Effectiveness of orthodontic temporary anchorage devices in canine retraction and anchorage preservation during two-step technique: A systematic review and meta-analysis

Abstract

Background: To assess the effectiveness of orthodontic temporary anchorage devices in canine retraction during two-step technique.

Methods: The search was systematically performed up to June 2019 in five electronic databases (PubMed, Embase, Cochrane Central Register of Controlled Trials, Web of Science, Scopus). A risk of bias assessment was performed using the Cochrane Risk of Bias Tool for Randomized Controlled Trials (RCTs) and the Risk of Bias in Nonrandomized Studies - of Interventions (ROBINS-I) tool for controlled clinical trials (CCTs) . The Grades of Recommendation, Assessment, Development and Evaluation (GRADE) approach was applied for quality assessment. Data concerning the mean difference in mesial molar movement and extent of canine retraction were extracted for statistical analysis. The mean difference and 95% confidence interval were analyzed for continuous data. A meta-analysis with a random-effects model for comparable outcomes was carried out.

Results: Three RCTs and five CCTs were finally included. Meta-analysis showed a significant increase not only in anchorage preservation in the implant anchorage group in both the maxilla (1. 56 mm , 95% CI: 1.14 to 1.98, P <0.00001 ) and the mandible (1.62 mm , 95% CI: 1.24 to 2.01, P <0.00001 ) but also in canine retraction in the implant anchorage group in both the maxilla (0.43 mm , 95% CI: 0.16 to 0.69, P =0.001 ) and the mandible (0.26 mm , 95% CI: 0.02 to 0.49, P =0.03 ).

Conclusions: Very low-quality evidence shows that implant anchorage is more efficient than conventional anchorage during canine retraction. Further high-quality studies are needed.

1 BACKGROUND

Extracting the premolars and closing the extraction space completely are necessary for orthodontic treatment, especially for patients with bimaxillary protrusion^1,2 who desire a good profile. Additionally, maximum posterior anchorage preservation is crucial for space closure^3 − 5. Although transpalatal arches (TPAs)⁶, Nance arches⁷ and headgear⁸ have been widely used for anchorage reinforcement, anchorage loss, mesial inclination of the dental anchorage and molar extrusion, which are undesirable, are still common in orthodontic practice. Temporary anchorage devices (TADs) have been used since the last century and have become an alternative reinforcement method to provide anchorage during space closure^9,10. Many studies have investigated the efficiency of TADs and have shown that space closure^{10 − 12}, tooth intrusion¹³ and maxillary expansion¹⁴ can be aided with TADs.

Two-step retraction and en masse retraction are two methods for achieving extraction space closure^15,16. Both techniques are efficient for space closure, and there is no significant difference between the two methods in the extent of anterior tooth retraction or molar anchorage loss^5,15,17. Nevertheless, two-step retraction has been used for space closure longer than has en masse retraction^5,18.

A published systematic review⁵ compared the difference between en masse and two-step retraction regarding extraction space closure and concluded that en masse retraction with TADs may be superior in anchorage preservation and incisor retraction, but whether two-step retraction combined with TADs may achieve the same effect remained inconclusive, and this information is necessary for application of the technique in orthodontic practice. Canine retraction is the first step of the two-step retraction method, the completion of which is crucial for subsequent incisor retraction. A previous study¹² indicated that TADs made no significant difference in anchorage preservation compared with conventional anchorage during canine retraction, whereas others found a positive effect^11,19,20. In addition to implant anchorage being more expensive, whether implant anchorage is more effective than conventional anchorage in terms of reducing anchorage loss, increasing canine retraction and reducing other undesirable movement remains unclear to orthodontic professionals.

Therefore, this systematic review and meta-analysis aimed to compare the potential of TADs and conventional anchorage in terms of anchorage preservation and canine retraction during the initial canine retraction step of the two-step technique.

2 METHODS

This systematic review was carried out according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement²¹.

Study design: Prospective randomized and controlled clinical trial. The exclusion criteria were as follows: review articles, animal studies, case reports, lack of a control group, partial canine retraction and en masse retraction of the anterior teeth, and space closure not performed with sliding mechanics.

Population: Orthodontic patients requiring extraction of the bilateral first premolars and retraction of the canines during the two-step technique.

Intervention: Miniscrew implants for anchorage preservation during the first phase of the two-step retraction technique.

Comparison: Conventional anchorage methods for anchorage preservation during the first phase of the two-step retraction technique.

Outcomes: The primary outcomes were mesial movement of the first molars (anchorage loss) and the extent of canine retraction in both the maxilla and mandible. The secondary outcomes were tipping of the canines and molars and vertical molar movement.

3 RESULTS

3.1 Study selection

The study selection process is illustrated in Figure 1. A total of 583 articles were identified, and upon review of the titles and abstracts, 420 were excluded, leaving 19 articles. After reading the full texts, 8 studies were included in the present review for qualitative and quantitative synthesis. The 8 remaining studies included three RCTs^11,19,20 and five CCTs^12,24-27. Information about the excluded records is summarized in Additional file 2.

3.2 Study characteristics

The characteristics of the included studies are presented in Table 1, and the relevant data extracted from the included articles are shown in Table 2. Three RCTs^11,19,20 and five CCTs^12,24-27 were included in the present review. Six studies investigated direct implant anchorage for canine retraction, while two studies used indirect implant anchorage. Four studies^11,25-27 compared TADs with dental anchorage in a split-mouth study. Two studies^19,20 compared TPAs with TADs in the maxilla in a parallel study; one²⁰ also compared lingual bars with TADs in the mandible. The other one¹² compared midpalatal implant-reinforced TPAs with conventional TPAs in the maxilla. One study²⁴ compared midpalatal implants with dental anchorage in the maxilla and TADs with dental anchorage in the mandible. Three studies^11,25,26 inserted implants in both the maxilla and the mandible when the patients’ ANB angle was between 2° and 4° but in only the maxilla when the ANB angle was greater than 5° as a part of camouflage treatment.

3.3 Risk of bias assessment

Three RCTs^11,19,20 were considered to have a high risk of bias because none of them had an appropriate strategy for blinding participants and personnel. The study by Davis et al, 2018¹¹, used only a computer-generated random allocation of sides and not allocation concealment. The randomization method in the study by Sharma et al, 2012¹⁹, was random numbers generated by computer, but allocation was performed by alternation, which leads to a high risk of bias in allocation concealment. The third study²⁰ did not report any randomization method, which resulted in an unclear risk of bias. Blinding of the outcome assessment was also difficult in the studies because the TADs could be observed in lateral cephalograms. However, Sharma et al, 2012¹⁹, removed the miniscrew implants and TPAs before obtaining the postcanine retraction cephalometric radiographs, resulting in a low risk. Davis et al, 2018¹¹, used guide wires to differentiate the right and left sides on the lateral cephalograms, resulting in a high risk. Gökçe et al, 2012²⁰, did not report a process for blinding the assessor, resulting in an unclear risk. The quality assessment results of the RCTs are summarized in Figure 2.

Five CCTs^12,24-27 were assessed using the ROBINS-I²³ tool. The study by Hedayati et al, 2007²⁴, gave inadequate information regarding the patient inclusion criteria, Thiruvenkatachari et al, 2006²⁵, and Thiruvenkatachari et al, 2008²⁶, only inserted implants in the maxilla when the ANB angle was greater than 5° as a part of camouflage treatment, which led to a moderate risk of bias in selection. In the measurement of outcomes, Thiruvenkatachari et al, 2006²⁵, and Thiruvenkatachari et al, 2008²⁶, used wires identifiers, and Chaudhary et al, 2014²⁷, used CBCT-generated 2D cephalometric with implants clearly seen on it, which led to a serious risk of bias in the measurement of outcomes. Borsos et al, 2012¹², used an opaque marker in the approximate position of the implant in both groups, which led to a low risk of bias. Finally, Hedayati et al, 2007²⁴, did not present information regarding outcome measurements. Therefore, the overall bias across studies was serious bias in three studies^25-27, moderate bias in one study²⁴ and low bias in another study¹². The risk of bias information for the included CCTs is summarized in Table 3.

3.4 Primary outcome measures

3.4.1 Mesial molar movement (anchorage loss)

Seven studies^{11,12,19,20,24,25,27} were qualified for meta-analysis, and the total and subgroup analysis results are given in Figure 3(a, b). In the maxilla, the results showed a total mean difference of 1.56 mm (95% CI: 1.14 to 1.98), with statistical significance (P<0.00001). Subgroup analysis showed a mean difference of 1.74 mm (95% CI: 1.32 to 2.17, P<0.00001) in the direct group and a mean difference of 0.93 mm (95% CI: -1.04 to 2.90, P=0.35) in the indirect group. In the mandible, the results showed a total mean difference of 1.62 mm (95% CI: 1.24 to 2.01), with statistical significance (P<0.00001). Subgroup analysis showed a mean difference of 1.45 (95% CI: 1.13 to 1.78, P<0.00001) in the direct group. Only one study²⁴ included a mandibular indirect group; the results showed a mean difference of 2.73 mm (95% CI: 1.98 to 3.48, P<0.00001). In both the maxilla and mandible, the direct and indirect groups showed substantial heterogeneity, with I²> 50%.

3.4.2 Distal canine movement

Four studies^11,20,26,27 were qualified for meta-analysis of both maxillary and mandibular data, and the results are given in Figure 3(c, d). In the maxilla, the results showed a total mean difference of 0.43 mm (95% CI: 0.16 to 0.69), with statistical significance (P=0.001); I²=0. In the mandible, the results showed a total mean difference of 0.26 mm (95% CI: 0.02 to 0.49), with statistical significance (P=0.03); I²=0.

3.5 Secondary outcome measures

One study¹¹ included mesial tipping of the maxillary and mandibular molars with direct TADs. The results showed a mean tipping of 0.30° degrees in the TAD group and a mean tipping of 2.45° in the conventional anchorage group in the maxilla (P=0.000); in the mandible, the values were 0.1875° and 2.6875° (P=0.001), respectively.

One study²⁴ included vertical displacement of the maxillary and mandibular molars with indirect TADs. The results showed a mean intrusion of 0.33 mm in the study group and 0.95 mm in the control group in the maxilla; in the mandible, the results showed a mean intrusion of 0 mm in the study group and 1.02 mm in the control group. With consideration of the cephalometric error (-0.55 mm), slight maxillary molar extrusion and mandibular molar intrusion were observed.

One study²⁷ included distal tipping of the canines in the maxilla and mandible with direct TADs. The results presented tipping of 9.51° in the study group and 6.51° in the control group in the maxilla (P=0.106); in the mandible, the results showed tipping of 7.88° in the study group and 4.34° in the control group (P=0.057).

4 DISCUSSION

4.1 Summary of the evidence

Since all meta-analyses included comparable results regardless of the study type (RCT or CCT), the GRADE assessment was processed according to study type for each result. The GRADE recommendations represented very low quality for all of the results. The evidence for all comparisons was determined as being very low quality owing to risk of bias, inconsistency and imprecision. Detailed information is given in Table 4.

All eight studies^{11,12,19,20,24-27} included patients requiring maximum anchorage for space closure. Although there were three articles^11,25,26 using different implant strategies, this did not seem to affect the final results, since the mandibular data without implants were not included in the study.

4.2 Summary of the results

Anchorage reinforcement during the space closure stage is a major issue in orthodontic treatment⁴. Conventionally, anchorage is provided by the molar units, a transpalatal arch (TPA), a Nance button or headgear; however, undesirable significant anchorage loss can still occur²⁸. TADs are regarded as an ideal alternative method for reinforcing anchorage in en masse retraction, but whether they produce the same effect in canine retraction is inconclusive. The purpose of this systematic review was to evaluate the effectiveness of TADs during canine retraction.

The results of the meta-analysis show that minimizing mesial molar movement is most effectively achieved with TADs. Specifically, overall anchorage preservation of 1.61 mm and 1.62 mm was found in the maxilla and mandible, respectively, which is meaningful compared with that achieved by conventional anchorage methods. However, the results of the subgroup analysis are different. TADs between the second premolar and the first molar on the buccal side cause the molar not to be subjected to any force that will lead to movement. However, indirect TADs in the maxilla had no significant effect on anchorage preservation. The reason may be that the forces in different directions cannot be completely offset, which results in the anchoring teeth being subjected to force, despite indirect reinforcement of the teeth by a steel wire or TPA. The use of indirect implant anchorage is controversial. Ozkan et al²⁹ noted that the form of implant anchorage did not affect the results; however, Jang et al³⁰ indicated that an indirectly anchored tooth will move mesially with indirect implant anchorage. Additionally, deformation of the TPA^31,32 brought about by orthodontic force might be another reason for mesial molar movement in the indirect implant group. There is evidence suggesting that some extent of molar retraction may be achieved with TADs, as reported by Chaudhary et al, 2014²⁷, and Hedayati et al, 2007²⁴. However, the purpose of these two studies was not to distalize molars, but only to preserve anchorage. The tight fastening between the molar and implant for indirect implants, which are located more distally²⁴, and friction between the buccal tube and the archwire¹⁰ for direct implants may be reasons for molar retraction. Therefore, on the basis of very low-quality evidence, direct implant anchorage reinforcement can be considered clinically significant. However, considering the few published articles, the role of indirect implant anchorage with respect to anchorage preservation during canine retraction remains inconclusive.

In our review, two included studies^12,24 applied palatal implants to reinforce posterior teeth with or without a TPA for indirect implant anchorage in the maxilla. A TPA with a palate implant may cause a marked foreign body sensation and patient discomfort³². Substantial clinical heterogeneity existed in the meta-analysis because the included studies varied significantly in the use of osseointegrated and nonosseointegrated implants, study type, bracket slot sizes, archwires and measurement methods.

Canine retraction is the first step of the two-step technique for space closure¹⁷. Clinically, the extent of canine movement is of great importance for subsequent incisor retraction, especially for patients with dentoalveolar protrusion. Some studies^11,20,27 have measured the rate of canine retraction, but considering that different magnitudes of force are used in canine retraction, only the extent of retraction was included in the statistical synthesis. In particular, 0.41 mm and 0.25 mm of canine retraction in the maxilla and mandible, respectively, was consistent with greater anchorage preservation, and greater canine retraction could be achieved with direct implant anchorage. No studies of indirect anchorage were included in this meta-analysis. Therefore, no conclusions regarding indirect implant anchorage can be drawn. Generally, on the basis of very low-quality evidence, direct implant anchorage could facilitate greater canine retraction.

Anchorage loss may also be accompanied by tipping of the molars, but with direct anchorage using TADs, the retraction force acts directly on the canines and away from the molars during retraction. The molars will not be subjected to any force that may lead to excessive molar tipping.

Vertical molar displacement indicates movement of the molar perpendicular to the occlusal plane, usually with intrusion or extrusion. The mesial tipping and extrusion of a molar may lead to an undesirable change in the vertical dimension of the face, which is crucial for the orthodontic treatment of high-angle patients³³. Tightened ligation between the implant and tooth may exert force to intrude the molar²⁴. The implant does have the ability to intrude molars in open-bite cases with elastomeric traction³⁴. Implants with a relatively gingival position are more closely or elastically connected, and indirect implants may have the effect of molar intrusion. An implant between the second premolar and the first molar can act as a direct implant, and a ligature wire engaged between the second premolar and the implant can also act as an indirect implant, as reported by Sharma et al¹⁹.

Bodily canine movement is important for achieving a class I canine relationship, and tipping is undesirable. Herman et al³ indicated that canine tipping is related to the method used to ligate the canines to the archwire, with the most bodily canine retraction, perhaps with slight tipping, being achieved using direct implants. However, the bracket slot, archwire size and residual gap may affect canine tipping the most. The better matched the size, the lesser is the tilt³⁵. In terms of biomechanics, the occurrence of bodily movement or tipping depends on the relationship between the center of resistance and the direction of the force, i.e., whether the direction of the forces passes through the resistance center. The results show greater canine tipping in the implant group. However, adjustment of the height relationship between the crimpable hook and implant may allow the desired bodily tooth movement to be achieved³⁶. Implant anchorage may allow the direction of the force to vary to adjust the extent of tipping during the process.

Limitations

The number of studies that could be included was relatively small, and the overall quality of the RCTs and CCTs was very low. In particular, there are few studies regarding indirect implant anchorage, which makes drawing a definitive conclusion impossible. The heterogeneity in the meta-analysis of anchorage preservation was relatively high. Due to the small number of articles, publication bias could not be assessed by funnel plot.

Conclusions

1. During canine retraction, direct TADs can result in better anchorage preservation and canine retraction than conventional anchorage methods.
2. Very low-quality evidence prevents a credible conclusion from being drawn. Further high-quality studies comparing conventional anchorage and TADs during canine retraction are needed.

Abbreviations

Declarations

Ethics approval and consent to participate

Not applicable

Consent for publication

Not applicable

Availability of data and materials

All data generated or analysed during this study are included in this published article and its supplementary information files.

Competing interests

The authors declare that they have no competing interests.

Funding

This work was supported by etiology and prevention research of oral diseases of Chongqing Medical University (CXTDG201602006) for data collection, analysis, and interpretation and in writing the manuscript.

Authors' contributions

THN and XCM have made contributions to study design, acquisition of data and draft the manuscript. YHM and LM have been involved in analysis and interpretation of data. RAS have been involved in revising manuscript critically and given final approval of the version to be published. All authors have read and approved the manuscript.

Acknowledgements

Not applicable

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Tables

Table 2. Data extracted from the included studies.

Table 3. Assessment of bias using the Risk of Bias In Non-randomised Studies (ROBINS-I) tool.

Table 4. Summary of findings table according to the GRADE approach