Effect of High-Speed Sintering on the Optical Properties, Microstructure, and Phase Distribution of Multilayered Zirconia Stabilized with 5 mol% Yttria.

As dental 5 mol% yttria-stabilized (5Y-) zirconia demand high esthetics, it is necessary to clarify how the optical properties are affected by high-speed sintering, which is not yet fully understood. Our study aimed to investigate the effect of high-speed sintering on the translucency and opalescence parameters (TP and OP, respectively), as well as their related microstructure and phase distribution, using two types of multilayered 5Y-zirconia. Multilayered 5Y-zirconia (Cercon xt ML, Lava Esthetic) were cut layer-by-layer, followed by conventional and high-speed sintering. The TP and OP values were subsequently obtained using a spectrophotometer, and field emission scanning electron microscopy images were used to analyze the average grain size. The phase fractions were analyzed using X-ray diffraction. Regardless of the zirconia type, the TP was slightly lowered by high-speed sintering in all the layers except the dentin layer (DL) for Lava Esthetic (p < 0.05). The OP decreased by high-speed sintering in the DL for Cercon xt ML and in all the layers for Lava Esthetic (p < 0.05). The decrease in translucency after high-speed sintering was attributed to a decrease in the yttria-rich t'-phase with low tetragonality, along with an increase in the yttria-lean t-phase with high tetragonality.

Effect of superspeed sintering on translucency, opalescence, microstructure, and phase fraction of multilayered 4 mol% yttria-stabilized tetragonal zirconia polycrystal and 6 mol% yttria-stabilized partially stabilized zirconia ceramics.

STATEMENT OF PROBLEM: The optical properties of recently developed multilayer zirconia have mainly been studied for the effects of conventional sintering and speed sintering but not as much for the effect of superspeed sintering. As superspeed sintering protocols typically require a higher sintering temperature and higher heating and cooling rates than speed- and conventional sintering protocols, the optical properties of superspeed sintered zirconia may be affected differently. PURPOSE: The purpose of this in vitro study was to investigate the effect of superspeed sintering on the optical properties, microstructure, and phase fraction of multilayered 4 mol% yttria-stabilized (4Y-) and 6 mol% yttria-stabilized (6Y-) zirconia. MATERIAL AND METHODS: Multilayered 4Y- and 6Y-zirconia were sectioned. After conventional and superspeed sintering, the translucency parameter (TP), and opalescence parameter (OP) were measured with a spectrophotometer (n=10). To obtain the grain sizes from the field emission scanning electron microscopy (FE-SEM) images for each layer (n=2), more than 500 (6Y-zirconia) and 800 grains (4Y-zirconia) were measured by linear intercept methods. The phase fractions were obtained through X-ray diffraction (XRD) analysis by using the Rietveld method (n=1). The results were analyzed by 3-way ANOVA and post hoc Tukey honest significant difference tests (TP and OP) and by 3-way ANOVA and post hoc Scheffé tests (grain size) (α=.05). RESULTS: No layers exhibited a significant difference in TP after superspeed sintering, except the dentin layer (DL) and transition layer 2 (T2) of 4Y- and 6Y-zirconia, respectively. The TP increased (P<.05) in DL for superspeed sintered 4Y-zirconia and decreased (P<.05) in T2 for the superspeed sintered 6Y-zirconia. However, the difference in TP by superspeed sintering was lower than the perceptibility thresholds of 50:50%. The OP decreased (P<.05) in the DL and T2 of 4Y-zirconia after superspeed sintering. For 6Y-zirconia, the OP decreased (P<.05) in all layers except for the transition layer 1 (T1) after superspeed sintering. However, the difference in OP values was minimal, with only a 1.1 difference observed for Zolid Gen-X (4Y) and a range of 1.22 to 1.62 for Katana UTML (6Y) when using superspeed sintering. No significant change was found in the grain size after superspeed sintering of either zirconia. Regardless of the sintering speed, the average grain size of the 6Y-zirconia (conventional: 2.09 to 2.21 µm; superspeed: 2.11 to 2.20 µm) was larger than that of the 4Y-zirconia (conventional: 0.50 to 0.52 µm; superspeed: 0.52 to 0.54 µm). Owing to superspeed sintering, the metastable tetragonal (T') phase content increased while the tetragonal (T) phase decreased in 4Y-zirconia; in 6Y-zirconia, the cubic (C) phase content increased, while the T'-phase content decreased. CONCLUSIONS: Superspeed sintering did not result in any clinically significant changes in the translucency and opalescence of 4Y- or 6Y-zirconia.

Effect of Cooling Rate on Mechanical Properties, Translucency, Opalescence, and Light Transmission Properties of Monolithic 4Y-TZP during Glazing.

A standard cooling rate has not been established for glazing; therefore, the effects of the cooling rate on the properties of zirconia need to be evaluated to predict outcomes in clinical practice. 4Y-TZP glazed at three different cooling rates was analyzed to estimate the effect of cooling rate during glazing on the mechanical and optical properties. Hardness tests, field-emission scanning electron microscopy analysis, X-ray diffraction analysis, flexural strength measurement, and optical property evaluations were performed. When 4Y-TZP was glazed at a higher cooling rate (Cooling-1) than the normal cooling rate (Cooling-2), there was no significant difference in grain size, flexural strength, average transmittance, and translucency parameters. The hardness was slightly reduced. The opalescence parameter was reduced for the 2.03 mm thick specimens. When 4Y-TZP was glazed at a lower cooling rate (Cooling-3) than the normal cooling rate, there was no significant difference in hardness, grain size, flexural strength, and translucency parameters. In addition, the average transmittance and opalescence parameters were slightly reduced for the 0.52 and 2.03 mm specimens, respectively. The effects of the cooling rate during glazing on the mechanical and optical properties of 4Y-TZP appear to be minimal and clinically insignificant. Therefore, even if the cooling rate cannot be strictly controlled during glazing, the clinical outcomes will not be significantly affected.

Optical Properties, Microstructure, and Phase Fraction of Multi-Layered Monolithic Zirconia with and without Yttria-Gradient.

The differences in the optical properties of multi-layered zirconia with and without yttria-gradient are not fully understood. This study aimed to evaluate and compare the optical properties, related microstructures, and phase fractions of multi-layered zirconia with and without yttria-gradient. For this, multi-layered zirconia of 5 mol% yttria (5Y) stabilized (Katana STML) and 4Y/5Y stabilized (e.max MT Multi) were cut layerwise, sintered, and analyzed using the opalescence parameter (OP), average transmittance (AT%), translucency parameter (TP), and contrast ratio (CR). The average grain size and phase fractions were obtained from field-emission scanning electron micrographs and X-ray diffraction patterns, respectively. Although the TP values of Katana STML and e.max MT Multi did not show a significant difference (except for transition layer 1), the results of AT and CR showed that the translucency of e.max MT Multi was slightly higher than that of Katana STML (p < 0.05). The opalescence gradient was higher in Katana STML than in the e.max MT Multi. In both zirconia types, translucency increased from the dentin to enamel layer based on the AT, TP, and CR results, while OP decreased (p < 0.05). The higher translucency from the dentin to enamel layer in Katana STML was caused by the pigmentation gradient, while in e.max MT Multi, it was caused by the difference in phase fraction and the pigmentation gradient.

Effect of Cooling Rate during Glazing on the Mechanical and Optical Properties of Monolithic Zirconia with 3 mol% Yttria Content.

Glazing is the final heat treatment process in the manufacturing of a monolithic zirconia prosthesis. Herein, the effect of cooling rate during zirconia glazing was investigated. A 3 mol% yttria-stabilized tetragonal zirconia polycrystal was glazed at the general cooling rate suggested by the manufacturer, as well as at higher and lower cooling rates, and the differences in flexural strength, hardness, optical properties, and crystal structure were evaluated. A higher cooling rate did not affect the flexural strength, hardness, grain size, optical properties, or crystal structure; however, the Weibull modulus decreased by 1.3. A lower cooling rate did not affect the flexural strength, optical properties, or crystal structure; however, the Weibull characteristic strength increased by 26.7 MPa and the Weibull modulus increased by 0.9. The decrease in hardness and the increase in grain size were statistically significant; however, the numerical differences were negligible. This study revealed that a lower cooling rate provides more reliable flexural strength. Therefore, glazing can proceed at a general cooling rate, which takes 3-4 min; however, glazing at a lower cooling rate will provide a more consistent flexural strength if desired, despite being time-consuming.

Effect of cooling rate on hardness and microstructure of Pd-Ag-In-Sn-Ga alloy during porcelain firing simulation.

This study examined the effect of the cooling rate on the hardness and its effect on the microstructure during porcelain firing simulation of a Pd-Ag-In-Sn-Ga metal-ceramic alloy. In practice, after each firing step for porcelain bonding, the prosthesis is cooled to room temperature before proceeding to the next firing step. The cooling step is known to allow the hardness of the metal substructure to increase. The aim of the study was to determine whether controlling the cooling rate after each porcelain-firing step increases the hardness of the Pd-Ag-based metal-ceramic alloy. The results showed that the hardness of specimens cooled at a higher cooling rate increased after each firing step compared to specimens cooled at a lower cooling rate (p < 0.05). During cooling after the firing simulation the InPd3-based phase of tetragonal structure precipitated from the Pd-Ag-rich matrix of the face-centered cubic structure. Hardening by cooling at a higher cooling rate after firing was the result of the coherency strains that formed at the interface of the Pd-Ag-rich matrix and the metastable phase based on the InPd3 phase. . The reduced hardness obtained in the specimen cooled at a lower cooling rate after firing resulted from the loss of coherency strains as the fine metastable phases based on the InPd3 phase were transformed into the coarser stable phase with decreased (c/a) of 0.88. This finding revealed that controlling the cooling rate during porcelain firing simulation improves the hardness of the Pd-Ag-In-Sn-Ga metal-ceramic alloy without an additional heat treatment of the alloy.

Effect of ice quenching after oxidation with or without vacuum on the hardness of Pd-Ag-Au-In alloy during porcelain firing simulation.

This study examined the effect of ice-quenching after oxidation treatment with or without vacuum, on the change in the hardness of a Pd-Ag-Au-In metal-ceramic alloy during porcelain-firing simulation. The aim of the present study is to determine whether ice quenching after oxidation renders a Pd-Ag metal-ceramic alloy soft enough for easy processing without the need for an additional solution treatment and whether it affects the final hardness of the Pd-Ag metal-ceramic alloy after porcelain firing simulation. The oxidation treatment resulted in the as-cast specimen becoming homogenized, which was progressed further by vacuuming. The bench-cooling to room temperature after the oxidation resulted in precipitation. From the next firing step, the precipitation occurred during the firing process as well as subsequent bench-cooling; this was owing to the presence of a phase boundary wherein the single phase is separated into two phases between the temperatures of the oxidation treatment (1010 °C) and post-oxidation treatment (~960 °C). During the firing process until main bake, the specimen that was ice-quenched after oxidation maintained a higher hardness than the bench-cooled specimen, particularly for the oxidation treated specimen with vacuum (p < 0.05). The mechanism of ice-quenching after oxidation with vacuum to induce further hardening during the firing process involved more active precipitation; this was attributed to the further progress of homogenization during the oxidation. The precipitation reaction in the present study corresponded to the Pd-In binary phase diagram, illustrating that as the firing proceeded, the Pd3(In,Sn,Ga) phase was precipitated from the Pd-Ag-Au-rich matrix. The findings revealed that ice quenching after oxidation makes the alloy soft enough for easy processing without an additional heat treatment and does not affect the final hardness of the Pd-Ag metal-ceramic alloy after porcelain firing simulation.

Effect of ice-quenching after oxidation treatment on hardening of a Pd-Cu-Ga-Zn alloy for bonding porcelain.

This study examined the effect of ice-quenching after oxidation treatment on hardness change of a Pd-Cu-Ga-Zn metal-ceramic alloy during porcelain firing simulation. Although not statistically significant, the alloy was softened slightly during porcelain firing simulation with conventional slow cooling rate. On the other hand, the hardness increased significantly by ice-quenching instead of the slow cooling after oxidation (p<0.001). The gap in the final hardness depending on ice-quenching occurred in the matrix and plate-like precipitates but not in the particle-like structure without plate-like precipitates (p<0.05). The mechanism of ice-quenching after oxidation to prevent softening and induce hardening during porcelain firing simulation involved the more active precipitation and retardation of microstructural coarsening. In conclusion, for practical work on Pd-Cu-Ga-Zn alloys, the oxidation treatment followed by ice-quenching instead of slow cooling is recommended for the simultaneous oxidation and hardening effects on the alloy.

Effect of ice-quenching on the change in hardness of a Pd-Au-Zn alloy during porcelain firing simulation.

This study examined the effect of ice-quenching after degassing on the change in hardness of a Pd-Au-Zn alloy during porcelain firing simulations. By ice-quenching after degassing, the specimens were softened due to homogenization without the need for an additional softening heat treatment. The lowered hardness by ice-quenching after degassing was recovered greatly from the first stage of porcelain firing process by controlling the cooling rate. The increase in hardness during cooling after porcelain firing was attributed to the precipitation of the f.c.t. PdZn phase containing Au, which caused severe lattice strain in the interphase boundary between the precipitates and matrix of the f.c.c. structure. The final hardness was slightly higher in the ice-quenched specimen than in the specimen cooled at stage 0 (the most effective cooling rate for alloy hardening) after degassing. This was attributed to the more active grain interior precipitation during cooling in the ice-quenched specimen after degassing.

Hardening by cooling rate control and post-firing heat treatment in Pd-Ag-Sn alloy for bonding porcelain.

The aim of this study was to determine the hardening effect by controlling the cooling rate during the porcelain firing process and performing an additional post-firing heat treatment in a Pd-Ag-Sn alloy. The most effective cooling rate for alloy hardening was determined by cooling the specimens at various cooling rates after oxidation treatment. A subsequent porcelain firing simulation followed by cooling at the selected cooling rate was performed. A post-firing heat treatment was then done at 600°C in a porcelain furnace. The hardening mechanism was characterized by a hardness test, X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Alloy softening occurred during the porcelain firing process followed by cooling at a controlled cooling rate. A post-firing heat treatment allowed apparent precipitation hardening. It is advisable to perform a postfiring heat treatment at 600°C in a porcelain furnace by annealing metal substructure after porcelain fusing.

Interaction of LED light with coinitiator-containing composite resins: effect of dual peaks.

OBJECTIVES: Recently the colour stability of composite resins has been an issue due to the emphasis on the aesthetics of restored teeth. The purpose of the present study was to investigate how dual-peak LED units affect the polymerization of coinitiator-containing composite resins. MATERIALS AND METHODS: Five composite resins [coinitiator-containing: Aelite LS Posterior (AL), Tetric EvoCeram (TE), and Vit-l-escence (VI); only CQ-containing: Grandio (GD) and Filtek Z350 (Z3)] were light cured using four different light-curing units (LCUs). Among them, Bluephase G2 (BP) and G-light (GL) were dual-peak LED LCUs. Microhardness, polymerization shrinkage, flexural, and compressive properties were measured. RESULTS: BP and GL had no consistent effect on the microhardness of AL, TE, and VI on the top and bottom surfaces of resin specimens. Among the specimens, AL and VI showed the least (9.86-10.41 µm) and greatest (17.58-19.21 µm) polymerization shrinkage, respectively. However, the effect of BP and GL on the shrinkage of specimens was not consistent. Among the specimens, GD showed the greatest flexural properties [strength (FS) and modulus (FM)] and TE showed the lowest flexural and compressive properties [strength (CS) and modulus (CM)]. In same resin product, maximum FS and CS differences due to the different LCUs were 10.3-21.0% and 3.6-9.2%, respectively. Furthermore, the influences of BP and GL on FS and CS were not consistent. CONCLUSION: The tested dual-peak LED LCUs had no consistent synergic effect on the polymerization of coinitiator-containing composite resins as compared with QTH and single-peak LED LCUs. CLINICAL SIGNIFICANCE: The dual-peak LED LCUs achieve a similar degree of polymerization in coinitiator-composite resins as QTH and single-peak LED LCUs did. Choice of LCU does not appear to be a determinant of the light curing of coinitiator-composite resins.

Effect of hydrogen peroxide on microhardness and color change of resin nanocomposites.

PURPOSE: To examine the effect of hydrogen peroxide on the microhardness and color change of resin composites containing nanofillers. METHODS: Three resin nanocomposites with three different shades and two different tooth whitening agents were used. The specimens were given a 3-week treatment with one of three protocols: (1) 7 hours/day treatment of carbamide peroxide (CP) + 17 hours/day immersion in distilled water (DW); (2) 1 hour/week treatment of hydrogen peroxide (HP) + immersion in DW for the rest of the week; and (3) immersion in DW for 24 hours/day. The microhardness and color changes were measured after treatment. RESULTS: After treatment with the whitening agents, there was an 8.1-10.7% decrease in the original microhardness. These values were similar to those obtained from the samples treated with distilled water. In the same resin product, the decrease was similar regardless of the test agents used. In most cases, the color change was only slight (deltaE*=0.5-1.4). Hydrogen peroxide enhanced the color change but the absolute color change values were similar in the same product and shade, regardless of the test agent used.

Effect of different blue light-curing systems on the polymerization of nanocomposite resins.

OBJECTIVES: To examine the degree of polymerization of nanocomposite resins to test the possibility of using a diode-pumped solid state (DPSS) laser as a light-curing source on behalf of the argon laser. BACKGROUND: DPSS lasers emitting light at 473 nm have many advantages over argon lasers on account of their compactness, efficiency, and price. MATERIALS AND METHODS: A 473-nm DPSS laser (LAS) was used with three other light-curing units (a quartz-tungsten-halogen lamp-based unit, a light emitting diode-based unit, and a xenon lamp-based plasma arc unit) to polymerize dental nanocomposite resins. The degree of polymerization was determined by measuring the microhardness, maximum polymerization shrinkage, and increase in temperature during and after light curing. The results were analyzed statistically. RESULTS: The specimens light cured with LAS showed a microhardness that was similar or superior to the values obtained from the specimens cured with the other light-curing units and maximum polymerization shrinkage values. The maximum increase in temperature by LAS was much lower than that induced by the other light-curing units. CONCLUSION: LAS effectively polymerizes dental nanocomposite resins to an extent similar to that of recently available light-curing units. The results suggest that LAS has good potential as a light source for light curing of dental nanocomposite resins.

The effects of light intensity and light-curing time on the degree of polymerization of dental composite resins.

The aim of this study was to investigate the effects of light intensity and light-curing time on the polymerization of composite resins. Four composite resins were light-cured with different light-curing conditions. In the non-thermocycled case, specimens showed almost the same or similar microhardness values if energy density was identical or similar. As the energy density decreased, maximum polymerization shrinkage decreased. At higher energy densities, specimens had a lower coefficient of thermal expansion than at lower energy densities. At the same or similar energy density, most resin products showed coefficient values which were not statistically different. After 10,000 thermocycles, specimens showed decreases of 2.4-16.5% and 4.6-25.2% in microhardness and coefficient of thermal expansion respectively. Within the limitations of the present study, it was found that light-curing composite resins with higher energy density was beneficial to acquiring higher microhardness values and lower coefficients of thermal expansion.

The applicability of DPSS laser for light curing of composite resins.

The applicability of diode-pumped solid state (DPSS) laser for light curing the composite resins was tested with a quartz-tungsten-halogen lamp-based unit and a light emitting diode unit. The emission spectra of the light-curing systems used match with the absorption spectrum of camphorquinone. Among the light-curing systems, DPSS laser showed the narrowest emission bandwidth. The light intensity of DPSS laser was approximately 64% of the other two light-curing units. In most specimens, DPSS laser showed the least attenuation of the number of incident photons. On the top surface, specimens cured with DPSS laser showed similar microhardness values compared to the specimens cured with the other two light-curing units. During the light curing, DPSS laser induced the lowest temperature rise (25.5-35.5 degrees C) in the specimens compared to the other two light-curing units (34.2-41.7 degrees C). In conclusion, DPSS laser has high potential to be an alternative to the other light-curing units or a new light-curing unit.

Effect of acetic NaF solutions on fluoride-containing dental restorative materials.

The aim of this study was to evaluate the effect of acetic NaF solutions on fluoride-containing restorative materials. As the pH value of solution decreased, the degree of microhardness change in restorative materials increased- regardless of product. Dyract AP (DA) and F2000 (F2) (polyacid-modified resin composites) showed the greatest decrease in microhardness after immersion for three days. Similarly, as the pH value decreased, volumetric weight change (loss) increased in all products. DA and F2 showed the greatest--but similar-weight change in pH 3.5 solution among the products. In terms of color change, most specimens showed a slight color change after immersion for one and three days-regardless of pH value. However, F2 in pH 3.5 solution showed a noticeable color change (deltaE*=2.1). In terms of surface morphology, specimens in distilled water showed only minor surface modification. However, in pH 3.5 solution, DA and F2 showed randomly propagating cracks, while Solitaire 2 and Tetric Ceram (resin composites) lost many fillers less than 2 microm in size.

Effect of pH and temperature on orthodontic NiTi wires immersed in acidic fluoride solution.

Orthodontic arch wires can confront diverse pH and temperature conditions in the oral cavity after replacement. The current study evaluated the effect of pH and temperature on orthodontic NiTi arch wires after immersion in an acidic fluoride solution. The acetic acid added for the adjustment of pH forms hydrofluoric acid (HF). More HF was formed in a solution of lower pH with higher temperature than that of the higher pH with lower temperature. Within the same pH value, the temperature of the solution affected the concentration of HF. Each as-received wire exhibited quite different microhardness values. The reduction of microhardness, 1.2-5.7%, occurred after immersion. Within the same product, however, the pH and temperature had minor influence on the reduction. The volumetric weight change, concentration of the released elements, and surface morphology were influenced by pH and temperature. At pH 3.5 of 60 degrees C solution, the greatest weight loss, release of elements, and corrosion of surface occurred from the wires. At pH 6, on the other hand, no such loss or release occurred regardless of temperature. At 5 degrees C solution, the surface exhibited minor corrosion regardless of pH value.

Evaluation of polymerization of light-curing hybrid composite resins.

The quality of polymerization of hybrid composite resins was tested to explore their feasibility for dental restorations. For this, microhardness, polymerization shrinkage, the coefficient of thermal expansion, and surface morphology were evaluated during or after light curing in conjunction with the thermocycling process. Each product had different microhardness values. The repeated thermal stimulus has no specific effect on the change of microhardness. The difference of microhardness between the thermocycled specimens and specimens stored only in distilled water was minor. The measured microhardness had a linear correlation with the filler content (vol %) of the tested specimens. The polymerization shrinkage had rapidly increased only during the light curing, and then it reached a plateau. Among the specimens, Z250 showed the least amount of shrinkage for all tested thicknesses. Regardless of the product, the shrinkage values increased as the specimens became thick. The coefficient of thermal expansion of the control specimens ranged between 42 and 55 microm/degrees C in the temperature range of 30-80 degrees C. The coefficient showed an inverse correlation with the filler content. Through the thermocycling process, Palfique Estelite showed randomly propagating cracks on the surface. Larger fillers showed a more apparent detachment than the smaller fillers.

Detection of incipient carious lesions formed on human teeth in vitro using ultraviolet laser.

OBJECTIVE: A 325-nm ultraviolet (UV) laser was tested for effectiveness in the detection of incipient carious lesions on teeth. BACKGROUND DATA: The combination of early detection with new intervention methods and caries management will be the preferred dentistry of the future. METHODS: Carious lesions from extracted teeth or from demineralized teeth were irradiated by UV laser, and the fluorescence spectrum was measured. The peak ratio between two peak intensities in the spectrum was determined. RESULTS: Fluorescence peak intensity of approximately 425 nm was gradually decreased as carious lesions formed, whereas the change 625 nm was less significant. The peak ratio change between peak intensities of approximately 425 and at 625 nm was observed after 30 min of demineralization. Morphological changes were barely observable in this range. CONCLUSIONS: A 325-nm UV laser showed high efficacy in the detection of incipient carious lesions. By evaluating peak ratio, the incipient carious lesions could be detected.

Effect of acidic fluoride solution on beta titanium alloy wire.

The interaction between acidic fluoride solution and beta titanium alloy was investigated to explore the changes that occur in beta titanium alloy by fluoride-containing acetic acid solutions. For this, alloy crystal structure, tensile strength, and elements released from the alloy wires were determined using four solutions (0.05%/pH 6, 0.05%/pH 4, 0.2%/pH 6, and 0.2%/pH 4) for 1 or 3 days. The immersed wire did not form any identifiable new crystal structure compared with the as-received wire. The tensile strength of the immersed wires was significantly reduced compared to the as-received wires in the test solutions if the period of immersion increased from as-received to 3 days. The fractured area of the immersed wire was reduced compared to the as-received one. The dimple pattern at the inner part and a cup-cone morphology at the outer part of the fractured wires were similar in both as-received and immersed wires. After a 3-day immersion, the amount of the released Ti and Mo has much increased for higher NaF concentration and lower pH value. During the long-period orthodontic treatment, both patient and clinical doctor should carefully use the fluoride-containing products to minimize unexpected damage on orthodontic wires.