Ikuya Watanabe

Nagasaki University, Nagasaki, Nagasaki, Japan

Are you Ikuya Watanabe?

Claim your profile

Publications (75)147.6 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This study compared biomechanical patterns between finite element models (FEM) and a fresh dog mandible tested under molar and incisal physiological loads in order to clarify the effect of the bone transport distraction osteogenesis surgical process. Three FEM of dog mandibles were built in order to evaluate the effects of bone transport distraction osteogenesis. The first model evaluated the mandibular response under two physiological loads resembling bite processes. In the second model, a 5.0 cm bone defect was bridged with a bone transport reconstruction plate (BTRP). In the third model, new regenerated bony tissue was incorporated within the defect to mimic the surgical process without the presence of the device. Complementarily, a mandible of a male American foxhound dog was mechanically tested in the laboratory both in the presence and absence of a BTRP, and mechanical responses were measured by attaching rosettes to the bone surface of the mandible to validate the FEM predictions. The relationship between real and predicted values indicates that the stress patterns calculated using FEM is a valid predictor of the biomechanics of the bone transport distraction osteogenesis procedures. The present study provides an interesting correlation between the stiffness of the device and the biomechanical response of the mandible affected for bone transport.
    Journal of biomechanical engineering. 08/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We evaluated the influence of composition and powder/liquid (P/L) ratio on the setting characteristics and mechanical properties of autopolymerized hard direct denture reline resins composed of methyl methacrylate (MMA, monomethacrylate) and ethylene glycol dimethacrylate [EGDMA, dimethacrylate (cross-linking agent)], with poly (ethyl methacrylate) used as the powder, and a mixture of MMA and EGDMA containing p-tolyldiethanolamine as the monomer. Setting times were determined using an oscillating rheometer and mechanical properties were based on ISO specifications. Setting time increased exponentially with an increase in the ratio of EGDMA to MMA and decrease in P/L ratio. Materials with a liquid component of approximately 75-85 wt% EGDMA and a higher P/L ratio showed higher ultimate flexural strength and flexural modulus. Our results suggest that setting characteristics are more influenced by the ratio of monomethacrylate and cross-linking agent, whereas mechanical properties are more influenced by P/L ratio.
    Dental Materials Journal 07/2014; · 0.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Tricalcium silicate cements have been successfully employed in the biomedical field as bioactive bone and dentin substitutes, with widely acclaimed osteoactive properties. This research analyzed the effects of different tricalcium silicate cement formulations on the temporal osteoactivity profile of human bone marrow-derived mesenchymal stem cells (hMW-MSCs). These cells were exposed to 4 commercially-available tricalcium silicate cement formulations in osteogenic differentiation medium. After 1, 3, 7 and 10 days, quantitative real time-polymerase chain reaction and Western blotting were performed to detect the expression of target osteogenic markers ALP, RUNX2, OSX, OPN, MSX2, and OCN. After 3, 7, 14 and 21 days, alkaline phosphatase assay was performed to detect changes in intracellular enzyme level. Alizarin Red S assay was performed after 28 days to detect extracellular matrix mineralization. In the presence of tricalcium silicate cements, target osteogenic markers were downregulated at the mRNA and protein levels at all time-points. Intracellular alkaline phosphatase enzyme levels and extracellular mineralization of the experimental groups were not significantly different from the untreated control. Quantitative polymerase chain reaction results showed increases in downregulation of RUNX2, OSX, MSX2 and OCN with increase in time of exposure to the tricalcium silicate cements, while ALP showed peak downregulation at day 7. For Western blotting, OSX, OPN, MSX2 and OCN showed increased downregulation with increased exposure time to the tested cements. Alkaline phosphatase enzyme levels generally declined after day 7. Based on these results, it is concluded that tricalcium silicate cements do not induce osteogenic differentiation of hBM-MSCs in vitro.
    Acta biomaterialia 04/2014; · 5.09 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Bone transport distraction osteogenesis (BTDO) is a surgical procedure that has been used over the last 30 years for the correction of segmental defects produced mainly by trauma and oncological resections. Application of BTDO has several clinical advantages over traditional surgical techniques. Over the past few years, several BTDO devices have been introduced to reconstruct mandibular bone defects. Based on the location and outline of the defect, each device requires a uniquely shaped reconstruction plate. To date, no biomechanical evaluations of mandibular BTDO devices have been reported in the literature. The present study evaluated the mechanical behavior of three different shaped prototypes of a novel mandibular bone transport reconstruction plate and its transport unit for the reconstruction of segmental bone defects of the mandible by using numerical models complemented with mechanical laboratory tests to characterize strength, fatigue, and stability. The strength test evaluated device failures under extreme loads and was complemented with optimization procedures to improve the biomechanical behavior of the devices. The responses of the prototypes were characterized to improve their design and identify weak and strong regions in order to avoid posterior device failure in clinical applications. Combinations of the numerical and mechanical laboratory results were used to compare and validate the models. In addition, the results remark the importance of reducing the number of animals used in experimental tests by increasing computational and in vitro trials.
    Journal of Medical Devices-Transactions of the Asme. 01/2014; 8(2).
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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. 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). 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. The experimental calcium aluminosilicate cement exhibits similar osteogenic/dentinogenic properties to WMTA and may be a potential substitute for commercially available tricalcium silicate cements.
    Journal of endodontics 09/2013; 39(9):1161-6. · 2.95 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this study was to investigate the proper time to restore composite resin over mineral trioxide aggregate (MTA). Thirty-five samples of MTA blocks were divided into 7 groups with 3 different times (10 minutes, 1 day, and 7 days) selected for restoring the composite resin over MTA with and without bonding resin, and a control group was included for comparison. After 21 days, the distances between MTA and the composite resin or between MTA and the bonding agent on sectioned planes along the long axis were measured using a scanning electron microscope (×2,000 magnification). The hardness of the MTA near the composite resin was presented as the Vickers microhardness. There were no gaps at the interface in the 10-minute groups, the 1-day group with a bonding agent, and the 7-day group with a bonding agent. The groups without a bonding agent at 1 and 7 days presented a separation or gap at the interface. The value of the Vickers microhardness in the 1-day groups was significantly decreased compared with those of the other groups regardless of the presence or absence of a bonding agent. These findings suggest that composite resin with a bonding agent over MTA can be restored almost immediately after MTA mixing during a single visit.
    Journal of endodontics 09/2013; 39(9):1167-70. · 2.95 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: CPoint is a polymeric endodontic point that takes advantage of water-induced, non-isotropic radial expansion to adapt to canal irregularities. This study evaluated the effects of CPoint on the viability and mineralization potential of odontoblast-like cells. The biocompatibility of CPoint and commercially available gutta-percha points was evaluated by using a rat odontoblast-like cell line (MDPC-23). Cell viability was evaluated with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, flow cytometry, and confocal laser scanning microscopy. The mineralization potential of MDPC-23 cells, in the presence of the root-filling materials, was evaluated by examining the changes in osteogenic gene marker expression (quantitative real-time polymerase chain reaction), alkaline phosphatase activity, alizarin red S assay, and transmission electron microscopy. CPoint showed higher initial cytotoxicity compared with gutta-percha and Teflon (P < .05), which became nonsignificant after 4 immersion cycles. Significant differences were also found between eluents from CPoint and gutta-percha at 1:1 concentration (P < .05) but not at 1:10 or 1:100 concentration. Both materials induced minimal apoptosis-induced alteration in plasma membrane permeability, as evidenced by flow cytometry and confocal laser scanning microscopy. Compared with the Teflon negative control, CPoint and gutta-percha groups showed up-regulation of most osteogenic gene markers except for dentin sialophosphoprotein, which was down-regulated. Alkaline phosphatase activity and alizarin red assay for CPoint and gutta-percha were both significantly higher than for Teflon but not significantly different from each other (P > .05). Transmission electron microscopy showed discrete nodular electron-dense mineralization foci in all 3 groups. The in vitro biocompatibility of CPoint is comparable to gutta-percha with minimal adverse effects on osteogenesis after elution of potentially toxic components.
    Journal of endodontics 07/2013; 39(7):883-8. · 2.95 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study evaluated the effects of the fluorinated monomer of 2,2,2-trifluoroethyl methacrylate (TFEMA) on the properties of autopolymerized hard direct denture reline resins. Iso-butyl methacrylate (i-BMA) and 2-hydroxyethyl methacrylate (2-HEMA) containing 30% TFEMA by weight were used as monomers, while poly(ethyl methacrylate) was used as a powder. Setting characteristics, dynamic mechanical properties, and changes over time, as well as wettability were determined by use of an oscillating rheometer, dynamic viscoelastometer, and contact angle meter. Water absorption and solubility were also measured according to ISO specifications. The reline resin based on i-BMA had greater elasticity and stiffness properties, while that based on 2-HEMA showed fewer dynamic mechanical property changes over time with the addition of TFEMA. Furthermore, water absorption and solubility tended to be reduced and contact angle increased. The results of this study suggest that TFEMA improves mechanical properties and durability of reline resins over time.
    Dental Materials Journal 01/2013; 32(5):744-752. · 0.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mineral trioxide aggregate (MTA) has been used successfully for perforation repair, vital pulpotomies, and direct pulp capping. However, little is known about the interactions between MTA and glass ionomer cement (GIC) in final restorations. In this study, 2 null hypotheses were tested: (1) GIC placement time does not affect the MTA-GIC structural interface and hardness and (2) moisture does not affect the MTA-GIC structural interface and hardness. Fifty cylinders were half filled with MTA and divided into 5 groups. The other half was filled with resin-modified GIC either immediately after MTA placement or after 1 or 7 days of temporization in the presence or absence of a wet cotton pellet. The specimens were then sectioned, carbon coated, and examined using a scanning electron microscope and an electron probe microanalyzer (SEM-EPMA) for interfacial adaptation, gap formation, and elemental analysis. The Vickers hardness numbers of the interfacial MTA were recorded 24 hours after GIC placement and 8 days after MTA placement and analyzed using the analysis of variance test. Hardness testing 24 hours after GIC placement revealed a significant increase in hardness with an increase of temporization time but not with a change of moisture conditions (P < .05). Hardness testing 8 days after MTA placement indicated no significant differences among groups. SEM-EPMA showed interfacial adaptation to improve with temporization time and moisture. Observed changes were limited to the outermost layer of MTA. The 2 null hypotheses were not rejected. GIC can be applied over freshly mixed MTA with minimal effects on the MTA, which seemed to decrease with time.
    Journal of endodontics 08/2012; 38(8):1126-9. · 2.95 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To investigate the effect of laser surface treatment of cast titanium alloy on microstructure and mechanical properties. Dumbbell- and plate-shaped cast titanium specimens were prepared for mechanical testing and microstructure analysis. After the cast surfaces of each specimen were laser-treated using a dental Nd:YAG laser machine at 240 V and 300 V with and without argon gas shielding, tensile testing and microstructure analysis were conducted. Hardness depth profiles were also made from the cross-section of laser-treated cast specimens. Microstructural and chemical analysis were performed by means of the SEM, XRD, AES and WDS. The results of tensile testing and Vickers hardness depth profiling showed that laser treatment improved the mechanical properties. Bulk microstructure of as-cast titanium was mainly composed of α-grains with acicular and widmanstatten patterns. The laser melted zone was characterized by columnar beta grains. When the emission voltage of laser increased to 300V, a larger grain size was promoted. The XRD analysis indicated that the beta phase formation was clearly noticeable after laser surface treatment. Supplementary marked peaks of the TiO, TiO(2) and Ti(2)N were detected without argon gas shielding. When argon shielding gas was used, the presence of titanium oxide was significantly reduced and the peaks of titanium nitride disappeared. Laser treatment on cast titanium surfaces showed significant enhancement of mechanical properties and modification of microstructures, and therefore could produce reliable titanium metal frameworks for dental prostheses.
    Dental materials: official publication of the Academy of Dental Materials 05/2012; 28(9):945-51. · 2.88 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To compare the deflection load characteristics of homogeneous and heterogeneous joints made by laser welding using various types of orthodontic wires. Four kinds of straight orthodontic rectangular wires (0.017 inch × 0.025 inch) were used: stainless-steel (SS), cobalt-chromium-nickel (Co-Cr-Ni), beta-titanium alloy (β-Ti), and nickel-titanium (Ni-Ti). Homogeneous and heterogeneous end-to-end joints (12 mm long each) were made by Nd:YAG laser welding. Two types of welding methods were used: two-point welding and four-point welding. Nonwelded wires were also used as a control. Deflection load (N) was measured by conducting the three-point bending test. The data (n  =  5) were statistically analyzed using analysis of variance/Tukey test (P < .05). The deflection loads for control wires measured were as follows: SS: 21.7 ± 0.8 N; Co-Cr-Ni: 20.0 ± 0.3 N; β-Ti: 13.9 ± 1.3 N; and Ni-Ti: 6.6 ± 0.4 N. All of the homogeneously welded specimens showed lower deflection loads compared to corresponding control wires and exhibited higher deflection loads compared to heterogeneously welded combinations. For homogeneous combinations, Co-Cr-Ni/Co-Cr-Ni showed a significantly (P < .05) higher deflection load than those of the remaining homogeneously welded groups. In heterogeneous combinations, SS/Co-Cr-Ni and β-Ti/Ni-Ti showed higher deflection loads than those of the remaining heterogeneously welded combinations (significantly higher for SS/Co-Cr-Ni). Significance (P < .01) was shown for the interaction between the two factors (materials combination and welding method). However, no significant difference in deflection load was found between four-point and two-point welding in each homogeneous or heterogeneous combination. Heterogeneously laser-welded SS/Co-Cr-Ni and β-Ti/Ni-Ti wires provide a deflection load that is comparable to that of homogeneously welded orthodontic wires.
    The Angle Orthodontist 11/2011; 82(4):698-702. · 1.18 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This case report presents treatment of two patients with the usual characteristics of Cleidocranial Dysostosis. A multidisciplinary approach using the disciplines of prosthodontics, orthodontics, and oral surgery was effected. Exfoliation of the patient's deciduous teeth and failure of permanent anterior tooth eruption led to emotional, social, and self-esteem issues in both patients. Due to the psychosocial issues confronting these two patients, esthetics was addressed prior to active intervention with orthodontics and after some surgical intervention. The use of two interim overdenture prostheses with magnetic retention is described.
    Journal of Prosthodontics 10/2011; 20 Suppl 2:S20-5. · 0.68 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To investigate the effects of internally connected engaging component position in screw-retained fixed cantilevered prostheses. Twenty-one three-unit fixed dental prostheses (FDPs) were cast in high-palladium alloy in three groups. In group A, engaging components were incorporated into the units away from the cantilevered segment; proximal units received nonengaging components. In group B, these positions were reversed. Control specimens were fabricated using all nonengaging components. Specimens were attached to internally connected 3.5 (diameter) × 13 mm (length) implants, torqued to 32 Ncm, and embedded into epoxy resin. Specimens were tested in cyclic fatigue with a 2 Hz sine wave and 0.1 min/max load ratio. Load amplitude started at 1.8 N and increased by 1.8 N every 60 cycles until fracture. Log-rank statistic, ANOVA, Spearman's correlation, and LIFETEST procedures were used to evaluate level of statistical significance within the results. In the control group, the mean number of cycles to fracture was 31,205 ± 2639. Mean axial force at fracture was 932 ± 78 N. In group A, these numbers were 38,160 ± 4292 and 1138 ± 128 N, and in group B, 31,810 ± 3408 and 949 ± 101 N. Statistical significance levels for number of cycles to fracture were: Control versus group A, p = 0.0117, and groups A versus B, p = 0.0156 (statistically significant). Control versus group B, p = 0.357 (not statistically significant). Log-rank statistic for the survival curves is greater than would be expected by chance; there was a statistically significant difference between survival curves (p = 0.012). The location and mode of failure were noteworthy (always in the abutment screw). The position of the engaging component had significant effects on the results. Within the limitations of this investigation, it can be concluded that using an engaging abutment in a screw-retained fixed cantilevered FDP provides a mechanical advantage, and engaging the implant furthest from the cantilever when designing a screw-retained cantilever FDP increased resistance to fracture of the distal abutment screw.
    Journal of Prosthodontics 05/2011; 20(5):348-54. · 0.68 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This study investigated the effect of laser treatment on the fatigue resistance of a 3.5-mm diameter implant with an internal trilobe connection. Twenty two implants were embedded into acrylic resin blocks. Half the specimens were used as control group, and the other half were laser treated circumferentially around the 1.5-mm polished collar with argon shielding. Implants were fatigue tested using a step-stress accelerated lifetime test in a servo-hydraulic test machine. Despite the trend pointing towards higher fatigue resistance of laser treated specimens versus controls, step-stress analysis did not determine significant differences in the fatigue lifetimes.
    The European journal of prosthodontics and restorative dentistry 03/2011; 19(1):2-6.
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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). 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. 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. 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.
    Journal of endodontics 03/2010; 36(3):524-8. · 2.95 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study investigated the cytotoxicity of elemental ions contained in four fixed prosthodontic materials (gold, nickel-chromium, stainless-steel alloys and CAD-CAM ceramics). According to the determination of elements released from prosthodontic materials by using inductively coupled plasma mass spectroscopy, similar amounts of elements Pd, Ag, Zn, Cu, Ni, Cr, Mo, Be, Fe, Al, and K were prepared as salt solutions. Wells with a tenfold higher concentration of the tested elements were used as positive controls, while a well without any tested element was used as a negative control. These salt solutions were tested for cytotoxicity by culturing mouse L-929 fibroblasts in the salt solutions for a 7-day period of incubation. Then, the percentage of viable cells for each element was measured using trypan blue exclusion assay. The data (n=5) were statistically analyzed by ANOVA/Tukey test (p<0.05). The results showed a statistically significant difference for the cytotoxic effect of the tested elements salt solutions. For the released element concentrations the lowest percentage of viable cells (mean+/-SD) was evident with Zn, Cu or Ni indicating that they are the highly toxic elements. Be and Ag were found to be intermediate in cytotoxic effect. Fe, Cr, Mo, Al, Pd or K were found to be the least cytotoxic elements. Zn and Cu released from gold alloys, and Ni released from nickel-chromium alloys, which are commonly used as fixed prosthodontic restorations, show evidence of a high cytotoxic effect on fibroblast cell cultures.
    Dental materials: official publication of the Academy of Dental Materials 09/2009; 25(12):1551-5. · 2.88 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Reducing the force between the implant and the bone by recapitulating a similar matrix has the potential to reduce implant failure. To begin to pursue the goal of creating a periodontal ligament interface between a dental implant and bone, the mechanism of cellular attachment to dental implant surfaces must be characterized. In this study we examined the role of integrin receptors in the attachment of periodontal ligament fibroblasts to titanium surfaces utilized on dental implants; those surfaces included smooth polished titanium, acid pickled titanium, ground titanium, sandblasted and acid etched titanium, non-oxidized titanium that has been sandblasted and acid etched, hydroxyapatite coated titanium, titanium plasma sprayed or uncoated titanium. For these studies integrin mediated fibroblast attachment was blocked by the integrin blocking peptide GRGDSP or anti-integrin beta1 antibody or a combination of the two. Quantitation of periodontal ligament fibroblast attachment was completed by counting cells on the various implant surfaces after culturing in vitro for 24h with and without the integrin receptor blockers. Antibody and peptide treatment significantly reduced the number of fibroblasts cells attached to the various implant surfaces but this effect varied significantly depending on the surface. Moreover, increased levels of peptide further decreased fibroblasts attachment in a dose dependent manner. Blocking studies suggest first, that integrin receptors function in periodontal ligament attachment to titanium surfaces and second, that different integrin subunits are important in attachment to a particular surface.
    Dental materials: official publication of the Academy of Dental Materials 03/2009; 25(7):877-83. · 2.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Journal of endodontics 03/2009; 35(3):401-3. · 2.95 Impact Factor
  • Waleed Elshahawy, Ikuya Watanabe, Mari Koike
    [Show abstract] [Hide abstract]
    ABSTRACT: Elemental release is important because it plays a significant role in material biocompatibility. The aim of this study was to investigate the release of metal ions from four fixed prosthodontic materials. Specimens were prepared using the conventional lost wax technique for gold and nickel-chromium (Ni-Cr) alloys, and by cutting blocks and bar for CAD-CAM ceramic and stainless-steel (St-St) alloy, respectively. All specimens were polished (600grit SiC paper), and ultrasonically cleaned with ethanol for 5min. After they were immersed in 0.9% sodium chloride (NaCl) and 1% lactic acid, and were kept at 37 degrees C for 7 days, the elemental release (mug/cm(2)) from each material was analyzed by using inductively coupled plasma mass spectroscopy. The rate (n=5) was statistically analyzed by ANOVA/Tukey test (p<0.05). Two immersion blank solutions were used as a negative control group. Higher elemental release (mean+/-S.D.) of all elements from all materials was evident into the lactic acid solution except for Ag. In the gold alloy, there was significant difference (p<0.05) between Zn and other released elements in the NaCl solution, and it also revealed significant difference between Pd or Ag and Cu which detection value was more than Zn (but no statistical difference) into lactic acid solution. The Ni was significantly more released from Ni-Cr alloy than the other elements into both NaCl and lactic acid solutions. The same was observed for Fe released from St-St alloy. There was more significant release of K than Al from CAD-CAM ceramic in only NaCl solution. Transient exposure of tested materials to an acidic environment is likely to significantly increase the elemental release from them. The significant higher release of Ni from Ni-Cr alloy, and Zn, Cu from gold alloy was evident.
    Dental materials: official publication of the Academy of Dental Materials 03/2009; 25(8):976-81. · 2.88 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this study was to investigate the effect of laser surface treatment on the mechanical properties of cast titanium and to compare with those of the Co-Cr alloy. Dumbbell-shaped cast specimens were prepared for commercially pure titanium (grade 2) and Co-Cr alloy. The cast titanium specimens were laser-treated on the surface using a dental Nd:YAG laser machine at 240 V and 300 V. After laser treatment, tensile testing was conducted to obtain the tensile strength, percent elongation and modulus of elasticity. The hardness depth profile was made from the cast subsurface (25 microm) to 1500 microm in depth using the cross-sections of the cast rods with the same diameter as the dumbbell. The data were statistically analyzed by ANOVA/post hoc tests (p<0.05). The highest tensile strength was obtained for the titanium specimens laser-treated with 300 V followed by the 240 V and the control specimens. The laser-treated titanium specimens with 300 V showed a tensile strength equivalent to the Co-Cr alloy. Although the highest modulus of elasticity was found for the specimens laser-treated with 240 V, there were no significant differences in elastic modulus among 240 V, 300 V and Co-Cr. The laser-treated groups showed significantly lower hardness at the subsurface of 25 microm and maintained their hardness until the depth of 400 microm. The hardness of the control group was very high at 25 microm depth, and dramatically decreased until the 200 microm depth. The results of tensile testing and hardness depth-profiling indicated that the laser treatment significantly improved the mechanical properties of cast titanium by improving the surface integrity of the cast surface contamination.
    Dental materials: official publication of the Academy of Dental Materials 01/2009; 25(5):629-33. · 2.88 Impact Factor

Publication Stats

706 Citations
147.60 Total Impact Points

Institutions

  • 1994–2014
    • Nagasaki University
      • • Department of Dental and Biomedical Materials Science
      • • School of Dentistry
      Nagasaki, Nagasaki, Japan
  • 1999–2011
    • Baylor College of Dentistry
      • • Division of Biomaterials Science
      • • Department of Endodontics
      Dallas, Texas, United States
  • 2007
    • Kagawa University
      • Faculty of Engineering
      Takamatsu-shi, Kagawa-ken, Japan
  • 2000–2006
    • Tsurumi University
      • Department of Removable Prosthodontics
      Yokohama, Kanagawa, Japan
  • 2005
    • Texas A&M University System Health Science Center
      Bryan, Texas, United States