Effect of joint design and welding type on the flexural strength and weld penetration of Ti-6Al-4V alloy bars.
BACKGROUND
Framework longevity is a key factor for the success of complete-arch prostheses and commonly depends on the welding methods. However, no consensus has been reached on the joint design and welding type for improving framework resistance.


OBJECTIVE
The purpose of this study was to assess the effect of different joint designs and welding methods with tungsten inert gas (TIG) or laser to join titanium alloy bars (Ti-6Al-4V).


METHODS
Seventy titanium alloy bar specimens were prepared (3.18 mm in diameter × 40.0 mm in length) and divided into 7 groups (n=10): the C-control group consisting of intact specimens without joints and the remaining 6 groups consisting of specimens sectioned perpendicular to the long-axis and rejoined using an I-, X30-, or X45-shaped joint design with TIG welding (TI, TX30, and TX45) or laser welding (LI, LX30, and LX45). The specimens were tested with 3-point bending. The fracture surfaces were first evaluated with stereomicroscopy to measure the weld penetration area and then analyzed with scanning electron microscopy (SEM). The data were statistically analyzed with 2-way ANOVA and the Tukey post hoc test, 1-way ANOVA and the Dunnett test, and the Pearson correlation test (α=.05).


RESULTS
Specimens from the X30 and X45 groups showed higher flexural strength (P<.05) and welded area (P<.05) than specimens from the I groups, regardless of the welding type. TIG welded groups showed significantly higher flexural strength than the laser groups (P<.05), regardless of the joint design. TIG welding also resulted in higher welded areas than laser welding for the I-shaped specimens. No significant differences were found for the weld penetration area in the X45 group, either for laser or TIG welding. SEM analysis showed more pores at the fracture surfaces of the laser specimens. Fracture surfaces indicative of regions of increased ductility were detected for the TIG specimens.


CONCLUSIONS
TIG welding resulted in higher flexural strength for the joined titanium specimens than laser welding. For both welding methods, X30- and X45-shaped joint designs resulted in higher flexural strength and welding penetration than the I-shaped joint design.
Professor, Department of Occlusion, Fixed Prosthodontics and Dental Materials, School of Dentistry, Federal University of Uberlândia, MG, Brazil. Electronic address: psimamoto@foufu.ufu.br.
Paulo Cézar
PC
Simamoto Júnior
Professor, Department of Operative Dentistry and Dental Materials, School of Dentistry, Federal University of Uberlândia, MG, Brazil.
Veridiana
V
Resende Novais
Graduate student, Department of Occlusion, Fixed Prosthodontics, and Dental Materials, School of Dentistry, Federal University of Uberlândia, MG, Brazil.
Asbel
A
Rodrigues Machado
Professor, Department of Operative Dentistry and Dental Materials, School of Dentistry, Federal University of Uberlândia, MG, Brazil.
Carlos José
CJ
Soares
Professor, Department of Occlusion, Fixed Prosthodontics and Dental Materials, School of Dentistry, Federal University of Uberlândia, MG, Brazil.
Luís Henrique
LH
Araújo Raposo
D000497:Alloys; D003722:Dental Alloys / Q000737:chemistry*; D012994:Dental Soldering / Q000295:instrumentation / Q000379:methods*; D004548:Elasticity; D004566:Electrodes; D006801:Humans; D007834:Lasers; D008422:Materials Testing; D008853:Microscopy; D008855:Microscopy, Electron, Scanning; D005741:Noble Gases / Q000737:chemistry; D018583:Pliability; D016062:Porosity; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*; D014414:Tungsten / Q000737:chemistry
D000497:Alloys; D003722:Dental Alloys; D005741:Noble Gases; C031462:titanium alloy (TiAl6V4); D014025:Titanium; D014414:Tungsten