Treatment Effects of Microimplant-Aided Sliding

ORIGINAL ARTICLE

Treatment effects of microimplant-aided slidingmechanics on distal retraction of posterior teeth

Young-Hee Oh,a Hyo-Sang Park,b and Tae-Geon Kwonc

Daegu, Korea

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470

Introduction:Our objective was to quantify the treatment effects of microimplant-aidedmechanics on group distalretraction of the posterior teeth. Methods: The pretreatment and posttreatment cephalometric radiographs anddental casts of 23 patients (mean age, 22.16 5.17 years), treated with distalization of the posterior teeth againstmicroimplant anchorage and without extraction of the premolars or other teeth except the third molars, were used.The soft-tissue, skeletal, and dental measurements in the vertical and anteroposterior dimensions were analyzed.The changes in interpremolar and intermolar widths and rotations of the molars were analyzed with dental casts.Results: The upper and lower lips were repositioned distally. The Frankfort horizontal to mandibular plane anglewas decreased in the adult group. Themaxillary posterior teethwere distalized by 1.4 to 2.0mmwith approximately3.5� of distal tipping, and the mandibular posterior teeth were also distalized by 1.6 to 2.5 mm with approximately6.6� to 8.3� of distal tipping. The maxillary posterior teeth showed intrusion by 1 mm. There were increases in archwidths at the premolars andmolars. The overall success of microimplants was 89.7%; a well-experienced clinicianhad a higher success rate (98%) than did novices in this sample. The mean treatment time was 206 4.9 months.Conclusions:With microimplant-aided sliding mechanics, clinicians can distalize all posterior teeth together withless distal tipping. The technique seems effective and efficient to treat patients who have mild arch lengthdiscrepancy without extractions. (Am J Orthod Dentofacial Orthop 2011;139:470-81)

There have been many attempts to distalize molarswith intraoral distalizing appliances.1-5 The sideeffects of these appliances are anchorage loss at

the reactive part, flaring of the incisors, distal tipping,and rotation of the distalized molars.

To reduce these consequences, dental implants,6

miniscrews,7-9 and microscrews10,11 were tried. All ofthese skeletal devices can provide suitable anchorage.Miniscrews and microimplants, which have manyadvantages such as easy surgical placement andremoval, low costs, and a small enough size to be placedinto the interradicular bone between the roots ofadjacent teeth, have achieved popularity over otherskeletal anchorage devices. Dental implants6 andminiscrew implants7,8 are placed in the anterior or

the School of Dentistry, Kyungpook National University, Daegu, Korea.arch fellow, Department of Orthodontics.ssor and clinical director, Department of Orthodontics.ciate professor, Department of Oral and Maxillofacial Surgery.rted by the Korea Science and Engineering Foundation grant funded byorea government (R13-2008-009-01003-0).uthors report no commercial, proprietary, or financial interest in the prod-r companies described in this article.t requests to: Hyo-Sang Park, Department of Orthodontics, School of Den-Kyungpook National University, 188-2, Samduk 2-Ga, Jung-Gu, Daegu,700-412; e-mail, [email protected], February 2009; revised and accepted, May 2009.5406/$36.00ight � 2011 by the American Association of Orthodontists..1016/j.ajodo.2009.05.037

midpalate and connected to the premolars for applyingdistal force to the molars. Alternatively, the distalizingforce is applied to the molars from skeletal anchoragedevices. With skeletal anchorage, the side effects on thereactive part were alleviated, but distal tipping androtation of distalizing molars are still issues.7,8 The 1-by-1 tooth movement is effective, but it tends to produceside effects of rotation and tipping movement when theforce does not pass the center of resistance of a tooth.

Group distal retraction of the whole dentition withmicroimplants was introduced and showed severalgood treatment results.12,13 The distal force wasapplied to the canines or anterior hooks attached onthe main archwire from microimplants placed betweenthe roots of the posterior teeth. By moving teethtogether, individual tooth movements, rotation, andtipping were prevented.

Several clinical case reports showed the efficacy ofmicroimplants and the efficiency of the treatment me-chanics in distalization of the whole dentition.12,13

However, only 1 pilot study evaluated the treatmenteffects of these mechanics with cephalometricanalysis.14 Therefore, the purpose of this study was toquantify the treatment effects of en-masse retractionof the posterior teeth againstmicroimplants by analyzingcephalometric radiographs and dental casts, and withclinical examinations.

mailto:[email protected]

Oh, Park, and Kwon 471

MATERIAL AND METHODS

The cephalometric radiographs and dental casts of 23patients who had been treated with 0.022-in straight-wire brackets at the orthodontic department ofKyungpook National University Hospital in Korea werecollected. Consecutively treated patients who receivedthe microimplants for distal movement of the posteriorteeth without extraction of the premolars or other teethexcept the third molars and had a complete set of recordswere selected. The first step of treatment planning for allpatients was setting the goal for the soft-tissue profile.The position of the anterior teeth was determinedaccording to the ratio of soft-tissue change to theamount of anterior teeth retraction. After transferringthe anteroposterior position of the anterior teeth to theocclusogram, all teeth were aligned from anterior to pos-terior. All patients required distal movement of the poste-rior teeth. The maxillary and mandibular posterior teethwith or without the anterior teeth were distalized to re-solve crowding or improve the facial profile. The microim-plants were placed between the roots of the posteriorteeth. Microimplants were used for distalization of themaxillary or mandibular dentitions. Eighteen of the 23patients had microimplants in both jaws. One patienthad microimplants only in the maxilla, and 4 patientshad microimplants only in the mandible. All patientswere between the ages of 12 years 9 months and 31 years7 months (mean, 22.16 5.17 years). The descriptive dataof the patients are given in Table I. Most patients hada moderate amount of arch length discrepancy, except2 patients with anterior spacing and 2 with no arch lengthdiscrepancy. Four patients also required distal movementof the posterior teeth to improve their facial profile. Allpatients had erupted second molars in both arches atthe beginning of treatment.

We used 70 microimplants (Absoancho, Dentos,Daegu, Korea) and 12 surgical microscrews (Osteomed,Dallas, Tex). In the maxilla, 32 microimplants wereplaced in the buccal alveolar bone between the secondpremolars and the first molars. Six microimplants wereplaced in the palatal slope between the first and secondmolars in 3 patients who were treated with lingualbrackets. In the mandible, 14 microimplants were placedinto the bone distobuccally to the mandibular secondmolars, 26 into the alveolar bone between the mandib-ular first and second molars, and 4 into the alveolar bonebetween the mandibular second premolar and the firstmolar. Detailed surgical procedures have already beendiscussed.15

We used 0.022-in slot straight-wire brackets in allpatients, and distalizing forces of approximately 200 gwere applied from the maxillary and mandibularmicroimplants to the canines or premolars with nickel-

American Journal of Orthodontics and Dentofacial Orthoped

titanium closing-coil springs or elastomeric threads(Super thread, Rocky Mountain Orthodontics, Denver,Colo) in the maxillary and mandibular arches (Fig 1).After making space mesial to the canines by distalizingthe buccal teeth, the anterior teeth were aligned. Duringthe initial alignment, the anterior teeth were ligatedloosely to prevent forward movement. The archwiresused during distalization were initially rectangularbeta-titanium alloy and were switched to 0.016 30.022-in stainless steel in the maxilla and 0.017 30.025-in stainless steel in the mandible. After anteriorteeth alignment, the 6 anterior teeth were tied together,and the distalizing force was applied to the canines or tothe short anterior hooks attached between the lateral in-cisors and the canines.12-14 The directions of the appliedforces were backward and upward in the maxillary arch,and backward and downward in the mandibular arch.13

All cephalograms were taken with the CX-90SP(Asahi, Kyoto, Japan) with 10% magnification. All pre-treatment and posttreatment cephalograms were tracedby 1 examiner (Y.-H.O.). The soft-tissue and skeletal mea-surements, dental angular measurements, and dental lin-ear measurements are illustrated in Figures 2 through 4.

When there was a double image, the midpoint be-tween the 2 points was traced. The measurement pointsfor the soft-tissue, skeletal, and maxillary dental linearand angular measurements were the same as used byGhosh and Nanda.1 The centroid point, the midpointon a horizontal line between the greatest mesial and dis-tal convexity of the crowns, was used for dental linearmeasurements. To determine the amount of horizontalmovement of maxillary teeth, the pterygoid vertical(PTV) plane was used.16 The vertical movement of themaxillary teeth was determined from superimpositionon the palatal plane (PP). The horizontal movement ofthe mandibular teeth was determined by measuringand comparing the distance from the centroid point ofthe teeth to the mandibular lingual cortex (MLC),whereas the vertical measurements were determinedfrom superimposition on the mandibular plane (MP).Angular changes of tooth positions were determinedby the inclination of the long axes of the teeth to thesella-nasion plane (SN) in the maxillary arch and to theMP in the mandibular arch.

Arch length discrepancies and intermolar widths ofthe maxillary and mandibular arches that were distalizedwere measured before and after treatment on dentalcasts by using a digital caliper. The 3 lingual patientswere removed from the sample when evaluating archwidths and rotation of the molars. To evaluate therotation of the distalized molars, the transversemeasurements were recorded between the buccal cusptips of the maxillary and mandibular second premolars

ics April 2011 � Vol 139 � Issue 4

Table I. Descriptive distribution of the patients

Patient(sex) Age

Brand and type ofmicroimplant(H, diameter)

Location ofmicroimplant placement

Duration offorce

application1. (F) 22 y 11 mo Dentos AX 1311-107, -106

Dentos AN 12-106#15-16 B, #25-26 B

#36-37 B, #46-47 B17 mo, 17 mo

10 mo, 10 mo2. (M) 24 y 4 mo Dentos SH 1312-106 #37 DB, #47 DB 19 mo, 19 mo3. (F) 28 y 3 mo Osteomed (1.2

H,10 mm)

Osteomed (1.2H,6 mm)

#37 DB, #47 DB#16-17 P, #26-27 P

9.2 mo, 9.2 mo9.2 mo, 9.2 mo

4. (F) 24 y 2 mo Dentos AX 13-1065Dentos AX 1311-107

#15-16 B, #25-26 B#36-37 B, #46-47 B

14 mo, 14 mo14 mo, 14 mo

5. (F) 26 y 9 mo Dentos SH 1312-107, -110Dentos SH 1312-106

#16-17 P, #26-27 P#36-37 B, #46-47 B

11 mo, 11 mo14 mo, 14 mo

6. (F) 15 y 3 mo Osteomed (1.2H,6 mm) #37 DB, #47 DB 16 mo, 16 mo

7. (M) 23 y 1 mo Dentos SH 1312-107Dentos SH 1312-107

#15-16 B, #25-26 B#36-37 B, #46-47 B

11 mo, 11 mo11 mo, 11 mo

8. (F) 29 y 3 mo Dentos AX 1311-108Dentos ATX 1311-105

#15-16 B, #25-26 B#36-37 B, #46-47 B

21 mo, 21 mo15 mo, 15 mo

9. (F) 18 y 11mo Dentos ATX 1311-108Dentos AX 12-106

#15-16 B, #25-26 B#37 DB, #47 DB

20 mo, 22 mo19 mo, 19 mo

10. (F) 22 y 5 mo Osteomed (1.2H,6 mm) #37 DB, #47 DB 13 mo, 13 mo

11. (M) 31 y 7 mo Dentos SH 1312-107Dentos SH 1312-106

#15-16 B, #25-26 B#36-37 B, #46-47 B

17 mo, 17 mo17 mo, 17 mo

12. (F) 21 y 1 mo Dentos ATX 1311-108Dentos AN 13-105

#15-16 B, #25-26 B#35-36 B, #45-46 B

19 mo, 19 mo19 mo, 19 mo

13. (M) 23 y 3 mo Osteomed (1.2H,6 mm) #37 DB, #47 DB 21 mo, 21 mo

14. (M) 13 y 9 mo Osteomed (1.2H,6 mm)

Dentos AN 12-204#15-16 B, #25-26 B

#37 DB, #47 DB17 mo, 17 mo

17 mo, 17 mo15. (M) 16 y Dentos SH 1312-107

Dentos SH 1311-106,Dentos SH 1412-105

#15-16 B, #25-26 B#36-37 B, #46-47 B

13 mo, 13 mo7 mo, 7 mo

16. (F) 12 y 9 mo Dentos SH 1312-107Dentos SH 1312-106

#15-16 B, #25-26 B#36-37 B, #46-47 B

18 mo, 21 mo11 mo, 11 mo

17. (F) 20 y 9 mo Dentos ATX 1311-107Dentos AX 12-107

#15-16 B, #25-26 B#36-37 B, #46-47 B

15 mo, 15 mo14 mo, 14 mo

18. (F) 21 y 1 mo Dentos SH 1312-107 #15-16 B, #25-26 B 8 mo, 8 mo19. (F) 26 y 3 mo Dentos AX 1311-107

Dentos AX 1311-107#15-16 B, #25-26 B

#36-37 B, #46-47 B22 mo, 22 mo

15 mo, 19 mo20. (M) 16 y 11 mo Dentos SH 1311-107

Dentos AX 12-106#15-16 B, #25-26 B

#35-36 B, #45-46 B8 mo, 8 mo

23 mo, 23 mo21. (M) 13 y 3 mo Dentos SH 1312-107

Dentos SH 1312-106#15-16 B, #25-26 B

#36-37 B, #46-47 B10 mo, 20 mo

13 mo, 13 mo22. (F) 26 y 11 mo Dentos ATX 1311-107

Dentos AX 12-106#16-17 P, #26-27 P

#36-37 B, #46-47 B12 mo, 12 mo

13 mo, 13 mo23. (M) 30 y 2 mo Dentos ATX 1412-07

Dentos ATN 1312-05#15-16 B, #25-26 B

#36-37 B, #46-47 B25 mo, 25 mo

21 mo, 21 mo

ALD, arch length discrepancy; B, buccal; DB, distobuccal; P, palatal; Y, yes; N, no; Mx, maxillary; Mn, mandibular.

472 Oh, Park, and Kwon

along with the mesiobuccal and distobuccal cusp tips ofthe first and second molars.1,5

Statistical analysis

The statistical analyses were performed with SPSSsoftware (version 14.0, SPSS, Chicago, Ill). A pairedt test and a Wilcoxon signed rank test were used.When the sample showed normal distribution asevaluated by the Kolmogorov-Smirnov test, the P values

April 2011 � Vol 139 � Issue 4 American

of the paired t test were illustrated, unless the P values ofthe Wilcoxon signed rank test were illustrated.

RESULTS

To calculate the error of measurements, 20 cephalo-metric films and models from 10 patients were retraced,redigitized, and remeasured 1 month later. Measure-ment errors were calculated based on the differencesbetween the first and second values with a paired

Journal of Orthodontics and Dentofacial Orthopedics

Failure(month afterplacement)

Replacement(location,

period of use)

Pericoronitis onmandibularsecond molar

Duration oftreatment

Microimplanttreatment

ALDMx/Mn(mm)

N Operculum 17 mo Mx/Mn �5.43/�4.45

Y (17 mo) Y (2 mo) Operculum 20 mo Mn �10.73/�6.31N 10 mo Mx/Mn �4.21/�4.74

N 15 mo Mx/Mn �3.50/�1.10

N 14 mo Mx/Mn �0.75/�3.97

N 16 mo Mn �10.16/�5.66Y (1 mo) Y (8 mo) 21 mo Mx/Mn 5.49/�1.78

N 23 mo Mx/Mn �4.46/�0.44

N 22 mo Mx/Mn �3.13/0

N 13 mo Mn �3.23/020 mo Mx/Mn 0/�1.57

N 19 mo Mx/Mn �1.23/�1.23

N 21 mo Mn 0/�1.49N 17 mo Mx/Mn �5.36/�1.49

Y (1 mo) Y (27 mo) 28 mo Mx/Mn �7.19/�9.50

N 30 mo Mx/Mn �1.43/�2.06

Y (2 mo) Y (12 mo) 15 mo Mx/Mn �1.11/�1.41

N 27 mo Mx �4.02/0N Operculum 22 mo Mx/Mn �1.46/�6.60

N 23 mo Mx/Mn �0.81/0.70

N Mild 34 mo (2 phase)21 mo (fixed)

Mx/Mn �3.0/�4.0

Y (1, 7 mo) Y (9, 6 mo) Mild 22 mo Mx/Mn �4.45/�2.3

Y (2 mo) Y (19 mo) 25 mo Mx/Mn 3.06/0

Table I. Continued


t test. There was no significant difference between the 2measurements. To measure the range of methodologicerrors, Dahlberg’s formula17 was used, and the resultswere 0.3� for angular measurements and 0.1 mm forlinear measurements.

Themean distal repositionings of the upper and lowerlips relative to the E-line were 0.72 and 1.18 mm,respectively. The lower lip moved distally more thanthe upper lip (Table II).

The skeletal changes during treatment (before distal-ization to posttreatment) are summarized in Table II andshowed that the Frankfort horizontal-mandibular plane


angle (FMA) decreased with statistical significance. Theother measurements were not statistically different. Thedistance of ANS-Me increased (0.66 mm), but it wasnot statistically significant. To preclude the effect ofgrowth and to quantify the treatment effect only, thesample was divided into adult and growing groups.In the adults, the FMA decreased with statistical signif-icance, and the distance of ANS-Me also decreased by–0.32 mm, although it was not statistically significant(Table III). In the growing patients, however, ANS-Meincreased by 2.07 mm with statistical significance. Inthe adults, after the maxillary and mandibular


Fig 1. A, Initial leveling stage: to gain space for alignment of anterior teeth, distalizing force was appliedto the canines from microimplants; B, en-masse retraction, with the 6 anterior teeth tied together;C, en-masse retraction (lateral view), with the retraction force applied to the canines; D, schematicdrawing of the whole dentition retraction.

Fig 2. Cephalometric measurements used in this study: 1, upper lip to E-line; 2, lower lip to E-line;3,\SN-PP (SN-palatal plane angle); 4,\SN-OP (SN-bisected occlusal plane angle); 5,\FMA(Frankfort-mandibular plane angle); 6, PTV to Point A; 7, PTV to Point B; 8, ANS to Me.


dentitions were distalized, Points A and B moved pos-teriorly with statistical significance only for Point B(Table III).


The movement of the maxillary and mandibular teethwas evaluated in the patient groups in which themaxillary and mandibular teeth were distalized against


Fig 3. Cephalometric dental angular measurements(maxilla): 1, SN-incisor; 2, SN-first premolar; 3, SN-firstmolar; 4, SN-second molar; (mandible) 5, MP-incisor;6, MP-first premolar; 7, MP-firstmolar; 8, MP-secondmolar.

Fig 4. Cephalometric dental linear measurements. Hori-zontal measurements in the maxilla: 1, PTV-incisor tip;2, PTV-first premolar centroid; 3, PTV-first molar centroid;4, PTV-second molar centroid. Vertical measurements inthe maxilla: 5, PP-incisor; 6, PP-first premolar centroid;7, PP-first molar centroid; 8, PP-second molar centroid.Horizontal measurements in the mandible: 9, MLC-firstpremolar centroid; 10, MLC-first molar centroid;11, MLC-second molar centroid. Vertical measurementsin the mandible: 12, MP-incisor; 13, MP-first premolarcentroid; 14, MP-first molar centroid; 15, MP-secondmolar centroid.


the microimplants, respectively. The long axes of themaxillary central incisors, maxillary first premolars, andmaxillary first molars to the SN plane decreased by3.68�, 3.43�, and 3.47�, respectively, on average, mean-ing that the teeth were tipped distally (Table IV). Therewere mean decreases of 2.62, 1.42, 1.51, and 1.95 mm,respectively, in the horizontal distances from themaxillary central incisors, first premolars, and first andsecond molars to the PTV plane, and all measurementswere statistically significant (Table IV). This means thatall maxillary teeth were distalized. There were decreasesin the vertical distances from the centroid points of themaxillary central incisors, first premolars, first molars,and second molars to the PP, with mean decreases of0.36, 0.55, 1.00, and 1.12 mm, respectively (Table IV).Among these, there was statistical significance for themaxillary first and second molars.

All mandibular teeth were tipped distally. The meandecreases in the angle of the long axes of mandibularcentral incisors, first premolars, and first and secondmo-lars to the mandibular plane were 2.45�, 6.64�, 7.62�,and 8.25�, respectively (Table IV). Statistically significantvalues were found for the first premolars, and the firstand second molars. The horizontal distances from thecentroid points of the mandibular first premolars, andthe first and second molars to the MLC, increased by1.60, 2.45, and 2.08 mm, respectively (Table IV), mean-ing that all mandibular teeth were moved distally. Thevertical distance from the centroid point of the


mandibular second molars to the mandibular planewas decreased by 1.07 mm with statistical significance(Table IV).

There were significant differences in maxillary andmandibular intermolar widths before and after distaliza-tion. There were mean expansions of 1.25 mm in themaxilla and 0.98 mm in the mandible (Table V). Themaxillary first and second molars and the mandibularfirst molar were rotated distally by minimal amounts,whereas significant mesial rotation was evident on themandibular second molars. The distance between themesiobuccal cusps of the maxillary first molars on bothsides increased by 1.41 mm, and the distobuccal cuspdistance increased by 0.5 mm. Therefore, the differencein expansion between the mesiobuccal and distobuccalcusps was 0.91 mm. The differences in expansionbetween the mesiobuccal and distobuccal cusps of themaxillary second molars, and the mandibular firstand second molars, were 0.61, 0.30, and –0.14 mm,respectively.

Seventy microimplants and 12 microscrews wereused in the 23 patients. Among the 82 microimplants,4 microimplants (in 1 patient) were excluded becausea student removed the microimplants intentionally to


Table II. Descriptive statistics of cephalometric measurements at pretreatment, posttreatment, and pretreatment toposttreatment (n 5 23)

Measurement

Pretreatment Posttreatment Change Significance

Mean SD Mean SD Mean SD t WSoft tissueUpper lip to E-line (mm) �1.22 2.19 �1.94 1.91 �0.72 1.29 0.014* -Lower lip to E-line (mm) 1.17 2.78 �0.01 1.93 �1.18 1.42 0.001y -Skeletal -SN-PP (�) 9.26 3.68 9.50 3.82 0.24 1.31 0.391 -SN-OP (�) 17.32 5.36 17.78 4.92 0.03 3.29 0.970 -FMA (�) 26.00 5.23 25.30 5.05 �0.70 1.25 0.014* -PTV-A (mm) 48.99 2.59 48.93 2.74 �0.07 1.43 0.829 -PTV-B (mm) 50.30 4.83 49.77 4.45 �0.53 2.01 0.223 -ANS-Me (mm) 75.03 7.29 75.69 7.27 0.66 2.02 0.130 -

Dental-angular (�)SN-U1 108.75 6.90 106.48 9.84 �2.28 8.08 0.212 -SN-U4 85.91 6.52 81.72 6.18 �4.19 7.18 0.015* -SN-U6 75.12 5.53 72.84 4.89 �2.28 6.09 0.102 -SN-U7 65.17 11.93 65.97 9.32 0.80 7.04 0.617 -MP-L1 93.62 6.85 92.83 7.72 �0.79 6.75 0.579 -MP-L4 82.61 5.42 77.52 7.65 �5.09 9.40 - 0.004y

MP-L6 80.53 4.78 73.35 9.44 �7.18 8.12 - \0.0001y

MP-L7 81.71 8.49 72.93 10.10 �8.78 7.27 - \0.0001y

Dental-linear (mm)PTV-U1 59.96 3.91 58.18 3.37 �1.79 3.08 0.015* -PTV-U4 40.30 2.90 38.75 3.10 �1.55 2.11 0.003y -PTV-U6 23.33 3.12 21.59 3.36 �1.75 2.01 0.001y -PTV-U7 12.58 2.85 10.93 3.83 �1.75 2.12 0.002y -PP-U1 31.76 3.72 31.30 3.83 �0.45 1.41 0.157 -PP-U4 25.43 3.06 25.07 2.88 �0.36 1.18 0.174 -PP-U6 21.99 5.19 22.31 2.50 0.32 4.14 - 0.121PP-U7 19.67 3.28 19.46 2.65 �0.22 2.54 - 0.111MLC-L4 5.00 3.13 6.80 3.88 1.80 1.89 0.0002y -MLC-L6 21.60 2.64 24.19 3.32 2.58 2.10 \0.0001y -MLC-L7 33.94 3.18 35.78 3.47 1.84 1.99 - \0.0001y

MP-L1 45.56 3.74 45.93 4.07 0.37 1.82 0.336 -MP-L4 37.59 4.07 38.35 4.22 0.76 1.89 0.066 -MP-L6 33.01 3.58 33.11 3.52 0.10 1.31 0.735 -MP-L7 30.35 3.26 29.61 3.61 �0.74 1.29 0.013* -

t, t test; W, Wilcoxon signed rank test.*P\0.05; yP\0.01.


change the position during the treatment period. Thesuccess rate was calculated for 78 microimplants. Se-venty of 78 microimplants were maintained during forceapplication, and the success rate was 89.7%.

There was a difference in the success rates betweenthe professor (H.-S.P.) and the postgraduate students.The success rate for the professor was 98.1% (53 of 54microimplants); the students had a lower success rateof 70.8% (17 of 24 microimplants). The mean treatmenttime was 20 6 4.9 months (range, 13-30 months).

When the full mandibular dentition was distalized,opercula were noted in 3 patients, distal to the secondmolars, and mild pericoronitis was seen in 2 patients.


DISCUSSION

Ngantung et al4 reported that, when distalizationappliances such as the distal jet or the pendulum areused, the anterior teeth tend to move forward duringdistalization of the molars. Then the anterior teethneed to be retracted against the distalized molars. Ac-cordingly, the anterior teeth suffered round-trip move-ment and were exposed to jiggling forces. To preventthis side effect, a dental implant or miniscrew implantshave been used with the distalization appliance for an-chorage reinforcement.6-8 However, the mechanics ofretraction of the whole dentition with microimplantsprevent the round tripping movement of the anterior


Table III. Skeletal changes in adults vs growing patients

Measurement


Mean SD Mean SD Mean SD t WAdult patients (n 5 16)SN-PP (�) 9.99 3.74 9.93 4.10 �0.06 1.32 0.867 -SN-OP (�) 17.42 5.58 17.37 5.03 �0.05 3.30 0.952 -FMA (�) 26.22 5.90 25.31 5.72 �0.91 1.13 0.006y -PTV-A (mm) 49.02 2.64 48.63 2.77 �0.39 1.15 0.193 -PTV-B (mm) 50.93 4.67 49.84 4.59 �1.09 1.52 0.0497* -ANS-Me (mm) 75.51 8.45 75.20 8.00 �0.32 1.91 - 0.222

Growing patients (n 5 7)SN-PP (�) 7.57 3.16 8.50 3.13 0.93 1.07 0.061 -SN-OP (�) 18.21 5.15 18.71 4.91 0.20 3.53 0.886 -FMA (�) 25.51 3.61 25.30 3.41 �0.21 1.48 0.716 -PTV-A (mm) 48.93 2.66 49.61 2.75 0.69 1.80 0.352 -PTV-B (mm) 48.86 5.24 49.61 4.45 0.76 2.50 0.454 -ANS-Me (mm) 75.03 6.57 77.10 7.16 2.07 1.40 0.008y -


Table IV. Dental changes of cephalometric measurements at pretreatment, posttreatment, and pretreatment to post-treatment in patients with molars distalized

Measurement


Mean SD Mean SD Mean SD t WMaxillary dental change (n 5 19)Dental-angular (�)

SN-U1 109.43 8.11 105.75 10.87 �3.68 6.92 0.080 -SN-U4 84.28 5.61 80.85 5.24 �3.43 4.94 - 0.023*SN-U6 75.61 6.79 72.14 4.32 �3.47 5.92 0.056 -SN-U7 64.93 10.37 65.89 6.53 0.96 7.11 0.634 -

Dental-linear (mm)PTV-U1 60.96 4.27 58.34 3.84 �2.62 3.16 0.011* -PTV-U4 40.60 2.83 39.18 3.53 �1.42 1.87 0.018* -PTV-U6 23.88 2.65 22.37 3.45 �1.51 1.59 0.005y -PTV-U7 13.08 2.62 11.14 3.53 �1.95 1.48 0.0005y -PP-U1 31.68 3.77 31.32 3.92 �0.36 1.42 0.375 -PP-U4 25.52 2.81 24.97 2.57 �0.55 1.04 0.084 -PP-U6 23.23 2.45 22.23 2.26 �1.00 1.15 0.009y -PP-U7 20.31 2.39 19.19 2.31 �1.12 1.16 0.005y -

Mandibular dental change (n 5 22)Dental-angular (�)

MP-L1 93.76 7.30 91.31 7.58 �2.45 5.29 0.095 -MP-L4 82.77 6.21 76.13 8.97 �6.64 10.85 - 0.010*MP-L6 79.77 4.75 72.15 10.85 �7.62 9.63 - 0.001y

MP-L7 79.89 8.16 71.65 11.84 �8.25 6.80 0.0003y -Dental-linear (mm)

MLC-L4 5.19 2.97 6.79 3.67 1.60 1.59 0.002y -MLC-L6 21.38 2.50 23.83 3.21 2.45 2.18 - 0.0001y

MLC-L7 33.45 2.91 35.53 3.22 2.08 1.06 \0.0001y -MP-L1 46.18 3.85 46.20 4.15 0.02 1.87 0.968 -MP-L4 38.23 4.33 38.43 4.47 0.21 1.93 0.685 -MP-L6 33.77 3.78 33.35 3.96 �0.43 1.07 0.145 -MP-L7 30.78 3.68 29.71 4.24 �1.07 1.32 0.008y -



American Journal of Orthodontics and Dentofacial Orthopedics April 2011 � Vol 139 � Issue 4

Table V. Changes in intermolar width and arch length discrepancy

Measurement (mm)


Mean SD Mean SD Mean SD t WMaxillary archIntersecond premolar width 50.09 2.69 52.23 1.87 2.14 1.68 0.0002y -Intermolar width 41.49 2.24 42.74 2.41 1.25 0.83 \0.0001y -Arch length discrepancy �2.06 3.14 0 0 2.06 3.14 0.016* -

Mandibular archIntersecond premolar width 42.34 2.80 43.91 1.88 1.57 1.92 0.005y -Intermolar width 41.96 2.28 42.94 2.21 0.98 1.47 0.008* -Arch length discrepancy �2.98 2.67 0 0 2.98 2.67 - \0.0001y


Fig 5. Summary of cephalometric changes after distali-zation of the posterior and anterior teeth with microim-plants.


teeth. The distalization of the canines with the posteriorteeth by applying distal force to the canines frommicroimplants could make spaces to align the anteriorteeth. After alignment of the anterior teeth, the fulldentition was retracted.12,13 Because the rotatedanterior teeth were not ligated tightly during the initialalignment, there was no force to move the anteriorteeth forward, and the resulting round trippingmovement could be avoided.14


The upper and lower lips relative to the E-line moveddistally after distal retraction of the anterior teeth by0.72 and 1.18 mm, respectively (Table V). The initialmean arch length discrepancies of –2.06 mm in themaxilla and –2.98 mm in the mandible were resolved(Table V). This means that the posterior teeth weredistalized sufficiently to resolve crowding as well as toobtain a better profile after distal movement of the an-terior teeth. Figure 5 is a summary of the cephalometricchanges.

Although the FMA was decreased, the distance ofANS-Me was increased slightly (Table III). However, inthe adult group, with no effect of growth, the distanceof ANS-Me did not change (Table III). The force fromthe microimplants to the canine brackets is backwardand in an apical direction. With these forces, the teethmight experience distal movement and intrusion.When distal force is applied to the canines, they mighttip distally, and this would exert an intrusion force onthe posterior teeth. The maxillary and mandibular sec-ond molars were intruded by 1.12 and 1.07 mm, respec-tively (Table IV). This result suggests that, although thefull dentitions of the maxilla and the mandible were dis-talized, the intrusion of the second molar prevents thewedging effect and the increases of the FMA. The intru-sion of the molars during distal movement could keepthe anterior facial height. The intrusion of the posteriorteeth might produce a lateral open bite, which can beminimized by bonding a posterior bracket or buccaltube gingivally.

On the other hand, in growing patients, the distanceof ANS-Me was increased significantly (Table III). Thismight reflect the growth pattern of the mandible thatlower facial height is increased as the mandible grows.Ghosh and Nanda1 and Chiu et al3 reported that theFMA was increased when molars were distalized with in-traoral distalizing appliances. In this study, however, theFMA was decreased in the adult group with statistical


Fig 6. Maxillary and mandibular superimpositions of pretreatment and posttreatment (yellow) digitaldental models of a patient showing expansion of the dental arch.

Table VI. Means, standard deviations, and minimum and maximum values for changes in the transverse measure-ments from dental casts

Measurement (mm) Mean SD Minimum Maximum tMaxillary transverseBetween first molars

Mesiobuccal cusp 1.41 0.90 0.2 2.8 .0002*Distobuccal cusp 0.50 0.93 -1.7 2.0 .056

Between second molarsMesiobuccal cusp 0.75 1.73 -1.6 4.0 .184Distobuccal cusp 0.14 1.40 -1.7 2.3 .754

Mandibular transverseBetween first molars

Mesiobuccal cusp 1.74 1.80 -1.0 4.8 .001*Distobuccal cusp 1.44 2.06 -1.5 5.7 .011*

Between second molarsMesiobuccal cusp 1.67 1.85 -1.0 5.5 .005*Distobuccal cusp 1.81 2.06 -2.0 6.5 .006*

t, t test.*P\0.01.


significance and also decreased in the growing patients,although it was not statistically significant. This sug-gests that we could distalize the full dentition of themaxilla and the mandible, and the FMA can be main-tained or decreased, if necessary. Therefore, these me-chanics seem a better treatment in high-angle patientsthan in low-angle patients. When treating low-anglepatients with these mechanics, other devices—eg,a bonded anterior bite plane—should be placed tomaintain or increase the vertical dimension.

With the distal jet appliance, Ghosh and Nanda1 haddistal tipping of the maxillary first and second molars of8.36� and 11.99�, respectively, during distalization. Itwas stated that the molar key could be corrected by a tip-ping movement of the molar, but the retention would bedoubtful during distal retraction of the incisors. The


molar distalizing appliances anchored by screws alsoshowed distal tipping of the distalized maxillary firstmolars by 8.8�8 and 10.9�.7 In our study, the maxillaryfirst molar tipped distally by 3.47�; this was far smallerthan in previous reports.1,7,8 Moreover, the maxillarysecond molar tipped mesially by 0.96�. This might beexplained because the treatment mechanics used inthis study were sliding mechanics with a rigid mainarchwire without loops, and tipping of the teeth couldbe alleviated. By distalizing the posterior teeth withbodily movement, the stability of the treatment wouldbe good. The distal movement of the maxillary molarswas evident, but the amount of distal movement wasapproximately 1.4 to 1.5 mm (Table IV). This was lessmovement than other molar distalizing appliances inwhich the maxillary first molars moved distally by 3.8



mm7 and 3.9 mm.8 However, because of less distaltipping of the distalized molars and the measurementsmade on the centroid point of the crown, not onthe tip of the crown as in the previous studies, theamount of real tooth movement might be similar.7,8

The amounts of distal movement of the mandibularfirst and second molars were 2.45 and 2.08 mm,respectively; these were greater than movements of themaxillary molars (Table IV). It might be because severalpatients had an anterior crossbite or an edge-to-edgebite initially, and we needed to retract the teeth toa greater extent to obtain proper incisal relationships.This produced greater distal repositioning of the lowerlip than of the upper lip. The mandibular molars showedmore distal tipping than did the maxillary molars. Thiswas because the mandibular posterior teeth needed tobe tipped distally to level the curve of Spee and toupright to the occlusal plane.

There were increases in maxillary interpremolar andintermolar widths by 2.14 and 1.25 mm, respectively.These amounts were greater than in the mandible inwhich interpremolar width was increased by 1.57 mm,and a 0.98-mm increase was evident at the intermolarwidth (Table V). Because the distal force was appliedto the canines, there might be a tendency of arch expan-sion in the canine and premolar areas. This can be pre-vented by using a rigid archwire with a slightconstriction around the canines. Figure 6 gives superim-positions of the digital images of the initial and finalcasts. It shows the increases in intermolar width at post-treatment. When a distal force is applied to the canines,they tip distally. The distal tipping of the caninesproduces an intrusion force on the molars. The intrusionforce on buccal brackets can bring about buccal upright-ing of molars and result in expansion of intermolarwidth.

One drawback of pendulum appliances might be therotation of distalized molars. Ghosh and Nanda1 showedthat the width between the mesiobuccal cusps of theright and left maxillary first molars increased by 1.4mm, whereas that between the distobuccal cuspsshowed only 0.04 mm of increase. The difference inwidth increases between the mesiobuccal and distobuc-cal cusps was about 1.36 mm. For the maxillary secondmolars, the width difference between the mesiobuccal(2.33 mm) and the distobuccal cusps (1.59 mm) was0.74 mm. This implies mesiobuccal rotation of themolars. This rotation might improve the dental relation-ships and gain additional space in a Class II malocclu-sion. With the distal jet appliance, the difference inwidth between the mesiobuccal and distobuccal cuspsof the first molars was 0.2 mm (2.9-2.7 mm), and thatof the second molars was 0.3 mm (1.1-0.8 mm).5


Therefore, the pendulum appliance produced more rota-tion of the distalized molars than did the distal jet appli-ance. In this study, the difference in width increasesbetween the mesiobuccal and distobuccal cusps of themaxillary first molars was 0.91 mm (1.41-0.5 mm).That for the second molars was 0.61 mm (0.75-0.14mm) (Table VI). The rotation of the distalized molarswith these mechanics lies between the pendulum andthe distal jet appliances. For the mandible, the differencein width increases between the mesiobuccal and disto-buccal cusps of the first molars was 0.30 mm (1.74-1.44 mm), and that for the second molars was –0.14mm (1.67-1.81 mm). The distalized molars in the man-dibular arch experienced less rotation than those in themaxillary arch, and the mandibular second molarsshowed distobuccal rotation, whereas the other molarsrotated mesiobuccally. In the treatment of Class II mal-occlusion, mesiobuccal rotation of the maxillary molarsimproves dental relationships and yields additionalspace. However, in the treatment of distal retraction ofboth maxillary and mandidular dentitions, this rotationmight not be a favorable movement. To minimize rota-tion of the molars, it is better to bond molar brackets orbuccal tubes slightly distal to the middle of the crown orto use buccal tubes with no offset.

The overall success rate of the microimplants was89.7%. The success rates were 98.1% for a well-experienced clinician and 70.8% for postgraduate stu-dents. Many factors affect the success of microimplants.The success seems to be influenced by the operator‘sskill. The success rate follows the learning curve. Thesuccess rate of the microimplants in this sample wassimilar to or higher than in previous reports.18-21 Thesuccess rates in previous studies ranged from 93.3%18

to 81%.20

Regarding treatment time, Ngantung et al4 reportedthat mean treatment time was 25.7 6 3.9 months tocomplete treatment with the distal jet appliance withfull bracket appliance therapy. Chiu et al3 reported thatthe treatment time for the distal jet appliance was 28months, consisting of 10 months for distalization ofthe molars and 18 months for the second phase of fixedappliance treatment. The treatment time for the pendu-lum appliance was 31months, consisting of 7months fordistalization of the molars and another 24 months forfixed appliance therapy. The mean treatment time inthis study was 20 6 4.9 months. It was much shorterthan that with intraoral distalizing appliances. Thismightbe because, in molar distalizing appliance treatment,treatment starts at an early age, and it is a step-by-steptreatment consisting of molar distalization and incisorretraction. However, with microimplant sliding mechan-ics, treatmentwas started after the eruption of the second



molars or started in adult patients, and all teeth in thearch were distalized at the same time. For individualteeth, the movement was slow because the molars weredistalized by 1.5 to 2 mm during a year of treatment.However, by moving all teeth together, treatment timecan be shortened. Alveolar surgery could accelerate therate of tooth movement.22 To enhance distal movementof the molars, the third molars can be extracted justbefore applying the distal force.

Distal movement of the mandibular posterior teethcan produce pericoronitis by the accumulation of softtissue over the crown of the second molar. In 3 patients,opercula were observed; these patientsmight need an op-erculectomy.23Mild pericoronitis distal to themandibularsecond molar was observed in 2 patients. Therefore, toprevent this, the available space distal to themolar shouldbe checked when determining the treatment plan.

CONCLUSIONS

With microimplant-aided sliding mechanics, clinicianscan distalize all teeth together with less distal tipping androtation of distalized molars, and retract the upper andlower lips to improve facial esthetics. The technique seemseffective and efficient to treat patients who have a mildarch length discrepancy without extractions.

REFERENCES

1. Ghosh J, Nanda RS. Evaluation of an intraoral maxillary molar dis-talization technique. Am J Orthod Dentofacial Orthop 1996;110:639-46.

2. Bussick TJ, McNamara JA Jr. Dentoalveolar and skeletal changesassociated with the pendulum appliance. Am J Orthod DentofacialOrthop 2000;117:333-43.

3. Chiu PP, McNamara JA Jr, Franchi L. A comparison of two intraoralmolar distalization appliances: distal jet versus pendulum. Am JOrthod Dentofacial Orthop 2005;128:353-65.

4. Ngantung V, Nanda RS, Bowman SJ. Posttreatment evaluation ofthe distal jet appliance. Am J Orthod Dentofacial Orthop 2001;120:178-85.

5. Bolla E, Muratore F, Carano A, Bowman SJ. Evaluation of maxillarydistalization with the distal jet: a comparison with other contem-porary methods. Angle Orthod 2002;72:481-94.


6. Onca�g G, Akyalcin S, Arikan F. The effectiveness of a single os-teointegrated implant combined with pendulum springs formolar distalization. Am J Orthod Dentofacial Orthop 2007;131:277-84.

7. Kircelli BH, Pektas ZO, Kircelli C. Maxillary molar distalization witha bone-anchored pendulum appliance. Angle Orthod 2006;76:650-9.

8. Gelg€or IE, B€uy€ukyilmaz T, Karaman AI, Dolanmaz D, Kalayci A.Intraosseous screw-supported upper molar distalization. AngleOrthod 2004;74:838-50.

9. Creekmore TD, Eklund MK. The possibility of skeletal anchorage.J Clin Orthod 1983;17:266-9.

10. Park HS. The skeletal cortical anchorage using titaniummicroscrew implants. Korean J Orthod 1999;29:699-706.

11. Park HS, Bae SM, Kyung HM, Sung JH. Micro-implant anchoragefor treatment of skeletal Class I bialveolar protrusion. J Clin Orthod2001;35:417-22.

12. Park HS. The use of micro-implant as orthodontic anchorage. 2nded. Seoul, Korea: Nare Publishing; 2001:257–288.

13. Park HS, Kwon TG, Sung JH. Nonextraction treatment withmicroscrew implants. Angle Orthod 2004;74:539-49.

14. Park HS, Lee SK, Kwon OW. Group distal movement of teeth usingmicroscrew implant anchorage. Angle Orthod 2005;75:602-9.

15. Park HS, Bae SM, Kyung HM, Sung JH. Simultaneous incisor re-traction and distal molar movement with microimplant anchorage.World J Orthod 2004;5:164-71.

16. Enlow DH, Kuroda T, Lewis AB. The morphological and morpho-genetic basis for craniofacial form and pattern. Angle Orthod1971;41:161-88.

17. Houston WJ. The analysis of errors in orthodontic measurements.Am J Orthod 1983;83:382-90.

18. Park HS. Clinical study on success rate of microscrew implants fororthodontic anchorage. Korean J Orthod 2003;33:151-6.

19. Park HS, Jeong SH, Kwon OW. Factors affecting the clinical successof screw implants used as orthodontic anchorage. Am J OrthodDentofacial Orthop 2006;130:18-25.

20. Miyawaki S, Koyama I, Inoue M, Mishima K, Sugahara T,Takano-Yamamoto T. Factors associated with the stability of tita-nium screws placed in the posterior region for orthodontic anchor-age. Am J Orthod Dentofacial Orthop 2003;124:373-8.

21. Kuroda S, Sugawara Y, Deguchi T, KyungHM, Takano-Yamamoto T.Clinical use ofminiscrew implants as orthodontic anchorage: successrates and postoperative discomfort. Am J OrthodDentofacial Orthop2007;131:9-15.

22. Ren A, Lv T, Kang N, Zhao B, Chen Y, Bai D. Rapid orthodontictooth movement aided by alveolar surgery in beagles. Am J OrthodDentofacial Orthop 2007;131:160.e1-10.

23. Kravitz ND, Kusnoto B. Soft-tissue lasers in orthodontics: an over-view. Am J Orthod Dentofacial Orthop 2008;133(Suppl):S110-4.


Treatment Effects of Microimplant-Aided Sliding

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