Bond strength, interfacial characterizat ion, and fracture surface analysis for a new stress-breaking bonding agent

M i c h a l S t a n i n e c , D D S , a G r a y s o n W. M a r s h a l l , Jr . , D D S , M P H , P h D , b M a s a h i r o K a w a k a m i , D D S , c a n d A r t h u r L o w e d

School of Dentistry, University of California at San Francisco, San Francisco, Calif.

T h r e e c o m m e r c i a l d e n t i n b o n d i n g s y s t e m s w e r e a n a l y z e d b y t e n s i l e b o n d t e s t ing , area a n a l y s i s o f f r a c t u r e d sur faces , a n d SEM a n a l y s i s o f th e t o o t h - r e s i n i n t e r fa c e s . T e n s i l e b o n d s t r e n g t h s in m e g a p a s c a l s ( S D ) w e r e T e n u r e - M a r a t h o n V ([T-M]; 8.8613.02]), n e w s y s t e m w i t h l o w - v i s c o s i t y r e s i n ([K-LVR-P]; 6.5012.01]), a n d n e w s y s t e m w i t h o u t l o w - v i s c o s i t y r e s i n ([K-P] -- 7.2811.75]), w h i c h w e r e s i g n i f i c a n t l y g r e a t e r t h a n Scotch- b o n d 2-P50 ([SB-P50]; 3.9611.02]). Gaps t h a t r a n g e d up to 5.6 Inn ( m e a n for the group) w e r e o b s e r v e d a r o u n d m o s t o f t h e r e s t o r a t i o n s at d e n t i n s u r f a c e s a n d l e s s so at e n a m e l sur faces , w h e r e s o m e o f t h e r e s t o r a t i o n s r e m a i n e d free o f gaps . T h e g a p s n e a r t h e d e n t i n m a r g i n w e r e s i g n i f i c a n t l y sma l l er for K-LVR-P t h a n for SB-P5O. Th e t e n s i l e t e s t r e v e a l e d m i x e d fa i lure m o d e s in al l s y s t e m s , a n d in t h e c r o s s s e c t i o n s o f c lass V r e s t o r a t i o n s , the g a p s w e r e c o n f i n e d to t h e d e n t i n - r e s i n j u n c t i o n . (J PROSTHET DENT 1995;74:469-75.)

R e c e n t advances in dent in bonding systems have signif icantly improved the i r bond s t rengths to dentin. The ma in advantages of grea ter bond s t rength are bet ter re tent ion in cavities in dent in wi thout mechanical under- cuts and inhibi t ion of gap formation, which leads to microleakage. In spite of the improved bond strengths, the bonds stil l do sometimes fail and create gaps, as repor ted in severa l in vi t ro studies I"3 and in one repor t of clinically observed postoperat ive sensit ivity. 4

Dent in adhesives are most commonly tes ted for bond s t rength in tension or shear on flat dent ina l surfaces. 57 An approximate assessment of the location of failure is some- t imes reported, but a sys temat ic effort to quant i fy this lo- cation is rare. The location of fai lure is important , because i t demons t ra tes the weakes t l ink in the system, which needs to be addressed in the design of new adhesive ma- ter ia ls and techniques. The location of fai lure can be s tudied by examining the pa th or location of a crack in cross-sections or by examining debonded surfaces to de- t e rmine which mate r i a l is exposed. Some recent reports indicate tha t bond tes t ing with the s t ronger bonding agents can often resul t in a failure wi th in dentin. 8 The thickness of the bonding agent has been repor ted as a fac- tor t ha t affects the bond strength, 9 whereas other studies

Supported in part by a grant from Kuraray Co., Ltd., Osaka, Ja- pan and NIH/NIDR grant PO1 DE 09859.

aClinical Professor, Department of Restorative Dentistry. bprofessor, Department of Restorative Dentistry. cPrivate Practice, Osaka, Japan; and Instructor, Department of

Operative Dentistry, Osaka University, Faculty of Dentistry. dDental Student. Copyright �9 1995 by The Editorial Council of THE JOURNAL OF

PROSTHETIC DENTISTRY. 0022-3913/95/$5.00 + 0. 10/1/66161

T I C

Fig . 1. Cross section of tensi le tes t ing appara tus wi th beveled cavity. U, Upper par t of jig; L, lower par t of j ig ; / , in terchangeable insert ; S, screw for holding two par ts of j ig together; C, beveled cavity; LH, lower handle; B, l inear ball bearing; T, th read for a t tach ing upper handle.

d ispute th is finding.i~ I t has been suggested tha t a th icker layer of the bonding agent will act as an elastic buffer to absorb the stresses re la ted to polymerizat ion shr inkage and other forces. 11

Recently a new sys tem was introduced, and it consists of surface t r ea tmen t of enamel and dent in s imul taneously with a citric acid and calcium chloride conditioner (ST conditioner) followed by a solution of N-methacryloy-5- amino salicylic acid (SA Primer) , then a phosphate es ter t ha t contains adhesion promoter (Photobond, Kura ray Co., Ltd, Osaka, Japan) and a low-viscosity resin liner. The low-viscosity resin l iner is a l ight ly filled res in and is added

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THE JOURNAL OF PROSTHETIC DENTISTRY STANINEC ET AL

Table I. Mater ia l s used in s tudy

Group T-M K-LVR-P K - P SB-P50

Enamel conditioner Phosphoric acid gel ST Conditioner (citric ST Conditioner (citric Phosphoric acid gel (Lot 7423) acid, CaC12 in acid, CaC12 in (Lot 7423)

water, Lot TST-47) water, Lot TST-47) Dentin conditioner Tenure dentin ST Conditioner (citric ST Conditioner (citric Scotchprep (Lot OHD)

conditioner (Lot acid, CaC12 in acid, CaC12 in 1141) water, Lot TST-47) water, Lot TST-47)

Dentin primer Tenure solution (Lot SA Primer SA Primer - - 1146) N-methacryloyl-5- N-methacryloyl-5-

aminosalicylic acid aminosalicylic acid Bonding resin Visar seal (Lot 3806) Clearfil photobond Cleartll Photobond Scotchbond 2 (Lot

(Lots 230 and 128) (Lots 230 and 128) OEB) Liner - - Protect Liner (LVR) - - - -

(Lot TRT-215) Composite resin Marathon V, Cleartil Photo Clearfil Photo P-50 Shade U (Lot

light-cured, shade Posterior Shade Posterior Shade ODDI) A2 (Lot 5441) US (Lot 1031) US (Lot 1031)

Manufacturer DenMat Corp., Kuraray Co., Ltd, Kuraray Co., Ltd, 3M Co., St. Paul, Santa Maria, Osaka, Japan Osaka, Japan Minn. Calif.

The K-LVR~P sys tem was in exper imenta l packag ing a t the t ime of s tudy init iation. I t was la te r m a r k e t e d unde r the t rade n a m e Liner Bond.

before the bulk composite resin filling mate r ia l is placed. This s tudy compared the adhesive propert ies of the new

dent in bonding sys tem with those of two exist ing commer- cial systems. Improvements in bond strength, decrease in interfacial crack formation, or changing the location of fai lure away from the dent in-res in interface, where i t is leas t desirable, were examined and compared. The tes t ing was conducted by (1) tensile adhesion tes t ing and SEM analys is of the failure sites, and (2) SEM analysis of cross- sections of composite resin res tora t ions in class V cavities.

MATERIAL A N D M E T H O D S

H u m a n molar tee th free of caries, restorat ions, or other defects were s tored in tap wa te r wi thout addit ives a t room t empera tu re before testing. The enamel on the occlusal surface was removed, and the exposed dent in surfaces were ground with 600 gri t wet silicone carbide paper . For tensi le tes t ing an appa ra tus wi th a beveled cavity (Fig. 1) was used. 7 The bond s t rength of composite to etched enamel as measured in this appa ra tus was previously re- ported to be 16 MPa.

The teeth, with exposed occlusal dentin, were mounted in the appa ra tus wi th die stone. A Mylar mat r ix with a round hole 5 m m in d iamete r was used to l imit the a rea to match the d iamete r of the beveled cavity. These specimens were divided into four groups. The res tora t ive mater ia l s (Table I) were placed as outl ined in Table II. For the T-M and SB-P50 groups the separa te enamel conditioning steps were not conducted, because only dent in was involved in the tensi le tests . The comparison mater ia l s were chosen because they were popular representa t ive commercial

mater ia l s a t the t ime the s tudy was ini t iated. Scotchbond 2 was selected in pa r t because i t had been reported to be par t icu la r ly affected by the thickness of the bonding agent.

After 24 hours of s torage in 100% humidi ty a i r a t room tempera ture , the bond s t rengths of nine specimens of each group were determined. The crosshead speed of the me- chanical tes t ing machine was set a t 0.5 mm/minute. The resul ts of the tensi le tests were expressed in megapascals, and means for groups were compared with analysis of var iance (ANOVA) and Student -Neuman-Keuls test at a confidence level of 95%.

The debonded surfaces were examined with a scanning electron microscope in the backsca t te r mode directly with- out metal coating. The appara tus was a type of environ- menta l SEM known as a wet SEM (ISI SX-40A wet SEM, ISI Inc., Milpitas, Calif.). The specimen chamber was ma in ta ined from 20 to 100 mTorr, and the specimens were kept flat and perpendicu lar to the scanning direction at a s t andard working dis tance of 17 mm. Most of the speci- mens were measured in the middle two thirds of the field of view to minimize distort ion effects.

Both the dent in side and the composite resin side were examined at a magnificat ion of • which included the ent i re area, and a magnificat ion of • to examine each dis t inct a rea in grea te r detail . F rom the photographs tha t included the ent i re bonded area, the areas of the following fai lure sites were es t imated: (1) a t the dent in surface (sep- a ra t ion of the bonding resin from dentin), (2) within the dentin, (3) within the bonding resin, and (4) within the composite resin. This measuremen t was recorded on pho- tographs by use of a polar p lan imete r and was expressed

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STANINEC ET AL THE JOURNAL OF PROSTHETIC DENTISTRY

Table II. Material-placement steps

T-M K-LVR-P K - P SB-P50

Surface Enamel surface etched Both enamel and dentin Both enamel and dentin conditioning with etching gel for 15 surfaces conditioned surfaces conditioned

seconds, rinsed for 15 with ST agent for 60 with ST agent for 60 seconds and dried; seconds, rinsed for 15 seconds, rinsed for 15 dentin surface seconds and dried seconds, and dried conditioned with Tenure Dentin Conditioner for 20 seconds, rinsed for 15 seconds, and dried for 30 seconds

Surface Tenure Solution A and SA primer applied to SA primer applied to priming Tenure Solution B dentin with a brush dentin with a brush

mixed and applied to and gently dried and gently dried all surfaces with a brush, dried for 20 seconds, then a new drop of each solution mixed and applied again

Bonding resin Dried for 20 seconds, Clearfil Photo Bond Clearfil Photo Bond application then Visar Seal applied to all surfaces applied to all surfaces

applied to all surfaces and photocured for 10 and photocured for 10 and photocured for 20 seconds seconds seconds

Liner Protect liner brushed on application all surfaces and

photocured for 20 seconds

Composite Marathon-One bulk Photo Posterior bulk Photo Posterior bulk resin placed and cured for placed and photocured placed and photocured placement 60 seconds for 60 seconds to 60 seconds

Enamel surface etched with etching gel for 15 seconds, rinsed for 15 seconds, and dried, dentin surface scrubbed with Scotchprep for 60 seconds, dried 15 seconds

Scotchbond 2 applied to all surfaces and photocured for 20 seconds

P-50 bulk placed and photocured to 60 seconds

in mm2; then the measurement was converted to a per- centage of the total area. The location of failure was con- firmed by examining both the composite side of the debonded area and the dent in side. For example, a site was deemed to be a failure at the dent in interface only when the dent in side was composed of dent in without any resin and the resin side was composed of only resin without any pieces of dent in attached.

For examinat ion of the cross-sections of class V restora- tions, 12 extracted caries-free h u m a n molar teeth tha t were stored in water after extraction were used. Class V

cavities were prepared at the cementoenamel junct ions on the buccal and l ingual surfaces of each tooth with a carbide

bur (no. 58) in a water-cooled high-speed handpiece. The cavities were V-shaped, 2 mm in depth, and 3 mm in width occlusogingivally, with one margin 1.5 mm above the cementoenamel junct ion and the other margin 1.5 mm be- low the cementoenameljunct ion. The size of the cavity was chosen because it is a typical moderate size tha t results in a sufficient interfacial area to examine the gap and resin

thickness. The cavities were divided into four groups of three teeth and restored as outlined in Table II.

The restored teeth were stored in distilled water for 24 hours, finished with Sofiex disks (3M, St. Paul, Minn.), then thermocycled 1000 times between water baths of 4 ~ C and 60 ~ C with a dwell time of 60 seconds in each bath. The teeth were sectioned in a buccolingual plane through the center of the restorations with a water-cooled diamond saw. The sections were polished sequentially with metal-

lurgic diamond pastes from 45 lam to ~4 !am. The sections were cleaned in distilled water with sonication for 1 minute, and then impressions were taken in a low-viscos- ity polyvinyl siloxane material (Extrude, Kerr Mfg. Co, Romulus, Mich.). Sonication was necessary to remove pol- ishing debris. Although effects of sonication were not spe- cifically addressed in this study, no obvious deleterious ef- fect on the composites was observed. The impressions were cast in epoxy resin (Stycast, Emerson & Cuming, Inc., Woburn, Mass.), and the replicas were sputter-coated with gold and then examined by scanning electron microscopy. 12

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TI-I~ JOURNAL OF PROSTHETIC DENTISTRY STANINEC ET AL

% failure areas % failure areas

A

I~ bonding Tes~n In composite in bonding resin

~.~ In composite ~ 74

Atdentin 51,3

M e a n b o n d s t r e n g t h - 8 . 9 M P a B M e a n b o n d s t r e n g t h - 3 . 9 6 M P a

% failure areas % Of failure areas

In bonding resin In bonding resin 23,6 16.3

In composite ~:~$'~ ':~: ~ i ~,:;.,~ /

At dentin At dentin " 70,6 70,1

C M e a n bond strength = 7 . 2 8 M P a D M e a n bond s t r e n g t h - 6 . 4 8 M P a

Fig . 2. A, Percentage of failure areas in tensile test for T-M group. B, Percentage of fail- ure areas in tensile test for SB-P50 group. C, Percentage of failure areas in tensile test for K-P group; D, Percentage of failure areas in tensile test for K-LVR-P group.

T a b l e III. Results

T . M (N ffi 9) K - L V R - P (N = 9) K - P (N = 9) S B - P 5 0 (N = 9 )

Bond strength 8.86 (3.02) a 6.50 (2.01) a 7.28 (1.75) a 3.96 (1.02) b Gaps

Margin, enamel 2.8 (4.8) a 0.7 (1.3) a 0.0 (0.0) a 0.0 (0.0) a Margin, dentin 2.8 (2.5) ab 0.4 (0.4) a 2.5 (1.2) ab 5.4 (1.7) b Apex 5.3 (1.9) a 3.7 (1.3) a 2.6 (0.6) a 5.6 (3.4) a

Resin Thickness Margin, enamel 11.1 (3.8) a 15.5 (8.3) ab 0.0 (0.0) b 1.8 (3.1) b Margin, dentin 12.9 (9.0) a 19.4 (8.0) ab 0.0 (0.0) b 0.8 (1.3) b Apex 26.4 (9.9) b 89.2 (58.0) ab 23.6 (29.1) b 126.4 (42.2) a

a,b, Statist ical groupings for each horizontal line.

The specimens were also examined by a scanning elec-

tron microscope in the wet backscatter mode directly

without meta l coating. The images were stored and re-

tr ieved for analysis on a monitor screen (Kevex's Image

Analysis wi th Features II software, San Carlos, Calif.).

From the replicas the measurements of the gap sizes were

made. From the actual specimens the thickness of the

bonding resin was measured. In this manner the mea-

surement of any gaps tha t resulted from SEM artifacts was

avoided. One image of each specimen tha t included the

entire restoration was stored, and close-up images of the

areas near the enamel margin, the dentin margin, and at

the apex of the V-shaped cavities were obtained. For each

specimen bonding resin thickness and gap size were mea-

sured in each of the areas. The smallest, the largest, and

the average widths were recorded for each area. The aver-

472 VOLUME 74 NUMBER 5

STANINEC ET AL THE J O U R N A L OF PROSTHETIC DENTISTRY

Fig. 3. A, Apex of restoration from K-LVR-P group. (Arrows indicate gap.) (Original magnification • B, Replica of apex of restoration from K-LVR-P group. (Arrows in- dicate gap.) (Original magnification x300.) C, Enamel margin, K-P group. (Original mag- nification x300.) D, Replica, enamel margin for K-P group. (Original magnification • d, Dentin; b, bonding resin; c, composite; e, enamel.

age width was computed from 20 measurements 4.5 pm apart along the length of the interface in the area of inter- est. Thus the reported gap at the margin is the average gap of the interface from the margin to a depth of 90 pm. The reported gap at the apex is the average gap in the area 45 pm apical and 45 pm occlusal to the apex of the restoration.

RESULTS

The results of the tensile test, the size of gaps, and the thickness of the bonding resin are presented in Table III. Statistical groupings obtained by ANOVA and Student- Neuman-Keuls tests are included. The failure area per- centages are illustrated in Fig. 2. In all groups the domi- nant fracture path was at the dentin-resin interface. The greatest proportion of this failure type was in the SB-P50 group, and the lowest was in the T-M group. This propor- tion roughly corresponds to the inverse of the trend of the bond strength results for these groups. The SB-P50 group had the lowest bond strength at 3.96 MPa, and the T-M group had the greatest at 8.86 MPa. However, only the SB-P50 group had bond strength significantly different from that of the other groups (Table III).

Fig. 3, A and B display SEMs of the apex of a K-LVR-P restoration and a corresponding replica of the same region. The bonding resin (b) is clearly visible in the restoration (Fig. 3, A), as are a crack and a large gap (arrows), which are assumed to be due to drying of the sample and shrink-

age of dentin while under the SEM vacuum. The much smaller gap (Fig. 3, B, arrows) visible in the replica is as- sumed to be representative of the gap in the actual spec- imen, because the replica was taken before any drying of the specimen or exposure to vacuum occurred.

Fig. 3, C and D illustrate the enamel margin of a sample from the K-P group. No bonding resin layer and no gap are visible. All of the observed gaps were at the dentin-resin interface. Fig. 4 show corresponding debonded composite and resin surfaces of a sample in the T-M group. The same region is shown at higher magnification to demonstrate a

mixed failure with areas of exposed dentin with open tu - bules (dr) where resin pulled away from the dentin surface. The corresponding resin surface (rd) appears to have rep- licated this surface without forming long tags. A fractured dentin surface where cohesive fracture of dentin occurred (d) is visible, as are a region of failure within the bonding resin (b) and a region of cohesive failure within t he composite (c). The cohesive failure in dentin was observed only in a few small regions. They were not measurable a t the low-power view and thus are not included in the pro- portions presented in Fig. 2.

DISCUSSION

The effect of the low-viscosity resin is seen as a difference between the K-P and K-LVR-P groups. The only difference between these groups is an increased proportion of failure

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THE JOURNAL OF PROSTHETIC DENTISTRY STANINEC E T AL

Fig. 4. A, Debonded composite surface for T-M group (higher magnification), b, Cohesive failure within bonding resin; c, cohesive failure within composite resin; d, cohesive failure within dentin; rd, resin surface from which dentin was debonded (adhesive failure). B, Debonded dentin surface of same region, dr, Dentin surface from which resin was debonded (adhesive failure). (Original magnification x500.)

in the composite resin in the lat ter group at the expense of the failures within the bonding resin. The proportion of failure at the dentin-resin interface is nearly the same.

The trends in the gap sizes (Table III) are not consistent with bond strength results, but they are consistent w i th previously obtained microleakage results 13 particularly a t the dentin margin, where K-LVR-P had the lowest g a p width and SB-P50 the greatest. The gap sizes measured were between 0 and 12 pm. The bond strengths revealed the same trends but were somewhat lower than previously obtained results in our laboratory 13 and were possibly t h e result of operator differences.

The measurements of bonding resin thickness (Table I I I ) revealed that by far the greatest amount of bonding res in was found at the apex of the V-shaped restorations, w i th measurements for the K-LVR-P and SB-P50 groups in t h e 100 pm range. Large differences are seen between the K-P and K-LVR-P groups, so most of the resin thickness mea- sured in the K-LVR-P group was probably attributable to the low-viscosity resin. It was a surprise that in the K-P group no bonding resin was discernible near the margins, possibly because Photobond, which was used in this region, appears to be somewhat less viscous than the other two bonding resins that were used.

The location of the failure may be important for several reasons. Dentin is often etched to obtain maximum adhe- sion, 14 and although etching acid by itself may not be a n irritant, it is well known that dentinal tubules opened b y etching present a pathway for toxins to penetrate into t h e pulp and cause inflammation. 15 Most class V composite restorations will develop gaps at the cervical margin solely because of polymerization shrinkage or the stress a f te r thermal cycling. 1~ If the failure occurs between the bond- ing resin and dentin, toxins could penetrate the dent inal tubules opened by this debonding activity. To protect t h e dentin from this penetration, it would be desirable for t h e failure to occur between the bonding resin and composite

and have a protective layer of bonding resin remain on t h e dentin, thus maintaining a seal.

Adhesion of composite to dentin is usually measured i n shear or tension. The earlier generations of dentin bonding agents were not effective because of low bond strength 17 and were reported to fail at the resin-dentin interface. More recently bond strengths have increased, and some studies on bond strength have reported failures that occurred in the dentin, s presumably because bond strength between composite and dentin exceeded the strength of the dentin itself. As in this study the adhesive testing in most studies is done by bonding a cylinder of composite to a flat

surface of dentin and then debonding it under a shear or tensile load. Although the results from these tests roughly correspond to reported increased clinical success in reten- tion provided solely by adhesion, it is doubtful that such a test truly simulates the clinical situation and the type of failure that might occur clinically. The fairly rapid appli- cation of a gradually increasing force until failure occurs is seldom encountered clinically. Rather, it is more likely that a restoration will be subjected to repetitive stresses with smaller forces resulting from thermal changes, mechanical flexing, and so forth. In this study smaller repetitive stresses were placed on the restorations by thermal cy- cling, and the failures, observed in cross sections as gaps, were always adhesive at the dentin surface. In contrast, a variety of failure modes occurred in the tensile test. The new system tested in this study was tested for microleak- age after occlusal load cycling, and it was found to resist the stress and maintain a seal better than other tested systems, is

If a composite restoration fails between the dentin and the bonding layer, it is possible that resin tags might remain deep in the dentinal tubules and thus occlude them. These remnants of resin tags may not be visible on the debonded dentin surface, and such a surface may be morphologically classified as an adhesive failure because

474 VOLUME 74 NUMBER 5

STANINEC ET AL THE JOURNAL OF PROSTHETIC DENTISTRY

of t h e S E M a p p e a r a n c e . T h i s p h e n o m e n o n w a s n o t inves -

t i g a t e d in d e t a i l in t h i s s tudy . I t is a lso poss ib le t h a t du r -

i ng d e b o n d i n g , r e s i n t a g s of s e v e r a l m i c r o n s l e n g t h c a n be

pu l l ed o u t of t h e d e n t i n a l t u b u l e s . 16

T h e r e s i n t h i c k n e s s i n t h e K-P g r o u p w a s found to be

r e l a t i v e l y low or n e a r zero. A poss ib l e e x p l a n a t i o n of t h i s

p h e n o m e n o n is t h a t P h o t o b o n d a d h e s i v e r e s i n is m o r e in-

h i b i t e d by oxygen t h a n o t h e r b o n d i n g a g e n t s a n d m a y n o t

c o m p l e t e l y cu re u n t i l i t is covered e i t h e r b y compos i t e or by

low-viscos i ty r e s in . W h e n compos i t e is p l aced d i rec t ly on

t h e P h o t o b o n d a d h e s i v e r e s i n l ayer , i n t e r m i x i n g m a y

occur, so no s e p a r a t e un f i l l ed b o n d i n g l aye r is v i s ib le on

SEM.

T h e b o n d s t r e n g t h r e s u l t s of t h i s s t u d y a r e s o m e w h a t

lower t h a n t h o s e p r e v i o u s l y r e p o r t e d for t h i s g e n e r a t i o n of

b o n d i n g a g e n t s . O n e r e a s o n is t h e t e s t i n g m e t h o d , w h i c h

g ives a v a l u e of 16 M P a for compos i t e b o n d e d to e t c h e d

e n a m e l , as p r e v i o u s l y r epor t ed . 7 O t h e r r e a s o n s m a y in-

c lude o p e r a t o r d i f fe rences , t o o t h d i f fe rences , a n d t h e t e n -

si le m o d e of t e s t i ng , r a t h e r t h a n t h e m o r e c o m m o n s h e a r

mode. Also, S c o t c h b o n d 2 b o n d i n g a g e n t , a v a i l a b l e w h e n

t h i s s t u d y w a s i n i t i a t e d , h a s s ince b e e n s u p e r s e d e d b y

S c o t c h b o n d M u l t i p u r p o s e b o n d i n g a g e n t , a n d i t is l ike ly

t h a t t h i s m a t e r i a l wou ld give d i f f e r en t r e su l t s .

S U M M A R Y A N D C O N C L U S I O N S

T h e n e w b o n d i n g s y s t e m p e r f o r m e d s i m i l a r l y to T e n u r e

w i t h M a r a t h o n a n d s ign i f i c an t l y b e t t e r t h a n S c o t c h b o n d 2

b o n d i n g a g e n t w i t h P-50 in t e r m s of t e n s i l e b o n d s t r e n g t h

to d e n t i n . All t h e t e s t e d s y s t e m s t e n d e d to fa i l a d h e s i v e l y

a t t h e d e n t i n - r e s i n in te r face . In t h e n e w s y s t e m t h e addi -

t i o n of t h e low-viscos i ty r e s i n d e c r e a s e d t h e p r o p o r t i o n of

t h e f a i l u r e a r e a w i t h i n t h e b o n d i n g a g e n t b u t d id no t affect

t h e f a i l u r e p r o p o r t i o n a t t h e d e n t i n sur face . In cross

sec t ions a l l of t h e o b s e r v e d f a i l u r e s w e r e adhes ive , w i t h

g a p s a t t h e r e s i n - d e n t i n in te r face . I n al l s y s t e m s more g a p s

w e r e o b s e r v e d a t d e n t i n su r f aces t h a n a t e n a m e l sur faces .

Rep l i ca s a r e i m p o r t a n t for e x a m i n i n g gaps , b e c a u s e t h e

S E M e n v i r o n m e n t c a u s e s c r acks a n d l a r g e r gaps to be

fo rmed .

R E F E R E N C E S

1. Asmussen E. The effect of temperature changes on adaptation of resin fillings. I. Acta Odont Scand 1974;32:161-71.

2. Fujimitsu T, Kato H, Itoh K, Wakumoto S. Adaptation of composites te the dentin cavity wall. Dent Mater J 1989;8:141-6.

3. Kate H, Itoh K, Wakumoto S. The bonding efficiency of chemically and visible light cured composite systems. Dent Mater J 1988;7:13-8.

4. Eick JD, Welch FH. Polymerization shrinkage of posterior composite resins and its possible influence on postoperative sensitivity. Quintes- sence Int 1986;17:103-11.

5. Zidan O, A1Jabab A. Evaluation of the bond mediated by eight DBA's to enamel and dentin. Dent Mat J 1990;6:158-61.

6. Barkmeier WW, Cooley RL. Shear bond strength of the Tenure Solu- tion dentin bonding system. Am J Dent 1989;2:263-5.

7. Staninec M, Torii Y, Watanabe LG, Kawakami M, Tonn EM. Tensile adhesion evaluation in a new universal test. Am J Dent 1992;5:187-91.

8. Gwinnett AJ. Moist vs dry dentin: its effect on shear bond strength. Am J Dent 1992;5:127-9.

9. Erickson RL. Mechanism and clinical implications of bond formation for two dentin bonding agents. Am J Dent 1989;2:117-23.

10. Retief DH, Wendt SL, Bradley EL. The effect of adhesive thickness on the shear bond strength of Scotchbond 2/Silux to dentin. Am J Dent 1989;2:341-4.

11. Van Meerbeek B, Lambrechts P, Inokoshi S, Braem M, Vanherle G. Factors affecting adhesion to mineralized tissues. Oper Dent 1992;(sup- pl 5):111-24.

12. Marshall GW, Marker VA, Bayne SC. Replication technique for mon- itoring intraoral processes with SEM. Quintessence Int 1978;9:75-7.

13. Staninec M, Kawakami M. Adhesion and microleakage tests of a new dentin bonding system. Dent Mater 1993;9:204-8.

14. Kanca A III. Bonding to tooth structure: a rational rationale for a clin- ical protocol. J Esthet Dent 1989;1:135-8.

15. Brannstrom M. Infection beneath composite resin restorations: can it be avoided? Oper Dent 1987;12:158-63.

16. Staninec M, Mochizuki A, Tanizaki K, Fukuda K, Tsuchitani Y. Change in interfacial space, marginal leakage, and enamel cracks around com- posite resins. Oper Dent 1986;11:14-24.

17. Mitchem JC, Gronas DG. Effects of time after extraction and depth of dentin on resin dentin adhesives. J Am Dent Assoc 1986;113:285-7.

18. Davidson CL, Abdalla AI. Effect ofocchisal load cycling on the marginal integrity of adhesive Class V restorations. Am J Dent 1994;7:111-4.

Reprint requests to: MICHAL STAN1NEC, DDS BOX 0758 UCSF SCHOOL OF DENTISTRY SAN FRANCISCO, CA 94143~0758

C O N T R I B U T I N G A U T H O R

J a n e t D o , D e n t a l S t u d e n t , School of D e n t i s t r y , U n i v e r s i t y of C a l i f o r n i a a t S a n Franc i sco , S a n F ranc i sco , Calif.

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