Characterization of the coatings covering esthetic orthodontic archwires and their influence on the bending and frictional properties.

OBJECTIVE: To analyze the coatings covering esthetic orthodontic wires and the influence of such coatings on bending and frictional properties. MATERIALS AND METHODS: Four commercially available, coated esthetic archwires were evaluated for their cross-sectional dimensions, surface roughness (Ra), nanomechanical properties (nanohardness, nanoelastic modulus), three-point bending, and static frictional force. Matched, noncoated control wires were also assessed. RESULTS: One of the coated wires had a similar inner core dimension and elasticity compared to the noncoated control wire, and no significant differences between their static frictional forces were observed. The other coated wires had significantly smaller inner cores and lower elasticity compared to the noncoated wires, and one of them showed less static frictional force than the noncoated wire, while the other two coated wires had greater static frictional force compared to their noncoated controls. The dimension and elastic modulus of the inner cores were positively correlated (r = 0.640), as were frictional force and total cross-sectional (r = 0.761) or inner core (r = 0.709) dimension, elastic modulus (r = 0.777), nanohardness (r = 0.802), and nanoelastic modulus (r = 0.926). The external surfaces of the coated wires were rougher than those of their matched controls, and the Ra and frictional force were negatively correlated (r = -0.333). CONCLUSIONS: Orthodontic coated wires with small inner alloy cores withstand less force than expected and may be unsuitable for establishing sufficient tooth movement. The frictional force of coated wires is influenced by total cross-section diameter, inner core diameter, nanohardness, nanoelastic modulus, and elastic modulus.

Effects of bonding materials on the mechanical properties of enamel around orthodontic brackets.

OBJECTIVE: To determine if the enamel around orthodontic brackets is significantly altered after demineralization followed by application of adhesives with and without fluoride-releasing ability. MATERIALS AND METHODS: One hundred eight noncarious human premolars were divided into six groups of 18 each and exposed to a demineralization solution. Stainless steel brackets were bonded using two conventional composite resin etch-and-rinse systems, three self-etching primer (SEP) composite resin systems, and one resin-modified glass ionomer cement (RMGIC) system. One conventional and one SEP composite resin adhesive did not have fluoride-releasing ability, which was claimed for the other four adhesives. The elastic modulus and hardness of the enamel were determined with a nanoindenter at 10 equidistant depths ranging from 1-46 µm and at four regions: control (not exposed) enamel surface, under the adhesive, and at 50 µm and 100 µm from the bracket edges. Using the Kruskal-Wallis and Mann-Whitney U-tests (P < .0125 for statistical significance), these properties were compared at different regions. RESULTS: The same behavior was observed for values of elastic modulus and hardness. Significant differences were found within approximately 21 µm of the enamel surface for etching with 35% phosphoric acid or priming with SEP, but only minimal changes occurred for the SEP adhesive. Increases in near-surface elastic modulus and hardness of enamel were found with the SEP adhesive and RMGIC with fluoride-releasing ability. CONCLUSIONS: Clinical use of the fluoride-releasing adhesives investigated may prevent demineralization of enamel around brackets during orthodontic treatment.

Effects of sodium fluoride mouth rinses on the torsional properties of miniscrew implants.

INTRODUCTION: Effects of sodium fluoride (NaF) mouth rinse solutions on torsional properties of a miniscrew implant were investigated. METHODS: As-received Ti-6Al-4V miniscrew implants (AbsoAnchor [Dentos, Inc., Daigu, Korea]) were immersed in 0.1% or 0.2% NaF mouth rinse solution (pH 5.12 and 5.14, respectively) for 1 hour or 24 hours. Miniscrew implants selected as controls were not immersed. Each implant was subjected to increasing torque until fracture (n = 5 in sample groups). Mean moment and twist angle for fracture were compared using 1-way analysis of variance (ANOVA). Surfaces of implants after immersion were observed with a scanning electron microscope (SEM). Electron microprobe and micro-x-ray diffraction analyses were performed to obtain composition information about deposits on implant surfaces. RESULTS: Pits and cracks formed on the implant surfaces after immersion in both NaF mouth rinse solutions. Corrosion products, probably sodium aluminum fluoride (Na(3)AlF(6)), were observed on the implants after immersion in both NaF solutions for both time periods. There were no significant differences for mean torque (P = 0.063) and twist angle (P = 0.696) at fracture compared with control implants. CONCLUSIONS: Although titanium alloy miniscrew implants corroded slightly from immersion in 0.1% or 0.2% NaF solutions, mouth rinsing by patients with the same fluoride solution concentrations should not cause deterioration of their torsional performance.

Relationship between the metallurgical structure of experimental titanium miniscrew implants and their torsional properties.

The aims of this study were to investigate the torsional properties of three experimental titanium miniscrew implants for orthodontic anchorage and to determine the relationship between the torsional properties and metallurgical structures. Experimental miniscrew implants with a diameter of 1.4 mm were fabricated from commercially pure (CP) titanium (alpha-titanium), Ti-4Al-4V (duplex alpha-beta-titanium), and Ti-33Nb-15Ta-6Zr (beta-titanium). Micro-X-ray diffraction (XRD) was performed to identify phases, and microstructures of etched cross-sections were obtained with scanning electron microscopy (SEM). Implants were loaded in torsion (n = 5), and mean moments and twist angles at fracture were statistically compared using the Kruskal-Wallis and Mann-Whitney U-tests. Cyclic torsional moment for fracture of starting square wires (2 × 2 × 30 mm) was measured (n = 3). At fracture, the Ti-4Al-4V and Ti-33Nb-15Ta-6Zr implants demonstrated significantly higher mean torque than the CP titanium implant, while the Ti-33Nb-15Ta-6Zr implant had a significantly higher mean twist angle than the other two implants. The CP titanium and Ti-33Nb-15Ta-6Zr implants displayed good fatigue performance and excellent ductility. Ti-33Nb-15Ta-6Zr beta-titanium alloy is suitable for manufacturing miniscrew implants since it has excellent torsional properties.

Effect of bracket bonding on nanomechanical properties of enamel.

INTRODUCTION: In this study, we investigated the nanohardness and elastic modulus of enamel after debonding metal brackets. METHODS: The surfaces of 3 maxillary premolars were subdivided into 3 regions. Two regions were exposed to a conventional etching system (Transbond XT, 3M Unitek, Monrovia, Calif) and a self-etching system (Transbond Plus primer, 3M Unitek); the third region was not etched. Metal brackets were bonded with Transbond XT composite to the 2 etched regions. After storage for 24 hours in distilled water, the brackets and residual adhesive were removed, and the teeth were sectioned transversely. Seven nanoindentations (2 mN load) were placed 1 to 25 µm from the surface in each region. Mean nanohardness and elastic modulus were compared with analysis of variance (ANOVA) and the Scheffé test. RESULTS: Locations 1 and 5 µm from the enamel surface had significantly (P < 0.05) lower nanohardness and elastic modulus values for the conventional system compared with the self-etching system and the unetched region. All other locations for the conventional system and all locations for the self-etching system and unetched area had no significant differences. The nanohardness was much higher than the Vickers hardness for enamel. CONCLUSIONS: The minimal effect of the self-etching system on the nanomechanical properties of enamel arises from much lower chemical attack. The much greater effects of the conventional system require further study.

Effect of mechanical properties of fillers on the grindability of composite resin adhesives.

INTRODUCTION: The purpose of this study was to investigate the effect of filler properties on the grindability of composite resin adhesives. METHODS: Six composite resin products were selected: Transbond XT (3M Unitek, Monrovia, Calif), Transbond Plus (3M Unitek), Enlight (Ormco, Glendora, Calif), Kurasper F (Kuraray Medical, Tokyo, Japan), Beauty Ortho Bond (Shofu, Kyoto, Japan), and Beauty Ortho Bond Salivatect (Shofu). Compositions and weight fractions of fillers were determined by x-ray fluorescence analysis and ash test, respectively. The polished surface of each resin specimen was examined with a scanning electron microscope. Vickers hardness of plate specimens (15 × 10 × 3 mm) was measured, and nano-indentation was performed on large filler particles (>10 µm). Grindability for a low-speed tungsten-carbide bur was estimated. Data were compared with anlaysis of variance (ANOVA) and the Tukey multiple range test. Relationships among grindability, filler content, filler nano-indentation hardness (nano-hardness), filler elastic modulus, and Vickers hardness of the composite resins were investigated with the Pearson correlation coefficient test. RESULTS: Morphology and filler size of these adhesives showed great variations. The products could be divided into 2 groups, based on composition, which affected grindability. Vickers hardness of the adhesives did not correlate (r = 0.140) with filler nano-hardness, which showed a significant negative correlation (r = -0.664) with grindability. CONCLUSIONS: Filler nano-hardness greatly influences the grindability of composite resin adhesives.

Corrosion behavior of ion implanted nickel-titanium orthodontic wire in fluoride mouth rinse solutions.

This study investigated the corrosion properties of ion implanted nickel-titanium wire (Neo Sentalloy Ionguard) in artificial saliva and fluoride mouth rinse solutions (Butler F Mouthrinse, Ora-Bliss). Non ion implanted nickel-titanium wire (Neo Sentalloy) was used as control. The anodic corrosion behavior was examined by potentiodynamic polarization measurement. The surfaces of the specimens were examined with SEM. The elemental depth profiles were characterized by XPS. Neo Sentalloy Ionguard in artificial saliva and Butler F Mouthrinse (500 ppm) had a lower current density than Neo Sentalloy. In addition, breakdown potential of Neo Sentalloy Ionguard in Ora-Bliss (900 ppm) was much higher than that of Neo Sentalloy although both wires had similar corrosion potential in Ora-Bliss (450 and 900 ppm). The XPS results for Neo Sentalloy Ionguard suggested that the layers consisted of TiO(2) and TiN were present on the surface and the layers may improve the corrosion properties.

Effects of long-term storage and thermocycling on bond strength of two self-etching primer adhesive systems.

The effects of 2 years of storage and 6000 thermocycles on the shear bond strength (SBS) of two self-etching adhesive systems were studied. Two self-etching primer (SEP) systems (Transbond Plus and Beauty Ortho Bond) and one etch and rinse system (Transbond XT) were used to bond brackets to 126 human premolars that were then stored in artificial saliva for 24 hours or 2 years and thermocycled in distilled water before SBS testing with a universal testing machine. The adhesive remnant index (ARI) scores were calculated. Data were compared by two-way analysis of variance and chi-square analysis. Enamel/adhesive interfaces were examined by scanning electron microscopy. There was no significant difference in the mean SBS for the bonding materials among the three conditions. ARI scores showed that Transbond XT and Beauty Ortho Bond had less adhesive remaining on the teeth after ageing compared with storage for 24 hours. Specimens bonded with Beauty Ortho Bond showed leakage between the resin adhesive and enamel after ageing. Both SEP systems produced adequate SBS even after 2 years or 6000 times thermocycling. Thermocycling is an appropriate technique for determining the durability of orthodontic bracket bonding materials.

Effects of application time and agitation for bonding orthodontic brackets with two self-etching primer systems.

The purpose of this study was to evaluate the shear bond strength, adhesive remnant index (ARI) and etching effect of two self-etching systems (Transbond Plus, Beauty Ortho Bond) at different application times (3, 10, 30 seconds) with and without agitation. Share bond strengths were examined and the ARI score was estimated (n=15). Enamel surfaces after priming were examined by SEM. Increasing application time and applying agitation of self-etching primers produced slightly increased etching efficacy. Increasing application time did not significantly increase the shear bond strength. Also, agitation did not significantly increase the shear bond strength except for specimen bonded with the Beauty Ortho Bond with 10 seconds application time. No significant difference was found in bond-failure sites among 10 groups. Although increasing application time and applying agitation of both self-etching primers did not affect the shear bond strength, increasing application time in indirect bonding technique should not cause remarkable adverse effect.

Torsional properties and microstructures of miniscrew implants.

INTRODUCTION: Titanium miniscrew implants are popular in orthodontics, but there is little information about their torsional performance. METHODS: Four brands of miniscrew implants (A-D) with 1.6-mm diameters were compared, with miniscrew A implants also having diameters of 1.2 to 2.0 mm. Nominal compositions of the implants were determined by x-ray fluorescence (n = 8). The miniscrews were loaded to failure in torsion, and the mean moment and twist angle were determined for each group (n = 8). Data were compared by ANOVA and the Tukey multiple range tests. Micro x-ray diffraction (n = 3) was used to identify phases in the implants, and the phases were also examined in etched cross-sections with a scanning electron microscope. RESULTS: Miniscrew A and C implants were pure titanium, whereas miniscrew B and D implants contained small amounts of vanadium, aluminum, iron, and manganese. Only alpha-titanium peaks were detected for all implants by micro x-ray diffraction, but beta titanium was observed in the microstructures of miniscrew B and D implants, which had significantly higher torsional moments at failure. CONCLUSIONS: Addition of small amounts of other elements to titanium yielded significantly improved torsional performance for miniscrew implants. Research to develop optimum compositions for mechanical properties and biocompatibility is needed.

Bond strength comparison and scanning electron microscopic evaluation of three orthodontic bonding systems.

This study sought to assess the efficacy of two self-etching primer systems (Transbond Plus and Beauty Ortho Bond) on orthodontic brackets. Therefore, shear bond strengths and bracket-adhesive failure modes (ARI scores) were determined and compared against an etch-and-rinse adhesive system (Transbond XT) under two experimental conditions (dry and saliva application). Shear bond strength test was performed at a crosshead speed of 0.5 mm/min, while enamel surfaces and enamel-adhesive interfaces were examined with SEM. There were no significant differences between Transbond XT (9.15 MPa) and Transbond Plus (9.74 MPa) under the dry condition, whereas that of Beauty Ortho Bond (6.47 MPa) was significantly lower than these two systems. Under SEM examination, both self-etching primers showed a milder etching effect and decreased depth of resin penetration into intact enamel than Transbond XT. In conclusion, results of this study showed that both self-etching systems seemed to offer more merits than conventional acid etching because of fewer irreversible changes to enamel.

Joining characteristics of orthodontic wires with laser welding.

Laser welding 0.016 x 0.022 in. beta-Ti, Ni-Ti, and Co-Cr-Ni orthodontic wires was investigated by measuring joint tensile strength, measuring laser penetration depth, determining metallurgical phases using micro X-ray diffraction (micro-XRD), and examining microstructures with an scanning electron microscope (SEM). Welding was performed from 150 to 230 V. Mean tensile strength for Ni-Ti groups was significantly lower (p < 0.05) than for most other groups of laser-welded specimens. Although mean tensile strength for beta-Ti and Co-Cr-Ni was significantly lower than for control specimens joined by silver soldering, it was sufficient for clinical use. The beta-Ti orthodontic wire showed deeper penetration depth from laser welding than the Ni-Ti and Co-Cr-Ni orthodontic wires. Micro-XRD patterns of laser-welded beta-Ti and Ni-Ti obtained 2 mm from the boundary were similar to as-received specimens, indicating that original microstructures were maintained. When output voltages of 190 V and higher were used, most peaks from joint areas disappeared or were much weaker, perhaps because of a directional solidification effect, evidenced by SEM observation of fine striations in welded beta-Ti. Laser welding beta-Ti and Co-Cr-Ni wires may be acceptable clinically, since joints had sufficient strength and metallurgical phases in the original wires were not greatly altered.

Joining characteristics of beta-titanium wires with electrical resistance welding.

The goal of this research was to investigate the effects of different conditions for electrical resistance welding of beta-titanium orthodontic wires. Three electrode types were used with a range of power settings on an electrical resistance welding machine to join beta-titanium wires (Resolve, GAC International). Forces that caused bond failures for joined specimens were obtained with tensile loading, and the values were compared using one-way ANOVA and the Tukey test (alpha = 0.05). Metallurgical phases in the joint region were determined by micro-X-ray diffraction. Mean tensile forces for bond failure ranged from 5 to 20 kgf for the eight specimen groups and were dependent on electrode type and power setting. All X-ray diffraction peaks in the joint region were indexed to beta-titanium. Superior bond strength was achieved with the use of wide electrodes. The absence of phases other than beta-titanium in the joint area suggests that the electrical resistance welding may not adversely affect clinically important mechanical properties. Scanning microscope observations indicated that the localized permanent deformation and the formation of an undesirable equiaxed grain structure occurred with the use of narrow electrodes.

Micro-XRD study of beta-titanium wires and infrared soldered joints.

OBJECTIVE: The purpose of this study was to investigate the metallurgical phases in beta-titanium soldered joints prepared by infrared soldering, using the Micro X-ray diffraction technique (Micro-XRD), and to characterize the Vickers hardness in the soldered beta-titanium wires. METHODS: Beta-titanium wires with cross-section dimensions of 0.032in.x0.032in. (TMA, Ormco), and both titanium-based solder (Ti-30Ni-20Cu, Selec) and silver-based solder (Ag-22Cu-17Zn-5Sn, Tomy) were selected. Soldering was performed using infrared radiation (RS-1, Morita) under argon atmosphere. Micro-XRD analyses were performed at room temperature. Micro-XRD spectra were obtained for the boundary region of the soldered beta-titanium wires using 50microm and 10microm diameter analysis regions. Hardness was measured at 30microm intervals from boundary of the diffusion layer and beta-titanium wire. The Kruskal-Wallis test with the Bonferroni and Wilcoxson Mann-Whitney tests for nonparametric means were employed as statistical methods (P<0.05). RESULTS: For both types of soldered beta-titanium samples, the Micro-XRD spectra contained four major peaks for body-centered cubic (bcc) beta-titanium. Additional peaks at about 41 and 45 degrees are attributed to Cu-Ti intermetallic phase(s), which may be metastable under soldering conditions. The diffusion layer had greater hardness than bulk beta-titanium for both types of soldered specimens (P<0.05). SIGNIFICANCE: Soldering of beta-titanium orthodontic wire by infrared radiation may be acceptable for clinical use, since Micro-XRD spectra revealed that both types of soldered specimens largely retained the bcc beta-titanium structure. Further research is needed to investigate the mechanical properties and corrosion behavior of infrared-soldered beta-titanium wire.

Galvanic corrosion behavior of orthodontic archwire alloys coupled to bracket alloys.

The purpose of this study was to provide a quantitative assessment of galvanic corrosion behavior of orthodontic archwire alloys coupled to orthodontic bracket alloys in 0.9% NaCl solution and to study the effect of surface area ratios. Two common bracket alloys, stainless steels and titanium, and four common wire alloys, nickel-titanium (NiTi) alloy, beta-titanium (beta-Ti) alloy, stainless steel, and cobalt-chromium-nickel alloy, were used. Three different area ratios, 1:1, 1:2.35, and 1:3.64, were used; two of them assumed that the multibracket appliances consists of 14 brackets and 0.016 inch of round archwire or 0.016 x 0.022 inch of rectangular archwire. The galvanic current was measured for 3 successive days using zero-impedance ammeter. When the NiTi alloy was coupled with Ti (1:1, 1:2.35, and 1:3.64 of the surface area ratio) or beta-Ti alloy was coupled with Ti (1:2.35 and 1:3.64 of the surface area ratio), Ti initially was the anode and corroded. However, the polarity reversed in 1 hour, resulting in corrosion of the NiTi or beta-Ti. The NiTi alloy coupled with SUS 304 or Ti exhibited a relatively large galvanic current density even after 72 hours. It is suggested that coupling SUS 304-NiTi and Ti-NiTi may remarkably accelerate the corrosion of NiTi alloy, which serves as the anode. The different anode-cathode area ratios used in this study had little effect on galvanic corrosion behavior.

Microstructures of beta-titanium orthodontic wires joined by infrared brazing.

The microstructures and interdiffusion in brazed beta-titanium orthodontic wires were investigated by scanning electron microscopy and electron probe microanalysis, respectively. Beta-titanium wire (Ti-11Mo-6Zr-4Sn) with cross-section dimensions of 0.032 in. x 0.032 in., titanium-based braze alloy (Ti-30Ni-20Cu), and silver-based braze alloy (Ag-22Cu-17Zn-5Sn) were selected for the study. Brazing was performed using infrared radiation (RS-1) under an argon atmosphere. Specimens were etched with two solutions (2.5% HF + 2.5% HNO(3) + 95% H(2)O; 25% HN(4)OH + 30% H(2)O(2) + 45%H(2)O). It was found that the silver-based braze alloy has a eutectic structure. In the diffusion layer between the beta-titanium wire and this silver-based braze alloy, Cu and Ti were enriched on the wire side, and Sn and Ti were enriched on the braze alloy side. The titanium-based braze alloy has a dendritic structure. Beta-titanium wire specimens brazed with the titanium-based braze alloy had a thicker intermediate area compared to the silver alloy; Ti in the diffusion layer had an irregular concentration gradient, and the braze alloy side had higher Ti concentration. The original microstructure of the beta-titanium wire was not altered with the use of either braze alloy. Infrared brazing of beta-titanium orthodontic wire is acceptable for clinical use, since the wire microstructure did not deteriorate with either the titanium-based or silver-based braze alloy. The differing microstructures of the joint regions for the two braze alloys suggest that the joint strengths may also differ.