I J Pre Clin Dent Res 2014;1(4):100-106 International Journal of Preventive & October-December Clinical Dental Research All rights reserved

Metal Free : A Review

Abstract With the increase in the number of adults undergoing orthodontic 1 2 Syed Rafiuddin , Reji Abraham treatment, there has been a corresponding increase in demand for more esthetic orthodontic appliances. These new appliances combine both 1Senior Lecturer, Department of Orthodontics acceptable esthetics and adequate technical performance. This article & Dentofacial Orthopedics, Sri Hasanamba presents the currently available appliances and discusses the potential Dental College & Hospital, Hassan, Karnataka, problems associated with each. Recent advances have also been India 2Professor, Department of Orthodontics & described. Dentofacial Orthopedics, Sri Hasanamba Key Words Dental College & Hospital, Hassan, Karnataka, Esthetics; brackets; archwires India

INTRODUCTION to moderate alignment cases, especially in the adult Since 1990’s there has been a growing demand for patient. However, complex cases still require fixed esthetic orthodontic appliances. Orthodontic appliance treatment and numerous brackets & patients, including a growing population of adults, archwires are now available for those clinicians and not only want an improved smile, but they are also patients that are aesthetically orientated. increasingly demanding better aesthetics during BRACKETS treatment. This demand has led to the development Two of the materials used for traditional aesthetic of orthodontic appliances with acceptable esthetics bracket manufacturing are plastic and both for patients and clinicians. The development of brackets. appliances that combine both acceptable aesthetics Plastic Brackets for the patient and adequate technical performance Plastic brackets were introduced into the market in for the clinician is the ultimate goal. There has been early 1970’s. Initially they were constructed from a recent trend towards the development of smaller acrylic followed by unfilled polycarbonate. The brackets but although these generally disadvantages with these materials were they provide the technical performance required by the resulted in staining and odours but more importantly orthodontist the aesthetic advantage over they lacked strength and stiffness resulting in conventional sized appliances is limited. Lingual bonding problems, tie wing fractures[1] and orthodontics satisfies the aesthetic criteria but it can permanent deformation or creep. Permanent be argued that it produces a decrease in the deformation occurs when a material is subjected to performance of the appliance and considerable a constant load over an extended period of time and additional technical difficulties and time is particularly important for thermoplastic materials requirement for the orthodontist. Most of the such as polycarbonate resins. Polycarbonate bracket orthodontic appliances are metallic and silver in slots distorted with time under a constant color and at the beginning of esthetic production, physiologic stress rendering them insufficiently there were transparent brackets made of ceramic or strong to withstand longer treatment times or composite. But the archwires were still made of transmit torque.[2] Polycarbonate brackets also metals such as , reported significantly higher torque losses and titanium, or stainless steel. Recently, coated metallic lower torquing moments with compared to metal and fiber-reinforced have been introduced to brackets.[3] To compensate for the lack of strength solve esthetic appearance problem. A more recent and rigidity of the original polycarbonate brackets, addition to the orthodontist’s armamentarium is high-grade medical polyurethane brackets and Invisalign. This aesthetically orientated technique polycarbonate brackets reinforced with ceramic or uses a series of clear plastic aligners to treat simple fibreglass fillers and/or metal slots have been 101 Metal free orthodontics Rafiuddin S, AbrahamR recently introduced. Polycarbonate brackets with Composition & Types of Ceramic Brackets metal reinforced slots demonstrated significantly are a broad class of materials consisting less creep than conventional polycarbonate brackets of metal oxide elements and non-metal elements although torque problems still exist. Approximately that include precious stones, glasses, clays and 15% loss in torque over 24 hours has been observed mixtures of ceramic compounds.[7] Alumina is a with both ceramic reinforced and metal lined typical member of modern ceramics, formed when polycarbonate brackets.[4] Torque deformation aluminum is added to steel to remove characteristics of seven commercially available dissolved in the steel.[8] Alumina may be used as a plastic brackets both against each other & with single-crystal material or as a polycrystalline stainless steel brackets were compared in a study. material. Both monocrystalline and polycrystalline The results showed that metal slot reinforced alumina are used to manufacture orthodontic brackets were subjected to the lowest degree of ceramic brackets.[9] Ceramic brackets are composed deformation, followed by pure polyurethane, pure of aluminium oxide in one of two forms: polycarbonate and fibreglass reinforced polycrystalline or monocrystalline, depending on polycarbonate brackets. Ceramic reinforced their method of fabrication. Monocrystalline polycarbonate brackets showed the highest brackets are manufactured by milling from single deformation under torque stresses. The addition of crystals of sapphire using diamond tools whereas ceramic and fibreglass in the plastic brackets also polycrystalline brackets are sintered using special failed to improve the torque stability of the binders to thermally fuse the particles together. The polycarbonate brackets and pure polyurethane manufacturing process plays a very important role brackets showed no significant difference from pure in the clinical performance of the ceramic brackets. polycarbonate at optimal torque. A comparison with The production of polycrystalline brackets is less stainless steel brackets illustrated that plastic complicated, and thus these brackets are more brackets are only suited for clinical application if readily available at present. The most apparent they have a metal slot.[5] A recent advancement to difference between polycrystalline and single aesthetic brackets are self-ligating aesthetic crystal brackets is in their optical clarity. Single brackets. A study conducted to measure and crystal brackets are noticeably clearer than compare the level of frictional resistance generated polycrystalline brackets and hence are translucent. between stainless steel self-ligating brackets, Both single crystal and polycrystalline brackets polycarbonate self-ligating brackets, and resist staining and discoloration.[9] Polycrystalline conventional stainless steel brackets showed that zirconia brackets which reportedly have the greatest polycarbonate self-ligating brackets generated toughness amongst all ceramics, have been offered significantly greater static and kinetic frictional as an alternative to alumina ceramic brackets.[10] forces than stainless steel self-ligating brackets but They are cheaper than the monocrystalline ceramic were comparable to conventional stainless steel brackets but they are very opaque and can exhibit brackets.[6] intrinsic colours making them less aesthetic. Good Ceramic Brackets sliding properties have been reported with both In an attempt to improve esthetics while stainless steel and nickel-titanium archwires along maintaining bracket strength has resulted recently in with reduced plaque adhesion, clinically acceptable the development of a ceramic bracket. Ceramic bond strengths and bond failure at the brackets were introduced in the 1980’s. The bracket/adhesive interface.[11] However, zirconia advantages ceramic brackets offer over brackets did not offer any significant advantage conventional aesthetic brackets are that they provide over polycrystalline alumina brackets with regard to higher strength, more resistance to wear and frictional characteristics.12 As the clinical deformation, better colour stability and, most performance of alumina ceramic brackets has important to the patient is they offer superior continued to improve over recent years, zirconia aesthetics. Ceramic brackets are available in a brackets have become obsolete. variety of structures including true Siamese, semi- Clinical problems encountered with ceramic Siamese, solid and Lewis/Lang designs and also brackets and their management various appliance systems including Begg and Various problems encountered with the use of variable force ligation brackets. ceramic brackets in clinical practice are- Increased

102 Metal free orthodontics Rafiuddin S, AbrahamR bond strength, friction, bracket breakage, iatrogenic similar frictional characteristics as stainless steel enamel damage & debonding. brackets.[17] Whereas a study conducted by Nishio et Increased bond strength al.,[19] demonstrated significantly higher frictional Early ceramic brackets used a silane-coupling agent forces with ceramic brackets with metal slots to act as a chemical mediator between the ceramic compared to stainless steel brackets. In another bracket base and the adhesive resins as the ceramic study Thorstenson and Kusy[20] observed that the brackets did not bond chemically with acrylic and addition of stainless steel inserts to polycrystalline diacrylate bonding adhesives due to their inert brackets did not considerably improve the resistance aluminium oxide composition. This chemical to sliding over those aesthetic brackets without retention resulted in extremely strong bonds that inserts. To reduce friction some manufacturers have caused the enamel/ adhesive interface to be stressed come out with silica-lined slots as well as during debonding, risking irreversible enamel introducing bumps along the floor of the slots as damage in the form of crack and delamination that alternatives to metal lined slots. often required dental restorations. Consequently, the Bracket breakage challenge was to develop a bond between the Ceramic brackets have a higher incidence of bracket ceramic bracket base and the enamel that clinically breakages than with stainless steel brackets due to has adequate strength to accomplish treatment but its low fracture toughness. Tie wings can easily can be broken at debond without damage to the fracture due to the high torsional forces exhibited by enamel surface. The majority of the currently rectangular wires and surface flaws within ceramic available ceramic brackets rely solely on brackets can lead to cracks and fractures when the mechanical retention, using standard light or bracket is stressed. Injection moulded brackets have chemically cured adhesives, without the need for a much smoother finish than machined brackets thus additional special bonding agents. Numerous reducing the number of surface flaws. mechanical base designs are now available ranging Iatrogenic enamel wear from microcrystalline, mechanical ball, dovetail, Ceramic brackets are nine times harder than dimpled chemo/mechanical, silane coated buttons stainless steel brackets or enamel and severe enamel and polymeric bases with many manufacturers abrasion from ceramic brackets might occur rapidly, claiming consistent bond strengths and debonding if contacts between teeth and ceramic brackets exist. characteristics comparable to that of stainless steel Rapid and severe enamel wear to the opposing mesh. Several studies have compared the bond dentition has been reported when ceramic brackets strength of ceramic brackets with different retention are placed in the lower arch.[21] The use of mechanisms and concluded that mechanically polycarbonate brackets in the lower arch has been retained brackets have adequate bond strength and recommended if is a concern as they are appear to cause less enamel damage at debond less abrasive to the opposing dentition. compared to the chemically retained brackets.[13-15] Alternatively metal brackets might also be used in Friction lower arch. Ceramic brackets vary in fracture toughness and Debonding strength depending on the extent of the surface Many alternative debonding methods have been roughness. This in turn affects the overall frictional suggested, to avoid the complications associated properties of the bracket. Polycrystalline ceramics, with ceramic bracket removal. Few of the have a higher coefficient of friction than debonding methods currently used are-Conventional monocrystalline ceramics and stainless steel due to debonding pliers, Hows, Weingarts or ligature their rougher & more porous surface. cutters, Ceramic bracket specific debonding pliers, Polycrystalline brackets have shown to generate Electrothermal debonding, Ultrasonic scaler, Laser significantly greater frictional forces than stainless aided debonding & Debonding agents. steel brackets with any of the archwire ARCHWIRES combination.[16] In order to overcome the frictional Coated metallic and transparent non-metallic characteristics of ceramic brackets metal reinforced archwires are the two types which have been archwire slots have been introduced. Studies done introduced to solve esthetic appearance problem.[22] on these metal inserts have shown conflicting Coated metallic archwires results. In a study conducted by kusy et al., metal Coating on archwire material have been introduced lined ceramic brackets were shown to possess to enhance esthetics and to decrease friction. These 103 Metal free orthodontics Rafiuddin S, AbrahamR wires are designed to be esthetically more the mouth, exposing the underlying metal.[26,27] acceptable by the patient. Coated metal archwires Elayyan et al.,[28] stated that coated archwires had are nickel-titanium or stainless steel wires treated low esthetic value because 25% of coating was lost with a polytetrafluoroethylene (PTFE), epoxyresin, within 33 days in vivo and surface quality revealed parylene-polymer, or less commonly severe deterioration. covering to impart an enamel hue. Manufacturers Transparent non- metallic archwires vary with regard to the coating material, thickness In the past 20 years, significant advancements have of the coating, and steps within the application been made to create non-metallic arches whose process to maximize aesthetics, flake resistance, and properties resemble metal alloys. Flexible mechanical efficiency. Currently, the two most nonmetallic arches are typically made from glass common aesthetic archwires available in the market spindles embedded in a polymeric matrix. Some are coated with either PTFE or epoxy-resin. examples of non-metallic arches include fiber- PTFE, Teflon. PTFE, commonly recognized by the reinforced polymer (FRP),[29,30] or newer self- DuPont Co brand name Teflon, is a synthetic reinforced polymer (SRP).[31] Fiber reinforced polymer consisting wholly of and fluorine. composite wires for orthodontic purposes are Due to the strength of the carbon-fluorine bonds, fabricated using a procedure called pultrusion32. PTFE is nonreactive, heat-resistant, and Fiber bundles are pulled through an extruder, in hydrophobic. PTFE coating is applied to an which they are wetted with a monomer resin. Next, orthodontic by thermal spraying; a process in the monomer is cured with heat and pressure, which finely heated materials are sprayed in a resulting in polymerization. During curing, the molten condition onto a surface to form a coating wetted fiber is formed into a desired cross sectional The PTFE layer adds a minimal thickness (.0008 to morphology, which may be circular or rectangular. .001 inch) to the archwire. This wire may be also be further shaped into a Epoxy-resin. Epoxy is a synthetic resin made by different morphology by further curing, a process combining epoxide with another compound. known as beta staging. These arches allow for a few They are widely used in orthodontic materials, millimeters of deformation and may be suitable for including composite resins, molds, and levelling and aligning in patients with Class I polyurethane aligners. Epoxy-resin coating is with mild to moderate crowding. applied to an orthodontic archwire by electrostatic More importantly, they display the translucency and coating, or E-coating. Electrostatic coating is a transparency ideal for ceramic brackets. Burstone process that uses electrostatically charged particles and Kuhlberg33 have described the clinical to more efficiently coat a workpiece. The epoxy application of a new fiber reinforced composite coating does add a more significant thickness (.002 called "Splint-It" which incorporates S2 glass fibers inch) to the archwire. Therefore, a .0180-inch NiTi in a bis GMA matrix. This is available in various wire becomes .020-inch diameter with an epoxy configurations such as rope, woven strip and coating, or alternatively, the manufacturer may unidirectional strip. These materials are only partly choose to use a smaller diameter wire to polymerized during manufacture (pre-pregs), which compensate for the thickness of the coating. Coating makes them flexible, adaptable and easily improves aesthetics, but creates a modified surface, contourable over the teeth. Later they are which can affect friction, corrosive properties, and completely polymerized and can be bonded directly the mechanical durability of the wires. There are to teeth. They can be applied for various purposes different opinions in the literature concerning such as post treatment retention, as full arches or coated archwires. An evaluation of sliding sectional arches, and to reinforce by properties and adherence of coating to the archwires joining teeth together. A particular advantage is that revealed that the plastic coating decreased friction due to direct bondability to teeth, they can obviate between archwires and brackets.[23] The coated the need for brackets in specific situations. In wires are also found to be routinely damaged from addition, they are highly esthetic, and could thus be mastication and activation of enzymes,[24] due to an effective alternative to lingual appliances. which this coating has been described as Optiflex archwire[30] is a non metallic orthodontic undurable.25 Other authors have also experienced wire designed by M.F. Talass in 1992 to combine difficulties, claiming that the colour tends to change unique mechanical properties with a highly esthetic with time and that the coating splits during use in appearance. Structure of Optiflex archwire is that it 104 Metal free orthodontics Rafiuddin S, AbrahamR is made of clear optical fiber comprising of three rotation and angulation control. Indications of layers A – Silicon Dioxide Core, B – Silicon Resin invisalign includes mildly crowded and malaligned Middle Layer, C – Nylon Outer Layer. Silicon teeth (1–5 mm), spacing problems (1–5 mm), deep dioxide core provides the force for moving teeth. overbite problems (Class II division 2 type Silicon resin middle layer protects core from malocclusions) where the overbite can be reduced moisture and adds strength & Nylon outer layer acts by and advancement of incisors & narrow as stain resistant & also prevents damage to wire arches that can be expanded without tipping the and further increases the strength. Its advantages are teeth too much. Limitations of invisalign include that it is completely stain resistant, effective in crowding or spacing over 5 mm, skeletal antero- moving teeth with light continuous forces, very posterior discrepancies of more than 2 mm, centric flexible, has wide range of actions & it can be used relation and centric occlusion discrepancies, with any bracket system. Nonmetallic archwires are severely rotated teeth (more than 20 degrees), open brittle and allow for only moderate deformation. bites (anterior and posterior) that need to be closed, Excess deformation or forceful grip with pliers can extrusion of teeth, severely tipped teeth (more than lead to permanent deformation and irreversible 45 degrees), teeth with short clinical crowns, arches cracks, referred to as “craze lines.” These clear with multiple missing teeth & closure of bicuspid arches are restricted with regard to torque, detailing, extraction spaces.[34] and changes in arch width, and they are currently ESSIX APPLIANCE not suitable for patients requiring consolidation or The Essix appliance[35] is a light, almost invisible anteroposterior correction. removable plastic device that snaps over the teeth INVISALIGN and is used mainly for retention. They are fabricated Invisalign is an orthodontic technique that uses a from .030" Essix plastic sheet, which is reduced to series of clear plastic aligners to move teeth. .015" during thermoforming. There are two types of Invisalign was the brainchild of Zia Chishti and Essix plastics: types A and C. Typical applications Kelsey Wirth, graduate students in Stanford for type A are for minor tooth movement with University's MBA program. The aligners are made divots and windows, bite planes, TMJ splints and from thin, see through plastic, which fits over the intrusion appliances. Type A must be used when buccal, lingual and occlusal surfaces of the teeth. bonding acrylic to the appliance. Essix type C Invisalign uses 3-D computer imaging technology plastic has poorer aesthetics compared with type A, to depict the complete treatment plan from the but its abrasion resistance is better than Type A. initial position to the final desired position from Type C is best used for anterior and full arch which a series of custom-made, clear "aligners" are retainers. The 2 primary methods of creating a produced. Each "aligner" moves teeth incrementally tooth-moving force with the appliance are by spot- and is worn for about two weeks, then replaced by thermoforming with a specific pliers and by means the next in the series until the final position is of a mounding procedure that alters the surface of achieved. Like brackets and arch wires are to braces the tooth to be moved by sequentially placing small invisalign aligners move teeth through the layers of bonding composite on the tooth. The many appropriate placement of controlled force on the types of tooth movements that can be attained with teeth. The principal difference is that invisalign not the Essix appliance are tipping, differential bodily only controls forces, but also controls the timing of movement, rotation around a vertical axis, torque, the force application. At each stage, only certain lateral movements into space created by stripping, teeth are allowed to move, and these movements are and the use of Class II and Class III determined by the orthodontic treatment plan for attached to the appliance. that particular stage. This results in an efficient CONCLUSION force delivery system. Generally, invisalign handles There are a variety of appliances available today for simple to moderate nonextraction alignments better an orthodontist to cater to the growing demand of than mild to moderate extraction corrections. This is patients towards esthetic appliances. Every primarily because invisalign only has a limited appliance has its own merits demerits & its ability to keep teeth upright during space closure. limitations. Hence one must explore the available Attachments, formed by bonding tooth coloured appliances within their spectrum to combine restorative material in a vertical bar to the buccal aesthetics with adequate technical performance. surface of certain teeth, can give the aligners greater 105 Metal free orthodontics Rafiuddin S, AbrahamR

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