Dentai Research

The dentinal surface: Its influence on dentinal adhesion. Part IIIJ. David Eick*/Scott J. Robinson**/Robert P. Chappdl***/Charles M. Cobb****/Paulette Spencer*****

This final paper in a series of three mes transmission and scanning electron microscopyto compare the category HI dentinal adhesive systems—those with shear bond strengthvalues near or exceeding ¡7 MPa. Contemporary commercial denlinal adhesive systemssuch as Superbond and Seotchbond Multi-Purpose, chosen for their varied chemicalpretreatments. are contrasted: a contemporary commercial system (Prisma UniversalBond 3) with characteristics of category I and H dentinal adhesives is also included forcomparison. The shear bond strength values attained with most category III systemsare high enough to cause cohesive failure of the dentin during bond strength testing-This result is attributed to a combination of factors that include effective wetting andpenetration of the prepared dentinal .surface as well as a tendency to leave collagenfibers al ¡he adhesive-den tin interface in an apparently structurally iniaci stale.(Quintessence Int, 1993:24:571-582.)

Introduction

In the first two parts of this series.'- it was stated thatdentinal adhesives can be categorized broadly intothree groups according to chronology, chemistry, andshear bond strength. The category I dentinal adhe-sives, including Seotchbond Dual Cure (3M Dental),Dentin Adhesit (Vivadent), and Gluma (Miles), whichproduced shear bond strength values of 5 to 7 MPa,were discussed, along with a brief review of the effects

Curators' Professor atid Chairmûti, Departmetlt of Oral Bi-ology. University of Mrssotiri-Kansas City, School of Deti-listry, 650 East 25lh Street, Kansas City, Missouri 64108.Manager, Electron Microscope Laboratory. Department ofOral Biology, University of Missouri-Han sa s City.Professor Emeritus, Department of Oral Biology, LIuivetsilyof Missouri-Kansas City.

Professor of Periodontics and Oral Biology, University ofMissouri-Kan sas City,

Assistatil Professor of Oral Biology and Pédiatrie Dentistry,University of Missouri-Kan sa s City.

of the smear layer, in part L' The second publication^concerned category II dentinal adhesives, which in-clude the experimental and commercial products de-rived from Bowen's-*" work with ferric and aluminumoxalates and have produced shear bond strength val-ues between 8 and M MPa. Part til will discuss cat-egory III dentinal adhesive systems, specifically Su-perbond (Sun Medical). Seotchbond 2 and Scotch-bond Multi-Purpose (3M Dental), and All-Bond(Bisco Dental). These adhesives have producedshear bond strength values equal to or greater than17 MPa,**-" Prisma Universal Bond 3 (Caulk/Dents-ply), a contemporary dentinal adhesive that does notfit the criteria for category III materials, will also beanalyzed for comparative purposes.

The use of transmission electron microscopy (TEM)and scanning electron microscopy (SEM) has dem-onstrated that characteristics of the dentinal adhesivesdiscernible at the microscopic level contribute signif-icantly to understanding of the effects of the variousadhesive systems on the prepared tooth surface. Aprimary characteristic, visible by TEM, is the degreeof wetting or penetration that the adhesive systemsexhibit when applied to the smear layer, the modifiedsmear layer, or the cleansed and conditional dentinal

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Table ! Materials tested atid their mean shear bond strengths

Product Chemical composition Shear bond strength(MPa)

Primer — alcohol solution of a phosphoric acid ester 11.2 + 5.4(PENTA) and HEMAAdhesive — Urethane elastoineric resin plus PENTA and0.70% glutaraldehydeConditioner — a reaction product of SA and HEMA 15.6 ± 4.9(pH 4.4)Primer:

NTG-GMABPDM

Bonding resin — bis-GMA and HEMAPrimer — aqueous solution of organic acid (maleic) and 22.9 + 10.8"hydrophilic methacrylate monomer (HEMA) 11.4 + 2.8^Adhesive — hydrophUic niethaerylate monomer (HEMA);hydrophobic bis-GMA photoinitiator and viscositymodifier (5% by wt)Etchant — 10% citric acid and 3% ferric chloride 22.9 + 6.9Adhe.^ive liquid— 4-META in MMA initiated by partial-ly oxidized TBBAdhesive powder — polymethylmethacrylateEtchani — 10% maleic acid and a non-silica-containing 25.0 + 6.0thickenerPrimer — aqueous solution of HEMA and a polyalkenoieacid CO polymerAdhesive — hydrophobic his-GMA, hydrophilic HEMA,and a photoinitiator

HEMA = 2-hydroxyethyl methacrylate: SA = siiccinic anhydride: NTG-GMA = N-(p-tolyl) glycine glycidyl melhacrylate; BPDM =biphenyl dimethacrylate; bis-GMA = 2,2'-bis [4 (2-hydroxy-3-methacryloylofLypropyloxy phenyl propane)]: UDMA = ureihane dimetha-crylate; 4-META = 4-methacryloxycthyl trimellitic anhydride; MMA = methyl methacrylate: TBBO = tri-N-butyl borane• From Chappell el al."°' From Chappell et al."

Prisma Universal Bond 3

All-Bond

Scotchbond 2

Superbond

ScotchbondMulti-Pnrpose

surface. Il has been shown that as the wettability orpenetration of the various adhesive systems improves,shear bond strength similarly improves.'- The objec-tive of this paper is to analyze the third category ofdentinal adhesives using shear bond strength data andscanning and transmission electron microscopy. Themicrostructure ofthe category III dentinal adhesivesat the dentin-adhesive interface will be discussed inrelation to shear bond strength values.

Method and materials

Previous publications have described in detail thetechniques involved in preparation of specimens for

TEM and SEM.''^''^'* Fresh, noncarious, uneruptedhuman third molars were used. After they werecleaned and immersed in 0.9% saline solution, andwithin 24 hours of extraction, the teeth were sectionedthrough the occlusal one third with a low-speed dia-mond saw (Buebler), mounted in cold-curing polymer(Unitek), abraded with wet 320-grit silicon carbidepaper to produce a smear layer,'' and treated with theappropriate adhesive system. Manufacturer's instruc-tions were followed for each commercial product.

Specimens prepared for SEM were mounted on 12-mm aluminum stubs with cyanoacrylatc cement anddried in desiccators with calcium sulfate desiecant(Drierite, Fisher Scientific). After at least 1 week of

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Figia Transmission electron mieroscopic photomiero-graph of ttie smear iayer treated witti Prisma UniversaiBond 3 primer, (PSL) Primed smear layer; (D) nondemin-eralized dentin; (DT) dentinai tubule. Bar = 1 um.

Fig Ib Transmission electron microscopic photomicro-graph of Prisma Universal Bond 3 adhesive applied to theprimed smear layer surface. (PA) Prisma Universal Bond3 adhesive; (PAD) Prisma Universai Bond 3 adhesive-den-tin interface, (D) nondemineralized dentin. Bar = 1 tm.

desiccation, the teeth were sputter coated with ap-proximately 75 mn of gold-palladium and observedwith a Philips SEM 515 scanning electron microscopeat 15 kV and a 20-nm spot size.

The TEM samples were prepared as described pre-viously,'•-•^•'=' ''' Thin sections 90 to 100 nm thick werestained, first with uranyl acetate and then with leadcitrate. The sections were observed and photographedwith a Phihps EM 300 transmission electron micro-scope at 60 or 80 kV. In some cases thin sections wereunstained; they were observed and photographed withthe Philips CM12 scanning transmission electron mi-croscope at 100 kV,

The methods for obtaining shear bond strength val-ues have been detailed by Chappell et af'" and Car-racho et al," The materials tested m this study, theirchemieal composition, and their shear bond strengthsare shown in Table \.

Results and discussion

Prisma Universal Bond 3

Prisma Universal Bond 3 produced an average shearbond strength of 11,2 + 5.4 MPa, This adhesive is acategory I material based on its chemistry and a cat-egory II material based on its shear bond strengthvalues. Prisma Universal Bond 3 is a chlorophosphateester bonding agent, similar to the older, light-curingScotchbond, Bondlite, and Light Curing Dentin-En-

amel Bonding Agent (Johnson & Johnson Dental),'^There is a significant difference in the shear bondstrength values of these latter materials (5 to7 MPa)'' ' and that of Prisma Universal Bond 3(11 MPa). Prisma Universal Bond 3 includes anacidic conditioner containing phosphoric acid ester(PENTA) and HEMA (2-hydroxyethyl methacrylate)as a pretreatment. The other three materials did notuse a HEMA-containing conditioner. Improvedbond strengths have been ascribed to HEMA-con-taining pretreatments,"-' and this may account forthe improved shear bond strength of Prisma UniversalBond 3, Testing in this laboratory has shown thatthis adhesive has a mean shear bond strength of11 MPa, which is much lower than that of the cate-gory III materials, Barkmeier and Cooley," however,have obtained shear bond strength values for PrismaUniversal Bond 3 in excess of 18 MPa; this resultwould put this material in the category III classifi-cation.

Figures la and lb are two TEM photomicrographsof a tooth treated with the Prisma Universal Bond 3adhesive system. The smear layer has been treatedwith primer in Fig la, and the primed smear layer hasbeen treated with adhesive in Fig lb. The primer, analcohol solution of a phosphoric acid ester (PENTA)and HEMA, altered the morphology of the smearlayer, but did not produce a large decalcified zone(Fig la),'-"""* However, when the adhesive, a ure-thane elastomeric resin plus PENTA and 0.70% glu-

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Fig 2a Transmission electron microscopic photomicro-graph Prisma Universal Bond 3 adhesive applied to theprimed smear layer surface, (PA) Prisma Universal Bond3 adhesive; (PAD) Prisma Universal Bond 3 adhesive-den-tin interface; (D) nondemtneralized dentin. Bar = 0.5 [im.

Fig 2b Same specimen as in Fig 2a at higher magnifica-tion. Bar = 0,1 um.

taraldehyde, was applied to the conditioned surfaee,the appearance of the outer surface of the dentinchanged significantly (Fig lb). The denlin is in thelower right half of the photomicrograph, the dentina!surface runs diagonally from the lower left to the up-per right corner, and the Prisma Universal Bond 3adhesive is shown in the upper left section {Fig lb).These photomicrographs suggest that the PENTA-HEMA pretreatment increased the ability of the ad-hesive to penetrate the conditioned smear layer; itappears that the adhesive penetrated the dentin to adepth of approximately 1 (jm. The enhanced penetra-tive capability of the adhesive was further demon-strated at higher magnification (Figs 2a and 2b),These figures support the results obtained in otherstudies," •'

Scanning electron microscopy of shear bondstrength specimens for Prisma Universal Bond 3showed that all the failures occurred at or near theadhesive-den tin interface; none of the shear bondstrength specimens showed cohesive failure of the den-tin or the composite resin. A typical failure pattern isshown in Figs 3a to 3d, Figures 3a and 3b show thetooth side of a shear bond strength specimen; Figs 3cand 3d show the composite resin side of the samespecimen. Failure occurred at or near the adhesive-dentin interface. It has been shown previously that ashear bond strength value of at least 17 M?a is gen-erally necessary before cohesive dentin failure is notedin the fracture pattern,'-'*'-'

All-Bond

The average shear bond strength for All-Bond ad-hesive was 15,6 + 4,9 MPa, This adhesive incorpo-rates HEMA into the conditioner as well as the bond-Ing resin. Two separate dentin-adhesive interfaces areshown in Figs 4a and 4b, Figure 4a is a TEM pho-tomicrograph of the interface of All-Bond adhesiveand the dentin. The adhesive penetrated the condi-tioned dentin surface to a depth of 2 to 3 |im, andseveral dentinal tubules (DT) filled with adhesive werefound at the base of the penetration zone. There ap-peared to be crystalline precipitates at the outermostsurfaee ofthe penetrated dentin, and there was a con-centration of apparent precipitate at the bottom ofthe penetration zone next to the dentin, A higher mag-nification of the same interface is shown in Fig 4b,demonstrating the same characteristics as Fig 4a. Thecrystalline precipitates at the top of the penetrationzone appeared to have affected the wetting of thesurface, because air was entrapped around some ofthem. The banded structure of the collagen wasalso seen in the hybrid or penetration zone. The pres-ence of the hybrid layer has been described previ-ously'• •' " '• " • ^ and has been shown to have a sig-nificant effect on the strength of the adhesive.

The failure pattern for the All-Bond shear bondstrength specimens is shown in Figs 5a to 5d, Againthe failure was predominantly at the adhesive-dentininterface, A smail area of cohesive failure ofthe ad-

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Fig 3a Scanning eiectron microscopic photomicrograph ofshear bond strength specimen ol Prisma Universai Bond3; tooth side, ¡F) Fracture surface. Bar - 1 tnm.

Fig 3b Same specimen as in Fig 3a at '.igher magnifica-tion. Bar = 10 |im.

%^^£_

,11! JiJ

•f l B u m l S e k i J

^ ^

Wl2 5 0 E 3 6 PUB

fl9

Fig 3c Same specimen as in Fig 3a; composite resin side,¡F) Fracture surface. Bar = 1 mm.

Fig 3d Same specimen as in Fig 3c at higher magnifica-tion. Bar = 10 |im.

Fig 4a Transmission electron microscopic photomicro-graph of the interface ot All-Bond adhesive and dentlh, ¡D)Nondemineraiized dentin; (DA) dentin-Ali-Bond adhesiveinterface; f/lJAIi-Bond adhesive; fDrj dentinal tubules; ¡CP)crystalline precipitates; ¡open arrows) apparent precipitateat the bottom of the penetration zone. Bar = 1 jam.

Fig 4b Area similar to that in Fig 4a at higher magnifica-tion, (D) Nohdemineraiized dentin; ¡A) Ali-Bond adhesive;¡CP) crystaliine; ¡BC) banded coiiagen, (open arrows) ap-parent precipitate at the bottom of the penetration zone.

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Fig 5a Scanning electron microscopic photomicrograph ofshear bond strength specimen of All-Bond adhesive; toothside, (arrows) Cohesively failed adhesive and compositeresin. Bar = 1 mm.

Fig 5c Same specimen as in Fig 5a; composite resin side.(arrows) Space where cohesiveiy faiied adhesive and com-posite resin had fractured out. Bar = 1 mm.

Fig 5b Same specimen as in Fig 5a, center section, alhigher magnification. Bar = 10 pm.

lSinlS.ekU 2,5 )E3 eee5xQe nLLB-c3 |

FigSd Same specimen as in Fig Sc, center section, athigher magnification. Bar = 10 jam.

hesive and composite resin appears in the iower rightcorner on the tooth specimen (Fig 5a). Its mirror im-age, the area fractured out, appears in the middle leftsection on the composite resjn side of the specimen(Fig 5c). None of the All-Bond shear bond strengthspecimens fractured cohesively in the dentin,

Scolchbond 2

When first tested, Seotchbond 2 exhibited an averageshear bond strength of 22,9 ± 10.8 MPaJ" However.when the same lot of materia! was tested about 1 yearlater in another project," an average shear bondstrength of 1Í .4 + 2.8 MPa, about half the original

value, was obtained. According to Erickson {EricksonRL, personal communication, July 1992), there is areaction over time between the maleic acid and theHEMA in the pritner; as this reaction proceeds, bondstrength decreases, Erickson^^ has discussed the im-portance of the primer with Seotchbond 2- Shear bondstrength values of 10 to 12 MPa have been routinelyreported for Seotchbond 2,"'"-'-^" The TEM andSEM specimens analyzed in this report are from thefresh Seotchbond 2 material that produced the 22,9MPa average shear bond strength value.'"

Figures 6a and 6b show TEM photomicrographsof the dentin-Scotchbond 2 interface. These surfaeeswere treated with the rnaleic aeid and HEMA primer

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» ^ • - . • ( • . . - • " '

•HL

•BHI

Fig 6a Transmission electron microscopic photomicro-grapti of the interface of primed Scotctibond 2 adhesiveand dentin. (D) Nondemineralized dentin; (DT) dentinal tub-ule; (HL) hybrid layer; (SB) Scotchbond 2 adtiesive. Bar =0.5 |xm.

Fig 6b Area similar to that in Fig 6a. (arrows) Depth ofdemineralization of the peritubular dentin and the penetra-tion of the Scotchbond 2 adhesive. Bar = 1 p.m.

followed by the application of the Scotchbond 2 ad-hesive. In Fig 6a, the nondemineralized dentin is inthe lower portion, an obliquely cut dentinal tubulefilled with Scotchbond 2 adhesive is in the center, thehybrid layer with the remnants of banded collagenruns from left to right in the middle, and the Scotch-bond 2 adhesive is in the upper portion. Microfillerparticles in the Scotchbond 2 adbesive did not pene-trate the hybrid layer; however, the primer or the ad-hesive appeared to have impregnated the hybrid layerdown to the untreated dentin. In Fig 6b, a dentinaltubule cut in a longitudinal direction displays pene-tration of tbe Scotchbond 2 adhesive several micronsdown its length. Of particular interest in this photo-micrograph are the etching effect of the maleic acidand HEMA primer on the dentin and the deminer-alization of the peritubular dentin to about halfwaydown the illustrated portion of the tubule. TheScotchbond 2 adhesive apparently penetrated to thelevel where the dentin was deminerahzed by theprimer; it does not appear that the adhesive extendedbeyond this point.

In more than half of the Scotchbond 2 shear bondtest specimens made from this lot of material, failureoccurred cohesively in the dentin, A typical failurepattern is shown in Figs 7a to 7d. Figure 7a is a low-power SEM photomicrograph of the tooth side of ashear bond strength specimen. The circular failurepattern in dentin is clearly delineated. The outer ad-hesive-dentin interface of this specimen is shown at

higher magnifieation in Fig 7b. The adhesive is on theleft half of the photomicrograph, and the dentin, withpartially occluded dentinal tubules, is on the right halfof the figure. The Scotchbond 2 adhesive remainedtenaciously attached to the dentin. The composite res-in side of the same shear bond strength specimen isshown in Figs 7c and 7d. The fractured dentin isshown in the top half of the photomicrograph (Fig7c}; the adhesive and composite resin are shown inthe lower half. In the higher-magnification photomi-crograph of the same composite resin specimen, themirror surface of the fractured dentin is in the upperportion and the adhesive in the lower portion of thephotomicrograph. The adhesive-dentin interface runsdiagonally from the lower left corner to the upperright corner. Adhesive tags that had penetrated thedentinal tubules are visible.

Super bond

Superbond (C & B Metabond in the United States)was one of the first dentinal adhesive systems to dem-onstrate a well-impregnated hybrid layer,' '-''"^^ Forthis system, the treatment ofthe dentinal surface withboth 10% citric acid and 3% ferric chloride has beenshown' "-'•- "-'' to be critical for achieving effective pen-etration and the formation of a hybrid layer. Perhapsbecause of tbis layer, Superbond has consistently pro-duced shear bond strengths greater than 17 MPa, Weobtained a mean value of 22.9 ± 6,9 MPa. Other

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Fig 7a Scanning eiectron microscopic photomicrograph otshear bond strength specimen of Scotchbond 2; tooth side.(PD) Fractured dentin, (ADI) Scotchbond 2 adhesive-dentininterface. Bar = 1 mm.

Fig 7c Same specimen as in Fig 7a; composite resin side,(FD) Fractured dentin; (SB) Scotchbond 2 adhesive; (C)composite resin. Bar = 1 mm.

Fig 7b Same specimen as in Fig 73 at higher magnifica-tion. (SB) Scotchbond 2 adhesive; (ADI) Scotchbond 2 ad-hesive-dentin interface; (D) dentin; (DT) dentinai tubules.Bar = 10 pm.

Fig7d Same specimen as in Fig 7c at higher magnifica-tion, (FD) Fractured dentin; (ADI) Scotchbond 2 adhesive-dentin interface: (SB) Scotchbond 2 adhesive; (AT) Scotch-bond 2 adhesive tags. Bar ^ 10 \im.

investigators"'^' have obtained similar sbear bondstrength values for this material.

Figures 8a and 8b show TEM photomicrographsof the dentin-Superbond interface. The dentinai sur-faces were pretreated with 10% citric acid and 3%ferric chloride, and the Superbond adhesive (4-METAin MMA) was applied. The dentinai surface was de-mineralized to a depth of 1 to 2 ¡xm, and the adhesiveresin penetrated completely through this zone to theunderlying nondemineralized dentin. Banded collagenremained in the demineralized layer that was pene-trated by the Superbond adhesive (Fig Sb),

Not only is it important for the dentinai adhesiveto completely penetrate the treated dentinai layer, but

the integrity of the remaining coilagen structure mayalso have a significant influence on adhesive strength.Certainly a demineraiized zone in which the collagenremained banded and presumably structurally intactwould be tougher or more rigid than a demineralizedlayer in which the collagen had been broken downinto a gel by the acid pretreatment. Superbond is oneof the few dentinai adhesives that we have studiedmorphologically that appears to preserve the integrityof the banded collagen to any great extent. It is pos-sible that banded collagen may be important inachieving a micromechanical interlocking of dentinaiadhesive into the layer of demineralized dentin, it mayplay just as significant a role in achieving adequate

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Fig 8a Transmission electron microscopic photomicro-graph of dentin treated with 10% citric acid and 3% ferricchloride with Superbond adhesive appiied, (SBA) Super-bond adhesive; (DL) demineraiized layer; (D} nondeminer-alized dentin. Bar — 1 pm.

Fig 8b Same specimen as in Fig 8a, (DL) Demineraiizedlayer; (D) nondemineralized denlin; (BC) banded collagen.Bar = 0,5 i m.

bonding strengths as does the complete penetrationand wetting of the adhesive into the demineraiizeddentin. Both of these phenomena appear to be majorcontributing factors to the achievement of high den-tinal bonding strengths. An excellent state-of-the-artliterature review of dentin- and enamel-bondingagents that briefly alludes to these points has recentlybeen published."

More than half of the Superbond shear bondstrength specimens failed cohesively in dentin, A typ-ical failure pattern of the tooth and composite resinside of a shear bond strength specimen is shown inFigs 9a to 9d, A large section of dentin fractured fromthe looth (Figs 9a and 9b) and was retained on thecomposite resin side of the shear bond strength spec-imen (Figs 9c and 9d), As discussed previously, whenshear bond strengths exceed 17 MPa, a majority ofthe failures occur cohesively in the dentin,

Scotchbond Multi-Purpo.se

Scotchbond M u Iti-Pur pose produced shear bondstrength values of 25,0 + 6,0 MPa, More than halfofthe failures occurred cohesively in the dentin, andmany others failed cohesively in the composite resin.Only 2 of 16 shear bond strength specimens failednear or at the adhesive interface.

Figures 10a and 10b show TEM photomicrographsof the interface of Scotchbond Multi-Purpose anddentin. The dentinal surface was etched with 10%

maleic acid and primed with an aqueous solution ofHEMA and a polyalkenoic acid copolymer. The ad-hesive, a hydrophobic bis-GMA and hydrophilicHEMA with a photoinitiator, was then applied to theprimed surface. As was true for Superbond, theScotchbond Multi-Purpose adhesive effectively wet-ted and penetrated the demineraiized layer of dentin.Although the maleic acid may denature the collagenmore than does the citric acid etchant used with Su-perbond, the interwoven fibrous collagen is still pres-ent, and some of the eollagen remains banded. Theinterlocked, banded collagen is clearly shown in Fig10b, The apparently structurally intact nature of theremaining collagen and the wetting and penetrationof the Scotchbond Multi-Purpose adhesive seem tohave significantly affected the shear bond strength.

The majority of the Scotchbond Multi-Purposeshear bond strength specimens failed cohesively indentin, producing failure patterns similar to thosewith Superbond. The typical failure patterns areshown in Figs 11 a to lid.

Based on these observations of category III dentinaladhesives and the Prisma Universal Bond 3 adhesivesystem, it is clear that the HEMA component.'' -'shared by many of these materials, plays a significantrole in the wetting and penetration of the adhesiveand therefore has a potential effect on shear bondstrength values. Current investigations in this labo-ratory are focused on labeling the HEMA monomerso that its path of penetration can be traced by using

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Fig 9a Scanning eiectron microscopic photomicrograph ofshear bond strength specimen of Superbond; tooth side,¡FD) Fractured dentin. Bar = 1 mm.

Fig 9b Same specimen as in Fig 9a at higher magnifi-cafion, ¡FD) Fractured dentin; ¡DT) dentinal tubule. Bar =10 tim.

Fig 9c Same specimen as in Fig 9a; composite resin side.(FD) Fractured dentin. Bar = 1 mm.

Fig 9d Same specimen as in Fig 9c at higher magnifica-tion. ¡FD) Fractured denfin; ¡DT) dentinal tubules. Bar =10 iim.

Fig 10a Transmission electron microscopic photomicro-graph of dentin treated with 10% maleic acid and Scotch-bond Muiti-Purpose primer and adhesive. (D) Dentin; ¡DT)dentinai tubules, ¡DL) demineralized layer; (SMR) remnantof the smear layer. Bar = 1 pm.

Fig 10b Same specimen as in Fig 10a, ¡D) Dentin; (DT)dentinai tubule; ¡¡JL) demineralized layer; ¡SMfí) remnantof fhe smear layer; ¡BC) banded collagen. Bar = 0,5 |im.

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Fig 11a Scanning electron microscopic photomicrographot shear bond strength specimen ol Seotchbond Multi-Pur-pose; tooth side. (FD) Fractured dentin. Bar = 1 mm.

Fig l ib Same specimen as in Fig 11a at higher magnifi-cation. (FD) Fractured dentin; (DT) dentinal tubules. Bar =10 |.tm.

Fig 11c Same specimen as in Fig 11a; composite resinside. (FD) Fractured dentin. Bar = 1 mm.

Fig l id Same specimen as in Fig 11c at higher magnifi-cation. (FD) Fractured dentin; (DT) dentinal tubules. Bar =10 |im.

a combination of scanning transmission electron mi-croscopy and energy-dispersive spectroscopy. Withthese techniques we will be able to further define thecharacteristics of the dentin-adhesive interface.

Summary

The results presented in Part I and Part II of thisseries, together with those presented in this paper,indicated that as the wetting and penetration of theadhesive systems improved, the shear bond strengthvalues for the dentinal adhesives also increased. Basedon these data, an effective dentin-adhesive bond de-pends on several factors, including the wetting and

penetration characteristics of the dentinal adhesivesystem and the reactivity of the treated dentinal sur-face. The present study also showed that the structureof the collagen in the demineralized dentin layer mayinfluence the behavior of the bond. Adhesive systemsthat did not eotnplctely denature the fibrous collagenand left interwoven, banded collagen in the demitier-ahzed layer, such as Superbond and Seotchbond Mul-ti-Purpose, produced superior bond strengths. Thesecategory III adhesives provide enough adhesivestrength that most bond failures occur cohesively inthe dentin or possibly in the cornposite resin. Thecategory III dentinal adhesives should provide thedentist with excellent materials for clinieal use.

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Acknowledgments

This project was supported in par! by research grant Nos. DE08223and DEÛ9696 Trom the National Insliltites of Health/Nalional In-stitute of Dental Reseai-ch. The authors gratefully acknowledge theassisiance of Ms Delores Sacktivich and Ms Charlotte Merrill

References

t. Eick JD, CobbCM, Ctiappell RP, Spencer P, RobinsonSJ. Ttiedentinal surface: Its influence on dentinal adhesion. Part I.Quinleasence Int 1991 ;22:967-977.

2. Kick JD, Robinson SJ, Cobb CM, Chappell RP, Spencer P. Thedentinal surface: Ils influence on dentinal adhesion. Part II,Qtiintessence Int 1992;23:43-51,

3. Bowen RL. Adhesive bonding of various materials to hardtooth tissues — solubility of denlinal smear layer in dilnte acidbuffers. Inl Dent J t978;28:97-107.

4. Bowen RL, Eick JD, Henderson DC, et a l Smear layer: Re-moval and bonding considerations. Oper Dert I984;(suppl 3):30-35.

5. Bowen RL. Bonding agents and adhiisives: Reactor responseAdv Dent Res 1988;2:155-t57.

6. Bowen RL, Tung MS, Blosser RL, et a l Denlin and enamelbonding agents. Int Dent J 1987;37:158-I61.

7. Blosser RL. Bowen RL. Effects of purified ferric o.xalale/nitricacid solutions as prelreatment for the NTG-GMA and PMDMbonding system. Dent Mater 19S7;4:225-23t.

8. Eick JD, Bowcn RL, Erickson R, et al. TEM of the smear layerand den tin-adbesive interface [abstract 1295], J Denl Res1987;66:268,

9. Chappell RP, Eick JD, Morgan R. Shear bond strength andSÉM observation ofthe newest dentin adhesives [abstract 513].J Dent Res 1992;71.17O

10, Chappell RP, Eick JD, Theisen FC, Carracho AJL, et al. Shearbond strength and scanning electron microscopic observationof current dentinal adhesives, Ouinlessence int 1991;22:831-839.

11, Carracho AJL, Chappell RP. Glaros AG, Purk JH, Eick JD.The efTecl of storage and Ihermocycling on the shear bondstrength of three chemical adhesives. Quintessence Int1991:22:745-752.

12, Eick JD, Wilko RA, Anderson CH, et al. Scanning electronmicroscopy of cut tooth surfaces and identification of debris byuse of Ihe electron microprobe. J Dent Res 1970;49:1359-]368,

13, Eick JD, Welch FH. Dentin adbesives —Do they protect thedentin from acid etchmg'? Quintessence Int 1986; 17:533-544.

14. Eick JD, Welch FH. Polymerization shrinkage of posteriorcomposite resins and its possible influence on postoperative sen-sitivity. Quintessence Int 1986;I7:IO3-111.

15. Eick JD, Cobb CM. SEM and TEM of the smear layer anddentin adhesive interface: A review, SEM, and x-ray micro-analysis in dentistry. Presented at the SEM Meeting, Hamilton,Ont, Canada, 1987.

16. Eick JD, Spencer P, Chappell RP, et al. Further SEM/TEM ofihe smear layer and dentin-adhesive interface, J Dent Res1989:68:321,

17. Eick JD. Materials for today's adhesive dentistry. J Dent Educ1991:55:22,

18. Eick JD. Smear layer-materials surface. Prot Fin Dent Sec1992;88{suppl l):225-242,

19. Nakabayashi N, Takarada K. Effect of HEMA on bonding todenlin. J Dent Res 1991:70:363.

20. Nakabayashi N, Takarada K. Effect of HEMA on bonding lodenlin. Dent Mater 1992:8:125-130.

21. Gerbeno C, Nakabayashi N, Effect of HEMA treatment onbonding to EDTA pretreated dentin, J Dent Res 1992;7I.615.

22. Barkmeier WW, Cooley RL. Laboratory evaluation of adhesivesystems. Oper Dent 1992;(suppl 5):50-61.

23. Nakabayashi N, Resin reinforced dentine due lo infiltration ofmonomers into the dentine at the adhesive interface, J Jpn DentMater 1982:L78-86.

24. Nakabayashi N, Watanabe A. SEM and TEM observation ofdentin interface treated for adhesion. Rep Inst Med Denl Eng1983:17:45-55.

25. Nakabayashi N. The hybrid layer: A resin-dentin composite.Proc Finn Dent Soc 1992:88{suppl l|:321-329.

26. Nakabayashi N, Ashizawa M, Nakamura M. Identification ofa resin-dentin hybrid layer in viial human dentin created in vivo:Durable bonding to vital dentin. Quintessence Int 1992;23:135-141.

27. Davidson CL, DeGee AJ. Relocation of polymerization con-traction stresses by flow in dental composites. J Dent Res1984:63:146-148.

28. Van Meerbeck B, Inokoshi S, Braem M, Lambrechts P, Van-herleG. Morphological a gen Is of theresin-denlininterdilTusionzone with different dentin adhesive systems. J Denl Res1992;71:] 530-1540.

29. Erickson RL, Surface interactions of denlin adhesive materials.Oper Dent 1992:(suppl 5):81-94.

30. Retief DH, Manaras RL, Russell CM. Relationship betweenshear bond strength and quantiialive microleakage, J Denl Res1992:71:615.

31. Nakabayashi N. Adhesive bonding with 4-META. Oper Dent1992;(suppl 5):125-nO.

32. Tao L, Tagami J, Pashley DH, Pulpal pressure and bondstrengths of Superbond and Gluma, Am J Denl 1992;4:73-76,

33. Van Meerbeck B, Vanherle G, Lambrecbts P, Braem M. Den-tin- and enamel-bonding a gen IS, Peno Rest Dent 1992;! 17-127.

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