Evaluation of space closure rate during canine retraction with nickel titanium closed coil spring and elastomeric chain

Aims: . To investigate the rates of space closure achieved by elastomeric chain and nickel titanium coil springs with the evaluation of the effects of using different bracket types on the rate of space closure during its retraction along different sizes of orthodontic arch wires using typodont simulation system (Ormco). Materials and Methods: The standardization criteria were all typodont teeth situated in well aligned position, covered and immobilized by the acrylic bite except canine, elastic chain and nickel – titanium closed coil spring exerting 180 gm of force on canine measured carefully by tension gauge. The available space was 13.5mm (the rate of space closure). Results: The present study showed that when using elastic chain as a method of canine retraction gave rise to a a significant decrease in the rate of space closure as compared with nickel – titanium closed coil spring also sliding the canine using ceramic brackets gave rise significant reduction in the rate of space closure than when using stainless steel brackets. Another finding of the present study showed that sliding the canine on large rectangular arch wire (0.019x0.025 inch) gave rise to a significant reduction in the rate of space closure when compared with 0.018 inch and 0.018x0.022 inch arch wires were used. Conclusions: It was concluded that the canine retraction with 0.018 inch wire on Roth stainless steel bracket by closed coil spring gave rise a large amount of space closure rate. While the opposite is true for canine retraction with 0.019x0.025 inch wire on standard ceramic bracket by elastic chain retraction method.


INTRODUCTION
Reducing the duration of orthodontic treatment is of great interest to orthodontists. (1)(4)(5)(6) The most time-consuming stage of premolar extractionbased orthodontic treatment is canine retraction.Any procedure which reduces the time required to perform this stage will also serve to shorten overall treatment time. (7)aluation of space closure rate during canine retraction with nickel titanium closed coil spring and elastomeric chain.
Space closure via sliding mechanics can be done via various methods, but the appropriate force is applied via elastic chain or coil springs (8) .(11) As a result .NiTi springs are an alternative in wide spread use .NiTi springs have reported advantage of giving significantly quicker and more constant rate of space closure , ( 2,11-12) but are relatively expensive to use.(13)   The objectives of this study were: (1)  To investigate the difference in the space closure rate between the elastic chain and NiTi closed coil spring during canine retraction .(2) To evaluate and compare the rate of space closure, during canine retraction with sliding mechanics in different bracket types (standard and Roth for both stainless steel and ceramic brackets).(3)  To evaluate and compare the rate of space closure among different sizes of orthodontic arch wires, during canine retraction with sliding mechanics.

MATERIALS AND METHODS
The sample of this study consisted of 24 set of orthodontic brackets (only lower incisors, canines and second premolars) divided into different types (standard and Roth for both stainless steel and ceramic), 240 stainless steel arch wires divided into three sizes( 0.018 inch, 0.018x0.022inch and 0.019x0.025inch), 120 closed coil nickel titanium spring and600 elastic chain ring .all the study was conducted using two typodont models.Retraction of canine by sliding mechanics was done by using one possibility of the 24 different combinations (four different brackets and three different arch wires and two methods of retraction) 24 brackets/arch wire/ method of retraction combination were tested 10 times for each variable (space closure rate, degree of tipping, degree of rotation and vertical assessment of canine) leading to a total of 240 trials for every variable.Two typodonts were prepared; one for standard edgewise bracket system and the other for Roth system.17)(18) This was done by placing the arch wires in the lower arch that were progressively upgraded through leveling and aligning, and finally to a 0.019 X 0.025" inch stainless steel wire, after immersing the typodont in a water bath for 5 minutes.The arch wire was ligated to the bracket by using elastomeric ligature because the high variability of tying ligatures makes the use of elastic ligatures the most consisted and reproducible . (19)Both the nickel titanium close coil spring and the elastomeric power chain were stretched to deliver 180 gm, using tesion gauge. (20)1. Elastic chain was stretched between the hook on the buccal surface of the molar band and canine bracket where the elastic chain attachment can be circumferential around the four tie wings . (3). A NiTi closedcoil spring was engaged between the first molar band hook and the power arm of canine bracket . (21)efore starting movement of canine (left canine only) into first premolar site, criteria of the following important points should be established:1)All typodont teeth situated in well aligned position and covered by the acrylic bite plane (except canines).2)Thedistance between the distal wing of canines bracket and the mesial wing of second premolar's bracket was (13.5 mm).This distance considered as the available space and measured by digital vernia . (13)ate of space closure was measured after each method of canine movement where again the distance between the distal wing of canine's bracket and the mesial wing of second premolar's bracket is measured (11) by using digital vernia.This distance is considered as the remaining space, therefore; Rate of space closure = available spaceremaining space The data was analyzed by using Statistical Package for Soft ware System (SPSS version 11.0 Inc., Chicago) Program was used.
1)Descriptive statistics: To show minimum and maximum values, meam and standard deviation for each variable and in each method of measurements.2)Analysis of Variance (ANOVA): data achieved from previous measurements were initially analyzed by using the three way ANOVA test.3)Duncan's Multiple Range test: These data were then analyzed by Duncan's Multiple Range test to determine the significant differences among the groups.4)Student's ttest: to compare the mean value between the elastic chain and closed coil spring.

RESULTS
The descriptive statistics that include mean, standard deviations, minimum and maximum value of space closure for the 30 experimental groups of this study are listed in Table (1).ANOVA test show significant differences in all variables at p <0.05 in Tables (2,3).4)revealed that in all groups, closed coil spring showed highest mean value for the rate of space closure than elastic chain except on 0.019x0.025inch wire for both standard stainless steel and Roth stainless steel bracket showed no significant differences in the rate of space closure.
Comparison of the Space Closure Rate among Different Bracket Types as demonstrated in Table (4) showed that in both methods of retraction and for the three types of arch wire, the group that use ceramic standard bracket showed the lowest mean value of space closure rate.However, there was no significant difference be-tween standard and Roth type for ceramic and stainless steel bracket in elastic chain retraction group.While in closed coil spring group, the rate of space closure was greater in the Roth type as compared to the standard type for both ceramic and stainless steel brackets in all types of arch wires.
In both methods of retraction as shown in Table (2), sliding the canine along 0.018 inch wire by using four types of brackets produced the highest mean value of the rate of space closure, on the other hand using 0.019x0.025inch wire produced the lowest one.While sliding the canine along 0.018x0.022inch arch wire fell and distributed on a statistical level between the other two arch wires.

DISCUSSION
The present study showed that the sliding method that include Roth type for both stainless steel and ceramic brackets combined with close coil spring on 0.018 inch stainless steel wire gave rise to the highest mean for the rate of space closure.In contrast attachment of elastic chain on ceramic bracket along 0.019x0.025inch wire showed the lowest mean for the rate of space closure.Many reasons affect this result:

Effect of Bracket Materials and Types:
Stainless steel bracket in the present study showed the highest mean value for the rate of space closure that may attribute to the low frictional force value of stainless steel bracket. (22)Comparison of frictional forces produced in ceramic and stainless steel brackets when different wires were used, suggested that for most sizes, the wire in ceramic brackets produced significant greater friction (23) which, in turn, demonstrate greater resistance to sliding . (24)Frictional force generated at the bracket archwire interface tends to impede the desired movement (15) , if it is so great it can minimize or prevent tooth movement . (25)The size of wider brackets is the other contributor that produces greater friction than narrower bracket, so the large size of ceramic bracket around which the stretched modules exert a greater normal force . (15)Narrow bracket (stainless steel) result in increased inter bracket distance, increases wire flexibility and decreases the resultant frictional force . (26)Bishara and Fehr (27) stated that ceramic brackets can cause nicks in the arch wire resulting in more friction between the bracket and arch wire.This can decrease the efficiency of tooth movement.The main advantage of straight wire is the simplicity of the system because after the leveling phase all bracket slots lie in the same plane, this because the Roth bracket have contoured bracket base with built in torque, so that the brackets' slots runs parallel to the horizontal plane such that the midpoint of the slot run through the LA point.This configuration permits sliding mechanics or movement of groups of teeth. (28)This is in agreement with the results of the present study that found sliding the canine using Roth brackets with closed coil spring gave rise a higher space closure than standard brackets.

.Arch Wire Shape and Size:
In the present study, the rate of space closure with round arch wire was greater than rectangular arch wire.This is in agreement with Frank and Nikolai (29) who cited that the distribution of normal force may be a significant factor, where the round wire makes only point contact with a bracket slot edge, while the rectangular wire makes line contact.Also Tecco et al. (30) showed that large rectangular arch wires generate higher friction than round small arch wires.
The amount of tooth movement decreases with an increase wire size . (31)his is in agreement with the present result.Increasing the size of the arch wire increases its stiffness . (32)Here more force is required to slide a bracket along a larger arch wire than smaller one . (33)Also Matarese et al. (34) showed that wires with larger cross sections increase the impact of binding and notching on resisting sliding during dental alignment.

Methods of Retraction:
The choice of force system and the optimum force magnitude are the decisive factors for obtaining the desired tooth movement . (35)Since the use of elastomeric chains and closed coil spring to translate canines during retraction is common in clinical circumstances (19) .It was decided to implement the same systems of retraction in this study.
This study showed that rate of space closure is significantly greater with nickel titanium closed coil spring.These results agreed with other studies . (2,11,18)One possible explanation is that nickeltitanium close coil spring delivers a constant force unlike elastic chain which loses its force rapidly, (37) characterized by an initial exponential decrease reaching 50% because of stress relaxation as reported by Eliades et al. , (37) Eliades and Bourauel (17) and Kim et al. (38) and these results gained of this study.)(41) While Brooks and Hersheg (42) found that when the elastomeric modules were heated the force decreased approximately 30% of the initial force.Also Nattrass et al. (33) confirmed that force decay with elastomeric chains is affected by environment and temperature.Nickeltitanium spring gave the most rapid rate of space closure and may be considered the treatment of choice (13) and more effective in terms of movement . (44)

CONCLUSIONS
1.There was no significance difference in the space closure rate between standard and Roth design for both stainless steel and ceramic bracket in elastic chain retraction group for the three types of arch wire except the rate of space closure on stainless steel bracket along 0.018x0.022inch.2. Sliding the canine by using Roth bracket design with closed coil spring gave rise a higher space closure rate than standard design.3. When using stainless steel bracket, the rate of space closure increase.The opposite is true with ceramic bracket.4. Canine sliding over arch wire of round cross section significantly increases the rate of space closure .The opposite is true with large size rectangular arch wire.

Table ( 1
) Descriptive statistics with comparison of the rate of space closure among all 24 groups.

Table ( 2
) Comparison of the space closure rate among different bracket types Means with different letters vertically have significant difference at p<0.05 according to Duncan test.Number for each group = 10; Measurements in millimeters; * at p<0.05 Table (3) Comparison of the space closure rate among three sizes of arch wires and between elastic chain and closed coil spring.
Means with different letters vertically and horizontally in each bracket type have significant difference at p<0.05 according to Duncan test.Number for each group = 10; Measuremes in millimeters; * at

Table ( 4
) Comparison of the space closure rate between elastic chain and closed coil spring.