[Show abstract][Hide abstract] ABSTRACT: In the present study, sol–gel derived nanoparticle calcium silicate bioactive glass was added to the resin-modified light cure glass-ionomer cement to assess the influence of additional bioactive glass nanoparticles on the mechanical and biological properties of resin-modified glass-ionomer cement. The fabricated bioactive glass nanoparticles added resin-modified glass-ionomer cements (GICs) were immersed in the phosphate buffer solution for 28 days to mimic real condition for the mechanical properties. Resin-modified GICs containing 3, 5 and 10 % bioactive glass nanoparticles improved the flexural strength compared to the resin-modified glass-ionomer cement and the samples containing 15 and 20 % bioactive glass nanoparticles before and after immersing in the phosphate buffer solution. Characterization of the samples successfully expressed the cause of the critical condition for mechanical properties. Cell study clarified that resin-modified glass-ionomer cement with high concentrations of bioactive glass nanoparticles has higher cell viability and better cell morphology compare to control groups. The results for mechanical properties and toxicity approved that the considering in selection of an optimum condition would have been a more satisfying conclusion for this study.
Full-text · Article · Jan 2016 · Journal of Materials Science Materials in Medicine
[Show abstract][Hide abstract] ABSTRACT: This study assessed methods for evaluation of glass transition temperature (Tg) of autopolymerized hard direct denture reline resins using dynamic mechanical analysis and differential scanning calorimetry in addition to the dynamic mechanical properties. The Tg values of 3 different reline resins were determined using a dynamic viscoelastometer and differential scanning calorimeter, and rheological parameters were also determined. Although all materials exhibited higher storage modulus and loss modulus values, and a lower loss tangent at 37˚C with a higher frequency, the frequency dependence was not large. Tg values obtained by dynamic mechanical analysis were higher than those by differential scanning calorimetry and higher frequency led to higher Tg, while more stable Tg values were also obtained by that method. These results suggest that dynamic mechanical analysis is more advantageous for characterization of autopolymerized hard direct denture reline resins than differential scanning calorimetry.
Full-text · Article · Feb 2015 · Dental Materials Journal
[Show abstract][Hide abstract] ABSTRACT: This study investigated the possibility of electrical and laser welding to connect titanium-based alloy (beta-titanium and nickel-titanium) wires and stainless-steel or cobalt-chromium alloy wires for fabrication of combination arch-wires. Four kinds of straight orthodontic rectangular wires (0.017 × 0.025 inch) were used: stainless-steel (S-S), cobalt-chromium (Co-Cr), beta-titanium alloy (β-Ti), and nickel-titanium (Ni-Ti). Homogeneous and heterogeneous end-to-end joints (15 mm long each) were made by electrical welding and laser welding. Non-welded wires (30 mm long) were also used as a control. Maximum loads at fracture (N) and elongation (%) were measured by conducting tensile test. The data (n = 10) were statistically analyzed using analysis of variance/Tukey test (P < 0.05).The S-S/S-S and Co-Cr/Co-Cr specimens showed significantly higher values of the maximum load (ML) at fracture and elongation (EL) than those of the Ni-Ti/Ni-Ti and β-Ti/β-Ti specimens for electrical welding and those of the S-S/S-S and Co-Cr/Co-Cr specimens welded by laser. On the other hand, the laser-welded Ni-Ti/Ni-Ti and β-Ti/β-Ti specimens exhibited higher values of the ML and EL compared to those of the corresponding specimens welded by electrical method. In the heterogeneously welded combinations, the electrically welded Ni-Ti/S-S, β-Ti/S-S and β-Ti/Co-Cr specimens showed significantly (P < 0.05) higher ML and EL than those of the corresponding specimens welded by laser. Electrical welding exhibited the higher values of maximum load at fracture and elongation for heterogeneously welded combinations than laser-welding.
No preview · Article · Jan 2015 · Journal of Materials Science Materials in Medicine
[Show abstract][Hide abstract] ABSTRACT: Anodic oxidation has been successfully used as a surface modification for orthopedic and dental implants in the past few decades. This chapter will overview the anodic oxidation of titanium and will discuss about processing parameters, microstructure, and composition. Finally, it will clarify the biological responses and the mechanism of enhanced osteoblast functions on the anodized titanium which is pertinent to dental implants.
[Show abstract][Hide abstract] ABSTRACT: The objective of this study was to investigate the effect of laser beam parameters on the mechanical and physical properties of cast commercially pure titanium. Dumbbell-shaped test specimens (ISO6871) were cast with ASTM grades 2 and 3 Ti. The cast surfaces were laser-treated with various laser emission parameters (current: 200, 220, and 240 A; spot diameter: 1.0, 1.6 mm; pulse duration: 10, 1 ms) under argon shielding. Tensile testing was conducted at a crosshead speed of 1.0 mm/min. Data of tensile strength and elongation were statistically analyzed using ANOVA/Tukey’s test (α=0.05). Hardness depth profiles were made with cross sections of rod-shaped specimens after laser treatments. Control specimens without laser treatment were also prepared. The laser-treated specimens showed significantly higher tensile strengths than those of control specimen for both grades 2 and 3 Ti. The specimens treated with 1.0 mm spot diameter indicated higher tensile strengths than those treated with 1.6 mm spot diameter for both currents (200 A and 240 A). The laser treatment decreased the subsurface hardness and increased the hardness between 75 μm and 400 μm in depth when compared to the hardness of control specimens. Laser surface treatment for cast commercially pure titanium modified integrity of cast surface and significantly improved mechanical and physical property.
Preview · Article · Dec 2014 · Journal of Spectroscopy
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to investigate the cytotoxic effects of elements released from gold and CAD-CAM fabricated ceramic crowns.Materials and methodsAccording to the determination of elements released from gold alloy1 and CAD-CAM fabricated ceramic2 crowns into saliva of fixed prosthodontic patients by using inductively coupled plasma mass spectroscopy, similar amounts of elements (Au, Pd, Ag, Zn, Cu, Al, Si) were prepared as salt solutions. 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 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).ResultsThe lowest percentage of viable cells (Mean ± SD) was evident with Zn and Cu released from gold crowns indicating that they are the most toxic elements. Ag was found to be intermediate in cytotoxic effect. Au, Pd, Al, Si were found to be the least cytotoxic elements.Conclusion
Zn and Cu released from gold alloy full crowns showed evidence of prominent cytotoxic effect on fibroblasts cell cultures.
[Show abstract][Hide abstract] ABSTRACT: Introduction
This study investigated the surface, fractured structure, and physicochemical properties related to cyclic fatigue in various nickel-titanium (NiTi) files.
Among a total of 10 groups of NiTi files, conventional NiTi files (ProFile [Dentsply Maillefer, Ballaigues, Switzerland] and K3 [SybronEndo, Orange, CA]) and new-generation NiTi files (ProFile Vortex [PV; Tulsa Dental Specialties, Tulsa, OK], Vortex Blue [VB; Tulsa Dental Specialties], and K3 XF [XF; SybronEndo, Orange, CA]) with the same tip diameter (ISO size 25) and 2 types of taper (0.04 and 0.06) were used in this study. Scanning electron microscopy of the file surface structure, differential scanning calorimetry, and cyclic fatigue resistance tests were conducted.
Many mechanical grooves were recognized on the file surface. The surface in the ProFile group was extremely smooth compared with that observed for the other files. Many shallow hollows besides mechanical grooves were noted on the surface in the XF group. A smooth curve was observed in the ProFile, K3, and PV groups. Defined peaks in differential scanning calorimetry were observed in the VB and XF groups. The 0.04 taper files exhibited a statistically higher number of cycles to fracture than the 0.06 taper files in all groups (P < .05). Cracks along the mechanical grooves were observed in the NiTi files, with the exception of the XF group. The start of cracking was detected at U-shape sites in the ProFile group, the cutting edge in the PV and VB groups, and radial islands in the K3 and XF groups.
The present findings suggest that new-generation NiTi files are not necessarily improved compared with conventional files.
No preview · Article · Sep 2014 · Journal of Endodontics
[Show abstract][Hide abstract] ABSTRACT: Many different types of alloys are now available in the market to be used for dental restorations and fixed prostheses. The common criterion for all these fixed prosthodontic materials is the permanent existence of them in the oral cavity for prolonged time without the ability to be removed by the patient. Therefore, knowledge about the biocompatibility of dental alloys is of great importance. This article presents a literature review on the biocompatibility of dental alloys. A PubMed database search was conducted for studies pertaining to the biocompatibility of dental alloys. The search was limited to peer-reviewed articles published in English between 1985 and 2013. Available data revealed that substances are released from alloys into the surrounding tissues; mainly nickel, zinc, and copper. Some alloys such as nickel–chromium alloy have shown to be cytotoxic in vitro. Also, elements released from gold alloy showed in vitro cytotoxic effect. Therefore, clinicians should give up assuming that gold alloy is completely inert and biocompatible with oral tissues. The clinical relevance of these findings remains unclear. Further in vitro studies, as well as controlled clinical trials, are needed due to possible exceptions.
[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.
Full-text · Article · Aug 2014 · Journal of Biomechanical Engineering
[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.
[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.
Full-text · Article · Jun 2014 · Journal of Medical Devices
[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.
No preview · Article · Apr 2014 · Acta biomaterialia
[Show abstract][Hide abstract] ABSTRACT: Objective: To nvestigate the possibility of electrical and laser welding to connect titanium-based alloy (beta-titanium and nickel-titanium) wires and stainless-steel or cobalt-chromium alloy wires for fabrication of combination arch-wires and to evaluate the joint strengths of connected alloy wires in tensile mode.
Method: Four kinds of straight orthodontic rectangular wires (0.017 x 0.025 inch) were used: stainless-steel (S-S), cobalt-chromium (Co-Cr), beta-titanium alloy (β-Ti), and nickel-titanium (Ni-Ti). Homogeneous and heterogeneous end-to-end joints (15 mm long each) were made by electrical welding and laser welding. Non-welded wires (30 mm long) were also used as a control. Maximum loads at fracture (N) and elongation (%) were measured by conducting tensile test. The data (n=10) were statistically analyzed using analysis of variance/Tukey test (P<0.05).
Result: When the electrical welding was used for homogeneous welding, the S-S/S-S and Co-Cr/Co-Cr specimens showed significantly higher values of the maximum load at fracture and elongation than those of the Ni-Ti/Ni-Ti and β-Ti/β-Ti specimens and those of the S-S/S-S and Co-Cr/Co-Cr specimens welded by laser. On the other hand, the laser-welded Ni-Ti/Ni-Ti and β-Ti/b-Ti specimens exhibited higher values of the maximum load at fracture and elongation compared to those of the corresponding specimens welded by electrical method. In the heterogeneously welded combinations, the electrically welded Ni-Ti/S-S, β-Ti/S-S and β-Ti/Co-Cr specimens showed significantly (P<.05) higher maximum loads at fracture and elongations than those of the corresponding specimens welded by laser.
Conclusion: In homogeneous welding, laser welding indicated high value of maximum load at fracture and elongation for welding of titanium based alloy wires, whereas the S-S and Co-Cr alloy wires showed high load values when electrical welding was used. Electrical welding exhibited the higher values of maximum load at fracture and elongation for heterogeneously welded combinations than laser-welding.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to evaluate and compare the bond strengths between resin composite veneer and laser-sintered cobalt-chromium (Co-Cr) alloy with and without retention devices (Laser-R and Laser-N respectively). Cast Co-Cr alloy with and without retention devices (Cast-R and Cast-N respectively) were also prepared for fabrication technique comparison. Disk-shaped Co-Cr alloy specimens were air-abraded with alumina and veneered with a veneering system, Estenia C&B (ES) or Ceramage (CE). After 20,000 thermocycles, tensile testing was performed. Data were analyzed by ANOVA and multiple comparison test. When no retention devices were present, no significant differences were observed between Laser-N/ES and Cast-N/ES, or between Laser- N/CE and Cast-N/CE, but ES exhibited significantly higher bond strength than CE. With retention devices, Laser-R/ES, Cast- R/ES and Laser-R/CE showed no significant differences, and their retention strengths were significantly higher than that of Cast- R/CE. Compared to cast Co-Cr alloy, laser-sintered Co-Cr alloy with retention devices provided better retention durability for resin composite-veneered prostheses.
No preview · Article · Nov 2013 · Dental Materials Journal
[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.
No preview · Article · Oct 2013 · Dental Materials Journal
[Show abstract][Hide abstract] ABSTRACT: Objectives: This study evaluated the marginal accuracy of cast titanium using a three-unit fixed partial denture (FPD). Methods: A two-abutment stainless-steel die was used to duplicate a set made of a stone die and an epoxy master die. The FPD wax pattern made on a stone die was invested in a mold. Commercially pure titanium (Titanium Ind., Rockaway, NJ) was cast using a centrifugal casting unit in a magnesia mold. As controls, nickel-chromium (Talladium, Valencia, CA) and gold alloys (Tokuriki Honten, Tokyo, Japan) were cast centrifugally into phosphate and cristobalite molds, respectively. Overall burnout schedules followed manufacturers' instructions. Each casting was luted to the epoxy die under a 2 kgf static load. The luted assembly was cut longitudinally at the center of the casting. The clearance between the die and the casting was measured at different measurement locations along the cervical shoulder, and data (μm) for the exterior or the interior shoulders (n= 4 bridges; 8 shoulders) were averaged in terms of the vertical gap (VG) and the horizontal discrepancy (HD), then were statistically analyzed by ANOVA/Tukey test (P <0.05). Results: The VG and HD values of the titanium specimens showed less marginal accuracy compared to the others at all measurement locations of the exterior shoulders. However, there was no statistical difference (P > 0.05) among the cast metals at the interior shoulder except at I-J location (Horizontal Discrepancy) in which all the horizontal discrepancy values were negative. Conclusions: Using a magnesia investment, marginal accuracy of cast titanium was evident to be less than that of conventional alloys of simulated FPD restoration. The correlation between thermal expansion and titanium bridge accuracy is still high.
[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.
No preview · Article · Sep 2013 · Journal of endodontics
[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.
No preview · Article · Sep 2013 · Journal of endodontics
[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.
No preview · Article · Jul 2013 · Journal of endodontics