Ira T. A Comparison Of Hydrogen/Oxygen And Natural Gas/Oxygen Torch .
Ira A. Culiier, DDSVorfc UniversityRobert T. Martini,DDS"Long Island College HospitalA Comparison ofHydrogen/Oxygen andNatural Gas/Oxygen TorchSoldering TechniquesIra D. ZInner, DDS.Francis V. Patino,MSD'"DDS"'*New York UniversityThe tensiie strength of connectors joining bars of palladium-siiver alloy andformed using hydrogen/oxygen flame soidering was compared to thoseformed using conventionai gas/oxygen soidering. As-cast specimens servedas the controi. No significant differences were found between the as-cast,hydrogen/oxygen fiame soldered, or the naturai gas/oxygen fiame solderedspecimens, Int) Prosthodont 1994;7:258-263.Arareiy reported.'"" The most practicai use in dentistry was for orthodontic soidering where the partsto be joined were smaii. Aithough the strength oforthodontic connectors formed using a hydrogenfiame and torch was found to be equai,'" hydrogensoldering apparentiy never gained significantacceptance in fixed prosthodontic procedures.The purpose of this investigation was to evaiuatethe tensiie strength of soldered connectors of testspecimens formed using a hydrogen/oxygen torchfiame and naturai gas/oxygen flame and comparethese to as-cast specimens.fixed partial prosthesis may be either cast inone piece or in sections to be joined by soidering. The soidering method has the advantage ofpermitting each individual retainer to be fitted toits abutment instead of fitting the entire prosthesisto muitipie abutment teeth.'Soldering techniques have not changed in manyyears. Traditionaiiy, hand-heid gas/air or gas/oxygentorches have been used to heat the components.'Little information has been pubiished regarding thejoining of metals by methods other than conventional torch soidering or oven soidering techniques. " in aeronautics, oxidatitjn of simiiar aiioys isreduced by soidering parts in protective atmospheres such as heiium, argon, or hydrogen gas, orin high-power vacuums," iHydrogen gas is a strongreducing agent that ignites at 574 C.''* it is readiiyabsorbed into the surface of certain metals, inciuding paliadium.' Hydrogen torch soidering has beenreported to have been used in dental laboratoryprocedures for over 50 years,'' but its use has beenMaterials and MethodsThirty specimen rods, 41 mm iong and 3 mm indiameter, were made from prefabricated wax tensiie test patterns ( .M. Ney, Í3ioomfield, CT). Eachspecimen had eniarged ends that couid be grippedin a universai testing machine (Fig 1 ].Aii specimens were individuaiiy invested in 2inch-diameter steel casting rings (J.M. Ney) using anoncarbon phosphate bonded investment {H\Temp casting investment. Whip Mix, Louisviiie,KY) with tbe manufacturer's recommended iiquid/powder ratio of 14.5 mL of speciai iiquid concentrate to 90 g of powder. The patterns were castusing 50% new and 50% used aiioy ( 10%) (Fig2). The metai, a 60% pailadium/28% siiver ailoy(PD 60, Five Stars Aiioys, Haci ensaci , N)). washeated in a new iarge-fused siiica casting crucible(Kerr, Romuius, Mi). Castings were made with ahydrogen/oxygen fiame torch (Hydrogen Flame'Professor and Director of Fixed Prostbodontics, Division ofRestorative and Prostbodontic Sciences, College of Dentistry."Resident."'ClinicalProfessor, Division of Restorative and PiosthodonticSciences, College of Dentistry.""Professorand Head, Division of Restorativedantic Sciences, Coiiege of Dentistry.andProstho-Reprint requests: Dr Gulker, Director, FixedProstbodontics,New York University Coiiege of Dentistry, 345 East 24tb Street,New York, New York i 0010.louriiai ul Prosthodontii258Voiump 7, Niiir\b
en and r atural Cis/Oxyger Torch SoldeFig 1Prefabricated wax pattern tor tensile test rod.Fig 2Fig 3Altjminum jig.Fig 4 Aiuminum ;ig with casting parts aligned and 0.005inch gap set.Fig 5Ten randomly selected castings were reservedfor testing without sectioning or soldering. Each ofthe 20 remaining castings was placed in a customjig (Fig 3] and cut in half with a #51 78 doublesided, 7/8 inch, 0,015-inch-thick carborundum"wafer thin" disc (Dedeco, Long Fddy, NY¡ using astraight handpiece held parallel to each casting.The cut ends were not subjected to any polishingprocedures but were cleaned ultrasonically usingdistilled water. Further contact with the interfacesto be soldered was avoided.Cut specimens were aligned and stabilized inthe previously mentioned mounting jig, and 0.005Inch shim stock was used to set the gap distance(Fig 4),'- Specimens were then joined with anautopolymerizing acrylic resin (GC Pattern Resin,G-C America, Chicago, IL), Each assembly wasplaced in a silicone mold to standardize the sizeand shape of the investment block. Solderinginvestment (Biovest, Dentsply) was vibrated intothe mold and allowed to set overnight before separation (Fig 5), The time between investing and soldering varied from 5 to 10 days.Specimen invested for soidenng.model FHeraeus FHT-150, Technical IndustrialProducts, Philadelphia, PA) used to heat the alloyin the crucible that was held in an open, brokenarm, centrifugal casting machine. Each casting wasallowed to cool to room temperature, devested,and airborne particle-abraded (Comeo MB102microblaster. Sun Valley, CA) using 50- jm nonrecycled aluminum oxide.-.umber 3, t994Specimen cast in pailadium-siiver alloy.259Journai of Frosthodonliqs
d N.ituríil GaB/Oxysen Torcli SoidcSolderingfor 20 minutes. Ten specimens were soldered usinga natural gas/oxygen flame and 10 using a hydrogen/oxygen source.Immediately upon removal of the sample fromthe oven, a preceramic flux (Ney Soldering Flux,J.M. Ney) was placed in position, and a strip of solder (High-fusing ceramic solder, Ivoclar, NorthAmerica) was held against the ¡oint ends until thegap was filled. The listed composition of the solderwas 45% gold, 41.5% silver, and 12.5% palladium.The heat from the torch was directed at eachspecimen in a back and forth motion until solderflowed into the 0.005-inch gap. A hydrogen/oxygentorch (Hydrogen Flame model Heraeus HT-150,Technical Industrial Products) at a temperature ofabout 4,500''F and a gas/oxygen torch (Niranium,Long Island City, NY) with natural gas were usedfor alternate specimens (Fig 6). The hydrogen/oxygen machine uses a 120-volt current to separatehydrogen and oxygen from a solution of electrolyteand distilled water by hydrolysis. A single unit cansupply up to 300 liters of combined gases per hour,sufficient to cast and/or solder any fixed prosthodontic alloy. It is reported to produce a flame of6,000*'F, which can be reduced to 4,500''F by passing the gases through a canister of alcohol.' Thegenerator of the hydrogen/oxygen unit is about12 X 12 X 10-inch deep in size. The gases are generated naturally in tbe 2:1 ratio needed for efficientflame combustion.' The hydrogen and oxygen aremixed, and the mixture is sent through a singlehose to the torch (Fig 7).All specimens were bench cooled. After devesting and airborne particle-abrading using 50-[jmaluminum oxide at 90 pounds pressure, all excesssolder was removed using a handpiece and greenabrasive stone at low speed. The diameter at thecenter of each rod was recorded as the average ofthree measurements made for each rod using amicrometer accurate to 0.001 mm (Mitutoyo MDC293 Sevrei, Milutoyo, Tokyo, apan). This locationcoincided with the solder joint for the 20 solderedspecimens.The resin was eliminated by placing the samplesinto a cold oven, raising the temperature 100 F/min to 130O''F, and maintaining Ihat temperatureFig 6 Hydrolysis machine (source of hydrogen and oxygengases).Voltage control to producethe desired rate ofgas generationOrdinary 110 or 220V AC powerIS converted to DC. Distilled water plus an eieotroiyteto catalyze dissociationTestingSpecially designed grips were used to hold the30 samples in a universal testing machine {ModelTTB, Instron, Canton, MA). The tensile load required to fracture each specimen was recorded.The pressure gauge indicatesthe gas pressure at the tipFlame temperature may bereduced with an increase in BTUcontent by using a BoosterFig 7ResultsStrength values were calculated from the maximum load recorded before tensile failure dividedDiagram of hydroiysis-generator functions.The Iniernational260Volume 7, Numb
Hydrogen/Oxygen and Nalural Gas/Ony en Torch Sotderfnsby the computed cross-section area to give themaximum stress (force/unit area). All solderedspecimens fractured at the solder joint and strengthvalues ranged from 3,040 to 5,805 kg/cnv. As-casitest specimens fractured at a mean value of 4,706kg/cm (SD 754 kg/cm-). Ultimate tensilestrength, mean, and standard deviations of thethree groups are shown (Table 1, Figs 8 and 9).The three groups were compared using a oneway ANOVA with pairwise comparisons using theScheffe procedure. No significant differences wereStrength(Kg/cm 2]6000-5000-4000-3000-2000-Table 1 Ultimate Tensile Strengths of EachSpecimenMeanStandard Deviaticn1000-As 683040470644094333754639695Fig 9 Ultimate tensile strengthsof (median, interquartile range,and range) specimens.1Minimum 1Mean11SDas cast11 natural gas/oxygen11 hydrogen/oxygenFig 8 Ultimate tensile strengths (minimums, means, maximums, and SDs) of specimens.Strengt ti(Kg/cm')Key:*Uz- Med an- Interquartile range- RangeGroup10nber 3, 1994Maximum261The Internal ion a310I oí ProsLhodontit
i-lydrogen/Oxyüen and N.nurai Gas/Oxygen Torch Soiderin.;found, F 12,27) ,7649, NS, Using Cohen's criteriafor effect size, the probabiiity of detecting a moderate difference (25% of the variance) with this sampie size is about 60%, About 70 specimens wouldbe required in each group to delect medium differences; 600 specimens wouid be required in eachgroup to detect smaii differences at a power of 80,Since (he observed differences belween conditionswere iess than the standard error of measurement,it is uniikeiy that ciinicai differences exist betweenthe groups.Separation of the soider from the cast aiioy wasconsidered evidence of adhesive failure. Cohesivefaiiure was seen as fracture through the soider, thecast aiioy, or both. Both adhesive and cohesiveconnector failures were observed in boih soideredgroups. Seven cohesive failures were found in Ihenatural gas/o\ygen group and eight in the hydrogen/oxygen group.the recorded vaiues. Even when care is exercisedin aii procedures, a smail sampie size, voids typicai of pailadium silver castings, soldering voids,irreguiar cross-sections, and testing apparatus variabiiily may yieid iess than ideai resuits.ConclusionsAs-cast and soidered pailadium-siiver rods werefabricated and tested in tension. Under the conditions of the study, the foilowing conciusions maybe made:1. Specimens soldered by naturai gas/oxygen orhydrogen/oxygen torch showed no significantdifference in ultimate tensiie strengths,2. The ultimate tensiie strength of specimenssoidered using naturai gas/oxygen torch orhydrogen/oxygen torch was not significantlydifferent from that of as-cast specimens.DiscussionAcknowledgmentsThe weakest part of a fixed partial denture melalframework is usuaiiy the soidered connection," Aconnector made by sound soidering procedurescan approximate the strength of a cast connector,'*A connector that is soidered by either hydrogen/oxygen or natural gas/oxygen fiame can be successfuliy fabricated and used for fixed prosthodontic procedures, Aithough the equipment varies,the procedure for both soidering procedures canbe performed using simiiar processes and times.Technique sensitivity did not seem to differ forthe two methods. Advantages of the hydrogen/oxygen fiame soidering may be its high heat, itschoice of flame tips (14- to 30-gauge orifices), andits simplicity, ali of which may aid soidering in thedesired shortest possible time,'" Aithough the costof the unit is significant, water as a fuei has a negiigibie cost, it is always avaiiabie and it presents nodanger of fire or expiosion. No physicai danger isencountered from weighty tanks. The simpiicity oftorch use is important. The iearning curve with ahydrogen/oxygen torch is short and daiiy use issimpie. Nozzles never require any adjustment.Further investigations into the strength, accuracy,and microstructure of hydrogen/oxygen flame casting and soldering appear warranted.In this study, the specimens generaliy exhibitedfaiiure at lower values than expecled and therewas aiso a reiativeiy wide range of values. Thetype of failure did not seem to be related to thevaiues recorded. The presence and size of voidswere not documented, bul it was observed thatvoids at the fracture sites did seem to be reiated toThe International lojrnal uf ProithoibntKTiie authors wisii to thank Paul Federico, CDT, MDT, PatrickReid, CDT, MDT, and Sam Pomerantz, CDT, MDT for their aidin laboratory procedures and Dr Eugene Hitteiman for his aid instatistical evaiuaLions, All are members of the faculty of tiieNew York University Coiiege of Dentistry,References1, Beck DA, Moon PC, Janus CE, A quantitative study of preporcelain soldered connector sirengiii with pailaditjmbssed-porcefain bonding alloys, i Prostinel Dent 1986;56:301-306.2, Lorenzana RE, Staffanou RS, Mari er VA, Okabe T Strengthproperties of soidered joints for a gold-palladium alloy anda palladium alloy, Prosiiiet Dent 19H7;57:450-454,3, Cattaneo C, Wagnild G, Marshail G, Watsnabe L,Comparison of tensiie strength of solder joints by infraredand conventional torch technique. J Prostlie! Dent 1992;68:33-37.4, Tehini GE, Stein RS, Comparative anaiysisoftwo techniquesfor soidered connectors. I Prosthet Dent 1993;69:16-19,5, Louiy AC, Mora AF, Moore BK, Andres CI, Goodacre C],Tensile strength of preceramic solder joints formed usingan infrared heat source, Intj Prosthodont 1991 ;4:425-,431,6, Sobieralski ]A, BrukI CE, Smith NK. Tensile strengths andmicroscopic analysis of nickel-chromium base metalpostceramic solder joints, Prosthel Dent 1987;S8:35-42,7, Hartipel EA (ed). The Encyclopedia of the ChemicalEiements. New york: Reinhold, 1968:276-277,8, The New Iliustrated Science and Invention Encyclopedia,Westport, CT: Stutman, 1987:1239,9, Skinner EW, The Science of Dental Materials, ed 2,revised, Philadelphia' Ssunders, 1940:292.10, Brown T, Mitcheli R, Barenie J, Evaiualion of five silversoidering techniques, ] Pedodont 1982;6:235-243,11, O'Toole T , Eurnish GM, von Fraunhofer ]A, TensileSlrength of soldered joints, ] Prosthet Dent 1985;53:350-3S2.2&2Voiume 7, Nun
Hydrogen/O.yBen and Natural Ga5/O vEen Torcti SoideringLautenschlager EP, Marker BC, Moore BK, Wilder R.Strength mechanisms ol dental solder joints. J Dent Res1974:53:1361-1367.Skinner EVi/, Phillips RW. The Science of Dentai Materials, ed 6, Philadelphia: Saunders, 1967:562.12. Stacktiouse I. Assembly of dental units by soldering. Prosthet Dent 1967;13:131-139,13. The Henes Flame Generator. Brochure. PhiladelptiiaiTechnical Industrial Products, 1986,14. Kriebel R, Moore BK, Gûodacre C , Dykema RW. A comparison of the strength of base metal and gold solderjoints. I Pro5thet Dent 1984;51 ;6O-66,nbcr 3, 1994263The Internal i on a
formed using hydrogen/oxygen flame soidering was compared to those formed using conventionai gas/oxygen soidering. As-cast specimens served as the controi. No significant differences were found between the as-cast, hydrogen/oxygen fiame soldered, or the naturai gas/oxygen fiame soldered specimens, Int) Prosthodont 1994;7:258-263.
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