significantly greater than that in the headgeargroup (4.50 mm) (P \0.01). En-masse retraction withminiscrew-supported modified transpalatal arches notonly increases maxillary incisor retraction, but alsocauses a significant skeletal change in the anteroposte-rior position of the maxillary base.

In both groups, the occlusal plane showed significantrotations in the clockwise direction. No statistical signif-icance was found between the 2 groups. The steepeningof the occlusal plane is an appreciable source of sagittalcorrection of a Class II malocclusion.27 The clockwiserotation of the occlusal plane facilitated the correctionof the Class II molar relationship because the maxillaryfirst molars occluded more distally on the mandibularfirst molars. Braun and Legan28 discussed the geometricand mathematic relationships between dental occlusion


and rotation of the occlusal plane. They showed thateach degree of rotation of the occlusal plane wouldresult in a 0.5-mm horizontal change in the molar rela-tionship. Successful correction of a Class II malocclusiondepends on vertical control of the horizontal planes,particularly the occlusal plane.

However, an interesting finding in this study was thatmaxillary molar movements showed different character-istic features depending on the anchorage reinforcing sys-tem. The headgear group had extrusion of the maxillarymolars, whereas the miniscrew group displayed intrusionof themaxillary molars (Fig 7). Despite the intrusive forcesexerted on the maxillary first molars by the high-pullheadgear and the conventional transpalatal arch in theheadgear group, the maxillary molars showed extrusion.In other words, although the high-pull headgear wasdesigned to restrict extrusion movements of the molarsin the headgear group, maxillary molar extrusion never-theless occurred. Kim29 criticized the use of high-pull


Fig 7. Mean values of tooth displacements and a changein maxillary occlusal plane angle (OLs/NSL) betweenpretreatment (black line) and posttreatment (red line):A, headgear group; B, miniscrew group.

248 Lee et al

headgear for molar intrusion. However, the extrusion ofthe maxillary first molars might have been less thannormal because of the intrusive forces exerted on them.

On the other hand, intrusion of the maxillary molarswas noted in the miniscrew group, with statistical signif-icance. The significant clockwise rotation of the occlusalplane was attributed to this intrusive movement of themaxillary molars. In the miniscrew group, the clockwiserotation of the occlusal plane depended on 2 factors:intrusion of the maxillary molars and control of themaxillary incisor edge positions. Although the sameanterior retraction mechanics were used, the maxillaryincisor edge did not have a significant vertical changein the headgear group. However, in the miniscrew group,significant intrusion of the maxillary incisor edge wasobserved; this was associated with intrusion of themaxillary molars. Using a modified transpalatal archand connecting it to 2 midpalatal miniscrews, it waspossible to intrude the maxillary molars first. Dependingon the elasticity of the continuous archwire, it is prob-able that the intrusive displacement of the posteriorsegment affected the anterior segment.23,30,31 Byintruding the maxillary molars first, the maxillaryanterior teeth were consequently retracted andintruded at the same time. The simultaneous intrusionand retraction of the maxillary anterior teeth in theminiscrew group might have been effectively obtained


using miniscrew-supported modified transpalatalarches, without any intervention involving additionalintrusive mechanics. Thus, midpalatal miniscrews mighteffectively manage the entire maxillary dentition by con-trolling the molars through the modified transpalatalarch appliance. In addition, the intrusion of the maxillaryincisors could have been because Class II elastics werenot used in the miniscrew group, in which the verticalforce vector might have caused extrusion of the maxil-lary incisors.

For extrusion of mandibular molars, high-pull head-gear and conventional transpalatal arches are commonlyincorporated in the treatment mechanics for patientswith Class II malocclusions to reinforce the maxillaryposterior anchorage. These are most likely followed byClass II elastics, which are worn to retract the maxillaryanterior teeth and to mesialize the mandibular posteriorteeth. However, extrusion of the mandibular molars isoften observed when a patient wears Class II elastics.This side effect can have a negative impact on thecorrection of a Class II malocclusion, especially for pa-tients with hyperdivergent facial types. The mandibularmolars showed significant extrusions of 1.79 mm inthe headgear group and 1.52 mm in the miniscrewgroup, with no significant difference between thegroups. The extrusion of the mandibular molars in theheadgear group was caused primarily by the verticalcomponent of the force from the Class II elastics.32 Inthe miniscrew group, it is difficult to explain why signif-icant extrusion of the mandibular molars occurred,because Class II elastics were not used. This extrusionof the mandibular molars might be attributed to thecompensatory process by which the mandibular molarsunderwent extrusion to develop occlusal contacts withthe opposing teeth, together with the intrusion of themaxillary molars. During leveling of the curve of Speein adults, the muscles of mastication do not adapt andenable changes in the vertical dimension. If the maxillarymolars are intruded, the mandibular molars have addi-tional space to ascend during leveling of the curve ofSpee. The craniofacial complex, including the mastica-tory system, is highly complicated and should not beperceived as a simple articulator.

As for skeletal changes, studies have reported that inhyperdivergent facial types, orthodontic forward move-ment of posterior teeth after premolar extractions led toreductions in the vertical dimensions.33,34 In theheadgear group, due to anchorage loss, the first molarsmoved mesially by averages of 3.63 mm in the maxillaand 3.32 mm in the mandible. However, even with thetendency toward reduction in the mandibular planeangle to NSL, no significant decrease was observed inthe headgear group. These results suggested the


Lee et al 249

limitations of conventional orthodontics to significantlyalter skeletal vertical dimensions. Most orthodontic forceapplications tend to cause extrusion of the molars.35,36

The mesial movements of the maxillary andmandibular molars coincided with their extrusion tosuch an extent that they maintained the mandibularplane angle, thus nullifying any bite-closing effectfrom protraction of the posterior segment.32,37 Thiscould explain the constancy of the facial dimensions inthe headgear group, in which both extrusion andprotraction of the molars were recorded.

The miniscrew group displayed significant intrusionof the maxillary molars and closing rotation of themandible. Many studies have reported that intrusion ofthe molars is important for closing the rotation of themandible.38,39 However, intrusion of posterior teethhas been difficult because of the lack of anchorage. Inthis study, it was confirmed that modified transpalatalarches supported by 2 midpalatal miniscrews canintrude the maxillary molars and close the mandibularrotation; these corrections were difficult withtraditional high-pull headgear anchorage reinforce-ment. However, a significant difference between the 2groups was not found in the amount of mandibularmolar extrusion, suggesting that the mandibular molarsdid not cause differences in changes to the vertical facialdimensions in this study.

The change from Class II to Class I occlusion wasgenerally made by horizontal movements of the teethalong the occlusal plane. However, the vertical dimen-sion also had to be managed to achieve the desired pre-treatment goals. Vertical control can facilitate horizontalcorrection.40 The key to successful orthodontic treat-ment involves both anteroposterior and verticalanchorage control. The miniscrew-supported modifiedtranspalatal arch seems to be a more effective anchoragereinforcement appliance than the traditional anchoragesystem.

CONCLUSIONS

This study shows the versatility of 2 miniscrews in themidpalatal suture; this proved to be better suited forboth anteroposterior and vertical anchorage control formaxillary posterior teeth. Our conclusions can be sum-marized as follows.

1. The miniscrew-supported modified transpalatalarch can provide better anteroposterior control ofthe maxillary posterior teeth for anchorage preser-vation. The skeletal anchorage achieved greatermaxillary incisor retraction and less anchorage lossof the maxillary first molars than did the traditionalhigh-pull headgear anchorage.


2. The miniscrew-supported modified transpalatalarch can facilitate more proper vertical control ofthe maxillary molars. The maxillary molars weresignificantly intruded; this allowed the maxillaryocclusal plane to rotate in a clockwise direction.With the skeletal anchorage, the mandibular planeangle significantly decreased, whereas the mandibleshowed significant closure.

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Midpalatalminiscrewsandhigh-pullheadgearfor ...lingually during the en-masse retraction. When the extraction space measured 2 to 3 mm, a 0.018 3 0.025-in stainless steel archwire with