extraccion de segunda moler meaw

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Abstract The purpose of the present study was to probeinto the effects of maxillary second molar extraction ondentofacial morphology by the use of cephalometric radio-

graphs taken before and after anterior open-bite treatment.The subjects were 30 Japanese patients who had receivedmultiloop edgewise archwire therapy without premolarextraction. They were divided into two groups. Group 1consisted of 15 patients who had their maxillary secondmolars removed. Group 2 comprised 15 patients who hadbeen treated without extraction of maxillary second molars.Lateral cephalograms were taken before and after treat-ment. Seventeen angular and 31 linear measurements wereobtained from the lateral cephalograms. Paired and unpairedttests were used to determine the significance of differencesin measurements. The retrusion and extrusion of the maxil-lary incisors, the distal movement of the maxillary first

molars, and the uprighting of the maxillary first premolarsand the mandibular first molars were greater in group 1than in group 2. Moreover, the maxillary first molarsintruded significantly in group 1 but extruded insignificantlyin group 2. Extraction of maxillary second molars, as wellas nonextraction, can be an effective operating procedurefor open-bite correction of the permanent dentition.

Key words Open bite Maxillary second molar extraction Nonextraction Multiloop edgewise archwire therapy Lateral cephalogram

Introduction

Anterior open-bite is a very common anomaly, yet its treat-ment is most difficult because relapse occurs easily.1,2 High-pull headgears,2,3 high-pull chin caps,3,4 tongue cribs,3,4 molarbite blocks,5 functional orthodontic appliances,6 edgewiseappliances,13 and vertical elastics13 are used in the treat-ment of growing young patients, and edgewise appliancesare almost exclusively employed for adult patients.Edgewise appliances have been also used in surgical orth-odontic treatment for severe skeletal open-bite cases.7Recently, zygomatic implants8 or microscrew implants9have come to be used as anchorage units together withedgewise appliances. Open-bite treatment modalities usingedgewise appliances include premolar extraction2,10,11 or

nonextraction treatment

1,1214

in addition to molar extrac-tion treatment.10,11,1416 Changes in dentofacial morphologycommonly seen in these types of open-bite treatment arereported to be retroclination, retrusion, and extrusion ofmaxillary as well as mandibular incisors, and increasedfacial height due to extrusion of molars.1,1214 Some investi-gators have demonstrated the mesial movement of molarsand a marked retroclination of anterior teeth in premolarextraction treatment,3 while others have reported the distalmovement of premolars and first molars in second molarextraction treatment.15

Among the factors contributing to the incidence of openbite, molar crowding15 and posterior discrepancies16 havebeen suggested. Kim and colleagues3,10 eliminated posteriordiscrepancies by extracting the third or second molar andsucceeded in treating open-bite cases using a multiloopedgewise wire (MEAW) therapy.

As long as X-rays show nothing wrong with coronal mor-phology or the direction of tooth eruption, extraction ofmaxillary and mandibular second molars is performedin the treatment of various forms of malocclusion to elimi-nate posterior discrepancies.1519Moffit18 and Basdra et al.19found that maxillary third molars replaced second molarsquite successfully. Chipman20 stated that there are concernsabout the prognosis of replacement of mandibular second

Odontology (2009) 97:4350 The Society of The Nippon Dental University 2009DOI 10.1007/s10266-008-0093-0

Koji Kojima Toshiya Endo Shohachi Shimooka

Effects of maxillary second molar extraction on dentofacial morphology

before and after anterior open-bite treatment: a cephalometric study

K. Kojima (*) T. EndoOrthodontic Dentistry, The Nippon Dental University NiigataHospital, 1-8 Hamaura-cho, Chuoh-ku, Niigata 951-8580, JapanTel. +81-25-267-1500; Fax +81-25-265-5819e-mail: [email protected]

S. ShimookaDepartment of Pediatric Dentistry, The Nippon Dental UniversitySchool of Life Dentistry at Niigata, Niigata, Japan

Received: July 11, 2008 / Accepted: August 25, 2008

ORIGINAL ARTICLE


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molars by third molars, and for that reason maxillary secondmolars are extracted more frequently than their mandibularcounterparts.

In our previous study, we cephalometrically examinedchanges in dentofacial morphology of patients with anterioropen-bite malocclusion who had undergone MEAWtherapy without extraction of premolars, and consideredthat maxillary second molar extraction would contribute

effectually to open-bite correction because maxillarycanines and premolars were uprighted marvelously com-pared with those in the nonextraction group.14

The purpose of the present study was to probe into theeffects of maxillary second molar extraction on dentofacialmorphology by the use of cephalometric radiographs takenbefore and after anterior open-bite treatment.

Materials and methods

The subjects selected for this study consisted of 30 consecu-tive Japanese patients with anterior open-bite malocclusion

who had received successful orthodontic treatment withoutpremolar extraction at the orthodontics clinic of the NipponDental University Niigata Hospital (Niigata, Japan).

They were selected according to the following criteria:mandibular central incisor edges positioned beneath themaxillary occlusal plane on the lateral cephalometric radio-graphs; full eruption of all the maxillary and mandibularteeth up to the second molars; Angle class I malocclusion;no craniofacial anomalies; no prior orthodontic or pros-thetic treatment; and willingness to participate in ourstudy.

The subjects were divided into two groups. The meanages of the two groups at pretreatment (T1) and posttreat-

ment (T2) and the mean length of time required for treat-ment (T2 T1) are shown in Table 1. Group 1 consisted of15 individuals (three male and 15 female patients) who hadtheir maxillary left and right second molars removed. Sincepretreatment lateral cephalometric radiographs did notreveal any sex difference in craniofacial morphology, datafor male and female patients were combined. They all hadmaxillary third molars on both sides. There was nothinganomalous about the coronal morphology or eruptiondirection of the third molars. After active treatment, all ofthe maxillary third molars erupted in the very place that thesecond molars should have occupied, and came into contactwith the distal proximal surface of the maxillary first molars.

In 14 of the 15 subjects, mandibular third molars on both

sides were observed, and in the remaining subject, a man-dibular right third molar was observed. All of the mandibu-lar third molars were extracted before or during the activetreatment.

Group 2 comprised 15 female subjects who had beentreated without extraction of maxillary second molars. Ineight of the 15 subjects, there were no maxillary or man-dibular third molars on either side. In three others, four

third molars were observed in the maxillary or mandibulararch; in an additional two subjects, mandibular third molars;in another, a maxillary right third molar; and in the oneremaining subject, a mandibular left third molar. All ofthese third molars were removed before or during the activetreatment.

Treatment methods

Standard edgewise appliances (0.018 0.025 inches;0.4572 0.635 mm) were used in the treatment with MEAWtherapy. For leveling and alignment, 0.016-inch (0.4064 mm)

nickel-titanium wires were used first, and then 0.016 0.016inch nickel-titanium wires. To close the open bite andachieve a correct occlusion, maxillary and mandibularmultiloop stainless steel archwires (0.016 0.022 inches;0.4064 0.5588 mm) with anterior vertical elastics wereused. After active orthodontic treatment, Hawley retainerswere used in the maxillary and mandibular arches.

Cephalometric analysis

Lateral cephalometric radiographs of each subject weretaken at the T1 and T2 stages using the same cephalostat at

a standard setting. Cephalometric tracings were drawn onmatte acetate paper, and linear and angular measurementswere made by one researcher (K.K.). The measurementswere recorded to the nearest 0.1 mm and 0.5.

For each tracing, 20 reference points were marked,and 17 angular and 31 linear measurements were madewith a protractor and a vernier micrometer (Fig. 1,Table2). Seventeen linear measurements (for example, U1e-xand U1e-y for distances from the maxillary incisor edgeto the x-axis and the y-axis, respectively) were made usinga coordinate system with the x-axis parallel to theFrankfort horizontal plane and the y-axis perpendicular tothe Frankfort horizontal plane through the sella turcica

(Fig. 1, Table 2).

Table 1. Mean ages of the two groups at pretreatment and posttreatment and the mean durationof treatment

Age (years)

Treatment timePretreatment (T1) Posttreatment (T2)

Mean SD Mean SD Mean SD

Group 1 15.3 2.8 17.3 2.4 2.0 0.8Group 2 20.4 6.5 22.0 6.5 1.7 1.0


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y-axis

x-axis

SN

PP

RP

MPY-axis

OP

FHOr

Po

S

N

ANS

PNS

Ptm

A

Go

MeGnPog

B

L1e

U1eL6

U6

U1

L1

Ar

U6

L6L4

U4

U4

L4

Fig. 1. Reference points and lines used for lateral cephalometric analy-sis. N, nasion; S, sella turcia; Or, orbitale; Po, porion; Ar, articulare;ANS, anterior nasal spine; PNS, posterior nasal spine; Ptm, pterygo-

maxillary fissure; A, point A; U1e, maxillary incisor edge; L1e, man-dibular incisor edge; B, point B; Pog, pogonion; Gn, gnathion; Me,menton; Go, gonion; U4, the tips of the maxillary first premolar buccalcusp; L4, the tip of the maxillary first premolar buccal cusp; U6, themost superior point on the maxillary first molar buccal groove; L6, themost superior point on the mandibular first molar buccal groove; SN,sella turcica-nasion plane; FH, Frankfort plane; PP, palatal plane; OP,occlusal plane; MP, mandibular plane; RP, ramus plane; Y-axis, sellaturcica-gnathion line; U1, long axis of maxillary central incisor; L1,long axis of mandibular central incisor; U4, long axis of maxillary firstpremolar; L4, long axis of mandibular first premolar; U6, long axis ofmaxillary first molar; L6, long axis of mandibular first molar; x-axis, aline parallel to the Frankfort horizontal plane through the sella turcica;y-axis, a line perpendicular to the Frankfort horizontal plane throughthe sella turcica

Statistical analysis

Analyses were carried out with the StatMate III statisticalprogram (ATMS, Tokyo, Japan). Paired t tests were usedto determine the significance of differences in measure-ments in each group made from T1 and T2 cephalometricradiographs. Unpaired t tests were used to test the signifi-cance of differences in measurements between groups 1 and2 before treatment and the significance of differences inchanges in measurements from T1 to T2 between the twogroups.

Method error

For evaluation of errors in tracing, landmark identification,and measurements, 20 randomly selected cephalometricradiographs were retraced and measured again by the sameresearcher 1 month later. Students t test with a 95% confi-dence interval did not find any systematic errors. Methoderrors, calculated according to Dahlbergs formula,21 did notexceed 0.4 or 0.3 mm, which were acceptable in thisstudy.1,2,12,14

Results

Unpaired t tests showed that the mean pretreatment agediffered significantly between groups 1 and 2 (P< 0.01), butno significant differences in the mean length of time requiredfor treatment were noted between two groups. The mea-surements from lateral cephalometric radiographs and theresults of statistical analyses are shown in Tables 3 and 4.Between groups 1 and 2, significant differences were notedonly in prognathism of the maxillary alveolar bone (SNA),ramus height (Go-Ar), maxillary molar inclination (U6-PP), and lower posterior facial height (Ar-Go) at the pre-treatment stage (Table 3: S1). Since significant differenceswere noted in no more than four items out of a total of 48measurement items, we thought it worthwhile compare thetwo groups (Table 3: S1).

Cranial base measurements

None of the cranial base measurements showed any signi-ficant changes in either group 1 or group 2 (Tables 3 and4: S2) or between the two groups (Table 3: S3) from T1to T2.

Maxillary and mandibular measurements

No significant changes in measurements from T1 to T2 wereobserved in group 1 (Table 3: S2). In contrast, a significantincrease in measurements for facial convexity (ANB) wasnoted in group 2 (Table 4; S2). None of the measurementitems showed any significant difference in values from T1

to T2 in either group 1 or group 2 (Table 3: S3).

Dentoalveolar measurements

In groups 1 and 2, the posttreatment measurements revealedthat the distance from the maxillary incisor edge to thex-axis (U1e-x), from U4 to the palatal plane (U4-PP), fromthe mandibular incisor edge to the mandibular plane (L1e-MP), from L4 to the mandibular plane (L4-MP), and fromL6 to the mandibular plane (L6-MP) and overbite and theinterincisal angle (U1-L1) increased significantly, while themaxillary incisor inclination (U1-SN), maxillary first pre-molar inclination (U4-PP), mandibular incisor inclination(L1-MP), mandibular first premolar inclination (L4-MP),maxillary molar inclination (U6-PP) ,and mandibular molarinclination (L6-MP) decreased significantly (Tables 3 and4: S2). These results indicate the occurrence of extrusionand retroclination of maxillary and mandibular central inci-sors, extrusion and uprighting of maxillary and mandibularfirst premolars and first molars, and uprighting of maxillaryfirst molars. In group 1, moreover, the distance from themaxillary incisor edge to the y-axis (U1e-y), the distancefrom U6 to the y-axis (U6-y), and the distance from U6 tothe palatal plane (U6-PP) decreased significantly, indicating


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Table 2. Definitions of reference points and lines

Measurement Definition

Cranial base measurementsS-N (mm) Anterior cranial base lengthS-Ar (mm) Overall cranial base lengthN-Ar (mm) Posterior cranial base lengthN-S-Ar () Cranial base angle

Maxillary and mandibular measurements

ANS-PNS (mm) Maxillary lengthA-y (mm) Distance from point A to they-axisPtm-y (mm) Distance from pterygomaxillary fissure to they-axisS-N-A () Prognathism of maxillary alveolar bonePP-SN () S-N to palatal plane angleMe-Go (mm) Mandibular body lengthGo-Ar (mm) Ramus heightAr-Me (mm) Maximum mandibular lengthB-y (mm) Distance from point B to they-axisS-N-B () Prognathism of mandibular alveolar boneMP-SN () Mandibular plane angleY axis-SN () Y-axis inclination relative to S-N planeRP-SN () Ramus inclinationMP-RP () Gonial angleA-N-B () Facial convexity

Dentoalveolar measurements

U1e-x (mm) Distance from maxillary incisor edge to thex-axisU1e-y (mm) Distance from maxillary incisor edge to they-axisU1-SN () Maxillary incisor inclinationL1e-x (mm) Distance from mandibular incisor edge to thex-axisL1e-y (mm) Distance from mandibular incisor edge to they-axisL1-MP () Mandibular incisor inclinationL1e-MP (mm) Distance from mandibular incisor edge to mandibular planeOverjet (mm) OverjetOverbite (mm) OverbiteU4-PP (mm) Distance from U4 to palatal planeU4-PP () Maxillary first premolar inclinationL4-MP (mm) Distance from L4 to mandibular planeL4-MP () Mandibular first premolar inclinationU6-x (mm) Distance from U6 to the x-axisU6-y (mm) Distance from U6 to the y-axisU6-PP () Maxillary first molar inclination

U6-PP (mm) Distance from U6 to palatal planeL6-x (mm) Distance from L6 to the x-axisL6-y (mm) Distance from L6 to the y-axisL6-MP () Mandibular molar inclinationL6-MP (mm) Distance from L6 to mandibular planeU1-L1 () Interincisal angleOP-SN () Occlusal plane inclination

Vertical measurementsN-Me (mm) Total anterior facial heightANS-N (mm) Upper anterior facial heightANS-Me (mm) Lower anterior facial heightS-Go (mm) Total posterior facial heightS-Ar (mm) Upper posterior facial heightAr-Go (mm) Lower posterior facial height

that in group 1 retrusion of the maxillary central incisorsand intrusion and distal movement of the maxillary firstmolars were evident. In both groups, as a result of the extru-sion of the maxillary and mandibular first premolars, theocclusal vertical dimension in the first premolar regionsincreased. In group 1, the extrusion of the mandibular firstmolars exceeded the intrusion of the maxillary first molarswith the result that the occlusal vertical dimension in thefirst molar regions increased. In group 2, the extrusion ofthe maxillary and mandibular first molars increased thevertical dimension of occlusion in the first molar regions.

The U1e-x, U6-y, and U6-PP distances, and the U4-PPand L6-MP angles, showed significant differences in theamount of change from T1 to T2 between the two groups(Table 3: S3).

Vertical measurements

Significant increases were noted in total anterior facialheight (N-Me) and lower anterior facial height (ANS-Me)from T1 to T2 in both groups (Tables 3 and 4: S2). In terms


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Table 3. Lateral cephalometric analysis in group 1

Pretreatment (T1) S1 Posttreatment (T2) S2 Treatment change S3


Cranial base measurementsS-N (mm) 68.3 2.5 NS 68.4 2.5 NS 0.1 1.0 NSS-Ar (mm) 36.2 2.1 NS 36.6 2.5 NS 0.4 1.7 NSN-Ar (mm) 93.9 2.8 NS 94.2 4.0 NS 0.3 2.3 NSN-S-Ar () 125.2 4.0 NS 124.0 4.6 NS 1.2 3.1 NS

Maxillary and mandibular measurementsANS-PNS (mm) 48.8 3.5 NS 48.8 3.4 NS 0.0 1.0 NSA-y (mm) 64.2 3.1 NS 64.3 3.8 NS 0.1 1.6 NSPtm-y (mm) 17.8 2.8 NS 17.3 2.9 NS 0.5 1.3 NSS-N-A () 78.6 2.8 * 79.0 2.7 NS 0.3 1.3 NSPP-SN () 8.7 4.0 NS 8.4 3.8 NS 0.3 2.1 NSMe-Go (mm) 71.5 4.6 NS 72.4 4.1 NS 0.8 1.5 NSGo-Ar (mm) 45.3 4.0 * 46.5 3.9 NS 1.2 3.4 NSAr-Me (mm) 107.5 4.8 NS 108.7 6.1 NS 1.2 3.3 NSB-y (mm) 58.2 5.6 NS 57.2 6.2 NS 1.0 2.6 NSS-N-B () 76.7 2.8 NS 76.7 3.5 NS 0.1 1.3 NSMP-SN () 41.0 4.2 NS 41.4 4.4 NS 0.4 2.6 NSY axis-SN () 73.7 3.0 NS 72.1 8.9 NS 1.6 8.5 NSRP-SN () 91.8 4.9 NS 92.8 7.0 NS 1.0 5.3 NSMP-RP () 129.0 6.0 NS 128.2 5.4 NS 0.8 2.3 NS

A-N-B () 1.9 3.5 NS 2.3 3.7 NS 0.4 1.3 NSDentoalveolar measurementsU1e-x (mm) 76.4 3.3 NS 79.4 2.9 *** 3.0 2.0 *U1e-y (mm) 72.0 4.5 NS 70.0 4.3 * 1.9 2.8 NSU1-SN () 111.1 6.6 NS 102.7 9.5 ** 8.5 9.3 NSL1e-x (mm) 77.3 3.3 NS 78.1 2.9 NS 0.8 2.8 NSL1e-y (mm) 68.5 4.7 NS 67.7 4.2 NS 0.8 2.1 NSL1-MP () 94.6 8.3 NS 90.7 8.2 * 3.9 5.8 NSL1e-MP (mm) 44.5 2.4 NS 46.7 3.2 *** 2.3 1.7 NSoverjet (mm) 3.5 3.2 NS 2.3 0.5 NS 1.1 3.0 NSoverbite (mm) 0.9 1.6 NS 1.3 0.9 *** 2.2 1.5 NSU4-PP (mm) 26.2 1.4 NS 27.8 1.8 ** 1.6 1.6 NSU4-PP () 98.6 8.5 NS 83.2 6.3 *** 13.4 7.6 *L4-MP (mm) 39.2 2.0 NS 41.7 2.7 ** 2.5 2.4 NSL4-MP () 84.0 7.5 NS 76.4 5.5 ** 6.6 7.1 NSU6-x (mm) 68.3 2.8 NS 69.4 3.0 NS 1.1 2.3 NS

U6-y (mm) 36.4 4.5 NS 34.3 3.9 ** 2.1 2.3 *U6-PP () 77.5 5.3 ** 73.6 5.2 * 3.9 5.2 NSU6-PP (mm) 21.6 1.3 NS 21.1 1.4 * 0.5 0.9 **L6-x (mm) 71.9 3.2 NS 73.1 4.3 NS 1.3 2.7 NSL6-y (mm) 39.1 4.6 NS 37.7 4.0 NS 1.4 2.8 NSL6-MP () 86.4 5.1 NS 79.0 6.5 *** 7.4 6.2 *L6-MP (mm) 33.1 2.9 NS 34.2 3.0 ** 1.2 1.1 NSU1-L1 () 113.4 9.4 NS 124.1 6.9 *** 10.7 8.0 NSOP-SN () 20.0 4.2 NS 20.3 5.0 NS 0.4 4.1 NS

Vertical measurementsN-Me (mm) 126.6 4.6 NS 129.3 6.2 * 2.7 4.0 NSANS-N (mm) 56.4 2.7 NS 57.2 3.3 NS 0.9 1.6 NSANS-Me (mm) 70.3 2.8 NS 72.0 4.3 * 1.7 2.8 NSS-Go (mm) 77.8 4.0 NS 78.5 5.1 NS 0.8 4.4 NSS-Ar (mm) 32.9 4.1 NS 32.5 2.3 NS 0.4 3.5 NSAr-Go (mm) 44.9 4.4 * 46.0 4.4 NS 1.2 4.5 NS

***P< 0.001; **P< 0.01; *P< 0.05; NS not significantS1, statistical comparison between groups 1 and 2 at T1; S2, statistical comparison between T1 and T2; S3, statistical comparison of treatmentchanges between groups 1 and 2


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Table 4. Lateral cephalometric analysis in group 2

Pretreatment (T1) Posttreatment (T2) S2 Treatment change


Cranial base measurementsS-N (mm) 67.9 3.4 68.2 3.5 NS 0.3 0.6S-Ar (mm) 36.4 3.4 36.0 3.0 NS 0.4 1.0N-Ar (mm) 93.7 5.0 93.6 4.9 NS 0.0 1.4N-S-Ar () 125.4 3.8 125.2 4.0 NS 0.2 2.3

Maxillary and mandibular measurementsANS-PNS (mm) 51.0 3.2 52.0 2.6 NS 1.1 2.3A-y (mm) 65.9 4.4 66.9 4.6 NS 1.0 2.3Ptm-y (mm) 18.2 2.3 18.1 2.2 NS 0.0 0.7S-N-A () 81.7 3.4 81.9 3.3 NS 0.2 1.9PP-SN () 10.5 2.4 10.2 3.1 NS 0.2 1.9Me-Go (mm) 73.2 5.2 73.5 5.3 NS 0.3 2.5Go-Ar (mm) 49.0 5.3 49.8 4.9 NS 0.7 2.0Ar-Me (mm) 110.6 7.0 111.0 7.0 NS 0.4 2.0B-y (mm) 59.4 8.3 58.9 7.9 NS 0.5 3.7S-N-B () 78.6 4.0 77.9 3.8 NS 0.7 1.5MP-SN () 38.2 5.0 39.0 5.5 NS 0.8 3.1Y axis-SN () 73.0 4.7 73.1 4.3 NS 0.2 2.2RP-SN () 93.6 7.5 94.4 6.3 NS 0.8 3.8MP-RP () 125.3 7.2 123.9 8.3 NS 1.4 3.0

A-N-B () 3.1 3.2 4.0 2.8 ** 0.9 1.0Dentoalveolar measurementsU1e-x (mm) 79.1 5.6 80.3 6.3 * 1.2 2.2U1e-y (mm) 73.7 5.8 72.2 5.2 NS 1.6 3.4U1-SN () 108.4 9.1 100.9 8.0 ** 7.5 7.3L1e-x (mm) 79.9 6.3 79.4 6.6 NS 0.5 2.8L1e-y (mm) 70.1 6.8 69.7 5.0 NS 0.3 3.6L1-MP () 96.1 7.7 92.4 9.1 ** 3.7 4.0L1e-MP (mm) 44.6 3.4 46.1 3.6 *** 1.4 1.0overjet (mm) 3.7 3.2 2.5 0.8 NS 1.2 3.2overbite (mm) 0.8 1.7 0.9 0.9 ** 1.7 1.8U4-PP (mm) 27.1 2.1 28.1 2.0 ** 1.0 1.0U4-PP () 95.1 5.5 87.2 5.3 *** 6.8 5.6L4-MP (mm) 40.1 3.4 41.7 2.8 ** 1.7 1.7L4-MP () 83.9 6.9 77.8 6.4 *** 5.3 4.7U6-x (mm) 70.4 4.8 71.2 5.5 NS 0.7 2.0

U6-y (mm) 36.9 6.0 36.6 5.3 NS 0.3 2.5U6-PP () 82.8 4.4 80.7 4.7 * 2.0 3.3U6-PP (mm) 22.8 2.2 23.4 2.3 NS 0.6 1.1L6-x (mm) 73.6 5.0 73.7 5.3 NS 0.1 1.8L6-y (mm) 40.1 6.1 39.8 5.5 NS 0.2 2.9L6-MP () 84.1 5.4 81.0 6.5 * 3.0 4.8L6-MP (mm) 34.3 4.1 35.0 4.3 * 0.7 1.3U1-L1 () 115.1 10.0 126.0 8.9 *** 10.9 7.3OP-SN () 20.3 3.7 20.9 5.1 NS 0.6 4.6

Vertical measurementsN-Me (mm) 128.3 6.9 129.7 7.6 * 1.4 1.9ANS-N (mm) 57.5 2.0 57.8 2.1 NS 0.3 0.9ANS-Me (mm) 70.8 6.0 71.9 6.9 * 1.1 1.9S-Go (mm) 80.8 6.7 81.4 6.4 NS 0.6 2.5S-Ar (mm) 31.7 3.6 32.1 2.8 NS 0.3 1.6Ar-Go (mm) 49.1 5.2 49.4 5.1 NS 0.3 2.8

***P< 0.001; **P< 0.01; *P< 0.05; NS not significantS2, statistical comparison between T1 and T2


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of the amount of change, none of the measurement itemsshowed significant differences between the two groups(Table 3: S3).

Discussion

The results of our study did not show any significant changein cranial base measurements or maxillary and mandibularmeasurements during active orthodontic treatment in eithergroup, except for the ANB angle in group 2. These findingsare in agreement with those of studies on anterior open-bitetreatment in the permanent dentition.1,2,10,12,14 Our findingsalso indicated that facial growth and development had beenalmost completed in all subjects, which led us to believe thatthe difference in the mean age between the two groups atT1 had not affected the treatment outcome despite the factthat the mean age difference was statistically significant. Ingroup 2, the ANB angle increased significantly. Conceiv-ably, this might have resulted from downward rotation of

the mandible due to the statistically significant extrusion ofthe maxillary and mandibular first premolars and the man-dibular first molars and the extrusion of the maxillary firstmolars, since facial growth had ceased. This conjectureis based on the observations made by Isaacson et al.22 thatthe mandible rotates backward if the sum of the verticalincreases at the facial sutures and the alveolar processexceeds the vertical increases at the mandibular condyle.We inferred that the significantly increased ANB angleswere reflected in the reduced prognathism of the mandibu-lar alveolar bone (SNB) after treatment in our study,although there was no significant difference in the amountof reduction.

Many other studies of cephalometric changes with ante-rior open-bite treatment in the permanent dentition haveyielded such findings as extrusion1,2,1214 and retroclina-tion1,2,11,12,14 ofthe maxillary central incisors, extrusion14 anduprighting13,14 of the maxillary premolars, uprighting of themaxillary first molar,10,13,14 extrusion1,2,1014 and retroclina-tion1012,14 of the mandibular central incisors, extrusion12,14and uprighting13,14 of the mandibular first premolars, andextrusion1,12,14 and uprighting1,12,14 of the mandibular firstmolars. In the present study, both groups also exhibitedthese changes significantly.

In our study, the most interesting findings were obtainedafter the active orthodontic treatment. To be specific, retru-sion and extrusion of the maxillary incisors, distal move-ment of the maxillary first molars, uprighting of the maxillaryfirst premolars and the mandibular first molars were greaterin group 1 than in group 2. Moreover, the maxillary firstmolars intruded significantly in group 1 but extruded insig-nificantly in group 2. We presumed that the extraction ofthe maxillary second molars in group 1 must have elimi-nated the posterior discrepancies effectively, and that theMEAW therapy must have forced the maxillary first molarsto move distally and the maxillary first premolar to tip dis-tally. As a consequence, the area of intercuspal contactbetween the maxillary and mandibular first molars must

have decreased, thus giving rise to the distal tipping of themandibular first molars being greater in group 1 than ingroup 2.

The distal movement of the maxillary first molars ingroup 1 must have hastened the extrusion of the maxillarycentral incisors. Richardson and Richardson15 reported thatin anterior open-bite treatment, extraction of maxillary andmandibular second molars permits overbites to progress as

compared with nonextraction. This observation ties in withour findings that the maxillary central incisors extrudedsignificantly and that overbites became deeper, though notsignificantly, in group 1 than in group 2.

The report by Waters and Harris17 that the extraction ofmaxillary second molars without a headgear causes the firstmolars to effectively move in the distal direction also sup-ports our finding about group 1.

The results of the present study that the ANS-Medistance increased in groups 1 and 2 alike tallies with thefindings of many preceding studies on anterior open-bitetreatment in the permanent dentition,1,2,12 but conflicts withthe observations by Kim et al.10 that anterior facial height

remain unchanged with MEAW therapy. This is probablybecause Kim et al.10 did not refer to the mesiodistal inter-maxillary relations in the cases used for their study nor dis-tinguish extractions from nonextractions of premolars andmolars. Our findings indicated that by MEAW therapy thelower facial height increased with increases in occlusal verti-cal dimensions in the areas of the maxillary and mandibularfirst premolars and molars, resulting in backward and down-ward rotations of the mandible. These findings are in agree-ment with the statement by Isaacson et al.22 to the effectthat if the mandible rotates backward, the lower facialheight will increase.

Extraction of maxillary second molars, as well as non-

extraction, can thus be chosen as an effective operating pro-cedure for open-bite correction in the permanent dentition.The present study dealt only with dentofacial morphologicalchanges based on measurements taken from cephalometricradiographs before and after active orthodontic treatment.Additional studies should be done regarding the stability ofMEAW therapy during and after the retention period.Further research into this theme will enable us to gain a newinsight into the important factors responsible for the relapseof malocclusion after correction.

References

1. Janson G, Valarelli FP, Henriques JFC, de Freitas MR, CancadoRH. Stability of anterior open bite nonextraction treatment in thepermanent dentition. Am J Orthod Dentofacial Orthop 2003;124:26576.

2. de Freitas MR, Beltrao RT, Janson G, Henriques JF, Cancado RH.Long-term stability of anterior open bite extraction treatment inthe permanent dentition. Am J Orthod Dentofacial Orthop 2004;125:7887.

3. Kim YH. Anterior openbite and its treatment with multiloop edge-wise archwire. Angle Orthod 1987;57:290321.

4. Pedrin F, Almeida MR, Almeida RR, Almeida-Pedrin RR,Torres F. A prospective study of the treatment effects of a remov-able appliance with palatal crib combined with high-pull chincup


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therapy in anterior open-bite patients. Am J Orthod DentofacialOrthop 2006;129:41823.

5. Dellinger EL. A clinical assessment of the active vertical corrector.A nonsurgical alternative for skeletal open bite treatment. Am JOrthod 1986;89:42836.

6. McNamara JA Jr, Brudon WL. Orthodontic and orthopedic treat-ment in the mixed dentition. Ann Arbor, MI: Needham; 1995.

7. Frost DE, Fonseca RJ, Turvey TA, Hall DJ. Cephalometric diag-nosis and surgical-orthodontic correction of apertognathia. Am JOrthod 1980;78:65769.

8. Erverdi N, Usunmez S, Solak A. New generation open-bite treat-ment with zygomatic anchorage. Angle Orthod 2006;76:51926.9. Kuroda S, Sugawara Y, Tamamura N, Yamamoto T. Anterior

open bite with temporomandibular disorder treated with titaniumscrew anchorage evaluation of morphological and functionalimprovement. Am J Orthod Dentofacial Orthop 2007;131:55060.

10. Kim YH, Han UK, Lim DD, Serraon ML. Stability of anterioropenbite correction with multiloop edgewise archwire therapy: acephalometric follow-up study. Am J Orthod Dentofacial Orthop2000;118:4354.

11. Katsaros C, Berg R. Anterior open bite malocclusion: a follow-upstudy of orthodontic treatment effects. Eur J Orthod 1993;15:27380.

12. Kucukkeles N, Acar A, Demirkaya AA, Evrenol B, Enacar A.Cephalometric evaluation of open bite treatment with NiTi arch

wires and anterior elastics. Am J Orthod Dentofacial Orthop1999;116:55562.

13. Chang YI, Moon SC. Cephalometric evaluation of the anterioropen bite treatment. Am J Orthod Dentofacial Orthop 1999;115:2938.

14. Endo T, Kojima K, Kobayashi Y, Shimooka S. Cephalometricevaluation of anterior open-bite nonextraction treatment, usingmultiloop edgewise archwire therapy. Odontology 2006;94:518.

15. Richardson ME, Richardson A. Lower third molar developmentsubsequent to second molar extraction. Am J Orthod DentofacialOrthop 1993;104:56674.

16. Sato S. Case report: developmental characterization of skeletalclass III malocclusion. Angle Orthod 1994;64:10511.17. Waters D, Harris EF. Cephalometric comparison of maxillary

second molar extraction and nonextraction treatments in patientswith Class II malocclusions. Am J Orthod Dentofacial Orthop2001;120:60813.

18. Moffit AH. Eruption and function of maxillary third molars afterextraction of second molars. Angle Orthod 1998;68:14752.

19. Basdra EK, Stellzig A, Komposch G. Extraction of maxillarysecond molars in the treatment of Class II malocclusion. AngleOrthod 1996;66:28792.

20. Chipman MB. Second and third molars: their role in orthodontictherapy. Am J Orthod 1961;47:498520.

21. Dahlberg G. Statistical methods for medical and biologicalstudents. London: George Allen and Unwin; 1940. p. 12232.

22. Isaacson JR, Isaacson RJ, Speidel TM, Worms FW. Extreme varia-

tion in vertical facial growth and associated variation in skeletaland dental relations. Angle Orthod 1971;41:21929.


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