SUMMARY

BACKGROUND:

No randomized controlled trial has tried to compare treatment outcomes between the sliding en-masse retraction of upper anterior teeth supported by mini-implants and the two-step sliding retraction technique employing conventional anchorage devices.

OBJECTIVE:

To evaluate skeletal, dental, and soft tissue changes following anterior teeth retraction.

DESIGN AND SETTING:

Parallel-groups randomized controlled trial on patients with class II division 1 malocclusion treated at the University of Al-Baath Dental School in Hamah, Syria between July 2011 and May 2013.

PARTICIPANTS:

One hundred and thirty-three patients with an upper dentoalveolar protrusion were evaluated and 80 patients fulfilled the inclusion criteria. Randomization was performed using computer-generated tables; allocation was concealed using sequentially numbered opaque and sealed envelopes. Fifty-six participants were analysed (mean age 22.34±4.56 years). They were randomly distributed into two groups with 28 patients in each group (1:1 allocation ratio).

INTERVENTION:

Following first premolar extraction, space closure was accomplished using either the en-masse technique with mini-implants or the two-step technique with transpalatal arches (TPAs).

MAIN OUTCOME MEASURE:

The antero-posterior displacements of upper incisal edges and upper first molars were measured on lateral cephalograms at three assessment times. Assessor blinding was employed.

RESULTS:

A bodily retraction (−4.42mm; P < 0.001) with a slight intrusion (−1.53mm; P < 0.001) of the upper anterior teeth was achieved in the mini-implants group, whereas upper anterior teeth retraction was achieved by controlled palatal tipping in the TPA group.

CONCLUSIONS:

When retracting anterior teeth in patients with moderate to severe protrusion, the en-masse retraction based on mini-implants anchorage gave superior results compared to the two-step retraction based on conventional anchorage in terms of speed, dental changes, anchorage loss, and aesthetic outcomes.

Introduction

Camouflage treatment involves displacement of teeth relative to their supporting bone to compensate for an underlying jaw discrepancy (Profitt et al., 2007). Treatment of one-unit class II malocclusions by extracting two maxillary premolars requires anchorage to avoid mesial movement of the posterior segment during retraction of the anterior teeth (Kuroda et al., 2009). To address the problem of anchorage loss, many appliances and techniques have been devised: Nance holding arch, transpalatal bars, extraoral traction, and multiple teeth serving as one anchorage segment, anchorage preparation, and employing light forces (Renfroe, 1956). Recently, titanium-alloy mini-implants have been suggested as a source of skeletal orthodontic anchorage (Costa et al., 1998).

Various orthodontic techniques, such as sliding mechanics (Park and Kwon, 2004), frictionless loop mechanics (Chae, 2006), labial and lingual orthodontic appliances (Hong et al., 2005) were described to retract the anterior teeth. Closing extraction spaces using sliding mechanics can be performed by separating canine retraction and closing extraction space in two steps rather than one (Profitt et al., 2007), or by an en-masse retraction of anterior teeth with anchorage reinforcement (Root and Sagehorn, 1981).

With the emergence of mini-implants’ applications, many studies have been performed to investigate the efficacy of them as anchorage source for en-masse retraction of anterior teeth (Garfinkle et al., 2008; Upadhyay et al., 2008a,b; Yao et al., 2008; Kuroda et al., 2009; Liu et al., 2009), and many studies compared the treatment outcomes between them and traditional orthodontic mechanics such as headgear (Yao et al., 2008) or transpalatal arches (TPAs; Liu et al., 2009) during sliding en-masse retraction (Garfinkle et al., 2008; Upadhyay et al., 2008a,b; Yao et al., 2008; Kuroda et al., 2009; Liu et al., 2009), but up to date, no randomized controlled trial (RCT) has tried to compare between the sliding en-masse retraction supported by mini-implants as an anchorage device and the two-step sliding retraction techniques aided with traditional anchorage devices.

Over the last decade, increasing numbers of adults have become aware of the benefits orthodontic treatment (Sood, 2010). Achieving satisfactory functional occlusal outcomes and stable treatment results are not only the primary interests of orthodontists and their patients but also obtaining high-quality treatment and optimal aesthetic appearance with a short period of time have become important goals for every practitioner and patient.

The camouflage treatment of class II division 1 malocclusion using two-step retraction techniques employing sliding mechanics with TPAs as an anchorage tool is a treatment modality that is still used in the daily practice of orthodontics (Sharma et al., 2012). But there is no evidence-based answer to the question of the quality of the achieved results by this method compared to those obtained by sliding en-masse retraction supported by mini-implants anchorage. Therefore, the objectives of this RCT were to compare the skeletal, dental, and soft tissue treatment outcomes between sliding en-masse retraction of upper anterior teeth employing mini-implants and the two-step sliding retraction approach employing conventional anchorage in patients with class II division 1 malocclusion.

Materials and methods

Patients’ recruitment

This RCT was accomplished at the University of Al-Baath Dental School in Hamah, Syria (UBDS-1851PG), approved by the related local research ethics committee, and was funded by the University of Al-Baath Postgraduate Research Budget. Sample size was calculated using Minitab® Version 15 (Minitab Inc., State College, Pennsylvania, USA; Figure 1 with the calculation assumptions). Two primary outcome measures were used in these calculations: the displacement of the upper incisal edges and the upper first molars antero-posteriorly. The variance of these two measurements was obtained from a previous paper (Heo et al., 2007) and a sample size of eight patients for each group was required in relation to the horizontal movement of upper first molars and 27 patients for each group in relation to the horizontal movement of upper incisal edges. Therefore, the larger number was taken as our target size.

Figure 1

The assumptions for the calculation of sample size; U1-Dis: the upper central incisor displacement; SD, standard deviation.

Figure 1

The assumptions for the calculation of sample size; U1-Dis: the upper central incisor displacement; SD, standard deviation.

The inclusion criteria are illustrated in Supplementary Figure 1, available online. Fifty-six patients (35 females and 21 males) were included in this trial and their baseline sample characteristics are given in Table 1. Information sheets were given and their informed consents were obtained. A flow chart of recruitment and follow-up is given in Figure 2. Simple randomization was performed by one of the academic staff at the Department of Orthodontics (not involved in this research). He created a randomization list using Minitab® Version 15 with an allocation ratio of 1:1. The allocation sequence was concealed from the principal researcher (SA-S) enrolling and assessing participants in sequentially numbered opaque and sealed envelopes. To prevent subversion of the allocation sequence, the name and the date of birth of each participant was written on the envelope and these data were transferred onto the allocation card inside each envelope. Corresponding envelopes were opened only after completing all baseline assessments and the time came to allocate the intervention. The treatment plan of all patients in both groups involved extraction of the bilateral maxillary first premolars. MBT pre-adjusted appliances with slot size of 0.022″ × 0.028″ (RMO®, Denver, Colorado, USA) were bonded.

Table 1

Baseline sample characteristics. SD, standard deviation; T1, at the beginning of the treatment.

 Group A Group B 
Number of patients 28 28 
Gender distribution 19 females and 9 males 16 females and 12 males 
Protrusion of upper anterior teeth (moderate/ severe) 12/16 13/15 
Crowding (no/minimal) 7/21 11/17 
Facial divergence (normal/ hyperdivergent) 9/19 14/14 
Posterior crossbite (no/yes) 26/2 24/4 
Mean age at T1 (SD) 23.02 years (6.23 years) 20.46 years (4.84 years) 
 Group A Group B 
Number of patients 28 28 
Gender distribution 19 females and 9 males 16 females and 12 males 
Protrusion of upper anterior teeth (moderate/ severe) 12/16 13/15 
Crowding (no/minimal) 7/21 11/17 
Facial divergence (normal/ hyperdivergent) 9/19 14/14 
Posterior crossbite (no/yes) 26/2 24/4 
Mean age at T1 (SD) 23.02 years (6.23 years) 20.46 years (4.84 years) 
Figure 2

Patients’ recruitment, assignment, and follow-up flow diagram.

Figure 2

Patients’ recruitment, assignment, and follow-up flow diagram.

The mini-implants group: skeletal anchorage

Mini-implants group included 28 patients (19 females and 9 males). Intraoral periapical radiographs with metal guide bars were taken to identify the precise location for implant placement to avoid contact with dental roots (Supplementary Figure 2, available online). Self-drilling titanium mini-implants (1.6mm diameter and 7mm length; Dewimed®, Tuttlingen, Germany) were used. After administration of local anaesthesia, they were inserted between the maxillary second premolar and first molar at approximately 8–10mm above the archwires at the mucogingival junction and checked for primary stability (mechanical retention). Rectangular stainless steel archwires (0.019″ × 0.025″) with anterior 8mm height soldered hooks (True-chrome; RMO®) distal to the laterals were inserted and a 150g force was applied on each side using two elastic chains (Energy Chain Closed; RMO) attached between the mini-implants and the soldered hooks in a direction approximately parallel to the occlusal plane for conducting an en-masse retraction (Figure 3). Elastic chains were replaced every 3 weeks. Retraction was stopped when a class I canine relationship was achieved and a good incisor relationship was obtained.

Figure 3

Closed elastic power chain extending from the 8mm vertically oriented soldered hook to the mini-implant with a direction of force parallel to the occlusal plane.

Figure 3

Closed elastic power chain extending from the 8mm vertically oriented soldered hook to the mini-implant with a direction of force parallel to the occlusal plane.

The TPAs group: conventional anchorage

The TPAs group included 28 subjects (16 females and 12 males). Passive TPAs soldered to the upper molar bands (bent using 0.9mm stainless steel wire with the Coffin loop centred to the mid-palatal line and placed at about 1–2mm distant from the palate surface) were applied at the beginning of the treatment (Figure 4). Rectangular stainless steel archwires (0.019″ × 0.025″; True-chrome, RMO®) were inserted after levelling and alignment and canines were moved distally using closed elastic chains. After space closure or reaching a class I canine relationship, they were congregated with the posterior units to form one group and the anterior four incisor teeth were then sliding en-masse retracted (Figure 5). Patients were seen every 3 weeks until achieving a complete retraction of the four incisors or a good incisor relationship.

Figure 4

Passive transpalatal arches soldered to the upper molar bands.

Figure 4

Passive transpalatal arches soldered to the upper molar bands.

Figure 5

The anterior four incisor teeth were en-masse retracted after canine retraction.

Figure 5

The anterior four incisor teeth were en-masse retracted after canine retraction.

Cephalometric analysis and the primary outcome measures

Standardized lateral cephalometric radiographs were taken at three assessment times: T1, at the beginning of the treatment; T2, after levelling and alignment, and T3, after achieving a class I canine relationship and a good incisor relationship regardless of the molar relationship and any possible residual slight spaces distal to the canines. Dental measurements (linear and angular) are shown in Figures 6 and 7 and their definitions are given in Supplementary Table 1, available online. The primary outcome measures were the movement of the upper anterior teeth and the upper first molars along the mid-sagittal plane, whereas landmarks’ displacements in the vertical plane and skeletal and soft tissue variables were the secondary outcome measures in this study. To avoid assessment bias, a blinding procedure of the cephalograms was performed by professional Photoshop™ designer who familiarized herself with the appearance of TPAs, mini-implants, and soldered hooks on radiographs after a period of training and adaptation. Using Adobe Photoshop CS3 (Adobe systems Inc., Parc Ave, San Jose, California, USA), pre-designed templates representing the shape of mini-implants and soldered hooks were inserted into cephalograms of patients in the TPA group, whereas templates simulating the shape of TPAs were inserted into cephalograms of patients in the mini-implant group. The native resolution of images was not changed and care was given not to mask areas of important landmarks. Therefore, all radiographs had the three elements (TPAs, soldered hooks, and mini-implants) regardless to which group they belonged.

Figure 6

Angular measurements. 1, SNA; 2, SNB; 3, ANB; 4, SN-GoMe; 5, MM; 6, UI.SN; 7, LI.Go-Me; 8, IIA; 9, nasolabial angle. (See Supplementary Table 1, available online, for variables’ definitions).

Figure 6

Angular measurements. 1, SNA; 2, SNB; 3, ANB; 4, SN-GoMe; 5, MM; 6, UI.SN; 7, LI.Go-Me; 8, IIA; 9, nasolabial angle. (See Supplementary Table 1, available online, for variables’ definitions).

Figure 7

A horizontal plane (SN) was constructed by clockwise rotating of sella-nasion line 7°, and a line perpendicular to it through sella was constructed (S_vertical or Sv). 1, UIT-H; 2, UIT-V; 3, UIA-H; 4, UIA-V; 5, UCH-H; 6, UCH-V; 7, DUM-H; 8, DUM-V; 9, Ls-E line; 10, Li-E line.

Figure 7

A horizontal plane (SN) was constructed by clockwise rotating of sella-nasion line 7°, and a line perpendicular to it through sella was constructed (S_vertical or Sv). 1, UIT-H; 2, UIT-V; 3, UIA-H; 4, UIA-V; 5, UCH-H; 6, UCH-V; 7, DUM-H; 8, DUM-V; 9, Ls-E line; 10, Li-E line.

Digitisation, tracing, and analysis of the blinded radiographs were performed by the first author (SA-S). A co-ordinate system was constructed on the baseline radiographic cephalogram and was transferred to the T2 and T3 tracings (after software-based superimpositioning of T2 and T3 tracings on the T1 tracing using the anterior cranial base) in order to calculate landmarks’ displacements. Figure 7 shows the positions of these landmarks and the co-ordinate system used. A special cephalometric program Viewbox® (Version 4.0.0.98; dHAL Software, Kifissia, Greece( was used by the principal researcher (S.A-S), and data were exported as Excel files (Office Excel 2007; Microsoft Corporation, Redmond, Washington, USA) for further statistical analysis.

Statistical analysis

All statistical analyses were performed using the Minitab® 15 (Minitab Inc.). Anderson–Darling normality tests were performed to check the distribution of data, paired-sample t-tests or Wilcoxon matched-pairs signed-rank tests were used to evaluate intragroup changes, whereas two-sample t-tests or Mann–Whitney U-tests were used to examine intergroup differences.

Results

Error of the method and general parameters

The error of the method according to Dahlberg’s formula (Dahlberg, 1940) was minimal (Supplementary Table 2, available online). Measurements used were highly reliable and no systematic error was detected for all the variables [employing Houston’s recommendations for error assessment (1983); Supplementary Table 2, available online]. The mean treatment duration of the upper dental arches in the mini-implants group (from T1 to T3) was less than that of the TPA group (12.90 months and 16.97 months, respectively). During the retraction period, three mini-implants became loosened and 53 showed apparent stability throughout the treatment. Loosened implants were replaced in the neighbouring bone subsequently.

Descriptive statistics of all the measured variables at the three assessment times in both groups is given in Supplementary Table 3, available online. There was an overall (T3–T1) significant reduction in the SNA angle in the mini-implants group (−0.84 degrees; P = 0.001; Table 2) and the TPAs group (−0.80 degrees; P = 0.001; Table 3), whereas no significant change in the SNB angle was evident in both groups. Vertically, the SN-MP angle showed significant reduction in the TPAs group (−1.38 degrees), but no significant differences were detected in the mini-implants group. The overall changes in the MM angle were significant in both groups A and B (−1.32 degrees and −1.55 degrees, respectively; P < 0.001). Statistically significant reductions were observed in the mean face height index values during the retraction phase (T2–T3) in the mini-implants group (P = 0.023) and in the TPAs group (P = 0.003). Generally, no significant differences were detected intergroup for most of the skeletal variables at all assessment times (Table 4).

Table 2

Descriptive statistics of the observed changes between assessment times in group A and their statistical significance. SD, standard deviation.

Variable T2–T1 T3–T2 T3–T1 
Post-levelling changes only Retraction changes only Overall changes 
Mean SD P value Mean SD P value Mean SD P value 
SNA −0.46 0.94 0.112 −0.38 0.82 0.042* −0.84 0.77 0.001** 
SNB −0.49 1.52 0.205 0.08 0.91 0.732 −0.42 1.16 0.191 
ANB −0.01 1.25 0.702 −0.61 0.93 0.021* −0.62 1.19 0.056 
SN.GoMe −0.05 1.69 0.856 −0.35 1.47 0.220 −0.41 1.46 0.305 
MM −0.42 0.90 0.080 −0.90 0.84 0.001** −1.32 0.75 <0.001*** 
Bjork −0.58 1.39 0.121 −1.36 1.36 <0.001*** −1.94 1.27 <0.001*** 
UI.SN −3.07 3.31 <0.001*** −1.96 0.82 <0.001*** −5.03 3.39 <0.001*** 
LI.GoMe −0.13 1.22 0.507 −0.65 1.34 0.095 −0.78 1.26 0.023* 
IIA 2.52 1.97 <0.001*** 1.64 1.30 0.001** 4.16 2.29 <0.001*** 
F.H.I 0.03 1.65 0.920 −0.66 1.10 0.023* −0.63 1.42 0.095 
L.L.Esth −0.98 1.27 0.004** −1.52 1.72 0.002** −2.50 1.91 <0.001*** 
U.L.Esth −0.84 1.35 0.047* −2.14 0.76 <0.001*** −2.98 1.48 <0.001*** 
NasoLab 3.87 2.85 <0.001*** 5.22 3.38 <0.001*** 9.08 4.99 <0.001*** 
UIT_H −1.44 1.47 0.001** −4.48 1.28 <0.001*** −5.92 2.01 <0.001*** 
UIT_V −0.07 0.71 0.587 −1.46 0.71 <0.001*** −1.53 0.89 <0.001*** 
UIA_H −0.15 1.05 0.673 −4.42 1.53 <0.001*** −4.56 1.38 <0.001*** 
UIA_V 0.05 0.73 0.952 −1.21 0.87 0.001** −1.16 0.91 <0.001*** 
UCH_V −0.77 1.02 0.006** −0.42 1.53 0.142 −0.90 1.45 0.006** 
UCH_ H −0.48 1.16 0.095 −3.42 1.70 0.002** 23.70 1.60 0.002** 
DUM_H 0.14 0.61 0.615 −0.89 0.59 <0.001*** −0.75 0.63 0.001** 
DUM_V 0.27 0.73 0.131 −0.25 0.83 0.191 0.02 0.93 0.984 
Variable T2–T1 T3–T2 T3–T1 
Post-levelling changes only Retraction changes only Overall changes 
Mean SD P value Mean SD P value Mean SD P value 
SNA −0.46 0.94 0.112 −0.38 0.82 0.042* −0.84 0.77 0.001** 
SNB −0.49 1.52 0.205 0.08 0.91 0.732 −0.42 1.16 0.191 
ANB −0.01 1.25 0.702 −0.61 0.93 0.021* −0.62 1.19 0.056 
SN.GoMe −0.05 1.69 0.856 −0.35 1.47 0.220 −0.41 1.46 0.305 
MM −0.42 0.90 0.080 −0.90 0.84 0.001** −1.32 0.75 <0.001*** 
Bjork −0.58 1.39 0.121 −1.36 1.36 <0.001*** −1.94 1.27 <0.001*** 
UI.SN −3.07 3.31 <0.001*** −1.96 0.82 <0.001*** −5.03 3.39 <0.001*** 
LI.GoMe −0.13 1.22 0.507 −0.65 1.34 0.095 −0.78 1.26 0.023* 
IIA 2.52 1.97 <0.001*** 1.64 1.30 0.001** 4.16 2.29 <0.001*** 
F.H.I 0.03 1.65 0.920 −0.66 1.10 0.023* −0.63 1.42 0.095 
L.L.Esth −0.98 1.27 0.004** −1.52 1.72 0.002** −2.50 1.91 <0.001*** 
U.L.Esth −0.84 1.35 0.047* −2.14 0.76 <0.001*** −2.98 1.48 <0.001*** 
NasoLab 3.87 2.85 <0.001*** 5.22 3.38 <0.001*** 9.08 4.99 <0.001*** 
UIT_H −1.44 1.47 0.001** −4.48 1.28 <0.001*** −5.92 2.01 <0.001*** 
UIT_V −0.07 0.71 0.587 −1.46 0.71 <0.001*** −1.53 0.89 <0.001*** 
UIA_H −0.15 1.05 0.673 −4.42 1.53 <0.001*** −4.56 1.38 <0.001*** 
UIA_V 0.05 0.73 0.952 −1.21 0.87 0.001** −1.16 0.91 <0.001*** 
UCH_V −0.77 1.02 0.006** −0.42 1.53 0.142 −0.90 1.45 0.006** 
UCH_ H −0.48 1.16 0.095 −3.42 1.70 0.002** 23.70 1.60 0.002** 
DUM_H 0.14 0.61 0.615 −0.89 0.59 <0.001*** −0.75 0.63 0.001** 
DUM_V 0.27 0.73 0.131 −0.25 0.83 0.191 0.02 0.93 0.984 

Variable definitions are given in Supplementary Table 1, available online.

Employing paired t-tests (or Wilcoxon matched-pairs signed-rank tests when appropriate).

*P<0.05;**P<0.01;***P<0.001

Table 3

Descriptive statistics of the observed changes between assessment times in group B and their statistical significance. SD, standard deviation.

Variable T2–T1 T3–T2 T3–T1 
Post-levelling changes only Retraction changes only Overall changes 
Mean SD P value Mean SD P value Mean SD P value 
SNA −0.26 0.64 0.131 −0.54 0.74 0.009** −0.80 0.93 0.001** 
SNB −0.15 0.54 0.205 0.08 0.45 0.409 −0.07 0.68 0.732 
ANB −0.25 0.73 0.178 −0.50 0.66 0.005** −0.75 1.02 0.055 
SN.GoMe −0.68 1.12 0.056 −0.70 0.67 0.001** −1.38 1.25 <0.001*** 
MM −0.24 0.91 0.481 −1.32 0.57 <0.001*** −1.55 1.01 <0.001*** 
Bjork −0.80 0.95 0.005** −2.20 1.26 <0.001*** −2.99 1.60 <0.001*** 
UI.SN −2.25 1.88 0.001** −5.70 2.28 <0.001*** −7.94 2.51 <0.001*** 
LI.GoMe 0.21 1.78 0.286 0.08 1.17 0.365 0.30 1.47 0.051 
IIA 2.58 2.03 0.001** 4.76 1.25 <0.001*** 7.34 2.02 <0.001*** 
F.H.I 0.17 1.22 0.920 −0.74 0.77 0.003** −0.57 1.62 0.103 
L.L.Esth −0.75 0.97 0.009** −1.07 1.07 0.001** −1.42 1.52 0.001** 
U.L.Esth −0.78 1.01 0.004** −1.69 1.47 <0.001*** −2.47 1.79 <0.001*** 
NasoLab 2.00 2.69 0.005** 3.93 2.11 <0.001*** 5.93 3.57 <0.001*** 
UIT_H −1.31 1.04 <0.001*** −3.48 2.51 <0.001*** −4.79 2.34 <0.001*** 
UIT_V 0.28 0.80 0.220 0.64 0.57 0.001** 0.92 1.05 0.001** 
UIA_H 0.47 1.38 0.165 −0.76 1.70 0.073 −0.29 1.80 0.433 
UIA_V 0.27 0.87 0.344 0.62 0.62 0.002** 0.89 0.74 <0.001*** 
UCH_V −0.49 0.88 0.073 −0.18 0.72 0.344 −0.67 0.93 0.023* 
UCH_ H −0.44 1.34 0.121 −2.88 1.05 <0.001*** −3.32 1.23 <0.001*** 
DUM_H 0.26 0.06 0.120 1.50 1.25 0.001** 1.76 1.01 <0.001*** 
DUM_V 0.32 0.80 0.052 0.06 0.68 0.825 0.38 0.74 0.009** 
Variable T2–T1 T3–T2 T3–T1 
Post-levelling changes only Retraction changes only Overall changes 
Mean SD P value Mean SD P value Mean SD P value 
SNA −0.26 0.64 0.131 −0.54 0.74 0.009** −0.80 0.93 0.001** 
SNB −0.15 0.54 0.205 0.08 0.45 0.409 −0.07 0.68 0.732 
ANB −0.25 0.73 0.178 −0.50 0.66 0.005** −0.75 1.02 0.055 
SN.GoMe −0.68 1.12 0.056 −0.70 0.67 0.001** −1.38 1.25 <0.001*** 
MM −0.24 0.91 0.481 −1.32 0.57 <0.001*** −1.55 1.01 <0.001*** 
Bjork −0.80 0.95 0.005** −2.20 1.26 <0.001*** −2.99 1.60 <0.001*** 
UI.SN −2.25 1.88 0.001** −5.70 2.28 <0.001*** −7.94 2.51 <0.001*** 
LI.GoMe 0.21 1.78 0.286 0.08 1.17 0.365 0.30 1.47 0.051 
IIA 2.58 2.03 0.001** 4.76 1.25 <0.001*** 7.34 2.02 <0.001*** 
F.H.I 0.17 1.22 0.920 −0.74 0.77 0.003** −0.57 1.62 0.103 
L.L.Esth −0.75 0.97 0.009** −1.07 1.07 0.001** −1.42 1.52 0.001** 
U.L.Esth −0.78 1.01 0.004** −1.69 1.47 <0.001*** −2.47 1.79 <0.001*** 
NasoLab 2.00 2.69 0.005** 3.93 2.11 <0.001*** 5.93 3.57 <0.001*** 
UIT_H −1.31 1.04 <0.001*** −3.48 2.51 <0.001*** −4.79 2.34 <0.001*** 
UIT_V 0.28 0.80 0.220 0.64 0.57 0.001** 0.92 1.05 0.001** 
UIA_H 0.47 1.38 0.165 −0.76 1.70 0.073 −0.29 1.80 0.433 
UIA_V 0.27 0.87 0.344 0.62 0.62 0.002** 0.89 0.74 <0.001*** 
UCH_V −0.49 0.88 0.073 −0.18 0.72 0.344 −0.67 0.93 0.023* 
UCH_ H −0.44 1.34 0.121 −2.88 1.05 <0.001*** −3.32 1.23 <0.001*** 
DUM_H 0.26 0.06 0.120 1.50 1.25 0.001** 1.76 1.01 <0.001*** 
DUM_V 0.32 0.80 0.052 0.06 0.68 0.825 0.38 0.74 0.009** 

Variable definitions are given in Supplementary Table 1, available online.

Employing paired t-tests (or Wilcoxon matched-pairs signed-rank tests when appropriate).

*P<0.05;**P<0.01;***P<0.001

Table 4

P values of significance tests of the observed changes between the two groups.

Variable Group A versus group B 
T2–T1 T3–T2 T3–T1 
Post-levelling changes only Retraction changes only Overall changes 
P values P values P values 
SNA 0.838 0.448 0.579 
SNB 0.748 1.000 0.293 
ANB 0.466 0.793 0.683 
SN.GoMe 0.170 0.381 0.056 
MM 0.640 0.199 0.884 
Bjork 0.502 0.025* 0.051 
UI.SN 0.977 <0.001*** <0.001*** 
LI.GoMe 0.170 0.381 0.061 
IIA 0.977 <0.001*** <0.001*** 
F.H.I 0.977 0.759 0.930 
L.L.Esth 0.381 0.661 0.058 
U.L.Esth 0.748 0.080 0.307 
NasoLab 0.036* 0.321 0.062 
UIT_H 0.953 0.009** 0.008** 
UIT_V 0.179 <0.001*** <0.001*** 
UIA_H 0.189 <0.001*** <0.001*** 
UIA_V 0.521 <0.001*** <0.001*** 
UCH_V 0.815 0.335 0.540 
UCH_ H 0.466 0.502 0.108 
DUM_H 0.053 <0.001*** <0.001*** 
DUM_V 0.414 0.231 0.044* 
Variable Group A versus group B 
T2–T1 T3–T2 T3–T1 
Post-levelling changes only Retraction changes only Overall changes 
P values P values P values 
SNA 0.838 0.448 0.579 
SNB 0.748 1.000 0.293 
ANB 0.466 0.793 0.683 
SN.GoMe 0.170 0.381 0.056 
MM 0.640 0.199 0.884 
Bjork 0.502 0.025* 0.051 
UI.SN 0.977 <0.001*** <0.001*** 
LI.GoMe 0.170 0.381 0.061 
IIA 0.977 <0.001*** <0.001*** 
F.H.I 0.977 0.759 0.930 
L.L.Esth 0.381 0.661 0.058 
U.L.Esth 0.748 0.080 0.307 
NasoLab 0.036* 0.321 0.062 
UIT_H 0.953 0.009** 0.008** 
UIT_V 0.179 <0.001*** <0.001*** 
UIA_H 0.189 <0.001*** <0.001*** 
UIA_V 0.521 <0.001*** <0.001*** 
UCH_V 0.815 0.335 0.540 
UCH_ H 0.466 0.502 0.108 
DUM_H 0.053 <0.001*** <0.001*** 
DUM_V 0.414 0.231 0.044* 

Variable definitions are given in Supplementary Table 1, available online.

Employing two-sample t-tests (or Mann–Whitney U-tests when appropriate).

*P<0.05;**P<0.01;***P<0.001

The upper incisor edges were significantly retracted and intruded in the mini-implants group (−5.92mm and −1.53mm; P < 0.001, respectively; Table 2), but they were significantly retracted and extruded in the TPAs group [−4.79mm (P < 0.001) and 0.92mm (P = 0.001), respectively; Table 3]. Significant differences were found intergroup at T2 and T3 (P = 0.009 and P = 0.008, respectively; Table 4).The upper incisor apices were retracted and intruded significantly in the mini-implants group (−4.56mm and −1.16mm; P < 0.001), whereas they did not show any significant change in the TPAs group.

The upper molars were significantly distilised a mean of 0.89mm following retraction in the mini-implants group, whereas there was a significant forward displacement of upper molars in the TPAs group (1.50mm). Significant molar extrusion was detected in the TPAs group at T3 (P = 0.009). There was a statistically significant backward retraction of the upper and lower lips in both groups (−2.98mm and −2.47mm upper lip retraction in groups A and B, respectively). In general, changes in soft tissues were more prominent in the mini-implants group than in the TPAs group.

Discussion

The mini-implants behaved in this study as ankylosed teeth providing not only an absolute anchorage but also a statistically significant distal movement (0.89mm) of the upper molars as a result of the retraction force applied to anterior teeth, which was translated to posterior teeth through interdental contacts; a finding documented in other published papers (Upadhyay et al., 2008a,b; Liu et al., 2009). Surprisingly, some papers reported a mesial movement of the upper molars despite the use of mini-implants as an anchorage tool (Yao et al., 2008; Kim et al., 2009; Kuroda et al., 2009). This may be due to the physiological mesial movement that occurred after early extraction of the upper first premolars at the beginning of the treatment with a delayed initiation of the retraction process (Yao et al., 2008; Kuroda et al., 2009), or due to the use of retraction utility archwires directly supported by mini-implants without engaging the upper molars in active treatment (Kim et al., 2009). The picture of posterior teeth behaviour would logically be different if an indirect molar anchorage was employed by tightening a ligature wire between the molar tubes and mini-implants’ exposed heads. This kind of indirect anchorage requires further exploration.

The TPA did not significantly enhance orthodontic anchorage in this study despite retracting anterior teeth in two stages. This goes in line with the concept that TPAs are secondary means of anchorage and cannot be employed in cases with maximum anchorage requirements such as severe crowding or protrusion. In this study, evaluation of anchorage loss could have been accomplished using TPAs with an en-masse retraction of the upper anterior six teeth as has been performed by Liu et al. (2009) who found a mean of 1.47mm anchorage loss, but a decision was made in this study to avoid en-masse retraction of anterior six teeth and employ a two-step sliding mechanism hoping to reduce anchorage needs and obtain a molar movement similar to what would be expected in the mini-implants group. However, this was not achieved and a mean value of 1.50mm of anchorage loss was detected in this study.

This RCT is similar to that of Sharma et al. (2012) in which a comparison was made between mini-implants and TPAs as anchorage devices in relation to dental movements following retraction. However, their RCT included an evaluation of only canine retraction, whereas the complete picture of the whole upper anterior teeth retraction is presented in this paper. Sharma et al. (2012) found no movement of molars in the mini-implants group and a mean of 2.48±0.71mm mesial movement in the TPA group, whereas this RCT showed a distal movement of molars with mini-implants and a less anchorage loss with TPAs. This study is different from those two published RCTs by Upadhyay et al. (2008a,b) in that a comparison was made in our research work between the en-masse retraction of anterior teeth and the two-step retraction technique, whereas Upadhyay’s RCTs did not consider the two-step retraction results at all.

The findings of this RCT cannot be directly compared with those obtained by Xu et al. (2010) although their RCT evaluated the relative effectiveness of anchorage conservation between the en-masse and the two-step retraction techniques in cases with maximum anchorage requirements. The whole study design and many minor technical details are different between the two RCTs: (1) we employed mini-implants as an anchorage device for the en-masse retraction group and TPAs for two-step retraction group, whereas they used the different types of headgear with or without TPAs as anchorage devices for both groups, (2) the choice of tooth extraction was standardized for all patients in our study, whereas their extraction decisions were variable, (3) we included patients with moderate to severe dentoalveolar protrusion, whereas Xu’s RCT included only severe cases, (4) we did not employ lacebacks to initiate or control canine retraction either in the one-step or two-step retraction approaches, whereas they surprisingly used lacebacks to perform partial or even complete retraction of canines in their groups (Xu et al., 2010). Therefore, we believe that this study design presented and compared two treatment scenarios that were closer the real daily practice of orthodontics in patients with dentoalveolar protrusion than those proposed by Xu et al. (2010).

Sliding mechanics using mini-implants anchorage with a horizontal force axis located at 8mm above the archwire resulted in a mean of 4.5mm of translational backward movement of upper incisors. This is due to the passing of the applied force axis close to the centre of resistance of the maxillary anterior teeth, which is impossible to achieve when the force axis passes along the basic archwire as observed in the TPA group. In the TPA group, the upper incisor edges were retracted a mean of 5mm approximately, whereas their apices did not show any significant change. Therefore, upper incisors had primarily controlled palatal tipping with no bodily movement. These results agree with those of the conventional anchorage group in the study of Lee and Kim (2011) in which headgears and TPAs had been used as anchorage devices and Upadhyay et al. (2008b) study in which many types of conventional anchorage reinforcement that best suited patients’ needs had been used.

The amount of translational movement of the upper incisors varies between the studies that employed mini-implants as anchorage devices during en-masse retraction. Park and Kwon (2004) achieved up to 7mm of bodily retraction, whereas Yao et al. (2008) reported that greater translational movement than controlled tipping was observed in their mini-implants group. In this study, about 4.5mm of bodily retraction was achieved, whereas only about 1.0mm of bodily retraction was reported in the study of Upadhyay et al. (2008b) and this might be explained by their use of 0.017″ × 0.025″ stainless steel archwires in 0.022″ bracket-slots, which had made torque control difficult during retraction (Upadhyay et al., 2008b).

The upper incisor edges and apices were significantly intruded in the mini-implants group (−1.53mm and −1.16mm, respectively), this is due to the position of mini-implant at 8–10mm apical to the bracket slot with the anterior hooks placed at 8mm gingival to the bracket slot, whereas the upper incisor edges and apices were significantly extruded in TPA group (0.92mm and 0.89mm, respectively). The study revealed that the upper incisor axis showed an optimal inclination of 102.20±2.91 degrees with the anterior cranial base at the end of retraction stage in the mini-implants group, whereas they were palatally tipped in the TPA group (a mean of 97.79±1.45 degrees). In other words, the first approach resulted in a better incisal inclination, which is one of the difficult treatment goals in conventional camouflage corrections (Park et al., 2008).

In terms of soft tissues changes, it has been suggested that the way of anchorage management determines the magnitude of anterior dental retraction and the resulting change in lip position (Burstone, 1982). Since the upper incisors moved more distally in the mini-implants group, upper and lower lips were retracted and the nasolabial angle increased to a greater extent in the mini-implants group than in the TPA group. These results are similar to those published by Upadhyay et al. (2008a) and Liu et al. (2009).

It seems to be that en-masse retraction with mini-implants not only eases the biomechanics involved but also controls the antero-posterior and vertical movements of the anterior and posterior teeth due to the possibility of passing the force axis close to the centre of resistance of the maxillary anterior teeth. Avoidance of disto-palatal rotations and distal tipping of retracted canines, and eliminating the appearance of unsightly spaces distal to the lateral incisors following canine retraction make the en-masse retraction more favourable than the two-step retraction approach to both orthodontists and patients. Treatment with mini-implants enables the orthodontist to avoid using molar bands and replace them with molar tubes, and saves the time required for laboratory work to fabricate the TPAs. Another shortcoming of the two-step technique compared to the en-masse technique is that the last technique shortens the treatment duration significantly and enables the patients to observe a significant improvement during a short time; this is expected to enhance patient cooperation and motivation.

Finally, this report raises some findings that enable us to consider the en-masse retraction with sliding techniques and mini-implants anchorage a better alternative to the conventional two-step retraction with TPA anchorage and may be a better choice when planning an extraction-based treatment for patients with moderate to severe upper dentoalveolar protrusion.

Conclusions

When retracting upper anterior teeth in patients with moderate to severe protrusion, the en-masse retraction based on mini-implants anchorage gave superior results compared to the two-step retraction based on conventional anchorage in terms of speed, anterior and posterior dental changes, anchorage loss, and aesthetic outcomes.

Supplementary material

Supplementary material is available at European Journal of Orthodontics online.

Funding

The University of Al-Baath Postgraduate Research Budget (71901200984DEN)

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Supplementary data