Document Type : Review Article
Authors
1 Department of Orthodontics, Faculty of Dental Medicine of Rabat, Mouhammed V University, Rabat, Morocco
2 Faculty of Dental Medicine of Rabat, Mouhammed V University, Rabat, Morocco
Abstract
Keywords
Main Subjects
Canine retraction after the first premolar extraction is a widespread orthodontic procedure. Clinicians always try accelerating tooth movements while preserving periodontal integrity (1). The optimum force for retracting the canine is 150 to 250 grams (2). Furthermore, when using fixed appliances, the time required to achieve complete retraction of the maxillary canine is approximately five months (3). Canine retraction can be achieved through sliding or non-sliding (frictionless) mechanics (4). Closing loops are frequently used to close the extraction space and can be fabricated in a sectional or full archwire. The primary advantage of loop mechanics is the lack of friction between the bracket and archwire during space closure, whereas the main disadvantages are the undesired tooth rotations in the transverse and sagittal planes and the time-consuming fabrication of the loops.
Sliding mechanics are popular among clinicians for the space closure phase of orthodontic therapy. Sliding mechanics involve moving the brackets along an archwire and sliding the archwire through brackets and tubes. This technique creates friction, leading to adverse rotational movements, decreased tooth movement, and increased anchorage loss (5). Various force transmission mechanisms have been proposed for space closure via sliding mechanics, such as elastomeric chains and coil springs. Elastomeric materials are more widely used because they are more convenient and cost-effective. However, most elastomeric chains typically undergo force decay ranging from 50% to 70% within the initial 24 hours (6, 7). On the other hand, NiTi coil springs have the advantage of providing a light, continuous force, albeit at a higher cost than elastomeric chains (8, 9).
Although previous systematic reviews (10, 11) have compared the efficacy of closed NiTi coils springs and elastomeric chains on canine retraction, they did not address the adverse effects of this treatment procedure, such as undesirable periodontal effects or root resorption. In addition, patient-related outcomes, such as pain, were not explored.
The primary objective of this systematic review was to evaluate the efficacy of canine retraction using NiTi coil springs and elastomeric chains. Secondary objectives included comparing the association between these methods and orthodontic anchorage, tooth tipping and rotation, root resorption, plaque control, and pain intensity perceived by patients.
Materials and methods
This study was registered in the PROSPERO database under the number CRD42023450713 and followed the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) (12).
Eligibility criteria
The PICOS (population, intervention, comparison, outcome, and study design) for this study was defined as follows:
P: Patients of all ages undergoing fixed orthodontic therapy and requiring canine retraction after premolar extraction
I: Canine retraction with NiTi coil springs
C: Canine retraction with elastomeric chains
O: The clinical efficiency of canine retraction methods regarding space closure rate.
S: Randomized clinical trials (RCTs)
|
Figure1. Flow diagram of the study process according to the PRISMA statement
|
We excluded non-randomized prospective studies, retrospective studies, in vitro investigations, case series, case reports, review articles, animal studies, and studies involving participants suffering from diseases that could influence dental movements.
Search strategy
Electronic searches were carried out in the following databases: PubMed, Science Direct, Scopus, and Web of Science, by two reviewers (MC and AH). A manual search of the references for the articles included was also conducted. Studies published until May 8th, 2024, were included without language restrictions. The search strategy used several MeSH terms joined by boolean operators: ((Canine retraction) OR (Canine distalization) OR (Orthodontic space closure)) AND ((Nickel-titanium spring) OR (Nickel titanium coil)) AND ((Elastomeric chain) OR (Power chain)).
Study screening and data extraction
Two independent authors initially reviewed the title and abstract of the related studies (MC and BE), and studies were selected according to the inclusion and exclusion criteria. The same authors retrieved and reviewed the full texts of qualifying studies. If an article did not comply with the selection criteria, it was excluded from the review. The study selection procedure is presented in the PRISMA flowchart in Figure 1.
One of the authors (MC) extracted data from the eligible studies and checked them with another researcher (FZ). The desired information included the
|
Figure 2. Risk of bias assessment of RCTs using the ROB-2 tool. The different domains have been defined by D1 to D5 (D 1: Randomization process; D 2: Deviations from the intended intervention; D 3: Missing outcome data; D 4: Measurement of the outcome; D5: Selection of the reported result)
|
names of the study authors, the year of publication, the study design, sample size, the age and gender distribution, the magnitude of force applied with NiTi coil springs and elastomeric chains, the type of archwire utilized, and the protocol of applying force.
Quality assessment
Two authors (MC and BE) assessed the quality of the selected studies using Cochrane's risk of bias tool for randomized clinical trials (RoB 2.0). The RoB 2.0 assessment tool is organized into five different domains: randomization process, deviation from intended intervention, missing outcome data, measurement of outcome, and selection of reported result. Each domain was assessed using one of the following options: low risk, some concern, or high risk. Any disagreements between the two authors were resolved through discussion.
Results
Study selection
A total of 2400 studies were initially identified through electronic (2380) and hand searching (20). After eliminating the duplicates, the titles and abstracts were checked for eligibility, and all papers that did not meet the selection criteria were discarded. The full texts of 40 studies were retrieved and reviewed. Finally, 11 studies were included in this systematic review (4, 13-22).
Risk of bias
Figure 2 summarizes the risk of bias in the evaluated studies. One study exhibited a low risk of bias (4), two studies were judged to have a high risk of bias (14, 21), and the remaining studies were considered to have some concerns about the risk of bias.
Study characteristics
A total of 11 RCTs were included in this analysis. Six RCTs presented with a split-mouth design (4, 14, 15, 17-19), and five presented with a parallel-group design (13, 16, 20-22). The included studies primarily evaluated the space closure and anchorage loss rate after using different canine retraction methods. Some studies assessed the intensity of associated pain and the level of plaque control. Other side effects, such as tooth rotation, tipping, and root resorption, were also evaluated in some studies. The characteristics of the included studies are presented in Table 1.
|
Table 1. Characteristics of the included studies
*NiTi-CS: Nickle Titanium coil springs *EC: Elastomeric Chain *EPC: Elastomeric power chain *EMC: Elastomeric memory chain *RCT: Randomized clinical trial *SS: Stainless steel
|
|
Table 2. Rate of space closure in different studies
|
|||||||||||||||||||||||||||||||||||||||
Results of individual studies
Table 2 presents the mean rate of tooth displacement reported in each study. The results showed that the space closure with NiTi coil springs was faster than elastomeric chains, showing a rate of 0.79-1.85 mm/month versus 0.58-1.68 mm/month, respectively. However, in the study by Khanemasjedi et al. (4), the canine retraction rate was significantly faster in the group that received elastomeric memory chains.
As presented in Table 3, four studies measured and compared the amount of anchorage loss after using NiTi coil springs and elastomeric chains for canine retraction (13, 14, 17, 18). The differences in the obtained values are mainly explained by the different anchorage devices used.
|
Table 3. Rate of anchorage loss in different studies
Table 4. Comparison of rate of additional variables in different studies
CR: Canine rotation. CT: Canine tipping. MR: Molar rotation. MT: Molar tipping.
|
||||||||||||||||||||||||||||||||||||||||||||||||||||
The amount of canine and molar rotation and tipping was reported in two RCTs (17, 18). The results showed greater tipping and rotation with NiTi coil springs. Barsoum et al. (18) compared the amount of root resorption secondary to canine retraction with NiTi coil springs and elastomeric chains and reported 0.76 mm and 0.82 mm of resorption for each method, respectively. According to studies by Badran et al. (15) and Barsoum et al. (18), there were no statistically significant differences in pain intensity during space closure between NiTi coil springs and elastomeric chains. The study by Bardan et al. (15) was the only one to compare the plaque control level between the two canine retraction methods. The authors did not reveal any statistically significant differences between the two methods regarding plaque scores at 6 and 12 weeks after force application (P=0.078 and P=0.582, respectively). Table 4 compares the evaluated studies regarding the amount of molar and canine tipping, level of associated pain, root resorption, and plaque control.
Discussion
This systematic review summarizes evidence from RCTs on canine retraction rate following first premolar extraction using NiTi coil springs and elastomeric chains, the two most commonly used force delivery methods. The evaluated studies either had a split-mouth or parallel-group design. In the split-mouth designs, each patient acts as their control, so inter-subject variability is eliminated, making it possible to increase the study power or reduce the number of participants required. However, apart from the similarity of the sites in split-mouth design, cross-effects between the intervention and control sides are possible due to the lack of a natural barrier, potentially distorting the results. Consequently, the split-mouth study design is not ideal for comparing different space closure systems, as space closure in one quadrant will affect the position of teeth in the other quadrant (10, 23, 24).
The results of the included RCTs showed that NiTi closed coil springs exhibited a greater rate of space closure than conventional elastomeric chains. Systematic reviews by Mohammed et al. (11) and Sebastian et al. (10) also support this finding. However, the memory chain force delivery system showed more effective space closure than the NiTi coil spring (1.89 mm versus 1.67 mm of tooth displacement over 3 months) (4).
Force decay in orthodontic closing appliances refers to the gradual reduction in force generated by devices like elastomeric chains or coil springs (25). The effectiveness of these appliances depends on maintaining a continuous force, but the force they apply tends to diminish over time due to various factors. Multiple interactions can contribute to this force degradation phenomenon, such as the oral environment, masticatory forces, oral hygiene patterns, salivary enzyme activity, and changes in the oral temperature. Several studies (26-28) reported that maximum force decay occurs within the initial days after elastomeric chain placement. A systematic review by Halimi et al. (29) revealed that the force provided by elastomeric chains diminishes over time. Moreover, a recent systematic review and meta-analysis by Andhare et al. (30) showed that the force decay of elastomeric chains reported in clinical studies was greater than that reported in in vitro settings. However, this difference was not statistically significant.
The problem of rapid force decay in elastomer chains has led some clinicians to opt for NiTi coil springs. The latter can provide light and continuous forces, potentially allowing teeth to move more efficiently (31). Previous studies have also shown that NiTi coil springs were minimally affected by oral temperature and other intraoral environmental factors (29, 32). However, it should be considered that the forces exerted by NiTi closed coil springs also degrade over time. Cox et al. (33) reported a reduction of approximately 12% after 4 weeks of clinical use and an additional 7% force decay occurring within 4 to 8 weeks of using NiTi closed coil springs.
Elastomeric memory chains have been engineered to provide gentle, consistent forces with minimal decay over time (34). Khanemasjedi et al. (4) evaluated and compared the clinical efficiency of a modern elastic memory chain versus a NiTi coil spring space closure system. They concluded that the canine can be retracted at a speed comparable to that obtained using NiTi coil springs by employing an elastic memory chain and replacing it monthly. This performance is attributed to the unique properties of polyurethane materials, which, while not perfectly elastic, exhibit a degree of plasticity over time (35). An in vitro study by Dadgar et al. (36) compared the amount of force decay between elastomeric memory chains and conventional chains after using three different types of mouthwashes and two types of toothpaste. The results showed that memory chains delivered greater forces than conventional chains and were more resistant to the effects of various chemical treatments when evaluated on the first and 28th day after placement.
The present study did not reveal any statistically significant differences between NiTi coil springs and elastomeric chains regarding the amount of anchorage loss. According to the pooled results, NiTi coil springs showed 1.1 mm of anchorage loss after 4 months and 0.29 mm after 6 months (13, 18). An average anchorage loss of 0.82 mm and 0.13 mm were observed after using elastomeric chains for 4 and 6 months, respectively (13, 18). Since different anchorage devices were used in each study, we could not compare the anchorage loss values. Bokas and Woods (14) used a transpalatal arch, and Barsoum et al.(18) used temporary anchorage devices (TADS) to support anchorage. This is while no anchorage control device was used in studies conducted by Chaudhari and Tarvade (13) and Hashemzadeh et al. (17). The amount of anchorage loss significantly improved using skeletal anchorage.
When the force is applied at a distance to the center of resistance of a tooth, it results in undesired movement. Two studies compared the tipping and rotation of canines and molars between the NiTi coil springs and the elastomeric chains. Barsoum et al.(18) found no clinical or statistical difference in canine tipping and rotation between the two groups.
Orthodontic movements may be accompanied by pain and root resorption. According to the findings reported by Barasoum et al. (18) and Badran et al. (15), the pain intensity reported by patients was comparable between the NiTi coil springs and elastomeric chain force delivery systems. However, Badran et al. (15) stated that NiTi coil springs were significantly less comfortable than elastomeric chains. After the initial activation, 71% of patients reported more discomfort on the side with coil springs compared to the side with power chains. After the second activation, 75% of patients reported more severe pain on the side with NiTi coil springs (15). The cited authors also noted that patients found it more challenging to maintain appropriate oral hygiene when NiTi coil springs were in place. Plaque scores were greater on the coil spring than on the power chain side, although this difference was not statistically significant. These findings indicate that patient cooperation is more important than the type of force delivery system for maintaining good oral hygiene. Barsoum et al. (18) compared the amount of root resorption between the NiTi coil spring and elastomeric chain force delivery systems. The results showed no statistically significant differences between the two methods (18).
The main limitation of this systematic review was that it was impossible to conduct a meta-analysis. The main reason was the differences in the designs of studies used in this systematic review. Split-mouth and parallel-group studies require different analytical approaches. If both types of trials are included in a meta-analysis without considering their methodological differences, the results may be unreliable. Separate analyses for split-mouth and parallel-group studies also reduce the number of studies included in each meta-analysis. In addition, there was significant variability in the data extracted from different studies, such as the types of elastomeric chains, difference force magnitude, archwire size, patients' age, and inconsistent follow-up periods. All of these factors complicate the performance of a meta-analysis. More qualified clinical trials are required to clarify the superiority of different force delivery systems in sliding mechanics.
Conclusions
NiTi coil springs and elastomeric chains are effective force delivery systems for orthodontic space closure after the first premolar extraction. A faster rate of canine retraction was observed in the NiTi coil spring than in the elastomeric chain force delivery system. Space closure with elastic memory chains was more rapid than NiTi-closed coil springs. When using NiTi coil springs, canine, and molar tipping and rotation were higher. There was no clinical or statistical difference regarding the amount of anchorage loss, associated pain, plaque control, and root resorption between NiTi coil springs and elastomeric chains.
Acknowledgments
I would like to thank my department head for providing the opportunity to conduct this review, my professor for their guidance and support, and my colleagues for their assistance in locating the final articles used in the analysis.
Conflicts Of Interest
The authors declared that they have no conflict of interest.
Authors’ Contribution Statement
ZF and AH contributed to the management, supervision. BE and MC were responsible for data collection, analysis, and interpretation. , and writing of the manuscript. All authors contributed to the project design, research initiation, and data analysis. All authors have read and approved the final manuscript.
Ethical approval
Not applicable.
Funding
There was no source of funding to declare.
)