|Year : 2017 | Volume
| Issue : 2 | Page : 103-109
Alignment efficiency of standard versus tandem wire mechanics using conventional and self-ligating brackets: A pilot study
Prarthana Bhardwaj1, Saurabh Sonar2, Puneet Batra3
1 Senior Lecturer, Department of Orthodontics, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh, India
2 Prof, Department of Orthodontics, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh, India
3 Prof. and Head, Department of Orthodontics, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh, India
|Date of Submission||16-Nov-2016|
|Date of Acceptance||15-Mar-2017|
|Date of Web Publication||17-Apr-2017|
Department of Orthodontics, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Objective: The objective of this study is to evaluate the clinical efficiency of 0.018″/0.022″ slot self-ligating (SL) bracket system (standard and tandem mechanics) in terms of rate of alignment by comparing it with a 0.022″ slot conventional ligating appliance system (MBT). Settings and Sample Population: The Department of Orthodontics. Materials and Methods: The pilot study was carried out using randomized controlled trial design. Forty patients having Little's irregularity index (II) of 6–15 mm, treated by all first premolars extractions, were randomly allocated to 0.022″ slot conventional ligating bracket system, 0.018″ slot SL bracket system, 0.018″ slot SL bracket system (tandem archwires), 0.022″ slot SL bracket system, and 0.022″ slot SL bracket system (tandem archwires). The rate of alignment for each bracket system was measured from the difference in the II of serial casts taken at pretreatment and at the end of alignment, divided by the number of days between the two measurements. A one-way ANOVA model with post hoc Bonferroni multiple comparison procedures was used to identify intergroup differences. Results: The mean value of alignment efficiency was not found to be statistically significant in any of the five groups using digital models (P = 0.104). Conclusions: Alignment efficiency was not different between SL versus conventional ligating group, the 0.018″ slot versus 0.022″ slot and tandem versus standard mechanics.
Keywords: Alignment efficiency, self-ligation, tandem archwires
|How to cite this article:|
Bhardwaj P, Sonar S, Batra P. Alignment efficiency of standard versus tandem wire mechanics using conventional and self-ligating brackets: A pilot study. J Indian Orthod Soc 2017;51:103-9
|How to cite this URL:|
Bhardwaj P, Sonar S, Batra P. Alignment efficiency of standard versus tandem wire mechanics using conventional and self-ligating brackets: A pilot study. J Indian Orthod Soc [serial online] 2017 [cited 2019 Jun 16];51:103-9. Available from: http://www.jios.in/text.asp?2017/51/2/103/204608
| Introduction|| |
There have always been innovations and advancements in the field of orthodontics. Advancements and innovations are made either to increase the treatment efficiency or to increase patient comfort. A significant change in the history of brackets was the introduction of self-ligating (SL) brackets. Self-ligation is always associated with several advantages, including lower forces and moments and higher rates of tooth movement, because of the reduced friction., Nonetheless, for most of these appliances, there is little evidence about the characteristics and capabilities claimed by the manufacturers, and in some cases, it seems that marketing-derived principles rather than scientific evidence are used to substantiate their well-advertised clinical performance.
In SL brackets, the bracket slot lumen and the small round archwires allow for significant play in the system, so there is some loss of control. It is this play that allows for the effortless unraveling of crowded teeth, but it also presents a challenge when clinician wants to control these movements. Light initial archwires in standard mechanics will begin leveling and aligning of the teeth, but not complete it. Once the archwire is no longer being deflected, due to the “play” between the small round archwires and the bracket slot, the unloading forces are diminished, and tooth movement stops. Tandem archwires [Figure 1] can be ligated at this time (0.014″ and 0.014″ in 0.018″ slot and 0.014″ and 0.016″ in 0.022″ slot) which will provide the needed control for both the first- and second-order corrections. It has been promoted that these archwires provide complete rotational and angulation correction as well as full vertical correction due to the vertical alignment of the two archwires.
|Table 1: Pretreatment irregularity index and postleveling and alignment irregularity index|
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In addition, there has been debate about the relative advantages of two slot sizes, i.e., 0.018″ and 0.022″ over each other. The 0.018″ bracket slot can be filled earlier in treatment to provide early torque control of anterior teeth. In addition, the smaller, more flexible finishing archwires used with the 0.018″ slot are easier to manipulate late in orthodontic treatment. Conversely, the 0.022″ slot allows more freedom of movement for the starting wires, which keeps forces lighter initially. Later in treatment, the steel rectangular working wires of 0.019″ × 0.025″ are stiffer, and they show less deflection and more binding during space closure. With little clinical evidence to show advantages of either of the bracket systems, orthodontists are forced to make clinical decisions with little scientific guidance.
The purpose of this study was to compare the clinical efficiency of 0.022″ slot conventional ligating preadjusted edgewise appliance system (MBT) in terms of rate of alignment with following: (1) 0.018″ versus 0.022″ slot SL bracket system and (2) standard versus tandem mechanics.
| Materials and Methods|| |
A total of 46 patients requiring orthodontic treatment were prospectively selected for the study who visited the Department of Orthodontics. Ethical approval was obtained from the Ethical Committee of the hospital. The following inclusion criteria were taken into consideration for case selection: Good general health, no medical contraindications, permanent dentition, having no previous orthodontic treatment, 14–25 years of age, periodontally sound dentition, Class I and Class II Division 1 cases with Little's incisor irregularity index (II) of 6–15 mm, orthodontic treatment plan, including extraction of all first premolars. All patients were informed of the purpose of the study. All recruited patients signed a consent letter indicating their voluntary participation. The patients were treated by five different clinicians in the department. Six patients failed to meet the selection criteria. Out of the remaining 40, five were lost to follow-up (three due to refusal of getting extractions done and two due to change of residence) and finally 35 patients were analyzed. The patients were compliant with the treatment because they attend the sessions of the treatment on time.
The baseline comparability was checked by comparing the pretreatment II of all the groups using the ANOVA test. The difference was not found to be statistically significant (P = 0.442).
The patients were randomly allocated for treatment with either bracket system using a restricted random number table to ensure the equivalence of numbers in each group. Allocation concealment was done using sealed envelopes.
Because the brackets were visible to both the patient and the orthodontist, blinding of bracket allocation was impossible. Blind evaluation was done as all measurements were made by the same examiner after de-identification of all the digital models. Statistician could not be blinded to results but was blinded to treatment assignment.
No co-interventions were used during the study.
To compare alignment efficiency
Mandibular and maxillary dental study casts were prepared at the following time intervals: (a) pretreatment (T1) and (b) at placement of stainless steel wire (T2). The rate of alignment for each bracket system was measured from the difference in the Little's II  of serial casts taken at T1 and T2, divided by the number of days between the two measurements.
The II, defined as the summed displacement of adjacent anatomic contact points of the six mandibular anterior teeth, was used to quantify the degree of malalignment. Although formulated for use on the lower arch, it has also been applied to the upper arch.
Although contact points of the anterior teeth can vary in the vertical plane also, but all vertical discrepancies of contact points are disregarded using this index. Hence, to overcome this disadvantage, digital models were prepared. Both horizontal and vertical discrepancies of the contact points are taken into consideration while measuring II on digital models.
Three-dimensional (3D) scanning of the plaster models was performed using the White Light scanner (COMET5, 100-200-400, Steinbichler Optotechnik, Germany) and 3D reverse modeling software program. The 3D models obtained were stereolithographic models in STL format [Figure 2]. Measurements were done using COMET INSPECT Inspection Software (Steinbichler Optotechnik, Germany) to the nearest 0.001 mm (resolution = ±0.000001 mm) [Figure 3].
All measurements were done three times, and the mean was recorded to decrease the bias.
| Results|| |
Forty patients met the inclusion criteria. Out of 40, five were lost to follow-up and finally, 35 patients were analyzed. CONSORT  flowchart is given in [Figure 4].
|Figure 4: CONSORT flow chart of participants through each stage of the trial|
Click here to view
The data were analyzed using the Statistical Package for Social Sciences version 16.0 (Chicago, SPSS Inc.). Mean and standard deviation (SD) for each of the five groups were calculated for digital models, and one way ANOVA test were conducted for the following factors: pretreatment and postleveling and alignment II, number of days required to achieve leveling and alignment, alignment efficiency.
Post hoc tests–Bonferroni multiple comparison test were done for each group with other four groups.
The values are represented in number (n), mean (υ), and SD. Significance between groups was calculated at 5% level, i.e., P < 0.05 was counted as statistically significant.
Irregularity assessed using digital models
Pretreatment irregularity index and postleveling and alignment irregularity index
Mean pre-II and post-II values are tabulated in [Table 1] and [Figure 5]. The differences in the mean values of II of different groups were compared using the ANOVA test. The difference was not found to be statistically significant (P = 0.442).
|Table 1: Pretreatment irregularity index and postleveling and alignment irregularity index|
Click here to view
|Figure 5: Mean pretreatment irregularity index and postirregularity index for different groups using digital models|
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Difference (pretreatment irregularity index − postirregularity index)
Mean values for difference are tabulated in [Table 1]. The mean value of II in 0.022″ conventional ligating group was 10.52 ± 5.20 mm, in 0.018″ SL group (standard mechanics) was 11.87 ± 6.81 mm, in 0.018″ SL group (tandem mechanics) was 10.96 ± 2.69 mm, in 0.022″ SL group (standard mechanics) was 11.97 ± 5.87 mm, and in 0.022″ SL group (tandem mechanics) was 11.64 ± 4.42 mm. The difference in the mean value of alignment efficiency with different groups was compared using the ANOVA test. The difference was not found to be statistically significant (P = 0.936).
Time required to achieve leveling and alignment
Mean values for number of days required to achieve leveling are tabulated in [Table 1] and [Figure 6]. The 0.022″ conventional ligating group required 92.50 ± 11.71 days, 0.018″ SL group (standard mechanics) required 105.86 ± 28.11 days, 0.018″ SL group (tandem mechanics) required 126.21 ± 8.08 days, 0.022″ SL group (standard mechanics) required 90.29 ± 6.73 days, and 0.022″ SL group (tandem mechanics) required 127.86 ± 8.24 days. The number of days required for different groups were compared using the ANOVA test. The difference was found to be statistically significant (P = 0.000). Post hoc Bonferroni test showed that number of days required to complete leveling were significantly more in 0.018″ SL group (tandem mechanics) and 0.022″ SL group (tandem mechanics) than all other groups.
|Figure 6: Mean of number of days required to achieve leveling and alignment|
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The mean value of alignment efficiency in 0.022″ conventional ligating group was 0.12 ± 0.06 mm/day, in 0.018″ SL group (standard mechanics) was 0.11 ± 0.05 mm/day, in 0.018″ SL group (tandem mechanics) was 0.09 ± 0.02 mm/day, in 0.022″ SL group (standard mechanics) was 0.13 ± 0.06 mm/day and in 0.022″ SL group (tandem mechanics) was 0.09 ± 0.03 mm/day. The difference in the mean value of alignment efficiency with different groups was compared using the ANOVA test. The difference was not found to be statistically significant (P = 0.104) [Table 1].
| Discussion|| |
The conventionally ligated bracket independently is unable to effect and control tooth movement because it relies on ligature to secure archwire to it. The limitation imposed by this bracket-ligature-archwire relationship compromises the clinical efficiency of the appliance. Moreover, conventional ligated brackets causes increased levels of frictional resistance through the elastomeric attachment between the bracket and archwire. With tie wing brackets, an improvement in control is usually at the cost of an increase in friction, especially with elastomeric ligatures. This point has been well illustrated by Matasa. To reduce unwanted friction, various SL bracket systems have been developed. With self-ligation, the requirement for an elastomeric attachment is eliminated and is associated with considerably reduced friction with different archwires. SL brackets also offer more certain archwire engagement, a requirement for less chair-side assistance, and faster archwire removal and ligation. Significantly, reduction in overall treatment, time has been associated with these appliances., However, this is not necessarily associated with more faster tooth alignment.,
Various studies have shown that SL brackets generate significantly lower levels of in vitro friction than do conventionally ligating brackets.,,, This has led to the promotion of SL brackets on the assumption that decreased friction leads to enhanced clinical efficiency. However, the present study concurs with the growing body of evidence that there is no statistically significant difference in treatment efficiency between SL and conventionally ligating brackets during initial alignment.
The present study has shown that there is no statistically significant difference in alignment efficiency of the conventional ligating appliance and SL appliance system, either with 0.018″ or 0.022″ slot [Table 1]. Clinical effectiveness was measured in terms of rate of tooth alignment.
Early clinical studies by Eberting et al. and Harradine  reported decreased total treatment times and fewer appointments for patients treated with Damon SL brackets. However, these retrospective studies were potentially subject to bias. The effect of confounding factors might have been considerable because the selection criteria were not well detailed, and the pretreatment characteristics of the sample were not tested for equivalence.
In the present study, the pre-II was checked for equivalence and it was found that there were no significant differences between pre-II of all the five groups. Archwire sequence was different for different groups as the slot sizes were different.
Well-designed prospective studies reported no significant differences in treatment efficiency between SL and conventionally ligating brackets during initial alignment.,,, Most of these studies evaluated the alignment efficiency of the mandibular anterior arch because rotations, irregularity and small interbracket distances are typically encountered in this region. In the present study, the data for both maxillary and mandibular arches were pooled as there was no statistically significant difference in the alignment efficiency of maxillary or mandibular arches.
In the present study, the anterior alignment of both arches was investigated with the II. Crowding was selected as a model for examining the efficiency of brackets because correction of this discrepancy largely depends on the “free play” or clearance of the archwire inside the slot walls. Alleviation of crowding is a treatment process, in which both initial and final stages can be quantitatively determined with the II, and measurements can be made regardless of tooth inclinations or rotations, as opposed to retracting canines, where these two parameters can interfere with the assessment of crown spatial orientation.
Various authors have drawn the same conclusions irrespective of the particular brand of SL bracket. Miles et al. and Miles  did not find any significant differences when they prospectively compared Damon SL and SmartClip (3M Unitek) SL with Victory Series conventionally ligating brackets during initial alignment. Pandis et al. also found no difference when comparing the time to alignment in the mandibular arch between Damon 2 (Ormco) self-ligating and Microarch (GAC International, Bohemia, NY, USA) conventionally ligating brackets. A large, retrospective study concluded that Innovation (GAC) SL brackets had no measurable advantages over victory series conventionally ligating brackets in initial alignment time, total treatment time, or number of appointments. Scott et al. conducted a randomized controlled trial of patients having mandibular first premolar extractions. They concluded that Damon 3MX brackets were no more efficient during mandibular alignment than synthesis (Ormco) CL brackets.
However, for moderate crowding with an II of <5 mm, there is some evidence that Damon 2 brackets can produce faster correction although this becomes marginally insignificant for more severe crowding. A possible explanation for this finding is that as teeth become more displaced, free sliding of the archwire in the bracket slot is negated. This might explain the lack of a significant difference between appliance systems in the present study, where the mean initial II was about 12.765 mm, representing more severe crowding.
Tandem versus standard mechanics
One of the unique aspects of passive SL appliance systems is the ability to control first- and second-order movements with the use of small dimension round nickel titanium archwires that deliver low forces. However, as the bracket slot lumen and the small round archwires allow for significant play in the system, there is some loss of control. It is this play that presents a challenge when we want to control the movements. Initial archwires will begin leveling and aligning of the teeth, but not complete it. Once the archwire is no longer being deflected, the unloading forces are diminished and tooth movement stops. Tandem archwires can be ligated at this time (0.014″and 0.014″ in 0.018″ slot and. 014″and. 016″ in 0.022″ slot) which will provide the needed control for both the first- and second- order corrections. It has been promoted that these archwires provide complete rotational and angulation correction, as well as full vertical correction due to the vertical alignment of the two archwires.
In the present study, it was evaluated whether tandem mechanics is more or less efficient in alignment of arches as compared to standard mechanics. No statistically significant difference was found between the efficiency of tandem versus standard mechanics [Table 1]. Clinically, it was found that tandem groups were less efficient than the corresponding standard mechanics groups. This can be explained on the basis of the archwire sequence used. Tandem groups received one extra archwire, i.e., tandem archwires, so number of days before the tandem archwire was placed was increased in these groups. As alignment efficiency was calculated by dividing the difference of II by number of days, so alignment efficiency of 0.018″ SL and 0.022″ SL tandem groups was found to be lower.
0.018″ versus 0.022″ slot
There has been debate about the relative advantages of two slot sizes, i.e., 0.018″ and 0.022″. This trial was done to evaluate the clinical efficiency of 0.018″/0.022″ slot SL bracket in terms of rate of alignment by comparing it with a preadjusted edgewise appliance system (MBT). Results showed that there was no difference in the alignment efficiency of 0.018″/0.022″ slot SL versus 0.022″ conventional ligating brackets [Table 1].
| Conclusions|| |
There is no difference in terms of alignment efficiency between:
- SL versus conventional ligating bracket systems
- 0.018″ versus 0.022″ slot brackets
- Standard versus tandem mechanics.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]