OBJECTIVETo study micro morphology and element-mixing distribution of different alloys welded in laser and analyze the feasibility of laser welding different alloys.

METHODSAlloys and titanium were matched into 4 groups: Au-Pt with Ni-Cr; Au-Pt with pure Ti; pure Ti with Ni-Cr; Ni-Cr with Co-Cr. They were welded in laser. Changes in metallography after hybridization of crystalline grain, ranges of heat-affected zone and pores were observed through SEM with ultra-thin windowed X-ray energy atlas. Meanwhile 10 testing points were chosen with area of 300 micro m x 900 micro m along the welding surface from the side A alloy to the side B alloy, than the element mixing distribution and tendency were analyzed with X-ray energy atlas.

RESULTS1. Hybridization of different alloys: (l) in the group of Au-Pt with Ti, there was titanium element mixing into Au-Pt tissue gradually and evenly on the Au-Pt side of the interface without clear boundary and increasing in size of crystalline grain. However, there was titanium crystalline grain increasing in size, irregular morphology and small sacks on the titanium side with clear boundary. (2) in the group of Ni-Cr with Ti, there was mixing regularly, slow transition and interlocks between crystalline grains on the Ni-Cr side of the in terface. Poor transition, clear boundary and small cracks were observed on titanium side. (3) in the group of Co-Cr with Ni-Cr, there was good transition, obscure boundary on both sides resulting from network, cylinder and branch structure growing. 2. Element-mixing distribution of different alloys. In fusion zone, the metal elements in matched groups mixed well and hybridized into new alloys except titanium blocks. The location of wave peak depended on the composition of alloys. Most of elements were from the alloy far from the fusion zone.

CONCLUSIONThe hybridization between pure titanium and any other alloys is not good The effect of laser welding different alloys is ideal except with pure titanium.

Alloys ; Chromium Alloys ; chemistry ; Dental Alloys ; chemistry ; Dental Soldering ; Titanium ; chemistry ; Welding

OBJECTIVETo investigate the change of retentive forces of cast cobalt-chromium (Co-Cr) alloy clasp in cyclic fatigue test.

METHODSSamples of three types of cast Co-Cr alloy (Group A: Hardalloy; B: Regalloy™; C: Vera PDN™) clasps were fabricated and placed at undercut depths of 0.25 mm, 0.50 mm. The clasps were drawn from the model molar cyclicly to simulate 5 years of clinical use in an universal testing machine. Retentive force were record at 21 different time point for each clasp during the whole fatigue testing process. Data were subjected to ANOVA, Chi-square test and linear regression analysis.

RESULTSAll clasps showed decreasing retention during the cyclic fatigue test. Clasps engaged in 0.50 mm undercut depth exhibited greater initial retentive force [Group A: (8.714 +/- 1.104) N, B: (9.072 +/- 0.653) N, C: (9.588 +/- 1.980) N] as well as greater loss of retention [Group A: (4.408 +/- 0.662) N, B: (3.484 +/- 0.494) N, C: (3.290 +/- 1.484) N] at the end of the test than clasps engaged in 0.25 mm undercut did [initial forces were (7.940 +/- 0.357), (7.834 +/- 1.308) and (8.156 +/- 1.067) N for Group A, B, C, respectively; loss of retention were (2.444 +/- 0.736) N, (2.954 +/- 1.048) N and (1.832 +/- 1.180) N for group A, B, C, respectively]. Negative correlation was found between the clasp retention and the logarithm of cycling times.

CONCLUSIONSCo-Cr alloy cast clasp could provide adequate retentive force for 5 years of clinical use.

Chromium Alloys ; chemistry ; Dental Alloys ; chemistry ; Dental Casting Technique ; Dental Clasps ; Dental Stress Analysis ; Denture Retention

Ceramics ; Dental Alloys ; chemistry ; Dental Porcelain ; Dental Restoration, Permanent ; Humans ; Metal Ceramic Alloys ; chemistry

OBJECTIVETo study the bonding characteristic of Titanium and RG experiment porcelain.

METHODS5 specimens with a size of 10 mm x 5 mm x 1.4 mm were cast from pure titanium. Then 1 mm of RG experiment opaque and body porcelain were fused on the surface of the titanium specimens. The interface of titanium and porcelain was analyzed with a scanning electron microscope with energy-despersive spectrometry; 6 metal specimens with the size of 25 mm x 3 mm x 0.5 mm were cast from Ni-Cr alloy and a uniform thickness of 1 mm of VMK 99 porcelain was veneered on the central area of 8 mm x 3 mm 18 metal specimens as the same size were cast from pure titanium. The uniform thickness of 1 mm of VITA TITANKERAMIK porcelain, of Noritake super porcelain Ti-22 and of RG experiment porcelain were veneered on every 6 specimens respectively in the central area of 8 mm x 3 mm. The specimens were subjected to a three-point bending test on a load-test machine with a span of 20 mm, then the failure loads were recorded and statistically analysised. The RG porcelain/titanium crown was fabricated by fusing RG opaque porcelain and body porcelain to cast titanium substrate crown.

RESULTSThe SEM results show no porosity and crackle were found in the interface. The energy-dispersive spectrometry show that there are Si, Ti and O in the 1 micro m layer between porcelain and titanium, which suggesting titanium and experiment porcelain bonding well. The three point test showed the fracture force for the combinations of titanium/VITA TITANKERAMIK porcelain, titanium/Noritake super porcelain Ti-22 and titanium/RG experiment porcelain were (7.233 +/- 2.539) N, (5.533 +/- 1.199) N and (6.316 +/- 1.433) N respectively. There were not statistically significant differences among them (t test, P < 0.01). The fracture force for the Ni-Cr alloy/VMK99 porcelain combination (12.733 +/- 3.297) N was significantly greater than those of the cast titanium/porcelain (t test, P > 0.05). The crown was translucent with no crack.

CONCLUSIONRG porcelain is well compatible with titanium.

Dental Porcelain ; chemistry ; Metal Ceramic Alloys ; chemistry ; Titanium ; chemistry

OBJECTIVEThe aim of this study was to establish sol-gel technique of coating titanium on the surface of Ni-Cr alloy (PFM) in order to enhance corrosion resistance and reduce corrosive rate in oral cavity.

METHODSThe sol-gel technique included four steps: (1) pre-treatment; (2) preparation of sol; (3) coating; (4) heat treatment. Elements on the surface of Ni-Cr alloy were analyzed with X-ray photoelectron spectroscopy.

RESULTSAfter coating Ti, the surface of Ni-Cr alloy looked light golden without particles, blisters and fragments. Besides Ni and Cr, titanium was found on surface of Ni-Cr alloy after coating. With Ar(+) ion carving-corrosion figure, the thickness of titanium was about 20 - 80 microm.

CONCLUSIONWith sol-gel technique, titanium could be coated on the surface of Ni-Cr alloy.

Chromium Alloys ; chemistry ; Coated Materials, Biocompatible ; Dental Alloys ; chemistry ; Dental Materials ; Gels ; Humans ; Materials Testing ; methods ; Nickel ; chemistry ; Titanium ; chemistry

OBJECTIVETo investigate the effect of pH value and fluoride ions on the corrosion resistance of pure Ti and Ni-Cr-Ti alloy in the artificial saliva.

METHODSElectrochemical technique was used to measure the electric potential of corrosion (Ecorr), current density of corrosion (Icorr) and polarization resistance (Rp) of pure titanium and Ti-Ni-Cr alloy in the artificial saliva with different pH value and fluoride concentrations. After electrochemical analysis, microstructure and phase diffraction were examined by FSEM.

RESULTSWith the lower pH value, the Ecorr and Icorr of pure titanium and Ti-Ni-Cr alloy increased, the Rp decreased, there was a significant difference (P<0.05). The Ecorr and Icorr increased markedly, the Rp significantly reduced in the artificial saliva containing 0.2% NaF (P<0.01). FSEM showed that pure titanium and Ti-Ni-Cr alloy surface corrosion, pure titanium in the artificial saliva containing 0.2% NaF was most serious.

CONCLUSIONLower pH value decreases the corrosion resistance of pure titanium and Ti-Ni-Cr alloy and the artificial saliva containing fluoride ions decreases the corrosion resistance of pure titanium.

Chromium Alloys ; chemistry ; Corrosion ; Dental Alloys ; chemistry ; Electrochemistry ; Fluorides ; chemistry ; Hydrogen-Ion Concentration ; Materials Testing ; Metal Ceramic Alloys ; chemistry ; Nickel ; chemistry ; Saliva, Artificial ; chemistry ; Surface Properties ; Titanium ; chemistry

OBJECTIVETo investigate the influence of mold temperature on the mechanical properties of Ti-Zr alloy castings.

METHODSTi-Zr alloy was cast into a mold which was made of a zircon (ZrO2.SiO2) investment with a casting machine (China) designed as vacuum, pressure and centrifuge. At three mold temperatures (room temperature, 300 degrees C, 600 degrees C) the Ti-Zr alloy was cast separately. The ultimate tensile strength (sigmab), 0.2% offset yield point strength (sigma0.2), and elongation to fracture (delta) were determined by a universal testing machine with 15 mm pre-marked gauge interval. The surface micro-structures of Ti-Zr alloy castings at three mold temperatures were observed by optical microscope.

RESULTSAt a higher mold temperature during casting, the tensile strength and yield strength of Ti-Zr alloy were significantly increased, while the elongations were significantly decreased. The micro-structure of the surface was different from the inner part. There was a reacted layer in the outermost surface. The thickness of reacted layers at the three mold temperatures was about 35.5 man (room temperature), 55.0 microm (300 degrees C) and 65.5 microm (600 degrees C), respectively. The inner part of microstructure composed of main a phases within the prior alpha grain boundaries.

CONCLUSIONThe mold temperature is one of the major factors influencing Ti-Zr alloy mechanical properties. Comparing with Ti6Al4V alloy and Co-Cr alloy castings, Ti-Zr alloy is more suitable for denture frame.

Dental Alloys ; chemistry ; Dental Casting Technique ; Temperature ; Titanium ; chemistry ; Zirconium ; chemistry

Various engine-driven NiTi endodontic files have been indispensable and efficient tools in cleaning and shaping of root canals for practitioners. In this review, we introduce the relative terms and conceptions of NiTi file, including crystal phase composition, the design of the cutting part, types of separation. This review also analysis the main improvement and evolution of different generations of engine-driven nickel-titanium instruments in the past 20 years in the geometric design, manufacturing surface treatment such as electropolishing, thermal treatment, metallurgy. And the variety of motion modes of NiTi files to improve resistance to torsional failure were also discussed. Continuous advancements by the designers, provide better balance between shaping efficiency and resistance to of NiTi systems. In clinical practice an appropriate system should be selected based on the anatomy of the root canal, instrument characteristics, and operators' experience.
Dental Alloys/chemistry* ; Dental Instruments ; Equipment Design ; Nickel/chemistry* ; Root Canal Preparation ; Titanium/chemistry*

OBJECTIVETo investigate the elastic limit and relevant enclasp force of the non-precious metal casting clasp.

METHODSCasting clasp samples of five cobalt-chromium alloys and one 18 - 8 nickel-chromium alloy were made from prefabricated clasp wax by invesing, casting, sandblasting, and ultrasonic cleaning. The process of casting clasp samples deflected by loading and returned by unloading was tested and electric signals were collected by an omnipotent material machine. The analog electric signal was converted to digital signal by an analog to digital converter and stored in a computer. The elastic limit and the relevant enclasp force were analyzed using a relative software.

RESULTSThe elastic limit and the relevant enclasp force of the casting clasp made from the 18 - 8 nickel-chromium alloy were smallest and those of the clasps made from the cobalt-chromium alloys in various brands were different. The range of the elastic limit of the cobalt-chromium alloy casting clasp with the length of 5.0 mm in undercut was 0.28 mm-0.33 mm and the relevant enclasp force was 14.42 g-19.28 g.

CONCLUSIONSIn clinic, we should select the suitable undercut deepness wherein the cobalt-chromium alloy casting clasps, according to different brands of the casting alloy, undercut length, undercut slope, and the clasp thickness.

Chromium Alloys ; Cobalt ; Dental Alloys ; Dental Clasps ; Dental Stress Analysis ; Denture, Partial, Removable ; Elasticity ; Humans ; Nickel ; chemistry ; Stress, Mechanical

OBJECTIVETo introduce cryotreat technique into prosthetic dentistry by testing the tensile properties of CW-H Co-Cr-Mo cast alloy before and after cryotreat and to observe the image changes by SEM to study the mechanism that changes the tensile properties of the alloy.

METHODS15 CW-H cast alloy were divided into 3 groups, i.e. control group (G1), cryotreated group (G2) and cryotreated plus post-cryogenic treated group (G3). The gauge test technique was employed to test the modulus of elasticity. Then the strength and percentage elongation (PE) were tested. SEM images were used to analyze the mechanism that improved the tension properties of the alloy.

RESULTSFor CW-H alloy the strength and the modulus of elasticity of both G2 and G3 were effectively increased but PE effectively decreased than G1. There was no effectively difference between G2 and G3, but G3 was larger than G2. SEM images of G2 and G3 showed that secondary-carbonide separated out all over the alloy.

CONCLUSIONThe results obtained above suggest that cryotreat is an effective method in enhancing tensile properties of CW-H Co-Cr-Mo cast alloy.

Dental Alloys ; chemistry ; Dental Casting Technique ; Elasticity ; Hardness ; Temperature ; Tensile Strength ; Vitallium ; chemistry