in conventional dental brazing - defined as soldering over a temperature of 450c - the parent metals are joined with different types of metals , which may reduce corrosion resistance because of galvanic corrosion between metals57 . the results of solmi , et al.14 ( 2004 ) highlighted the superior biological quality of laser - welding over brazing . other authors characterized orthodontic materials as non cytotoxic except for silver soldered joints10 . while testing the cell reactions of osteoblasts , fibroblasts and keratinocytes , sestini . et al.13 ( 2006 ) found a good tolerance of electrical resistance and laser welding , while traditional silver solder was toxic for osteoblast differentiation , fibroblast viability and keratinocyte growth . the strength of silver soldered joints used to fabricate space maintainers and orthodontic appliances is critical to their success10,12,13,2830 . another method employed for joining metal frameworks is laser welding14,8,1720 . in order to weld dental alloys , crystals of yttrium aluminum garnet ( yag ) doped with neodymium ( nd ) the factors affecting the mechanical strength of laser welded joints are the wave length , peak pulse power , pulse energy , output energy , pulse duration , pulse frequency , and spot diameter of the laser - welding machine , and the type of metal used9,11,15,21 . many laser welding machines used in dentistry have variable settings for output energy ( voltage or current ) , spot diameter and pulse duration . different combinations of these conditions can change the penetration depth of the laser into the metals and affect the joint strength of the laser welded restoration9,11,15,21,24 . in 2005 two different devices for orthodontic purposes were developed based on tungsten inert gas ( tig ) welding , a well known arc welding process . the welding heat is produced with the aid a light bow between tungsten anode and metal . laser and tig welding can weld parent metals without solder or with material consisting of the same parent metal16 . therefore , the corrosion resistance may be increased because the same metal is used . due to their advantages , currently , only little information concerning the mechanical strength of these joints is available in dental literature . therefore , the aim of this study was to compare the mechanical strength of joints made by conventional brazing , tig and laser welding with and without filling material . five standardized joint configurations of the orthodontic wire material forestanit ( lot : 272 ; forastadent , pforzheim , germany ) in spring hard quality ( 0.9 mm diameter for all joints , 0.5 mm diameter for filling material ) was used ( figures 1 to 5 ) . the joints were made by 5 different methods : brazing with universal silver solder , tig welding with and without filling material ( welder , schtz dental , germany ) and laser welding with and without filling material ( lwi , schtz dental ) . laser parameters and welding conditions followed the manufacturer 's recommendations ( table 1 ) . for each joining method , 10 specimens were carefully produced . the tensile strength of the original wire material with the diameters of 0.9 mm ( n=10 ) were also measured . measurements of joint length took place at x34 magnification with the aid of a computer - assisted video inspection system vmzm/40 ( jena engineering company , germany ) . fracture strength measurement of different welding and brazing methods was carried out using a universal testing machine ( zwick 005 . the wire length between the cross - heads of the machine was standardized as 5 mm . the full scale load was set at 2000 n with a crosshead speed of 10 mm / min . the recorded data were analyzed using spss 12.0 statistical software package ( spss inc . , statistical analysis was undertaken by one - way analysis of variance ( anova , p=0.05 ) and bonferroni post hoc test ( p=0.05 ) . means , minima , maxima and standard deviations of the joint length are given in table 2 . no significant differences between the various joint configurations except for the connections of band to orthodontic wire were found ( anova , p<0.05 ) ( table 3 ) . in this configuration , the mean joint length made by brazing was between 0.5 and 1.0 mm longer than in laser 1 or laser 2 . means , minima , maxima and standard deviations of the fracture strength of the different joining method are given in table 4 . mean tensile strengths of the original orthodontic wire ( n=10 , diameter 0.9 mm : 1492  55 compared to these findings welding and brazing significantly decreased the fracture strength ( anova , p<0.001 ) ( table 4 ) . according to manufacturer 's guidance , tig - welding of orthodontic wire to orthodontic band could not been carried out . for brazing , the highest fracture strength means were observed in the band - to - wire configuration ( 406.7  116.1 n ) . the lowest means for brazing were found in the cross joints ( 185.9  36.0 n ) . for tig - welding , the highest fracture strength means were observed in the 3-mm - long joints with filling material ( tig 2 : 866.1  136.9 n ) . the lowest fracture strength means were shown in the 9-mm - long joints ( tig 1 : 548.9  105.3 n ) . except for the cross joints , higher fracture strength means were found for tig welding with filling material . in the present study , the absolute highest fracture strength means were found in laser welding to joining orthodontic wire of 3 mm length with additional use of filling material ( laser 2 : 997.9  281.7 n ) . the lowest fracture strength means in laser welding were found in the configuration orthodontic wire to band without filling material ( laser 1 : 328.8  31.7 n ) the anova results are shown in table 5 . in general , statistically significant differences ( p<0.05 ) were found among the various joining configurations and soldered or welded specimens . statistical comparison of single groups demonstrated a significant decrease of fracture strength means in brazing related to tig- or laser welding except for the band to wire joints ( bonferroni post hoc test , p<0.001 ) ( table 6 ) . ns= non significant ; level of significance : using additional filling materials higher fracture strength means were achieved with both tig- or laser welding . statistically significant differences ( bonferroni post hoc test , p<0.05 ) were found between the 9-mm - long joints produced by tig- or laser welding with and without filling materials ( table 6 ) . except for the joints of 9 mm and the band - to - wire configuration , no significant differences ( bonferroni post hoc test , p>0.05 ) concerning the band - to - wire joints , the mean values of fracture strength did not differ significantly between laser 1 and brazing , but a slight tendency to lower means in laser welding without filling material was found ( bonferroni post hoc test , p>0.05 ( table 6 ) . significantly higher fracture strength means of the band - to - wire joints were shown in laser welding with filling material . studies about mechanical behavior of welded or soldered orthodontic wires are rare . up to date , a direct comparison of different brazing and welding methods is missing and the influence of different tig- or laser welding devices can not be estimated . no scientific studies were found to evaluate the effects of filling material on the fracture strength of tig- or laser welded orthodontic wires . the results of fracture strength measurements of welded precious and non - precious cast alloys used in fixed or removable prosthodontics can be transferred to orthodontic purposes only with strong limitations8,10 . the factors affecting the mechanical strength of welded joints have been described in different studies : wavelength , peak pulse power , pulse energy , output energy , pulse duration , pulse frequency and spot diameter of the laser - welding machine , and the type of metal used5,6,2226 . various authors have demonstrated changes in the welding area and the so - called heat - affected zone in ni - cr - mo , co - cr - mo or titanium alloys depending on welding conditions3,18 . these authors pointed out that this is probably due to the different refining in the grain size and the substructure that appears during the rapid solidification stage . wiskott , et al.27 ( 2001 ) found a correlation between definite increase in grain size and increased heat application in brazing , electric resistance and laser welding of au - pd alloy . however , the authors could not correlate the element analysis with the fracture strength of the specimens . bertrand , et al.3 ( 2004 ) have observed that a small change in the chemical composition of the ni - based alloys caused a very important difference in the weldability . accordingly , the results of other authors investigating laser - welded titanium indicated that , under the appropriate conditions , the joint strength of laser - welded titanium was not significantly different from the non - welded parent metal4,9 . in contrast to these findings , watanbe and topham25 ( 2004 ) did not achieve the same fracture load of non - welded ti- , gold- or co - cr alloys in different configurations of laser welding . specially for gold- and co - cr alloys only 50% or less of the original measurements were obtained . babe , et al.2 ( 2004 ) found that the fracture strength for all laser - welded cocr - alloy specimens tended to be lower than those for the controls . depending on welding conditions the mean fracture force ranged from 224 to 622 n for single - welded specimens and from 252 to 1292 n for the 1.0-mm double welded specimens . only at currents of 270 and 300 a significant differences could not be found from the results for the non - welded control specimens ( 1733 n ) 2 . rocha , et al.11 ( 2006 ) compared laser and tig welding of non precious alloys . tig welding increased the flexural strength of ti , co - cr , ni - cr whereas the welded cylinders presented higher flexural strength than non - welded cylinders . the highest means were observed for co - cr weld by tig and non - welded co - cr . in contrast , laser welding achieved only 17.5% of the flexural strength of co - cr alloy . the controversial results of decreasing or increasing mechanical strength of welded precious and non - precious cast alloys were not found for orthodontic materials . krishnan , et al.8 ( 2004 ) evaluated three orthodontic arch wire alloy materials - stainless steel , beta titanium and timolium  as to their laser weld characteristics . fracture strength differed significantly between the three materials ( stainless steel 363  22 mpa , beta titanium 463  27 mpa , timolium 344  25 mpa ) . although a comparison to original wires was missing in this study , it could be assumed that laser - welded specimens showed significant lower fracture strength than pure metals ( approximately 1500 - 1800 mpa ) . a recent study using additional filling material demonstrated higher flexural strength for ti- ( + 18% ) , nicr- ( + 66% ) and cocr- ( + 69% ) laser welded alloys11 . in the present study , the increase in fracture strength ranged from 16% and 35% in tig- and laser welding . an additional benefit was observed . in the present investigation , a direct comparison between brazing , tig- and laser welding was performed for the first time . defects of our tests were equal to the clinical findings of complete ruptures without a real conjunction between two metal frameworks . tig and laser welding showed significantly higher fracture strength means , but the tensile strength of original wire was not achievable . therefore , welding changed the material attributes and the fact of missing spring hard quality has to be considered in planning of orthodontic appliances . testing the fracture strength , the brand new tig welding appeared to be comparable to the laser welding method and is an interesting low cost and solder free alternative for orthodontic purposes . however , it should be highlighted that the impossibility to create band - to - wire joints limits the clinical use of tig - welding in orthodontics . further research is needed to determine the optimal welding parameters for each device and different joining methods , especially to joining orthodontic wires with orthodontic bands . the use of additional filling material in tig- and laser welding improved the mechanical behavior of orthodontic wire joint configuration and can be recommended for achieving higher fracture strength .