Analyses of rampant corrosion in stainless-steel retainers of orthodontic patients.

Retainers were collected from private, university, and dental labs. After viewing these corroded and control appliances using scanning electron microscopy, corroded maxillary and mandibular retainers were selected along with a control stainless-steel retainer for in-depth chemical analysis. Using electron spectroscopy for chemical analysis, monochromated Al x-rays were rastered over areas 1.5 x 0.3 mm. After survey spectra were acquired, high-resolution multiplex scans were obtained and binding energy shifts were noted. Using Auger electron spectroscopy, a spot size of approximately 30 nm was analyzed. Photos, survey scans, and depth profiles were acquired using a 3.5kV Ar(+) ion beam that was calibrated using a SiO2 standard. Via electron spectroscopy for chemical analysis, the brown stains contained Fe and Cr decomposition products in which three carbon species were present. Proteinaceous N was found as amines or amides. No Ni was present because it had solubilized. The Cr:Fe ratio indicated severe Cr depletion in the stained regions (0.2) versus the control regions (1.3). The stained regions appeared mottled, having both dark and light areas. Via AES, the dark versus light areas of the stained regions indicated that there was an absence versus a presence of both Cr and Ni. In the dark areas corrosion penetrated 700 nm; in the light areas the depth equaled 30 nm. By comparison, the passivated layer of the control retainer was 10-nm thick. After sputtering away the affected areas, all specimens had similar spectra as the control regions. The bacterial environment created the mottled appearance and induced electrochemical potential differences so that, upon reducing the passivated layer, an otherwise corrosion-resistant alloy became susceptible to rampant corrosion. An integrated biological-biomaterial model is presented for the classic case of an orthodontic acrylic-based stainless steel retainer subject to crevice corrosion.

Frictional resistances of metal-lined ceramic brackets versus conventional stainless steel brackets and development of 3-D friction maps.

The frictional resistances of 2 metal-lined ceramic brackets (Luxi and Clarity) were compared with 2 conventional stainless steel brackets (Mini-Taurus and Mini-Twin) in vitro. In method 1, we varied the second-order angulation from 0 degrees to 12 degrees while maintaining the normal or ligature force constant at 0.3 kg; in method 2, we varied the ligature force from 0.1 kg to 0.9 kg while maintaining the angulation at theta = 0 degrees or theta = 11 degrees. The hardware simulated a 3-bracket system in which the interbracket distances were always 18 mm. All couples were evaluated at 34 degrees C using the same size stainless steel archwire (19 x 26 mil) and ligature wire (10 mil). In the passive region, the static and kinetic frictional forces and coefficients of friction were key parameters; in the active region, the static and kinetic binding forces and coefficients of binding were critical parameters. From outcomes of methods 1 and 2, the 4 aforementioned parameters, and a knowledge of the critical contact angle for binding, 3-dimensional friction maps were constructed in the dry and wet states from which the frictional resistances could be determined at any ligature force or second-order angulation. Those 3-dimensional maps show that metal-lined ceramic brackets can function comparably to conventional stainless steel brackets and that 18-kt gold inserts appear superior to stainless steel inserts. As the morphologies of metal inserts are improved, these metal-lined ceramic brackets will provide not only good esthetics among ceramic brackets but also minimal friction among conventionally ligated brackets.

Resistance to sliding of self-ligating brackets versus conventional stainless steel twin brackets with second-order angulation in the dry and wet (saliva) states.

The frictional properties of conventional stainless steel brackets that were coupled with rectangular stainless steel archwires and ligated with stainless steel ligature wires and the frictional properties of closed self-ligating brackets coupled with the same archwires were compared in terms of second-order angulation. The slides of these self-ligating brackets passively restrained the archwires within the slots. As a control, the frictional properties of the opened self-ligating brackets, which were ligated with stainless steel ligature wires, were measured. The resistance to sliding of the conventional brackets and the opened self-ligating brackets were measured at ligation forces ranging from 200 to 600 cN and at angles from -9 degrees to 9 degrees. The resistances to sliding of the closed self-ligating brackets were measured at the same angles, but no external ligation forces were applied. In the passive configuration, the conventional brackets exhibited similar frictional resistance as the opened self-ligating brackets, whereas the closed self-ligating brackets exhibited no friction. In the active configuration, all brackets exhibited increased resistance to sliding as the angulation increased. At all angles, the resistances to sliding of the closed self-ligating brackets were lower than those of the conventional brackets because of the absence of a ligation force when the slide restrained the archwire.

Mechanical characteristics of various tempers of as-received cobalt-chromium archwires.

The mechanical characteristics of 24 of the 36 wire cross-sectional configurations were investigated in the as-received state from among the 4 tempers of a cobalt-chromium product. After engineering mechanics were used to validate the efficacy of the span combinations, each wire was measured in flexure to determine its elastic modulus and in tension to determine its yield strength, ultimate tensile strength, and ductility. Other combined characteristics were evaluated, including flexibility, resilience, and the yield strength criterion. In these as-received materials the formability sometimes followed expectations, but the flexibility and resilience characteristics were variable and independent of temper. And although the elastic modulus was independent of testing parameters, it was affected by the loss of material at the corners of rectangular wires. Overall, the stiffnesses of cobalt-chromium wires in round configurations were comparable to those of multi- and single-stranded stainless steel wires but were 3 and 6 times greater than the stiffnesses of beta-titanium and nickel-titanium wires, respectively. In the final analysis, these as-received wires do not meet their potential as a variably formable and variably resilient alternative to stainless steel. Perhaps this is why cobalt-chromium wires have never had the impact on the profession that was expected from them several years ago.

Evaluation of titanium brackets for orthodontic treatment: Part II--The active configuration.

After each archwire was ligated into a bracket with a 0.010-in stainless steel wire, both stainless steel and beta-titanium archwires (0.017- x 0.025-in) were slid through commercially pure titanium brackets (0.018-in slot size) at 34 degrees C in both the dry and wet conditions. As controls, stainless steel archwire versus stainless steel bracket couples were used with comparable dimensions. The drawing forces were measured at 5 angulations (0 degrees, 3 degrees, 7 degrees, 9 degrees, and 11 degrees ) for 5 normal forces (nominally 0.2, 0.4, 0.6, 0.8, and 1.0 kg). Regression lines were determined for each frictional couple (P <.05). In the passive configuration, the kinetic frictional coefficients of control and test couples in the dry condition were comparable to previously reported values at 0.11 +/- 0.01 for stainless steel versus stainless steel, 0.12 +/- 0.00 for stainless steel versus titanium, and 0.26 +/- 0.02 for beta-titanium versus titanium. As the angulation was increased from 0 degrees to 11 degrees and the normal force was maintained at 0.2 kg, the resistance to sliding values increased by 208 g for stainless steel versus stainless steel, by 222 g for stainless steel versus titanium, and by 185 g for beta-titanium versus titanium. When the normal force was increased to 1.0 kg, the resistance to sliding values increased to 277 g, 246 g, and 245 g, respectively. Although resistance to sliding increased with angulation and normal force, the passive layer did not breakdown. Titanium brackets remained comparable to stainless steel brackets in the active configuration.

Resistance to sliding of orthodontic appliances in the dry and wet states: influence of archwire alloy, interbracket distance, and bracket engagement.

Having established dimensional and mechanical characteristics, the resistances to sliding (RS) were measured in vitro for various archwires against stainless steel brackets. Using stainless steel ligatures, a constant normal force (300g) was maintained while second-order angulation (straight theta) was varied from -12 degrees to +12 degrees. Using miniature bearings to simulate contiguous teeth, five experiments each were run in the dry or wet states with human saliva at 34 degrees C as a function of four archwire alloys, five interbracket distances, and two bracket engagements. Outcomes were objectively analyzed to establish when theta=0, and the relative contact angles ( theta(r)) were replotted. Critical contact angles (theta(c)) that were determined via experimentation were in good agreement with theory. Slopes and y-intercepts were tabulated from linear regression equations of RS against theta plots in both the passive (theta < or = theta (c)) and active ( theta > or = theta(c)) configurations, for which theta = theta(c) identified the boundary between classical friction and binding phenomena. Stiffer archwires and shorter interbracket distances exacerbated binding, whereas, once corrected for differing bracket engagement, RS was independent of slot dimension. Unlike earlier results in the passive configuration, in the active configuration couples comprised of titanium alloys (NiTi and (beta-Ti) had higher RS values in the wet versus the dry state. For those archwire alloys evaluated, two empirical expressions were adduced that comprise the binding component, the yield strength or elastic limit, and the beam length, which implicitly represent the stiffness, flexibility, and interbracket distance.

Ongoing innovations in biomechanics and materials for the new millennium.

Material innovations are reviewed within the context of ongoing biomechanical developments that relate the critical contact angle of second-order angulation (theta c) to the overall resistance to sliding (RS). As a science in its embryonic stage of development, RS is partitioned into classical friction (FR), elastic binding (BI), and physical notching (NO). Both FR and BI are defined in terms of normal forces (N) and kinetic coefficients (mu k). The angulation at which NO occurs (theta z) is introduced as a second boundary condition to theta c. Given this scientific backdrop, material modifications are sought that reduce RS. Approaches include minimizing mu k or N within the context of FR and theta < theta c, as, for example, by surface modifications of arch wires and brackets or by engineering novel ligation materials. Stabilizing theta at theta approximately equal theta c should provide more efficient and effective sliding mechanics by developing innovative materials (eg, composites) in which stiffness (EI) varies without changing wire or bracket dimensions. Between the boundaries of theta c and theta z (ie, theta c < theta < theta z), BI may be reduced by decreasing EI or increasing interbracket distance (IBD), independent of whether a conventional or composite material is used.

Influence of ceramic and stainless steel brackets on the notching of archwires during clinical treatment.

The surface topography of 100 clinically used archwires of stainless steel, beta-, or nickel-titanium were investigated that had contacted either ceramic or stainless steel brackets. One group consisted of two sets: 60 wires with no treatment records accessed to bias analyses, and 40 wires for which extensive clinical records were available, half of which were used with ceramic or stainless steel brackets. A control group consisted of two sets: 30 unused wires comprised of five round and rectangular wires of each alloy, and four wires that were ligated and immediately removed from patients' mouths. After ultrasonic cleaning, each wire was inspected under an optical and/or a scanning electron microscope. Notches were categorized with regard to frequency, patterns, and severity, and mapped as a function of wire aspect (lingual, facial, and occlusal/gingival) and anatomical regions (molar, premolar, canine, and incisor). From these data the average severity of notch patterns and a notching index were derived. Although no recognizable defect patterns were observed in the control group, seven basic patterns were recognized for each wire cross-sectional shape in the clinically used wires. These wires appeared most damaged on their lingual aspect and least damaged on their facial aspect. With regard to anatomical regions, notching was prevalent in the anterior regions and sparse in the molar regions. The notch activity and the severity were nearly three times greater from ceramic brackets than from stainless steel brackets. Over one-third of all notches documented in ceramic bracket cases had severity numbers of 3 and penetrated at least one-quarter of each wire's dimension, However, over two-thirds of all notches documented in stainless steel bracket cases had severity numbers of 1. From these tabulations a theory of notch formation was proposed in which vertical movement from tooth or wire during mastication caused fretting wear, and horizontal movement during orthodontic procedures such as space closure, tipping, or bodily movement caused sliding wear.

Sliding mechanics of coated composite wires and the development of an engineering model for binding.

A tribological (friction and wear) study, which was designed to simulate clinical sliding mechanics, was conducted as part of an effort to determine the suitability of poly(chloro-p-xylylene) coatings for composite orthodontic archwires. Prototype composite wires, having stiffnesses similar to those of current initial and intermediate alignment wires, were tested against stainless steel and ceramic brackets in the passive and active configurations (with and without angulation). Kinetic coefficient of friction values, which were determined to quantify sliding resistances as functions of the normal forces of ligation, had a mean that was 72% greater than uncoated wire couples at 0.43. To improve analysis of the active configuration, a mathematical model was developed that related bracket angulation, bracket width, interbracket distance, wire geometry, and wire elastic modulus to sliding resistance. From this model, kinetic coefficients of binding were determined to quantify sliding resistances as functions of the normal forces of binding. The mean binding coefficient was the same as that of uncoated wire couples at 0.42. Although penetrations through the coating were observed on many specimens, the glass-fiber reinforcement within the composite wires was undamaged for all conditions tested. This finding implies that the risk of glass fiber release during clinical use would be eliminated by the coating. In addition, the frictional and binding coefficients were still within the limits outlined by conventional orthodontic wire-bracket couples. Consequently, the coatings were regarded as an improvement to the clinical acceptability of composite orthodontic archwires.

Stress relaxation and recovery behaviour of composite orthodontic archwires in bending.

The viscoelastic behaviour of prototype composite orthodontic archwires was evaluated using a bend stress relaxation test. Archwires having 10 different volume fractions of reinforcement were subjected to constant bending radii in a water bath at 37 degrees C for time periods of up to 90 days. The wires were subsequently released and left unconstrained for the same testing conditions. Creep-induced changes in the unconstrained bending radii of the wires were measured at specific times during both phases (stress relaxation and recovery) of the test. The statistical analysis showed that stress relaxation behaviour was strongly correlated with the archwire reinforcement level. The final relaxation varied, with decreasing reinforcement, from 2 to 8 per cent. Archwire recovery was not correlated with reinforcement level, and revealed a final viscous loss of only 1 per cent. The relaxed elastic moduli in bending of the composite wires were similar to the elastic moduli in bending of several conventional orthodontic archwire materials. Losses that were associated with the viscoelastic behaviour varied with decreasing reinforcement level from 1.2 to 1.7 GPa. Because these modulus losses were minimal, each archwire retained sufficient resilience to be applicable to the early and intermediate stages of orthodontic treatment.

Physical and mechanical characteristics of a chlorine-substituted poly(para-xylylene) coating on orthodontic chain modules.

A 10 microm film of a chlorine-substituted poly(para-xylylene) was evaluated as a protective coating for commercial chain modules. Segments of modules were either non-coated or coated using five modes: 0%, 100%, and 200% elongation during coating and shipping; and 100% and 200% elongation only during coating. Prior to hydration, coating coverage was examined via light and electron microscopy. When hydrated, the presence or absence of the coating did not appreciably change the total weight gain (1.5%). However, when the modules were post-coating elongated to either 100% or 200%, neither the non-coated nor the coated modules sorbed water. Hydration did not significantly change the mechanical properties of the modules. As expected, most of the mechanical properties of the coated modules were greater than the properties for the uncoated modules. With regard to the coated modules only the properties of those modules having 0% elongation during coating and shipping were, in general, significantly different from the other coated modules. Post-coating elongation reduced the stiffness of the coated modules more than 79%. In regard to stress relaxation, the non-coated and coated modules recovered approximately 74% and 62% of the peak loading, respectively. Using the load-time data from these curves, Maxwell-Weichert models accurately predicted the decay profiles of both the non-coated and coated modules. Because the water sorption and the mechanical properties of these coated modules were favorable, they should be further characterized for staining.

Variation in flexural properties of photo-pultruded composite archwires: analyses of round and rectangular profiles.

Prototype continuous, unidirectional, fiber-reinforced composite archwires were manufactured into round and rectangular profiles utilizing a photo-pultrusion process. Both 0.022 inch (0.56 mm) diameter and 0.021 x 0.028 inch (0.53 x 0.71 mm) rectangular composites were formed utilizing commercially available S2-glass reinforcement within a polymeric matrix. Reinforcement was varied according to the number, denier and twists per inch (TPI) of four S2-glass yarns to volume levels of 32-74% for round and 41-61% for rectangular profiles. Cross-sectional geometry was evaluated via light microscopy to determine loading characteristics; whereas two flexural properties (the elastic moduli and flexural strengths) were determined by 3-point bending tests. Morphological evaluation of samples revealed that as the TPI increased from 1 to 8, the yarns were more separated from one another and distributed more peripherally within a profile. For round and rectangular profiles utilizing 1 TPI fibers, moduli increased with fiber content approaching theoretical values. For round profiles utilizing 1 TPI and 4 TPI fibers, flexural strengths increased until the loading geometry was optimized. In contrast, the flexural strengths of composites that were pultruded with 8 TPI fibers were not improved at any loading level. Doubling the denier of the yarn, without altering the loading, increased both the moduli and flexural strengths in rectangular samples; whereas, the increases observed in round samples were not statistically significant. At optimal loading the maximum mean moduli and strengths equaled 53.6 +/- 2.0 and 1.36 +/- 0.17 GPa for round wire and equaled 45.7 +/- 0.8 and 1.40 +/- 0.05 GPa for rectangular wires, respectively. These moduli were midway between that of martensitic NiTi (33.4 GPa) and beta-titanium (72.4 GPa), and produced about one-quarter the force of a stainless steel wire per unit of activation. Values of strengths placed this composite material in the range of published values for beta-titanium wires (1.3-1.5 GPa).

Types of corrosion in removable appliances: annotated cases and preventative measures.

Three different types of electrochemical corrosion cells are discussed - composition, concentration, and stress cells. Annotated cases are presented for each type of corrosion cell in removable appliances using conventional photography, scanning electron microscopy, and X-ray elemental analyses. The complexity that corrosion can attain is illustrated via the case of a palatal expansion device. Specific examples of galvanic cells, which are possible in orthodontic practice, are summarized in terms of the anodic and cathodic half-cells. These include material differences, oxygen gradients, presence of debris, changes in pH, induced stress levels, changes in stress states, and variations in as-received history. A galvanic series is constructed from the orthodontist's perspective that includes titanium, nickel-titanium, cobalt-chromium, and stainless steel alloys, as well as glass-fiber-reinforced polymer-matrix composites. Preventative measures are presented from the perspectives of the raw material manufacturers, the dental laboratories, the chair-side practitioner, and the patient. A list of materials is provided, which are known to promote corrosion in the event that stainless steels are sensitized as a consequence of improper handling. In the final analysis, however, retainers and removable appliances are reliable if corrosion cells are conscientiously averted and preventative measures are routinely employed.

Stress-relaxing composite ligature wires: formulations and characteristics.

A stress-relaxing composite ligature was developed that has both mechanical and esthetic characteristics that make it attractive for use in orthodontics. The neutrally-colored polymer-polymer composite was created by encasing ultra-high molecular weight poly(ethylene) fibers in a poly(n-butyl methacrylate) polymer, which was formulated from a polysol and an optimal benzoin ethyl-ether concentration. The resulting composite ligature exhibited a tensile strength more than twice that of dead-soft stainless steel ligature, and a stress-relaxation decay significantly greater than stainless steel ligature. With these characteristics, the material could be used as an orthodontic ligature when tooth movement with negligible friction due to ligation is desired. A Maxwell-Weichert model predicted the load-decay profiles that ultimately resulted in the general loss of frictional forces with time.

Influence of archwire and bracket dimensions on sliding mechanics: derivations and determinations of the critical contact angles for binding.

There is every indication that classical friction controls sliding mechanics below some critical contact angle, theta c. Once that angle is exceeded, however, binding and notching phenomena increasingly restrict sliding mechanics. Using geometric archwire and bracket parameters, the theta c is calculated as the boundary between classical frictional behaviour and binding-related phenomena. What these equations predict is independent of practitioner or technique. From these derivations two dimensionless numbers are also identified as the bracket and the engagement index. The first shows how the width of a bracket compares to its Slot; the second indicates how completely the wire fills the Slot. When nominal wire and bracket dimensions are calculated for both standard Slots, the maximum theta c theoretically equals 3.7 degrees. Thus, knowledge of the archwire or bracket alone is insufficient; knowledge of the archwire-bracket combination is necessary for theta c to be calculated. Once calculated, sliding mechanics should be initiated only after the contact angle, theta, approaches the characteristic value of theta c for the particular archwire-bracket combination of choice--that is, when theta approximately theta c.

Assessment of second-order clearances between orthodontic archwires and bracket slots via the critical contact angle for binding.

Twenty-six archwires and 24 brackets were selected from among the hundreds of products available that nominally have from 18 to 22 mil bracket slots and 14, 16, 17, 18, 19, and/or 21 mil archwire sizes. After the archwires and brackets were dimensioned, a minimization-maximization algorithm was applied to the measurements in order to establish the likely boundaries of the critical contact angle for binding (thetac) as defined by the presence and absence of second-order clearance. From among the myriad archwire-bracket permutations possible, 64 combinations were identified--20 using the bracket slot as the controlling dimension and 44 using the bracket width. Using a previously derived mathematical expression that relates the dimensions of each archwire-bracket couple to its calculated thetac, the corresponding sets of indices were plotted. The results show that the maximum value of the calculated thetac can never exceed about 5 degrees , or else sliding mechanics will always be hampered. Other outcomes were validated experimentally using 5 of the 64 archwire-bracket couples by measuring the resistance to sliding (RS) at 15 different contact angles (theta) ranging from theta=0 degrees to theta=12 degrees and by subsequently determining a measured thetac. These values agreed with the calculated thetac values. When the practitioner knows the thetac, treatment time might be reduced because the teeth do not need to be over-aligned prior to employing sliding mechanics (i.e., by not making theta<thetac) These results underscore the importance of exact wire and bracket dimensions on packaging; otherwise, sliding mechanics can be compromised by miscalculating thetac.

Influence of angulation on the resistance to sliding in fixed appliances.

The resistances to sliding were studied as a function of five angulations (0 degrees, 3 degrees, 7 degrees, 11 degrees, and 13 degrees) using nine different couples made of stainless steel, single crystal sapphire, or polycrystalline alumina brackets against stainless steel, nickel titanium, or beta-titanium arch wires. After 22 mil brackets were mounted to fixtures and 21 x 25 mil arch wires were ligated with 10 mil stainless steel ligatures, the arch wires were slid through the brackets at 1 cm/minute in the dry state at 34 degrees C. The resistance to sliding was measured by one computer while five normal forces (nominally 0.2, 0.4, 0.6, 0.8, and 1.0 kg) were serially maintained by another computer. A second couple was prepared for each material combination with five normal forces that were each 0.1 kg less. Statistical fits of linear regressions were such that p <.001 for most tests. When couples were in the passive configuration at low angulations, all stainless steel wire-bracket couples once again had the least resistance to sliding. When the angulation exceeded about 3 degrees, however, the active configuration emerged and binding quickly dominated as the resistance to sliding increased over 100-fold. Under these conditions, the relative rankings among the materials transposed; couples of stainless steel had the most resistance to sliding, whereas, couples of the more compliant alloys, such as nickel titanium wire, had the least. Results suggested that the active configuration and subsequent binding emerged when no bracket clearance remained. This binding component increased in importance with angulation and was additive to the frictional component, that is, they followed the principle of superposition.

Novel esthetic bonded retainers: a blend of art and science.

Novel esthetic S2-glass fiber-reinforced composite wires were fabricated in round (0.022 in.) and rectangular (0.021 x 0.028 in.) profiles, with flexural moduli comparable to martensitic nickel titanium and flexural strengths comparable to beta titanium wires. These wires were bonded clinically to the facial surfaces of teeth in three situations in which flexible-bonded retainers are conventionally used: the retention of a closed median diastema, the retention of space closure following premolar extraction, and the retention of a canine that had been severely malpositioned. These bonded esthetic wires were monitored clinically up to 12 months to ascertain patient's acceptance and structural integrity of the retainer. No clinically observable defects were noted during the study, and no patient described any adverse intraoral effects from the retainer's presence. In this report and on the site http://++www.clinorthodres.com/cor99-c-056, the indications for, and the present design philosophy of, flexible-bonded retainers are discussed, along with the wire properties necessary to achieve optimal stability of tooth position. In addition to demonstrating excellent esthetic characteristics, these photo-pultruded composite wires satisfy the flexural requirements necessary to achieve physiologic stability when used for flexible-bonded retention.

Evaluation of titanium brackets for orthodontic treatment: part I. The passive configuration.

The static and kinetic frictional coefficients of commercially pure titanium brackets were evaluated in the passive configuration in the dry and wet states against stainless steel, nickel-titanium, and beta-titanium arch wires. For comparison, stainless steel brackets were evaluated under identical conditions. Titanium brackets were grayer in color and rougher in texture than the stainless steel brackets. Bracket slots were up to 0.002 inch greater than the nominally stated values. Remarkably, the static and kinetic frictional coefficients of the couples formed by titanium and stainless steel brackets were comparable. When evaluated against stainless steel and nickel-titanium arch wires in the dry state at 34 degrees C, the static coefficient averaged.12 and.20, respectively, independent of bracket alloy. When evaluated against stainless steel and nickel-titanium wires in the wet state at 34 degrees C using human saliva, the static coefficient averaged.15 and.20, respectively, independent of bracket alloy. Only the beta-titanium arch wires increased by about 15%, when tested in either the dry or the wet state against titanium versus stainless steel brackets. Noteworthy, too, was the decrease of both coefficients in the beta-titanium wire couples from their previously reported values. Analyses of electron spectroscopy for chemical analysis spectra and depth profiles show that these new brackets are titanium only in the bulk. Indeed the immediate surfaces are composed of, at least, 80 atomic percent (at.%) carbon and oxygen; whereas, the titanium that is present (>11 at.%) is mostly in the form of titanium dioxide. The presence of this quite thin passivating layer, which resides on top of an oxygen-hardened titanium substrate, reduces the galling and fretting that would normally be expected in such materials. Pending the outcome of future angulation tests, these frictional measurements show that titanium brackets are not only comparable to stainless steel brackets but also are more biocompatible with nickel having been eliminated from their constitution.