Treatment effects of microimplant-aided sliding mechanics on distal retraction of posterior teeth

Introduction

Our objective was to quantify the treatment effects of microimplant-aided mechanics on group distal retraction of the posterior teeth.

Methods

The pretreatment and posttreatment cephalometric radiographs and dental casts of 23 patients (mean age, 22.1 ± 5.17 years), treated with distalization of the posterior teeth against microimplant 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 angle was decreased in the adult group. The maxillary posterior teeth were distalized by 1.4 to 2.0 mm with approximately 3.5° of distal tipping, and the mandibular posterior teeth were also distalized by 1.6 to 2.5 mm with approximately 6.6° to 8.3° of distal tipping. The maxillary posterior teeth showed intrusion by 1 mm. There were increases in arch widths at the premolars and molars. The overall success of microimplants was 89.7%; a well-experienced clinician had a higher success rate (98%) than did novices in this sample. The mean treatment time was 20 ± 4.9 months.

Conclusions

With microimplant-aided sliding mechanics, clinicians can distalize all posterior teeth together with less distal tipping. The technique seems effective and efficient to treat patients who have mild arch length discrepancy without extractions.

There have been many attempts to distalize molars with intraoral distalizing appliances. The side effects 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, miniscrews, and microscrews were tried. All of these skeletal devices can provide suitable anchorage. Miniscrews and microimplants, which have many advantages such as easy surgical placement and removal, low costs, and a small enough size to be placed into the interradicular bone between the roots of adjacent teeth, have achieved popularity over other skeletal anchorage devices. Dental implants and miniscrew implants are placed in the anterior or midpalate and connected to the premolars for applying distal force to the molars. Alternatively, the distalizing force is applied to the molars from skeletal anchorage devices. With skeletal anchorage, the side effects on the reactive part were alleviated, but distal tipping and rotation of distalizing molars are still issues. The 1-by-1 tooth movement is effective, but it tends to produce side effects of rotation and tipping movement when the force does not pass the center of resistance of a tooth.

Group distal retraction of the whole dentition with microimplants was introduced and showed several good treatment results. The distal force was applied to the canines or anterior hooks attached on the main archwire from microimplants placed between the roots of the posterior teeth. By moving teeth together, individual tooth movements, rotation, and tipping were prevented.

Several clinical case reports showed the efficacy of microimplants and the efficiency of the treatment mechanics in distalization of the whole dentition. However, only 1 pilot study evaluated the treatment effects of these mechanics with cephalometric analysis. Therefore, the purpose of this study was to quantify the treatment effects of en-masse retraction of the posterior teeth against microimplants by analyzing cephalometric radiographs and dental casts, and with clinical examinations.

Material and methods

The cephalometric radiographs and dental casts of 23 patients who had been treated with 0.022-in straight-wire brackets at the orthodontic department of Kyungpook National University Hospital in Korea were collected. Consecutively treated patients who received the microimplants for distal movement of the posterior teeth without extraction of the premolars or other teeth except the third molars and had a complete set of records were selected. The first step of treatment planning for all patients was setting the goal for the soft-tissue profile. The position of the anterior teeth was determined according to the ratio of soft-tissue change to the amount of anterior teeth retraction. After transferring the anteroposterior position of the anterior teeth to the occlusogram, all teeth were aligned from anterior to posterior. All patients required distal movement of the posterior teeth. The maxillary and mandibular posterior teeth with or without the anterior teeth were distalized to resolve crowding or improve the facial profile. The microimplants were placed between the roots of the posterior teeth. Microimplants were used for distalization of the maxillary or mandibular dentitions. Eighteen of the 23 patients had microimplants in both jaws. One patient had microimplants only in the maxilla, and 4 patients had microimplants only in the mandible. All patients were between the ages of 12 years 9 months and 31 years 7 months (mean, 22.1 ± 5.17 years). The descriptive data of the patients are given in Table I . Most patients had a moderate amount of arch length discrepancy, except 2 patients with anterior spacing and 2 with no arch length discrepancy. Four patients also required distal movement of the posterior teeth to improve their facial profile. All patients had erupted second molars in both arches at the beginning of treatment.

Table I
Descriptive distribution of the patients
Patient
(sex)
Age Brand and type of
microimplant
(∮, diameter)
Location of
microimplant placement
Duration of
force
application
Failure
(month after
placement)
Replacement
(location,
period of use)
Pericoronitis on
mandibular
second molar
Duration of
treatment
Microimplant treatment ALD
Mx/Mn
(mm)
1. (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 B
17 mo, 17 mo
10 mo, 10 mo
N Operculum 17 mo Mx/Mn −5.43/−4.45
2. (M) 24 y 4 mo Dentos SH 1312-106 #37 DB, #47 DB 19 mo, 19 mo Y (17 mo) Y (2 mo) Operculum 20 mo Mn −10.73/−6.31
3. (F) 28 y 3 mo Osteomed (1.2 ∮,10 mm)
Osteomed (1.2 ∮,6 mm)
#37 DB, #47 DB
#16-17 P, #26-27 P
9.2 mo, 9.2 mo
9.2 mo, 9.2 mo
N 10 mo Mx/Mn −4.21/−4.74
4. (F) 24 y 2 mo Dentos AX 13-1065
Dentos AX 1311-107
#15-16 B, #25-26 B
#36-37 B, #46-47 B
14 mo, 14 mo
14 mo, 14 mo
N 15 mo Mx/Mn −3.50/−1.10
5. (F) 26 y 9 mo Dentos SH 1312-107, -110
Dentos SH 1312-106
#16-17 P, #26-27 P
#36-37 B, #46-47 B
11 mo, 11 mo
14 mo, 14 mo
N 14 mo Mx/Mn −0.75/−3.97
6. (F) 15 y 3 mo Osteomed (1.2 ∮,6 mm) #37 DB, #47 DB 16 mo, 16 mo N 16 mo Mn −10.16/−5.66
7. (M) 23 y 1 mo Dentos SH 1312-107
Dentos SH 1312-107
#15-16 B, #25-26 B
#36-37 B, #46-47 B
11 mo, 11 mo
11 mo, 11 mo
Y (1 mo) Y (8 mo) 21 mo Mx/Mn 5.49/−1.78
8. (F) 29 y 3 mo Dentos AX 1311-108
Dentos ATX 1311-105
#15-16 B, #25-26 B
#36-37 B, #46-47 B
21 mo, 21 mo
15 mo, 15 mo
N 23 mo Mx/Mn −4.46/−0.44
9. (F) 18 y 11mo Dentos ATX 1311-108
Dentos AX 12-106
#15-16 B, #25-26 B
#37 DB, #47 DB
20 mo, 22 mo
19 mo, 19 mo
N 22 mo Mx/Mn −3.13/0
10. (F) 22 y 5 mo Osteomed (1.2 ∮,6 mm) #37 DB, #47 DB 13 mo, 13 mo N 13 mo Mn −3.23/0
11. (M) 31 y 7 mo Dentos SH 1312-107
Dentos SH 1312-106
#15-16 B, #25-26 B
#36-37 B, #46-47 B
17 mo, 17 mo
17 mo, 17 mo
20 mo Mx/Mn 0/−1.57
12. (F) 21 y 1 mo Dentos ATX 1311-108
Dentos AN 13-105
#15-16 B, #25-26 B
#35-36 B, #45-46 B
19 mo, 19 mo
19 mo, 19 mo
N 19 mo Mx/Mn −1.23/−1.23
13. (M) 23 y 3 mo Osteomed (1.2 ∮,6 mm) #37 DB, #47 DB 21 mo, 21 mo N 21 mo Mn 0/−1.49
14. (M) 13 y 9 mo Osteomed (1.2 ∮,6 mm)
Dentos AN 12-204
#15-16 B, #25-26 B
#37 DB, #47 DB
17 mo, 17 mo
17 mo, 17 mo
N 17 mo Mx/Mn −5.36/−1.49
15. (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 mo
7 mo, 7 mo
Y (1 mo) Y (27 mo) 28 mo Mx/Mn −7.19/−9.50
16. (F) 12 y 9 mo Dentos SH 1312-107
Dentos SH 1312-106
#15-16 B, #25-26 B
#36-37 B, #46-47 B
18 mo, 21 mo
11 mo, 11 mo
N 30 mo Mx/Mn −1.43/−2.06
17. (F) 20 y 9 mo Dentos ATX 1311-107
Dentos AX 12-107
#15-16 B, #25-26 B
#36-37 B, #46-47 B
15 mo, 15 mo
14 mo, 14 mo
Y (2 mo) Y (12 mo) 15 mo Mx/Mn −1.11/−1.41
18. (F) 21 y 1 mo Dentos SH 1312-107 #15-16 B, #25-26 B 8 mo, 8 mo N 27 mo Mx −4.02/0
19. (F) 26 y 3 mo Dentos AX 1311-107
Dentos AX 1311-107
#15-16 B, #25-26 B
#36-37 B, #46-47 B
22 mo, 22 mo
15 mo, 19 mo
N Operculum 22 mo Mx/Mn −1.46/−6.60
20. (M) 16 y 11 mo Dentos SH 1311-107
Dentos AX 12-106
#15-16 B, #25-26 B
#35-36 B, #45-46 B
8 mo, 8 mo
23 mo, 23 mo
N 23 mo Mx/Mn −0.81/0.70
21. (M) 13 y 3 mo Dentos SH 1312-107
Dentos SH 1312-106
#15-16 B, #25-26 B
#36-37 B, #46-47 B
10 mo, 20 mo
13 mo, 13 mo
N Mild 34 mo (2 phase) 21 mo (fixed) Mx/Mn −3.0/−4.0
22. (F) 26 y 11 mo Dentos ATX 1311-107
Dentos AX 12-106
#16-17 P, #26-27 P
#36-37 B, #46-47 B
12 mo, 12 mo
13 mo, 13 mo
Y (1, 7 mo) Y (9, 6 mo) Mild 22 mo Mx/Mn −4.45/−2.3
23. (M) 30 y 2 mo Dentos ATX 1412-07
Dentos ATN 1312-05
#15-16 B, #25-26 B
#36-37 B, #46-47 B
25 mo, 25 mo
21 mo, 21 mo
Y (2 mo) Y (19 mo) 25 mo Mx/Mn 3.06/0

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

We used 70 microimplants (Absoancho, Dentos, Daegu, Korea) and 12 surgical microscrews (Osteomed, Dallas, Tex). In the maxilla, 32 microimplants were placed in the buccal alveolar bone between the second premolars and the first molars. Six microimplants were placed in the palatal slope between the first and second molars in 3 patients who were treated with lingual brackets. In the mandible, 14 microimplants were placed into the bone distobuccally to the mandibular second molars, 26 into the alveolar bone between the mandibular first and second molars, and 4 into the alveolar bone between the mandibular second premolar and the first molar. Detailed surgical procedures have already been discussed.

We used 0.022-in slot straight-wire brackets in all patients, and distalizing forces of approximately 200 g were applied from the maxillary and mandibular microimplants to the canines or premolars with nickel-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 distalizing the buccal teeth, the anterior teeth were aligned. During the initial alignment, the anterior teeth were ligated loosely to prevent forward movement. The archwires used during distalization were initially rectangular beta-titanium alloy and were switched to 0.016 × 0.022-in stainless steel in the maxilla and 0.017 × 0.025-in stainless steel in the mandible. After anterior teeth alignment, the 6 anterior teeth were tied together, and the distalizing force was applied to the canines or to the short anterior hooks attached between the lateral incisors and the canines. The directions of the applied forces were backward and upward in the maxillary arch, and backward and downward in the mandibular arch.

Fig 1
A, Initial leveling stage: to gain space for alignment of anterior teeth, distalizing force was applied to 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, schematic drawing of the whole dentition retraction.

All cephalograms were taken with the CX-90SP (Asahi, Kyoto, Japan) with 10% magnification. All pretreatment and posttreatment cephalograms were traced by 1 examiner (Y.-H.O.). The soft-tissue and skeletal measurements, dental angular measurements, and dental linear measurements are illustrated in Figures 2 through 4 .

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.

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

Fig 4
Cephalometric dental linear measurements. Horizontal 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 in the 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-first premolar centroid; 10 , MLC-first molar centroid; 11 , MLC-second molar centroid. Vertical measurements in the mandible: 12 , MP-incisor; 13 , MP-first premolar centroid; 14 , MP-first molar centroid; 15 , MP-second molar centroid.

When there was a double image, the midpoint between the 2 points was traced. The measurement points for the soft-tissue, skeletal, and maxillary dental linear and angular measurements were the same as used by Ghosh and Nanda. The centroid point, the midpoint on a horizontal line between the greatest mesial and distal convexity of the crowns, was used for dental linear measurements. To determine the amount of horizontal movement of maxillary teeth, the pterygoid vertical (PTV) plane was used. The vertical movement of the maxillary teeth was determined from superimposition on the palatal plane (PP). The horizontal movement of the mandibular teeth was determined by measuring and comparing the distance from the centroid point of the teeth to the mandibular lingual cortex (MLC), whereas the vertical measurements were determined from superimposition on the mandibular plane (MP). Angular changes of tooth positions were determined by the inclination of the long axes of the teeth to the sella-nasion plane (SN) in the maxillary arch and to the MP in the mandibular arch.

Arch length discrepancies and intermolar widths of the maxillary and mandibular arches that were distalized were measured before and after treatment on dental casts by using a digital caliper. The 3 lingual patients were removed from the sample when evaluating arch widths and rotation of the molars. To evaluate the rotation of the distalized molars, the transverse measurements were recorded between the buccal cusp tips of the maxillary and mandibular second premolars along with the mesiobuccal and distobuccal cusp tips of the first and second molars.

Statistical analysis

The statistical analyses were performed with SPSS software (version 14.0, SPSS, Chicago, Ill). A paired t test and a Wilcoxon signed rank test were used. When the sample showed normal distribution as evaluated by the Kolmogorov-Smirnov test, the P values of the paired t test were illustrated, unless the P values of the Wilcoxon signed rank test were illustrated.

Results

To calculate the error of measurements, 20 cephalometric films and models from 10 patients were retraced, redigitized, and remeasured 1 month later. Measurement errors were calculated based on the differences between the first and second values with a paired t test. There was no significant difference between the 2 measurements. To measure the range of methodologic errors, Dahlberg’s formula was used, and the results were 0.3° for angular measurements and 0.1 mm for linear measurements.

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

Table II
Descriptive statistics of cephalometric measurements at pretreatment, posttreatment, and pretreatment to posttreatment (n = 23)
Measurement Pretreatment Posttreatment Change Significance
Mean SD Mean SD Mean SD t W
Soft tissue
Upper 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 0.001
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 0.004
MP-L6 80.53 4.78 73.35 9.44 −7.18 8.12 <0.0001
MP-L7 81.71 8.49 72.93 10.10 −8.78 7.27 <0.0001
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 0.003
PTV-U6 23.33 3.12 21.59 3.36 −1.75 2.01 0.001
PTV-U7 12.58 2.85 10.93 3.83 −1.75 2.12 0.002
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 0.121
PP-U7 19.67 3.28 19.46 2.65 −0.22 2.54 0.111
MLC-L4 5.00 3.13 6.80 3.88 1.80 1.89 0.0002
MLC-L6 21.60 2.64 24.19 3.32 2.58 2.10 <0.0001
MLC-L7 33.94 3.18 35.78 3.47 1.84 1.99 <0.0001
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.

P <0.01.

The skeletal changes during treatment (before distalization to posttreatment) are summarized in Table II and showed that the Frankfort horizontal-mandibular plane angle (FMA) decreased with statistical significance. The other measurements were not statistically different. The distance of ANS-Me increased (0.66 mm), but it was not statistically significant. To preclude the effect of growth and to quantify the treatment effect only, the sample was divided into adult and growing groups. In the adults, the FMA decreased with statistical significance, 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-Me increased by 2.07 mm with statistical significance. In the adults, after the maxillary and mandibular dentitions were distalized, Points A and B moved posteriorly with statistical significance only for Point B ( Table III ).

Table III
Skeletal changes in adults vs growing patients
Measurement Pretreatment Posttreatment Change Significance
Mean SD Mean SD Mean SD t W
Adult patients (n = 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 0.006
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 = 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 0.008
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Apr 13, 2017 | Posted by in Orthodontics | Comments Off on Treatment effects of microimplant-aided sliding mechanics on distal retraction of posterior teeth
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