ORIGINAL ARTICLE
Differences of treatment outcomes between self-ligating brackets with microimplant and headgear anchorages in adults with bimaxillary protrusion Mu Chen,a Zheng-Ming Li,a Xue Liu,b Bin Cai,c Da-Wei Wang,d and Zhi-Cai Fenge Shenzhen, Guangdong, and Guangzhou, China
Introduction: Our aim was to determine differences between the outcomes of treatment using microimplant anchorage compared with headgear anchorage in adult patients with bimaxillary protrusion treated with self-ligating brackets. Methods: Thirty-one adult orthodontic patients (13 men, 18 women; age, 25.87 6 3.37 years) who were diagnosed with bimaxillary protrusion were selected. All patients were treated with self-ligating brackets and maximum anchorage after extraction of 4 first premolars. Group 1 received microimplant anchorage, and group 2 received headgear. Lateral cephalometric radiographs were obtained before and after treatment. Differences in the skeletal and dental parameters between and within groups were analyzed. Results: No significant difference was observed in the mean treatment times between the groups (21.93 6 3.10 vs 23.88 6 2.68 months). There was no significant difference in skeletal measurements before or after treatment in patients who received microimplant anchorage. Patients who received headgear anchorage had an increase of the mandibular plane angle. The microimplant anchorage group had greater anterior tooth retraction and less maxillary molar mesialization than did the headgear group. Conclusions: In both the anteroposterior and vertical directions, microimplant anchorage achieved better control than did the traditional headgear appliance during the treatment of bimaxillary protrusion. (Am J Orthod Dentofacial Orthop 2015;147:465-71)
a Associate professor, Department of Stomatology, Nanshan Affiliated Hospital of Guangdong Medical College, Shenzhen, Guangdong, China. b Professor, Department of Stomatology, Nanshan Affiliated Hospital of Guangdong Medical College, Shenzhen, Guangdong, China. c Associate professor, Department of Orthodontics, Guanghua School of Stomatology and Institute of Stomarological Research, Sun Yat-sen University, Guangzhou, China. d Professor, Department of Orthodontics, Guanghua School of Stomatology and Institute of Stomarological Research, Sun Yat-sen University, Guangzhou, China. e Attending physician, Department of Orthodontics, Guanghua School of Stomatology and Institute of Stomarological Research, Sun Yat-sen University, Guangzhou, China. Mu Chen and Zheng-Ming Li are joint first authors and contributed equally to this work. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Partially supported by grants from the Project of the National Natural Science Foundation of China (number 81300862), the Project of Health and Family Planning Commission of Shenzhen Municipality (number 201302202), and the Project of Science and Technology Innovation Commission of Nanshan Municipality (number 2012040). Address correspondence to: Xue Liu, Department of Stomatology, Nanshan Affiliated Hospital of Guangdong Medical College, Shenzhen, 89#Taoyuan Lu, Nanshan District, Shenzhen, Guangdong 518052, PR China; e-mail, [email protected]. Submitted, September 2014; revised and accepted, November 2014. 0889-5406/$36.00 Copyright Ó 2015 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2014.11.029
B
imaxillary protrusion is a condition characterized by protrusive and proclined maxillary and mandibular incisors, and increased procumbency of the lips. It is seen commonly in African-American and Asian populations.1 In bimaxillary protrusion patients, the major orthodontic treatment goal includes retraction and retroclination of the maxillary and mandibular incisors with a resultant decrease in soft tissue procumbency.2 It is rather well accepted by clinicians that extraction of the 4 first premolars followed by retraction of the anterior teeth with maximum anchorage mechanics can be effective in the treatment of bimaxillary protrusion. Maximum anchorage to prevent forward movement of the maxillary posterior teeth during anterior tooth retraction can be provided with different approaches. Extraoral headgear appliances are commonly used to reinforce posterior anchorage during anterior tooth retraction or are directly applied to retract anterior teeth.3 However, wearing headgear full time is too demanding for most patients, and thus some anchorage loss and mesial movement of the maxillary molars are 465
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usually observed. Patient cooperation is an important factor for the effectiveness of extraoral appliances. Microimplants are increasingly used as orthodontic anchorage sources. It has been reported that implant anchorage can provide stable bony anchorage and overcome problems of anchorage loss during extraction space closure, which usually occurs with traditional anchorage preparations. Application of implant anchorage also makes teeth move more efficiently, without depending on patient cooperation in wearing an extraoral appliance, and consequently reducing treatment duration. However, in the treatment of bimaxillary protrusion in adults, only a few studies to date have statistically investigated the effectiveness of the implant anchorage system, with little statistical evaluation of the treatment effects of the implant anchorage system compared with the effects of headgear.4 Orthodontics, just as any other science, has undergone advances in technology that aim to improve treatment efficacy with a view to reducing treatment time, providing patients with comfort and achieving the expected, yet rarely obtained, long-term stability. Recently, there has been increased use of the self-ligating brackets (SLBs) in orthodontic clinics worldwide. SLBs are popular in orthodontics because of their proposed superior properties including low static frictional resistance, full and stable archwire engagement, improved oral hygiene, preserved anchorage, reduced chair time and therapeutic time, and prolonged therapeutic intervals. Several researchers compared therapeutic efficiency, friction, speed of archwire changes, therapeutic time, and initial alignment of the mandibular arch between self-ligating and conventional brackets.5-10 Although more patients were treated with SLBs, there is little research about whether there are significant clinical differences between microimplant anchorage and headgear anchorage in patients with bimaxillary protrusion malocclusion treated with SLBs. The objective of this study was to assess, in adults with bimaxillary protrusion, the effectiveness of orthodontic anchorage when using either microimplants or extraoral headgear with the SLB system. MATERIAL AND METHODS
Ethical approval was obtained from the ethics committee of the Guanghua College of Stomatology in China. A letter was sent to the subjects to seek consent for their participation in the study. This letter also informed them about the examination procedures and assured them of confidentiality of any information collected. Only patients who actively consented were included. A consecutive sample of adults seeking orthodontic care at a state-funded hospital clinic was recruited. We
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excluded those who lacked the data required for our research, missed 3 or more appointments, and had unclear pretreatment or posttreatment lateral cephalograms. Patients were diagnosed with bimaxillary protrusion based on cephalometric evaluations and study models, which required the extraction of 4 first premolars and maximum anchorage to obtain a satisfactory treatment. They were divided into 2 groups according to the type of anchorage preparation. The choice of microimplant or headgear anchorage was made by each patient according to his or her own judgment on compliance, because both modes of anchorage preparation were available. In group 1 (15 patients; 6 men, 9 women; age, 26.53 6 3.54 years), titanium microimplants were used for anchorage. Each patient received implantation of microimplants on the buccal aspect of the bilateral maxillary posterior teeth. After administration of local anesthesia, OrthoEasy (Forestadent, Pforzheim, Germany) orthodontic microimplants (length, 9.0 mm; diameter, 1.6 mm) were placed between the maxillary second premolars and the first molars without flap elevation at the apical level. In group 2 (16 patients; 7 men, 9 women; age, 25.25 6 3.19 years), the patients received traditional anchorage preparation with a headgear appliance (Shinye Odontological Materials, Hangzhou, China). The force level exerted by the headgear was 300 to 350 g. The directional pull of the headgear was adjusted according to the mandibular plane angle. All subjects received passive SLBs (Forestadent) brackets. In both groups, nickel-titanium wires for aligning and leveling were used with the same sequence of archwires beginning with 0.014-in, 0.016-in, and 0.018-in, until a 0.018 3 0.025-in base archwire was inserted. In both groups with either traditional extraoral anchorage or microimplant anchorage, the extraction space was closed by sliding mechanics with en-masse retraction after partial canine distalization to resolve the anterior crowding and to achieve good alignment of the 6 anterior teeth. All treatments and anchorage preparations were conducted after obtaining the patient's informed consent. Treatment procedures were taught and monitored by 1 clinical instructor (D.-W.W.) so that consistent mechanical principles were maintained. Lateral cephalometric radiographs were taken immediately before and after treatment for all subjects. Tracing, superimposition, and measurement were undertaken manually by 2 examiners (M.C., Z.-C.F.). Bilateral structures were bisected, and their midsagittal points were identified. The cephalometric parameters, including 8 skeletal measurements and 7 dental measurements used in this study, are shown diagrammatically according to the study of Yao et al2 (Fig 1).
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Fig 1. Skeletal and dentoalveolar measurements of the lateral cephalometric analysis: 1, SNA; 2, SNB; 3, ANB; 4, A-Nv; 5, Pog-Nv; 6, NAPog; 7, SN-OP; 8, SN-MP; 9, UI-SN; 10, UI-NPog; 11, U1-FH (distance of the maxillary central incisal edge relative to the Frankfort horizontal plane); 12, M-FH (distance of the mesiobuccal cusp tip of the first molar relative to the Frankfort horizontal plane); 13, AA0 (projection of Point A on the Frankfort horizontal plane); 14, UU0 ; 15, MM0 . Statistical analysis
Descriptive and analytical statistical analyses were performed with the Statistical Package for the Social Sciences (version 15.0; SPSS, Chicago, Ill) for Windows. To assess intraexaminer and interexaminer reliabilities, the cephalometric radiographs were retraced and remeasured by the same 2 examiners after a period of 3 months. The results of the analysis indicated no statistically significant differences between the original and repeated measurements at the 0.05 level. Statistical analysis was undertaken to determine whether any significant differences existed between groups 1 and 2 before treatment. For the microimplant and headgear groups, the means and standard deviations of the pretreatment and posttreatment cephalometric measurements were calculated and compared using pairedsamples t tests. Differences in treatment changes between the 2 groups were evaluated with the independent-samples t test. A P value less than 0.05 was considered statistically significant.
Table I. Comparison of cephalometric measurements
before treatment between group 1 (microimplant anchorage) and group 2 (headgear anchorage) Group 1
Age (y) Treatment duration (mo) Sex (male/female) Skeletal measurements SNA ( ) SNB ( ) ANB ( ) A-Nv (mm) Pog-Nv (mm) NAPog ( ) SN-OP ( ) SN-MP ( ) Dental measurements U1-SN ( ) U1-NPog (mm) U1-FH (mm) MFH (mm)
Group 2
Mean 26.53 21.93 6/9
SD 3.54 3.10
Mean 25.25 23.88 7/9
SD 3.19 2.68
P 0.30 0.07
81.53 78.60 2.93 0.83 12.94 11.00 17.10 33.60
2.70 3.09 2.52 0.20 2.04 2.04 3.69 5.45
80.31 78.19 2.13 1.00 12.09 9.75 17.56 34.75
3.20 1.80 2.47 0.37 2.09 2.07 3.43 6.38
0.26 0.65 0.38 0.13 0.26 0.10 0.72 0.60
113.27 17.93 60.33 51.30
5.70 3.99 4.19 3.00
117.13 19.00 63.06 53.19
5.40 3.69 3.60 2.64
0.06 0.45 0.06 0.07
RESULTS
No significant differences were found for any measurements before treatment in either group (Table I). The mean treatment duration of the microimplant group (21.93 6 3.10 months) was less than that of the headgear group (23.88 6 2.68 months). However, the difference did not reach statistical significance (P 5 0.07).
The original dentofacial characteristics and treatment changes measured from the paired pretreatment and posttreatment cephalograms of the 2 groups are shown in Table II. There were no significant differences in the skeletal measurements before or after treatment in group 1. In the dental measurements, the mean
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Table II. Comparisons of treatment changes in the microimplant and headgear groups Microimplant group Pretreatment Mean Skeletal measurements 81.53 SNA ( ) SNB ( ) 78.60 ANB ( ) 2.93 A-Nv (mm) 0.83 Pog-Nv (mm) 12.94 NAPog ( ) 11.00 SN-OP ( ) 17.10 33.60 SN-MP ( ) Dental measurements U1-SN ( ) 113.27 U1-NPog (mm) 17.93 U1-FH (mm) 60.33 MFH (mm) 51.30 AA0 (mm) UU0 (mm) MM0 (mm)
Posttreatment
Headgear group Difference
Pretreatment
Posttreatment
Difference
SD
Mean
SD
Mean
SD
P
Mean
SD
Mean
SD
Mean
SD
P
2.70 3.09 2.52 0.20 2.04 2.04 3.69 5.45
81.33 78.47 2.87 0.91 12.92 10.80 17.37 33.33
2.74 3.04 2.39 0.30 2.05 2.28 3.74 5.56
0.20 0.13 0.07 0.07 0.02 0.20 0.27 0.27
0.41 0.35 0.46 0.18 0.08 0.77 0.59 0.59
0.08 0.16 0.58 0.13 0.33 0.33 0.10 0.10
80.31 78.19 2.13 1.00 12.09 9.75 17.56 34.75
3.20 1.80 2.47 0.37 2.09 2.07 3.44 6.38
80.06 78.00 2.06 1.03 12.19 10.17 18.06 35.94
2.95 1.79 2.43 0.35 2.05 1.93 3.80 6.81
0.25 0.19 0.06 0.03 0.09 0.42 0.50 1.19
0.58 0.66 0.44 0.07 0.20 0.93 1.03 1.33
0.10 0.27 0.58 0.10 0.08 0.09 0.07 0.00*
5.70 3.99 4.19 3.00
101.40 9.57 60.20 51.20
5.77 3.13 4.16 3.08
11.87 8.37 0.13 0.10 0.27 10.27 0.87
1.51 1.96 0.52 0.21 0.55 3.51 1.46
0.00* 0.00* 0.33 0.08 0.08 0.00* 0.04*
117.13 19.00 63.06 53.19
5.40 3.69 3.60 2.64
106.00 12.38 63.25 53.25
5.11 2.78 3.82 2.77
11.13 6.63 0.19 0.06 0.22 6.88 2.19
1.82 2.55 0.54 0.31 0.54 2.55 1.68
0.00* 0.00* 0.19 0.43 0.13 0.00* 0.00*
Based on paired t tests: *P \0.05.
decreases were 11.87 in the proclination of the maxillary incisor (U1-SN angle) and 8.37 mm in the sagittal measurements of U1 (U1-NPog distance) (P \0.01). The tip of the maxillary incisor (UU0 ) was retracted by 10.27 mm (P \0.01), and mesial movement of the maxillary first molar (MM0 ) was 0.87 mm (P \0.05). In group 2, the SN-MP angle was significantly increased (1.19 , P \0.01) after treatment, but there were no significant treatment changes of other skeletal measurements. In dental measurements, the maxillary incisors were retroclined by a mean of 11.13 (U1-SN angle) and retracted by a mean of 6.63 mm (U1-NPog), whereas the tip of the maxillary incisor was retracted by 6.88 mm, and mesial movement of the maxillary first molar was 2.19 mm (P \0.01). To determine the statistical significance of these differences between anchorage systems, treatment changes of both groups were listed and compared using the independent-samples t test (Table III). Statistically significant differences were noted in the following measurements: SN-MP, U1-NPog, UU0 , and MM0 (P \0.05). Opening rotation of the mandible was observed in the headgear group because of the increase of the mandibular plane angle. Furthermore, the microimplant group had greater correction of maxillary incisor protrusion (U1-NPog and UU0 ) and less mesial movement of the maxillary first molar than did the headgear group.
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DISCUSSION
Adults who seek orthodontic treatment often desire that it be completed in as short a period as possible. At present, however, adults with bimaxillary protrusion needing maximum anchorage usually require at least 2 years of active treatment.11 In this study, there were no statistically significant differences between the microimplant group and the headgear group in terms of mean treatment times. The mean treatment times were 21.93 months for the microimplant group and 23.88 months for the headgear group; these are comparable with previous studies that applied conventional brackets in adults with bimaxillary protrusion. Recent studies have proposed that the microimplantreinforced anchorage was helpful in minimizing anchor loss and accepted heavy traction forces but did not bring about a faster rate of retraction.12 Several consecutive case series studies found that treatment with SLBs was quicker and required fewer visits than treatment with conventional appliances.7,13 According to the study of Prettyman et al,14 64% of orthodontists claimed shorter adjustment appointments with SLBs, and 66% of orthodontists indicated faster initial treatment with SLBs. However, several randomized controlled trials indicated that treatment with SLBs does not result in shorter treatment times.15-17 Although the self-ligating system offered quicker and arguably more efficient wire removal and placement for most orthodontic treatment stages,10
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Table III. Comparisons of treatment changes within and between the microimplant and headgear groups Microimplant group
Headgear group
Difference
Skeletal measurements SNA ( ) SNB ( ) ANB ( ) A-Nv (mm) Pog-Nv (mm) NAPog ( ) SN-OP ( ) SN-MP ( ) Dental measurements U1-SN ( ) U1-NPog (mm) U1-FH (mm) MFH (mm) AA0 (mm) UU0 (mm) MM0 (mm)
Difference
Mean
SD
Paired t test
Mean
SD
Paired t test
Between groups P value
0.20 0.13 0.07 0.07 0.20 0.20 0.27 0.27
0.41 0.35 0.46 0.18 0.77 0.77 0.59 0.59
0.08 0.16 0.58 0.13 0.33 0.33 0.10 0.10
0.25 0.19 0.06 0.03 0.09 0.42 0.50 1.19
0.58 0.66 0.44 0.07 0.20 0.93 1.03 1.33
0.10 0.27 0.58 0.10 0.08 0.09 0.07 0.00*
0.79 0.78 0.98 0.38 0.05 0.06 0.45 0.00*
11.87 8.37 0.13 0.10 0.27 10.27 0.87
1.51 1.96 0.52 0.21 0.55 3.51 1.46
0.00* 0.00* 0.33 0.08 0.08 0.00* 0.04*
11.13 6.63 0.19 0.06 0.22 6.88 2.19
1.82 2.55 0.54 0.31 0.54 2.55 1.68
0.00* 0.00* 0.19 0.43 0.13 0.00* 0.00*
0.23 0.04* 0.10 0.10 0.81 0.00* 0.03*
Based on Student t test: *P \0.05.
2 recent systematic reviews have concluded that there is insufficient evidence to support the view that treatment with SLBs results in fewer visits or shorter treatment.18,19 Nevertheless, some researchers have suggested that treatment with SLBs was considerably more comfortable for the patient as well as for the orthodontist; 27% of orthodontists reported that their patients experienced less discomfort during adjustments with SLBs.14 In a randomized clinical trial, patients in the SLB group reported lower mean maximum pain intensity and significantly lower mean pain intensity than did the patients with conventional twin bracket.20 In addition, 42% of orthodontists reported that they perceived better oral hygiene in patients with SLBs14 as a result of decreased plaque retention with the elimination of elastomeric ligatures.21 In bimaxillary protrusion patients, the major orthodontic treatment goal includes retraction and retroclination of the incisors with a resultant decrease in soft tissue procumbency.2 When the extraction of maxillary premolars is indicated to correct the malocclusion, the treatment mechanics must address space closure of the extraction sites by anterior tooth retraction, whereas mesial movement and extrusion of the maxillary posterior teeth should be restricted until the crowding and dentoalveolar protrusion are resolved. Well-controlled mechanotherapy can achieve satisfactory correction of dentoalveolar protrusion, leading to a positive soft tissue response, with reductions of lip eversion and protrusion. Since microimplants can effectively provide stable
anchorage without patient compliance, they are highly acceptable by adults. Compared with our previous case profile, more adults have accepted comprehensive orthodontic treatment since microimplants were adopted as a routine anchorage procedure in our department. In this study, the maxillary incisors in the microimplant and headgear groups were retroclined by means of 11.87 and of 11.13 , respectively. The results of U1-SN showed that the maxillary incisors were slightly more upright in the microimplant group than in the headgear group after treatment; however, the difference in the change of U1-SN between the 2 groups was not significant (P 5 0.23). The maxillary incisors in the different groups were retracted by means of 8.37 and 6.63 mm, respectively. Upon incisor retraction, the mean point U was retracted by 10.27 mm in group 1 and by 6.88 mm in group 2. Statistically significant differences in the change of U1-NPog and UU0 were observed between groups 1 and 2, indicating that the incisal edges of the maxillary central incisors also had significantly greater palatal retraction in the microimplant group than in the headgear group. Meanwhile, less mesial movement of the maxillary first molar was noted in the microimplant group than in the headgear group, thus confirming that the microimplant provided more stable maximum anchorage mechanics. After placement of a microimplant for most conditions, new bone forms, and osseointegration gradually occurs. The implant then behaves in the same manner as an ankylosed tooth, providing absolute anchorage without
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patient compliance; this may prevent or minimize any anchorage loss. By comparison, headgear enhances molar anchorage in an indirect and variable manner. Compliance in wearing headgear might have been questionable for these adults during the lengthy treatment. The anchorage molars will usually move forward somewhat, and the anterior teeth will often retract less when anchored by headgear than by a microimplant. Control of mandibular rotation is important in orthodontic treatment.22 Mandibular rotation after orthodontic treatment is influenced by changes in the vertical position of the maxillomandibular teeth and the cant of the occlusal plane.22 In this study, SN-MP was decreased after treatment in the microimplant group, but the difference between pretreatment and posttreatment did not reach statistical significance. These results agree with the study of Upadhyay et al.23 In the microimplant group, because of the implant site positions, retraction forces also produced intrusion forces to the dentition. Skeletal anchorage systems with titanium miniplates have been reported to predictably distalize or intrude the maxillary and mandibular molars.24 More remarkably, successful treatment of patients with severe anterior open bite using titanium skeletal anchorage to achieve genuine intrusion of the maxillary molars has consistently been achieved.25 Implant anchorage is recommended for Class II high-angle patients because intrusion of the maxillary molars is followed by counterclockwise rotation of the mandible, resulting in a decreased anteroposterior jaw discrepancy.2 With regard to maxillary molar intrusion in the microimplant group, sliding mechanics with absolute anchorage produced rotation of the entire dentition around the center of resistance, and the vertical intrusive force acts on the molars.22 The center of resistance for the entire maxillary dentition is approximately halfway from the root apex to the alveolar bone crest between the first and second premolars. Because the force used during retraction is not reciprocal, posteriorly it is negated not by the teeth but by the microimplant. As a result, either the entire arch or the anterior segment rotates around the center of resistance (Fig 2). In our study, microimplants were placed between the maxillary second premolars and first molars close to the alveolar bone crest. Therefore, the maxillary molar tended to intrude in the implant anchorage group because the line of retraction force was exerted below the center of resistance of the maxillary dentition.26 In contrast, increases in the SN-MP angle were observed in our headgear group after treatment (P \0.01). Opening rotation of the mandible might have occurred as a result of extrusion of the maxillary dentition, as reported in previous studies. Possible
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Fig 2. A, Effect of space closure with conventional sliding mechanics without a microimplant. Anterior and posterior segments rotate around the center of resistance of each segment; B, retraction force from microimplant anchorage with a continuous archwire produces rotation of the entire arch around the center of resistance of the dentition and rotation of the anterior segment around the center of resistance of the anterior teeth.
factors include inadequate wearing of the headgear, improper directional pull of the headgear relative to the center of resistance of the maxillary first molar, and loss of 3-dimensional control on the maxillary molars due to complex mechanics.26 It is difficult to control this rotation with conventional techniques using headgear.27 The use of headgear can also lead to counterclockwise rotation of the mandible, but it requires good patient compliance.28 Adults have esthetic and social concerns and may also not appreciate that vertical profile problems are as important as anteroposterior profile problems, making compliance more difficult to obtain when a headgear is introduced.29 Our results confirm that using an SLB appliance and microimplant anchorage can control the mandibular rotation. Therefore, this technique would be effective even without patient compliance or any extraoral appliance, especially in adults with a high mandibular plane angle, in whom it is necessary to control mandibular rotation and anchorage.26 CONCLUSIONS
For adult patients with bimaxillary protrusion, although SLBs with microimplant anchorage might not shorten the orthodontic treatment period, microimplant
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anchorage achieved better control in both the anteroposterior and vertical directions during treatment when compared with headgear anchorage. Microimplant anchorage might result in more retraction of the maxillary incisors and less anchorage loss of the maxillary first molar. REFERENCES 1. Bills DA, Handelman CS, BeGole EA. Bimaxillary dentoalveolar protrusion: traits and orthodontic correction. Angle Orthod 2005;75:333-9. 2. Yao CC, Lai EH, Chang JZ, Chen I, Chen YJ. Comparison of treatment outcomes between skeletal anchorage and extraoral anchorage in adults with maxillary dentoalveolar protrusion. Am J Orthod Dentofacial Orthop 2008;134:615-24. 3. Guray E, Orhan M. “En masse” retraction of maxillary anterior teeth with anterior headgear. Am J Orthod Dentofacial Orthop 1997;112:473-9. 4. Park HS, Yoon DY, Park CS, Jeoung SH. Treatment effects and anchorage potential of sliding mechanics with titanium screws compared with the Tweed-Merrifield technique. Am J Orthod Dentofacial Orthop 2008;133:593-600. 5. Read-Ward GE, Jones SP, Davies EH. A comparison of self-ligating and conventional orthodontic bracket systems. Br J Orthod 1997; 24:309-17. 6. Harradine NW. Self-ligating brackets and treatment efficiency. Clin Orthod Res 2001;4:220-7. 7. Eberting JJ, Straja SR, Tuncay OC. Treatment time, outcome, and patient satisfaction comparisons of Damon and conventional brackets. Clin Orthod Res 2001;4:228-34. 8. Khambay B, Millett D, McHugh S. Evaluation of methods of archwire ligation on frictional resistance. Eur J Orthod 2004;26: 327-32. 9. Miles PG. SmartClip versus conventional twin brackets for initial alignment: is there a difference? Aust Orthod J 2005;21:123-7. 10. Turnbull NR, Birnie DJ. Treatment efficiency of conventional vs self-ligating brackets: effects of archwire size and material. Am J Orthod Dentofacial Orthop 2007;131:395-9. 11. Iino S, Sakoda S, Miyawaki S. An adult bimaxillary protrusion treated with corticotomy-facilitated orthodontics and titanium miniplates. Angle Orthod 2006;76:1074-82. 12. Wahabuddin S, Mascarenhas R, D K MI, Husain A. Clinical application of micro-implant anchorage in initial orthodontic retraction. J Oral Implantol 2013 Apr 10 [Epub ahead of print]. 13. Damon DH. The rationale, evolution and clinical application of the self-ligating bracket. Clin Orthod Res 1998;1:52-61. 14. Prettyman C, Best AM, Lindauer SJ, Tufekci E. Self-ligating vs conventional brackets as perceived by orthodontists. Angle Orthod 2012;82:1060-6.
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15. Fleming PS, DiBiase AT, Lee RT. Randomized clinical trial of orthodontic treatment efficiency with self-ligating and conventional fixed orthodontic appliances. Am J Orthod Dentofacial Orthop 2010;137:738-42. 16. DiBiase AT, Nasr IH, Scott P, Cobourne MT. Duration of treatment and occlusal outcome using Damon3 self-ligated and conventional orthodontic bracket systems in extraction patients: a prospective randomized clinical trial. Am J Orthod Dentofacial Orthop 2011;139:e111-6. 17. Johansson K, Lundstrom F. Orthodontic treatment efficiency with self-ligating and conventional edgewise twin brackets. Angle Orthod 2012;82:929-34. 18. Fleming PS, Johal A. Self-ligating brackets in orthodontics. A systematic review. Angle Orthod 2010;80:575-84. 19. Chen SS, Greenlee GM, Kim JE, Smith CL, Huang GJ. Systematic review of self-ligating brackets. Am J Orthod Dentofacial Orthop 2010;137:726.e1-18:discussion, 726-7. 20. Pringle AM, Petrie A, Cunningham SJ, McKnight M. Prospective randomized clinical trial to compare pain levels associated with 2 orthodontic fixed bracket systems. Am J Orthod Dentofacial Orthop 2009;136:160-7. 21. Pandis N, Vlachopoulos K, Polychronopoulou A, Madianos P, Eliades T. Periodontal condition of the mandibular anterior dentition in patients with conventional and self-ligating brackets. Orthod Craniofac Res 2008;11:211-5. 22. Jung MH, Kim TW. Biomechanical considerations in treatment with miniscrew anchorage. Part 3: clinical cases. J Clin Orthod 2008;42:329-37. 23. Upadhyay M, Yadav S, Nagaraj K, Patil S. Treatment effects of mini-implants for en-masse retraction of anterior teeth in bialveolar dental protrusion patients: a randomized controlled trial. Am J Orthod Dentofacial Orthop 2008;134:18-29. 24. Sugawara J. Dr. Junji Sugawara on the skeletal anchorage system. Interview by Dr. Larry W. White. J Clin Orthod 1999;33:689-96. 25. Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intruding molars with titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593-600. 26. Koyama I, Iino S, Abe Y, Takano-Yamamoto T, Miyawaki S. Differences between sliding mechanics with implant anchorage and straight-pull headgear and intermaxillary elastics in adults with bimaxillary protrusion. Eur J Orthod 2011;33:126-31. 27. Ellen EK, Schneider BJ, Sellke T. A comparative study of anchorage in bioprogressive versus standard edgewise treatment in Class II correction with intermaxillary elastic force. Am J Orthod Dentofacial Orthop 1998;114:430-6. 28. Chae JM. A new protocol of Tweed-Merrifield directional force technology with microimplant anchorage. Am J Orthod Dentofacial Orthop 2006;130:100-9. 29. Ma J, Wang L, Zhang W, Chen W, Zhao C, Smales RJ. Comparative evaluation of micro-implant and headgear anchorage used with a pre-adjusted appliance system. Eur J Orthod 2008;30:283-7.
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Differences of treatment outcomes between self-ligating brackets with microimplant and headgear anchorages in adults with bimaxillary protrusion Mu Chen,a Zheng-Ming Li,a Xue Liu,b Bin Cai,c Da-Wei Wang,d and Zhi-Cai Fenge Shenzhen, Guangdong, and Guangzhou, China
Introduction: Our aim was to determine differences between the outcomes of treatment using microimplant anchorage compared with headgear anchorage in adult patients with bimaxillary protrusion treated with self-ligating brackets. Methods: Thirty-one adult orthodontic patients (13 men, 18 women; age, 25.87 6 3.37 years) who were diagnosed with bimaxillary protrusion were selected. All patients were treated with self-ligating brackets and maximum anchorage after extraction of 4 first premolars. Group 1 received microimplant anchorage, and group 2 received headgear. Lateral cephalometric radiographs were obtained before and after treatment. Differences in the skeletal and dental parameters between and within groups were analyzed. Results: No significant difference was observed in the mean treatment times between the groups (21.93 6 3.10 vs 23.88 6 2.68 months). There was no significant difference in skeletal measurements before or after treatment in patients who received microimplant anchorage. Patients who received headgear anchorage had an increase of the mandibular plane angle. The microimplant anchorage group had greater anterior tooth retraction and less maxillary molar mesialization than did the headgear group. Conclusions: In both the anteroposterior and vertical directions, microimplant anchorage achieved better control than did the traditional headgear appliance during the treatment of bimaxillary protrusion. (Am J Orthod Dentofacial Orthop 2015;147:465-71)
a Associate professor, Department of Stomatology, Nanshan Affiliated Hospital of Guangdong Medical College, Shenzhen, Guangdong, China. b Professor, Department of Stomatology, Nanshan Affiliated Hospital of Guangdong Medical College, Shenzhen, Guangdong, China. c Associate professor, Department of Orthodontics, Guanghua School of Stomatology and Institute of Stomarological Research, Sun Yat-sen University, Guangzhou, China. d Professor, Department of Orthodontics, Guanghua School of Stomatology and Institute of Stomarological Research, Sun Yat-sen University, Guangzhou, China. e Attending physician, Department of Orthodontics, Guanghua School of Stomatology and Institute of Stomarological Research, Sun Yat-sen University, Guangzhou, China. Mu Chen and Zheng-Ming Li are joint first authors and contributed equally to this work. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Partially supported by grants from the Project of the National Natural Science Foundation of China (number 81300862), the Project of Health and Family Planning Commission of Shenzhen Municipality (number 201302202), and the Project of Science and Technology Innovation Commission of Nanshan Municipality (number 2012040). Address correspondence to: Xue Liu, Department of Stomatology, Nanshan Affiliated Hospital of Guangdong Medical College, Shenzhen, 89#Taoyuan Lu, Nanshan District, Shenzhen, Guangdong 518052, PR China; e-mail, [email protected]. Submitted, September 2014; revised and accepted, November 2014. 0889-5406/$36.00 Copyright Ó 2015 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2014.11.029
B
imaxillary protrusion is a condition characterized by protrusive and proclined maxillary and mandibular incisors, and increased procumbency of the lips. It is seen commonly in African-American and Asian populations.1 In bimaxillary protrusion patients, the major orthodontic treatment goal includes retraction and retroclination of the maxillary and mandibular incisors with a resultant decrease in soft tissue procumbency.2 It is rather well accepted by clinicians that extraction of the 4 first premolars followed by retraction of the anterior teeth with maximum anchorage mechanics can be effective in the treatment of bimaxillary protrusion. Maximum anchorage to prevent forward movement of the maxillary posterior teeth during anterior tooth retraction can be provided with different approaches. Extraoral headgear appliances are commonly used to reinforce posterior anchorage during anterior tooth retraction or are directly applied to retract anterior teeth.3 However, wearing headgear full time is too demanding for most patients, and thus some anchorage loss and mesial movement of the maxillary molars are 465
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usually observed. Patient cooperation is an important factor for the effectiveness of extraoral appliances. Microimplants are increasingly used as orthodontic anchorage sources. It has been reported that implant anchorage can provide stable bony anchorage and overcome problems of anchorage loss during extraction space closure, which usually occurs with traditional anchorage preparations. Application of implant anchorage also makes teeth move more efficiently, without depending on patient cooperation in wearing an extraoral appliance, and consequently reducing treatment duration. However, in the treatment of bimaxillary protrusion in adults, only a few studies to date have statistically investigated the effectiveness of the implant anchorage system, with little statistical evaluation of the treatment effects of the implant anchorage system compared with the effects of headgear.4 Orthodontics, just as any other science, has undergone advances in technology that aim to improve treatment efficacy with a view to reducing treatment time, providing patients with comfort and achieving the expected, yet rarely obtained, long-term stability. Recently, there has been increased use of the self-ligating brackets (SLBs) in orthodontic clinics worldwide. SLBs are popular in orthodontics because of their proposed superior properties including low static frictional resistance, full and stable archwire engagement, improved oral hygiene, preserved anchorage, reduced chair time and therapeutic time, and prolonged therapeutic intervals. Several researchers compared therapeutic efficiency, friction, speed of archwire changes, therapeutic time, and initial alignment of the mandibular arch between self-ligating and conventional brackets.5-10 Although more patients were treated with SLBs, there is little research about whether there are significant clinical differences between microimplant anchorage and headgear anchorage in patients with bimaxillary protrusion malocclusion treated with SLBs. The objective of this study was to assess, in adults with bimaxillary protrusion, the effectiveness of orthodontic anchorage when using either microimplants or extraoral headgear with the SLB system. MATERIAL AND METHODS
Ethical approval was obtained from the ethics committee of the Guanghua College of Stomatology in China. A letter was sent to the subjects to seek consent for their participation in the study. This letter also informed them about the examination procedures and assured them of confidentiality of any information collected. Only patients who actively consented were included. A consecutive sample of adults seeking orthodontic care at a state-funded hospital clinic was recruited. We
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excluded those who lacked the data required for our research, missed 3 or more appointments, and had unclear pretreatment or posttreatment lateral cephalograms. Patients were diagnosed with bimaxillary protrusion based on cephalometric evaluations and study models, which required the extraction of 4 first premolars and maximum anchorage to obtain a satisfactory treatment. They were divided into 2 groups according to the type of anchorage preparation. The choice of microimplant or headgear anchorage was made by each patient according to his or her own judgment on compliance, because both modes of anchorage preparation were available. In group 1 (15 patients; 6 men, 9 women; age, 26.53 6 3.54 years), titanium microimplants were used for anchorage. Each patient received implantation of microimplants on the buccal aspect of the bilateral maxillary posterior teeth. After administration of local anesthesia, OrthoEasy (Forestadent, Pforzheim, Germany) orthodontic microimplants (length, 9.0 mm; diameter, 1.6 mm) were placed between the maxillary second premolars and the first molars without flap elevation at the apical level. In group 2 (16 patients; 7 men, 9 women; age, 25.25 6 3.19 years), the patients received traditional anchorage preparation with a headgear appliance (Shinye Odontological Materials, Hangzhou, China). The force level exerted by the headgear was 300 to 350 g. The directional pull of the headgear was adjusted according to the mandibular plane angle. All subjects received passive SLBs (Forestadent) brackets. In both groups, nickel-titanium wires for aligning and leveling were used with the same sequence of archwires beginning with 0.014-in, 0.016-in, and 0.018-in, until a 0.018 3 0.025-in base archwire was inserted. In both groups with either traditional extraoral anchorage or microimplant anchorage, the extraction space was closed by sliding mechanics with en-masse retraction after partial canine distalization to resolve the anterior crowding and to achieve good alignment of the 6 anterior teeth. All treatments and anchorage preparations were conducted after obtaining the patient's informed consent. Treatment procedures were taught and monitored by 1 clinical instructor (D.-W.W.) so that consistent mechanical principles were maintained. Lateral cephalometric radiographs were taken immediately before and after treatment for all subjects. Tracing, superimposition, and measurement were undertaken manually by 2 examiners (M.C., Z.-C.F.). Bilateral structures were bisected, and their midsagittal points were identified. The cephalometric parameters, including 8 skeletal measurements and 7 dental measurements used in this study, are shown diagrammatically according to the study of Yao et al2 (Fig 1).
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Fig 1. Skeletal and dentoalveolar measurements of the lateral cephalometric analysis: 1, SNA; 2, SNB; 3, ANB; 4, A-Nv; 5, Pog-Nv; 6, NAPog; 7, SN-OP; 8, SN-MP; 9, UI-SN; 10, UI-NPog; 11, U1-FH (distance of the maxillary central incisal edge relative to the Frankfort horizontal plane); 12, M-FH (distance of the mesiobuccal cusp tip of the first molar relative to the Frankfort horizontal plane); 13, AA0 (projection of Point A on the Frankfort horizontal plane); 14, UU0 ; 15, MM0 . Statistical analysis
Descriptive and analytical statistical analyses were performed with the Statistical Package for the Social Sciences (version 15.0; SPSS, Chicago, Ill) for Windows. To assess intraexaminer and interexaminer reliabilities, the cephalometric radiographs were retraced and remeasured by the same 2 examiners after a period of 3 months. The results of the analysis indicated no statistically significant differences between the original and repeated measurements at the 0.05 level. Statistical analysis was undertaken to determine whether any significant differences existed between groups 1 and 2 before treatment. For the microimplant and headgear groups, the means and standard deviations of the pretreatment and posttreatment cephalometric measurements were calculated and compared using pairedsamples t tests. Differences in treatment changes between the 2 groups were evaluated with the independent-samples t test. A P value less than 0.05 was considered statistically significant.
Table I. Comparison of cephalometric measurements
before treatment between group 1 (microimplant anchorage) and group 2 (headgear anchorage) Group 1
Age (y) Treatment duration (mo) Sex (male/female) Skeletal measurements SNA ( ) SNB ( ) ANB ( ) A-Nv (mm) Pog-Nv (mm) NAPog ( ) SN-OP ( ) SN-MP ( ) Dental measurements U1-SN ( ) U1-NPog (mm) U1-FH (mm) MFH (mm)
Group 2
Mean 26.53 21.93 6/9
SD 3.54 3.10
Mean 25.25 23.88 7/9
SD 3.19 2.68
P 0.30 0.07
81.53 78.60 2.93 0.83 12.94 11.00 17.10 33.60
2.70 3.09 2.52 0.20 2.04 2.04 3.69 5.45
80.31 78.19 2.13 1.00 12.09 9.75 17.56 34.75
3.20 1.80 2.47 0.37 2.09 2.07 3.43 6.38
0.26 0.65 0.38 0.13 0.26 0.10 0.72 0.60
113.27 17.93 60.33 51.30
5.70 3.99 4.19 3.00
117.13 19.00 63.06 53.19
5.40 3.69 3.60 2.64
0.06 0.45 0.06 0.07
RESULTS
No significant differences were found for any measurements before treatment in either group (Table I). The mean treatment duration of the microimplant group (21.93 6 3.10 months) was less than that of the headgear group (23.88 6 2.68 months). However, the difference did not reach statistical significance (P 5 0.07).
The original dentofacial characteristics and treatment changes measured from the paired pretreatment and posttreatment cephalograms of the 2 groups are shown in Table II. There were no significant differences in the skeletal measurements before or after treatment in group 1. In the dental measurements, the mean
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Table II. Comparisons of treatment changes in the microimplant and headgear groups Microimplant group Pretreatment Mean Skeletal measurements 81.53 SNA ( ) SNB ( ) 78.60 ANB ( ) 2.93 A-Nv (mm) 0.83 Pog-Nv (mm) 12.94 NAPog ( ) 11.00 SN-OP ( ) 17.10 33.60 SN-MP ( ) Dental measurements U1-SN ( ) 113.27 U1-NPog (mm) 17.93 U1-FH (mm) 60.33 MFH (mm) 51.30 AA0 (mm) UU0 (mm) MM0 (mm)
Posttreatment
Headgear group Difference
Pretreatment
Posttreatment
Difference
SD
Mean
SD
Mean
SD
P
Mean
SD
Mean
SD
Mean
SD
P
2.70 3.09 2.52 0.20 2.04 2.04 3.69 5.45
81.33 78.47 2.87 0.91 12.92 10.80 17.37 33.33
2.74 3.04 2.39 0.30 2.05 2.28 3.74 5.56
0.20 0.13 0.07 0.07 0.02 0.20 0.27 0.27
0.41 0.35 0.46 0.18 0.08 0.77 0.59 0.59
0.08 0.16 0.58 0.13 0.33 0.33 0.10 0.10
80.31 78.19 2.13 1.00 12.09 9.75 17.56 34.75
3.20 1.80 2.47 0.37 2.09 2.07 3.44 6.38
80.06 78.00 2.06 1.03 12.19 10.17 18.06 35.94
2.95 1.79 2.43 0.35 2.05 1.93 3.80 6.81
0.25 0.19 0.06 0.03 0.09 0.42 0.50 1.19
0.58 0.66 0.44 0.07 0.20 0.93 1.03 1.33
0.10 0.27 0.58 0.10 0.08 0.09 0.07 0.00*
5.70 3.99 4.19 3.00
101.40 9.57 60.20 51.20
5.77 3.13 4.16 3.08
11.87 8.37 0.13 0.10 0.27 10.27 0.87
1.51 1.96 0.52 0.21 0.55 3.51 1.46
0.00* 0.00* 0.33 0.08 0.08 0.00* 0.04*
117.13 19.00 63.06 53.19
5.40 3.69 3.60 2.64
106.00 12.38 63.25 53.25
5.11 2.78 3.82 2.77
11.13 6.63 0.19 0.06 0.22 6.88 2.19
1.82 2.55 0.54 0.31 0.54 2.55 1.68
0.00* 0.00* 0.19 0.43 0.13 0.00* 0.00*
Based on paired t tests: *P \0.05.
decreases were 11.87 in the proclination of the maxillary incisor (U1-SN angle) and 8.37 mm in the sagittal measurements of U1 (U1-NPog distance) (P \0.01). The tip of the maxillary incisor (UU0 ) was retracted by 10.27 mm (P \0.01), and mesial movement of the maxillary first molar (MM0 ) was 0.87 mm (P \0.05). In group 2, the SN-MP angle was significantly increased (1.19 , P \0.01) after treatment, but there were no significant treatment changes of other skeletal measurements. In dental measurements, the maxillary incisors were retroclined by a mean of 11.13 (U1-SN angle) and retracted by a mean of 6.63 mm (U1-NPog), whereas the tip of the maxillary incisor was retracted by 6.88 mm, and mesial movement of the maxillary first molar was 2.19 mm (P \0.01). To determine the statistical significance of these differences between anchorage systems, treatment changes of both groups were listed and compared using the independent-samples t test (Table III). Statistically significant differences were noted in the following measurements: SN-MP, U1-NPog, UU0 , and MM0 (P \0.05). Opening rotation of the mandible was observed in the headgear group because of the increase of the mandibular plane angle. Furthermore, the microimplant group had greater correction of maxillary incisor protrusion (U1-NPog and UU0 ) and less mesial movement of the maxillary first molar than did the headgear group.
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DISCUSSION
Adults who seek orthodontic treatment often desire that it be completed in as short a period as possible. At present, however, adults with bimaxillary protrusion needing maximum anchorage usually require at least 2 years of active treatment.11 In this study, there were no statistically significant differences between the microimplant group and the headgear group in terms of mean treatment times. The mean treatment times were 21.93 months for the microimplant group and 23.88 months for the headgear group; these are comparable with previous studies that applied conventional brackets in adults with bimaxillary protrusion. Recent studies have proposed that the microimplantreinforced anchorage was helpful in minimizing anchor loss and accepted heavy traction forces but did not bring about a faster rate of retraction.12 Several consecutive case series studies found that treatment with SLBs was quicker and required fewer visits than treatment with conventional appliances.7,13 According to the study of Prettyman et al,14 64% of orthodontists claimed shorter adjustment appointments with SLBs, and 66% of orthodontists indicated faster initial treatment with SLBs. However, several randomized controlled trials indicated that treatment with SLBs does not result in shorter treatment times.15-17 Although the self-ligating system offered quicker and arguably more efficient wire removal and placement for most orthodontic treatment stages,10
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Table III. Comparisons of treatment changes within and between the microimplant and headgear groups Microimplant group
Headgear group
Difference
Skeletal measurements SNA ( ) SNB ( ) ANB ( ) A-Nv (mm) Pog-Nv (mm) NAPog ( ) SN-OP ( ) SN-MP ( ) Dental measurements U1-SN ( ) U1-NPog (mm) U1-FH (mm) MFH (mm) AA0 (mm) UU0 (mm) MM0 (mm)
Difference
Mean
SD
Paired t test
Mean
SD
Paired t test
Between groups P value
0.20 0.13 0.07 0.07 0.20 0.20 0.27 0.27
0.41 0.35 0.46 0.18 0.77 0.77 0.59 0.59
0.08 0.16 0.58 0.13 0.33 0.33 0.10 0.10
0.25 0.19 0.06 0.03 0.09 0.42 0.50 1.19
0.58 0.66 0.44 0.07 0.20 0.93 1.03 1.33
0.10 0.27 0.58 0.10 0.08 0.09 0.07 0.00*
0.79 0.78 0.98 0.38 0.05 0.06 0.45 0.00*
11.87 8.37 0.13 0.10 0.27 10.27 0.87
1.51 1.96 0.52 0.21 0.55 3.51 1.46
0.00* 0.00* 0.33 0.08 0.08 0.00* 0.04*
11.13 6.63 0.19 0.06 0.22 6.88 2.19
1.82 2.55 0.54 0.31 0.54 2.55 1.68
0.00* 0.00* 0.19 0.43 0.13 0.00* 0.00*
0.23 0.04* 0.10 0.10 0.81 0.00* 0.03*
Based on Student t test: *P \0.05.
2 recent systematic reviews have concluded that there is insufficient evidence to support the view that treatment with SLBs results in fewer visits or shorter treatment.18,19 Nevertheless, some researchers have suggested that treatment with SLBs was considerably more comfortable for the patient as well as for the orthodontist; 27% of orthodontists reported that their patients experienced less discomfort during adjustments with SLBs.14 In a randomized clinical trial, patients in the SLB group reported lower mean maximum pain intensity and significantly lower mean pain intensity than did the patients with conventional twin bracket.20 In addition, 42% of orthodontists reported that they perceived better oral hygiene in patients with SLBs14 as a result of decreased plaque retention with the elimination of elastomeric ligatures.21 In bimaxillary protrusion patients, the major orthodontic treatment goal includes retraction and retroclination of the incisors with a resultant decrease in soft tissue procumbency.2 When the extraction of maxillary premolars is indicated to correct the malocclusion, the treatment mechanics must address space closure of the extraction sites by anterior tooth retraction, whereas mesial movement and extrusion of the maxillary posterior teeth should be restricted until the crowding and dentoalveolar protrusion are resolved. Well-controlled mechanotherapy can achieve satisfactory correction of dentoalveolar protrusion, leading to a positive soft tissue response, with reductions of lip eversion and protrusion. Since microimplants can effectively provide stable
anchorage without patient compliance, they are highly acceptable by adults. Compared with our previous case profile, more adults have accepted comprehensive orthodontic treatment since microimplants were adopted as a routine anchorage procedure in our department. In this study, the maxillary incisors in the microimplant and headgear groups were retroclined by means of 11.87 and of 11.13 , respectively. The results of U1-SN showed that the maxillary incisors were slightly more upright in the microimplant group than in the headgear group after treatment; however, the difference in the change of U1-SN between the 2 groups was not significant (P 5 0.23). The maxillary incisors in the different groups were retracted by means of 8.37 and 6.63 mm, respectively. Upon incisor retraction, the mean point U was retracted by 10.27 mm in group 1 and by 6.88 mm in group 2. Statistically significant differences in the change of U1-NPog and UU0 were observed between groups 1 and 2, indicating that the incisal edges of the maxillary central incisors also had significantly greater palatal retraction in the microimplant group than in the headgear group. Meanwhile, less mesial movement of the maxillary first molar was noted in the microimplant group than in the headgear group, thus confirming that the microimplant provided more stable maximum anchorage mechanics. After placement of a microimplant for most conditions, new bone forms, and osseointegration gradually occurs. The implant then behaves in the same manner as an ankylosed tooth, providing absolute anchorage without
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patient compliance; this may prevent or minimize any anchorage loss. By comparison, headgear enhances molar anchorage in an indirect and variable manner. Compliance in wearing headgear might have been questionable for these adults during the lengthy treatment. The anchorage molars will usually move forward somewhat, and the anterior teeth will often retract less when anchored by headgear than by a microimplant. Control of mandibular rotation is important in orthodontic treatment.22 Mandibular rotation after orthodontic treatment is influenced by changes in the vertical position of the maxillomandibular teeth and the cant of the occlusal plane.22 In this study, SN-MP was decreased after treatment in the microimplant group, but the difference between pretreatment and posttreatment did not reach statistical significance. These results agree with the study of Upadhyay et al.23 In the microimplant group, because of the implant site positions, retraction forces also produced intrusion forces to the dentition. Skeletal anchorage systems with titanium miniplates have been reported to predictably distalize or intrude the maxillary and mandibular molars.24 More remarkably, successful treatment of patients with severe anterior open bite using titanium skeletal anchorage to achieve genuine intrusion of the maxillary molars has consistently been achieved.25 Implant anchorage is recommended for Class II high-angle patients because intrusion of the maxillary molars is followed by counterclockwise rotation of the mandible, resulting in a decreased anteroposterior jaw discrepancy.2 With regard to maxillary molar intrusion in the microimplant group, sliding mechanics with absolute anchorage produced rotation of the entire dentition around the center of resistance, and the vertical intrusive force acts on the molars.22 The center of resistance for the entire maxillary dentition is approximately halfway from the root apex to the alveolar bone crest between the first and second premolars. Because the force used during retraction is not reciprocal, posteriorly it is negated not by the teeth but by the microimplant. As a result, either the entire arch or the anterior segment rotates around the center of resistance (Fig 2). In our study, microimplants were placed between the maxillary second premolars and first molars close to the alveolar bone crest. Therefore, the maxillary molar tended to intrude in the implant anchorage group because the line of retraction force was exerted below the center of resistance of the maxillary dentition.26 In contrast, increases in the SN-MP angle were observed in our headgear group after treatment (P \0.01). Opening rotation of the mandible might have occurred as a result of extrusion of the maxillary dentition, as reported in previous studies. Possible
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Fig 2. A, Effect of space closure with conventional sliding mechanics without a microimplant. Anterior and posterior segments rotate around the center of resistance of each segment; B, retraction force from microimplant anchorage with a continuous archwire produces rotation of the entire arch around the center of resistance of the dentition and rotation of the anterior segment around the center of resistance of the anterior teeth.
factors include inadequate wearing of the headgear, improper directional pull of the headgear relative to the center of resistance of the maxillary first molar, and loss of 3-dimensional control on the maxillary molars due to complex mechanics.26 It is difficult to control this rotation with conventional techniques using headgear.27 The use of headgear can also lead to counterclockwise rotation of the mandible, but it requires good patient compliance.28 Adults have esthetic and social concerns and may also not appreciate that vertical profile problems are as important as anteroposterior profile problems, making compliance more difficult to obtain when a headgear is introduced.29 Our results confirm that using an SLB appliance and microimplant anchorage can control the mandibular rotation. Therefore, this technique would be effective even without patient compliance or any extraoral appliance, especially in adults with a high mandibular plane angle, in whom it is necessary to control mandibular rotation and anchorage.26 CONCLUSIONS
For adult patients with bimaxillary protrusion, although SLBs with microimplant anchorage might not shorten the orthodontic treatment period, microimplant
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anchorage achieved better control in both the anteroposterior and vertical directions during treatment when compared with headgear anchorage. Microimplant anchorage might result in more retraction of the maxillary incisors and less anchorage loss of the maxillary first molar. REFERENCES 1. Bills DA, Handelman CS, BeGole EA. Bimaxillary dentoalveolar protrusion: traits and orthodontic correction. Angle Orthod 2005;75:333-9. 2. Yao CC, Lai EH, Chang JZ, Chen I, Chen YJ. Comparison of treatment outcomes between skeletal anchorage and extraoral anchorage in adults with maxillary dentoalveolar protrusion. Am J Orthod Dentofacial Orthop 2008;134:615-24. 3. Guray E, Orhan M. “En masse” retraction of maxillary anterior teeth with anterior headgear. Am J Orthod Dentofacial Orthop 1997;112:473-9. 4. Park HS, Yoon DY, Park CS, Jeoung SH. Treatment effects and anchorage potential of sliding mechanics with titanium screws compared with the Tweed-Merrifield technique. Am J Orthod Dentofacial Orthop 2008;133:593-600. 5. Read-Ward GE, Jones SP, Davies EH. A comparison of self-ligating and conventional orthodontic bracket systems. Br J Orthod 1997; 24:309-17. 6. Harradine NW. Self-ligating brackets and treatment efficiency. Clin Orthod Res 2001;4:220-7. 7. Eberting JJ, Straja SR, Tuncay OC. Treatment time, outcome, and patient satisfaction comparisons of Damon and conventional brackets. Clin Orthod Res 2001;4:228-34. 8. Khambay B, Millett D, McHugh S. Evaluation of methods of archwire ligation on frictional resistance. Eur J Orthod 2004;26: 327-32. 9. Miles PG. SmartClip versus conventional twin brackets for initial alignment: is there a difference? Aust Orthod J 2005;21:123-7. 10. Turnbull NR, Birnie DJ. Treatment efficiency of conventional vs self-ligating brackets: effects of archwire size and material. Am J Orthod Dentofacial Orthop 2007;131:395-9. 11. Iino S, Sakoda S, Miyawaki S. An adult bimaxillary protrusion treated with corticotomy-facilitated orthodontics and titanium miniplates. Angle Orthod 2006;76:1074-82. 12. Wahabuddin S, Mascarenhas R, D K MI, Husain A. Clinical application of micro-implant anchorage in initial orthodontic retraction. J Oral Implantol 2013 Apr 10 [Epub ahead of print]. 13. Damon DH. The rationale, evolution and clinical application of the self-ligating bracket. Clin Orthod Res 1998;1:52-61. 14. Prettyman C, Best AM, Lindauer SJ, Tufekci E. Self-ligating vs conventional brackets as perceived by orthodontists. Angle Orthod 2012;82:1060-6.
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15. Fleming PS, DiBiase AT, Lee RT. Randomized clinical trial of orthodontic treatment efficiency with self-ligating and conventional fixed orthodontic appliances. Am J Orthod Dentofacial Orthop 2010;137:738-42. 16. DiBiase AT, Nasr IH, Scott P, Cobourne MT. Duration of treatment and occlusal outcome using Damon3 self-ligated and conventional orthodontic bracket systems in extraction patients: a prospective randomized clinical trial. Am J Orthod Dentofacial Orthop 2011;139:e111-6. 17. Johansson K, Lundstrom F. Orthodontic treatment efficiency with self-ligating and conventional edgewise twin brackets. Angle Orthod 2012;82:929-34. 18. Fleming PS, Johal A. Self-ligating brackets in orthodontics. A systematic review. Angle Orthod 2010;80:575-84. 19. Chen SS, Greenlee GM, Kim JE, Smith CL, Huang GJ. Systematic review of self-ligating brackets. Am J Orthod Dentofacial Orthop 2010;137:726.e1-18:discussion, 726-7. 20. Pringle AM, Petrie A, Cunningham SJ, McKnight M. Prospective randomized clinical trial to compare pain levels associated with 2 orthodontic fixed bracket systems. Am J Orthod Dentofacial Orthop 2009;136:160-7. 21. Pandis N, Vlachopoulos K, Polychronopoulou A, Madianos P, Eliades T. Periodontal condition of the mandibular anterior dentition in patients with conventional and self-ligating brackets. Orthod Craniofac Res 2008;11:211-5. 22. Jung MH, Kim TW. Biomechanical considerations in treatment with miniscrew anchorage. Part 3: clinical cases. J Clin Orthod 2008;42:329-37. 23. Upadhyay M, Yadav S, Nagaraj K, Patil S. Treatment effects of mini-implants for en-masse retraction of anterior teeth in bialveolar dental protrusion patients: a randomized controlled trial. Am J Orthod Dentofacial Orthop 2008;134:18-29. 24. Sugawara J. Dr. Junji Sugawara on the skeletal anchorage system. Interview by Dr. Larry W. White. J Clin Orthod 1999;33:689-96. 25. Sherwood KH, Burch JG, Thompson WJ. Closing anterior open bites by intruding molars with titanium miniplate anchorage. Am J Orthod Dentofacial Orthop 2002;122:593-600. 26. Koyama I, Iino S, Abe Y, Takano-Yamamoto T, Miyawaki S. Differences between sliding mechanics with implant anchorage and straight-pull headgear and intermaxillary elastics in adults with bimaxillary protrusion. Eur J Orthod 2011;33:126-31. 27. Ellen EK, Schneider BJ, Sellke T. A comparative study of anchorage in bioprogressive versus standard edgewise treatment in Class II correction with intermaxillary elastic force. Am J Orthod Dentofacial Orthop 1998;114:430-6. 28. Chae JM. A new protocol of Tweed-Merrifield directional force technology with microimplant anchorage. Am J Orthod Dentofacial Orthop 2006;130:100-9. 29. Ma J, Wang L, Zhang W, Chen W, Zhao C, Smales RJ. Comparative evaluation of micro-implant and headgear anchorage used with a pre-adjusted appliance system. Eur J Orthod 2008;30:283-7.
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