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Tensile bond strength between glass ionomer cements and composite resins
J /O
A
A R T IC L E S
Etching or roughening the surface of glass ionomer cement before use of composite resins and bond agents produces bond strengths comparable to the bond strength between glass ionomers and dentin. Bond failure at such surfaces occurs within the glass ionomer. Adequate washing with water after acid etching the glass ionomer is essential to obtain optim al bond strength. Apparently, some combinations of ionomer cements and resins are more effective than are others in providing a good bond in the “sandwich technique. ”
Tensile bond strength between glass ionomer cements and composite resins Ko H inoura, DDS, DDSc B. Keith Moore, P h D R alp h W. P h illip s, MS, DSc
he adhesion of glass ionom er cements to enamel and dentin1-4 has resulted in the use of glass ion omer cements to restore cervical abrasion or erosion lesions5' 8 and to treat dentin hypersensitivity.9 Bonding to enamel and dentin requires little tooth preparation. As with silicate cement, fluoride release is available from glass ionomer cements for a prolonged period.2'10’11 Therefore, a cariespreventive effect can be expected. In con trast to pulp reaction to silicate cement, the p ulp reaction to glass ionomer cements appears m ild.12-14 Because teeth restored with glass iono mer cements usually are less pleasing in appearance and are less resistant to abra sion than are composite resins, the “sand wich technique” was developed. Although various modifications of the sandwich technique exist, the technique can be sum marized as follows. Standard Class I, II, III, or V cavities are cut. After all caries is removed, the cavity is filled with glass ion omer cement. Next, the enamel walls are cleaned of cement and the enamel and cement are etched with phosphoric acid. A bonding agent is applied, followed by a composite resin. In an eroded area, only a thin layer of the cement is applied and
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etched. T he area then is restored with a composite resin. The procedure makes optim al use of the adhesive properties and biocom patibility of the glass ionomer cement and the desirable surface and es thetic appearance of the composite resin. (This concept was first demonstrated in a course presented in 1976 by Drs. John W. McLean and R alph W. Phillips.) T he success of the sandwich technique
depends on achieving a reasonable bond strength between the etched glass ionomer cement and the composite resin and its bonding agent. Although enamel acid etch ing improves the bonding of resin to that surface, the bond strength of composite resin and bond agents to etched glass ion omer has not been reported. T his study evaluates the bond strength between sev eral glass ionomer cements and composite
Table 1 ■ Glass ionomer cements evaluated.* G lass io n o m er cem ent
M anufacturer
P ow der-to-liquid m ix in g ratio
B atch no.
G C lin in g cem ent F u ji Io n o m er T ype I F u ji Ionom er T ype II M iracle M ix Ketac-bond Ketac-silver
G C , Jap a n G C , Jap a n GC, Japan G C , Jap a n ESPE-Prem ier ESPE-Prem ier
1.2 g:1.0 g 1.35 g:1.0 g 2.3 g:1 .0 g 6.03 g:1.0 g 3.4 g:1.0 g 1.35 g:0.25 m L
060351/040351 280111/210111 040451/290351 040351/250351/041285 M092MD040285 M039MD020885
•P ublication of names of products does not imply endorsement by the American Dental Association.
Table 2 ■ Composite resins and bonding agents used. C om posite resin
B onding agent
M anufacturer
B atch no.
M icrorest AP V isio-dispers S ilux
G C Bond V isio-bond Scotchbond
GC, J a p a n ESPE-Prem ier 3M Co
101241 M023MD012385 031485
JADA, Vol. 114, February 1987 ■ 167
ARTICLES
Fig 1 ■ Cross-section of the apparatus used to measure the tensile bond strength. Key: A = a threaded cap with wires attached for the insertion in grip of the testing machine; B = a two-component mold (Delrin) with a 30° chamfer; C = resin or glass ionomer cement.
Fig 3 ■ Scanning electron microscope slides of Ketac-silver surfaces after treatments (orig mag X 200). Top left, smooth surface. Top right, etched surface with 30-second wash. Bottom left, etched surface with 5-second wash. Bottom right, ground surface.
00104 Fig 2 ■ Scanning electron microscope slides of GC lining cement surfaces after treatments (orig mag X 200). Left, smooth surface. Middle, etched surface. Right, ground surface.
168 ■ JADA, Vol. 114, February 1987
resins with their bond agents and compares various surface treatments of the cement. Methods and materials
Fig 4 ■ Scanning electron microscope slides of Miracle Mix surfaces after treatments (orig mag X 200). Left, smooth surface. Right, etched surface.
m Smooth surface
H
1 1 Etched surface
0
T h e bond strength was determ ined by subjecting paired cylinders of the m aterials to a tensile-type stress. A tw o -p art m old (D elrin), 12 m m in len g th a n d 4 m m in diam eter (Fig 1), was used to form a n d h o ld the cem ent a n d resin. A 30° cham fer was m achined at one end of each h alf of the m old to re ta in the m aterials d u rin g loading. Six glass ionom er cem ents were evaluated (T able 1). T h e G C lin in g cem ent, F u ji Ionom er T y p e I, F uji Ionom er T y p e II, M iracle M ix, a n d Ketacb ond were m ixed o n the p ap er pad as recom m ended by the respective m anufacturer. Ketacsilver w as m ixed in a n am alg am ato r (Vari-M ix II M) for 10 seconds a t a n M-2 setting, as recom m ended by the m anufacturer. T h e glass io n o m er cem ent was inserted in to the 6- X 4-m m m o ld a n d placed a g ain st a flat glass p late o n the end opposite the cham fer. After the glass io n o m er cem ent h a d set for 7 m inutes at room tem perature, the flat surface of
Smooth surface Etched surface Ground surface
Microrest AP (GC Bond)
m
Smooth surface
□
Etched surface
□
Ground surface
Visio-dispers (Visio-bond)
60 Fig 5 ■ Bond strength between Microrest AP/GC Bond (top left), Visio-dispers/Visio-bond (top right), and Silux/Scotchbond (bottom left) and varlonomer cements.
e ^60 40 H 20
-
LC
FI
F II
MM
KB
KS
Silux (Scotchbond)
H in o u ra -M o o re -P h illip s : BOND S T R E N G T H B ETW EEN GLASS IO N O M E R C E M E N T S AND RESINS ■ 169
ARTICLES
the glass ionom er was treated as follows: —G ro u p S: n o treatm ent, glass ionom er cem ent sets ag ain st glass (sm ooth surface). —G ro u p E: glass ionom er cem ent sets against glass, is etched w ith 37% p h o sp h o ric acid for 60 seconds, a n d w ashed w ith tap water for 30 seconds (etched surface). A 60-second etch was used to assure a m axim um etch pattern. H o w ever, in the clinical use of this technique, 30 seconds is adequate, p articularly w hen the layer of cem ent is thin. —G ro u p G: glass ionom er cem ent sets against glass a n d is ro ughened w ith 400-grit silicon car bide p ap er (ground surface). O ne h alf of the m old was a ligned w ith the o th er half, w hich was filled w ith cem ent and held in po sitio n w ith plastic electrical tape. T h ree m icrofilled com posite resins were used (T able 2). M icrorest AP, a chem ically cured resin, w as used w ith its chem ically cured enam el b o n d in g agent. T h e bon d in g agent was m ixed an d placed over the cem ent, a n d the resin was m ixed a n d b u lk placed to fill the m old. T h e open end was covered w ith a m atrix strip, and the specim en was allow ed to set for 1 hour. V isio-dispers a n d Silux and th eir respective b o n d in g agents are lig h t cured. In each case, the b o n d in g agent was placed and cured for 20 seconds u sin g a Kerr C om m and light. N ext, the com posite resin was condensed in to the m old in three increm ents, each of w hich was cured for 30 seconds. T h e finished specim ens set for 1 hour, at w hich tim e all assem bled specim ens were transferred to distilled water and stored at 37 C. After 24 hours, the electrical tapes were re m oved a n d the m olds were screwed in to the threaded caps to attach them to the testing m achine. T en sile bond strengths of seven spec im ens for each cem ent-resin com bination were determ ined (Instron T estin g M achine) w ith a crosshead speed of 0.5 m m /m in . T h e effect of the acid e tching on the surface of the glass ionom er cem ent also was studied on positive replicas usin g a scanning electron m i croscope. Im pressions of the surfaces were taken w ith Iight-body polyvinyl siloxane im pression m aterial (M irror 3), and a positive replica poured w ith epoxy (Stycast 1266). T h e effect of varying the w ashing tim e after e tching the glass ionom er cem ent was also stu d ied. Ketac-silver was allow ed to set against glass for 7 m in u te s a n d th en was etched w ith 37% p h o sp h o ric acid for 60 seconds a n d w ashed w ith tap w ater for either 5 or 30 seconds. These speci-
Fig 6 ■ Scanning electron microscope slide/frac ture showing failure in the cement (cohesive fail ure) surface between Ketac-silver and Siiux (orig mag X 35).
m ens were bonded to Visio-dispers a n d tested as described. T o determ ine the cohesive strength of the individual glass ionom er m aterials, the tensile strength of 24-hour-old specim ens was deter m ined by the app licatio n of a tensile load to cylinders of the m aterials. T h e m old a n d tech n iq u e used for these experim ents have been des cribed.15 T h e 24-hour tensile strengths were determ ined (Instron T esting M achine) at a cross head speed of 0.5 m m /m in .
Results S canning electron m icroscope pictures for the various glass ionom er surface treatm ents are show n in Figures 2-4. Figure 5 shows the tensile bond strength between three com posite resins and six glass ionom er cem ents w ith various su r face treatm ents. Bond strengths varied from 61.1 k g /c m 2 for Ketac-silver, etched, w ith S ilu x / Scotchbond to 1.4 k g /cm 2 for unetched G C lin in g cem ent bond to V isio-dispers/V isio-bond. W ith the sm ooth surface glass ionom er spec im ens, all failures occurred adhesively at the c em ent/bonding agent interface. W ith the etched
Table 3 ■ Effect of the surface treat
Table 4 ■ Effect of the composite resin
ments of the glass ionomer cement sur faces on the bond strength for all cements and resins.
and its bonding agent on the bond strength.
Surface treatm en t Etched surface G ro u n d surface Sm ooth surface
M ean (k g /c m 2) 37.7 32.0 21.6
C om posite re sin / b o n d in g agent S ilu x /S co tch b o n d V isio-dispers/V isio-bond M icrorest A P /G C B ond
M ean (k g /cm 2) 40.6 32.7 17.9
surface specim ens, all failures appeared to occur cohesively in the cem ent (Fig 6). T h e results were studied w ith analyses of var iance follow ed by T u k ey ’s tests. In T ables 3-7, values connected by vertical lines are n o t sig n ifi cantly different (P < .01). T a b le 3 show s the effect of the surface treat m ents of the glass ionom er cem ent surfaces on the bond strength for all cem ents and resins. T h e e tching o r m echanical ro u g h e n in g of the surface of the cem ent had a significant effect on the bond strength. T h e adhesion between glass ionom er cem ent a n d com posite resin was enhanced either by acid e tching or ro u g h en in g of the cem ent surface. E tching resulted in a modest increase in the bond strength as com pared w ith the ro u g h ened surface. T h e effect of the com posite resin a n d its b o n d in g agent on the bond strength is show n in T ab le 4, w hich includes all the cem ents and surface treatm ents. S ilux/S cotchbond had the highest bond strength, V isio-dispers/V isio-bond had the next highest bond strength, a n d M icro rest A P /G C B ond had the lowest bond strength. T h e effect of the glass ionom er cem ents on the bond strength is show n in T ab le 5. Ketac-silver an d M iracle Mix show ed the highest bond strength irrespective of the resin or surface treatm ent used, Fuji I and F uji II show ed m od erate bond strength, and K etac-bond a n d G C lin in g cem ent showed the lowest b ond strength. T ab le 6 shows the re lationship betw een the various com posite re sin s/b o n d in g agents and the surface treatm ents of the cem ent. Significant differences existed between etched, g ro u n d su r face, a n d sm ooth surfaces w ith the exception of the S ilux/S cotchbond system, w hich show ed no significant difference between the sm ooth and gro u n d surfaces. T hese data also m ay be analyzed to show the re la tio n sh ip between surface treatm ents and com posite resins in cluding all glass ionom er cem ents (T able 7). O n a sm ooth cem ent surface, the b ond of S ilux/S cotchbond was significantly stronger th an w as the bond of M icrorest A P /G C b o n d a n d Visio-dispers/Visio-bond. F o ra ll types of surface treatm ent, bond strengths of S ilu x / Scotchbond and V isio-dispers/V isio-bond were significantly stronger th an was the bond strength of M icrorest A P /G C Bond. T ab le 8 shows the effect of the w ashing tim e after e tching of the cem ent. T hese data were analyzed by S tudent’s i-test. A significant differ ence was found between the 30-second a n d 5-
Table 5 ■ Effect of the glass ionomer cements on the bond strength.* G lass ionom er cem ent
M ean (k g /c m 2)
Ketac-silver M iracle Mix F u ji Ionom er T y p e II F u ji Ionom er T ype I Ketac-bond G C lin in g cem ent
41.7 “ I: 41.4 ; 3 4 .6 “] 30.7 . 17.5“] 16.9
J J J
•Bond strengths connected by brackets on the right were n ot statistically different (P < .05).
170 ■ JADA, Vol. 114, February 1987
ARTICLES
Table 6 ■ Effect of composite resins and surface treatments.* C om posite re sin /b o n d in g agent an d surface treatm ent
M ean (k g /cm 2)
M icrorest A P /G C B ond Etched surface G ro u n d surface S m ooth surface V isio-dispers/V isio-bond Etched surface G ro u n d surface S m ooth surface S ilux/S cotch b o n d Etched surface G ro u n d surface Sm ooth surface
24.1 19.9 9.8 42.7 36.6 19.0 46.2 39 T \ 3 6 .JJ
•Bond strengths connected by brackets on the right were not statistically different (P < .05).
Table 7 ■ Effect of surface treatments and composite resins.* Surface treatm ent an d com posite resin Sm ooth surface Silux V isio-dispers M icrorest A P Etched surface Silux V isio-dispers M icrorest AP G ro u n d surface S ilux V isio-dispers M icrorest A P
Mean (k g /c m 2) 36.1 19.0 9.8 46.21 4 2 .7 1 24.1 39.6"l 3 6 .6 1 19.9
•Bond strengths connected by brackets on the right were not statistically different (P < .05).
second w ashing periods. T ab le 9 show s the tensile strengths of the six glass io n o m er cem ents. W hen the results were analyzed by N ew m an-K euls test w ith critical values at .05, they separated in to two groups. T h e h ig h er tensile strength g ro u p includes Fuji Ionom er T y p e II, Ketac-silver, M iracle M ix, and F uji Ionom er T ype I; b u t Ketac-bond a n d GC lin in g cem ent were included in the low er tensile strength g ro u p w ith the overlap g ro u p being Fuji Ionom er T ype I a n d Ketac-bond.
Discussion
Etching the surface of glass ionomer cement greatly increased the bond strength to all the composite resins/bonding agents stud ied. The matrix of the hardened glass ion omer cement dissolves in acid, resulting in a rough and porous surface. The bonding agent then can penetrate into the surface irregularities and harden. Specifically, the unfilled resin infiltrates the etched porosi ties and during polymerization creates re tentive tags at the interface. Bond strength is reliant on many factors, one of which is contact angle. On a rough surface the contact angle should be low so that the bonding agents can spread and
enter into the irregularities on the rough surface. Fukushim a16 reported that acid etching and applying low-viscosity bond ing agents to dentin appears to be im por tant in enhancing the resin’s adhesion to dentin. The three bonding agents used in this study had low viscosity. Apparently, the same principle applies in this tech nique; acid etching of the cement followed by application of a low-viscosity bonding agent is an im portant means of ensuring bonding to the composite resin. Sneed and Looper17 reported that the bond between an etched glass ionomer cement and a composite resin is stronger than is the cohesive strength of the glass ionomer cement. Their findings are sim ilar to the data presented in this report. An example of a cohesive failure is shown in Figure 6. These results indicate that Silux/Scotchbond showed the highest bond strength irrespective of glass ionomer cements or surface treatments. Next was Visio-dispers/ Visio-bond, and Microrest A P/GC Bond had the lowest strength. When comparing the bond strength on the smooth surface, Silux/Scotchbond was significantly strong er than was Visio-dispers/Visio-bond and
Microrest A P/G C Bond. For the etched or the ground surface, however, Silux/Scotch bond and Visio-dispers/Visio-bond were both significantly stronger than was Micro rest A P/G C Bond. This suggests that dif ferent types of chemical bonding may be found between glass ionomer cements and the bonding agents for Silux/Scotchbond and Visio-dispers/Visio-bond systems, in addition to any subtle differences in viscos ity of the bond agents. These results may also be related to the tensile properties of the three composite resins and their bond ing agents. There are even significant differences in bond strengths between the glass ionomer cements regardless of the resin used or the surface treatment. Ketac-silver and Miracle Mix showed the highest bond strength, Fuji Ionomer I and Fuji Ionomer II were classified into an intermediate group, and Ketac-bond and GC lining cement were classified into the lowest group. Ketacsilver and Miracle Mix surfaces set against glass show many small bubbles (Fig 3, 4). These small holes on the surface could con tribute to the m echanical interlocking between the cement and the composite resin. It is apparent that the washing time after etching is im portant to the bond strength. If washing time is too short, the debris rem aining on the surface of the etched cement results in an adhesive failure. T he shear bond strength of glass iono mer cement to dentin has been reported as approximately 2.5 mPa in vitro.14 Con versely, Powis and others3 found that the
Table 8 ■ Effect of the washing time after etching of the cement (N - 7).* W ashing tim e__________ K g/cm 2_________(SD) E tched and w ashed for 30 sec 50.4 (12.49) E tched and w ashed for 5 sec________30.7________ (12.71) •T h e different washing times were compared using the Student’s ¿-test. They were significantly different at t = 2.92, d f= 12.
Table 9 ■ Tensile strength of glass ion omer cement (N = 3).* G lass io n o m er cem ent
K g /c m 2
F uji Ionom er T ype II K etac-silver M iracle Mix F uji Ionom er T ype I K etac-bond G C L in in g cem ent
48.0 47.5 45.4 35.3 29.0 18.8
(SD)______ (4.53H (3.22) (7.08) (1.88) (9.82) (5.52)
•Strengths connected by brackets on the right were not statistically different (P 5~ .05).
H in o u ra -M o o re -P h illip s : BOND S T R E N G T H BETW EEN GLASS IO N O M E R CE M E N T S AN D RESINS ■ 171
ARTICLES
tensile bond strength of glass ionomer cement to dentin is between 1.8 and 7.3 mPa. In this study, the bond strengths between the etched glass ionomer cements and composite resins are between 0.9 and 6.1 mPa. These bond strengths seem to be adequate when compared with the data cited earlier on the glass ionomer-dentin bond. Some combinations of ionomer cements and resins appear to be more effective than others in providing a good bond. More research is needed to further determine the factors involved in achieving maximum bond strengths between etched ionomer cements and the respective bonding agentresin system. Summary Etching or surface roughening of a glass ionomer cementbefore the application of a composite resin bonding agent leads to a significant improvement in the resulting bond. Bond failure at the surfaces occurs cohesively within the glass ionomer. Ade quate washing with water after acid etch ing the glass ionomer is essential to obtain optimal bond strengths. Properly treated glass ionomer surfaces result in bond strengths to composite resins and their bonding agents comparable to the strengths
172 ■ JADA, Vol. 114, February 1987
reported between glass ionomer cements and dentin. The bond strength values mea sured in this study support the use of glass ionomer materials as an intermediate layer between tooth structure and an overlying composite resin in the sandwich technique. ---------------------- JM O A ---------------------Information about the manufacturers of the products mentioned in this article may be available from the author. Neither the authors nor the American Dental Association has any commercial interests in the pro ducts mentioned. The authors thank Hazel E. Clark for assistance with the analysis of the data. Dr. Hinoura is instructor, department of operative dentistry, Nihon University, Tokyo, and visiting pro fessor; Dr. Moore is professor; and Dr. Phillips is asso ciate dean for research and research professor, depart ment of dental materials, School of Dentistry, Indiana University, 1121 W Michigan St, Indianapolis, 46202. Address requests for reprints to Dr. Phillips. 1. Sato, S.; Sato, K.; and Hosoda, H. Adhesion of new dental cements. J Japan Res Dent Mat Appliances 35(l):68-79, 1978. 2. Maldonado, A.; Swartz, M.L.; and Phillips, R.W. An in vitro study of certain properties of a glass iono mer cement. JADA 96(5):785-791, 1978. 3. Powis, D.R., and others. Improved adhesion of a glass ionomer cement to dentin and enamel. J Dent Res 61(12):1416-1422, 1982. 4. Coury, T.L., and others. Adhesiveness of glassionomer cement to enamel and dentin; a laboratory
study. Oper Dent 7(l):2-6,1982. 5. McLean, J.W., and Wilson, A.D. The clinical development of the glass-ionomer cements. Formula tions and properties. Aust Dent J 22( 1);31 -36, 120-127, 190-195, 1977. 6. Mount, G. J., and Makinson, O.F. Clinical charac teristics of a glass-ionomer cement. BrDent J 145(3):6771, 1978. 7. Lawrence, L.G. Cervical glass ionomer restora tions: a clinical study. Can Dent Assoc J 45(2):58-59, 1979. 8. Phillips, R.W. The restoration of eroded cervical areas. CDS Rev 73(4):31-34,1980. 9. Onose, H. The treatment of dentin hypersensitiv ity by the glass ionomer cement mix application. J Int Coll Dent 14(l):29-35, 1984. 10. Swartz, M.L., and others. Fluoride distribution in teeth using a silicate model. J Dent Res 59(10):15961603, 1980. 11. Swartz, M.L.; Phillips, R.W.; and Clark, H.E. Long-term F release from glass ionomer cements. J Dent Res 6S(2):158-160,1984. 12. Tobias, R.S., and others. Pulpal response to a glass ionomer cement. BrDentJ 144(ll):345-350,1978. 13. Kawahara, H.; Imanishi, Y.; and Oshima, H. Biological evaluation of glass ionomer cement. J Dent Res 58(3):1080-1086, 1979. 14. Pameijer, C.H.; Segal, E.; and Richardson, J. Pulpal response to a glass-ionomer cement in primates. J Prosthet Dent 46(1 ):36-40, 1981. 15. Phillips, R.W., and others. Zinc oxide and eugenol cements for permanent cementation. J Prosthet Dent 19(2):144-150, 1968. 16. Fukushima, M. Tags of various restorative resins penetrated into dentin. Japanese J Conserv Dent 22(3):103-120, 1979. 17. Sneed, W.D., and Looper, S.W. Shear bond strength of a composite resin to an etched glass iono mer. Dent Mater J 1(4):127-128, 1985.
A
A R T IC L E S
Etching or roughening the surface of glass ionomer cement before use of composite resins and bond agents produces bond strengths comparable to the bond strength between glass ionomers and dentin. Bond failure at such surfaces occurs within the glass ionomer. Adequate washing with water after acid etching the glass ionomer is essential to obtain optim al bond strength. Apparently, some combinations of ionomer cements and resins are more effective than are others in providing a good bond in the “sandwich technique. ”
Tensile bond strength between glass ionomer cements and composite resins Ko H inoura, DDS, DDSc B. Keith Moore, P h D R alp h W. P h illip s, MS, DSc
he adhesion of glass ionom er cements to enamel and dentin1-4 has resulted in the use of glass ion omer cements to restore cervical abrasion or erosion lesions5' 8 and to treat dentin hypersensitivity.9 Bonding to enamel and dentin requires little tooth preparation. As with silicate cement, fluoride release is available from glass ionomer cements for a prolonged period.2'10’11 Therefore, a cariespreventive effect can be expected. In con trast to pulp reaction to silicate cement, the p ulp reaction to glass ionomer cements appears m ild.12-14 Because teeth restored with glass iono mer cements usually are less pleasing in appearance and are less resistant to abra sion than are composite resins, the “sand wich technique” was developed. Although various modifications of the sandwich technique exist, the technique can be sum marized as follows. Standard Class I, II, III, or V cavities are cut. After all caries is removed, the cavity is filled with glass ion omer cement. Next, the enamel walls are cleaned of cement and the enamel and cement are etched with phosphoric acid. A bonding agent is applied, followed by a composite resin. In an eroded area, only a thin layer of the cement is applied and
T
etched. T he area then is restored with a composite resin. The procedure makes optim al use of the adhesive properties and biocom patibility of the glass ionomer cement and the desirable surface and es thetic appearance of the composite resin. (This concept was first demonstrated in a course presented in 1976 by Drs. John W. McLean and R alph W. Phillips.) T he success of the sandwich technique
depends on achieving a reasonable bond strength between the etched glass ionomer cement and the composite resin and its bonding agent. Although enamel acid etch ing improves the bonding of resin to that surface, the bond strength of composite resin and bond agents to etched glass ion omer has not been reported. T his study evaluates the bond strength between sev eral glass ionomer cements and composite
Table 1 ■ Glass ionomer cements evaluated.* G lass io n o m er cem ent
M anufacturer
P ow der-to-liquid m ix in g ratio
B atch no.
G C lin in g cem ent F u ji Io n o m er T ype I F u ji Ionom er T ype II M iracle M ix Ketac-bond Ketac-silver
G C , Jap a n G C , Jap a n GC, Japan G C , Jap a n ESPE-Prem ier ESPE-Prem ier
1.2 g:1.0 g 1.35 g:1.0 g 2.3 g:1 .0 g 6.03 g:1.0 g 3.4 g:1.0 g 1.35 g:0.25 m L
060351/040351 280111/210111 040451/290351 040351/250351/041285 M092MD040285 M039MD020885
•P ublication of names of products does not imply endorsement by the American Dental Association.
Table 2 ■ Composite resins and bonding agents used. C om posite resin
B onding agent
M anufacturer
B atch no.
M icrorest AP V isio-dispers S ilux
G C Bond V isio-bond Scotchbond
GC, J a p a n ESPE-Prem ier 3M Co
101241 M023MD012385 031485
JADA, Vol. 114, February 1987 ■ 167
ARTICLES
Fig 1 ■ Cross-section of the apparatus used to measure the tensile bond strength. Key: A = a threaded cap with wires attached for the insertion in grip of the testing machine; B = a two-component mold (Delrin) with a 30° chamfer; C = resin or glass ionomer cement.
Fig 3 ■ Scanning electron microscope slides of Ketac-silver surfaces after treatments (orig mag X 200). Top left, smooth surface. Top right, etched surface with 30-second wash. Bottom left, etched surface with 5-second wash. Bottom right, ground surface.
00104 Fig 2 ■ Scanning electron microscope slides of GC lining cement surfaces after treatments (orig mag X 200). Left, smooth surface. Middle, etched surface. Right, ground surface.
168 ■ JADA, Vol. 114, February 1987
resins with their bond agents and compares various surface treatments of the cement. Methods and materials
Fig 4 ■ Scanning electron microscope slides of Miracle Mix surfaces after treatments (orig mag X 200). Left, smooth surface. Right, etched surface.
m Smooth surface
H
1 1 Etched surface
0
T h e bond strength was determ ined by subjecting paired cylinders of the m aterials to a tensile-type stress. A tw o -p art m old (D elrin), 12 m m in len g th a n d 4 m m in diam eter (Fig 1), was used to form a n d h o ld the cem ent a n d resin. A 30° cham fer was m achined at one end of each h alf of the m old to re ta in the m aterials d u rin g loading. Six glass ionom er cem ents were evaluated (T able 1). T h e G C lin in g cem ent, F u ji Ionom er T y p e I, F uji Ionom er T y p e II, M iracle M ix, a n d Ketacb ond were m ixed o n the p ap er pad as recom m ended by the respective m anufacturer. Ketacsilver w as m ixed in a n am alg am ato r (Vari-M ix II M) for 10 seconds a t a n M-2 setting, as recom m ended by the m anufacturer. T h e glass io n o m er cem ent was inserted in to the 6- X 4-m m m o ld a n d placed a g ain st a flat glass p late o n the end opposite the cham fer. After the glass io n o m er cem ent h a d set for 7 m inutes at room tem perature, the flat surface of
Smooth surface Etched surface Ground surface
Microrest AP (GC Bond)
m
Smooth surface
□
Etched surface
□
Ground surface
Visio-dispers (Visio-bond)
60 Fig 5 ■ Bond strength between Microrest AP/GC Bond (top left), Visio-dispers/Visio-bond (top right), and Silux/Scotchbond (bottom left) and varlonomer cements.
e ^60 40 H 20
-
LC
FI
F II
MM
KB
KS
Silux (Scotchbond)
H in o u ra -M o o re -P h illip s : BOND S T R E N G T H B ETW EEN GLASS IO N O M E R C E M E N T S AND RESINS ■ 169
ARTICLES
the glass ionom er was treated as follows: —G ro u p S: n o treatm ent, glass ionom er cem ent sets ag ain st glass (sm ooth surface). —G ro u p E: glass ionom er cem ent sets against glass, is etched w ith 37% p h o sp h o ric acid for 60 seconds, a n d w ashed w ith tap water for 30 seconds (etched surface). A 60-second etch was used to assure a m axim um etch pattern. H o w ever, in the clinical use of this technique, 30 seconds is adequate, p articularly w hen the layer of cem ent is thin. —G ro u p G: glass ionom er cem ent sets against glass a n d is ro ughened w ith 400-grit silicon car bide p ap er (ground surface). O ne h alf of the m old was a ligned w ith the o th er half, w hich was filled w ith cem ent and held in po sitio n w ith plastic electrical tape. T h ree m icrofilled com posite resins were used (T able 2). M icrorest AP, a chem ically cured resin, w as used w ith its chem ically cured enam el b o n d in g agent. T h e bon d in g agent was m ixed an d placed over the cem ent, a n d the resin was m ixed a n d b u lk placed to fill the m old. T h e open end was covered w ith a m atrix strip, and the specim en was allow ed to set for 1 hour. V isio-dispers a n d Silux and th eir respective b o n d in g agents are lig h t cured. In each case, the b o n d in g agent was placed and cured for 20 seconds u sin g a Kerr C om m and light. N ext, the com posite resin was condensed in to the m old in three increm ents, each of w hich was cured for 30 seconds. T h e finished specim ens set for 1 hour, at w hich tim e all assem bled specim ens were transferred to distilled water and stored at 37 C. After 24 hours, the electrical tapes were re m oved a n d the m olds were screwed in to the threaded caps to attach them to the testing m achine. T en sile bond strengths of seven spec im ens for each cem ent-resin com bination were determ ined (Instron T estin g M achine) w ith a crosshead speed of 0.5 m m /m in . T h e effect of the acid e tching on the surface of the glass ionom er cem ent also was studied on positive replicas usin g a scanning electron m i croscope. Im pressions of the surfaces were taken w ith Iight-body polyvinyl siloxane im pression m aterial (M irror 3), and a positive replica poured w ith epoxy (Stycast 1266). T h e effect of varying the w ashing tim e after e tching the glass ionom er cem ent was also stu d ied. Ketac-silver was allow ed to set against glass for 7 m in u te s a n d th en was etched w ith 37% p h o sp h o ric acid for 60 seconds a n d w ashed w ith tap w ater for either 5 or 30 seconds. These speci-
Fig 6 ■ Scanning electron microscope slide/frac ture showing failure in the cement (cohesive fail ure) surface between Ketac-silver and Siiux (orig mag X 35).
m ens were bonded to Visio-dispers a n d tested as described. T o determ ine the cohesive strength of the individual glass ionom er m aterials, the tensile strength of 24-hour-old specim ens was deter m ined by the app licatio n of a tensile load to cylinders of the m aterials. T h e m old a n d tech n iq u e used for these experim ents have been des cribed.15 T h e 24-hour tensile strengths were determ ined (Instron T esting M achine) at a cross head speed of 0.5 m m /m in .
Results S canning electron m icroscope pictures for the various glass ionom er surface treatm ents are show n in Figures 2-4. Figure 5 shows the tensile bond strength between three com posite resins and six glass ionom er cem ents w ith various su r face treatm ents. Bond strengths varied from 61.1 k g /c m 2 for Ketac-silver, etched, w ith S ilu x / Scotchbond to 1.4 k g /cm 2 for unetched G C lin in g cem ent bond to V isio-dispers/V isio-bond. W ith the sm ooth surface glass ionom er spec im ens, all failures occurred adhesively at the c em ent/bonding agent interface. W ith the etched
Table 3 ■ Effect of the surface treat
Table 4 ■ Effect of the composite resin
ments of the glass ionomer cement sur faces on the bond strength for all cements and resins.
and its bonding agent on the bond strength.
Surface treatm en t Etched surface G ro u n d surface Sm ooth surface
M ean (k g /c m 2) 37.7 32.0 21.6
C om posite re sin / b o n d in g agent S ilu x /S co tch b o n d V isio-dispers/V isio-bond M icrorest A P /G C B ond
M ean (k g /cm 2) 40.6 32.7 17.9
surface specim ens, all failures appeared to occur cohesively in the cem ent (Fig 6). T h e results were studied w ith analyses of var iance follow ed by T u k ey ’s tests. In T ables 3-7, values connected by vertical lines are n o t sig n ifi cantly different (P < .01). T a b le 3 show s the effect of the surface treat m ents of the glass ionom er cem ent surfaces on the bond strength for all cem ents and resins. T h e e tching o r m echanical ro u g h e n in g of the surface of the cem ent had a significant effect on the bond strength. T h e adhesion between glass ionom er cem ent a n d com posite resin was enhanced either by acid e tching or ro u g h en in g of the cem ent surface. E tching resulted in a modest increase in the bond strength as com pared w ith the ro u g h ened surface. T h e effect of the com posite resin a n d its b o n d in g agent on the bond strength is show n in T ab le 4, w hich includes all the cem ents and surface treatm ents. S ilux/S cotchbond had the highest bond strength, V isio-dispers/V isio-bond had the next highest bond strength, a n d M icro rest A P /G C B ond had the lowest bond strength. T h e effect of the glass ionom er cem ents on the bond strength is show n in T ab le 5. Ketac-silver an d M iracle Mix show ed the highest bond strength irrespective of the resin or surface treatm ent used, Fuji I and F uji II show ed m od erate bond strength, and K etac-bond a n d G C lin in g cem ent showed the lowest b ond strength. T ab le 6 shows the re lationship betw een the various com posite re sin s/b o n d in g agents and the surface treatm ents of the cem ent. Significant differences existed between etched, g ro u n d su r face, a n d sm ooth surfaces w ith the exception of the S ilux/S cotchbond system, w hich show ed no significant difference between the sm ooth and gro u n d surfaces. T hese data also m ay be analyzed to show the re la tio n sh ip between surface treatm ents and com posite resins in cluding all glass ionom er cem ents (T able 7). O n a sm ooth cem ent surface, the b ond of S ilux/S cotchbond was significantly stronger th an w as the bond of M icrorest A P /G C b o n d a n d Visio-dispers/Visio-bond. F o ra ll types of surface treatm ent, bond strengths of S ilu x / Scotchbond and V isio-dispers/V isio-bond were significantly stronger th an was the bond strength of M icrorest A P /G C Bond. T ab le 8 shows the effect of the w ashing tim e after e tching of the cem ent. T hese data were analyzed by S tudent’s i-test. A significant differ ence was found between the 30-second a n d 5-
Table 5 ■ Effect of the glass ionomer cements on the bond strength.* G lass ionom er cem ent
M ean (k g /c m 2)
Ketac-silver M iracle Mix F u ji Ionom er T y p e II F u ji Ionom er T ype I Ketac-bond G C lin in g cem ent
41.7 “ I: 41.4 ; 3 4 .6 “] 30.7 . 17.5“] 16.9
J J J
•Bond strengths connected by brackets on the right were n ot statistically different (P < .05).
170 ■ JADA, Vol. 114, February 1987
ARTICLES
Table 6 ■ Effect of composite resins and surface treatments.* C om posite re sin /b o n d in g agent an d surface treatm ent
M ean (k g /cm 2)
M icrorest A P /G C B ond Etched surface G ro u n d surface S m ooth surface V isio-dispers/V isio-bond Etched surface G ro u n d surface S m ooth surface S ilux/S cotch b o n d Etched surface G ro u n d surface Sm ooth surface
24.1 19.9 9.8 42.7 36.6 19.0 46.2 39 T \ 3 6 .JJ
•Bond strengths connected by brackets on the right were not statistically different (P < .05).
Table 7 ■ Effect of surface treatments and composite resins.* Surface treatm ent an d com posite resin Sm ooth surface Silux V isio-dispers M icrorest A P Etched surface Silux V isio-dispers M icrorest AP G ro u n d surface S ilux V isio-dispers M icrorest A P
Mean (k g /c m 2) 36.1 19.0 9.8 46.21 4 2 .7 1 24.1 39.6"l 3 6 .6 1 19.9
•Bond strengths connected by brackets on the right were not statistically different (P < .05).
second w ashing periods. T ab le 9 show s the tensile strengths of the six glass io n o m er cem ents. W hen the results were analyzed by N ew m an-K euls test w ith critical values at .05, they separated in to two groups. T h e h ig h er tensile strength g ro u p includes Fuji Ionom er T y p e II, Ketac-silver, M iracle M ix, and F uji Ionom er T ype I; b u t Ketac-bond a n d GC lin in g cem ent were included in the low er tensile strength g ro u p w ith the overlap g ro u p being Fuji Ionom er T ype I a n d Ketac-bond.
Discussion
Etching the surface of glass ionomer cement greatly increased the bond strength to all the composite resins/bonding agents stud ied. The matrix of the hardened glass ion omer cement dissolves in acid, resulting in a rough and porous surface. The bonding agent then can penetrate into the surface irregularities and harden. Specifically, the unfilled resin infiltrates the etched porosi ties and during polymerization creates re tentive tags at the interface. Bond strength is reliant on many factors, one of which is contact angle. On a rough surface the contact angle should be low so that the bonding agents can spread and
enter into the irregularities on the rough surface. Fukushim a16 reported that acid etching and applying low-viscosity bond ing agents to dentin appears to be im por tant in enhancing the resin’s adhesion to dentin. The three bonding agents used in this study had low viscosity. Apparently, the same principle applies in this tech nique; acid etching of the cement followed by application of a low-viscosity bonding agent is an im portant means of ensuring bonding to the composite resin. Sneed and Looper17 reported that the bond between an etched glass ionomer cement and a composite resin is stronger than is the cohesive strength of the glass ionomer cement. Their findings are sim ilar to the data presented in this report. An example of a cohesive failure is shown in Figure 6. These results indicate that Silux/Scotchbond showed the highest bond strength irrespective of glass ionomer cements or surface treatments. Next was Visio-dispers/ Visio-bond, and Microrest A P/GC Bond had the lowest strength. When comparing the bond strength on the smooth surface, Silux/Scotchbond was significantly strong er than was Visio-dispers/Visio-bond and
Microrest A P/G C Bond. For the etched or the ground surface, however, Silux/Scotch bond and Visio-dispers/Visio-bond were both significantly stronger than was Micro rest A P/G C Bond. This suggests that dif ferent types of chemical bonding may be found between glass ionomer cements and the bonding agents for Silux/Scotchbond and Visio-dispers/Visio-bond systems, in addition to any subtle differences in viscos ity of the bond agents. These results may also be related to the tensile properties of the three composite resins and their bond ing agents. There are even significant differences in bond strengths between the glass ionomer cements regardless of the resin used or the surface treatment. Ketac-silver and Miracle Mix showed the highest bond strength, Fuji Ionomer I and Fuji Ionomer II were classified into an intermediate group, and Ketac-bond and GC lining cement were classified into the lowest group. Ketacsilver and Miracle Mix surfaces set against glass show many small bubbles (Fig 3, 4). These small holes on the surface could con tribute to the m echanical interlocking between the cement and the composite resin. It is apparent that the washing time after etching is im portant to the bond strength. If washing time is too short, the debris rem aining on the surface of the etched cement results in an adhesive failure. T he shear bond strength of glass iono mer cement to dentin has been reported as approximately 2.5 mPa in vitro.14 Con versely, Powis and others3 found that the
Table 8 ■ Effect of the washing time after etching of the cement (N - 7).* W ashing tim e__________ K g/cm 2_________(SD) E tched and w ashed for 30 sec 50.4 (12.49) E tched and w ashed for 5 sec________30.7________ (12.71) •T h e different washing times were compared using the Student’s ¿-test. They were significantly different at t = 2.92, d f= 12.
Table 9 ■ Tensile strength of glass ion omer cement (N = 3).* G lass io n o m er cem ent
K g /c m 2
F uji Ionom er T ype II K etac-silver M iracle Mix F uji Ionom er T ype I K etac-bond G C L in in g cem ent
48.0 47.5 45.4 35.3 29.0 18.8
(SD)______ (4.53H (3.22) (7.08) (1.88) (9.82) (5.52)
•Strengths connected by brackets on the right were not statistically different (P 5~ .05).
H in o u ra -M o o re -P h illip s : BOND S T R E N G T H BETW EEN GLASS IO N O M E R CE M E N T S AN D RESINS ■ 171
ARTICLES
tensile bond strength of glass ionomer cement to dentin is between 1.8 and 7.3 mPa. In this study, the bond strengths between the etched glass ionomer cements and composite resins are between 0.9 and 6.1 mPa. These bond strengths seem to be adequate when compared with the data cited earlier on the glass ionomer-dentin bond. Some combinations of ionomer cements and resins appear to be more effective than others in providing a good bond. More research is needed to further determine the factors involved in achieving maximum bond strengths between etched ionomer cements and the respective bonding agentresin system. Summary Etching or surface roughening of a glass ionomer cementbefore the application of a composite resin bonding agent leads to a significant improvement in the resulting bond. Bond failure at the surfaces occurs cohesively within the glass ionomer. Ade quate washing with water after acid etch ing the glass ionomer is essential to obtain optimal bond strengths. Properly treated glass ionomer surfaces result in bond strengths to composite resins and their bonding agents comparable to the strengths
172 ■ JADA, Vol. 114, February 1987
reported between glass ionomer cements and dentin. The bond strength values mea sured in this study support the use of glass ionomer materials as an intermediate layer between tooth structure and an overlying composite resin in the sandwich technique. ---------------------- JM O A ---------------------Information about the manufacturers of the products mentioned in this article may be available from the author. Neither the authors nor the American Dental Association has any commercial interests in the pro ducts mentioned. The authors thank Hazel E. Clark for assistance with the analysis of the data. Dr. Hinoura is instructor, department of operative dentistry, Nihon University, Tokyo, and visiting pro fessor; Dr. Moore is professor; and Dr. Phillips is asso ciate dean for research and research professor, depart ment of dental materials, School of Dentistry, Indiana University, 1121 W Michigan St, Indianapolis, 46202. Address requests for reprints to Dr. Phillips. 1. Sato, S.; Sato, K.; and Hosoda, H. Adhesion of new dental cements. J Japan Res Dent Mat Appliances 35(l):68-79, 1978. 2. Maldonado, A.; Swartz, M.L.; and Phillips, R.W. An in vitro study of certain properties of a glass iono mer cement. JADA 96(5):785-791, 1978. 3. Powis, D.R., and others. Improved adhesion of a glass ionomer cement to dentin and enamel. J Dent Res 61(12):1416-1422, 1982. 4. Coury, T.L., and others. Adhesiveness of glassionomer cement to enamel and dentin; a laboratory
study. Oper Dent 7(l):2-6,1982. 5. McLean, J.W., and Wilson, A.D. The clinical development of the glass-ionomer cements. Formula tions and properties. Aust Dent J 22( 1);31 -36, 120-127, 190-195, 1977. 6. Mount, G. J., and Makinson, O.F. Clinical charac teristics of a glass-ionomer cement. BrDent J 145(3):6771, 1978. 7. Lawrence, L.G. Cervical glass ionomer restora tions: a clinical study. Can Dent Assoc J 45(2):58-59, 1979. 8. Phillips, R.W. The restoration of eroded cervical areas. CDS Rev 73(4):31-34,1980. 9. Onose, H. The treatment of dentin hypersensitiv ity by the glass ionomer cement mix application. J Int Coll Dent 14(l):29-35, 1984. 10. Swartz, M.L., and others. Fluoride distribution in teeth using a silicate model. J Dent Res 59(10):15961603, 1980. 11. Swartz, M.L.; Phillips, R.W.; and Clark, H.E. Long-term F release from glass ionomer cements. J Dent Res 6S(2):158-160,1984. 12. Tobias, R.S., and others. Pulpal response to a glass ionomer cement. BrDentJ 144(ll):345-350,1978. 13. Kawahara, H.; Imanishi, Y.; and Oshima, H. Biological evaluation of glass ionomer cement. J Dent Res 58(3):1080-1086, 1979. 14. Pameijer, C.H.; Segal, E.; and Richardson, J. Pulpal response to a glass-ionomer cement in primates. J Prosthet Dent 46(1 ):36-40, 1981. 15. Phillips, R.W., and others. Zinc oxide and eugenol cements for permanent cementation. J Prosthet Dent 19(2):144-150, 1968. 16. Fukushima, M. Tags of various restorative resins penetrated into dentin. Japanese J Conserv Dent 22(3):103-120, 1979. 17. Sneed, W.D., and Looper, S.W. Shear bond strength of a composite resin to an etched glass iono mer. Dent Mater J 1(4):127-128, 1985.