A comparative evaluation of rate of retraction and anchorage loss using nickel titanium closed coil spring and active tiebacks during the en-mass retraction in mandibular arch-an in-vivo study

Objective:To compare clinical effectiveness of Nickel Titanium (Ni-Ti) closed coil spring and active tiebacks during space closure in mandibular arch. To compare rate of anterior retraction by using Ni-Ti closed coil spring and active tiebacks in mandibular arch. To compare amount of anchor loss in mandibular arch with Ni-Ti closed coil spring and active tiebacks. Materials and Methods: A total of 20 patients with Class 1 bimaxillary proclination undergoing fixed orthodontic treatment (MBT 0.022 slot) after first premolar extraction will be randomly selected from depatment of Orthodontics & Dentofacial Orthopaedics of K.D. Dental college, and will be divided into two groups for space closure. Patient will be informed about treatment and thesis procedure and consent regarding was taken. The space closure mechanics was allocated to the left or right side of same arch wire in each patient. Group 1 consisted of 10 patients in which right quadrant of maxillary arch, the space closure was done by Ni-Ti closed coil springs in 10 patients and by active ligature on left quadrant of the same 10 patients. Group 2 consisted of same 10 patients in which left quadrant of same arch, the space closure will be done by active ligature in 10 patients and by Ni-Ti closed coil springs on right quadrant of same 10 patients. The amount of anterior retraction, anchorage loss and rate of space closure was measured before start of retraction and patients will be called at six week interval for evaluation of retraction rate as T0, T1, T2, T3,T4. Results will be assessed on cast and Lateral Cephalogram were repeated at T4 for evaluation of anchorage loss. Result: Rate of anterior retraction and amount of anchorage loss was found to be slightly more with niti closed coil spring as compared to that of active tie back. Conclusion: NiTi closed coil springs achieved faster space closure as compared to the active tieback and significant amount of anchorage loss was also noted with NiTi closed coil when compared with active tieback.


Introduction
Anchorage is the nature and degree of resistance to displacement offered by an anatomic unit when used for the purpose of effecting tooth movement and Anchorage Loss (AL) is a reciprocal reaction that could obstruct the success of orthodontic treatment. Among the three stages of comprehensive fixed orthodontic treatment, the second stage i.e. space closure 3 is one of the most challenging aspects as it aims to correct the molar and buccal segment relationships to provide normal occlusion, close extraction spaces, and correct excessive or negative overjet. Previous studies 7 specifically considered the relationship between the rate of tooth movement and applied magnitudes of force in humans. Some studies [8][9] stated that super elastic NiTi coil springs resulted in a significantly greater and more consistent rate of space closure than elastic modules.

Materials and Methods
The present study was undertaken at the Department of Orthodontics and Dentofacial Orthopaedics, K.D. Dental College, Mathura. This study was conducted on 20 participants to evaluate Rate of Retraction and Anchorage loss using Nickel-Titanium Closed Coil Spring And Active tiebacks during theen masse retraction in mandibular arch. Unitek (USA), on rate of space closure in terms of en-mass retraction and anchore loss in mandibular arch. Space closure was carried out on 0.019 x 0.025 -inch stainless steel arch wires. with anchorage balance between the six anterior teeth against the second premolar and first molar. Space closure involved both incisor retraction and molar protraction, to varying degrees, in all patients with anchorage balance controlled by anterior torque adjustments in the arch wire. After the initial leveling and alignment ( Figure 1) with round NiTi wires upto rectangular SS wire i.e 0.019 × 0.025 SS. with crimpable hook of 8 mm in height distal to lateral incisors on 0.019 × 0.025 SS wire was placed , and was left for 4 weeks in all subjects for space closure. The space closure mechanics were allocated to the left or right side of same arch wire in each patient by random selection, to achieve within patient control.

Inclusion Criteria
Patients were randomly divided into two groups:-Group A consisted of 20 patients, in whom any one quadrant of mandibular arch space closure was done with Ni-Ti closed coil springs.
Group B consisted of same 20 patients in whom other quadrant of same arch space closure was done with active tiebacks (O-ring with 0.010" ss ligature wire.  After 4 weeks en-masse the retraction (Figure 7) was carried out in both the groups.In 20 patients belonging to group 1 retraction was done using a NiTi closed coil springs of 9 mm in length (G & H NiTi closed coil springs with eyelets, USA). The springs were not stretched to more than 12 mm (as suggested by Manhartsberger and Seidenbusch). In 20 patients belonging to group 2, retraction was done with active tiebacks (O-ring(3M Unitek, USA) with 0.010" ss ligature wire); which was placed from the first molar hook to the crimpable hook welded on the archwire. The active tiebacks was prestretched to approximately twice its resting length to reduce the force decay 18 and changed at each subsequent visit.

Assessment of outcomes
The amount of anterior retraction, anchorage loss and rate of space closure were measured before start of retraction and patients were called at six week interval for evaluation of retraction rate as T0, T1, T2, T3, T4. Results were assessed on cast and Lateral Cephalogram was repeated at T4 for evaluation of anchorage loss.
In all four visits measurements were taken with the help of verniercalipers and clinical photographs were taken ( Figure  8). Space closure was assessed by measuring the study models the distance from the cusp tip of the mandibular canine to the mesiobuccal groove of the first mandibular molar on both sides with the Vernier Calliper.  Anterior retraction = total retraction space closure − anchorage loss

Statistical Analysis
The observations obtained in the study were subjected to statistical analysis, so as to get their interpretation. All quantitative variables, e.g., space closure, anchor loss, anterior retraction were described using mean ± standard deviation (SD) and compared using students unpaired t-test. P < 0.05 was considered as significant.
The force values on the first and fourth month of retraction were tabulated and were subjected to: UnPaired sample Ttest

Discussion
In case of bimaxillary protrusion, extraction of 1st premolar is needed. Orthodontic treatment involving extraction of teeth, often there is a need to close extraction space, after the initial levelling and alignment.
The present study was designed to compare the rates of space closure, molar anchorage loss and rate of anterior retraction when using standard NiTi closed coil springs and active tiebacks.

Rate of Space closure
The rate of space closure was measured and calculated for both the groups (Table1). In this study, the NiTi closed coil springs produced rapid rate of tooth movement(0.92mm) as compared with conventional active tieback(0.49mm) which was statistically highly significant(p value 0.000). Our findings are also in accordance to the findings of Al-Sayagh 35 and Ismael and von Fraunhofer. 19

Fig. 12: Anchorage Loss
It was observed that the use of NiTi closed coil springs lead to more anchor loss(1.80 mm) as compared to active tieback(1.03 mm),which was found to be highly significant (P = 0.000) as shown in Table 2.

Rate of Anterior Retraction
The total amount of anterior retraction was calculated by deducting the anchor loss from the total retraction space. This was calculated for both the groups and the mean was found. This shows that the anterior retraction was comparatively more in NiTi closed coil groups(1.98 mm) when compared to active tieback(0.98 mm) and statistically revealed that this difference washighly significant (P = 0.001) as shown in Table 2.
In spite of more anchorage loss the effective anterior retraction was more in NiTi closed coil springs.

Fig. 14: Anterior retraction
However, actual force application is difficult to be determined in-vivo, due to biological and mechanical reasons (tooth morphology, root length and periodontal architecture, chewing etc.). In this study, these variations were not considered.

Results
When space closure was compared between NiTi closed coil group and active tie back group at T1, T2, T3 and T4, the mean value for group 1 was 0.93 mm, 0.85 mm, 0.95 and 0.95 mm whereas for group 2 was 0.48 mm, 0.50 mm, 0.50 mm and 0.48 mm respectively as shown in Table 1. The unpaired t-test, when applied, revealed that this difference was statistically highly significant (P = 0.000) at T1, T2, T3 and T4. This showed that there was a faster rate of space closure by NiTi closed coil springs as compared to active tieback. For NiTi closed coil group the average anchorage loss in 6 months was 1.80 mm while for active tieback group it was 1.03 mm as shown in Table 2  For NiTi closed coil group the average anterior retraction in 6 months was 1.98 mm while for active tieback group it was 0.98 mm as shown in Table 2. The unpaired t-test when applied revealed that this difference was statistically highly significant (P = 0.000). This shows that the anterior retraction was comparatively more in NiTi closed coil groups when compared to active tieback.

Conclusion
In this study we have used NiTi closed coil spring and active tie backs for space closure. The prospective observation of 20 patients and evaluating the results, the following conclusion would be drawn:-NiTi closed coil springs achieved faster space closure as compared to the active tieback. Significant anchorage loss was also noted with NiTi closed coil when compared with active tieback. In mild to moderate anchorage cases, space closure with NiTi closed coil springs with an increased rate of anterior retraction and anchor loss can be recommended. However, in critical anchorage cases, reinforcement of anchorage, while using NiTi closed coil springs for space closure, is recommended. This study also recommended further research in controlling anchorage loss and effective tooth retraction without causing any undesired biologically and physiological reaction and stable anchorage control.