Long- And Short-term Effects of Headgear Traction

Long- and short-term effewith and without the max

Nir Shpack,a Tamar Brosh,b Yoav Mazor,c Yoav Shapinko,Susanne Reimann,f Christoph Bourauel,g and Alexander DTel Aviv, Israel, and Bonn, Germany

Introduction: A quantitative assessment of maxillary rst mondmolar (M2) was carried out.Methods: Fifty-six cervicadontic treatment were divided into 2 groups: before (GM2molars (ages, 11.87 6 1.20, and 13.05 6 1.55 years, res(TDCP) and the space between the second premolar andof headgear force (0-15 N) at 3 intervals 6 months apart (tween space and TDCP, time, and presence or abse(P\0.001). The TDCP decreased and space increased winitial force beyond 6 to 9 N did not signicantly increaGM2 TDCP and space measurements were similar to th

talizwitheforer is rem J O

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es-a-larndentrst

thelarofthendf-

segment.2,9 It has been shown when using the

that distalization of the maxillary permanent rst molar

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All authors have completed and submitted the ICMJE Form for Disclosure ofPotential Conicts of Interest, and none were reported.

0889-5406/$36.00Copyright 2014 by the American Association of Orthodontists.

ORIGINAL ARTICLEpendulum appliance that once the maxillary secondmolars have erupted, distal movement of the maxillaryrst molar is slowed, and anchorage loss is morecommon,4 producing mesial movement of the anteriorteeth.10 Ten Hoeve2 and Jeckel and Rakosi3 concluded

Supported in part by a grant from the GIF (German-Israeli Foundation) (grant no.01910911).Address correspondence to: Nir Shpack, Department of Orthodontics, theMaurice and Gabriela Goldschleger School of Dental Medicine, Tel Aviv Univer-sity, Tel Aviv, Israel; e-mail, [email protected], September 2013; revised and accepted, June 2014.ciency.7,8 Previous studies with noncomplianceappliances have reported that before maxillary secondmolar eruption, the maxillary rst molar can bedistalized by 1 to 2 mm per month with little anchoragelossie, forward displacement of the anterior

gEndowed professor, Center of Dento-Maxillo-Facial Medicine, Faculty of Medi-cine, University of Bonn, Bonn, Germany.hProfessor, Department of Orthodontics, the Maurice and Gabriela GoldschlegerSchool of Dental Medicine, Tel Aviv University, Tel Aviv, Israel.Nir Shpack and Tamar Brosh are joint rst authors and contributed equally to thiswork.http:/t is an accepted treatment modality to direct extra-ral forces through the maxillary permanent rstolar to cause its distalization via headgear (HG).ever, this effect can vary considerably under

different HG loading conditions as well as in the prence or absence of teeth distal to the maxillary permnent rst molar.1 The presence of the second mo(M2) and third molar in different developmental aeruptive stages can also act as a physical impedimto the extent and direction of maxillary permanent molar distalization.2-5

Kloehn6 advocated early HG treatment to distalizemaxillary teeth into correct occlusionwith themandibudentition. It has also been proposed that treatmentClass II malocclusions should be performed beforeeruption of the maxillary permanent second molars acanines, since the latter might affect treatment e

r, Department of Orthodontics, the Maurice and Gabriela Goldschlegerl of Dental Medicine, Tel Aviv University, Tel Aviv, Israel.r, Department of Oral Biology, the Maurice and Gabriela Goldschlegerl of Dental Medicine, Tel Aviv University, Tel Aviv, Israel.te practice, Tel Aviv, Israel.uctor, Department of Orthodontics, the Maurice and Gabriela Goldschlegerl of Dental Medicine, Tel Aviv University, Tel Aviv, Israel.rer, Department of Orthodontics, the Maurice and Gabriela Goldschlegerl of Dental Medicine, Tel Aviv University, Tel Aviv, Israel.r researcher, Department of Oral Technology, Center of Dento-Maxillo-Medicine, Faculty of Medicine, University of Bonn, Bonn, Germany.second molar. From T0 to T1, maxillary rst molar disprevious headgear-alone study, initial distalizationConclusions: Headgear therapy is more effective berupts, the distalization pace of themaxillary rst molapace when the maxillary second molar is present. (A/dx.doi.org/10.1016/j.ajodo.2014.06.015cts of headgear tractionillary second molars

d Moshe Davidovitch,e Rachel Sarig,e

. Vardimonh

olar distalization with and without the maxillary sec-l headgear patients undergoing xed appliance ortho-) and after (G1M2) eruption of the maxillary secondpectively). The tightness of the dental contact pointthe maxillary rst molar were measured at 6 levelsT0, T1, T2). Results: Relationships were found be-nce of the maxillary second molar at T1 and T2ith increase in initial headgear force. An increase inse the initial maxillary rst molar distalization. Theose of G1M2 at T2 with the eruption of the maxillaryation was greater in G M2. In comparison with oura fully bonded appliance was reduced by 4-fold.the eruption of the maxillary second molar. Once itduced, but it can nevertheless be pursued at a slowerrthod Dentofacial Orthop 2014;146:467-76)is restrained by themaxillary secondmolar; consequently,

467

468 Shpack et althey recommended distalization before second molareruption. Similar ndings have been reported for severalintraoral molar distalization appliances.11,12

On the other hand, Muse et al,13 using a Wilson rapidmolar distalization appliance, and Ghosh and Nanda,14

using the pendulum appliance, found that the presenceof the maxillary second molar did not signicantly affectthe rate of rst molar movement. Additional studies withrepelling magnets15 and the pendulum appliance10,16

support the latter claims of the minor effect of themaxillary second molar on rst molar distalization.This diversity could be related to the interrupted forceregimen produced by HG compared with thecontinuous force of noncompliance appliances.

In a previous study, we demonstrated that an incre-mental increase in cervical HG force, applied per se,caused differences in the gap created between the maxil-lary rst molar and the second premolar, and that rstmolar distalization was inuenced by the absence orpresence of the maxillary second molar.2 In this study,we investigated whether similar effects on molar distal-ization can be expected when HG traction is appliedduring full-arch xed appliance therapy and over alonger period of time. Furthermore, we investigatedwhether HG therapy is affected by short-term (initialperiodontal ligament [PDL] reaction to HG placement)and long-term (bone remodeling) changes, and wedetermined the range for the initial HG force.

With respect to the latter, few previous studies haveexamined this issue, mostly describing the orthopediceffects of diverse HG forces. For example, Zentneret al17 studied orthopedic forces of 5.6 N (Newton 5101.97 gram-force 5 3.597 oz) vs orthodontic forcesof 3.5 N on a macerated human skull using holographicinterferometry. They reported that lower HG forces pro-duced signicantly greater deformations than did higherforces; this indicates that there might be an upper limitto the optimal force level.

Dental changes caused by HG therapy have beenreported in the literature. Andreasen and Johnson18

applied diverse forces in each side and found that overa 12-week period the molar receiving 4 N of HG forcedistalized 2.5 times more than did the other molar, whichreceived 2 N of force. After 8 weeks in the 2-N side, nofurther increase in molar distalization was found,whereas the 4-N side demonstrated continuation ofmolar distalization at the same pace to end of the study(12 weeks). This suggests that there might be a lowerlimit to the optimal force level.

The objectives of this study were to evaluate HGdistalization efcacy concomitant with edgewise xed

appliance treatment in relation to 4 variables: the absenceor presence of the maxillary second molar, the amount of

October 2014 Vol 146 Issue 4 Americandistal movement of the maxillary rst molar, the magni-tudeof theHG force, andmaxillary secondmolar eruption.

The null hypotheses were that at all stages oftreatment, the amount of distalization of the maxillaryrst molar is not affected by the presence or absenceof the maxillary second molar, and the initial forcemagnitude has no effect on initial maxillary rst molardistal displacement.

MATERIAL AND METHODS

The study sample comprised 56 patients presenting fortreatment at the Department of Orthodontics, Universityof Tel Aviv in Israel, diagnosed as having an Angle ClassII malocclusion and treated without extractions withcervical HG for at least 1 year for a minimum of 12 hoursper day. Subjects were included in the study when part oftheir malocclusion was related to maxillary dentoskeletalprotrusion (SNA,.83; mean, 85.96 2.03). Syndromicpatients (eg, cleft lip) were excluded, as were those withearly mesial drift of the maxillary rst molar (eg,congenitally missing second premolar) and adults(age, .16.5 year). The Class II severity ranged from ahalf-step to a full-step molar relationship. All treatmentsincluded the use of fully bonded edgewise applianceswithout intermaxillary or intramaxillary elastics. Datawere gathered at 3 time points: T0, start of HG therapy;T1, 6 months after T0; and T2, 12 months after T0.

The sample was divided into 2 groups: (1) G M2:both maxillary second molars were unerupted at T0 orshowed both clinically and radiographically no contactpoint between the rst and second molars (21 subjects:9 boys, 12 girls; mean age, 11.87 6 1.20 years), and (2)G 1 M2: at T0, both maxillary second molars werepresent in the oral cavity, with both clinically and radio-graphically an interproximal contact point between therst and second molars (35 subjects: 18 boys, 17 girls;mean age, 13.05 6 1.55 years).

In addition to determining the presence or absence ofthe second molars, we examined the Nolla19 stage ofmaxillary second molar development radiographically.

A 0.022 3 0.028-in preadjusted appliance wasbonded to the maxillary dentition, into which wasinserted an uncinched nickel-titanium archwire. Thearchwires were changed according to the progress inleveling, from 0.014 to 0.018 in. A Kloehn type of cervicalHG was delivered to the bands on the permanent rstmolars. The HG consisted of a medium outer bow, withU loops (3M Unitek, Monrovia, Calif); the outer armwas positioned horizontally (with no adjusted upwardtilt). The HG force was increased gradually from 0 to15 N in 3-N increments (0, 3, 6, 9, 12, and 15 N). Zero re-

ected the measurement when the facebow was insertedin the mouth without attaching the (activation) neck

Journal of Orthodontics and Dentofacial Orthopedics

mea

Shpack et al 469strap. Upon activation, the force created by the neck strapwas measured by a force gauge (weighing scale, springtype WS072; Narang Medical, New Delhi, India) (Fig 1).Displacement of the maxillary right rst molar wasmeasured by 2 direct methods at T0, T1, and T2. The rstmethod was as a function of the change in tightness ofthe contact point between the second premolar and therst molar using the tightness of dental contact point(TDCP) device, according to the method of Vardimonet al20-23 (Fig 2, A). Briey, the device measures theamount of force required to insert a metal strip(0.15 mm) between 2 adjacent dental contact points inTDCP units (Fig 2, B). The TDCP was measured on theright side and could be measured as long as the maxillaryrst molar displacement was smaller than 0.15 mm.

In the second method, custom-made metal gauges(leaves) were inserted at the contact point of the secondpremolar and the rst molar in serial fashion. The gauges(made at workshop of the Faculty of Physics, Tel AvivUniversity) differed in thickness from 0.1 to 0.6 mm, in0.05-mm increments (totaling 11 gauges) (Fig 3). Dis-placements less than 0.1 mm were considered to be nodisplacement. Each of the 2methodswasmeasuredwhilethe subject was seated in a dental chair reclined to 135,and the HG force was increased gradually. The total timefor TDCP and space measurements for the 6 force mag-

Fig 1. Force gauge used tonitudes was about 12 minutes. The measurements weretaken continuously. All measurements were taken bythe same investigator (Y.M.). The average HG forceworn by the patient during the 12 hours of wear was 4 N.

Statistical analysis

The random errors (calculated using the Dahlbergformula24) and the systematic error (calculated using apaired t test) of the 2 instruments were examined on 5subjects from each group; the 2 sets of measurementswere taken at 1-week intervals.

The Dahlberg formula is the following.

D5PN

i5Id2i2N

q

American Journal of Orthodontics and Dentofacial OrthopedD is the random error, di is the difference between therst and the second measurements, and N is the samplesize that was remeasured.

For repeated measures of the TDCP, the random errorwas 0.209 N (13%); for the space measurements, it was0.012 mm (8.6%). The larger error calculated in theformer was caused by stretching of the PDL during theinitial TDCP measurements; this affected subsequentmeasurements. Therefore, only the rst TDCP measure-ments were considered. No signicant differences werefound in the paired t tests between the rst and secondmeasurements, conrming the absence of systematicerror.

Analysis of variance (ANOVA) with repeated measureswith the post hoc Tukey test was used to analyze eachparameter (TDCP and space), where the HG force (0-15 N) and time (T0, T1, T2) were within factors, andmaxillary second molar presence or absence (G 1 M2,G M2) was the between factor. Since the TDCP valuesdid not show a normal distribution, the formula 1/(7 TDCP) was used to normalize the results: 7 reects themaximum TDCP value (in Newtons) that can be regis-tered by the TDCP device.

Pearson correlation analysis was used to analyze thecorrelations between TDCP and space for each timepoint at all HG forces.sure the applied HG force.RESULTS

Nolla stages of maxillary second molar developmentwere 7.66 0.5 (1/3 to 2/3 of the root was completed) forG M2 and 9.5 6 0.5 (root completed with open orclosed apex) for G 1 M2. These values correspond toprevious studies.25,26

At T0, there was no signicant difference in TDCP be-tween G 1 M2 and G M2. At no HG load force (0 N),the 2 groups had similar contact point tightness. In bothgroups, a nonsignicant decrease in contact point tight-ness was found as the HG force was increased; however,the decrease was greater in subjects without the secondmolar (G M2) (Fig 4).

ics October 2014 Vol 146 Issue 4

470 Shpack et alAt T1, minor to moderate corrections in the Class IIrelationship were found in both groups. At no force(0 N), the initial TDCP values were signicantly lowerthan the initial values at T0 (P\0.001). The decreasewas signicantly more evident in G M2 (P \0.01)(Fig 4).

At T2, in all subjects, the molar relationships wereimproved; Class I molar relationships were almostcompleted, meaning that the range of distalizationwas 3 to 6 mm. The TDCP values for GM2were signif-icantly higher than those obtained at T1 (P\0.001). The

Fig 2. A, The TDCP device for measuring interproximalforces comprises a handle and an electronic unit; BJ,bow jig; MS, metal strip; B, the handle includes a beam(B) with 2 integrated strain gauges (SG), and the bowjig with a 0.15-mm metal strip is connected to the beam;C, intraoral TDCP (blue arrow) measurement at the con-tact point of the second premolar and the rst molar, whilethe inner arch of the HG at a given force is connected tothe rst molar.

October 2014 Vol 146 Issue 4 Americaninitial TDCP value at no load decreased signicantly asthe force load increased (P\0.001) (Fig 4).

The ANOVA with repeated measures demonstrated asignicant (P\0.001) relationship among TDCP, space,and time in both groups (presence or absence of maxil-lary second molars) (Table I).

At T0, at 0 N, only a small space width was measuredin both groups. The increase in space wasmore evident inGM2as the force was increased, but the overall changewas not signicant for either group (P 5 0.10) (Fig 5).

HG force elevation was effective up to 9 N for bothgroups. Further increases in force did not cause an in-crease in space.

At T1, at 0 N, the space measurement was signi-cantly (P \0.001) higher in the G M2 than in theG 1 M2; the increase in space width was similar inboth groups as the HG force was increased (P\0.01)(Fig 5). The increase in space width was signicant inboth groups up to 3 N; after this, the force elevationwas not followed by a signicant space increase.

At T2, with 0 N, the space width was signicantlysmaller in GM2 than in G1M2 (P\0.001). However,the space increased signicantly more at the rst forceloading (3 N) in the GM2 group. Any additional forceloading produced a nonsignicant increase in spacewidth in both groups (Fig 5).

The ANOVA with repeated measures demonstratedrelationships among space, time, and the presence orabsence of the maxillary second molar (P \0.001)(Table I). An interaction was found between HG forceand the presence or absence of the maxillary secondmolar and space measurements (P\0.001). The interac-tion was well noted at T2 (Fig 5), since the effect of theforce was exhibited mainly at the low force load for theG M2 group.

In both groups, at all time points (T0, T1, T2), the in-crease in HG force was followed by a decrease in theTDCP and an increase in space opening (Figs 6 and 7).The changes in both types of measurements were similarbut inverse as the HG force increased from 0 to 15 N. Inboth groups, the major change occurred at 3 N for T1and T2 (Figs 6 and 7). At T0, in the G M2, the spaceand TDCP measurements substantially increased ordecreased progressively from 0 to 9 N, respectively(Fig 6). In contrast, in the G 1 M2, the space andTDCP measurements moderately increased or decreasedprogressively from 0 to 15 N, respectively (Fig 7). After9 N, a plateau was found for both parameters (Fig 6).That is, for G M2 at T0, increasing the HG forcefrom 9 to 15 N showed no increase or decrease in thespace and TDCP measurements, respectively (Fig 6).Pearson correlations (Table II) demonstrated signi-cant correlations between space and TDCP for all time


Shpack et al 471points (T0, T1, T2) and all HG loadings (0-15 N), besidesT0 at 0 and 3 N. Negative correlations between the TDCPand space were found as the HG force was elevated; ie,TDCP decreased, and space increased (Table II; Figs 6and 7). At T0, the correlation became signicant up to6 N. Highly signicant correlations were found at T1and T2 for all HG force magnitudes.

DISCUSSION

In this study, we investigated the effect of the pres-ence or absence of the maxillary second molar on thedistalization of the maxillary rst molar using HG trac-tion during edgewise xed appliance therapy, in boththe short term (PDL effect) and the long term (osseouseffect). This was measured as a function of the spacecreated between the maxillary rst molar and the secondpremolar and evaluated using the TDCP device andmetal leaves to measure contact point tightness andthe space at the contact point of the second premolarand the rst molar. Although the second premolar simul-taneously drifted distally with the rst molar during HG

Fig 3. A, Devices for measuring interproximal spacescomprise 11 metal leaves in different thicknesses from0.1 to 0.6 mm in 0.05-mm increments;B, spacemeasure-ment with a metal leaf (red arrow) at the contact point ofthe second premolar and the rst molar, while the innerarch of the HG at a given force is connected to the rstmolar.

American Journal of Orthodontics and Dentofacial Orthopedtreatment27 by the transseptal bers linkage, its drift isless than that of the rst molar27 because of its transsep-tal ber connection to the rst premolar. Since secondpremolar movement is a by-product of rst molar move-ment and was present in all compared groups, the dis-cussion is interpreted with respect to the reactions ofonly the rst and second molars.

The short-term effect was measured at T0, with no dif-ferences found between groups. As HG force was increasedfrom 0 to 15 N, there were a nonsignicant 13% decreasein TDCP value and a 15% increase in space width in theG1M2.A similar effect but of signicantly greatermagni-tude was found in the GM2, where TDCP decreased by25% and space increased by 31%. These ndings suggestthat the presence of the maxillary second molar has a sig-nicant effect on rst molar distalization and cause rejec-tion of the rst null hypothesis of this study.

In both groups, rst molar initial distalizationoccurred in the PDL space per se, since the gain in spacenever exceeded the maximum PDL space (150-380 mm).28 The displacement of the rst molar in thePDL space resulted at all levels of HG force and all 3time points. These ndings support those by Kinzingeret al,4 who illustrated the role of the PDL in rst molardistalization with a pendulum appliance during differentstages of eruption of the second and third molars. Thatno signicant changes were noted in the TDCP andspace values as the HG load continued to increase atT0 can be explained by the anatomy of the PDL space.Once this space is occluded, no further rst molar move-ment is expected without ensuing structural changes.This is responsible for the previously described lagperiod in orthodontic tooth movement.29-32

In our previous study, we found that after initiationof HG treatment, the maxillary rst molar was distalizedby 0.13 and 0.23 mm for HG treatment per se in G1M2and G M2, respectively, compared with 0.03 and0.05 mm for the combined HG with edgewise appliancesin the present study.5 The same amount of force wasapplied in both studies; however, in the previous studyit was calculated per molar (force changes, 0-7.5 N),and in this study it was calculated for both molars (forcechanges, 0-15 N).

This implies that the initial distalization was 4 and 5times more effective for HG treatment per se than thecombined edgewise and HG regimens. This can be ex-plained by molar distalization associated with distalcrown tip (up to 11.7).10,14 Basically, every initialmovement within the PDL without guiding measures(eg, bracket system) is characterized by an initial sharptipping movement.32 However, this effect can be

reduced by guiding the molar along an archwire15 orby producing a counteracting moment.33 Moreover,


3 6 gear

T1

ent

e secints (

472 Shpack et alfriction developed within the molar tube increases with

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0 3 6 9 12 15 0

P 2-M

1TD

CP (N

)

Head

T0

6 m

onth

s

Treatm600

Fig 4. Change in TDCP at the contact point of th(0-15 N) applied at 6-month intervals at 3 time po(patients without and with second molars).increasing crown tip and archwire size.34 This mightexplain the decrease in the HG effect in our study.Thus, HG treatment combined with a preadjustedbracket systemmight control the bodily distal movementof the rst molar but profoundly reduce the distalizationability.

At T1, both short-term and long-term HG effectswere present. The long-term effect was evident afterthe rst molar accomplished some distal movement dur-ing the rst 6-month period. This was observed by thedecline in TDCP at the HG force of 0 N from T0 to T1(15% and 50% for G 1 M2 and G M2, respectively).Thus, after 6 months of HG treatment, more initial spacewas obtained in G M2, which was measured as a3-fold greater TDCP decline than in G 1 M2. That is,the initial space at the contact point of the second pre-molar and the rst molar signicantly increased after6 months of HG traction from T0 to T1 at no forceload (0 N) by 70.5% in GM2 and by 35.7% in G1M2.

Comparing the long-term effect of HG with xed ap-pliances (present study) vs HG alone (previous study)demonstrated that initial distalizations of 0.2 mm forG M2 and 0.13 mm for G 1 M2 were accomplishedafter 6 months of treatment in the former and 3 monthsin the latter.5 That is, a 2-fold extension in time isneeded for the combined HG and brackets treatmentto accomplish the same initial distalization as with

October 2014 Vol 146 Issue 4 AmericanHG only. Because this study was conducted over a

9 12 15 0 3 6 9 12 15 force (N)

G+M TDCP

G-M TDCP

T2

6 m

onth

s

me (months) 126 12

M

M

ond premolar and the rst molar at 6 HG forcesT0, T1, T2) in the 2 groups, GM2 and G1M23-month period, we cannot compare HG treatment perse with 1 year of treatment of HG with brackets (T2).5

Most likely, in spite of the low force magnitude that lightnickel-titanium archwires exert, the counterclockwisemoment acting by these archwires on the rst molar(counteracting the clockwise moment: ie, distal tip ofthe HG) was effectual in decreasing the initial pace ofdistalization, probably due to the time factor (24-hourarchwire vs 12-hour HG). Additionally, the friction pro-duced by the archwire is not present when HG is used.

At T1, the short-term effect was found to be similarin the 2 groups. The peak change occurred at 3 N of HGinitial force for both TDCP and space. The pattern ofchange in TDCP and space with the increase in HG forcewas the same for both groups; ie, a decrease in TDCPwas highly correlated with an increase in space (R,approximately 0.7). The fact that TDCP values weresignicantly lower and space values higher in G M2in comparison with G 1 M2 is a product of the long-term effect: ie, the already accomplished rst molardistal movement during the 6-month period that ischaracterized by bone remodeling and PDL widening,which was more distinct in G M2.29-31 Although itwas not measured, most likely the distal relocation ofthe rst molar is not a pure translation; in the absenceof the second molar, more tipping of the rst molarwas expected.4


essiv

19

Shpack et al 473Table I. TDCP and space (mm) measurements with progranalysis (Tukey)

Group Time 0 3TDCP G 1 M2 T0 5.66 6 0.18 5.55 6 0.At T2, because the mean dental age of G M2reached that of G1M2 at T1, the presence of the eruptedsecondmolar in GM2was evident by the signicant in-crease in TDCP at 0 N of HG force fromT1 to T2. This pro-duced a resistance to distalization in GM2 as reectedby a sharp reduction in space at GM2at 0N ofHG forcefrom T1 to T2 (61%). The similarity between the 2 groups

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0 3 6 9 12 15 0 3 6

P 2-M

1sp

ace

(mm

)

Head gear

T0 T1

6 m

onth

s

Treatment m600

Fig 5. Change in space at the contact point of the sec(0-15 N) applied at 6-month intervals at 3 time points ((patients without and with second molars).

T1 4.78 6 0.27 3.95 6 0.24T2 4.43 6 0.27 3.76 6 0.25

Tukeysignicance

T0s T1s T2P\0.001

T0s T1s T2P\0.001

G M2 T0 5.47 6 0.35 5.24 6 0.36T1 2.69 6 0.53 1.98 6 0.42T2 5.19 6 0.24 4.01 6 0.21

Tukeysignicance

T0, T2s T1P 5 0.001

T0s T1s T2P 5 0.02

Space (mm) G 1 M2 T0 0.14 6 0.01 0.15 6 0.01T1 0.19 6 0.01 0.24 6 0.01T2 0.23 6 0.01 0.27 6 0.01

Tukeysignicance

T0s T1s T2P\0.001

T0s T1s T2P\0.001

G M2 T0 0.17 6 0.01 0.18 6 0.01T1 0.29 6 0.02 0.35 6 0.00T2 0.13 6 0.01 0.23 6 0.01

Tukeysignicance

T0s T1s T2P 5 0.035

T0s T1s T2P 5 0.017

American Journal of Orthodontics and Dentofacial Orthopede increases in HG force (015 N) at 3 times and post hoc

6 9 12 155.40 6 0.19 5.32 6 0.20 5.20 6 0.20 4.97 6 0.19at T2 (erupted secondmolar) was demonstrated by a par-allelmarkeddecrease in the TDCP reading and an increasein space readings with HG force elevation from 3 to 15 N.Besides the eruption of the second molar in G M2, atT2, this tooth most likely reached the Nolla tooth devel-opment stage of G 1 M2 at T0 (root completed withopen or closed apex). Consequently, it is suggested that

9 12 15 0 3 6 9 12 15force (N)

G+M spaceG-M space

T2

6 m

onth

se (months)

126 12

M M

ond premolar and the rst molar at 6 HG forcesT0, T1, T2) in the 2 groups, GM2 and G1M2

3.72 6 0.25 3.43 6 0.23 3.31 6 0.23 3.17 6 0.223.50 6 0.24 3.24 6 0.23 3.11 6 0.23 2.84 6 0.20

T0s T1s T2P\0.001

T0s T1s T2P\0.001

T0s T1s T2P\0.001

T0s T1s T2P\0.001

4.82 6 0.36 4.36 6 0.34 4.28 6 0.32 4.21 6 0.321.83 6 0.40 1.77 6 0.38 1.67 6 0.37 1.65 6 0.363.66 6 0.18 3.49 6 0.17 3.45 6 0.17 3.03 6 0.17

T0s T1s T2P 5 0.03

T0, T2s T1P 5 0.002

T0, T2s T1P 5 0.001

T0s T1s T2P 5 0.008

0.16 6 0.01 0.16 6 0.01 0.16 6 0.01 0.17 6 0.010.25 6 0.01 0.26 6 0.01 0.26 6 0.01 0.27 6 0.010.30 6 0.01 0.30 6 0.01 0.29 6 0.01 0.30 6 0.01

T0s T1s T2P\0.001

T0s T1s T2P\0.001

T0s T1s T2P\0.001

T0s T1s T2P\0.001

0.20 6 0.02 0.21 6 0.01 0.21 6 0.01 0.22 6 0.010.36 6 0.02 0.36 6 0.02 0.36 6 0.02 0.36 6 0.020.26 6 0.01 0.26 6 0.01 0.26 6 0.01 0.28 6 0.01

T0s T1s T2P 5 0.018

T0, T2s T1P 5 0.001

T0, T2s T1P\0.001

T0s T1s T2P 5 0.03


T1

t m

474 Shpack et al5.00

6.00T0

mon

ths

Treatmen600the enlargement in secondmolar root length contributedto the increase in resistance to distalization. In spite of theincreased resistance to initial distalization of the rstmolar, molar distalization continued but at a slowerpace. This nding corresponds with other studies thatfound on average a decrease in rst molar distalizationby second and third molar buds.2-4,10

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0 3 6 9 12 15 0 3 6 9

P 2-M

1TD

CP (N

)

Head gear

T0 T1

Treatment 600

6 m

onth

s

Fig 7. TDCP vs space at the contact point of the sec(0-15 N) applied in 6-month intervals at 3 time pointssecond molars).

0.00

1.00

2.00

3.00

4.00

0 3 6 9 12 15 0 3 6 9

P 2-M

1TD

CP (N

)

Head gear f

6

Fig 6. TDCP vs space at the contact point of the sec(0-15 N) applied in 6-month intervals at 3 time poinwithout second molars).

October 2014 Vol 146 Issue 4 American0.45

0.50T2

mon

ths

e (months) 126 12However, our study demonstrates that the initial dis-talization potential of the rst molar for G1M2 was thesame at T1 and T2; this is supported by the ndings ofAbed and Brin,35 who reported on the eruption path ofthe second molar during HG treatment, and can beexplained by the same stage of crown development ofthe third molar at this age (13-14 years).36 Therefore,

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

12 15 0 3 6 9 12 15

P 2-M

1sp

ace

(mm

)

force (N)

G+M TDCP

G+M space

T2

6 m

onth

s

me (months) 126 12

M

M

ond premolar and the rst molar at 6 HG forces(T0, T1, T2) in the G 1M2 group (patients with

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

12 15 0 3 6 9 12 15

P 2-M

1sp

ace

(mm

)

orce (N)

G-M TDCP

G-M space

6

M T

M

ond premolar and the rst molar at 6 HG forcests (T0, T1, T2) in the G M2 group (patients


et al. Numerical and clinical study of the biomechanical behaviour

7. Dewel BF. Objectives of mixed dentition treatment in orthodontics.

at 3

30.0.

0.0.

0.0.

Shpack et al 475our study does not support the recommendations ofKinzinger et al4 of prior germectomy of the third molarwhen a simultaneous distalization of the rst and secondmolars is required.

Regarding the effective initial HG force, at T0 (treat-ment initiation), G M2 had nonsignicant changes inthe TDCP and space measurements at 6 to 9 N. InG 1 M2, only a small change was observed for all forcelevels. That is, initial force elevation was effective up to6 N for G M2, whereas for G1M2 the effect was notsignicant. Our T0 data support those of Andreasen andJohnson,18 who reported decreased effectiveness below3 N of HG force.

At T1, the most signicant effect was observed at 3 N,and nonsignicant changes were observed beyond 6 Nfor both groups. Also at T2, the most signicant effectwas observed at 3 N, especially in G M2. The initialHG force load was most effective at 3 N, and only smallchanges were noted with HG forces greater than 6 N.Hence, regarding the effective initial force, there was apositive correlation between the initial HG force andthe initial distalization up to a measured force of 6 to9 N, after which any elevation of the initial force wasnot followed by a signicant increase in distalizationin either group. Most likely, additional factors such asmobility of the rst molar37 and enlargement of thePDL space over time38 affect the magnitude of the effec-tive initial force. This might be the reason that at T1 andT2 the greatest change in initial distalization (space)occurred from 0 to 3 N, whereas 9 N was required atT0 to reach the most efcient force level. This suggeststhat our ndings cause rejection of the second null hy-pothesis.

Table II. Pearson correlations between TDCP and space

Time Pearson correlation and P value 0T0 r 0.216

P 0.109T1 r 0.739

P 0.001T2 r 0.570

P 0.001CONCLUSIONS

1. It is recommended to start HG treatment beforeeruption of the maxillary second molar.

2. Maxillary rst molar distalization can be pursuedeven after eruption of the maxillary second molars.

3. Once the maxillary second molar erupts, maxillaryrst molar distalization continues at a slower pacesimilar to treatment initiated in the presence ofthe maxillary second molar.

American Journal of Orthodontics and Dentofacial OrthopedAm J Orthod 1964;50:504-19.8. Ricketts RM. The inuence of orthodontic treatment on facial

growth and development. Angle Orthod 1960;30:103-33.9. Locatelly R, Bednar J, Dietz V. Molar distalization with superelastic

NiTi wire. J Clin Orthod 1992;16:277-9.10. Bussick TJ, McNamara JA. Dentoalveolar and skeletal changesof teeth under orthodontic loading using a headgear appliance.Med Eng Phys 2009;31:539-46.

6. Kloehn SJ. Guiding alveolar growth and eruption of teeth toreduce treatment time and produce a more balanced dentureand face. Angle Orthod 1947;17:10-33.4. The initial effective HG force level is 3 to 6 N andshould not exceed 9 N.

5. HG per se is 4 times more effective than HG com-bined with an edgewise xed appliance.

ACKNOWLEDGMENTS

We thank Ilana Gelernter from the Department ofStatistics, Tel Aviv University, for her assistance.

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Long- and short-term effects of headgear traction with and without the maxillary second molarsMaterial and methodsStatistical analysis

ResultsDiscussionConclusionsAcknowledgmentsReferences

Documents

Long- And Short-term Effects of Headgear Traction