Basic Study On Clinical Appliance Of Laser-welded Titanium

Background and purposeTitanium and titanium alloys are being used more frequently in dentistry.A growingtrend involves the use of titanium as an economical and biocompatible replacement for exising alloys.Titanium and titanium alloys have biocompatibility,corrosion resistance,low cost and desirable physical and mechanical properties,such as low modulus,low thermal conductivity,high ductility,low density,and favorable microhardness,which make titanium and titanium alloys more attractive for dental prosthesis.In recent years,titanium and its alloys have been used as a metal for removable partial denture frame works,complete denture bases, implant denture,fixed bridge and crown in dental prosthesis.The increasing use of Ti for multiple-unit fixed prosthesis require a method to join two and more unites in a restorative prosthesis to reduce the contraction and distortion in casting process.Forthermore, titanium and its alloys have a high reactivity with oxygen,nitrogen,and hydrogen.especially with increasing temperature ,which leads to alterations in their composition and mechanical properties.When using titanium,laser welding is the best method and the one most used.So investigation of the influence of laser welding on titanium has great clinical significance. MethodsThese method were used in the study: scanning electron microgram,metallographicexamination, EDAX,tension test, three-bending test,measuer of Vickers microhardness values at welding area,etc.The aim of the study is to determine if laser welding technique will influence the properties of titanium and the bond strength of low-fusing porcelain to laser welded Ti.The experiments are divided into three sections:The first one is to investigate the quality of laser welded Ti by different gap distance .The second one is to investigate the corrosion properties of laser welded Ti,The third one is to investigate the bond strength of low-fusing porcelain to laser welded Ti. Results1 Tensile loads of laser welded titanium by different gaps(0.0mm:677.92 79.78MPa;0.25mm:605.00 68.23MPa;0.5mm:619.65 44.35MPa;1.0mm:632.95 + 87MPa)made no statistic difference from those of the original materials(593.19 42.52MPa).SEM showed no pores and other defects and some ductility at laser welding area. Metallographic examination showed a localized fusion and a heat-affected zone.these zones were limited to the surface region in the joined areas. Fine-grained acicular crystals could be seen at the fusion zone.High hardness values were measured near the fusion zone and tapered off outside the heat-affected zone throughout all the tested samples for laser welded cast titanium. With the welded area taken as the center,the range of increasing hardness was approximately 1mm.2 After stress-corrosion test ,there was no discoloration in the weld zone of the laser welded cast samples. SEM showed no microcrack on any sample' s surface at the fusion zone.The ultimate tensile strength (UTS) had no significant difference between the stress-corrosion group(657.06 54.04MPa) and the controlled group(609.81 37.24MPa).3 The SEM examination showed that the interfaces of the laser-welded groups and the controlled ones presented similar irregularities with a predominance .All specimens showed good wetting to the metal surface.No fracture lines in the porcelain layers were found in any speciments.The EDAX analyses revealed that titanium diffuses from titanium to porcelain,and silicon,potassium ,natrium,aluminium,and stannum diffused from porcelain to titanium in the interface.The thickness of elemental diffusion layer was approximate 10.6Hm.No significant difference of the bond strength was found between laser-weldedsamples(46.33 0.97MPa) and the controlled samples(40.71 0.93MPa). Conclusion1 the laser welding technique does not affect the mechanical properties by different gap distances,when gap distance is above 0.5mm,it is more difficult to operate in clinic appliance.2 the laser- welded Titanium shows superior corrosion-resistance pro...