The Loading And Unloading Properties Of Various Arch Wires As A Function Of Cross Sectional Dimension And Inter Bracket Span Width System

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1 The Loading And Unloading roperties Of Various Arch Wires As A Function Of Cross Sectional Dimension And Inter Bracket Span Width System Authors: Thomas Mathew MDS Orthodontics, Lecturer, Faculty of Dentistry, International Medical University. ABSTRACT It is the aim of all clinicians to accomplish biological tooth movement, which implies the use of low, continuous force. Constant unrelented search for a better wire, which can deliver optimal orthodontic force, has led to the invention of a lot of orthodontic wires such as Stainless steel, Beta Titanium, ickel Titanium and multi stranded wires. In this study, the loading and unloading properties of inch, 0.016x0.022 inch and 0.017x0.02 inch dimensions of stainless steel, conventional,, and arch wires were determined by means of a modified three point bending test for two inter bracket widths of mm and 6. mm for deflection of 1 to 3 mm. The applied forces dependence on cross-sectional size differs from the linear-elastic prediction in super elastic wires. The stainless steel wires had the highest force s on all the three dimensions and cross section. On loading and unloading, wires had force s in-between stainless steel, conventional and super elastic. The conventional had much lower force s compared to stainless steel and and were linearly progressing compared to. On loading and unloading the super elastic had force s in the range of conventional and had constant forces on higher deflection. The studies showed that the force was comparatively higher in mm inter bracket width than the 6. mm inter bracket width for all the cross section and dimension of wires. Key Words: Optimal Orthodontic force, Inter bracket span, Cross sectional dimension. Introduction Orthodontic tooth movement is greatly influenced by the characteristics of applied force by orthodontic wires. Kusy 1 has enumerated many factors which is required for an ideal arch wire namely strength, stiffness, range, frictional properties, formability and biocompatibility. Ideally, biomechanical considerations require forces that are low in magnitude and continuous in nature. Different phases of tooth movement in edgewise or pre-adjusted edgewise system requires arch wires of different stiffness with varying degree of flexibility and modulus of elasticity. Stiffness as defined by Brian 2 is the amount of force required per unit deflection. The factors that affect wire stiffness include wire alloy composition, strength, state of heat treatment and cross section. Stiffness is also affected by bracket width, inter bracket distance, length of wire and incorporation of loops. In mechanotherapy, the periodic change of wire from the initial phase of treatment to the finishing phase was mandatory. In the period prior to seventies, when gold and stainless steel were the only available materials, the stiffness of wire was affected by altering the cross section of the wire from round to rectangular and its dimension from small to large. This strategy of wire selection and usage is called variable cross section orthodontics 3. In mid seventies, a host of new arch wires such as itinol and Beta Titanium became available with widely varying moduli. It became possible for clinicians to select wires with lower moduli for the early stages of treatment. This approach has been termed by Burstone 4 as variable modulus orthodontics. In nineties, ickel Titanium arch wire that have super elastic and thermodynamic properties were introduced. By taking advantage of the body temperature and setting the alloys transformation temperature to the martensitic phase, transformation control of the memory phenomenon can be affected. This is called varying transformation temperature orthodontics. Studies on Stainless steel 6 and 7 wires have demonstrated linear loading characteristics and ickel-titanium alloy 8 wires have demonstrated a linear loading and unloading characteristic. However newer ickel-titanium alloys that exhibit the effect of super elasticity 9 have shown to demonstrate nonlinear loading and unloading behaviours with relatively constant force levels throughout their deactivations. Hence this present study was undertaken to evaluate the loading and unloading properties of stainless steel, 29 Malaysian Dental Journal Jan-Jun 2011 Vol 32 o The Malaysian Dental Association

2 The Loading And Unloading roperties Of Various Arch Wires As A Function Of Cross Sectional Dimension And Inter Bracket Span Width, Super Elastc and Beta Titanium arch wires of cross sectional dimension, inch, 0.016x0.022 inch and 0.017x0.02 inch on two different inter bracket widths of mm and 6. mm. Materials & Method The sample for the study consists of archwires of different cross section, dimension and composition as given in table 1. Table:1 Sample of arch wires for the study. Group o of Sample Composition Dimension Cross Section 1a 10 Stainless steel round 1a 10 Stainless steel x0.022 rectangular 1c 10 Stainless steel x0.02 rectangular 2a round 2b x0.022 rectangular 2c x0.02 rectangular 3a round 3b x0.022 rectangular 3c x0.02 rectangular 4a round 4b x0.022 rectangular 4c x0.02 rectangular All the wires were from the same manufacturer (Ormco Sybron dental specialities) to minimize the variation of the mechanical properties due to different manufacturing process, chemical composition and heat treatment of the alloy. Samples were divided into 12 groups based on composition, cross section and dimension. 30 mm of wire from the distal end of preformed arches were utilized for the study. Tests were carried on wires from each group with two different interbracket span of mm and 6. mm and thus a total of 120 wires. Acrylic Block Two acrylic blocks were fabricated using self cure acrylic. A cut was made in the 1st block to a depth of 10x10 mm and 13x10 mm in the centre of the 2nd block to allow deflection. A row of four pre-adjusted edgewise stainless steel brackets of Roth prescription of manufacturer GAC were embedded on to the acrylic blocks. In first partial acrylic block (Fig:1), 4 brackets were embedded in position representing both the lower central incisors, canines and 1st premolar, with the load cell acting as the displaced lateral incisor. The inter bracket width between central incisor and canine is 10 mm and load cell (acting as lateral incisor) in-between at mm. In second artial acrylic block (Fig:2), 4 brackets were embedded in the positions representing both upper central incisors, canines and 1st premolar, with the load cell acting as the displaced lateral incisor. The inter bracket width between central incisor and canine is 13 mm and load cell (acting as lateral incisor) in-between at 6. mm. Figure 1: 1st partial acrylic block. Figure 2: 2nd artial acrylic block. Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1 30

3 Thomas Modified Three - oint Bending A modified three point bending test enumerated by Wilkinson10 was carried out on various wires with an Instron 400 universal testing machine (Fig:3) fitted with a 100 load cell calibrated on 2 kg range and a deflecting rod (Fig:4) of diameter steel with a groove. The testing machine was operated at a crosshead speed of 2 mm/min and the analogue output was passed through computer and digital display. Figure 3: Instron 400 universal testing machine. The wire was loaded in buccolingual direction in the brackets on flat acrylic block model by elastic modules. The wires were deflected upto 3 mm in the loading deflection test. The loading and unloading force measured in ewton for all the 120 samples were recorded in the computer and subjected to statistical analysis. Statistical Analysis The s tabulated were subjected to analysis of variance. One way AOVA was used to compare the mean s between different study groups. Mean, standard deviation and test of significance were calculated between different types of wires within each group and enumerated in tables. 0.0 denoted the statistical significance. Results Figure 4: Deflecting rod. Loading and unloading of arch wires at mm and 6. mm inter bracket Span. On loading of inch wires on deflection of 1 mm to 3 mm with mm inter bracket width (Graph:1,Table:2). Stainless steel required the highest force for deflection from 14.4 for 1 mm to 21.9 for 3 mm deflection and stainless steel had a lesser force ( ) for 6. mm interbracket width (Graph:1,Table:3). had force s that were linearly increasing for mm inter bracket span ( ) and (2.1-.2) for 6. mm inter bracket span. had a force of 3.16 on 1 mm and.9 on 3 mm deflection for mm inter bracket span. For 6. mm inter bracket span, did not linearly progress from 2 mm to ( ). For wires the force were ( ) on deflection of 1 mm to 3 mm. 31 Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1

4 The Loading And Unloading roperties Of Various Arch Wires As A Function Of Cross Sectional Dimension And Inter Bracket Span Width Table:2 Loading and unloading of arch wires at mm inter bracket Span in, and. o of sample ± ± ±.130. Significant 2.214± ± ± ± ± ± ± ± ± ± ±.11.33± ± ± ± ± ± ± ±.200 Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1 32

5 Thomas Table:3 Loading and Unloading of arch wires at 6. mm inter bracket span in 1 mm, 2 mm and 3 mm. o of sample. 1.20± ± ± ± ± ± ± ± ± ±.288. Significant 2.08±8.13. Significant 14.2± ± ± ± ± ± ± ± ± ± ±.297 On unloading of inch wires on deflection from 3 mm to 1 mm with inter bracket width of mm (Graph:2,Table:2). stainless steel had the highest level of force on 3 mm deflection (8.4). did not recover to original position from 3 mm deflection (6.62) and no s on 2 mm because of permanent deformation. had linear degradation of force on unloading (3.06) for 3 mm and had the least force for both interspan width. had a constant force level on unloading (3.34) for mm and ( ) for 6. mm. wire had a force of (8.) on 3 mm deflection unloading. wires had force inbetween and ( ) for 6. mm inter bracket span. Graph:1 - Loading of arch wire at mm and 6. mm inter bracket span. 33 Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1

6 The Loading And Unloading roperties Of Various Arch Wires As A Function Of Cross Sectional Dimension And Inter Bracket Span Width X axis -- forces in ewton mm interbracket span Y axis -- deflection in mm. mm interbracket span L0, L1,L2,L3 Loading on 0 mm, 1 mm, 2 mm and 3 mm deflection. UL3, UL2, UL1- Unloading on 3 mm, 2 mm and 1 mm deflection. SE Superelastic, SS, Titanium Molybednum alloy Graph:2 - UnLoading of arch wire at mm and 6. mm inter bracket span. Loading & Unloading of x0.022 arch wires in mm and 6. mm inter bracket span. On loading of x0.022 inch arch wires (Graph:3,Table:4) on inter bracket width of mm, Stainless Steel had the highest force on 1 mm deflection (4.4) and linearly progressed to (8.) on deflection and (61.1) on 3 mm deflection. For 6. mm interbracket span(graph:3,table:), stainless steel had ( ) force s. linearly progressed ( ) for both mm interbracket span and ( ) 6. mm interbracket span. had much lesser force ( ) and remained constant on higher deflection. For 6. mm inter bracket span, had the least force ( ) and was remaining constant from 2 mm to 3 mm deflection ( ). had force s (2O ) between and. Table:4 Loading and unloading of x0.022 arch wires at mm inter bracket Span at, 2 mm and 3 mm. o of sample. 6.7± ± ± ±.7 4.4± ± ± ± ± ±.7.0± ± ± ±.372 Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1 34

7 Thomas 13.8±.23.4± ± ± ± ± ± ±4.2 On Unloading of 0.016x0.022 inch arch wires on mm inter bracket width (Graph:4,Table:4), Stainless Steel had the highest force on deflection (19.) and no on 2 mm unloading. For 6.mm inter bracket span (Graph:4, Table ) Stainless steel had the highest force (17.9) on 3 mm deflection and did not give s for 2 mm and 1 mm deflection. had constant force on loading (.4-4.3) and unloading (2.-2.2) on 2 mm and 3 mm deflection. had force s linearly decreasing and had recovered to original position for both mm and 6. mm inter bracket span. had force in-between and (10.2) for 3 mm deflection. Table: Loading and unloading of x0.022 arch wires at 6. mm inter bracket Span at, and. o of sample. 2.94± ± ±.301. Significant 2.484± Significant 36.4± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±.17 3 Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1

8 The Loading And Unloading roperties Of Various Arch Wires As A Function Of Cross Sectional Dimension And Inter Bracket Span Width Graph:3 - Loading of x0.022 arch wire at mm and 6. mm inter bracket span. X axis -- forces in ewton mm interbracket span Y axis -- deflection in mm. mm interbracket span L0, L1,L2,L3 Loading on 0 mm, 1 mm, 2 mm and 3 mm deflection. UL3,UL2,UL1- Unloading on 3 mm, 2 mm and 1 mm deflection. SE Superelastic, SS, Titanium Molybednum alloy Graph:4 - Unloading of x0.022 arch wire at mm and 6. mm inter bracket span. Loading & Unloading of x0.02" arch wire at mm and 6. mm inter bracket span. On loading of 0.017x0.02 inch arch wires (Graph:,Table:6) on inter bracket width of mm, Stainless Steel had the highest force and linearly progressed from (42-7). on large deflection had almost constant force (9.4 on 1 mm deflection, 13. on 2 mm,19.7 on 3 mm deflection). had force s more than super elastic and it linearly progressed ( ). wires had force s of ( ) from 1 mm to 3 mm loading. On unloading of x0.02 arch wires (Graph:6,Table:6) on inter bracket width of mm, had a constant force on unloading and was similar to force of 0.016x0.022 inch and inch super elastic arch wires ( ). Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1 36

9 Thomas Table:6 - Loading and unloading of x0.02 arch wires at mm inter bracket Span at,2 mm and 3 mm. o of sample. 9.42± ± ± ±.209. Significant 42.4± ± ± ± ± ± ± Significant 1.23± ± ± ± ± ± ± ± ± ± ± Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1

10 The Loading And Unloading roperties Of Various Arch Wires As A Function Of Cross Sectional Dimension And Inter Bracket Span Width Table:7 - Loading and unloading of x0.02 arch wires at 6. mm inter bracket Span at,2 mm and 3 mm. o of sample..96± ± ±.697. Significant 7.36±.416. Significant 34.2± ± ± ± ± ± ± ± ± ± ±3.4.98± ± ±.67. Significant 1.88± ± ± ±.19 did not return to the original position because of the permanent deformation. wires had force s in-between Stainless steel and wires ( ). had constant force s on higher deflection (.9 for 1 mm, 10.9 for 2 mm, 12.3 for 3 mm). had force s linearly progressing ( ). For, the force s linearly progressed from ( ) and for wires, the force s were in-between and ( ). On unloading of x0.02 arch wires on 6. mm inter bracket width (Graph:6, Table:7), had constant force (.9-4.3). had force s linearly decreasing from ( ). and did not recover to the original position because of the permanent deformation. Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1 38

11 Thomas Graph: - Loading of x0.02 arch wire at mm and 6. mm inter bracket span. X axis -- forces in ewton mm interbracket span Y axis -- deflection in mm. mm interbracket span L0, L1,L2,L3 Loading on 0 mm, 1 mm, 2 mm and 3 mm deflection. UL3,UL2,UL1- Unloading on 3 mm, 2 mm and 1 mm deflection. SE Superelastic, SS, Titanium Molybednum alloy Graph:6 - Unloading of x0.02 arch wire at mm and 6. mm inter bracket span. DISCUSSIO The ideal requisite for Orthodontic tooth movement is the application of light and continuous force11. Orthodontic wires which generate the biomechanical forces are the most important factor in the application of light and continuous force. In selection of wires for particular stage of treatment, the orthodontist should consider a variety of factors including the elastic range or spring back, formability or ease of manipulation and load deflection rate 12. Bending tests 13 have been popular for evaluation of the mechanical properties of archwires, especially the load deflection rate because of the relevance of bending deformation to the activation received. Three types of bending tests are usually performed: a cantilever bending, a three point bending and four point bending test 12. The standard method for evaluating orthodontic wires not containing precious metals is the three-point elastic bending test according to ADA specification no A modified version of the three point bending by Wilkinson etal10 was performed in this study to evaluate the load deflection rate, the most important parameter determining the biologic nature of tooth movement. This test was chosen mainly because of its close simulation to clinical application, reproducible results and the ability to differentiate wires with superelastic property. Cross section speed 10 for the load cell was chosen as 2 mm per minute to simulate the clinical situation of biologic tooth movement. The interbracket span was chosen as mm simulating a malaligned lower lateral incisor and 6. mm simulating a malaligned upper lateral incisor 8. Large interbracket distance 14, smaller dimension wires and as much as intra bracket space as possible is needed to get the greatest range or flexibilty of orthodontic wires. The use of inch slot bracket increases control, but sacrifices some of the flexibility associated with intrabracket space. So in this study, slot pre-adjusted edgewise brackets of Roth prescription were embedded in the partial acrylic blocks 1 and 21 to simulate the clinical condition 10. The modulus of elasticity in bending can be calculated from the force deflection plot using equation from solid mechanics. For three point bending, the maximum deflection (y) of the beam9 is given by y=fl3/48ei, where F is the applied force, L is the test span length, E represents the modulus of elasticity and I is the moment. The vertical axis of the force deflection plot represents force or bending moment and the horizontal axis represents the deflection or range. The clinical relevance16 of the load/deflection plot are the stiffness which is the slope of the initial linear region, the force or moment at which yielding takes place and the of deflection at the elastic limit termed the range. Since Stainless steel is the most commonly used arch wire material, it was compared to super elastic, beta titanium () and conventional wires to differentiate their mechanical properties. The results revealed a linear progression during loading of stainless steel arch wire for different wire cross section and additionally there was an increase in force with increasing wire cross section. On unloading, Stainless steel did not show any force because of the permanent deformation. This finding was similar for the varying inter bracket span in spite of the reduced force s with increased inter bracket span Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1

12 The Loading And Unloading roperties Of Various Arch Wires As A Function Of Cross Sectional Dimension And Inter Bracket Span Width The stainless steel wires delivered twice the force than wires and four times the force of nickel-titanium wires which was statistically significant in this study for a comparable degree of wire deflection. According to Drake etal 18, the modulus data indicated that stainless steel alloy deliver twice the force than and four times the force of. In this study, the Stainless steel arch wires had the highest force s on both interbracket distance for 0.016, x0.022 and x0.02 archwires and on Unloading, the Stainless steel wire did not recover to original position due to permanent deformation similar to studies of Kusy 19,1. According to Andersan Etal8, the properties of arch wires are the good spring back and flexibility compared to stainless steel and. In this study, the conventional wires exhibited linear progress of force s on loading on all the three cross sectional dimension (0.016, x0.022, x0.02 ). The force s are lesser than the stainless steel and which was statistically significant and similar to study of Rucker etal20. On unloading, the wires returned to their original position due to shape memory effect. The force s were lesser compared to the loading 8. Hurst 21 evaluated the recovery of commercial available wires which was around 90% and the recovery pattern was similar to this study. The super elastic property according to Brantley 21 is the ability of wires to withstand much higher elastic strain before permanent deformation and to provide constant forces at large deformation during unloading. In this study the superelastic wires exhibited constant forces on higher deflection of 2 mm and 3 mm on loading at both inter bracket width. On unloading of these super elastic wires, the force s were smaller than that on loading and there was constant 24 level of force compared to conventional, Stainless steel and. These findings demonstrate super elasticity and the results were similar to Khier etal 22 and Garrec eta l9 studies. Beta titanium wire was popularized in the 1980s. It is commercially available as. In this study, arch wires had load deflection s in-between Stainless steel and arch wires for both inter bracket width. Beta titanium wires delivered about half the amount of force compared to stainless steel. The archwires deflected almost twice as much as stainless steel without permanent deformation similar to the studies by Burstone etal 23 and Johnson 7. COCLUSIO The study showed that the force s were comparatively higher in mm inter bracket width than the 6. mm inter bracket width for all cross section and dimension of wires.the force s were lower on unloading compared to the loading for all the wires tested. The arch wires exhibited linear progress of force s on loading on all the three cross sectional dimension expect the wires which showed constant force. REFERECES 1. Kusy. Orthodontic biomaterials: From past to present. Angle orthodontics 2002; 72 : Brian K and Kusy. Elastic flexural properties of multi stranded stainless steel versus conventional ickel Titanium arch wires. Angle Orthodontics 2002; 72: Burstone J C and Goldberg J. Maximum forces and deflections from orthodontic appliances. American J orthod Dentofacial Orthop 1983; 84: Burstone J C. Variable modulus of orthodontics. American J orthod Dentofacial Orthop 1981; 80: Burstone J C, Qin B and Morton J. Chinese wire: A new orthodontic alloy. American J orthod Dentofacial Orthop 198; 87: Otljen J M, Manville G and anda R S. Stiffness deflection behavior of selected orthodontic wires. Angle Orthodontics 1997; 67: Johnson E. Relative stiffness of Beta Titanium arch wires. Angle Orthodontics 2003; 73: Andersan F G and Morrow E R. Laboratory and clinical analysis of itinol wire. American J orthod Dentofacial Orthop 1978; 73: Garrec and Jordan L. Stiffness in bending of super elastic i-ti orthodontic wire as a function of cross sectional dimension. Angle Orthod 2004; 74: Wilkinson D, Dsart S and James. A Load deflection characteristics of super elastic nickel titanium orthodontic wires. American J orthod Dentofacial Orthop 2002; 121: Theodosia. Bartzela, Christiane Senn, Andrea Wichelhaus Load-Deflection Characteristics of Superelastic ickel-titanium Wires. Angle Orthod: ovember 2007, Vol. 77, o. 6, pp Oltjen JM, Manville GDJ, Ghosh J. Stiffnessdeflection behavior of selected orthodontic wire. Angle Orthod.1997; 67: Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1 40

13 Thomas 13. Brantely A, Augat S and Winders V. Bending deformation studies of orthodontic wires. J Dent Res 1978; 7: Schudy G and Schudy F. Inter bracket space and inter bracket distance: Clinical factors in clinical orthodontics. American J orthod Dentofacial Orthop 1989; Hemingway R, Williams R and Hunt. The influence of bracket type on the force delivery of arch wires. Eur J of Orthod 2001; 23: Address for correspondence: Dr Thomas Mathew. MDS Orthodontics. Lecturer, Faculty of Dentistry. International Medical University. o 126,Jalan Jalil erkasa 19,Bukit Jalil,7 Kuala Lumpur,Malaysia. drthomas_m@yahoo.co.in H/ o arvizi F and ock W.The load deflection characteristics of thermally activated orthodontic arch wires. Eur J of Orthod 2001; 2: Jones M L, Stainford and Chan C. Comparison of superelastic and Multistranded Stainless steel wires in initial alignment. JCO 1990; 10: Drake R S, Wayne M D and owers M J. Mechanical properties of orthodontic wires in tension, bending and torsion.. American J orthod Dentofacial Orthop 1982; 82: Kusy R. A review of contemporary arch wires their properties and charechtreistics. Angle Orthod 1997 ; 67 : Rucker K and Kusy R.Elastic flexural properties of stainless steel versus conventional arch wires Angle orthod 2002;72: Brantley A W and Augat S. Bending deformation studies of orthodontic wires. J Dent Res 1978;7 : Khier E S and Brantely A. Bending properties of super elastic and non super elastic wires.. American J orthod Dentofacial Orthop 1991; Goldberg J and Burstone J C. An evaluation of Beta Titanium alloys for use in orthodontic appliances. J Dent Res 1979; Miura F, Mogi M and Ohura Y. The super-elastic property of the Japanese alloy wire for use in orthodontics. American J Orthod Dentofacial Orthop. 1986; 90: Malaysian Dental Journal Jan-Jun 2011 Vol 32 o 1