Electrochemical Properties of Nickel-Titanium Rotary Endodontic Instruments.

INTRODUCTION: Nickel-titanium rotary endodontic files have been commercially available for decades, but more recent innovations have introduced heat-treated and surface-treated files. This study investigated the corrosion properties of various nickel-titanium files in normal saline and sodium hypochlorite (NaOCl). METHODS: Ten different file brands of size 40 with a 0.04 taper were subjected to electrochemical testing in 0.9% NaCl (saline) and 5.25% NaOCl at room temperature. The Open Circuit Potential (OCP) was observed for 1 hour followed by a cyclic polarization test from -300 to 700 mV and back to -300 mV (vs OCP). Nonparametric ANOVA and a pairwise comparison (P < .05) were used for statistical analysis of the OCP at 1 hour and the corrosion current (Icorr) obtained via the cyclic polarization test. RESULTS: Significant differences (P < .05) were found between files with respect to OCP and Icorr in both solutions. Nine files exhibited significantly greater (P < .05) Icorrs in NaOCl than in saline. Conversely, pitting corrosion was observed in the saline solution but not NaOCl. Weak and/or moderate correlations existed between OCP and Icorr measures in the 2 solutions. CONCLUSION: Significant differences in electrochemical properties were observed among the 10 brands of files. Overall, there was not a clear trend between conventional, heat-treated, or surface-treated files among OCP or Icorr in either solution.

Edge chipping of translucent zirconia.

STATEMENT OF PROBLEM: More translucent dental zirconias have been developed by incorporating the cubic phase and reducing the tetragonal phase content that undergoes transformation toughening, leading to reduced mechanical properties. Whether the clinically relevant mechanical property of the edge chipping toughness of the material is also reduced is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the edge chipping toughness and translucency of translucent zirconia, 3mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP), and lithium disilicate. MATERIAL AND METHODS: Two translucent zirconia products, Katana and Lava Esthetic; one 3Y-TZP, Lava Plus; and one lithium disilicate, IPS e.max Press were prepared and tested for phase composition via X-ray diffraction (XRD) (n=3), translucency via a spectrophotometer (n=20), and edge chipping via a universal testing machine with a custom-machined specimen holder and diamond indenter (n=20). The 3Y-TZP and lithium disilicate served as the optimal control materials for edge chipping and translucency, respectively. Translucency was compared with 1-way ANOVA and edge toughness with ANCOVA (α=.05). RESULTS: The XRD showed the 3Y-TZP to be almost completely tetragonal phase compared with the 2 translucent zirconia products that were predominantly cubic. Katana UTML and IPS e.max Press had a statistically similar (P>.05) translucency that was significantly (P<.05) greater than that of Lava Esthetic and Lava Plus. The edge toughness of Katana UTML was 304 N/mm, IPS e.max Press was 354 N/mm, Lava Esthetic was 394 N/mm, and Lava Plus was 717 N/mm, with significance rankings of Katana UTM

Edge chipping resistance and flexural strength of polymer infiltrated ceramic network and resin nanoceramic restorative materials.

STATEMENT OF PROBLEM: Two novel restorative materials, a polymer infiltrated ceramic network (PICN) and a resin nanoceramic (RNC), for computer-assisted design and computer-assisted manufacturing (CAD-CAM) applications have recently become commercially available. Little independent evidence regarding their mechanical properties exists to facilitate material selection. PURPOSE: The purpose of this in vitro study was to measure the edge chipping resistance and flexural strength of the PICN and RNC materials and compare them with 2 commonly used feldspathic ceramic (FC) and leucite reinforced glass-ceramic (LRGC) CAD-CAM materials that share the same clinical indications. MATERIAL AND METHODS: PICN, RNC, FC, and LRGC material specimens were obtained by sectioning commercially available CAD-CAM blocks. Edge chipping test specimens (n=20/material) were adhesively attached to a resin substrate before testing. Edge chips were produced using a 120-degree, sharp, conical diamond indenter mounted on a universal testing machine and positioned 0.1 to 0.7 mm horizontally from the specimen's edge. The chipping force was plotted against distance to the edge, and the data were fitted to linear and quadratic equations. One-way ANOVA determined intergroup differences (α=.05) in edge chipping toughness. Beam specimens (n=22/material) were tested for determining flexural strength using a 3-point bend test. Weibull statistics determined intergroup differences (α=.05). Flexural modulus and work of fracture were also calculated, and 1-way ANOVA determined intergroup differences (α=.05) RESULTS: Significant (P<.05) differences were found among the 4 CAD-CAM materials for the 4 mechanical properties. Specifically, the material rankings were edge chipping toughness: RNC>LRGC=FC>PICN; flexural strength: RNC=LRGC>PICN>FC; flexural modulus: RNCLRGC=PICN>FC. CONCLUSIONS: The RNC material demonstrated superior performance for the mechanical properties tested compared with the other 3 materials.

Effect of toothbrushing on shade and surface roughness of extrinsically stained pressable ceramics.

STATEMENT OF PROBLEM: The effect of toothbrushing on extrinsically stained pressable ceramic materials is unknown. PURPOSE: The purpose of this in vitro study was to investigate the effects of toothbrushing on the shade and surface roughness of extrinsically stained, pressable ceramics. MATERIAL AND METHODS: Two materials, leucite-based (IPS Empress Esthetic [EE]; Ivoclar Vivadent AG) and lithium disilicate-based ceramic (IPS e.max Press [EP]; Ivoclar Vivadent AG), were studied. For each material, 24 disk-shaped specimens, 10 mm (diameter)×3 mm (height) were fabricated. Three different methods (n=8) of applying extrinsic stains were performed on each material: glazed only (G, control group); stained then glazed (SG); and stained and glazed together (T). The specimens were brushed with a multistation brushing machine under a load of 1.96 N at a rate of 90 strokes per minute with a soft and straight toothbrush (Oral-B #35) and a 1:1 toothpaste and distilled water slurry. Shade and roughness were measured at baseline and at 72, 144, 216, and 288 hours, which is equivalent to 3, 6, 9, and 12 years of simulated toothbrushing for 2 minutes twice a day. A repeated measures ANOVA with staining technique as a fixed factor was used to evaluate shade and roughness (α=.05). RESULTS: For EE groups, no significant change was found after 12 years of simulated toothbrushing regarding shade and surface roughness, irrespective of staining techniques (P>.05). However, EP groups demonstrated a significant shade change and an increase in surface roughness after 12 years of simulated toothbrushing. Shade change was found to depend on the method of applying stain. For the EP-SG technique, a significant shade change was observed only at the 9- to 12-year interval (P=.047). However, the EP-T technique demonstrated a significant difference in shade between baseline and 3 years (P=.005) and in the 6- to 9-year interval (P=.005). Surface roughness was only significantly affected at baseline and 3 years for the EP-T group (P=.005). CONCLUSIONS: For the shade and surface roughness of the EE groups, no statistically significant difference was found after 12 years of toothbrushing, irrespective of the staining technique. The shade and surface roughness of the EP groups were significantly statistically affected by toothbrushing time; only shade changes were found to depend on technique.

Surface and cross-sectional characterization of titanium-nitride coated nickel-titanium endodontic files.

BACKGROUND/PURPOSE: Although the effect of experimental surface modifications on various properties (e.g., fatigue, wear) on coated files have been tested in the past, there is no report for the coating quality of commercially available TiN coated files. The aim of this study was to characterize the surface and cross section of TiN coated endodontic files. MATERIALS AND METHODS: TiN coated nickel-titanium endodontic files (EasyShape) were surface and cross-sectionally analyzed via scanning electron microscopy backscattered electron imaging and energy-dispersive X-ray spectroscopy analysis in spot, area, and line scan modes. RESULTS: Surface imaging revealed parallel oblong regions with higher mean atomic contrast, a finding attributed to increased Ni content. Cross-sectional analysis showed that the coating's average total thickness was 0.31 µm and consisted of a thin layered film. Energy-dispersive X-ray spectroscopy analysis revealed the presence of Ti, Ni, N, and O in the coating, whereas only Ni and Ti were identified in the bulk of the file. Ti and O showed their peak compositions at the bulk/coating and coating/surface interfaces, respectively, whereas N displayed a rather constant content within the coated region. The N and O contents started increasing inner to the coating/bulk interface, denoting possible diffusion of both elements to the subcoating region. CONCLUSION: Surface and bulk characterization showed no uncoated areas of the files tested. Apart from Ti, Ni, and N, oxygen was also identified within the coating region.

Effect of Different Thicknesses of Pressable Ceramic Veneers on Polymerization of Light-cured and Dual-cured Resin Cements.

AIM: This study evaluated the effects of ceramic veneer thicknesses on the polymerization of two different resin cements. MATERIALS AND METHODS: A total of 80 ceramic veneer disks were fabricated by using a pressable ceramic material (e.max Press; Ivoclar Vivadent) from a Low Translucency (LT) ingot (A1 shade). These disks were divided into light-cured (LC; NX3 Nexus LC; Kerr) and dual-cured (DC; NX3 Nexus DC; Kerr) and each group was further divided into four subgroups, based on ceramic disk thickness (0.3, 0.6, 0.9, and 1.2 mm). The values of Vickers microhardness (MH) and degree of conversion (DOC) were obtained for each specimen after a 24-hour storage period. Association between ceramic thickness, resin cement type, and light intensity readings (mW/cm(2)) with respect to microhardness and degree of conversion was statistically evaluated by using analysis of variance (ANOVA). RESULTS: For the DOC values, there was no significant difference observed among the LC resin cement subgroups, except in the 1.2 mm subgroup; only the DOC value (14.0 ± 7.4%) of 1.2 mm DC resin cement had significantly difference from that value (28.9 ± 7.5%) of 1.2 mm LC resin cement (p < 0.05). For the MH values between LC and DC resin cement groups, there was statistically significant difference (p < 0.05); overall, the MH values of LC resin cement groups demonstrated higher values than DC resin cement groups. On the other hands, among the DC resin cement subgroups, the MH values of 1.2 mm DC subgroup was significantly lower than the 0.3 mm and 0.6 mm subgroups (p < 0.05). However, among the LC subgroups, there was no statistically significant difference among them (p > 0.05). CONCLUSION: The degree of conversion and hardness of the resin cement was unaffected with veneering thicknesses between 0.3 and 0.9 mm. However, the DC resin cement group resulted in a significantly lower DOC and MH values for the 1.2 mm subgroup. CLINICAL SIGNIFICANCE: While clinically adequate polymerization of LC resin cement can be achieved with a maximum 1.2 mm of porcelain veneer restoration, the increase of curing time or light intensity is clinically needed for DC resin cements at the thickness of more than 0.9 mm.

Die spacer thickness reproduction for central incisor crown fabrication with combined computer-aided design and 3D printing technology: an in vitro study.

STATEMENT OF PROBLEM: The inability to control die spacer thickness has been reported. However, little information is available on the congruency between the computer-aided design parameters for die spacer thickness and the actual printout. PURPOSE: The purpose of this study was to evaluate the accuracy and precision of the die spacer thickness achieved by combining computer-aided design and 3-dimensional printing technology. MATERIAL AND METHODS: An ivorine maxillary central incisor was prepared for a ceramic crown. The prepared tooth was duplicated by using polyvinyl siloxane duplicating silicone, and 80 die-stone models were produced from Type IV dental stone. The dies were randomly divided into 5 groups with assigned die spacer thicknesses of 25 µm, 45 µm, 65 µm, 85 µm, and 105 µm (n=16). The printed resin copings, obtained from a printer (ProJet DP 3000; 3D Systems), were cemented onto their respective die-stone models with self-adhesive resin cement and stored at room temperature until sectioning into halves in a buccolingual direction. The internal gap was measured at 5 defined locations per side of the sectioned die. Images of the printed resin coping/die-stone model internal gap dimensions were obtained with an inverted bright field metallurgical microscope at ×100 magnification. The acquired digital image was calibrated, and measurements were made using image analysis software. Mixed models (α=.05) were used to evaluate accuracy. A false discovery rate at 5% was used to adjust for multiple testing. Coefficient of variation was used to determine the precision for each group and was evaluated statistically with the Wald test (α=.05). RESULTS: The accuracy, expressed in terms of the mean differences between the prescribed die spacer thickness and the measured internal gap (standard deviation), was 50 µm (11) for the 25 µm group simulated die spacer thickness, 30 µm (10) for the 45 µm group, 15 µm (14) for the 65 µm group, 3 µm (23) for the 85 µm group, and -10 µm (32) for the 105 µm group. The precision mean of the measurements, expressed as a coefficient of variation, ranged between 14% and 33% for the 5 groups. CONCLUSIONS: For the accuracy evaluation, statistically significant differences were found for all the groups, except the group of 85 µm. For the precision assessment, the coefficient of variation was above 10% for all groups, showing the printer's inability to reproduce the uniform internal gap within the same group.

Early reaction kinetics of contemporary glass-ionomer restorative materials.

PURPOSE: To investigate polyalkenoate reaction rates in conventional glass-ionomer cement (GIC) and resin-modified glass ionomer (RMGI) restorative materials using infrared spectroscopy. MATERIALS AND METHODS: Nine conventional GIC and six RMGI restorative materials were prepared according to manufacturer's directions and placed on a FTIR (Fourier transform infrared spectroscopy) diamond ATR (attenuated total reflectance) surface. FTIR spectra (700 to 1800 cm-1) were obtained each minute for 3 h. VLC specimens were light polymerized after 1 min; at 5 min, all samples were covered with gauze saturated with deionized water. Polyalkenoate reaction was determined by measuring area growth (Å/cm-1) between 1375 and 1500 cm-1. Mean peak areas were determined at 5, 15, 30, 90, and 180 min and compared using ANOVA (p = 0.05) RESULTS: For all RMGI materials, VLC polymerization inhibited the polyalkenoate reaction rate. Compared to conventional GIC, RMGI materials demonstrated less polyalkenoate reaction. Compared to dark curing, RMGI light polymerization significantly inhibited the polyalkenoate reaction rate. CONCLUSIONS: The addition of resin components to glass-ionomer products significantly retards and impedes the polyalkenoate reaction. The polyalkenoate reaction rate of RMGI products was significantly lower than that of self-curing GIC restorative materials. Furthermore, light activation of RMGI products further retards the polyalkenoate rate. When clinicians require the therapeutic benefit of a polyalkenoate product, perhaps a conventional GIC restorative product should be the first material of choice.

Investigation of force decay in aesthetic, fibre-reinforced composite orthodontic archwires.

BACKGROUND/OBJECTIVES: Because polymer-based materials typically exhibit viscoelastic properties, the objective was to determine if commercially available, aesthetic, fibre-reinforced composite archwires maintain continuous forces without undergoing force decay when deflected continuously. MATERIALS/METHODS: Quasi force decay was evaluated by comparing three-point bending profiles of nickel-titanium (NiTi) and fibre-reinforced composite archwires (BioMers) prior to and after 30 days of continuous deflection of either 1 or 2mm. Paired t-tests or non-parametric signed rank tests were used to statistically compare pre- and post-deflection bending forces. A control group consisting of wires not subject to the 30-day constant deflection was tested to check whether the initial testing altered the second three-point bend test. RESULTS: Significant (P < 0.01) differences in the pre- and post-deflection deactivation force delivery were most evident in the composite 2mm deflection group and all of the NiTi groups. The composite 2mm deflection group failed to deliver consistent forces as the majority of the wires experienced crazing during the 30-day deflection period. The decrease in force delivery in the NiTi groups may be attributed to the small standard deviations. CONCLUSIONS: The composite 1mm deflection group demonstrated that fibre-reinforced composite archwires are able to deliver a consistent force after 30 days of deflection. However, the clinical applicability of these fibre-reinforced composite archwires may be limited as they are unable to sustain deflections of 2mm without experiencing crazing and loss of force delivery. LIMITATIONS: Clinical efficacy of the aesthetic, fibre-reinforced composite orthodontic archwires remains to be observed.

Effect of additives on mineral trioxide aggregate setting reaction product formation.

INTRODUCTION: Mineral trioxide aggregate (MTA) sets via hydration of calcium silicates to yield calcium silicate hydrates and calcium hydroxide (Ca[OH]2). However, a drawback of MTA is its long setting time. Therefore, many additives have been suggested to reduce the setting time. The effect those additives have on setting reaction product formation has been ignored. The objective was to examine the effect additives have on MTA's setting time and setting reaction using differential scanning calorimetry (DSC). METHODS: MTA powder was prepared with distilled water (control), phosphate buffered saline, 5% calcium chloride (CaCl2), 3% sodium hypochlorite (NaOCl), or lidocaine in a 3:1 mixture and placed in crucibles for DSC evaluation. The setting exothermic reactions were evaluated at 37°C for 8 hours to determine the setting time. Separate samples were stored and evaluated using dynamic DSC scans (37°C→640°C at10°C/min) at 1 day, 1 week, 1 month, and 3 months (n = 9/group/time). Dynamic DSC quantifies the reaction product formed from the amount of heat required to decompose it. Thermographic peaks were integrated to determine enthalpy, which was analyzed with analysis of variance/Tukey test (α = 0.05). RESULTS: Isothermal DSC identified 2 main exothermal peaks occurring at 44 ± 12 and 343 ± 57 minutes for the control. Only the CaCl2 additive was an accelerant, which was observed by a greater exothermic peak at 101 ± 11 minutes, indicating a decreased setting time. The dynamic DSC scans produced an endothermic peak around 450°C-550°C attributed to Ca(OH)2 decomposition. The use of a few additives (NaOCl and lidocaine) resulted in significantly less Ca(OH)2 product formation. CONCLUSIONS: DSC was used to discriminate calcium hydroxide formation in MTA mixed with various additives and showed NaOCl and lidocaine are detrimental to MTA reaction product formation, whereas CaCl2 accelerated the reaction.

The effect of water storage on the bending properties of esthetic, fiber-reinforced composite orthodontic archwires.

OBJECTIVE: To study the effect of water storage on the bending properties of fiber-reinforced composite archwires and compare it to nickel-titanium (NiTi), stainless steel (SS), and beta-titanium archwires. MATERIALS AND METHODS: Align A, B, and C and TorQ A and B composite wires from BioMers Products, 0.014-, 0.016, and 0.018-inch, and 0.019×0.025-inch NiTi, 0.016-inch SS, and 0.019×0.025-inch beta-titanium archwires were tested (n=10/type/size/condition). A 20-mm segment was cut from each end of the archwire; one end was then stored in water at 37°C for 30 days, while the other was stored dry. The segments were tested using three-point bending to a maximum deflection of 3.1 mm with force monitored during loading (activation) and unloading (deactivation). Statistical analysis was completed via two-way analysis of variance with wire and condition (dry and water-stored) as factors. RESULTS: In terms of stiffness and force delivery during activation, in general: beta-titanium was >TorQ B>TorQ A>0.019×0.025-inch NiTi and 0.016-inch SS>Align C>0.018-inch NiTi>Align B>0.016-inch NiTi>Align A>0.014-inch NiTi. Water exposure was detrimental to the larger translucent wires (Align B and C, TorQ A and B) because they were more likely to craze during bending, resulting in decreased forces applied at a given deflection. Align A and the alloy wires were not significantly (P>.05) affected by water storage. Overall, the alloy wires possessed more consistent force values compared to the composite wires. CONCLUSION: Environmental conditions are more likely to affect fiber-reinforced composite archwires compared to alloy wires.

An investigation into the mechanical and aesthetic properties of new generation coated nickel-titanium wires in the as-received state and after clinical use.

BACKGROUND/OBJECTIVES: The purpose of this study was to compare the mechanical, structural, and aesthetic properties of two types of aesthetic coated nickel-titanium (NiTi) wires compared with comparable regular NiTi wires in the as-received state and after clinical use. MATERIALS/METHODS: Sixty one subjects were randomly assigned to four groups (N = 61), two groups of coated wires and two groups of comparable, non-coated controls (n = 15/group). The period in the mouth ranged from 4 to 12 weeks after insertion. In total, 121 wires (61 retrieved and 60 as-received) were used in the study. The percentages of coating retention and loss were extrapolated from scans. A brief survey of five questions with three choices was given to all patients. Differential scanning calorimetry (DSC) and three-point bending tests were done on as-received and used wires. RESULTS: The surface characterization by the percentage of resin remaining indicated that most wires in both test groups lost a significant amount of coating. A patient survey indicated that this was a noticeable feature for patients. DSC analysis of the wires indicated that the metallurgical properties of the coated wires were not similar to the uncoated wires in the as-received condition. Three-point bending results indicate a wide variation in test results with large standard deviations among all the groups. LIMITATIONS: The extent of coating loss requires investigating, as do the biological properties of the detached coating. CONCLUSIONS: Both wires lost a significant amount of aesthetic coating after varying periods in the mouth. The metallurgical testing of these findings may indicate that these wires perform differently in the mouth.

3D full field strain analysis of polymerization shrinkage in a dental composite.

OBJECTIVE: The objective of this research was to study the polymerization shrinkage in a dental composite using 3D digital image correlation (DIC). METHODS: Using 2 coupled cameras, digital images were taken of bar-shaped composite (Premise Universal Composite; Kerr) specimens before light curing and after for 10 min. Three-dimensional DIC was used to assess in-plane and out-of-plane deformations associated with polymerization shrinkage. RESULTS: The results show the polymerization shrinkage to be highly variable with the peak values occurring 0.6-0.8mm away from the surface. Volumetric shrinkage began to significantly decrease at 3.2mm from the specimen surface and reached a minimum at 4mm within the composite. Approximately 25-30% of the strain registered at 5 min occurred after light-activation. Application of 3D DIC dental applications can be performed without the need for assumptions on the deformation field. SIGNIFICANCE: Understanding the local deformations and strain fields from the initial polymerization shrinkage can lead to a better understanding of the composite material and interaction with surrounding tooth structure, aiding in their further development and clinical prognosis.

Corrosion of orthodontic temporary anchorage devices.

Corrosion of orthodontic miniscrews or temporary anchorage devices (TADs) has been proposed as a contributor to inflammation, which in turn is a factor in the clinical success of miniscrews. The purpose of this study was to measure the electrochemical properties of orthodontic miniscrews in artificial saliva with and without fluoride. The corrosion properties of three miniscrew products (VectorTAS, Ormco Corp.; Unitek TAD, 3M Unitek; and Through-Hole Screw, American Orthodontics) were tested in an artificial saliva (Fusayama-Meyer) with (1500 ppm) or without fluoride (n = 10/product/solution). Open circuit potential (OCP), polarization resistance (R p), and corrosion current (I corr) were measured and statistically analysed with the Friedman/Tukey least significant difference tests. No significant differences (P > 0.05) between miniscrews with regard to OCP, R p, and I corr were found except that the American Orthodontics miniscrews had a significantly (P < 0.05) more noble OCP compared to the others. Incorporation of 1500 ppm fluoride in the artificial saliva significantly (P < 0.001) lowered the OCP, reduced the polarization resistance, and increased the corrosion current of each miniscrew product. Few differences existed in the electrochemical properties of miniscrews from the three different manufacturers; however, exposure to fluoride was detrimental to the corrosion properties of all miniscrews.

Torsion and bending properties of shape memory and superelastic nickel-titanium rotary instruments.

INTRODUCTION: Recently introduced into the market are shape memory nickel-titanium (NiTi) rotary files. The objective of this study was to investigate the torsion and bending properties of shape memory files (CM Wire, HyFlex CM, and Phoenix Flex) and compare them with conventional (ProFile ISO and K3) and M-Wire (GT Series X and ProFile Vortex) NiTi files. METHODS: Sizes 20, 30, and 40 (n = 12/size/taper) of 0.02 taper CM Wire, Phoenix Flex, K3, and ProFile ISO and 0.04 taper HyFlex CM, ProFile ISO, GT Series X, and Vortex were tested in torsion and bending per ISO 3630-1 guidelines by using a torsiometer. All data were statistically analyzed by analysis of variance and the Tukey-Kramer test (P = .05) to determine any significant differences between the files. RESULTS: Significant interactions were present among factors of size and file. Variability in maximum torque values was noted among the shape memory files brands, sometimes exhibiting the greatest or least torque depending on brand, size, and taper. In general, the shape memory files showed a high angle of rotation before fracture but were not statistically different from some of the other files. However, the shape memory files were more flexible, as evidenced by significantly lower bending moments (P < .008). CONCLUSIONS: Shape memory files show greater flexibility compared with several other NiTi rotary file brands.

An in vitro comparison of torsional stress properties of three different rotary nickel-titanium files with a similar cross-sectional design.

INTRODUCTION: The purpose of this study was to compare the in vitro torsional stress characteristics of Twisted Files (TFs; SybronEndo, Orange, CA) with 2 milled files of a similar cross-section: EndoSequence (Brasseler USA, Savannah, GA) and ProFile Vortex (DENTSPLY Tulsa Dental, Tulsa, OK). METHODS: File sizes of 25/.06 and 30/.06 from the 3 file types were compared (n = 20/group). Torsional stress resistance was evaluated by measuring the torque in grams per centimeters and the angle of rotation (°) required for instrument separation with the use of a torsiometer instrument. The fractured files were examined using a scanning electron microscope to look at deformation and fracture surface characteristics. The data were analyzed with analysis of variance to determine statistical differences. RESULTS: The 3 file types showed a statistically significant difference in both the maximum torsional stress and the angle of rotation before failure. TFs displayed the least amount of torsional stress resistance and the highest angle of rotation. The 30/.06 size files of all 3 types withstood more torsional stress than the size 25/06 files of the same type. Within each file design, there was not a statistically significant difference in angular rotation between the 25/.06 and 30/.06 groups. The scanning electron microscopic analysis of all 3 file types revealed dimpling near the center of rotation on the fractured surface indicative of torsional stress. CONCLUSIONS: The novel techniques used in manufacturing TFs do not make them more resistant to torsional stress as compared with milled nickel-titanium endodontic files of a similar cross-sectional design.

Three-point bending test comparison of fiber-reinforced composite archwires to nickel-titanium archwires.

AIM: Various alternatives to metal orthodontic archwires have produced varied successes over the years. This study sought to evaluate the bending properties of fiber-reinforced polymeric composite (FRC) archwires compared with similarly sized nickel-titanium (Ni-Ti) archwires. METHODS: Two different 0.018-inch translucent FRC orthodontic wires (Translucent Archwire I and Translucent Archwire II) were tested against 0.014-, 0.016-, and 0.018-inch nonsuperelastic nickel titanium orthodontic wires. The wires in each group (n = 10) were evaluated with three-point bending using a universal testing machine. Wire segments were deflected at midspan to 3.1 mm at a rate of 2 mm/min. Loading and unloading slope and modulus were calculated, as were force values during activation and deactivation and elastic recovery. RESULTS: It was found that the 0.018-inch Ni-Ti archwire demonstrated the highest force values at different deflection distances followed by Translucent Archwire II, 0.016-inch Ni-Ti, Translucent Archwire I, and finally 0.014-inch Ni-Ti. 0.016-inch Ni-Ti exhibited the highest modulus value, followed by 0.018-inch Ni-Ti, 0.014-inch Ni-Ti, Translucent Archwire II, and finally Translucent Archwire I. During deactivation, the elastic recovery of 0.014-inch Ni-Ti and 0.016-inch Ni-Ti was significantly greater than Translucent Archwire II. CONCLUSION: The bending properties of BioMer's FRC archwires were found to be comparable to Ni-Ti, as advertised by the manufacturer.

Elemental release from CoCr and NiCr alloys containing palladium.

PURPOSE: An entirely new subclass of casting alloy composition whereby palladium (∼approximately 25 wt%) is added to traditional base metal alloys such as CoCr and NiCr was recently introduced to the market. The purpose of this study was to evaluate the elemental release of new CoPdCr and NiPdCr alloys and compare them to traditional CoCr and NiCr alloys. MATERIALS AND METHODS: Five casting alloys were investigated: CoPdCr-A (NobleCrown NF, The Argen Corporation), CoPdCr-I (Callisto CP+, Ivoclar Vivadent), NiPdCr (NobleCrown, Argen), CoCr (Argeloy N.P. Special, Argen), and NiCr (Argeloy N.P. Star, Argen). Rectangular specimens (n = 6/alloy) were prepared and immersed in a lactic acid/NaCl solution at 37°C for 7 days according to ISO 10271. Solutions were analyzed with ICP-AES to determine elemental release. The concentrations of major ions (cobalt, nickel, palladium, chromium, and molybdenum) were compared using a generalized linear model (p < 0.05). Representative specimens were examined with optical microscopy before and after immersion. RESULTS: The CoPdCr alloys released a significantly greater amount of respective ions (Co, Cr, Mo, and total ions) compared to the traditional CoCr alloy. No significant differences in elemental release were noted between NiPdCr and NiCr. Optical microscopic examination showed abundant areas of corrosion in the palladium-containing CoCr alloys after immersion, whereas little difference was observed for the other alloys. CONCLUSIONS: Corrosion resistance measured via elemental release was compromised when CoCr was alloyed with palladium, but this effect was not observed with NiCr.

Bonding with self-etching primers--pumice or pre-etch? An in vitro study.

The purpose of this study was to compare the shear bond strengths (SBSs) of orthodontic brackets bonded with self-etching primer (SEP) using different enamel surface preparations. A two-by-two factorial study design was used. Sixty human premolars were harvested, cleaned, and randomly assigned to four groups (n = 15 per group). Teeth were bathed in saliva for 48 hours to form a pellicle. Treatments were assigned as follows: group 1 was pumiced for 10 seconds and pre-etched for 5 seconds with 37 per cent phosphoric acid before bonding with SEP (Transbond Plus). Group 2 was pumiced for 10 seconds before bonding. Group 3 was pre-etched for 5 seconds before bonding. Group 4 had no mechanical or chemical preparation before bonding. All teeth were stored in distilled water for 24 hours at 37°C before debonding. The SBS values and adhesive remnant index (ARI) score were recorded. The SBS values (± 1 SD) for groups 1-4 were 22.9 ± 6.6, 16.1 ± 7.3, 36.2 ± 8.2, and 13.1 ± 10.1 MPa, respectively. Two-way analysis of variance and subsequent contrasts showed statistically significant differences among treatment groups. ARI scores indicated the majority of adhesive remained on the bracket for all four groups. Pre-etching the bonding surface for 5 seconds with 37 per cent phosphoric acid, instead of pumicing, when using SEPs to bond orthodontic brackets, resulted in greater SBSs.

Galvanic corrosion between various combinations of orthodontic brackets and archwires.

INTRODUCTION: The purpose of this study was to compare galvanic currents generated by different combinations of commonly used brackets and archwires. METHODS: As-received stainless steel, nickel-titanium, and beta-titanium wires were coupled to stainless steel and titanium brackets in an artificial saliva medium. The galvanic current and amount of charge transferred for each pair were monitored with a zero resistance ammeter for 10 hours. RESULTS: Two-way analysis of variance (ANOVA) showed a significant difference in charge and galvanic currents when factored for type of bracket (P <0.001), but no significant difference between them when factored by type of wire (P >0.05). Specifically, a brazed stainless steel bracket was significantly greater in charge transferred and 10-hour galvanic current than metal injection molded stainless steel and titanium brackets (P <0.001), which were not different from each other (P >0.05). CONCLUSIONS: The method of bracket manufacturing might be of equal or more relevance to galvanic corrosion susceptibility than bracket composition.