Ikuya Watanabe

Cyclic Fatigue Analysis of a New Generation of Nickel Titanium Rotary Instruments

Recently, a new generation of nickel-titanium (NiTi) rotary instruments including the Twisted File (TF; Sybron Dental Specialties, Orange, CA) and ProFile GT Series X (GTX; Denstply, Tulsa Dental Specialties, Tulsa, OK) was introduced to the market. The purpose of this study was to determine if these new NiTi instruments were more resistant to cyclic fatigue compared with traditionally ground NiTi rotary instruments such as EndoSequence (ES; Brasseler, Savannah, GA) and ProFile (PF; Dentsply, Tulsa Dental Specialties). Size #25 TF, ES, and PF and size #20 GTX with .04 and .06 tapers were tested in a simulated canal with 60 degrees angle of curvature and a 3-mm radius. The number of rotations until fracture was recorded for each instrument. Among both .04 and .06 tapered files, #20 GTX files performed significantly better than all other files tested with tip sizes of #25 (p < 0.001); this may be because of the increased flexibility in the #20 files compared with #25 files. TF was significantly more resistant to cyclic fatigue than ES (p < 0.05) but not different from PF (p > 0.05) with the same tip size. The new manufacturing processes appeared to offer greater resistance to cyclic fatigue in a simulated canal model.

Electrochemical characterization of cast titanium alloys.

A reaction layer forms on cast titanium alloy surfaces due to the reaction of the molten metal with the investment. This surface layer may affect the corrosion of the alloy in the oral environment. The objective of this study was to characterize the in vitro corrosion behavior of cast titanium alloys. ASTM Grade 2 CP titanium, Ti-6Al-4V, Ti-6Al-7Nb and Ti-13Nb-13Zr alloys were cast into a MgO-based investment. Experiments were performed on castings (N=4) with three surface conditions: (A) as-cast surface after sandblasting, (B) polished surface after removal of the reaction layer, and (C) sandblasted surface after removal of the reaction layer. Open-circuit potential (OCP) measurement, linear polarization, and potentiodynamic cathodic polarization were performed in aerated (air+10% CO(2)) modified Tani-Zucchi synthetic saliva at 37 degrees C. Potentiodynamic anodic polarization was subsequently conducted in the same medium deaerated with N(2)+10% CO(2) gas 2 h before and during the experiment. Polarization resistance (R(P)) and corrosion rate (I(CORR)) were calculated. Numerical results were subjected to nonparametric statistical analysis at alpha=0.05. The OCP stabilized for all the specimens after 6 x 10(4)s. Apparent differences in anodic polarization were observed among the different surfaces for all the metals. A passivation region followed by breakdown and repassivation were seen on specimens with surfaces A and C. An extensive passive region was observed on all the metals with surface B. The Kruskal-Wallis test showed no significant differences in OCP, R(p), I(CORR) or break down potential for each of the three surfaces among all the metals. The Mann-Whitney test showed significantly lower R(P) and higher I(CORR) values for surface C compared to the other surfaces. Results indicate that the surface condition has more effect on corrosion of these alloys than the surface reaction layer. Within the oxidation potential range of the oral cavity, all the metal/surface combinations examined showed excellent corrosion resistance.

Joint strength of laser-welded titanium

OBJECTIVE The objective of this study was to examine the joint strength of titanium laser-welding using several levels of laser output energy [current (A)]. METHODS Cast titanium plates (0.5 x 3.0 x 40 and 1.0 x 3.0 x 40 mm(3)) were prepared and perpendicularly cut at the center of the plate. After the cut halves were fixed in a jig, they were laser-welded using a Nd: YAG laser at several levels of output energy in increments of 30A from 180 to 300A. The penetration depths of laser to titanium were measured under various conditions for output energy, pulse duration, and spot diameter to determine the appropriate conditions for these parameters. Based on the correlation between the results obtained for penetration depth and the size of the specimens (thickness: 0.5 and 1.0 mm, width: 3.0 mm), the pulse duration and spot diameter employed in this study were 10 ms and 1.0 mm, respectively. Three laser pulses (spot diameter: 1.0 mm) were applied from one side to weld the entire joint width (3.0 mm) of the specimens. Uncut specimens served as the non-welded control specimens. Tensile testing was conducted at a crosshead speed of 2 mm/min and a gage length of 10 mm. The breaking force (N) was recorded, and the data (n=5) were statistically analyzed. RESULTS For the 0.5 mm thick specimens, the breaking force of the specimens laser-welded at currents of 240, 270, and 300A were not statistically (P>0.05) different from the non-welded control specimens. There were no significant differences in breaking force among the 1.0mm thick specimens laser-welded at currents of 270 and 300A, and the non-welded control specimens. SIGNIFICANCE Under appropriate conditions, joint strengths similar to the strength of the non-welded parent metal were achieved.

Effect of Pressure Difference on the Quality of Titanium Casting

In casting titanium using a two-compartment casting machine, Herø et al. (1993) reported that the pressure difference between the melting chamber and the mold chamber affected the soundness of the castings. This study tested the hypothesis that differences in pressure produce castings with various amounts of porosity and different mechanical properties values. Plastic dumbbell-shaped patterns were invested with an alumina-based, phosphate-bonded investment material. Both chambers of the casting machine were evacuated to 6 x 10-2 torr; the argon pressure difference was then adjusted to either 50, 150, 300, or 450 torr. The porosity of the cast specimens was determined by x-ray radiography and quantitative image analysis. Tensile strength and elongation were measured by means of a universal testing machine at a strain rate of 1.7 x 10-4/s. The fractured surfaces were examined by SEM. Changes in Vickers hardness with depth from the cast surface were measured on polished cross-sections of the specimens. Raising the argon pressure difference to 300 and 450 torr caused a significant increase in internal porosity and a resultant decrease in the engineering tensile strength and elongation. The highest tensile strength (- 540 MPa), elongation (- 10%), bulk hardness (HV50g 209), and lowest porosity level (- 0.8%) occurred in the specimens cast at 150 torr. Turbulence of the metal during casting was thought to be responsible for the increase in porosity levels with the increase in argon pressure difference. By choosing an argon pressure difference (around 150 torr) suitable for this geometry, we could produce castings which have adequate mechanical properties and low porosity levels.

Physical and Chemical Properties of New-generation Endodontic Materials

INTRODUCTION Mineral trioxide aggregate (MTA), white and gray, has many uses in endodontic therapy but is limited by its difficult handling characteristics. This study compared the physical and chemical properties of white MTA (WMTA) with three experimental root-end filling materials: Capasio (Primus Consulting, Bradenton, FL), Ceramicrete-D (Tulsa Dental Specialties/Argonne National Laboratory, Argonne, IL), and Generex-A (Dentsply Tulsa Dental Specialties, Tulsa, OK). METHODS The setting time and radiopacity were tested using International Organization for Standardization (ISO) 6876 methods. Compressive strength was measured following the ISO 9917 method. The pH of the materials was measured after mixing. A novel test was developed for washout resistance of the materials immediately after placement. Data were compared by analysis of variance and Sidak post hoc analysis (p<0.05) for compressive strength and washout resistance. RESULTS The setting time of Generex-A was half that of WMTA. All materials met the ISO 6876 requirements for radiopacity. The compressive strengths after 7 days decreased in this order: Generex-A>Capasio>WMTA>Ceramicrete-D. The initial pH of Capasio and Generex-A were alkaline, similar to WMTA, whereas that of Ceramicrete-D was acidic. Significantly, alternative materials remained in situ after the washout test, whereas WMTA was displaced from the retropreparations. CONCLUSIONS The clinical handling and washout resistance of the alternative materials were far superior to WMTA. The radiopacity, compressive strength, and washout resistance make Generex-A and Capasio materials suitable for further study. Ceramicrete-D was weaker, less radiopaque, and initially acidic.

Shear bond strengths of polymethyl methacrylate to cast titanium and cobalt-chromium frameworks using five metal primers

STATEMENT OF PROBLEM Poor chemical bonding of a denture base resin to cast titanium frameworks often introduces adhesive failure and increases microleakage. PURPOSE This study examined the shear bond strengths of a denture base resin to cast pure titanium, Ti-6Al-4V, and a cobalt-chromium alloy using various adhesive primers. MATERIAL AND METHODS Disks (6.0 mm diameter, 2.5 mm thick) were cast of the 3 alloys. The disk surfaces were grit-blasted with 50 microm alumina and treated with 5 different metal primers (Metal Primer II ¿MP]; Cesead Opaque primer ¿OP]; Meta Base ¿MB]; experimental primer ¿EP]; Siloc bonding system ¿SI]). A denture base resin (Palapress Vario) was then applied on the disks with hole-punched sticky tape (bonding area of 5.0 mm) and a Teflon (PTFE, New Age Industries Inc, Willow Grove, Pa.) ring (6.0 mm diameter x 2.0 mm thick). Specimens without primer were also prepared as controls. All specimens were immersed in 37 degrees C water and thermocycled up to 2,000 cycles. Shear bond strength values were determined at a crosshead speed of 0.5 mm/min. Data were statistically analyzed using 3-way ANOVA, followed by 1-way ANOVA and the Scheffé multiple range test. RESULTS Primers significantly (P <.05) improved shear bond strengths of denture base resin to all metals, among which no significant differences were found. Specimens primed with OP, MP, and EP showed higher bond strengths than did those primed with MB. After thermocycling, the bond strengths of MB and SI decreased substantially; MB showed the least durability (22.8% to 35.5% decrease) among the primers. CONCLUSION The application of 5 primers significantly improved the shear bond strengths of a denture base resin to cast CP titanium, Ti-6Al-4V, and Co-Cr alloy. OP and MP primers exhibited greater bond strength and durability than did MB and SI.

Surface changes induced by fluoride prophylactic agents on titanium-based orthodontic wires☆

This study investigated the effect of fluoride prophylactic agents on the surfaces of titanium-based orthodontic wires. Four types of titanium-based orthodontic wires (2 nickel-titanium alloy wires [nickel-titanium and copper-nickel-titanium] and 2 beta-titanium alloy wires [titanium-molybdenum and titanium-niobium], all from Ormco, Glendora, Calif) with similar sizes were prepared and immersed in 5 fluoride prophylactic agents (2 acidulated phosphate fluoride agents [Nupro APF (Dentsply International, York, Pa) and Florentine III (Confi-Dental, Louisville, Colo)], 1 neutral agent [Neupro Neutral (Dentsply International)] and 2 stannous fluoride agents [Florentine II (Confi-Dental) and Perio-Med (Omni International, Warrenton, Va)]) for 5 minutes, 1 hour, and 24 hours. After immersion, average surface roughness and color changes were evaluated. The surface changes were observed with a scanning electron microscope. The average surface roughness data were statistically analyzed by analysis of variance and Tukey post hoc test at a significance level of alpha = 0.05. There were no significant differences in average surface roughness value among fluoride solutions or orthodontic wires, except for the titanium-molybdenum wire, which showed significantly (P <.05) higher average surface roughness values after immersion in Nupro APF for 24 hours. The results suggested that a few applications of acidulated phosphate fluoride agents might change the surface color of the beta-titanium alloy wires, particularly the titanium-molybdenum wire, which contains a large amount (about 80%) of titanium.

In vitro osteogenic/dentinogenic potential of an experimental calcium aluminosilicate cement.

INTRODUCTION Calcium aluminosilicate cements are fast-setting, acid-resistant, bioactive cements that may be used as root-repair materials. This study examined the osteogenic/dentinogenic potential of an experimental calcium aluminosilicate cement (Quick-Set) by using a murine odontoblast-like cell model. METHODS Quick-Set and white ProRoot MTA (WMTA) were mixed with the proprietary gel or deionized water, allowed to set completely in 100% relative humidity, and aged in complete growth medium for 2 weeks until rendered non-cytotoxic. Similarly aged Teflon disks were used as negative control. The MDPC-23 cell line was used for evaluating changes in mRNA expressions of genes associated with osteogenic/dentinogenic differentiation and mineralization (quantitative reverse transcription polymerase chain reaction), alkaline phosphatase enzyme production, and extracellular matrix mineralization (alizarin red S staining). RESULTS After MDPC-23 cells were incubated with the materials in osteogenic differentiation medium for 1 week, both cements showed up-regulation in ALP and DSPP expression. Fold increases in these 2 genes were not significantly different between Quick-Set and WMTA. Both cements showed no statistically significant up-regulation/down-regulation in RUNX2, OCN, BSP, and DMP1 gene expression compared with Teflon. Alkaline phosphatase activity of cells cultured on Quick-Set and WMTA were not significantly different at 1 week or 2 weeks but were significantly higher (P < .05) than Teflon in both weeks. Both cements showed significantly higher calcium deposition compared with Teflon after 3 weeks of incubation in mineralizing medium (P < .001). Differences between Quick-Set and WMTA were not statistically significant. CONCLUSIONS The experimental calcium aluminosilicate cement exhibits similar osteogenic/dentinogenic properties to WMTA and may be a potential substitute for commercially available tricalcium silicate cements.

Effect of two metal primers on adhesive bonding with type IV gold alloys.

Bond strengths of an adhesive resin bonded to two types of gold alloys were investigated in vitro with two different metal primers. Disk specimens were cast in a type IV gold alloy designed for resin-bonded restorations and in a low-temperature age-hardenable gold alloy. The specimens were primed with either a vinyl-thiol primer or a thiophosphate primer, then bonded with an adhesive resin initiated with tri-n-butyl borane derivative. Both primers effectively enhanced bond between gold alloys and the adhesive. The use of metal primers in conjunction with type IV gold alloys is useful for resin-bonded fixed partial dentures.

Accelerated bone formation on photo-induced hydrophilic titanium implants: an experimental study in the dog mandible

OBJECTIVES The purpose of this study was to investigate the effect of photo-induced hydrophilic titanium dioxide (TiO₂) on serum fibronectin (sFN) attachment, and further to evaluate initial osseointegration responses in the dog mandibles. MATERIALS AND METHODS To apply the anatase TiO₂ film, plasma source ion implantation (PSII) method followed by annealing was employed for the titanium disks and implants, which were then illuminated with UV-A for 24 h for the experimental groups. Non-deposited titanium disks and implants were prepared for the control group. Surface characterization was performed using the interferometer and contact angle analyzer. The attachments of sFN were evaluated using fluorescence emission analysis. Thereafter both groups of implants were placed in the mandible of six beagle dogs. Bone response was investigated with histological and histomorphometrical analyses after periods of 2 and 4 weeks. RESULTS The experimental groups exhibited strong hydrophilicity under UV-A illumination and showed significant improvement in sFN attachment. And further, the experimental implants enhanced the bone formation with the bone-to-implant contact of 42.7% after 2 weeks of healing (control: 28.4%). CONCLUSIONS The combined applications of plasma fibronectin and PSII to produce hydrophilic titanium surfaces could accelerate early osseointegration.