DTIC ADA530477: Acid-Assisted Consolidation of Silver Alloys for Direct Fillings

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by  Defense Technical Information Center

Volume103,Number5,September–October1998
Journal of Research of the National Institute of Standards and Technology
[J.Res.Natl.Inst.Stand.Technol.103,511(1998)]
Acid-Assisted Consolidation of Silver
Alloys for Direct Fillings
Volume 103 Number 5 September–October 1998
Frederick C. Eichmiller, Silver-richmetalpowderscold-weldedby flexuralstrength.Concentrationalonewas
Kathleen M. Hoffman, and consolidationhavebeeninvestigatedaspos- notasignificantfactorforflexural
sibledirectdentalfillingmaterial.Thesur- strengths,buttherewasasignificantinter-
Anthony A. Guiseppetti
faceofthesilverpowdermustundergoan actionbetweenconcentrationandpH
acidtreatmenttoremoveexistingcontami- (p<0.0001).Microscopyrevealedthatthe
American Dental Association nantsandpreventformationofnewsurface acid-treatedsilverpowderdemineralized
contaminantsduringconsolidation.This approximately2mmofdentinwhenused
Health Foundation, Paffenbarger
studywasdesignedtoinvestigatetheeffect withnoliner.Theuseofcopalor
Research Center, National Institute oftheacidtreatmentonthestrengthofthe polyamidevarnisheseliminatedmostofthis
of Standards and Technology, consolidatedalloy,itsreactivitywiththe demineralization,buttheuseofadentin
surroundingtoothstructure,anditsreac- adhesivelinerresultedinsomedislodgment
Gaithersburg, MD 20899-0001
tionswithcertaincavityliners. andbreakdownoftheadhesivefilmbythe
ThisstudyinvestigatedtheeffectsofpH acid.
and andconcentrationoffluoboricacidonthe Theresultsofthisstudyindicatethat
flexuralstrengthofsilverpowderconsoli- thissilverpowderwhentreatedwithdilute
datedintorectangularbeamsinapartial fluoboricacidatapHofapproximately1.0
Michael M. Wray and Rangall J. 434design.Thestudyalsoassessed,by canresultinafillingmaterialwithstrength
Avers visibleandscanningelectronmicroscopy, equivalenttocurrentlyusedconventional
whateffecttheacid-treatedpowdershad amalgam.Thedemineralizationoftooth
ondentinthathadbeenpre-coatedwith structureappearstobeminimalandcanbe
Naval Dental School
differentcavityliners.Meanflexural eliminatedwiththeuseofcavityliners.
Bethesda, MD 20899-5602 strengthsforbeamsconsolidatedusingden-
talhandinstrumentswereintherange
(77.069.28)MPato(166.1617.6)MPa, Keywords: acid-assistedconsolidation;
cold-welding;consolidatedsilver.
wherethequoteduncertaintiesarestandard
uncertainties(i.e.,onestandarddeviation
estimates).ANOVAindicatedthatfluoboric Accepted: July7,1998
acidpHwashighlysignificant(p<0.0001)
withlowerpHvaluesresultinginhigher Availableonline: http://www.nist.gov/jres
1. Introduction
Amalgamhasservedeffectivelyasadentalrestorative been overwhelmingly successful [7, 8].
materialsinceitsintroductionintotheUnitedStatesby Since 1992, scientists from the American Dental
the Crawcour brothers in 1833 [1]. Recently, there has Association Health Foundation and from the Electro-
beenmuchcontroversyovertheuseofamalgamdueto chemical Processing Group of the National Institute of
documented hypersensitivities, accidental over-expo- StandardsandTechnologyhavebeencollaboratingona
suresandthepotentialenvironmentalimpactassociated newmercury-freedentalfillingalloy.Thisnewalloyis
with its disposal [2,3,4]. In an attempt to reduce the acombinationofpowderedmetals,consistingmostlyof
release of potentially hazardous mercury, research has silver, that produce a filling material very similar in
led to the development of indium- and gallium-based properties to those of cohesive gold used for directly
admixed alloys [5, 6]. Despite improved mechanical placed restorations. The powdered metal is annealed,
properties, these gallium and indium alloys have not chemically treated to remove surface contaminants,
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1. REPORT DATE 3. DATES COVERED
JUL 1998 2. REPORT TYPE 00-00-1998 to 00-00-1998
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Acid-Assisted Consolidation of Silver Alloys for Direct Fillings
5b. GRANT NUMBER
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
5e. TASK NUMBER
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
Naval Dental School,Bethesda,MD,20899-5602 REPORT NUMBER
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S)
11. SPONSOR/MONITOR’S REPORT
NUMBER(S)
12. DISTRIBUTION/AVAILABILITY STATEMENT
Approved for public release; distribution unlimited
13. SUPPLEMENTARY NOTES
14. ABSTRACT

15. SUBJECT TERMS
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Volume103,Number5,September–October1998
Journal of Research of the National Institute of Standards and Technology
and compressed into a solid mass. Welding of the 2.1. Concentration and pH Effects
individualoxide-freeparticlesisaccomplishedbycold-
weldingthemetalatroomorbodytemperature,similar Theprecipitatedsilveralloypowderwasactivatedby
to the process used for cohesive gold. In addition to submersing a sample of the powder at mass 0.65 g in
cold-welding, another unique characteristic of this 350 mL of 10 % HBF (pH<1) in a glass beaker and
4
system is the condensability of the powders under the stirringitwithaslowlyrotatingoverheadstirringpaddle
liquidcarryingmedium.Thepowdersaredeliveredasa for 1 min. The alloy was allowed to settle for approxi-
slurryormixtureofmetalparticleswithinadiluteacid. mately4min.TheHBF wasthendecanted,leavingthe
4
The acid serves to both remove surface contaminants settledpowderaswetslurry.Theslurrywasthenrinsed
and protect the particles from reoxidizing during in500mLofasecondsolutionofselectedconcentration
consolidation. and pH (see Table 1) and slowly stirred for approxi-
Effective cleaning of the powder surface may be mately 5 s.
related to many factors. A dilute solution of aqueous
fluoboricacid(HBF ,dilutedfromanacqueousstarting
4
Table1. Therinseusedinthesecondstepforalloyconsolidation
solution with a mass fraction of 48 %) with a volume
fraction in the range of 2 % (pH=0.97) to 10 %1
Rinsesolution pH (volumefraction,%)
(pH<1) has proven effective in facilitating cold weld-
ing,butthemechanismofsurfacecleaningandeffectof 1. HBF (nobuffer) <1 10
4
acidpHorconcentrationareunknown.Thepurposeof 2. HBF (NaOH) 0.97 10
4
the first part of this study was to determine which fac- 3. HBF (NaOH) 2.57 10
4
tors or combination of factors related to the activation 4. HBF (NaOH) » 5.0 10
4
acidwouldhavethegreatesteffectontransverserupture 5. HBF (nobuffer) 0.97 2
4
strengthoftheconsolidatedsilverpowder.Thetwopri- 6. HBF (NaOH) 2.57 2
4
mary factors studied were solution concentration of 7. HBF4(NaOH) » 5.0 2
HBF4 and pH (H+ concentration) of the aqueous HBF4 8. SingleH2O(HBF4) 2.57
solution. 9. SingleH2O(HBF4) » 5.0
Since the powder/acid slurry is consolidated directly andNaOH)
into the tooth cavity, there exists the possibility of a 10. DoubleH2O » 5.0
reaction between the HBF and the tooth structure.
4
Traditional cavity preparations are often lined with
varnishes or adhesive polymers prior to placement of a
fillingmaterial.Theeffectivenessoftheselinersinthe Atotalof10rinsingtreatmentsweretested.ThepHof
presence of this powder/acid slurry, and possible reac- rinse solutions 2 to 4 and 6 and 7 were adjusted by
tions of the slurry with these liners are also unknown. addingsodiumhydroxide.Rinsesolutionnumber8was
Therefore, the purpose of the second part of this study distilled waterwith10%HBF4 addedtolowerthepH
was to determine if the dilute HBF acid would react to 2.57. The pH of 2.57 was chosen because residual
4
significantly with the tooth dentin, and if the use of 10%HBF4leftfromtheactivationinthepowderslurry
varnishes and liners would prevent any such reaction. loweredthepHofthedistilledwaterrinseto2.57.Rinse
Lastly, the use of lining materials in combination with solutionnumber9wasdistilledwaterwith10%HBF4
thepowder/acidslurrywastestedtoseeifthepresence addedtolowerthepHto2.57thenbufferedwithNaOH
of these liners would adversely affect the transverse to bring the pH to 5. Rinse solution 10 repeated the
rupture strength of the consolidated silver alloy. distilled water rinse twice.
After the powder had settled again and the second
rinse solution had been decanted, transverse rupture
2. Materials and Methods
strengthsamplesweremadebytransferringtheremain-
ing powder slurry to a steel mold with a rectangular
Thesilveralloypowderusedinthisstudywaschem-
cavity 14.01 mm in length by 3.01 mm in width by
ically precipitated using a reduction reaction in a solu-
20 mm in height. Consolidation of the silver powder
tionofsilverfluoroborate.Afterchemicalprecipitation,
was done by placing a single increment of the slurry
the silver powder was dried and sieved through a 200-
intothebaseofthemoldcavityandorganizingtheloose
meshsievetoremovethelargeagglomerates.Thesieved
powder was then annealed for 2 h at 4508C before powdertoformaflat,evenlayer.Thepowderwasthen
pressed with a flat-ended plunger using a hydraulic
activation in acid and consolidation.
pressataloadsufficienttodeliveranaveragestressof
1Allpercentvalueshereafterarevolumefractions. 150 MPa to the powder. This stress was chosen to
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Volume103,Number5,September–October1998
Journal of Research of the National Institute of Standards and Technology
matchthedensityachievedbyincrementallyconsolidat- Co.,Skokie,IL)copalresinwasplacedontheairdried
ingthesamepowderusinghanddentalinstruments.The preparationintwocoatswith30sairdryingaftereach
finalthicknessoftheconsolidatedsampleswasapprox- coat; Group 3: Barrier(cid:212) (Teledyne Getz, Elk Grove
imately 1.5 mm. Five samples were consolidated for Village, IL) polyamide varnish was placed on the air
each activation/rinsing treatment. After consolidation, dried preparation in one coat, left to dry for 15 s and
the samples were stored overnight in a desiccator and thenairdried;andGroup4:MirageABC(cid:212) (Chameleon
thendrypolishedinalongitudinaldirectionon1200grit Dental, Kansas City, KS) the air dried preparation was
siliconcarbidepaperuntilallsurfacesweresmoothand conditionedwith10%phosphoricacid(HPO)for15s
3 4
free of defects. Each sample was measured in all three followed by rinsing with water and lightly air drying.
dimensions and weighed. The polished samples were MirageprimerAandprimerBwerethenmixedandthe
then tested on a three point bending fixture with a adhesive resin was applied in five coats to the prepara-
fulcrum spacing of 10 mm using an Instron 5500R tion, lightly air drying after each coat.
universal testing machine (Instron Co., Canton, MA)2. Theexperimentalsilveralloywasactivatedfollowing
Load was applied to the center of the sample at a con- thesamemethodasinSec.2.1witharinseof2%HBF
4
stantcrossheadspeedof0.5mm/minuntilfailure.Den- (pH=0.97). The alloy was incrementally consolidated
sity and transverse rupture strength were calculated into five teeth of each lining group (total of 20 teeth)
fromthemeasureddimensions,weightandfailureload usinga1.15mmdiameter,serratedamalgamcondenser
of each individual sample. Transverse rupture strength under a load arising from approximately 2.5 kg to
(TRS),whichisastress(i.e.,forcedividedbyarea),was 3.5kg.Aloadtablewasusedtomeasuretheloaddeliv-
calculated for each specimen from the equation TRS = ered to the condenser as it was stepped over the entire
1.53106Fl/t2w,whereFistheloadatfailure,listhe area of the sample in half overlapping uniform steps.
distancebetweenfulcrums(l=10–2m=10mm),tisthe Fiveorsixincrementsweresequentiallyconsolidatedto
thickness of the specimen, and w is the width of the completelyfillthecavity.ExcessHBF wasremovedby
4
specimen.DatawasanalyzedbyANOVAandvaluesof absorbingtheacidoffthesurfaceofthesilveralloywith
TRS compared using Tukey’s multiple comparison. cotton rolls after consolidating each increment. After
consolidation was complete, the silver was burnished
2.2 Evaluation of Lining Materials and excess silver was removed with rotary polishing
burs.
Forty previously extracted, noncarious and TheTytin(cid:212) amalgamalloywasincapsuleformand
nonrestored human molar teeth were mounted in Ultra triturated per manufacturer instructions using a
Mount(cid:212) methyl methacrylate (Buehler Corp., Lake Vari-mix III(cid:212) amalgamator (Caulk/Dentsply, Milford,
Bluff, IL) and stored in 0.015 mol/L sodium azide. DE)for9sonmediumspeed.Theamalgamwasincre-
Class I cavity preparations were then placed in the mentally consolidated into the cavity preparation of 5
occlusal center of the teeth. The preparation was a teethofeachlininggroup(totalof20teeth)ontheload
“dogbone” retentive shape approximately 6 mm long tableataloadarisingfromapproximately1.5kginthe
and2mmwidewitha2mmdepthandroughlyparallel samemannerastheexperimentalsilveralloy.Thecon-
walls. Each preparation was cut using a new[557 bur solidation process was repeated for approximately four
and air/water spray just prior to restoring. The teeth totalincrementsofthealloyoruntilthecavityprepara-
were divided into four equal groups. Each group tionhadbeenslightlyoverfilled.Afterconsolidationwas
received one of the following: no liner, copal varnish, complete, the amalgam was burnished and excess was
polyamide varnish, or a polymer adhesive resin liner. removed with carvers.
Theliningmaterialwasselectedaccordingtotheorder Alltoothspecimenswerestoredindistilledwaterfor
providedinarandomnumbertabletominimizeoperator a minimum of 24 h at 378C after filling placement.
bias. Subsequently, each sample was sectioned with a
Thevarnishesandadhesivewereplacedpermanufac- diamondsawat300revolutionsperminuteusingahigh
turerinstructionasfollows.Group1:cavitypreparation concentration diamond-wafering blade and distilled
receivednoliner;Group2:Copalite(cid:212) (H.S.Bosworth water lubrication. The samples were polished sequen-
tiallyusing(1200,2400,and4000)gritsiliconcarbide
paper with distilled water lubrication on an optical
2Certaincommercialequipment,instruments,ormaterialsareidenti- polishingwheel.Theywerethenpolishedwith(6,3,1,
fiedinthispapertofosterunderstanding.Suchidentificationdoesnot and 1/4) mm Metadi(cid:212) II diamond polishing compound
implyrecommendationor endorsementbytheNationalInstituteof
(Buehler, Lake Bluff, IL) and DP-Lubricant Blue
Standards and Technology or the American Dental Association
HealthFoundation,nordoesitimplythatthematerialsorequipment (Struers,Westlake,OH).Thesampleswererinsedwith
identifiedisnecessarilythebestavailableforthepurpose. an ethanol stream and air-dried.
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Volume103,Number5,September–October1998
Journal of Research of the National Institute of Standards and Technology
Each half of each tooth was examined and variance on all of the treatment groups showed pH
photographed using reflective light microscopy on a havingasignificanteffectatp<0.0001andtheinterac-
Olympus BH2(cid:212) microscope (Olympus Co., Lake tion between pH and concentration was significant at
Success, NY) with polarized light and a Nomarski p<0.0001. Concentration alone was not a significant
differentialinterferencecontrast.Aphotomicrographof factor.ATukey’smultiplecomparisonatanalphalevel
a 0.01 mm calibration slide was taken for standardiza- of 0.05 resulted in groupings of similar treatments as
tion of measurements from the reflective light indicated by the letters in Table 2.
microscope. After this examination, one half of each
tooth was examined directly with a scanning electron
Table 2. The mean and sample standard deviation of transverse
microscope (SEM) and the other half indirectly. The
rupturestrengthforeachrinsingregimen(thelettersindicatestatisti-
halves for direct SEM observation were placed under calgroupingatp<0.05usingTukey’smultiplecomparison)
vacuumforatleast1weekpriortoexaminationinorder
toremovemoisture.Thehalfusedforindirectobserva- Rinsesolution MeanTRSandsample
tionwasimpressionedwithReprosil(cid:212) (Caulk/Dentsply, standarddeviation(MPa)
Milford,DE)hydrophilicvinylpolysiloxaneimpression
1. 10% pH<1 166.08617.58 (a)
material for the negative impression, and the positive 2. 10% pH=0.95 162.44614.59 (a)
replication made with Epon 828s (Shell Chem. Co., 3. 10% pH=2.57 139.70619.45 (a,b)
Houston, TX) low viscosity epoxy resin. The tooth 4. 10% pH» 5 77.0469.28 (d)
halves and epoxy replicas were mounted on aluminum 5. 2% pH=0.95 151.76617.03 (a)
6. 2% pH=2.57 115.2866.47 (b,c)
studs with carbon paint, gold sputtered using an Ultra-
7. 2% pH» 5 106.82613.86 (c)
spec 90 sputter coater (Energy Beam Sciences, 8. SingleHOrinse pH=2.57 113.23611.21 (b,c)
2
Agawam,MA)andexaminedat10keVonaJSM5300 9. SingleHOrinse pH» 5 118.1166.30 (b,c)
2
SEM (JEOL, Peabody, MA). Photomicrographs were 10. DoubleH2Orinse pH» 5 94.6465.54 (c,d)
obtained along the pulpal floor of each restoration and
measurements made to quantify any surface reaction
zone present in the tooth dentin. The measurements
wererecordedandthenaveragedforeachsample,along 3.2 Evaluation of Lining Materials
with a description in order to identify the location and
characteristics of the reaction zone. Scanning electron and light microscopy consistently
To investigate the possibility of contamination of the revealedretentionofthetwovarnishesunderallcondi-
alloy powder by the liner or varnish, 20 experimental tions.Therewasagapbetweentheamalgamandtooth
silveralloysampleswerepreparedfortransverserupture surfacewhennolinerornovarnishwasutilized.Gener-
strengthanalysis.Noliner,Copalite(cid:212) varnish,Barrier(cid:212) ally,therewasanarrowzoneofdemineralizationinthe
varnish,andMirage(cid:212) adhesive(n=5foreachmethod) samples restored with the new alloy and no liner. The
wereappliedtothewallsofarectangularstainlesssteel adhesivelinerhadavisiblereactedzoneofdentinwith
split mold 14.01 mm33.01 mm. The silver powder boththenewalloyandtheamalgamwhichisconsistant
alloywaspreparedandconsolidatedintothemoldincre- in appearence with an adhesive hybrid zone. The
mentallyusingthesameinstrumentsandmethodsused indirectreplicatetechniqueyieldednoadditionalinfor-
intheextractedteeth.Afterthemoldwasfilledandthe mation. Table 3 is a summary of the observations and
samplewasremoved,storedfor24hinadesiccator,and average thickness of the various lining materials in
drypolishedwith1200gritsiliconecarbidepaperuntil micrometers.
all surfaces were smooth and free of defects. Length,
width, thickness and weight were recorded for each Table3. Microscopyresults
sample.Thesamplesweretestedforthreepointflexural
strength by central loading in the same manner Experimentalalloya Amalgama
described in Sec 2.1.
Noliner 2.2(affected) 0.9(smearlayer)
5.4(shrinkagegap)
3. Results Copalvarnish 4.7(varnishlayer) 6.7(varnishlayer)
Polyamidevarnish 5.1(varnishlayer) 7.2(varnishlayer)
3.1 Concentration and pH Effects
Adhesive 6.9(hybridlayer) 6.0(hybridlayer)
ThemeanTRSandsamplestandarddeviationforeach aThenumbersarelayerthicknessinmm;affectedreferstothethick-
treatment group is given in Table 2. An analysis of nessofthedemineralizedzoneofdentin.
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Volume103,Number5,September–October1998
Journal of Research of the National Institute of Standards and Technology
Transverse rupture strengths were recorded for the would also limit the degree of demineralization that
fourgroupsofsilverconsolidatedinthepresenceofthe couldoccur.Theadaptationofthealloytothisdeminer-
different liners and the mean values given in Table 4. alizedsurfacewasverygoodandnoopeninterfacesor
Therewasnostatisticallysignificantdifferencebetween contractiongapswereobserved.Theconsolidatedalloy
the treatments (analysis of variance at p#0.05). did not undergo any shrinkage and did not exhibit the
shrinkagegapobservedintheamalgamrestorations.No
Table 4. Mean and sample standard deviations of TRS values of noticeablereactionwasobservedatanyoftheenamel/
silverconsolidatedinthepresenceofdifferentliners alloy interfaces.
According to Mertz-Fairhurst and Newcomer [10],
Varnish MeanTRSandsample
an average amalgam/tooth interface gap with a dis-
oradhesive standarddeviation(MPa)
persedphaseamalgamwasapproximatedat13mmwith
Noliner 103.268.3 asamplestandarddeviationof10mm.Brannstrom[11]
Copal 103.063.5 reported a 5 mm to 20 mm gap. These data appear
Polyamide 94.7612.0 consistent with the results obtained in this experiment.
Adhesive 91.7611.0
EamesandHollenback[12]reportedtheaveragethick-
nessofCopalite(cid:212) was2mm,andathicknessof3mm
to 9 mm was reported by Dolven [13]. An average
4. Discussion smearlayerwasreportedtobe5mm[11],againconsis-
tent with results presented here.
The results from Sec. 3.1 indicated that transverse Resultsfromscanningelectronmicroscopyweredif-
rupturestrengthisnotadverselyaffecteduntiltherinse ficult to interpret due to shrinkage artifacts introduced
pHrisesabove2.5.Concentrationwasnotasignificant duringdesiccationofthetoothsamples.Reflectedlight
factor,anditappearsthatusingarinseof2%HBF at microscopy avoided the problem with drying artifacts
4
thepHof0.97achievesadequatestrength.Thevolumes andseemedtoyieldmicrographsthatgaveafairrepre-
ofacidusedfortheseactivationexperimentswerevery sentation of tooth/silver interface.
largeandfurtherexperimentswillneedtoberuntofind Anotherconcernwithusinglinerswasthepossibility
thecriticalvolumes,times,andstirringregimensneces- of the lining material reacting with the surface of the
saryforactivation.Thesurfacecleaningofthepowder, powderparticlesandpreventingcold-welding.Thiswas
however,appearstoprovideforsufficientcold-welding especially a concern in the case of the adhesive resin
to occur at this pH. whereitwasobservedthattheacidbecamecloudyafter
In Sec. 3.2, the varnishes appeared to remain intact contacting the cavity wall. The flexural strength mea-
on the dentin surface but there was evidence that the surements made on samples where the mold was lined
resinadhesivehadbeendislodged.Largeinclusionsof withthevarnishesandresinindicatedthatthelinershad
the resin were observed in some specimens that noeffectonstrength.Apparently,noreactionsoccurred
appeared as agglomerated polymer that had been to interfere with the cold-welding of the silver.
removed from the cavity surface. The adhesive in the In an attempt to further investigate what was occur-
hybrid layer, however, was well retained. The resin ringwiththevariousliners,asimpleadditionalexperi-
adhesive liner caused the acid to rapidly produce a mentwasconducted.Theexperimentconsistedofplac-
cloudy dispersion when the powder/acid slurry was ing one coat of polyamide varnish, two coats of copal
condensedintothepreparation.Thismayhavebeendue varnishandfivecoatsofdentinadhesiveontoseparate
to the hydrolytic degradation of the surface adhesive glassslides.Adropof2%HBF wasplacedontoeach
4
that was not entangled with the collagen of the hybrid oftheseslides.Theadhesivewasrapidlydislodgedand
layer. disrupted from the slide while the two varnishes re-
Wherenolinerwasused,theobservedreactionzone mained intact. This supplemental experiment helped
appeared to be demineralized. The depth of this dem- confirm what was observed in the tooth samples.
ineralization, approximately 2 mm, was less than that
observed with the dentin adhesive and consistent with
the demineralization experienced with etchants used 5. Conclusions
with dentin adhesives [9]. The reason for this rather
shallow level of demineralization was probably due to Fromtheseexperiments,itappearsthatactivationof
the short contact time that the acid had with the tooth this silver powder can be adequately achieved using a
surfaceduringconsolidation.Thesmallvolumeofacid regimen consisting of an initial immersion in 10 %
that could remain at the interface during consolidation HBF aqueous solution followed by a rinse in a HBF
4 4
and the high buffering capacity of the tooth surface aqueous solution at a pH below approximately 2.5.
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Volume103,Number5,September–October1998
Journal of Research of the National Institute of Standards and Technology
A 2% aqueous solution of HBF demineralizes the About the authors: Frederick C. Eichmiller is a
4
dentincavitysurfacetoadepthofapproximately2mm mechanical engineer/dentist and directs the American
whennocavitylinerisused.Cavityvarnishesandadhe- Dental Association Health Foundation’s Paffenbarger
sive resin liners will prevent this demineralization. The Research Center at NIST. Kathleen M. Hoffman is a
adhesiveonthesurfaceofthecavitydoesnot,however, chemist and Anthony A. Guiseppetti is a metallurgical
remainadherenttothecavitywallinthepresenceofthe technician at the Paffenbarger Research Center. The
powder/acid slurry. In addition, no shrinkage gap PaffenbargerResearchCenterexistswithintheDental
appeared between the cavity wall and the consolidated andMedicalMaterialsGroupatNISTunderaCooper-
silver. ative Research and Development Agreement between
theADAHFandNIST.MichaelM.WrayandRandallJ.
Avers are U.S. Navy dental officers taking part in a
Acknowledgment residencyprogramattheNavyDentalSchool,National
Naval Medical Center in Bethesda, Maryland. The
This investigation was supported in part by the National Institute of Standards and Technology is an
USPHSResearchGrantP50DEO9322totheAmerican agencyoftheTechnologyAdministration,U.S.Depart-
Dental Association Health Foundation from the ment of Commerce.
National Institutes of Health–National Institute of
Dental Research and is a part of the dental research
program conducted by the National Institute of
Standards and Technology in cooperation with the
American Dental Association Health Foundation.
6. References
[1] R.G.Craig,RestorativeDentalMaterials,9thed.,C.V.Mosby
Co.,St.Louis(1993).
[2] J. R. Mackert, Dental amalgam and mercury, J. Am. Dent.
Assoc.122(9),54–56(1991).
[3] J.G.Bauer,Actionofmercuryindentalexposurestomercury,
Op.Dent.10(3),104–113(1985).
[4] I.M.C.Lundstrom,Allergyandcorrosionofdentalmaterials
inpatientswithorallichenplanus,Int.J.Oral.Surg.13(1),
16–24(1984).
[5] D.SmithandH.Caul,Alloysofgalliumandpowderedmetals
as a possible replacement for dental amalgam, J. Am. Dent.
Assoc.53,315–324(1956).
[6] W. V. Youdelis, Amalgam as a restorative material: is there
anythingnew?,J.Esthetic.Dent.4(2),61–63(1992).
[7] D.Smith,H.Caul,andW.Sweeney,Somephysicalproperties
ofgallium-copper-tinalloys,J.Am.Dent.Assoc.53,677–685
(1956).
[8] G. H. Johnson, A laboratory evaluation of two new dental
amalgam alloys, IADR Prog. Abstr. 64, Microfilmed paper
[921oftheDentalMaterialsGroup(1985).
[9] R. L. Bertolotti, Conditioning of the dentin substrate, Oper.
Dent.Supp.5(1992)pp.131–136.
[10] E.Mertz-FairhurstandA.Newcomer,Interfacegapatamal-
gammargins,Dent.Mater.4(3),122–128(1988).
[11] M. Brannstrom, Smear layer: pathological and treatment
considerations,Oper.Dent.Supp.3(1984)pp.35–42.
[12] W.EamesandG.M.Hollenback,Cavitylinerthicknessand
retentive characteristics, J. Am. Dent. Assn. 72 (1), 69–72
(1966).
[13] R.C.Dolven,Micromeasurementofcavitylining,usingultra-
violetandreflectedlight,andtheeffectofthelineronmarginal
penetration,evaluatedwithCa45,J.Dent.Res.45(1),12–15
(1966).
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