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FORCES RELEASED DURING ALIGNMENT WITH AESTHETIC AND STAINLESS STEEL PREADJUSTED APPLIANCES USING DIFFERENT LIGATION METHODS Matthew S. Baker, D.D.S. An Abstract Presented to the Faculty of the Graduate School of Saint Louis University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Dentistry 2009 ABSTRACT Purpose: The purpose of the study was to examine the alignment force deflection patterns of a 0.014-inch superelastic Niti archwire supported in aesthetic and metal brackets with varying ligation methods. Methods: First molar tubes and one of four sets of brackets were bonded to machined steel plates shaped as a maxillary arch. The brackets used in the study were In-Ovation-R (MSL), InOvation-C (CSL), Ovation (MST), and Mystique (CST) (all from GAC International, Bohemia, NY). 0.014-inch superelastic Niti wires were ligated into each bracket set with either 0.010-inch pre-formed steel ligatures (MST and CST) or the self-ligating clips (MSL and CSL). The 0.014inch wire was deflected 4 mm palatally, and the subsequent unloading forces were measured at 0.5 mm increments from 3.5 mm to 0.5 mm. Results: MSL and CSL were significantly different (p<0.05) at all seven deflection points. MST and CST were significantly different (p<0.05) at all deflection points except the 0.5 mm distance. All bracket group pairings were found to be significantly different (p<0.05) at all deflection distances except for the following pairings: CSL and MST at 3.0 mm; CSL and CST at 1.5 mm; MSL and CST at 1.0 mm; MSL and MST, MSL and CST, and MST and 1 CST at 0.5 mm. Conclusions: MSL produce statistically larger alignment forces than CSL throughout a 4 mm deflection of a superelastic Niti wire. MST produce statistically larger alignment forces than CST for superelastic wire deflections greater than 2 mm, but statistically smaller forces for deflections from 1 mm to 2 mm. Where a 4 mm palatally displaced canine is to be corrected with a 0.014-inch superelastic Niti wire, all the bracket groups (MSL,CSL,MST,CST) will behave similarly and provide clinically acceptable alignment forces. 2 FORCES RELEASED DURING ALIGNMENT WITH AESTHETIC AND STAINLESS STEEL PREADJUSTED APPLIANCES USING DIFFERENT LIGATION METHODS Matthew S. Baker, D.D.S. A Thesis Presented to the Faculty of the Graduate School of Saint Louis University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Dentistry 2009 COMMITTEE IN CHARGE OF CANDIDACY: Professor Eustaquio Araujo, Chairperson and Advisor Assistant Professor Ki Beom Kim Assistant Clinical Professor Christopher Klein i DEDICATION This thesis is dedicated to my beautiful wife, Brooke, and our precious “daughter”, Britney, whose tremendous love, support, and encouragement have helped carry me throughout my higher education. ii ACKNOWLEDGEMENTS The author would like to express appreciation for the time and effort provided by his committee members: Dr. Eustaquio Araujo, Dr. Ki Beom Kim, and Dr. Christopher Klein. This project would not have been possible without their support and advice. A special thanks to Dr. Heidi Israel for her contributions with the statistics of the project. The author would also like to thank GAC International for donating brackets and The Orthodontic Store for donating preformed ligature ties. iii TABLE OF CONTENTS List of Tables..............................................v List of Figures...........................................vii CHAPTER 1: INTRODUCTION.....................................1 CHAPTER 2: REVIEW OF THE LITERATURE Introduction.....................................4 Alignment Force..................................4 Frictional Components.........................5 Springback Potential..........................8 Leveling and Aligning Mechanics for a Palatally Malpositioned Canine............................10 Friction in Orthodontics........................12 Superelastic Wire Properties....................14 Aesthetic Brackets..............................16 Bracket Composition and Friction................19 Bracket Ligation and Friction...................21 Summary.........................................24 References......................................30 CHAPTER 3: JOURNAL ARTICLE Abstract........................................35 Introduction....................................37 Materials and Methods...........................41 Laboratory Tests.............................41 Statistical Analysis.........................46 Results.........................................47 Discussion......................................51 Conclusions.....................................55 References......................................57 Appendix: Tables..........................................61 Vita Auctoris..............................................70 iv LIST OF TABLES TABLE 2.1: Summarized portion of the studies regarding bracket composition and friction...............26 TABLE 2.2: Summarized portion of the studies regarding bracket ligation and friction................. 28 TABLE 3.1: Descriptive Statistics: Alignment Force (grams)....................................... 47 TABLE A.1: T-Tests Comparing Metal Self-Ligating and Ceramic Self-Ligating at Seven Deflection Points (p<0.05)............................... 61 TABLE A.2: T-Tests Comparing Metal Steel-Tied and Ceramic Steel-Tied at Seven Deflection Points (p<0.05)...................................... 62 TABLE A.3: Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 3.5 mm Deflection Distance (p<0.05)............................. 63 TABLE A.4: Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 3.0 mm Deflection Distance (p<0.05)............................. 64 TABLE A.5: Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 2.5 mm Deflection Distance (p<0.05)............................. 65 TABLE A.6: Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 2.0 mm Deflection Distance (p<0.05)............................. 66 TABLE A.7: Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 1.5 mm Deflection Distance (p<0.05)............................. 67 TABLE A.8: Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 1.0 mm Deflection Distance (p<0.05)............................. 68 v TABLE A.9: Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 0.5 mm Deflection Distance (p<0.05)............................. 69 vi LIST OF FIGURES FIGURE 2.1: Arrows representing normal forces exerted in bracket slots by archwire deflection and ligation. A, B, C: Facial views of both common edgewise and self-ligating brackets with wire. D: A gingival view of a sectioned common edgewise bracket with wire and ligature. E: A gingival view of a sectioned self-ligating bracket with wire and active clip..............7 FIGURE 3.1: The steel plate with brackets and tubes attached..................................... 42 FIGURE 3.2: The steel plate with brackets and wire positioned in the testing apparatus.......... 45 FIGURE 3.3: Unloading plot data for the self-ligating bracket groups at the seven deflection points....................................... 49 FIGURE 3.4: Unloading plot data for the steel-tied bracket groups at the seven deflection points....................................... 50 FIGURE 3.5: Unloading plot data for all bracket ligation groups at the seven deflection points........ 50 vii CHAPTER 1: INTRODUCTION Aesthetic concerns are visible throughout almost every facet of our present day culture. Orthodontics as a profession partially functions to meet these aesthetic demands by transforming patient smiles into beautiful and visual works of art. The end result of orthodontics is especially important, however, many patients also seek to maintain the aesthetics of their smile while undergoing treatment. With this ever-increasing demand for aesthetics in orthodontics, many patients desire more attractive treatment while improving their smile. This is especially true in the adult population, where patients would rather be as inconspicuous as possible while receiving orthodontic care. Orthodontic suppliers have been developing different brackets for years in order to meet this demand from both patients and their clinicians. Some of the first aesthetic brackets were marketed in the 1970s by manufacturers and made of plastic materials. These brackets had inherent structural problems, which led to decreased performance during treatment. Ceramic brackets were created in the 1980s with the intent to improve the clinical performance of aesthetic brackets, and they have since maintained their 1 popularity among clinicians. These brackets are not without their disadvantages, however, as they provide increased frictional resistance, impeding orthodontic movements and leading to a decrease in treatment progression. Self-ligating brackets were introduced into the marketplace with the intent to improve clinical performance and have gained acceptance by practitioners over recent years. Initially, they were only manufactured with metal components. These brackets failed to meet the aesthetic demands of patients, but gave their clinicians an increase in treatment performance. Recently, self-ligating brackets made of aesthetic materials have emerged. These brackets hold the possibility of meeting aesthetic and functional demands, thereby, satisfying both patients and their orthodontists. The goal of this research was to determine the simulated clinical performance of aesthetic self-ligating brackets when compared to metal self-ligating brackets using a palatally offset cuspid model. In addition, the method of ligating with steel ligatures and its application for improving conventional aesthetic bracket performance was evaluated. This final investigation was significant because it may be possible for conventional brackets with 2 steel ligatures to perform as well as self-ligating brackets. 3 CHAPTER 2: REVIEW OF THE LITERATURE INTRODUCTION This review of the literature begins with an explanation of the alignment force topic and the components that are present in the initial stages of orthodontics. The leveling mechanics for a malpositioned canine are then examined followed by a discussion of bracket composition and ligation methods. Comprehending these conceptual ideas leads to the justification for this research on alignment forces delivered by metal and aesthetic brackets with varying ligation methods. ALIGNMENT FORCE The alignment force is the force that is placed on a malpositioned tooth after a wire is deflected and ligated into its bracket slot. This force is used to level and align the tooth into the correct arch configuration during the initial phase of orthodontics. In the absence of separate oral forces and factors (perturbations, saliva, 4 plaque accumulation, etc.), the alignment force is broken down into two different components: a frictional force and a springback potential. FRICTIONAL COMPONENTS The frictional force is a negative component, which is present at the wire-bracket interfaces in orthodontics. Friction is defined as the force that counters the tangential movement of two bodies in contact. The Coulomb model of friction is identified by the following equation: F = N*µ where F is the frictional force, N is the normal force, and µ is the coefficient of friction.1,2 The coefficient of friction is determined based on the surface roughness of two objects that are sliding against one another; in this case, the Niti wire and the brackets of the adjacent teeth. The coefficient of friction is a constant and is associated with the surface characteristics of the materials. Each material has two coefficients of friction3: the coefficient of maximum static friction, which is the force necessary to begin movement, and the coefficient of kinetic friction, which is the component 5 opposing sliding of one surface over another at a steady speed.4 The maximum kinetic friction is typically the greatest resistance that occurs as an object starts to slide. The kinetic coefficient of friction is usually a smaller value than the maximum static coefficient of friction for a system.5,6 The normal force is that which is present at perpendicular angles where the wire and brackets are in contact. In this research example, where the wire is deflected to a palatally malposed, right canine bracket, the wire could possibly contact the disto-lingual and mesio-facial edges of the lateral incisor bracket slot and the mesio-lingual and disto-facial edges of the first bicuspid bracket slot. The number of normal forces of this description that occur depends on the magnitude of the wire deflection; the adjacent bracket edges to the wire deflection will always come into contact with the wire, however, the distal ends of the brackets to the deflection may not. There are also possible contacts between the wire and ligating mechanism. The ligation securing the wire in the slot could be a self-ligating door or ligature tie. Those possible normal forces between the wire and ligating 6 mechanism would be dependent on the direction and magnitude of the wire deflection within the bracket slot. Examples of potential normal forces are illustrated in Figure 2.1. A B D C E Figure 2.1: Arrows representing normal forces exerted in bracket slots by archwire deflection and ligation. A, B, C: Facial views of both common edgewise and self-ligating brackets with wire. D: A gingival view of a sectioned common edgewise bracket with wire and ligature. E: A gingival view of a sectioned self-ligating bracket with wire and active clip. Adapted from Thalman.7 The total factor of the normal forces combined with the coefficient values lead to the overall frictional component present in the system which functions as a 7 resistance to the alignment force, and therefore it will have a negative value. Unnecessary friction applied in orthodontic therapy can potentially convert to delayed tooth movement and consequently longer treatment time. However, friction may not always be a negative component to orthodontic mechanics; friction can provide an additional source of anchorage in certain clinical situations in order to result in desired tooth movements.8 SPRINGBACK POTENTIAL The springback component is the force that would be placed on the malposed tooth if there were no friction in the system. It is determined by the wire properties along with the distance that the wire is deflected. Usually, the further the wire is deflected, the higher that portion of the springback potential will be.9 The wire diameter and length are other portions of the springback potential. As the diameter of the wire increases, the stiffness also will increase. Conversely, as the length of wire within a section (between two brackets 8 for example) increases, the stiffness of the wire within that portion will decrease.10,11 As wire size increases, the stiffness of the wire increases to the power of four for round wires. Therefore, if a round wire is doubled in its dimensional size, then the stiffness will increase sixteen times. The dimension in the direction of flexure has the greatest influence on stiffness for rectangular wires.10,11 The specific wire material properties will also have an effect on its stiffness.11 These values have been determined for stainless steel, Niti alloys, and BetaTitanium alloys.12 Superelastic Niti alloys do not have specific stiffness values due to their deflection dependence13 and can vary from 7% to 41% of the stiffness of stainless steel.10,13 The springback potential is a positive component of the force that is placed on a malposed tooth, and the frictional force is subtracted from it to obtain the net alignment force that is theoretically placed on the tooth in the absence of oral forces. The archwire that is deflected and engaged into a malposed tooth’s bracket slot can create tooth movement using the springback force from the archwire.14 The net alignment force placed on the tooth 9 must be equal to or larger than the minimal force necessary to initiate tooth movement. LEVELING AND ALIGNING MECHANICS FOR A PALATALLY MALPOSITIONED CANINE Orthodontic treatment typically starts with a stage where small and flexible continuous archwires are deflected and ligated into the bracket slots to provide a force that is adequate for leveling and aligning all teeth in an arch. As discussed earlier, for the tooth movement to occur, the force generated from the springback potential of the activated archwire must surpass the minimal levels required for tooth movement. Therefore, the springback potential must provide an alignment force to the malpositioned tooth that exceeds the frictional force components opposing the deactivation of the wire.14-21 During this initial stage in orthodontics, the excess wire that is deflected into the malpositioned tooth’s bracket must slide through the adjacent bracket slots where the frictional forces are present and then travel out the distal end of the dental 10 arches, given that there are no stops placed on the wire.15,16 While using a continuous archwire that is ligated into a palatally offset canine, there are potential counteractive forces created in the adjacent bracket slots other than the forces that are placed on the canine. These forces on the adjacent teeth can result in negative tooth movements for the clinician who uses straight-wire mechanics during leveling and aligning.11 With a palatally offset canine, using a straight wire to level and align the tooth will tend to tip the adjacent teeth toward the canine. This can result in the buccal segment being intruded and lingually inclined since the canine is usually positioned higher in the palate than the occlusal plane. A severe outcome of these negative side effects could leave the patient with a canted occlusal plane, further complicating the orthodontic treatment. The clinician should use caution with the extent of archwire deflection in these cases and assure that strain on adjacent teeth is not detrimental.22 11 FRICTION IN ORTHODONTICS As previously discussed, the initial stage of leveling and aligning is a source of potential problems due to friction, if the force generated during the deactivation of the archwire is not adequate to overcome the opposing frictional forces within the system. If these frictional forces are strong enough, they can actually supersede the springback potential of the wire, causing frictional binding within the system and halting all leveling and aligning of the teeth in the arch.7,23 Another stage in orthodontics where friction is a major factor is when sliding mechanics are incorporated into treatment. The wire will contact the bracket and ligating mechanism resulting in frictional forces that act to hinder the orthodontic force being used, thus altering the movement that the clinician wishes to produce. Frank and Nikolai5 studied sliding mechanics and stated that tooth movement is initiated once the orthodontic force generated exceeds the maximum static frictional forces opposing the movement. The movement will temporarily stop once the resistance of the compressed periodontal ligament and the kinetic friction present overcome the orthodontic force 12 placed on the tooth. Due to the constant change in the ligament over time, the opposing force associated with the periodontal ligament will decrease. Since wire stability and occlusal forces are a factor, the average frictional forces between the bracket and wire can change resulting in the break of the frictional binding and commencement of tooth movement once again. Therefore, tooth movement appears to occur in short bursts rather than one, continuous motion. This sliding instability is known as the “stick-slip” phenomenon.3 This process will occur in sliding mechanics until the applied orthodontic force is no longer adequate to overcome the frictional forces within the system, halting all tooth movement until the appliance is activated once more. There are two types of sliding mechanics that are used in orthodontics. A tooth or group of teeth can have a force applied to them, and if this force is large enough to overcome the frictional forces present, movement will occur in the direction of the force as the brackets slide along the archwire. The other mechanism used involves an archwire sliding through brackets positioned on teeth that are stationary. The teeth that are ligated to the wire in the anterior portion of the arch during this en masse 13 retraction will travel through bone along with the moving archwire. There exists a high potential for frictional binding to occur within this system due to the high forces required to move the group of anterior teeth at once.24 SUPERELASTIC WIRE PROPERTIES Superelastic archwires have become the wire of choice from the clinician’s armamentarium in the initial stage of leveling and aligning due to their high levels of elasticity and initial form recognition.25 They have the ability to be deflected a great distance without undergoing permanent deformation, making them a perfect choice for cases where multiple first and second order malalignments are present. There are two types of superelastic archwires available on the market today: pseudoelastic alloys and thermoelastic alloys. They differ in what provokes their phase transformation from the body-centered austenitic form to the monoclinic martensitic form. Pseudoelastic archwires allow the clinician to apply a fairly constant force to maligned teeth over a wide range of tooth movement.26 This phenomenon exists due to the 14 wire’s ability to undergo physical property changes during its loading and unloading cycles. The pseudoelastic archwire is capable of having its magnitude of strain increased and decreased as the wire is deflected and unloaded while maintaining a nearly constant level of stress (force).25 This can be viewed on a stress-strain curve where the archwire displays horizontal regions on both the loading and unloading phases, all while the strain values are increasing and decreasing. This is due to the wire’s ability to undergo the phase transition from the austenitic form to the martensitic form as the strain on the wire is increased. During the unloading phase, the reverse transformation occurs, as the strain on the wire is decreased.19 Thermoelastic archwires undergo phase transformation as the alloy passes through a certain transition temperature range. This allows the phase form to change from martensitic to austenitic once this temperature level is reached. When the alloy is below the austenitic phase temperature, the archwire is quite pliable and can be permanently deformed with little strain placed on the wire. Once the alloy reaches the austenitic phase transition temperature, the archwire will exhibit the form memory and 15 return to its original shape.26 There are currently different phase transformation temperature ranges commercially available for these archwires, giving the clinician the ability to deform the alloys in room temperature and ligate them in the oral cavity where the wires have the capability to return to their original shape while leveling and aligning the teeth. There are currently large variations in physical properties of wires between and within manufacturers due to the range of factors that influence these superelastic archwires. Therefore, clinicians should take care to select the appropriate archwire for each application due to these variations in alloy behavior. The clinician should select the wire with the appropriate size, shape, and temperature transformation range (when applicable) to correctly influence the loading and unloading behavior of the alloy during the leveling and aligning stage. AESTHETIC BRACKETS Orthodontic suppliers have been developing different brackets for years in order to meet aesthetic demands by 16 both patients and their clinicians. Some of the first aesthetic brackets were marketed in the 1970s and constructed from plastic,27 initially being produced from acrylic substrates and later by polycarbonate materials. Their acceptance by clinicians was not very positive due to the inherent problems associated with them. The plastic materials stained easily after time and their lack of strength resulted in bonding failures, tie wing fractures, and permanent deformation.28 This became a significant issue as treatment progressed, leading to bracket slot deformation and rendering the brackets insufficient to express the correct prescription. More recently, high-grade polyurethane and polycarbonate brackets reinforced with ceramic or fiberglass have been introduced. These materials have significantly decreased the deformation issues, leading to an increased popularity in their production by manufacturers. Ceramic brackets were introduced in the 1980s as an alternative to plastic materials for the aesthetic bracket market. They provide better color stability and greater resistance to wear and permanent deformations.27 They are available in a variety of bracket types and various appliance systems, making them versatile and providing most 17 clinicians with an available option. Ceramic brackets are typically composed of aluminum oxide available in two forms: polycrystalline or monocrystalline structures. Polycrystalline brackets are manufactured and sintered using specific binders that fuse the particles together,29 whereas monocrystalline brackets are milled from single crystals of sapphire using diamond-cutting tools.30 The largest difference between the two types is their optical clarity, with the monocrystalline brackets having a better translucency. Polycrystalline zirconia brackets were later offered as an alternative to aluminum oxide brackets and have the highest strength of all ceramics.31 They have disadvantages, including an opaque appearance and a higher tendency to stain as treatment lengthens. As the clinical performance of aluminum oxide brackets has increased in recent years due to improved physical properties, zirconia brackets have essentially become obsolete because they are aesthetically inferior brackets. 18 BRACKET COMPOSITION AND FRICTION As discussed earlier, the coefficient of friction is a constant and is related to the surface characteristics of the bracket materials. This component of the frictional force is what differs between metal and aesthetic brackets, and thus could lead to a negative impact on the alignment force. Ceramic brackets can vary in the extent of surface roughness among the different types of ceramics and the range of manufacturers. Polycrystalline ceramics have a higher coefficient of friction than monocrystalline ceramics due to their more porous surface structure.27 Polycrystalline ceramic brackets are manufactured by one of two processes: injection moulding, which produces a smooth surface texture, or machining with diamond cutting tools, which results in a rougher finish texture. Omana et al.32 found that machined ceramic brackets produce significantly higher frictional forces than those that are injection moulded. Another interesting finding from ceramic bracket frictional studies is the conclusion that some ceramics can scratch archwires, leading to a further increase in frictional forces between the bracket and wire. Thorstenson and Kusy33 found stainless 19 steel debris from the wires on the outer slot wall edges of the ceramic brackets when completing frictional studies. It has been shown in the past that aesthetic brackets composed of ceramic substances typically have higher frictional levels when compared to stainless steel brackets.23,33-40 In these studies, both bracket systems were traditional twin brackets that were ligated with elastomers. Pratten et al.34 found that two ceramic brackets with different manufacturers both produced nearly twice the frictional levels when compared to stainless steel brackets. Tselepsis et al.36 compared stainless steel brackets with polycarbonate, sapphire, and porcelain aesthetic brackets and found that all three types of aesthetic brackets produced higher frictional levels than stainless steel. This problem of increased friction in aesthetic brackets has been partially overcome by manufacturers placing metal lined slots into the ceramic brackets. However, the frictional levels are still higher than those of all metal brackets in most cases.31,41-43 In addition to the placement of metal slots, some manufacturers have used silica-lined slots to potentially decrease the frictional resistance,27 however, this conclusion has not yet been proven. 20 A summary of a portion of the studies regarding bracket composition and friction is provided in Table 2.1. BRACKET LIGATION AND FRICTION As discussed previously, the ligation of the adjacent brackets to a malposed tooth is a source of normal forces impeding the alignment force placed on the malposed tooth. The ligation force on the adjacent teeth will vary based on the ligation method used, and therefore higher ligating forces placed on those brackets will increase the friction at the bracket and wire interface.44 There are varying types of ligation methods which can be used: elastomeric ligatures, wire ligatures, and self-ligating clips or doors. Wire and elastomeric ligatures have been the most common types of bracket ligation used in orthodontics. Elastomeric ligatures produce the highest ligating forces initially,16,18,45-47 and thus their use in ligating the adjacent brackets will induce wire binding at shorter deflection distances.2,7 However, as the elastomers relax after having been stretched over the brackets within the 21 oral environment for some time, they have sizable decreases in ligational force magnitudes.48 Stainless steel ligatures produce lower frictional levels when compared to elastomeric ligatures,1,35,45,46,49,50 however, this depends on how tightly the wire ligatures are tied. Nanda and Ghosh2 found that ligating forces from wire ligatures can range from 0 to 300 grams. Current literature suggests that twisting the stainless steel ligatures until taut (initially contacting the wire with the wire resting against the base of the bracket slot), and then untwisting them a quarter turn, reduces friction significantly and provides an acceptable way to standardize the method of ligature tying.1,45,49,51 Even though stainless steel ligatures can produce low frictional levels, they still may not provide levels equal to those of self-ligating brackets.52 Self-ligating brackets were introduced into the orthodontic market with the hope of reducing frictional levels both in the leveling/aligning stages and in sliding mechanics. They are unique in their method of ligation in which an integrated door or clip is closed over the slot to hold the wire in place. There are two types of selfligating brackets: the “active” bracket that contains an integrated clip which presses larger size wires in the slot 22 in latter stages of treatment; and the “passive” bracket that usually contains a door mechanism which closes off the slot and holds the wire in place. The wire is never fully pressed into the slot of “passive” brackets, therefore allowing the bracket to move freely along the archwire at any stage of treatment. Self-ligating brackets have the advantage of allowing faster wire removal and insertion at adjustment visit appointments due to the quick process of opening and closing their ligating mechanism.53 Some clinicians also believe that self-ligating brackets provide faster overall treatment times due to their lower frictional levels and efficient ability to move teeth. Self-ligating brackets have shown on numerous accounts to be superior in their ability to produce less frictional resistance than other methods of ligation.45,46,54,55 This leads to more of the wire’s springback potential being expressed in a malposed tooth as a higher alignment force to be used for leveling and aligning.17,19 A summary of a portion of the studies regarding bracket ligation and friction is provided in Table 2.2. 23 SUMMARY From this review of the literature, it can be clearly understood that friction and force levels present in orthodontics are multi-faceted. There are numerous factors present in the overall complexity of friction in orthodontics, and both manufacturers and clinicians have put much time and effort into producing ways to more efficiently move teeth with less friction. There has been ample research completed on low friction technology, from self-ligating brackets to high-tech wires, however, further research is necessary to describe how aesthetic brackets can play a part in this process. With the increasing popularity of “clear” brackets and “invisible” orthodontic treatment, the idea of applying low friction technology to aesthetic treatment may play a significant role in a clinician’s armamentarium. This study aims to evaluate the differences between aesthetic and nonaesthetic treatment using recently introduced “clear” selfligating brackets and comparing them to metal selfligation. The study will also describe any benefits of this newer self-ligating technology in comparison to more 24 conventional steel ligating mechanisms when used with aesthetic and non-aesthetic brackets. 25 Table 2.1. Summarized portion of the studies regarding bracket composition and friction. Author Objective Sample Method Results Omana et al.32 Compare frictional effects of various ceramic and SS brackets 7 brands of ceramic brackets; 1 brand of SS brackets Each bracket was tested on .018” x .025” straight sections of SS and Niti wire Injection moulded ceramic brackets produce lower friction than other ceramic brackets Thorstenson & Kusy33 Determine effect of SS inserts in aesthetic brackets Aesthetic brackets with and without SS inserts; conventional SS brackets The brackets were evaluated with various second-order angulations in the dry and wet states on 0.457 × 0.635 mm SS wires Frictional properties of aesthetic brackets with SS inserts are between aesthetic brackets and SS brackets when clearances exist Pratten et al.34 Compare frictional forces among SS and ceramic brackets 2 SS brackets; 2 ceramic brackets Rectangular SS and Niti wires were freely passed through the different brackets in dry and artificial saliva states The SS brackets had a lower frictional resistance than the ceramic brackets under all conditions Loftus et al.37 Evaluate friction in various bracket-arch wire combinations Various SS (conventional and s.l.) and ceramic brackets .019” x .025” SS, Niti, and TMA wires were tested with each bracket combination The ceramic brackets generated significantly higher friction than the other brackets 26 Table 2.1. Continued. Author Objective Sample Method Results Angolkar et al.38 Determine the frictional resistance offered by ceramic brackets when used with wires of different alloys and sizes Monocrystalli ne ceramic brackets; results from a similar study using SS brackets SS, cobaltchromium, TMA, and Niti wires were ligated with elastomers to the brackets; the friction was measured as the wire passed through the slots The wires in ceramic brackets generated significantly stronger frictional force than they did in SS brackets Kusy & Whitley39 Measure the coefficients of friction for sixteen arch wirebracket combinations One rectangular arch wire from each of the four wire alloy groups; one bracket from the SS and polycrystalli ne ceramic groups When tested over a series of eight incident angles, the optical surface roughness of the SS and ceramic brackets was measured The ceramic bracket coupled with the SS wire produced a higher coefficient of friction when compared to the SS bracket Cacciafesta et al.41 Compare the frictional resistance between ceramic brackets, ceramic brackets with SS slots, and SS brackets 3M Unitek ceramic bracket; 3M Unitek ceramic bracket with SS slot; 3M Unitek SS bracket; SS, Niti, and TMA wires Static and kinetic friction of each bracketarchwire combination was measured using a specially designed apparatus The ceramic brackets with SS inserts produced significantly less friction than the ceramic brackets, but more friction than the SS brackets Kusy & Whitley43 Compare the frictional resistances of metallined ceramic brackets and SS brackets 1 SS lined ceramic bracket; 1 gold lined ceramic bracket; 2 SS brackets; SS archwires Friction was measured as the secondorder angulations and ligature force among the bracketarchwire combinations was varied Metal-lined ceramic brackets can function comparably to SS brackets and gold inserts appear superior to SS inserts 27 Table 2.2. Summarized portion of the studies regarding bracket ligation and friction. Author Objective Sample Camporesi et al.18 Compare the forces released by ceramic brackets with lowfriction and elastomeric ligation 2 ceramic brackets; low-friction ligation clips; elastomeric ligatures; .014” Niti wire Alignment force was measured using the various bracket and ligation combinations Significantly greater alignment forces were measured when the brackets were combined with the lowfriction clip Hain et al.45 Compare the effect of different ligation methods on friction “Speed” selfligating brackets; SS and ceramic brackets ligated with TP slick modules, elastomerics, and SS ligatures Friction was measured while the various bracketligation combinations were moved along a .019” x .025” SS wire Loosely tied SS ligatures produced the lowest friction, followed by the slick modules, “Speed” brackets, and elastomers Henao, Kusy46 Compare the frictional behavior between conventional and selfligating bracket systems 4 conventional and 4 selfligating bracket systems; 3 standardized archwire sizes Analyses of the bracket types was completed by drawing samples of three archwires through progressively malocclused quadrants The selfligating brackets averaged significantly smaller drawing forces for each study design implemented Petersen48 Compare the alignment force between selfligating brackets and both relaxed and new elastomers “InnovationR” brackets with the self-ligating clip in place and removed; relaxed and new elastomers used to ligate without the clip; Niti wire The unloading force was plotted and measured for a full arch minus one cuspid model for each bracketarchwire combination Ligating with relaxed elastomeric ligatures results in unloading forces nearly equal to those in a self-ligating appliance 28 Method Results Table 2.2. Continued. Author Objective Sample Method Results Sirisaowaluk et al.49 To determine if the type of ligation influences the frictional resistance between SS wire and brackets 8 different variations of ligation using elastomers and SS ligatures; SS brackets; SS wire 80% of the minimum force required to overcome static friction was applied to the wire for 8 minutes and any sliding measured Frictional resistance was least when SS ligatures were figure-8 twisted until taut then untwisted 1/4 turn, and greatest with figure-8 elastomerics Khambay et al.50 Investigate the effect of elastomeric and SS ligatures on frictional resistance using a validated method 4 variations of elastomers; pre-formed SS ligatures; conventional SS brackets; “Damon II” self-ligation brackets Each bracket/wire combination with each method of ligation was tested in the presence of human saliva and the mean frictional force was recorded SS ligatures usually produced lower friction than elastomers; passive selfligating brackets are the only method of almost eliminating friction Hain et al.55 Examine the frictional properties of coated modules with those of other common ligation methods 6 elastomeric variations (including 1 with a special coating); “Speed” active selfligating brackets; “Damon II” passive selfligating brackets Each bracketligation combination’s resistance to movement was measured on a .019” x .025” SS wire The “Damon II” brackets produced no recordable friction of ligation; coated modules produced 50% less friction than all ligation methods except the “Damon II” 29 REFERENCES 1. Bednar JR, Gruendeman GW, Sandrik JL. A comparative study of frictional forces between orthodontic brackets and arch wires. Am J Orthod Dentofacial Orthop 1991;100:513522. 2. Nanda R, Ghosh J. Biomechanics in clinical orthodontics. Philadelphia: WB Saunders, 1997;188-217. 3. Rossouw PE, Kameluchuk LS, Kusy RP. A fundamental review of variables associated with low velocity frictional dynamics. Semin Orthod 2003;9:223-35. 4. Pizzoni L, Ravnholt G, Melsen B. Frictional forces related to self-ligating brackets. Eur J Orthod 1998;20:283-291. 5. Frank CA, Nikolai RJ. A comparative study of frictional resistances between orthodontic bracket and arch wire. Am J Orthod 1980;78:593-609. 6. Downing A, McCabe J, Gordon P. A study of frictional forces between orthodontic brackets and archwires. Br J Orthod 1994;21:349-357. 7. Thalman TD. Unloading behavior of superelastic orthodontic wires: A gingivally malposed cuspid model. St. Louis: Saint Louis University; 2008. 8. Rossouw PE. Friction: An overview. Semin Orthod 2003;9:218-222. 9. Fruge BJ. Forces from Superelastic Cu-Ni-Ti Orthodontic Leveling Wires, Deactivated in Two Directions through Active and Passive Self-Ligated Bracket Sets. St. Louis: Saint Louis University; 2008. 10. Proffit WR. Contemporary Orthodontics. 3rd Ed. St. Louis, MO: Mosby; 2000. 11. Burstone CJ. Application of Bioengineering to Clinical Orthodontics. In: Thomas M. Graber RLV, Katherine W.L. Vig, editor. Orthodontics: Current Principles and Techniques. St. Louis, MO: Elsivier, Mosby; 2005. 30 12. Burstone CJ. Variable-modulus orthodontics. Am J Orthod 1981;80:1-16. 13. Burstone CJ, Qin B, Morton JY. Chinese NiTi wire--a new orthodontic alloy. Am J Orthod 1985;87:445-452. 14. Nikolai RJ. Theoretical Orthodontic Biomechanics (Unpublished). St. Louis: Saint Louis University; 2001. 15. Nikolai RJ. Bioengineering Analysis of Orthodontic Mechanics. Philadelphia, PA: Lea & Febiger; 1985. 16. Franchi L, Baccetti T. Forces released during alignment with a preadjusted appliance with different types of elastomeric ligatures. Am J Orthod Dentofacial Orthop 2006;129:687-690. 17. Ward BL. Friction in Alignment Mechanics: The effects of ligation, perturbation, and wire size on orthodontic aligning forces. St. Louis: Saint Louis Univeristy; 2007. 18. Camporesi M, Baccetti T, Franchi L. Forces released by esthetic preadjusted appliances with low-friction and conventional elastomeric ligatures. Am J Orthod Dentofacial Orthop 2007;131:772-775. 19. Wilkinson PD, Dysart PS, Hood JA, Herbison GP. Loaddeflection characteristics of superelastic nickel-titanium orthodontic wires. Am J Orthod Dentofacial Orthop 2002;121:483-495. 20. Farrant SD. An evaluation of different methods of canine retraction. Br J Orthod 1977;4:5-15. 21. Staggers JA, Germane N. Clinical considerations in the use of retraction mechanics. J Clin Orthod 1991;25:364-9. 22. Stoner M. Force control in clinical practice. Am J Orthod 1960;46:163-86. 23. Kusy RP, Whitley JQ. Friction between different wirebracket configurations and materials. Semin Orthod 1997;3:166-177. 24. Nanda RS, Ghosh J. Biomedical considerations in sliding mechanics. In: Nanda R (ed). Biomechanics in Clinical Orthodontics. Philadelphia, PA: WB Saunders; 1997. 31 25. Miura F, Mogi M, Ohura Y, Hamanaka H. The super-elastic property of the Japanese NiTi alloy wire for use in orthodontics. Am J Orthod Dentofacial Orthop 1986;90:1-10. 26. Kusy RP. A review of contemporary archwires: their properties and characteristics. Angle Orthod 1997;67:197207. 27. Russell J. Current products and practice: aesthetic orthodontic brackets. Br J Orthod 2005;32:146-163. 28. Arid JO, Durning P. Fractures of polycarbonate edgewise brackets: a clinical and SEM study. Br J Orthod 1987;14:191-195. 29. Kusy RP. Morphology of polycrystalline alumina brackets and its relationship to fracture toughness and strength. Angle Orthod 1988;58:197-203. 30. Swartz ML. Ceramic brackets. J Clin Orthod 1988;22:8288. 31. Kusy RP. Orthodontic Biomaterials: From the Past to the Present. Angle Orthod 2002;72:501–12. 32. Omana HM, Moore RN, Bagby MD. Frictional properties of metal and ceramic brackets. J Clin Orthod 1992;26:425-32. 33. Thorstenson G, Kusy R. Influence of stainless steel inserts on the resistance to sliding of esthetic brackets with second-order angulations in the dry and wet states. Angle Orthod 2003;73:167–75. 34. Pratten DH, Dupli K, Germane N, Gunsolley JC. Frictional resistance of ceramic and stainless steel orthodontic brackets. Am J Orthod Dentofacial Orthop 1990;98:398-403. 35. Griffiths HS, Sherrif M, Ireland AJ. Resistance to sliding with three types of elastomeric modules. Am J Orthod Dentofacial Orthop 2005;127:670-75. 36. Tselepsis M, Brockhurst P, West VC. The dynamic frictional resistance between orthodontic brackets and archwires. Am J Orthod Dentofacial Orthop 1994;106:131-138. 32 37. Loftus BP, Årtun J, Nicholls JI, Alonzo TA, Stoner JA. Evaluation of friction during sliding tooth movements in various bracket-arch wire combinations. Am J Orthod Dentofacial Orthop 1999;116:336–45. 38. Angolkar PV, Kapila S, Duncanson MG, Nanda RS. Evaluation of friction between ceramic brackets and orthodontic wires of four alloys. Am J Orthod Dentofacial Orthop 1990;98:499–506. 39. Kusy RP, Whitley JQ. Coefficient of friction for arch wires in stainless steel and polycrystalline alumina bracket slots: The dry state. Am J Orthod Dentofacial Orthop 1990;98:300–12. 40. Kusy RP, Whitley JQ, Prewitt MJ. Comparison of the frictional coefficients for selected archwire-bracket slot combinations in the wet and dry state. Angle Orthod 1991;61:293–302. 41. Cacciafesta V, Sfondrini MF, Scribante A, Klersy C, Auricchio F. Evaluation of friction of conventional and metal-insert ceramic brackets in various bracket-archwire combinations. Am J Orthod Dentofacial Orthop 2003;124:4039. 42. Kapur Wadhwa R, Kwon HK, Close JM. Frictional resistances of different bracket-wire combinations. Aust Orthod J 2004;20:25-30. 43. Kusy RP, Whitley JQ. Frictional resistances of metallined ceramic brackets versus conventional stainless steel brackets and development of 3-D frictional maps. Angle Orthod 2001;71:364–74. 44. Edwards GD, Davies EH, Jones SP. The ex vivo effect of ligation techniques on the static frictional resistance of stainless steel brackets and archwires. Br J Orthod 1995;22:145-53. 45. Hain M, Dhopatkar A, Rock P. The effect of ligation method on friction in sliding mechanics. Am J Orthod Dentofacial Orthop 2003;123:416-22. 46. Henao SP, Kusy RP. Evaluation of the frictional resistance of conventional and self-ligating bracket designs using standardized archwires and dental typodonts. Angle Orthod 2004; 74:202-211. 33 47. Iwasaki LR, Beatty MW, Randall CJ, Nickel JC. Clinical ligation forces and intraoral friction during sliding on a stainless steel archwire. Am J Orthod Dentofacial Orthop 2003;123:408-415. 48. Petersen A. Force Decay of Elastomeric Ligatures: Influence on Unloading Force Compared to Self-Ligation. St. Louis: Saint Louis University; 2008. 49. Sirisaowaluk N, Kravchuk O, Ho C. The influence of ligation on frictional resistance to sliding during repeated displacement. Aust J Orthod 2006;22:141-6. 50. Khambay B, Millett D, McHugh S. Evaluation of methods of archwire ligation on frictional resistance. Eur J Orthod 2004;26: 327-32. 51. Iwasaki LR. Friction and orthodontic mechanics: Clinical studies of moment and ligation effects. Semin Orthod 2003;9: 290-7. 52. Read-Ward GE, Jones SP, Davies EH. A comparison of self-ligating and conventional orthodontic bracket systems. Br J Orthod 1997;24:309-17. 53. Turnbull NR, Birnie DJ. Treatment efficiency of conventional vs. self-ligating brackets: Effects of archwire size and material. Am J Orthod Dentofacial Orthop 2007;131:395-399. 54. Henao SP, Kusy RP. Frictional evaluations of dental typodont models using four self-ligating designs and a conventional design. Angle Orthod 2005;75:75-85. 55. Hain M, Dhopatkar A, Rock P. A comparison of different ligation methods on friction. Am J Orthod Dentofacial Orthop 2006;130:666-670. 34 CHAPTER 3: JOURNAL ARTICLE ABSTRACT Purpose: The purpose of the study was to examine the alignment force deflection patterns of a 0.014-inch superelastic Niti archwire supported in aesthetic and metal brackets with varying ligation methods. Methods: First molar tubes and one of four sets of brackets were bonded to machined steel plates shaped as a maxillary arch. The brackets used in the study were In-Ovation-R (MSL), InOvation-C (CSL), Ovation (MST), and Mystique (CST) (all from GAC International, Bohemia, NY). 0.014-inch superelastic Niti wires were ligated into each bracket set with either 0.010-inch pre-formed steel ligatures (MST and CST) or the self-ligating clips (MSL and CSL). The 0.014inch wire was deflected 4 mm palatally, and the subsequent unloading forces were measured at 0.5 mm increments from 3.5 mm to 0.5 mm. Results: MSL and CSL were significantly different (p<0.05) at all seven deflection points. MST and CST were significantly different (p<0.05) at all deflection points except the 0.5 mm distance. All bracket group pairings were found to be significantly different (p<0.05) at all deflection distances except for the following 35 pairings: CSL and MST at 3.0 mm; CSL and CST at 1.5 mm; MSL and CST at 1.0 mm; MSL and MST, MSL and CST, and MST and CST at 0.5 mm. Conclusions: MSL produce statistically larger alignment forces than CSL throughout a 4 mm deflection of a superelastic Niti wire. MST produce statistically larger alignment forces than CST for superelastic wire deflections greater than 2 mm, but statistically smaller forces for deflections from 1 mm to 2 mm. Where a 4 mm palatally displaced canine is to be corrected with a 0.014-inch superelastic Niti wire, all the bracket groups (MSL,CSL,MST,CST) will behave similarly and provide clinically acceptable alignment forces. 36 INTRODUCTION Aesthetics and treatment efficiency are two seemingly unrelated topics in orthodontics. However, current attempts by manufacturers for improvements in these areas by combining technological advancements to produce an aesthetic self-ligating bracket may prove otherwise. Aesthetic brackets have existed in orthodontics for years, although they have failed to perform as well as their metal counterparts in clinical situations where less friction is desired.1-9 Conventional aesthetic brackets ligated with elastomerics have typically provided a rougher surface area leading to increased friction, and therefore, decreased treatment efficiency. A summary of frictional properties in orthodontics is necessary in order for the interaction between aesthetic brackets and treatment efficiency to be fully understood. Friction and springback potential are two components that determine the magnitude of force placed on a malposed tooth, otherwise known as the alignment force. This can be represented by the following equation: Alignment Force = Springback Potential – Frictional Forces 37 The springback component is the force that would be placed on the malposed tooth if there were no friction in the system. It is determined by the wire properties along with the distance that the wire is deflected. Generally, the further the wire is deflected, the higher that portion of the springback potential will be.10 The frictional force is a negative component that is present at the wire-bracket interfaces in orthodontics. The frictional force is composed of two different parts: the normal force and the coefficient of friction.11-12 The normal force is present at perpendicular angles where the wire and brackets are in contact. In the current study, where the wire is deflected to a palatally malposed, right canine bracket, the wire could possibly contact the disto-lingual and mesio-facial edges of the lateral incisor bracket slot and the mesio-lingual and disto-facial edges of the first bicuspid bracket slot. The coefficient of friction is determined based on the surface roughness of two objects that are sliding against one another. The coefficient of friction is a constant and is associated with the surface characteristics of the materials. Each material has two coefficients of friction13: the coefficient of maximum static friction, which is the 38 force necessary to begin movement, and the coefficient of kinetic friction, which is the component opposing the sliding motion of one surface over another at a steady speed.14 These components of the frictional force are what differs between metal and aesthetic brackets and thus could lead to a negative impact on the alignment force. This problem has been partially overcome by manufacturers placing metal lined slots into the ceramic brackets; however, the frictional levels are still higher than those of all metal brackets.15-18 The recent release of selfligating ceramic brackets could potentially improve this problem of aesthetic brackets and high friction. The ligation force on the adjacent teeth will vary based on the ligation method used, and therefore, higher ligating forces placed on those brackets will increase the friction at the bracket and wire interface.19 Elastomeric ligatures have been shown to produce the highest ligating forces and thus their use in ligating the adjacent brackets will induce wire binding at shorter deflection distances.12,20 Stainless steel ligatures can produce lower frictional levels,4,11,21-24 however, they still may not 39 provide levels equal to those seen in self-ligating brackets.25 With the increasing popularity of clear brackets and “invisible” orthodontic treatment, the idea of applying low friction technology to aesthetic treatment may play a significant role in a clinician’s armamentarium. This study evaluated the differences between aesthetic and nonaesthetic treatment using recently introduced ceramic selfligating brackets and comparing them to metal selfligation. The study also described any benefits of the new self-ligating technology in comparison to more conventional steel ligating mechanisms when used with aesthetic and nonaesthetic brackets. 40 MATERIALS AND METHODS LABORATORY TESTS The arch model used in this study was constructed of 0.25-inch steel with pre-determined interbracket distances based on the standard distances (accurate to within 0.5mm) given by Moyers et al.26 for a male’s maxillary permanent dentition. Attached to the outer edge of the plate were two first molar tubes with zero rotation prescription (GAC International, Bohemia, NY) and nine brackets with 0.022inch slots from second premolar to second premolar, with the exception of the right canine. A 12 mm semicircular area was removed from the plate at the position of the right canine in order to allow palatal wire deflections. The fixed appliances used were from a maxillary set of brackets designated from one of the following types: metal self-ligating In-Ovation-R brackets (GAC International, Bohemia, NY), ceramic self-ligating In-Ovation-C brackets (GAC International, Bohemia, NY), conventional metal Ovation brackets (GAC International, Bohemia, NY), and conventional ceramic Mystique brackets (GAC International, 41 Bohemia, NY). Both ceramic bracket groups were composed of a polycrystalline structure and did not have metal inserts in their slots or bases. A 0.022-inch stainless steel archwire bent to match the shape of the plate was used to align the brackets and tubes. It was determined that this wire was adequate to completely align the brackets due to their 0.022-inch wide slots. The appliances were direct bonded to the plate using Transbond XT (3M Unitek, Monrovia, CA). See Figure 3.1. Figure 3.1: The steel plate with brackets and tubes attached. The ligating mechanism for the self-ligating brackets was the resilient clip on the bracket that locked into 42 place over the archwire slot, while the conventional twin brackets were ligated using 0.010-inch preformed stainless steel ligatures (The Orthodontic Store, Gaithersurg, MD). This method has been shown to produce frictional levels similar to self-ligating brackets in metal bracket studies,25 however, the magnitude of ligation is an important factor for the ligatures. For this study, the stainless steel ligatures were ligated in a manner where they delivered low ligation forces, allowing them to be compared to the self-ligating clips. Also, they were ligated in order to allow the method of ligation to be standardized for each bracket during all the tests. This method was approached using the preformed ligatures that were twisted until taut (initially contacting the wire with the wire resting against the base of the bracket slot), and then untwisted a quarter turn. The ligature subsequently held the wire in the mesial and distal ends of the bracket slot while potentially allowing a low friction system. A pilot study was completed performing this method of steel ligation using a pull-out friction test with a series of brackets. The various runs produced similar frictional levels (the differences were within the error range of the testing machine; i.e. a maximum difference of 3 grams was measured and the machine had a perceived error range of 2.5 43 to 5.0 grams), and it was therefore concluded that the method could be standardized for the final laboratory tests. This method has also been shown in other studies to provide a standardized method of ligating traditional twin brackets.11,21-22,27 The experiment was conducted with a universal testing machine (Model 1011, Instron Corp., Canton, MA) in a dry field temperature control case (36 ± 5˚ C). The steel plate assembly was fixed in order for the 0.01-inch-wide blade of the deflecting rod to contact the wire at the midpoint of the right canine space. Continuous 0.014-inch superelastic Niti wires (G&H Wire Company, Franklin, IN) matching the shape of the steel plate were ligated into the fixed brackets. See Figure 3.2. 44 Figure 3.2: The steel plate with brackets and wire positioned in the testing apparatus. A pilot study (10 runs per group) was completed in order to use a statistical power analysis to indentify the sample size. It was then determined that 40 tests per bracket group (metal self-ligating, ceramic self-ligating, ceramic conventional ligated with stainless steel, metal conventional ligated with stainless steel) would provide adequate statistical results. A new wire was selected for each individual test (160 wires total were used). During each test, the 0.014-inch wire was deflected palatally with the blade at the center of the right canine position. The wire was advanced to a distance of 4 mm with a cross-head 45 speed of 10 mm per minute and unloaded facially at a speed of 2 mm per minute. As the wire unloaded, the alignment force was recorded at every 0.5 mm increment from 3.5 mm to 0.5 mm for statistical analysis. STATISTICAL ANALYSIS Alignment force values were analyzed using the SPSS 15.0 for Windows (SPSS Inc., Chicago, IL) statistical package. Descriptive statistics were generated for each bracket-ligation group (Table 3.1). Independent T-Tests were run between the brackets within each ligation group to evaluate for statistical differences between the means at a 95% probability level. To further assess the results, a One-Way ANOVA was used to analyze for variance between all of the bracket-ligation groups at each deflection point. Bonferroni post-hoc tests were then run to identify significant differences between the variables at a 95% probability level. 46 Table 3.1. Descriptive Statistics: Alignment Force (grams) Deflection 3.5 mm 3.0 mm 2.5 mm 2.0 mm 1.5 mm 1.0 mm 0.5 mm Group Metal Self-Ligating Ceramic Self-Ligating Metal Steel-Tied Ceramic Steel-Tied Metal Self-Ligating Ceramic Self-Ligating Metal Steel-Tied Ceramic Steel-Tied Metal Self-Ligating Ceramic Self-Ligating Metal Steel-Tied Ceramic Steel-Tied Metal Self-Ligating Ceramic Self-Ligating Metal Steel-Tied Ceramic Steel-Tied Metal Self-Ligating Ceramic Self-Ligating Metal Steel-Tied Ceramic Steel-Tied Metal Self-Ligating Ceramic Self-Ligating Metal Steel-Tied Ceramic Steel-Tied Metal Self-Ligating Ceramic Self-Ligating Metal Steel-Tied Ceramic Steel-Tied Minimum 160.0 150.0 145.0 140.0 135.0 125.0 125.0 117.5 127.5 117.5 115.0 112.5 120.0 112.5 105.0 105.0 112.5 107.5 100.0 102.5 97.5 92.5 92.5 97.5 60.0 55.0 60.0 60.0 Maximum 172.5 165.0 155.0 155.0 147.5 135.0 137.5 135.0 137.5 130.0 127.5 125.0 135.0 130.0 117.5 122.5 125.0 127.5 112.5 120.0 110.0 105.0 102.5 110.0 72.5 67.5 67.5 67.5 Mean 167.3 157.3 151.7 144.8 139.8 130.9 130.7 126.1 130.9 123.4 121.3 118.6 126.5 118.2 111.6 114.1 118.3 113.4 106.9 111.4 103.7 99.6 97.6 102.9 64.6 61.6 64.3 65.0 SD 2.6 3.1 2.4 3.6 3.3 2.4 2.9 5.3 2.8 2.9 2.9 3.9 3.5 4.2 2.8 4.3 2.8 4.8 3.3 4.3 3.3 2.8 2.9 3.0 3.3 2.4 2.0 2.0 RESULTS The mean alignment forces at each deflection point were analyzed using two statistical tests. Independent T-Tests were used to compare the means of the metal versus ceramic bracket types for each ligation group at the seven deflection points (Tables A.1-A.2 in Appendix). When comparing within the self-ligating group, the ceramic and metal brackets were significantly different (p<0.05) at all 47 seven deflection points. Within the steel ligature group, the ceramic and metal brackets were significantly different (p<0.05) at every deflection point except the 0.5 mm distance. In addition, within the steel ligature group, the metal brackets had higher mean alignment forces for the 3.5-2.5 mm distances; however, the ceramic brackets provided more alignment force from the 2.0-0.5 mm distances. The metal brackets tested with higher mean alignment forces than the ceramic brackets at all deflection points within the self-ligating group. A One-Way ANOVA and Bonferroni post-hoc tests were used to further analyze the bracket-ligation groups in order to find statistical differences between all four of the brackets at each deflection point (Tables A.3-A.9 in Appendix). All bracket group pairings were found to be significantly different (p<0.05) at all deflection distances except for the following pairings: ceramic selfligating and metal steel-tied at 3.0 mm; ceramic selfligating and ceramic steel-tied at 1.5 mm; metal selfligating and ceramic steel-tied at 1.0 mm; metal selfligating and metal steel-tied, metal self-ligating and ceramic steel-tied, metal steel-tied and ceramic steel-tied at 0.5 mm. 48 Figures 3.3, 3.4, and 3.5 illustrate the unloading plot data. 160 Force (g) 140 120 100 Metal Self-Ligating 80 Ceramic Self-Ligating 60 40 0.5 1 1.5 2 2.5 3 3.5 Deflection (mm) Figure 3.3: Unloading plot data for the self-ligating bracket groups at the seven deflection points. 49 160 Force (g) 140 120 100 Metal Steel-Tied 80 Ceramic Steel-Tied 60 40 0.5 1 1.5 2 2.5 3 3.5 Deflection (mm) Figure 3.4: Unloading plot data for the steel-tied bracket groups at the seven deflection points. 160 Force (g) 140 120 100 Metal Self-Ligating Ceramic Self-Ligating 80 Metal Steel-Tied 60 Ceramic Steel-Tied 40 0.5 1 1.5 2 2.5 3 3.5 Deflection (mm) Figure 3.5: Unloading plot data for all bracket-ligation groups at the seven deflection points. 50 DISCUSSION The unloading plot illustrates the superelastic behavior exhibited by the 0.014 Niti archwire. For each bracket-ligation group, there was an area where the curve leveled off around the 2 mm to 3 mm deflection distance. Even though the stiffness of the wire would have varied throughout that distance, the Niti wire still exhibited a fairly constant force due to the superelastic properties inherent to the archwire.28 The alignment force in the rest of the unloading plots varied greatly due to the changing stiffness of the wire given the varying deflection amplitudes. Also, the frictional forces in the adjacent brackets opposed the sliding of the wire throughout the arch. Even though the alignment force levels were significantly different between each bracket-ligation group at most of the deflection points, Figure 3.5 does illustrate that the unloading patterns of the groups were similar throughout the deflection distances. Their frictional levels varied over most of the plots, however, they still exhibited similar unloading characteristics. This was primarily due to the wire properties since the same SE Niti wire was used for each group. Although, it 51 still remains significant as unloading plots have been remarkably different in previous studies with varying ligation methods where the wire was constant throughout the experiment.20 This shows that even though there were significant differences in frictional levels for the groups throughout most of the plots, they were still comparable enough to provide similar unloading characteristics. When comparing the ceramic and metal brackets within the self-ligating group, the metal brackets provided significantly higher alignment forces throughout the unloading plots. Since the bracket composition was the indirect variable among the bracket groups, it can be concluded that the ceramic composition provided higher frictional levels, and thus, lower unloading forces for the palatally offset canine. Pratten et al.3 and Loftus et al.6 produced similar results in experiments with conventional ceramic and stainless steel brackets. However, this trend did not hold true for the steel-tied group. The ceramic and metal brackets within this group were significantly different at all deflection points except for the 0.5 mm distance. Further analysis revealed the most significant finding within this group, that the ceramic brackets provided higher alignment forces from the 2.0 mm to 0.5 mm distances. This suggests that when steel ligatures are used 52 to ligate conventional brackets, the bracket composition is less of a factor when frictional levels are considered. After analyzing all of the 42 bracket-ligation group comparisons at the 7 deflection points using the One-Way ANOVA, there were only 6 pairings that did not show significant differences between their alignment forces. Among those non-significant findings, 3 of the groupings fell within the 0.5 mm deflection distance. These results suggest that the second indirect variable of ligation added among these groupings is less of a factor on frictional levels than the variable of bracket composition when selfligation is compared to steel ligatures. Since most of the non-significant findings were from the 1.5 mm to 0.5 mm distances, it can be concluded that the further the deflection amplitude of the Niti wire, the greater the variation between the bracket-ligation groups. In other words, the differing bracket composition and ligation methods had a greater effect on the frictional levels within the system as the wire was further deflected to engage an offset tooth. Overall, even though most of the comparisons were statistically significant, the actual differences in the alignment force magnitudes between each bracket-ligation group were perhaps clinically insignificant. The unloading 53 plots show the close relationships between the groups, and it could be assumed that each bracket-ligation combination would behave very similar in most clinical situations. For a palatally offset canine, the possible tooth movements typically expected are tipping, extrusion, or rotation. The optimum force levels for these movements are between 35-60 g according to Proffit,29 therefore each bracket-ligation group used in this study were more than adequate for the desired tooth movements. Factors not examined in this study that could affect clinical outcomes include extraneous intraoral forces and factors, varying interbracket distances, and wire diameter. The presence of saliva and plaque accumulation are factors that could both positively and negatively affect the clinical frictional force levels. Perturbations are intraoral forces that could momentarily decrease the frictional levels to zero, providing episodes of maximum alignment force.30 Altering the local wire curvature by increasing or decreasing the interbracket distances would have an affect on the normal forces in the system, therefore changing the unloading force. Varying wire diameters have been shown to alter alignment forces, and the unloading plot characteristics between bracket-ligation groups could change as well.10 54 Clinical recommendations can be deduced from the present study. Where there is a demand for maximum aesthetics and treatment efficiency, using brackets that are made of ceramic materials containing self-ligating mechanisms would be advantageous. The ceramic composition provides a time-tested way to obtain clear braces, while the self-ligation gives the clinician low friction levels and rapid wire changes. CONCLUSIONS 1. The springback potential of the 0.014-inch superelastic Niti wire is large enough to supersede the frictional forces present in all four of the bracket-ligation groups. 2. Metal self-ligating brackets will produce statistically larger alignment forces than ceramic self-ligating brackets throughout a 4 mm deflection of a superelastic Niti wire. 3. Metal steel-tied brackets will produce statistically larger alignment forces than ceramic steel-tied brackets for superelastic wire deflections greater than 2 mm, but statistically smaller forces for deflections from 1 mm to 2 mm. 4. Where a 4 mm palatally displaced canine is to be corrected with a 0.014-inch superelastic Niti, ceramic and 55 metal brackets that are self-ligating or steel-tied will behave similarly and provide clinically acceptable alignment forces. 56 REFERENCES 1. Kusy RP, Whitley JQ. Friction between different wirebracket configurations and materials. Semin Orthod 1997;3:166-177. 2. Thorstenson G, Kusy R. Influence of stainless steel inserts on the resistance to sliding of esthetic brackets with second-order angulations in the dry and wet states. Angle Orthod 2003;73:167–75. 3. Pratten DH, Dupli K, Germane N, Gunsolley JC. Frictional resistance of ceramic and stainless steel orthodontic brackets. Am J Orthod Dentofacial Orthop 1990;98:398-403. 4. Griffiths HS, Sherrif M, Ireland AJ. Resistance to sliding with three types of elastomeric modules. Am J Orthod Dentofacial Orthop 2005;127:670-75. 5. Tselepsis M, Brockhurst P, West VC. The dynamic frictional resistance between orthodontic brackets and archwires. Am J Orthod Dentofacial Orthop 1994;106:131-138. 6. Loftus BP, Årtun J, Nicholls JI, Alonzo TA, Stoner JA. Evaluation of friction during sliding tooth movements in various bracket-arch wire combinations. Am J Orthod Dentofacial Orthop 1999;116:336–45. 7. Angolkar PV, Kapila S, Duncanson MG, Nanda RS. Evaluation of friction between ceramic brackets and orthodontic wires of four alloys. Am J Orthod Dentofacial Orthop 1990;98:499–506. 8. Kusy RP, Whitley JQ. Coefficient of friction for arch wires in stainless steel and polycrystalline alumina bracket slots: The dry state. Am J Orthod Dentofacial Orthop 1990;98:300–12. 9. Kusy RP, Whitley JQ, Prewitt MJ. Comparison of the frictional coefficients for selected archwire-bracket slot combinations in the wet and dry state. Angle Orthod 1991;61:293–302. 57 10. Fruge BJ. Forces from Superelastic Cu-Ni-Ti Orthodontic Leveling Wires, Deactivated in Two Directions through Active and Passive Self-Ligated Bracket Sets. St. Louis: Saint Louis University; 2008. 11. Bednar JR, Gruendeman GW, Sandrik JL. A comparative study of frictional forces between orthodontic brackets and arch wires. Am J Orthod Dentofacial Orthop 1991;100:513522. 12. Nanda R, Ghosh J. Biomechanics in clinical orthodontics. Philadelphia. WB Saunders 1997;188-217. 13. 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A comparison of self-ligating and conventional orthodontic bracket systems. Br J Orthod 1997;24:309-17. 26. Moyers, RE, Van der Linden FPGM, Riolo ML, McNamara JA. Standards of human occlusal development. Ann Arbor: Center for Human Growth and Development; University of Michigan; 1976. 27. Iwasaki LR. Friction and orthodontic mechanics: Clinical studies of moment and ligation effects. Semin Orthod 2003;9:290-7. 28. Wilkinson PD, Dysart PS, Hood JA, Herbison GP. Loaddeflection characteristics of superelastic nickel-titanium orthodontic wires. Am J Orthod Dentofacial Orthop 2002;121:483-495. 59 29. Proffit WR. Contemporary Orthodontics. 3rd Ed. St. Louis, MO: Mosby; 2000. 30. Braun S, Bluestein M, Moore BK, Benson G. Friction in perspective. Am J Orthod Dentofacial Orthop 1999;115:619627. 60 APPENDIX: TABLES Table A.1. T-Tests Comparing Metal Self-Ligating and Ceramic Self-Ligating at Seven Deflection Points (p<0.05) Groups (mm) C.S.L. 3.5 C.S.L. 3.0 C.S.L. 2.5 M.S.L. 3.5 Sig. Diff. M.S.L. 3.0 M.S.L. 2.5 M.S.L. 2.0 M.S.L. 1.5 M.S.L. 1.0 M.S.L. 0.5 Sig. Diff. Sig. Diff. Sig. Diff. C.S.L. 2.0 Sig. Diff. C.S.L. 1.5 Sig. Diff. C.S.L. 1.0 Sig. Diff. C.S.L. 0.5 61 Table A.2. T-Tests Comparing Metal Steel-Tied and Ceramic Steel-Tied at Seven Deflection Points (p<0.05) Groups (mm) C.S.T. 3.5 C.S.T. 3.0 C.S.T. 2.5 M.S.T. 3.5 Sig. Diff. M.S.T. 3.0 M.S.T. 2.5 M.S.T. 2.0 M.S.T. 1.5 M.S.T. 1.0 M.S.T. 0.5 Sig. Diff. Sig. Diff. Sig. Diff. C.S.T. 2.0 Sig. Diff. C.S.T. 1.5 Sig. Diff. C.S.T. 1.0 NonSig. Diff. C.S.T. 0.5 62 Table A.3. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 3.5 mm Deflection Distance (p<0.05) Groups M.S.L. M.S.L. C.S.L. Sig. Diff. C.S.L. Sig. Diff. M.S.T. Sig. Diff. Sig. Diff. C.S.T. Sig. Diff. Sig. Diff. 63 M.S.T. Sig. Diff. Sig. Diff. C.S.T. Sig. Diff. Sig. Diff. Sig. Diff. Sig. Diff. Table A.4. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 3.0 mm Deflection Distance (p<0.05) Groups M.S.L. M.S.L. C.S.L. Sig. Diff. C.S.L. Sig. Diff. M.S.T. Sig. Diff. Non-Sig. Diff. C.S.T. Sig. Diff. Sig. Diff. 64 M.S.T. Sig. Diff. Non-Sig. Diff. C.S.T. Sig. Diff. Sig. Diff. Sig. Diff. Sig. Diff. Table A.5. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 2.5 mm Deflection Distance (p<0.05) Groups M.S.L. M.S.L. C.S.L. Sig. Diff. C.S.L. Sig. Diff. M.S.T. Sig. Diff. Sig. Diff. C.S.T. Sig. Diff. Sig. Diff. 65 M.S.T. Sig. Diff. Sig. Diff. C.S.T. Sig. Diff. Sig. Diff. Sig. Diff. Sig. Diff. Table A.6. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 2.0 mm Deflection Distance (p<0.05) Groups M.S.L. M.S.L. C.S.L. Sig. Diff. C.S.L. Sig. Diff. M.S.T. Sig. Diff. Sig. Diff. C.S.T. Sig. Diff. Sig. Diff. 66 M.S.T. Sig. Diff. Sig. Diff. C.S.T. Sig. Diff. Sig. Diff. Sig. Diff. Sig. Diff. Table A.7. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 1.5 mm Deflection Distance (p<0.05) Groups M.S.L. M.S.L. C.S.L. Sig. Diff. C.S.L. Sig. Diff. M.S.T. Sig. Diff. Sig. Diff. C.S.T. Sig. Diff. Non-Sig. Diff. 67 M.S.T. Sig. Diff. Sig. Diff. C.S.T. Sig. Diff. Non-Sig. Diff. Sig. Diff. Sig. Diff. Table A.8. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 1.0 mm Deflection Distance (p<0.05) Groups M.S.L. M.S.L. C.S.L. Sig. Diff. C.S.L. Sig. Diff. M.S.T. Sig. Diff. Sig. Diff. C.S.T. Non-Sig. Diff. Sig. Diff. 68 M.S.T. Sig. Diff. Sig. Diff. C.S.T. Non-Sig. Diff. Sig. Diff. Sig. Diff. Sig. Diff. Table A.9. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 0.5 mm Deflection Distance (p<0.05) Groups M.S.L. M.S.L. C.S.L. Sig. Diff. C.S.L. Sig. Diff. M.S.T. Non-Sig. Diff. Sig. Diff. C.S.T. Non-Sig. Diff. Sig. Diff. 69 M.S.T. Non-Sig. Diff. Sig. Diff. C.S.T. Non-Sig. Diff. Sig. Diff. Non-Sig. Diff. Non-Sig. Diff. VITA AUCTORIS Matthew Steven Baker was born on August 29, 1979, in Memphis, TN. Upon graduation from high school in 1997, he attended Furman University for one year. Matt then transferred to Indiana University, where he earned a B.S. degree in Biology in 2002. On May 25, 2002, Matt was married to Brooke Dixon in Newburgh, IN. Following graduation from IU, he entered dental school at Indiana University School of Dentistry. Matt received his D.D.S. degree from IU in 2006. Upon graduation, he entered the graduate program in orthodontics at Saint Louis University, where he is currently a candidate for the degree of Master of Science in Dentistry. After graduation from SLU in December of 2008, Matt and Brooke will relocate to the state of Florida to begin their professional careers in orthodontics and university education. 70