Dr. S.M. Shiva linga

Dr. Raghunath N

Abstract

KeyWords

" A Comparative Evaluation of Canine retraction and Anchorage loss using Self-ligating and conventional MDT Pre-adjusted edgewise bracket systems - A Clinical Study"

Authors:

Dr. Vikas Agrawal, B.D.S. (Corresponding author) Post Graduate Student, Department of Orthodontics & Dentofac ial Orthopedics, J. S.S. Denta l Col lege & Hospita l, 5.5. Nagar, Mysore (Karnatakal - 570015 . Phone: 09341854410.

Dr. B.M.Shivalinga, M.D.S. Professor, Dept. of Orthodontics and Dentofacial Orthopedics, J.S.S. Dental Co llege and Hospita l, 5.5. Nagar, Mysore (Karnatakal-5 70015. Phone: 09886844840.

Dr. Raghunath N., M.D.S. Associate Professor, Department of O rthodontics & Dentofacia l O rthopedics, J.S.S. Dental Co llege & Hospital , Mysore (Karnatakal - 570 015.

The purpose of th is clinica l study was to compare the rate of canine retraction between self-ligating SmartClip (3M Unitek) and conventional (3M Unitek) MBT preadj usted edgewise bracket systems. Anchorage loss as a result of this movement was also eva luated. The study sample consisted of B adolescent or adult patients in w hom first premolar extractions were indicated as a part of orthodontic treatment. Space closure was achieved on 0.019 x 0.022-inch stainless steel w ire w ith 9mm (150gmsl nickel-titanium closed coi l springs (3M Unitek) . The patients were recalled after every 4weeks unti l 1 side had complete retraction of canine. Measurements were performed by direct technique f rom stone cast obtained before and at the completion of retraction with the help of digital vernier ca liper. The rate of retraction and anchorage loss were eva luated. The resu lts indicated that the mean rate of retraction was 1.1717 mm 0.1 3562 mmlinterva l and 1.1209 mm 0.13298 mmlinterva l for self- ligating and conventional M BT preadjusted edgewise brackets respectively. The average difference in the rates of retraction was 0.0508 mmlinterval. There was no statistica lly significant difference in the rates between self- ligating and conventional brackets (p=0.060). The mean anchorage loss was 1.8375 mm 0.44381 mm for self- ligating bracket and 1.9500 mm 0.45591 mm for conventional bracket. The mean di fference in anchorage loss was 0.1 125 mm. The difference in the amount of anchorage loss was also not statistically significant (p=0.069). Self- ligating bracket, conventional bracket, rate of retraction, anchorage Loss.

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INTRODUCTION Ort hodontic treatment with sliding mechanics involves a relative displacement of wire through the bracket slots and whenever sliding occurs, frictional res istance is encoun tered .' Fri cti on may stop tooth movement entirely and/or jeopardize anchorage. The magnitude, contro l and cl inical signifi cance of thi s fri cti onal res istance are largely unknown.' Up to 60% of the applied force is dissipated as fri ction which reduces the force ava ilable for tooth movement, such that an adequate translating force must be appl ied in order to overcome the frictional force. With increasi ng frictional res istance, proporti onall y greater forces would be required.'

It has been stated that friction was determined mostl y by the nature of ligati on and not by dimensions of diiferent archwires. Friction is related to the appl ied normal force, which is influenced by the degree of tension of the ligature engaging the archwire into the slot and the coeffi cient of fri ction between the ligatu re and the arch w ire materi aL'

An approach to reducing fri ction has been to avoid using any form of ligation. Th is has been achieved by Self-ligating bracket systems.' The first Se lf-li gating bracket, the Russell attachment, was developed by a New York Orthodontic pioneer, Dr.Jacob Stolzenberg, in the early 1930s,. The mechanism of this revolutionary bracket was in sta rk contrast to the traditional approach oi tying steel l igatures tightly around each bracket. It had a i lat head sc rew seated snugly in a circular, threaded opening in the face of the bracket. '

Self-l igating brackets are ligature less bracket systems that have a mechanica l device, an acti ve clip or a pass ive slide built into the bracket to close off the edgewise s10t. 5 D ifferent bracket types w ith adjustable labial covers (Self- l iga t ion brackets) have been manu factured that suggest such brackets generate less friction, and allows for faster sliding mechanics because the labia l cover may not contact the arch w ire and therefore elimi nate one source of the normal force caused by pressure from conventional steel ties or elastomeric ligatures ' It would than be expected that the Se l f- l iga ting bracket may reduce the overall trea tment time.

To assess the efficiency and to examine the more recent bracket systems, this clin ica l study was conducted to compare and eva luate the rate of canine retraction and anchorage loss using self-ligating and conventional MBT pre-adj usted edgewise bracket systems tied w ith steel ligature w ire.

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AIMS AND OBJECTIVES OF THE STUDY: To determine the efficiency of self- ligating brackets during segmental canine retraction by compari son of

Rate of canine retraction using self-l igati ng and conventi onal MBT preadjusted edgew ise bracket systems tied w ith steel ligature w ire.

Anchorage loss after canine retraction using self- ligating and conventional M BT preadjusted edgewise bracket systems ti ed w ith steel ligature w ire.

MATERIALS AND METHODS: Eight orthodontic patients (5 female and 3 male) who needed first premolar extraction and canine retraction bilaterall y in the max illa as a part of orthodontic treatment were selected. The patients' age ranged from 13 to 25 years. The pati ents selected, were undergoing o rth odonti c trea tment in the D epartment of O rthodonti cs and Dentofacia l Orthopedics, J. S. S. Dental College and Hospital, Mysore. Each patient received two different brackets placed on oppos ite canine teeth within the max illary arch. The canine brackets used in the study were self-ligating (SmartCi ip) MBT preadjusted edgewise bracket, (0.022 inch Slot) on ri ght si de and conventional MBT preadjusted edgewise bracket, (0.022 inch Slot) on left side ..

SElECTION CRITERIA: Inclusion Criteria:

Subj ec ts w ho needed sepa rate ca nin e retraction and first premolar extraction as a part of orthodontic treatment.

Subjects w ith permanent dentit ion and who demonstrated Class I and/or class II division 1 molar relationship.

Canine retraction of atleast 3 mm was required. No previous orthodontic treatment has been

taken by any of the subjects. Exclusion Criteria:

Patients w ith oral mani festations of disease or a chronic debilitating disease.

Periodontally compromised patients.

DETERMINING RATE OF RETRACTION: The rate of retraction was ca lculated as the distance traveled divided by the time required to complete space closure. Thi s was recorded in millimeters per interval. An interval was defined as a 4-weeks period! The canines were retracted w ith Class 1 mechanics using 9mm (150gms) Nickel-Titanium (N iTi) Closed coil

spring (3M Unitek) extending from the first molar to the canine bracket in max illary arch.

Pati ents were seen at 4-weeks interva l until retraction was compl eted . A continuo us, pass ively fitt ed 0.01 9 x 0.02 5 inch stainless steel arch wire was used for canine retraction. Initial leveling and aligning was done as required and measurements of retraction and anchorage loss w ere not made until leveling procedure was completed in all patients. When the working arch w ire (0.019 x 0 .025 inch stainless steel) had been in place for atleast 4 weeks, prior to canine retraction, max ill ary arch impress ion (TO) was taken of each pa ti ent. It wa s no t known exactl y w hen ca nine retraction was completed w ithin an interva l. Thus the midpoint of the last interva l was declared as the end point of retraction and aga in maxi Ilary arch impression (T1 ) was taken of each patient. ' Measurements were performed by direct technique from stone casts obtained before (TO) and at the completion (Tl ) of retraction with the help of d igital verni er ca liper. Verni er ca liper was used to measure the maximum distance between the cusp tip of the canine to the central fossa of the first permanent molar at TO and T1 . The difference between the initial (TO) and final (T1 ) measurements w as ca lculated to give the distance of retracti on, and this was divided by the number of interva ls (months) to give the rate of retraction in millimeters per interval. This measurement was repea ted th ree times and the mea n va lue was taken.'

DETERMINING ANCHORAGE LOSS: Anchorage loss was recorded as the amount of movement in millimeters that occurred in the direction opposite to the d irecti on of the applied resistance. D irect cast measurements were used rather than radiographs. This method was considered to be easier and accurate, and did not subject pati ents to excessive radiation exposure. To measure the movement of each mo lar, an acryli c palatal plug was made on each maxillary arch. This plug could thus be transferred from initial cast (TO) to the final cast (Tl ) on the same pati ent. The plug was fabricated from acrylic w ith reference w ires (0 .019 x 0.025 inch stainless steel) embedded in the acry lic that extended to the cusp tip of the canine and to the central fossa of the first mo lar. The initial model (TO) was used to make the plug, which was then fitted to the final model (T1 ) on the completi on of re trac ti o n o f bo th ca nin es. (Fi g- 1,2,3). Thi s superimposition allowed for the direct observati on of the amount of molar protracti on (anchorage loss). ' .' The data obtained were subjected to stati sti ca l analys is. Descripti ve stati sti cs, Paired sa mpl e " t" test and

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Pearson's correlation coefficient tests were applied to the results.

Results: Rate of retraction of the canine: (Table I and Graphs I) The maximum rate for the self- ligating bracket was 1.36 mm/ interva l and for the conventional bracket it was 1.24 mm/ interva l. The min imum rate was 1.0 mml interval for the self- ligating bracket, and 0.91 mml interva l for the conventional bracket. The mean rate of retraction was 1.1 71 7 mm 0.13562 mm/interva l and 1.1 209 0.13298 mm/ interva l respecti ve ly. The average difference in the rates of retraction was 0.0508 mm/ interva l. There was no stati sti ca ll y significa nt difference in the rates between se lf- li ga ting and conventional brackets (P=0.060). Anchorage loss of molar: (Table II and Graph II) The self-ligating brackets max imum anchorage loss was 2.20 mm w ith a minimum of 0.8 mm and a mean of 1.8375 0.44381 mm. The convent ional bracket had a maximum anchorage loss of 2.4 5 mm, a minimum loss of 1.0 mm, and a mean loss of 1.9500 0.45591 mm. The mean difference in anchorage loss between self-ligating and conventional bracket was 0.11 25 mm. The difference in the amount of anchorage loss was also not stati sti ca ll y signi fica nt (P=0.069). Correlation of rate of retraction and anchorage loss for the self-ligating and conventional brackets. There was no stati sti ca ll y signifi ca nt correlat ion between anchorage loss and the rate of retracti on for se lf- liga ting (p=O.887) and convent ional bracket systems (P=O.820).

DISSCUSION: Self-liga ting brackets have been developed in an attempt to better approx imate the idea l properti es by overcoming the limitati on of steel and elastomeric ligatures in terms of comfort, efficiency, ease of use, discolouration, p laque accumulation and fri cti on.

Numerous in-v itro studi es have demonstrated a dramatic decrease in fri ction for Self- liga ting brackets, compared to conventional bracket des igns, 1.J.4.'11 with passi ve Self-ligating brackets showing less fricti on than acti ve Self-liga ting brackets. " " Such a reduction in fri c ti on ca n help shorter overall trea tment time, especia lly in extraction cases where tooth translation is achieved by sliding mechanics.

Interpreting the result of the present study, showed that there is small clini ca I difference in the rate of retracti on between pass ive se lf-liga tin g and conventi onal preadjusted edgewise bracket tied w ith stainless steel

ligature; which may be due to the "reduction in friction" but it was not signi ficant.

The results of the present study indicated that there was variability among the subjects. This was noted with the time interva ls, the rate of retract ion and the anchorage loss. This can be attributed due to the biologic response, and the individual variation in ti ssue reaction. The resu lts of the prior studies"'" concluded that the individual va ri ation in metabolic response was so great, that it overwhelmed any differences caused by the force magnitude. And also there was a large v;Hiation between patients, which precl udes the formation of simple theor ies rega rding force and anchorage. This indicated that the variable in metabolic response and not the magnitude of the force is accounted for the major source of va ri at ion. It is generall y considered va lid that higher forces produce more rapid movement than lighter forces, probably only wi thin the individual pat ient.

The in itial force application should be light, because th is produces desi rable biologic effects. This lighter force will produce less extensive hya linized tissue that can be readily replaced by cellular elements." It was estimated that a force between 100 and 200 gms wou ld be effi cient for canine retraction and the duration of applied force is far more influential than its magnitude, i.e. that light forces acting for atleast 4-6 hours have greater effect on the dentition than heavy forces which arc sustained momentarily. " ." Also it is stated that 150 to 250 gms of force for maxillary canines and 100 to 200 gms of force for mandibular canines is appropriate for translatory movement. ' Therefore, in the present study the force selected for canine retraction to close extraction space was 150 gms with the help of Nickel-Ti tani um (NiTi) Closed coil springs.

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"Anchorage loss" is the term traditionally used for mesia l movement of molars in the sagittal plane'" In the present study anchorage loss was determined in the max illary arch alone because the anterior palata l vau lt could be used as a stable reference point. In the present study direct cast measurements were used rather than radiographs. Th is method was considered to be eas ier and accurate and did not subject patients to excess ive radiation exposure.

The mean difference in anchorage loss found in present study between self- ligat ing and conventional PEA bracket was not statistica ll y and clinically signifi cant. Previous studies" has shown that 5% to 50% of the total extraction space can be taken up by an anchor unit made up of the first molar and the second premolar when used to retract canine.

A correlation test was performed for the anchorage loss and rate of retraction for both bracket system i.e. self-ligating and conventional MBT preadjusted edgewise bracket system. There was no statistically significant correlation between anchorage loss and the rate of retraction for either bracket system.

CONCLUSION: The following conclusion can be drawn from this study:

There was no significant difference in the rates of canine retraction between self-ligating and conventional MBT preadjusted edgewise bracket systems.

The difference in anchorage loss between self-ligating and conventional MBT preadjusted edgewise bra cket sys tems was also not significant.

LEGENDS OF FIGURES

Fig 1: Initial model with palatal plug and reference wires before canine retraction

Fig 2: Final model with palatal plug and reference wires after canine retraction

Fig 3: Magnifica tion illustrating anchorage 1055

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LEGENDS OF TABLES Table I : Mean rate of retraction

Groups N Minimum Maximum Mean S.D. Std. error (mm/interval) (mm/interval) (mm/interval) mean

Self-ligating bracket 8 1.00 1.36 1.1 717 0.13562 0.04795

Conventiona l bracket 8 0.91 1.24 1.1209 0.13298 0.04702

Table II : Mean anchorage loss

Groups N Minimum Maximum Mean S.D. Std. error (mm) (mm) (mm) mean

Self-ligating bracket 8 0.80 2.20 1.8375 0.44381 0.15691

Conventional bracket 8 1.00 2.45 1.9500 0.45591 0.1611 9

LEGENDS OF GRAPHS

Graph I: Mean rate of canine retraction self-ligating and conventional bracket

Graph II: Mean anchorage loss self-ligating and conventional bracket

"

~ 0.' 08 L I " 02 0

Self-liOating blacket Conventional bracket

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Conventional bracket

Self-ligating bracket

o 0.' 0.8 1.2 1.6 2 _ ...... ...

I~'

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