High Palladium Alloy

CHAVES ET AL THE JOURNAL OF PROSTHETIC DENTISTRY

JUNE 1998 677

CLINICAL IMPLICATIONS

The results of this investigation indicate that the strengths of high-palladium alloyjoints properly prepared by the torch, oven, and infrared soldering techniques are ac-ceptable for clinical use and have generally comparable values. The current resultsalso demonstrate the importance of having solder joints that are properly polished. Theapparent notch-sensitivity of solder joints in high-palladium alloy castings that con-tain finishing grooves suggests that there should be some concern when cyclic loads areapplied over a clinically appropriate period of time.

THE JOURNAL OF PROSTHETIC DENTISTRY

High-palladium alloys have become popular forthe fabrication of metal ceramic restorations and im-plant superstructures. Among the reasons for the greatinterest in these alloys are their cost, excellent mechani-cal properties, and good bonding with dental porcelain.1

The alloys and the investments used to fabricate castrestorations are selected carefully to compensate for di-mensional changes that occur during the fabrication pro-cess. For three-unit prostheses, the marginal adaptation,described by Ziebert et al.,2 was the same for solderedrestorations or one-piece castings. However, Gegauff andRosenstiel3 found that for three-unit fixed partial den-

This article is based on a thesis submitted in partial fulfillment of therequirements for the degree of Master of Science in the Gradu-ate School of The Ohio State University, 1997.

Presented at the AADR meeting in Orlando, Florida as a finalist forthe Arthur R. Frechette award competition, March 1997. Presentedat the Carl O. Boucher Conference, April 1997.

Supported by the Greater New York Academy of Prosthodontics andby NIDR Research Grant DE10147.

aSenior Resident, Advanced Education Program in Prosthodontics.bAssociate Professor and Chair, Section of Primary Care.cClinical Assistant Professor, Section of Restorative Dentistry, Prosth-

odontics and Endodontics; and Doctoral Graduate Student in OralBiology.

dProfessor, Section of Restorative Dentistry, Prosthodontics and En-dodontics; and Director, Graduate Program in Dental Materials.

Effects of three soldering techniques on the strength of high-palladium alloysolder joints

Marisol Chaves, DDS, MS,a Stanley G. Vermilyea, DMD, MS,b EfstratiosPapazoglou, DDS, MS,c and William A. Brantley, PhDd

College of Dentistry, The Ohio State University, Columbus, Ohio

Statement of problem. Little information is available on the optimum technique for soldering high-palladium alloys, which have gained considerable popularity for prosthodontic applications.Purpose. The objective of this study was to compare the flexural stress at the proportional limit of fournoble dental alloy specimens soldered with torch, oven, and infrared techniques.Materials and methods. The high-palladium alloys studied were Legacy XT (Jelenko), Freedom Plus(Jelenko), and IS 85 (Williams/Ivoclar). A gold-palladium alloy, Olympia (Jelenko), served as the control.Thirty round bars, 18 × 3 mm, were cast from each alloy, cut in half, aligned, and joined using OlympiaPre solder (Jelenko) for the gas-oxygen torch and the infrared technique and Alboro LF solder (Jelenko)for the oven technique. Each soldered bar was subjected to three-point bending, and the maximum elasticstress or strength of the solder joint was calculated at the proportional limit. Data were analyzed by two-way ANOVA and the Ryan-Einot-Gabriel-Welsch (REGW) multiple range test at the 0.05 level of signifi-cance.Results. There was no significant difference between torch and oven-soldering, but both were signifi-cantly different from the infrared technique. ANOVA showed a significant difference between alloys, butthis difference could not be detected with the REGW test. SEM examination of the fracture surfacesrevealed grooves associated with the path of crack propagation. X-ray energy-dispersive spectroscopicanalysis failed to detect copper in the solders, and there were no significant changes in the solder composi-tions after the melting procedures.Conclusions. All three techniques can yield satisfactory solder joints in high-palladium alloys. Thesejoints should be well-polished to achieve optimal strength. (J Prosthet Dent 1998;79:677-84.)

THE JOURNAL OF PROSTHETIC DENTISTRY CHAVES ET AL

678 VOLUME 79 NUMBER 6

tures (FPDs), the best adaptation was produced aftersoldering. Several studies have shown that, as the lengthof the prosthesis increases or involves the curvature ofthe arch, the potential for a poorly fitting prosthesis in-creases.4-6 With the recent development of implant-re-tained prostheses, which may often be long and mayneed the use of increased amount of casting alloy, fabri-cating a one-piece casting incorporating machined partsand having these machined surfaces accurately and pas-sively fit the implant superstructure becomes even moredifficult. As a result, the practitioner must have an ef-fective method of compensating for poorly fitting cast-ings.

Soldering provides a means of improving the fit of aprosthesis and, at the same time, joining the componentsrigidly.7 The strength of solder joints is of utmost impor-tance for clinical success of the prostheses. Many studieshave reported measurements of tensile strength for sol-der joints, with mixed results. Some investigators havefound that preceramic solder joints are stronger thanpostceramic solder joints.8 Monday and Asgar9 andLorenzana et al.10 reported that there was no significantdifference in the ultimate tensile strength of postceramicand preceramic solder joints. However, other authors11-13

indicated that the ultimate tensile strength of postceramicsolder joints was greater than that of preceramic solderjoints. Although tensile tests are useful in the evaluationof soldering effectiveness, dental prostheses are subjectedmainly to flexural loading during clinical use.14 A popularmethod to obtain the flexural strength of a material isthree-point bending, where a concentrated load is appliedto the center of a uniform beam that is supported neareach end. The flexural strength is often termed the modu-lus of rupture or transverse strength.

In this study, torch, oven, and infrared soldering tech-niques were compared for three high-palladium dentalalloys to determine the best method to join these met-als. A well-known gold-palladium alloy served as a con-trol for the experiments. A literature review indicatedthat there are no published studies comparing these sol-dering techniques for the high-palladium alloys.

MATERIAL AND METHODS

The specimens were fabricated from polystyrene plas-tic patterns used for the fabrication of tensile test speci-

mens according to ANSI/ADA Specification No. 5.15

The ends of the plastic patterns were cut with a dia-mond disk, leaving round bars 3 mm in diameter and20 mm in length. The specimens were then sprued withwax (10 bars per casting ring) and invested with a car-bon-free phosphate-bonded investment (High Span II,J.F. Jelenko and Co., Armonk, N.Y.). The manufacturer’srecommendations were followed for the special liquid-to-powder ratio and burnout schedule for the invest-ment.

The high-palladium alloys used to cast the specimenswere Freedom Plus, Legacy XT (Jelenko) and IS 85 (Wil-liams/Ivoclar, Amherst, N.Y.). A gold-palladium alloy(Olympia, Jelenko) served as the control. The alloy com-positions (wt%) are provided in Table I. Melting wasperformed with a multiorifice gas-oxygen torch, and thealloys were cast with a broken arm centrifugal castingmachine. The castings were permitted to bench coolbefore devestment. After air abrasion with 50 µm alu-minum oxide, castings were numbered at each end andrandomly assigned to treatment groups. Specimens werethen sectioned at their midpoint with a low-speed dia-mond saw (VR/50, Leco Corp., St. Joseph, Mich.) andwater coolant. After sectioning, the bars were ultrasoni-cally cleaned with acetone and dried.

Corresponding halves of each casting were placed ina lathe for proper alignment. A thickness gauge was usedto provide a 0.5 mm gap. Autopolymerizing resin (GCCorporation, Tokyo, Japan) was used to unite the halvesof each bar. Each bar was then invested in a siliconemold (Coltene, Whaledent Inc., Mahwah, N.J.) with Hi-Heat soldering investment (Whip Mix, Louisville, Ky.).The area to be soldered was left exposed during the in-vesting procedure, and an airway was created under thesoldering area to provide uniform heating of the joint.The invested blocks were preheated according to thealloy manufacturer’s instructions or those of the solder-ing equipment manufacturer (infrared technique). Olym-pia Pre Solder (Jelenko) was chosen for the torch andinfrared-soldering groups, and Alboro LF solder(Jelenko) for the oven technique groups.

For the torch-soldering, the investment blocks werepreheated to 1100° F, and a gas-oxygen torch with aNo. 2 orifice point was kept moving at an oblique angleto the preheated investment surface. A strip of approxi-

Table I. Nominal compositions (wt%) of alloys*

Alloy Pd Cu Ga In Au Ag Ru Sn

Freedom Plus** 78 8.0 5.0 6.0 2.0 — <1.0 —Legacy XT** 75.5 — 6.0 6.0 2.0 10.0 <1.0 —IS 85*** 82 — 6.0 3.5 2.5 2.5 — 3.5Olympia** 38.5 — 1.5 8.5 51.5 — <1.0 —

*Values were obtained from the product information literature.**J.F. Jelenko and Co., Armonk, N.Y.***Williams Division/Ivoclar North America, Amherst, N.Y.


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mately 5 mm of solder was placed over the joint, andthe solder was allowed to flow through the gap.

The oven-soldering experimental groups were sub-jected to the Vita Omega cycle (Vident, Baldwin Park,Calif.) under vacuum for porcelain application (twoopaque bakes, two body bakes and a low glaze bake),before the bar was cut with the diamond saw. After theblocks were preheated in the oven, a 5 mm strip of fluxedsolder was placed in contact with the parts to be sol-dered. Then the temperature in the oven was raised tothe melting temperature of the solder, allowing it to flowthrough the joint space. The soldering procedure wasperformed using the vacuum available with the porce-lain furnace.

For the infrared-soldering groups, the preheatedblocks were placed on the platform of the infrared sol-dering machine (Ney Infrared Unit, J.M. Ney Co.,Bloomfield, Conn.). The invested specimen and the sol-der strip were fluxed, and this solder strip was placed incontact with the parts to be soldered. The joint area wasplaced 1 mm below the alignment rod, and the infraredlamp was activated and held at maximum level until thesolder flowed. The soldered specimens were permittedto bench cool before devesting. The specimens werecleaned of residual investment, and the solder joints werefinished flush with the remainder of the bar. Mountedstones and rubber wheels were used with a low-speeddental handpiece, and the bars and the handpiece wereattached to the lathe. The diameter of each soldered jointwas measured, and external defects for each specimenwere noted.

The specimens were subjected to a three-point flex-ural load in a screw-driven mechanical testing machine(model 4204, Instron Corp., Canton, Mass.) at a cross-head speed of 0.25 mm per minute. The load and posi-tion of the crosshead were recorded by means of aPentium personal computer, with the software programLabview for Windows (National Instruments, Austin,Texas) and a data acquisition card with a frequency of1 Hz. The raw data from each test bar were stored inthe computer as a text file. The software program Excel(Microsoft Corporation, Redmond, Wash.) was used toplot and manipulate the data. The midspan flexural stresswas calculated at the proportional limit (just before thepoint of initial nonlinear deformation as determined froma graphic representation of load versus crosshead move-ment) or at the point of failure, whichever was lower.The equation used for the calculation of the maximumelastic flexural stress (σmax) developed at the midpoint ofa centrally loaded round beam was as follows:

σmax = 8Fl/πd3

where F = load, l = distance between support points (testspan length of 12.5 mm) and d = diameter. This equa-tion was developed from the well-known elastic flexureformula σmax = Mc/I, where M is the maximum bend-

ing moment (Fl/4 for three-point bending), I is themoment of inertia (πd4/64 for a circular cross-section),and c is the radius of the bar.16

Ten test specimens were prepared for each combina-tion of alloy and soldering technique for a total of 120specimens. A power analysis17 performed on the experi-mental data, assuming α = 0.05 and a power of 80%(β = 0.20), indicated that a sample size of 10 wouldshow significant differences of 185 MPa in the meanproportional limit or fracture stress between samplegroups. Bartlett’s test17 was performed to determine thehomogeneity of the variances for all of the specimengroups, and the mean values of flexural stress (propor-tional limit or fracture stress) values for all the groupswere ranked and subjected to two-way analysis of vari-ance (ANOVA) to examine the overall effects of alloyand soldering technique, as well as their interactions.The mean values for the specimen groups were ranked,and two-way ANOVA on the ranks18,19 showed that therewere highly significant differences between techniques.The Ryan-Einot-Gabriel-Welsch (REGW) multiplerange test20 with a significance level of α = 0.05 wasused on the ranks to determine which specific specimengroups were significantly different from each other. TheREGW test is considered to have less likelihood of TypeII statistical errors than the well-known Tukey multiplerange test. In addition, representative fracture surfaceswere randomly selected from each group and examinedwith a SEM (JSM-820, Jeol Ltd., Tokyo, Japan).

The two solders were also melted individually using thethree techniques, embedded in epoxy resin, ground with400 and 600 grit metallographic paper, and polished witha series of alumina slurries (from 15 to 0.05 µm particlesize). Quantitative elemental composition information wasprovided by x-ray energy-dispersive spectroscopic analyses(EDS), using a Link eXL microanalysis system with aPentaFET detector and an ultrathin window (Oxford In-struments Group, High Wycombe, England) coupled tothe SEM. A similar procedure was performed for the as-received unmelted solder, and the changes in the composi-tions of the solders after the melting procedures were de-termined.

RESULTS

The mean values with standard deviations of the pro-portional limit for ductile solder joints or the fracturestrength of brittle solder joints for the various specimengroups are summarized in Figure 1. Bartlett’s test showedthat the variances were significantly different from eachother. For this reason, the technique of ranking the ob-servations was used. Two-way ANOVA on the ranksshowed that there were highly significant differencesbetween techniques and a significant difference betweenalloys (Table II). There was no significant interactionbetween the alloys and soldering techniques. The sensi-tive REGW multiple range test showed that, even though



there were differences in the mean values for the fouralloys that ANOVA (Table II) indicated were significant(p = 0.048), these differences were not statistically sig-nificant when the results for the three soldering tech-niques were pooled (Table III). The REGW test wasalso used to analyze differences between the solderingtechniques used in this study where the results for thefour alloys were pooled. It showed no statistically sig-nificant differences between the torch-soldering andoven-soldering (Table IV). However, these two solder-ing techniques were significantly different from the in-frared-soldering technique. No specimen was rejectedfrom the statistical analysis after being fractured, regard-less of the amount of porosity.

The specimens soldered with the oven technique sepa-rated completely after being subjected to the three-pointbending test. No sign of bending or lines of fracture werevisually evident. The fracture path appeared to be com-pletely flat, giving the impression that an adhesive frac-ture had occurred between the parent metal and solder.

Flux was used on the oven-soldered specimens (asrecommended by the manufacturer) and on the infra-red-soldered specimens because of the impossibility forthe solder to flow without the flux. The results showedthat the flux did not perceptibly affect the solderabilityof the alloys, but further quantitative analysis of the ef-fect of the flux would be useful.

Figure 2 is a photomicrograph of the fracture surfacefor an oven-soldered IS 85 specimen. SEM examinationrevealed that the specimen fractured cohesively throughthe solder, even though visual examination suggested

Fig. 1. Values of proportional limit or fracture strength for sol-dered joints of high-palladium alloys obtained with three-pointbending test.

Fig. 2. SEM photomicrograph of fracture surface for oven-sol-dered IS 85 specimen. (Bar = 1 µm.)

Fig. 3. SEM photomicrograph of fracture surface of IS 85 alloyfor oven-soldered specimen shows ductile fracture character-istics of this alloy. (Bar = 10 µm.)

Fig. 4. SEM photomicrograph of torch-soldered Olympia speci-men. (Bar = 1 mm.)


JUNE 1998 681

that separation was between the solder and alloy. An in-tergranular fracture surface can be seen as well, withevident separation between some grains. This fracturesurface was characteristic of the solder. There was noevidence of microvoids or the dimpled rupture struc-ture indicative of ductile fracture.21

Oven-soldered Olympia alloy specimens were alsorandomly selected after fracture and observed at the samerange of magnifications used for the IS 85 specimens.The fracture surfaces for these specimens were similarto Figure 2, which would be expected because the samesolder was used (Alboro LF), and the fracture mode wasagain cohesive through the solder.

An area near the edge of an oven-soldered IS 85 speci-men is depicted in Figure 3. This photomicrograph in-dicates that cohesive ductile fracture also occurredthrough the IS 85 alloy, because of the characteristicdimpled rupture appearance resulting from themicrovoids. Previously, Stewart et al.22 found that thisalloy exhibited excellent ductility, as reported by themanufacturer.

SEM photomicrographs of fractured solder joints forLegacy XT and Freedom Plus specimens that had beenoven-soldered showed characteristics similar to those ofthe fractured solder joints for IS 85, which follows fromthe cohesive nature of the fracture process through thesame low-fusing solder.

The fracture of the torch-soldered and infrared-sol-dered specimens visually appeared to have initiated atthe tension side and propagated through the solder. Low-power SEM examination (Fig. 4) confirmed this obser-vation. For some of these specimens, fracture also oc-curred through the parent metal, but no separation ofthe specimen halves was observed. In contrast, the oven-soldered specimen halves of the alloys separated com-pletely during testing.

The fracture surface for a torch-soldered IS 85 speci-men is depicted in Figure 5. Substantial porosity and arounded structure for the solder below a void are evi-dent. Parallel grooves on the surface resulted from theexperimental procedure of holding each soldered speci-men in the lathe and polishing with stone followed byrubber wheel (with a handpiece). An association of thefracture boundary with the polishing grooves is appar-ent. This same pattern was observed on a representativefracture surface of an infrared-soldered Legacy XT speci-men. Again, there was a close association between thepolishing grooves and the path of fracture in the solder.

A low-magnification photomicrograph of an infrared-soldered specimen of Olympia after fracture is shown inFigure 6. This photomicrograph shows that the princi-pal path of fracture was in the alloy below the solder(white band in the center of the photomicrograph), i.e.,cohesive fracture through the alloy. Numerous voids inthe solder are also visible in Figure 6.

In the low-magnification photomicrograph (Fig. 4)of a fractured Olympia specimen that had been torchsoldered, an indentation in the solder where the bend-ing load was applied can be seen (center left edge ofphotomicrograph). The width of the solder joint appearsto be extended in a vertical direction near the right edgeof the photomicrograph (toward the tension side inbending), due in part to crack propagation. However,the indentation and this tapering suggest some ductilityof the solder. These observations were also made foranother fractured specimen that had been soldered bythe infrared technique.

X-ray EDS analyses were performed on the two sol-ders to determine their compositions. It was found thatthere was no copper in the composition of either solder.The compositions of the solders before melting and af-ter the melting procedures with the three techniquesare summarized in Table V. Only slight changes werefound in the compositions of the solders after the melt-ing procedures.

Table II. Two-way ANOVA results based on ranking the observations

Source DF ANOVA SS Mean square F value Prob. > F

Alloy 3 7784.65 2594.88333 2.72 0.04833Technique 2 22231.95 11115.97500 11.63 0.00003Alloy*technique 6 10776.10 1796.01667 1.88 0.09078Error 108 103192.80 955.48889 — —

Table III. Ryan-Einot-Gabriel-Welsch test results for the alloys*

Alloy Number of specimens Mean (MPa) REGW grouping

Freedom Plus 30 902.40 ALegacy XT 30 834.70 AIS 85 30 803.44 AOlympia 30 800.64 A

*Alloys with the same letter are not statistically different at the α =0.05 level.

Table IV. Ryan-Einot-Gabriel-Welsch test results for the solder-ing techniques*

Technique Number of specimens Mean (MPa) REGW grouping

Torch 40 881.62 AOven 40 868.79 AInfrared 40 755.48 B

*Techniques with the same letter are not statistically different at the α = 0.05level.



DISCUSSION

The development of the strength for a solder jointinvolves melting, flowing, and wetting of the solder bycapillary forces between the parent metal and the sol-der.23 All three techniques used in this study were con-sidered to be acceptable for soldering the three repre-sentative high-palladium alloys. It is important to con-sider the expertise of the operator for achieving solderjoints of similar characteristics. The problems that havebeen reported with the commonly used gas-oxygen torchfor soldering metal ceramic alloys are gas inclusions,voids, improper melting of the solder, and excessive oxi-dation of the pieces to be soldered.24 The main advan-tages with this technique are the availability of the gas-oxygen torch in the dental laboratories and the flexibil-ity of this method for use with the preceramic andpostceramic solders.

It was initially expected that the torch soldering wouldexhibit the greatest variation in results because of the rela-tively poor control in the temperature during the solder-ing procedure. However, this result was not always found.For example, the flexural strength of the Olympia speci-mens that were torch soldered had one of the smallerstandard deviations of all the groups (Fig. 1).

It has been previously noted that a power analysisshowed that the sample size of 10 used in this studywould be able to detect a significant difference (α = 0.05)between specimen groups of approximately 185 MPawith a power of 80% (β = 0.20). This difference wasapproximately 28% greater than the pooled standarddeviation of 144 MPa for all 12 specimen groups. Forexample, sample sizes of 15 and 41 would have beenrequired to show significant differences of 150 MPa and90 MPa, respectively, at the same α and β levels, andwould have necessitated much larger numbers of 180and 492 soldered specimens for the entire study. Al-though a larger sample size might have revealed statisti-cally significant differences between some additionalsample groups compared with the results obtained withthe current sample size, the general observations andclinical recommendations from this study would not besubstantially altered.

An alternative approach to the conventional torch oroven soldering is the use of an infrared heat source. Inthe commercially available unit (Ney) used in this study,infrared energy for soldering is supplied by a quartz-iodine-tungsten-filament lamp. Similar to the gas-oxy-gen torch, flux is required with the solder in this tech-

Table V. Energy-dispersive spectroscopic analysis (wt.%) for composition of solders

Solder Au Ag Zn Pd Sn

Alboro LF* 62.9 (0.1) 23.2 (0.5) 13.5 (0.7) — 0.4 (0.1)Olympia Pre* 70.5 (0.3) 16.5 (0.5) 0.9 (0.2) 10.9 (0.4) 1.1 (0.1)Alboro LF (oven)** 62.3 (0.6) 24.1 (0.6) 12.1 (0.5) 0.9 (0.4) 0.6 (0.2)Olympia Pre (infrared)** 72.1 (0.1) 16.7 (0.4) — 10.3 (0.6) 0.9 (0.1)Olympia Pre (torch)** 70.9 (0.8) 16.7 (0.5) — 10.3 (0.2) 1.3 (0.4)

*Solder as received from the manufacturer.**Solder after melting by the indicated technique.Entries are mean values with standard deviations in parentheses. Five analyses were performed on each type of solder and condition.

Fig. 6. SEM photomicrograph of fracture path through parentmetal of infrared-soldered Olympia specimen. (Bar = 100 µm.)

Fig. 5. SEM photomicrograph of torch-soldered IS 85 speci-men demonstrates solder porosity. (Bar = 10 µm.)


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nique.25 Some of the reported advantages of infraredsoldering are lack of gas inclusions, limitation of heat-ing area and less working time.25,26 Cheng et al.25 foundthat solder joints of a cobalt-chromium base metal alloyproduced by infrared soldering had higher ultimate ten-sile strength than those produced by the gas-oxygentorch. Other investigators reported little difference injoint integrity and strength, whether the thermal energywas delivered by a torch flame or infrared apparatus.27,28

Most of the infrared solder joints in this study frac-tured in a cohesive mode through the solder, but someshowed failure through the parent metal (Fig. 6). Thissoldering technique requires meticulous control of thefocal point because, if this is not achieved, the solderwill melt unevenly and result in weaker joints, or not atall. Careful attention to voltage fluctuations is necessarywhen using the infrared unit, because such changes couldalter the efficiency of the soldering procedure. The speci-mens soldered with the infrared technique were the weak-est for each alloy (Fig. 1 and Table IV), but they werejudged to be sufficiently strong for dental prostheses.

Oven soldering (postceramic soldering) is the bestchoice when porcelain application has been performed.The maximum temperature can be controlled to allowsolder flow without distorting the porcelain. Staffanouet al.11 observed that more consistent connectors, instrength and size, were obtained with oven solderingfor a wide range of dental alloys, when compared withtorch soldering. Stade et al.29 demonstrated that jointsof similar or superior strength to the parent metal wereobtained when oven soldering was used. However, ovensoldering requires a well-calibrated oven to achieve theproper temperature for melting the solder, and the sol-der should contact both sides of the parent metal to besoldered. This technique can only be used forpostceramic soldering, because most of the ovens donot achieve temperatures necessary to melt thepreceramic solder. In this study, all of the oven-sol-dered joints principally fractured cohesively throughthe solder and generally had few voids when observedwith the SEM.

Although all the alloys soldered well, producing jointsthat were judged strong enough to resist intraoral forces,SEM observations revealed that the fracture path of thesolder joints followed microscopic grooves produced bythe finishing procedures for the specimens. Another studyshould be performed to examine the relationships be-tween finishing procedures and strength of the solderjoints.

The general composition of dental solders is reported23

to consist primarily of the elements gold, silver, and cop-per. However, as previously noted, no copper was de-tected in the two solders used in this study (Table V).Other components, such as zinc (found in both solders),tin, and phosphorus, are included to reduce the fusiontemperature and improve flow.

CONCLUSIONS

Under the conditions of this study, the following con-clusions were drawn.

1. All three techniques used in this study were judgedto be adequate for soldering high-palladium alloys.

2. Infrared soldering yielded the lowest values of flex-ural strength among the three techniques used.

3. X-ray energy-dispersive spectroscopic analysis in-dicated that there is no copper in either of the two sol-ders used.

4. Elemental energy-dispersive spectroscopic analysisalso showed that there are only minor changes in thecomposition of each solder after the melting procedures.

5. Microscopic grooves on finished specimens wererevealed by the scanning electron microscope to have aclose association with the paths of crack propagation.This observation indicates that solder joints should bewell-polished to achieve optimal strength.

We thank John C. Mitchell, Senior Electron Microscopist, Depart-ment of Geological Sciences, for expert technical assistance in per-forming the SEM/EDS analyses.

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COLLEGE OF DENTISTRY

THE OHIO STATE UNIVERSITY

305 WEST 12TH AVE.ROOM 3005-L POSTLE HALL

COLUMBUS, OH 43210-1241

Copyright © 1998 by The Editorial Council of The Journal of Prosthetic Den-tistry.

0022-3913/98/$5.00 + 0. 10/1/88849

CONTRIBUTING AUTHOR

William M. Johnston, PhD, Professor, Section ofRestorative Dentistry, Prosthodontics and Endodontics,College of Dentistry, The Ohio State University.

Noteworthy Abstractsof theCurrent Literature

Microleakage of dentin-bonded crowns placed with differ-ent luting materialsPatel S, Saunders WP, Burke FJT. Am J Dent 1997;10:179-83.

Purpose. Microleakage at the margins of dentin-bonded crowns may be a cause of failure of thesetypes of restorations. This in vitro study assessed the microleakage of dentin-bonded porcelaincrowns placed with three luting materials.Material and Methods. Forty-five teeth were prepared by reducing the occlusal surface by 2 mm;removing the convexity from the mesial, buccal, distal, and lingual surfaces; and forming a knife-edge finish line. One half of the cervical margin was placed on dentin/cementum and the remain-der of the margin was placed on enamel. Individual crowns were fabricated in feldspathic porcelainand then cemented to the teeth with three luting materials, according to manufacturers recommen-dations. The teeth were stored in water for 2 weeks at 37° C before evaluating the microleakagewith a dye penetration technique. Teeth with crowns were immersed in a 2% solution of methyleneblue for 48 hours at 37° C. Specimens were then thermocycled while in the dye for an additional 6hours. The teeth were then sectioned in a bucco lingual plane and examined at ×10 magnificationwith a ranking criteria ranging from 0 = no leakage to 4 = dye penetration grater than two thirds ofthe length of the restoration-tooth interface.Results. All groups exhibited leakage at the dentin and enamel margins and at the restoration-cement interface. There were significant differences in leakage at the enamel margins for the threegroups but not at the margins of the finished dentin.Conclusions. The resin cement combinations were unable to prevent microleakage completely.Although there was no significant difference in leakage at the margin in dentin for all three materi-als, Mirage ABC/FLC did not perform as well at the enamel margin. 30 References. — MERAZZOOG

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