Bonding of Acrylic Resins to Dentin with 2-Cyanoacrylate Esters G. M. BRAUER, J. A, JACKSON, and D. J. TERMINI Dental and Medical Materials, National Bureau of Standards, Washington, DC 20234 Strength and durability of the dentin-acrylic resin joint cemented with 2-cyanoacrylate esters were studied. Maximum adhesion is obtained with isobutyl 2-cyanoacrylate after 1% acid pretreatment of the dentin. Hydrolytic stability is somewhat improved by addition of polymer to the adhesive or coating around the joint. J Dent Res 58(9):1900-1907, September 1979
Introduction. A previous study in this laboratory of the bond strength of bone specimens cemented together with alkyl esters of 2-cyanoacrylates indicated that the isobutyl and amyl homologues are the most effective adhesives.1 However, bond strengths decreased on prolonged storage in water. The tendency to debond was significantly reduced by increasing the length of the ester group. Thus, after six-month storage in water, the n-amyl, isoamyl and viscous isoamyl 2-cyanoacrylatebonded specimens retained from 70% to 73% of their one-day bond strength. The ability of the anionically polymerized 2-cyanoacrylate monomers to adhere, at least temporarily, to wet surfaces has stimulated interest in their use for dental applications. The adhesives, mainly the methyl, ethyl and butyl homologues, have been employed with varying success as adhesives to dentin, pulp capping materials, cavity varnishes, in the restoration of broken teeth without pins, and for the adhesion of pins to retain amalgam restorations.2 17 Beech reported that the adhesive bond between dentin and ethyl 2-cyanoacrylate is quite stable after one-week water exposure.2 Beech and Kurer9 reported promising clinical results after an 18-month period using ethyl 2-cyanoacrylate to retain compoReceived for publication September 5, 1978 Accepted for publication October 23, 1978 This work was supported by the National Institutes of Health-National Institute of Dental Research, Interagency Agreement YOI-DE-4001.
site restorations to non-undercut shallow cervical erosion cavities. The objective of this study was as follows: (1) to determine which 2-cyanoacrylate esters were effective adhesives for bonding dentin to acrylic resins, (2) to measure the strength of the bond after its exposure to an aqueous environment for various periods of time, and (3) to explore means for improving the long-term stability of the bond by (a) modification of the 2-iyanoacrylate adhesive, (b) pretreatment of the dentin surface, and (c) covering the adherentadhesive surface with a protective coating.
Materials and methods.* The following alkyl 2-cyanoacrylates were obtained: isobutyl 2-cyanoacrylate (Alpha Ace Ch-4)t and fluorinated 2-cyanoacrylate (MBR 4197)t. Several cyanoacrylates# were also obtained. Poly(ethyl 2cyanoacrylate) was synthesized by the anionic polymerization given for the methyl ester. 17 Bis-GMA [isopropylidene bis(p-phenoxy[2-hydroxytrimethylene ] ) dimethacrylate] ;¶ trimethylolpropane trimethacrylate (SR-350) and 1,6-hexamethylene glycol dimethacrylate (PB 135);** 1H, IH, 5Hoctafluoropentyl acrylate and 2,2,2-tri-
*Certain commercial instruments and materials are identified in this report to adequately specify the experimental procedure. In no instance does such identification imply recommendation or endorsement by the National Bureau of Standards neither does it imply that the instrument or material is necessarily the best available for the purpose. tAlpha Techno Co., Osaka, Japan
tMedical Products Div., 3M Co., St. Paul,
MN #Dr. C. Wade, U.S. Army Research and Development Laboratory, Ft. Detrick, MD ¶ Freeman Chemical Co., Milwaukee, WI **Sartomer, Westchester, PA
1900 Downloaded from jdr.sagepub.com at The University of Iowa Libraries on July 12, 2015 For personal use only. No other uses without permission.
Vol. S8 No. 9
BONDING OFACR YLIC TO DENTIN
1901
fluoroethyl methacrylate;// pentafluorooctyl The film was cured by irradiation for one methacrylate;* * * N,N-dimethylaminopheny- minute by moving a UV light source (Nuvalacetic acid was synthesized in this labora- Lite) circularly around the joint at a distory,19 and the polyfluorooligoether poly- tance of 2 mm. All specimens, after curing, were immediacrylatett were obtained from their respective companies. The UV initiator employed ately stored in water at 370C or thermoto cure the protective coating was benzoin cycled at 50C and 55°C (540 cycles per day) ethyl ether. 1 $ The photo crosslinking agent for the desired length of time. Adhesion strength was determined with a used was 1-aza-5-acryloxymethyl-3 ,7-dioxabicyclo [ 3,31 octaine,## an experimental ma- modification of the tensile test of Lee, terial. All other chemicals used were reagent Swartz and Culp.20 A stainless steel washer grade and were obtained from chemical was slipped over the rod, and the assembly was positioned into the gripper attached to supply houses. The bond strength of bovine dentin the lower jaw of the universal testing macemented with 2-cyanoacrylates to poly chine. To align the assembly, a pin was (methyl methacrylate) was determined using placed through a hole near the top of the mandibular anterior teeth of yearling calves acrylic rod and through holes in a gimbal. embedded in resin.¶ Flat dentin surfaces The top jaws of the universal testing machine gripped a metal strip which supported were prepared using a sectioning machine with a diamond cut-off wheel cooled with a the gimbal. The load was applied at a headwater spray. The smooth specimens were speed of 5 mm/min. To obtain statistically stored in distilled water. In preparation for valid results, the strength of five joints was adhesion testing, the specimens were first determined for each adhesive treatment. blotted dry with filter paper. They were There was no statistically significant difthen pretreated, if desired, by swabbing the ference in the results of the bonding tests surface for 30 sec. with a cotton pledget with surfaces of new and reused dentin if saturated with the respective solution, they were cut in the same manner. The rinsing the surface with distilled water one dentin specimens which were reused were minute after starting the treatment, and resurfaced by cutting down into the healthy blotting the surface dry with filter paper tissue to insure that all previous test materials prior to applying the adhesive. A drop of had been removed. adhesive was placed on the dentin surface, onto which an approximately 4-cm-long acrylic rod of 0.32 cm diameter was posi- Results and discussion. tioned. To obtain vertical alignment, the rod Results of the strength of dentin bonded was guided onto the surface through a 0.34 to acrylic rod are given in Table 1. Only cm hole in an acrylic Cylinder (2.5 cm in the ethyl-, isobutyl- and viscous isoamyl diameter and 2.5 cm high). A 200 gm 2-cyanoacrylate cure within the three-minweight on top of the rod served to maintain ute period that a force is applied to the intimate contact of the surfaces to be assembly (Table 1). The best bond strength bonded. After three minutes, the excess (5.5 MPa) is obtained with the commercial adhesive was removed from the dentin isobutyl 2-cyanoacrylate. The bond strengths surface. reported here are lower than those deterA thin film of a hydrophobic coating of mined previously for bone-to-bone cemented monomeric liquid was brushed around the joints.1 Pretreatment with N,N-dimethylinterface of some dentin-acrylic resin joints. p-toluidine (DMPT), a nucelophilic agent which speeds up curing of the adhesive, sometimes lowers the bond strength (Table 2). Acid-etch pretreatment of the dentin //PCR, Gainesville, FL ***Columbia Organic Chemical Co., Columbia, surface with 37% phosphoric acid greatly SC increases adhesion, thereby giving a onettJ. Griffith, Naval Research Laboratory, day tensile strength of 7.23 MFa (1080 Washington, DC PSI) for the dentin-acrylic rod joint. Howt tAldrich Chemical Co., Milwaukee, WI ever, this bond strength rapidly decreases ##Sun Chemical Corp., Carlstadt, NJ Lee Pharmaceutical Co., South El Monte, with storage time. After 90 days, the tensile adhesion of the joint cemented with isoCA Downloaded from jdr.sagepub.com at The University of Iowa Libraries on July 12, 2015 For personal use only. No other uses without permission.
1902
J Dent Res September 1 9 79
BRA UER, ET AL.
TABLE 1 TENSILE STRENGTH OF THE DENTINACRYLIC JOINT BONDED WITH VARIOUS
CYANOACRYLATES - 3 minutes, stored in H20 for 24 hours. Tensile Strength, MPaa 2-Cyanoacrylate
Curing Time
Standarda Ethyl (Alpha Ace) n-Butyl Isobutyl Isobutyl (Eastman) n-Amyl Isoamyl Isoamyl, viscous
Mean
Deviation
2.80 Did not cure 2.54 5.54 Did not cure Did not cure 2.29
0.34b
0.80b 2.29b
1.21b
aAverage of 5 determinations
bStandard deviation butyl- and viscous isoamyl 2-cyanoacrylate is reduced to 1.89 and 0.25 MPa, respectively. One-day thermocycling also reduces the bond strength (Table 3). Thus, the phosphoric acid-etched dentin has a one-day bond strength of 7.2 MPa after storage in water at 370C, but this value is reduced to 5.7 MPa after thermocycling for the same time period. Even the acid-etched specimens show minimal adhesion or completely destroyed bonds after 30 days of thermocycling. The results of the cycling test give the same ranking for the decrease in the adhesive bond strength as those of the long-term isothermal storage studies. Therefore, ther-
mocycling is valuable as an accelerated procedure in predicting long-term performance of adhesive joints. All subsequent tensile adhesion tests were performed using the accelerated aging thermocycling test with 540 temperature cycles per day. Typical cross-linking agents were incorporated into the isobutyl 2-cyanoacrylate monomer so that, after curing, an insoluble, more hydrolytically stable polymeric adhesive might be formed. However, addition of potential cross-linking agents such as 20% diallyl phthalate, 10% ethylene glycol dimethacrylate, 1% maleic anhydride or 1% itaconic anhydride, to the isobutyl 2cyanoacrylate adhesive did not increase the strength of the dentin-poly(methyl methacrylate) joint (Table 4). Thirty-second pretreatments of the dentin with very dilute acid solutions are more promising than the incorporation of crosslinking agents into the monomer adhesive. Results of these tensile adhesion measurements for treated dentin surfaces are given in Table 5. Swabbing the dentin surface with diluted ethanol prior to bonding increases adhesion, due to the cleansing action of this pretreatment. Etching with 1% phosphoric acid prior to bonding the dentin to the acrylic rod yields a bond strength of 12.4 MPa (1800 PSI). Etching the dentin with 1% succinic, methacrylic or aconitic acid or maleic anhydride does not improve tensile adhesion. Best results are obtained using a 1% solution of citric acid in dilute alcohol (1:2 ETOH/H20 by volume). The bond strength after 30-second pretreatment of the dentin with this solution, and after curing
TABLE 2 TENSILE STRENGTH OF THE DENTIN-ACRYLIC JOINT BONDED WITH VARIOUS CYANOACRYLATES Tensile Strength, MPa Mean SD* 2-Cyanoacrylate Treatment Days in H20 1.67 0.97 Ethyl (Alpha Ace) DMPT 1 3.50 2.65 Isobutyl DMPT 1 7.23 2.86 Isobutyl 37% H3P04 1 1.89 0.56 Isobutyl 37% H3PO4 90 Did not cure n-Amyl DMPT 3.22 0.39 Isoamyl DMPT 1 2.65 0.70 Isoamyl, viscous DMPT 1 3.00 1.09 Isoamyl, viscous 37% H3PO4 1 0.25 0.38 Isoamyl, viscous 37% H3PO4 90 *SD -Standard deviation for 5 measurements Downloaded from jdr.sagepub.com at The University of Iowa Libraries on July 12, 2015 For personal use only. No other uses without permission.
1903
BONDING OFA CR YLIC TO DENTIN
Vol. 58 No. 9
TABLE 3 TENSILE STRENGTH OF THE DENTIN-ACRYLIC JOINT BONDED WITH VARIOUS CYANOACRYLATES
Temperature of water: 5 C and 55 C Frequency of cycles: 540 per day Tensile Strength in MPa after cycling 30 days 7 days 1 day
Surface 2-Cyanoacrylate
Treatment
Isobutyl Isobutyl Isoamyl Isoamyl, viscous Isoamyl, viscous
37% H3PO4 37% H3PO4
5.65 (2.40) --
37% H3PO4
2.38 ( .68)
0.12 ( .27)* 3.32 (2.71) -0.00 2.53 ( .43)
0.25 ( .56) 0.00 -0.00
*Standard deviations are given in parentheses TABLE 4 STRENGTH OF DENTIN-ACRYLIC RESIN JOINT BONDED WITH MODIFIED ISOBUTYL 2-CYANOACRYLATE
Joint was thermocycled in 5 C and 55 C water for one day (540 cycles) Modifier Added to Adhesive* ---
20% v/v Diallyl Phthalate 10% Ethylene Glycol Dimethacrylate 5% Poly(methyl methacrylate) + 10% Dibutyl Phthalate 1% w/v Itaconic Anhydride 1% w/v Maleic Anhydride
Tensile Strength, MPa SD** Mean
5.38 0 0.58 2.60*** 3.12 0
3.00 0 1.00 3.40 1.47 0
*Percentages given for solid modifiers dissolved in the monomer are in w/v; for liquid modifiers they are in v/v.
**Standard deviation. ***Mean determined on 10 specimens rather than 5.
and thermocycling for one day is 14.10 dition of copolymerizable allyl compounds MPa (2050 PSI). This value is considerably to the uncured adhesive, coupled with 1% higher than any adhesion to smooth dentin citric acid pretreatment of the dentin surfaces which has been previously reported. substrate, does not improve adhesion (Table The bond strength is slightly decreased when 6). Incorporation of a fluorinated 2-cyanomore dilute citric acid solutions are used. acrylate into the monomer or substitution of Pretreatment with solutions containing 0.5 n-amyl 2-cyanoacrylate for the uncured or 0.1% citric acid gives bond strength adhesive also does not increase the bond values of 13.4 MPa and 10.7 MPa, respec- strength. Increasing the length of storage of the tively. Other pretreatments yielding tensile adhesion values above 10 MPa include solu- joined (citric acid pretreated) specimens tions of 1% alcoholic (1:2) citraconic in the thermocycled water bath to one week anhydride, 1% alcoholic tetrahydrofuran or one month considerably decreases the -2,3 ,4,5-tetracarboxylic acid, and 1% aqueous tensile adhesion. Seven-day bond strength ethylenediaminetetraacetic acid tetrasodium values of 2.5 to 4.9 MPa are obtained with the pretreated specimens using the unmodsalt. Pretreatment of the dentin with allyl ified isobutyl 2-cyanoacrylate adhesive compounds potentially capable of copoly- (Table 7). Again, addition of 2-5% crossmerization with isobutyl 2-cyanoacrylate linking monomer such as diallyl maleate, has no beneficial effect on adhesion. Ad- triallyl phosphate or triallyl cyanurate does Downloaded from jdr.sagepub.com at The University of Iowa Libraries on July 12, 2015 For personal use only. No other uses without permission.
JDent Res September 1979
BRAUER ET AL.
1904
TABLE 5 STRENGTH OF PRETREATED DENTIN-ACRYLIC RESIN BOND AFTER THERMOCYCLING FOR ONE DAY
Adhesive: Isobutyl 2-Cyanoacrylate Tensile Strength, MPa Stand. Dev. Mean
Dentin Pretreatment* Aq. Ethanol (1:2) 1% Phosphoric Acid 1% Alc. (1:2) Succinic Acid 1% Alc. (1:2) Methacrylic Acid 1% Alc. (1:2) Aconitic Acid 1% Alc. Maleic Anhydride 1% Alc. Abietic Acid 1% Aq. Citric Acid 1% Alc. (1:2) Citric Acid 0.5% Alc. (1:2) Citric Acid 0.1% Alc. (1:2) Citric Acid 1% Alc. (1:2) Itaconic Acid 1% Alc. (1:2) Itaconic Anhydride 1% Alc. (1:2 Citraconic Anhydride 1% Alc. (1:2) Tetrahydrofuran 2,3,4,5tetracarboxylic acid 1% Alc. TriaUlyl Phosphate 1% Alc. Triallyl Cyanurate 0.5% Alc. Triallyl Cyanurate
7.79 12.38 2.83 3.68 2.75 4.94 4.28 12.60 14.10** 13.44 10.68 8.29*** 5.80 11.13 10.22
1.97 2.75 3.89 1.59 2.57 1.61 2.36 3.62 4.46 3.91 3.89 3.25 2.42 2.83 2.75
2.51
2.84 4.31
4.25 1.17
1.69 2.84 2.51 0.2% Alc. Triallyl Cyanurate 0.18 0.12 1% Aq. Calcium Hydroxide 2.54 11.66 1% Aq. EDTA Tetrasodium salt ethanol (1:2) or *Percentages given are weights of solids or volumes of liquids dissolved in volume of water. **Mean of 10 measurements ***Mean of 20 measurements
TABLE 6 STRENGTH OF DENTIN-ACRYLIC RESIN BOND AFTER THERMOCYCLING FOR ONE DAY
Dentin pretreated with 1% alc. (1:2) citric acid Adhesive: modified isobutyl 2-cyanoacrylate
Adhesive Modifier*
5% Triallyl Phosphate 5% Diallyl Maleate 5% Diallyl Phthalate 2% Triallyl Cyanurate 5% Alyl Methacrylate 10% Triethylene Glycol Dimethacrylate 20% Fluorinated 2-Cyanoacrylate 100% n-Amyl 2-Cyanoacrylate
Tensile Strength, MPa Stand. Dev. Mean
7.77 8.03 0 8.60 7.95 0 7.22 3.97
1.57 2.15 0 1.32 3.41 0 1.48 1.22
*Percentages given for solid modifiers dissolved in the monomer are in w/v; for liquid modifiers, they are v/v.
appreciably increase the hydrolytic stability. Addition of 3% to 30% poly(ethyl 2-cyanoacrylate) to the isobutyl 2-cyanoacrylate monomer, however, yields a bond with
greater resistance to water. Thus, the sevenday bond strength of adhesive containing 5% poly(ethyl 2-cyanoacrylate) is 8.7 MPa, compared to 3.7 MPa for the unmod-
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Vol. S8 No. 9
1905
BONDING OFACR YLIC TO DENTIN
TABLE 7 STRENGTH OF DENTIN-ACRYLIC RESIN JOINT BONDED WITH ISOBUTYL 2-CYANOACRYLATE AFTER THERMOCYCLING*
Adhesive Modifierl
Length of Thermocycling days
_2 -3 -4 -
5% Allyl Methacrylate 5% Allyl Methacrylate 5% Triallyl Phosphate 5% Diallyl Maleate 2% Triallyl Cyanurate 3% Poly(ethyl 2-cyanoacrylate) 5% Poly(ethyl 2-cyanoacrylate) 12% Poly(ethyl 2-cyanoacrylate) 20% Poly(ethyl 2-cyanoacrylate) 30% Poly(ethyl 2-cyanoacrylate) 40% Poly(ethyl 2-cyanoacrylate) 50% Poly(ethyl 2-cyanoacrylate)
7 7 30 7 7 7 7 30 7 7 7 7 7 7 7 7 7 7
Tensile Strength, MPa Stand. Dev. Mean 2.57 3.71 0.12 3.87 2.98 4.88 3.72 0 2.89 3.18 4.35 5.84 8.67 6.59 6.77 6.28 1.51 1.18
1.73 1.34 0.25 1.78 1.72 1.98 2.05 -
1.35 2.61 2.34 1.47 1.68 1.12 1.92 2.69 0.82 0.88
Percentages are given as weight of solids dissolved in volume of liquid and volume of liquid dissolved in liquid
2Dentin pretreatment: 0.5% alc. (1:2) citric acid
3Dentin pretreatment: 1% alc. (1:2) itaconic acid 4Dentin pretreatment: 1% alc. (1:2) citraconic acid *Dentin pretreated with 1% alc. (1:2) citric acid
ified adhesive. Formulations containing more than 30% of dissolved polymer become quite viscous, and their bond strength is quite low. Results of 30-day thermocycling tests employing isobutyl 2-cyanoacrylate with or without 5% allyl methacrylate are disappointing, giving a bond strength of 0.1 MPa for the unmodified adhesive. To reduce or eliminate debonding, a hydrophobic sealant, which was polymerized by a UV-light source, was placed around the dentin-methacrylate interface. The rationale for this procedure is that the coating would seal off the adhesive from contact with water, or at least the water permeation through the protective film to the adhesive surface would be reduced. Thus, it was hoped that hydrolytic degradation of the bond would be minimized. Suitable protective formulations should (1) cure within one minute, (2) be hydrophobic, (3) be compatible with the etched dentin and the cured cyanoacrylate adhesive, and (4) be storage stable for at least 24 hours. A number of
monomeric resin formulations were prepared (Table 8) which were capable of polymerization after irradiation with the Nuva-Lite UV light source for 30 seconds. Four compositions with contact angles varying from 54 degrees to 80 degrees were studied further. A thin film of these compositions was painted around the dentin-acrylate joint immediately after the adhesive had set. The protective coating was then cured with the UV light source and the joints were placed immediately into water. A significant improvement in the shorter-term stabilization of the bond was obtained with a composition containing 43% hexamethylene glycol dimethacrylate, 41% Bis-GMA, 12% 1H,1H,5H-octafluoropentyl acrylate,2% benzoin ethyl ether UV initiator and 2% of UV photo cross-linking agent (1 oxa-5-acryloxymethyl-3 ,7-dioxabicyclo[3,3 ,0J octane). After seven days of thermocycling, the bond strength of dentin-resin joints coated witlh a protective film of this composition averaged 8.9 MPa (1340 PSI). However, after 30
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1906
J Dent Res September 19 79
BRAUER ET AL.
TABLE 8 STRENGTH OF DENTIN-ACRYLIC RESIN JOINT COVERED WITH A PROTECTIVE COATING AFTER THERMOCYCLING
Adhesive: Isobutyl 2-cyanoacrylate Dentin pretreated with 1% alcoholic (1:2) citric acid Protective Coating
Curing Time
H20 Contact
sec.
Angle
Adhesive Tensile Strength, MPa 7 day 30 day
30
590
5.11 (2.00) 0.98 (0.68)
-
-
30
600
8.92 (3.88) 0.59 (0.63)
43% Urethane dimethacrylate 43% Hexamethylene glycol dimethacrylate 10% Pentadecafluorooctyl methacrylate 2% UV initiator; 2% photo crosslinking agent
30
540
3.58 (1.06)
70% Polyfluoropolyacrylate 30% Pentadecafluorooctyl methacrylate 2% UV initiator 0.3% Dimethylaminophenylacetic acid
30
800
4.40 (1.64)
days of thermocycling the adhesive strength reduced to 1 MPa. The other formulations containing a urethane dimethacrylate or the most hydrophobic composition, which contained a fluoropolyacrylate, gave coatings that resulted in only marginal improvement in stability of the bond. Addition of polymeric 2-cyanoacrylate to the adhesive prior to applying the coating did not yield a statistically significant increase in bond strength. The results indicate that, even after applying a protective coating, the adhesive compositions studied cannot be recommended for use where a long-term bond is required. Studies, especially by Stanley and coworkers,21 have shown that etching of dentin with rather concentrated acid solutions, such as 37% or 50% phosphoric acid, give an undesirable pulp response. If our present pretreatment of the dentin proves successful in in vitro studies, it will then
be necessary to determine whether or not very dilute solutions of citric acid (0.1 to 1%) can be tolerated clinically.
Composition 60% Bis-GMA 25% Trimethylolpropane trimethacrylate 10% 2,2,2-Trifluoroethyl methacrylate 2% UV initiator; 3% photo crosslinking agent Same as above but adhesive containing 5% poly(ethyl 2-cyanoacrylate) 41% Bis-GMA 43% Hexamethylene glycol dimethacrylate 12% lH,1H,5H-Octafluoropentyl acrylate 2% UV initiator, 2% photo crosslinking agent
was
5.27 (2.77)
It should be realized, however, that the abrupt temperature changes during the cycling procedure will result in considerable stress formation in the joined substrates which may not be encountered under clinical conditions; i.e., the accelerated test may be so excessively severe as not to be predictive of the clinical long-term applicability of this treatment. many
Conclusions. 1. The isobutyl ester is the most effective 2-cyanoacrylate for bonding dentin to acrylic resins. 2. Pretreatment of the dentin with dilute acids, such as 1% solution of citric acid in dilute alcohol (1:2), greatly increases bond strength.
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Vol. 58 No. 9
BONDING OFACR YLIC TO DENTIN
1907
3. The strength of the bond decreases on 10. BUCK, C. J.: Modified Cyanoacrylate Monoprolonged water exposure. mers, U.S. Patent 4,041,063, August 9, 1977. U.S. Patent 4,041,061, August 9, 1977. 4. Addition of a 2-cyanoacrylate polymer to the adhesive or application of a protec- 11. BUCK, C. J.: Blocked bis 2-cyanoacrylate Monomers, U.S. Patent 4,003,942, Jan. 18, tive coating to the bonded surface in1977. creases the hydrolytic stability of the 12. MATEEVA, K.; TSOLOVA, E.; and POPOV, bond. K.: Impregnation of Dental Surfaces by a 5. Isobutyl 2-cyanoacrylate may be useful 2-Cyanoacrylate Adhesive (Communication clinically as a short-term adhesive if it I), Stomatologiya (Sofia) 58:127-131, 1976, is found to be biocompatible. (Through CA 85:166597e, 1976). 13. ALEKSIEVA, K. and CHAKMAKOV, D.: REFERENCES 1. BRAUER, G. M.; KUMPULA, J. W.; TERMINI, D. J.; and DAVIDSON, K. M.: Durability of the Bond Between Bone and Various 2-Cyanoacrylates in an Aqueous Environment, J Biomed Mat Res (in press). 2. BEECH, D. R.: Bonding of Alkyl 2-Cyanoacrylates to Human Dentin and Enamel, JDentRes 51:1438-1442, 1972. 3. BAKLAND, T. and BAUM, L.: Cyanoacrylate in the Cementation of Threaded Retentive Pins, J Ga Dent Assoc 47:13-16, Summer, 1973. 4. DILTS, W.; COLLARD, E. W.; and DUNCANSON, M. G.: Retention of Pins with a Cyanoacrylate Bonding System, IADR Progr & Abst 53:47, 1973. 5. TRABERT, R. C. and CAPUTO, A. A.: Effects of Cement Type and Thickness upon Retention of Serrated Pins, IADR Progr & Abst 53:50, 1973. 6. STANFORD, J. S.: Cyanoacrylate Cements -Precautions, JADA 90:727, 1975. 7. LAMBERT, R. L.: Retentive Properties of Stainless Steel Pins Cemented with Ethyl Cyanoacrylate, J Prosthet Dent 34:187-
191, 1975. 8. BAUM, L.: Cementing Pins with Cyanoacrylate (An Appraisal of Biodegradability), Gen Dent 24:32-34, Jul-Aug 1976. 9. BEECH, D. R. and KURER, H. G.: An In vitro Study of a Cyanoacrylate as an Adhesive for Composite Restorations, IADR Progr & Abst 54:1356, 1974.
14.
15. 16.
17.
18. 19. 20. 21.
In vitro Study of the Strength of Some Alkyl a-Cyanoacrylates with Hard Dental Tissues, Probi Stomatol 2:109-116, 1974. (Through CA 86:161266g, 1977). BOYANOV, B.; ALEKSIEVA, K.; CHAKMAKOV, D.; and RAICHEY, L.: Study of the Effect of Fluoride on the Insulation Properties of Some Alkyl 2-Cyanoacrylate Preparations for Caries Prevention, Probl Stomatol 4:9-10, 1976. (Through CA 88:83415, 1978). TAKEUCHI, M. and OTSUKI, A.: Adhesive Pit and Fissure Sealant, UfS. Patent 4,012,840, March 22, 1977. FUKUSHI, Y.: Treatment of Cavity Walls with Cyanoacrylates: I. The Effect on Adhesion of Composite Resins, Kokubyo Gakkai Zasshi 44:101-107, 1977. (Through CA 88: 27780h, 1978). OTSUKI, A. and TAKEUCHI, M.: Simple Fissure Sealant and its Tensile Bond Strength to Etched Bovine Enamel, Caries Res 10: 463472, 1976. COOVER, H. W. and McINTIRE, J. M.: Poly(Methyl 2-Cyanoacrylate) Macromolec Synth 5:51-54, 1974. BRAUER, G. M.; DULIK, D. M.; ANTONUCCI, J. M.; and ARGENTAR, H.: unpublished data. LEE, H. L.; SWARTZ, M. L.; and CULP, G.: Static Load Testing of Dental Adhesives, J Dent Res 48:211-216, 1969. STANLEY, H. R.; GOING, R. E.; and CHAUNCEY, H. H.: Human Pulp Response to Acid Pretreatment of Dentin and to Composite Restoration, JADA 91:817-825, 1975.
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Introduction. A previous study in this laboratory of the bond strength of bone specimens cemented together with alkyl esters of 2-cyanoacrylates indicated that the isobutyl and amyl homologues are the most effective adhesives.1 However, bond strengths decreased on prolonged storage in water. The tendency to debond was significantly reduced by increasing the length of the ester group. Thus, after six-month storage in water, the n-amyl, isoamyl and viscous isoamyl 2-cyanoacrylatebonded specimens retained from 70% to 73% of their one-day bond strength. The ability of the anionically polymerized 2-cyanoacrylate monomers to adhere, at least temporarily, to wet surfaces has stimulated interest in their use for dental applications. The adhesives, mainly the methyl, ethyl and butyl homologues, have been employed with varying success as adhesives to dentin, pulp capping materials, cavity varnishes, in the restoration of broken teeth without pins, and for the adhesion of pins to retain amalgam restorations.2 17 Beech reported that the adhesive bond between dentin and ethyl 2-cyanoacrylate is quite stable after one-week water exposure.2 Beech and Kurer9 reported promising clinical results after an 18-month period using ethyl 2-cyanoacrylate to retain compoReceived for publication September 5, 1978 Accepted for publication October 23, 1978 This work was supported by the National Institutes of Health-National Institute of Dental Research, Interagency Agreement YOI-DE-4001.
site restorations to non-undercut shallow cervical erosion cavities. The objective of this study was as follows: (1) to determine which 2-cyanoacrylate esters were effective adhesives for bonding dentin to acrylic resins, (2) to measure the strength of the bond after its exposure to an aqueous environment for various periods of time, and (3) to explore means for improving the long-term stability of the bond by (a) modification of the 2-iyanoacrylate adhesive, (b) pretreatment of the dentin surface, and (c) covering the adherentadhesive surface with a protective coating.
Materials and methods.* The following alkyl 2-cyanoacrylates were obtained: isobutyl 2-cyanoacrylate (Alpha Ace Ch-4)t and fluorinated 2-cyanoacrylate (MBR 4197)t. Several cyanoacrylates# were also obtained. Poly(ethyl 2cyanoacrylate) was synthesized by the anionic polymerization given for the methyl ester. 17 Bis-GMA [isopropylidene bis(p-phenoxy[2-hydroxytrimethylene ] ) dimethacrylate] ;¶ trimethylolpropane trimethacrylate (SR-350) and 1,6-hexamethylene glycol dimethacrylate (PB 135);** 1H, IH, 5Hoctafluoropentyl acrylate and 2,2,2-tri-
*Certain commercial instruments and materials are identified in this report to adequately specify the experimental procedure. In no instance does such identification imply recommendation or endorsement by the National Bureau of Standards neither does it imply that the instrument or material is necessarily the best available for the purpose. tAlpha Techno Co., Osaka, Japan
tMedical Products Div., 3M Co., St. Paul,
MN #Dr. C. Wade, U.S. Army Research and Development Laboratory, Ft. Detrick, MD ¶ Freeman Chemical Co., Milwaukee, WI **Sartomer, Westchester, PA
1900 Downloaded from jdr.sagepub.com at The University of Iowa Libraries on July 12, 2015 For personal use only. No other uses without permission.
Vol. S8 No. 9
BONDING OFACR YLIC TO DENTIN
1901
fluoroethyl methacrylate;// pentafluorooctyl The film was cured by irradiation for one methacrylate;* * * N,N-dimethylaminopheny- minute by moving a UV light source (Nuvalacetic acid was synthesized in this labora- Lite) circularly around the joint at a distory,19 and the polyfluorooligoether poly- tance of 2 mm. All specimens, after curing, were immediacrylatett were obtained from their respective companies. The UV initiator employed ately stored in water at 370C or thermoto cure the protective coating was benzoin cycled at 50C and 55°C (540 cycles per day) ethyl ether. 1 $ The photo crosslinking agent for the desired length of time. Adhesion strength was determined with a used was 1-aza-5-acryloxymethyl-3 ,7-dioxabicyclo [ 3,31 octaine,## an experimental ma- modification of the tensile test of Lee, terial. All other chemicals used were reagent Swartz and Culp.20 A stainless steel washer grade and were obtained from chemical was slipped over the rod, and the assembly was positioned into the gripper attached to supply houses. The bond strength of bovine dentin the lower jaw of the universal testing macemented with 2-cyanoacrylates to poly chine. To align the assembly, a pin was (methyl methacrylate) was determined using placed through a hole near the top of the mandibular anterior teeth of yearling calves acrylic rod and through holes in a gimbal. embedded in resin.¶ Flat dentin surfaces The top jaws of the universal testing machine gripped a metal strip which supported were prepared using a sectioning machine with a diamond cut-off wheel cooled with a the gimbal. The load was applied at a headwater spray. The smooth specimens were speed of 5 mm/min. To obtain statistically stored in distilled water. In preparation for valid results, the strength of five joints was adhesion testing, the specimens were first determined for each adhesive treatment. blotted dry with filter paper. They were There was no statistically significant difthen pretreated, if desired, by swabbing the ference in the results of the bonding tests surface for 30 sec. with a cotton pledget with surfaces of new and reused dentin if saturated with the respective solution, they were cut in the same manner. The rinsing the surface with distilled water one dentin specimens which were reused were minute after starting the treatment, and resurfaced by cutting down into the healthy blotting the surface dry with filter paper tissue to insure that all previous test materials prior to applying the adhesive. A drop of had been removed. adhesive was placed on the dentin surface, onto which an approximately 4-cm-long acrylic rod of 0.32 cm diameter was posi- Results and discussion. tioned. To obtain vertical alignment, the rod Results of the strength of dentin bonded was guided onto the surface through a 0.34 to acrylic rod are given in Table 1. Only cm hole in an acrylic Cylinder (2.5 cm in the ethyl-, isobutyl- and viscous isoamyl diameter and 2.5 cm high). A 200 gm 2-cyanoacrylate cure within the three-minweight on top of the rod served to maintain ute period that a force is applied to the intimate contact of the surfaces to be assembly (Table 1). The best bond strength bonded. After three minutes, the excess (5.5 MPa) is obtained with the commercial adhesive was removed from the dentin isobutyl 2-cyanoacrylate. The bond strengths surface. reported here are lower than those deterA thin film of a hydrophobic coating of mined previously for bone-to-bone cemented monomeric liquid was brushed around the joints.1 Pretreatment with N,N-dimethylinterface of some dentin-acrylic resin joints. p-toluidine (DMPT), a nucelophilic agent which speeds up curing of the adhesive, sometimes lowers the bond strength (Table 2). Acid-etch pretreatment of the dentin //PCR, Gainesville, FL ***Columbia Organic Chemical Co., Columbia, surface with 37% phosphoric acid greatly SC increases adhesion, thereby giving a onettJ. Griffith, Naval Research Laboratory, day tensile strength of 7.23 MFa (1080 Washington, DC PSI) for the dentin-acrylic rod joint. Howt tAldrich Chemical Co., Milwaukee, WI ever, this bond strength rapidly decreases ##Sun Chemical Corp., Carlstadt, NJ Lee Pharmaceutical Co., South El Monte, with storage time. After 90 days, the tensile adhesion of the joint cemented with isoCA Downloaded from jdr.sagepub.com at The University of Iowa Libraries on July 12, 2015 For personal use only. No other uses without permission.
1902
J Dent Res September 1 9 79
BRA UER, ET AL.
TABLE 1 TENSILE STRENGTH OF THE DENTINACRYLIC JOINT BONDED WITH VARIOUS
CYANOACRYLATES - 3 minutes, stored in H20 for 24 hours. Tensile Strength, MPaa 2-Cyanoacrylate
Curing Time
Standarda Ethyl (Alpha Ace) n-Butyl Isobutyl Isobutyl (Eastman) n-Amyl Isoamyl Isoamyl, viscous
Mean
Deviation
2.80 Did not cure 2.54 5.54 Did not cure Did not cure 2.29
0.34b
0.80b 2.29b
1.21b
aAverage of 5 determinations
bStandard deviation butyl- and viscous isoamyl 2-cyanoacrylate is reduced to 1.89 and 0.25 MPa, respectively. One-day thermocycling also reduces the bond strength (Table 3). Thus, the phosphoric acid-etched dentin has a one-day bond strength of 7.2 MPa after storage in water at 370C, but this value is reduced to 5.7 MPa after thermocycling for the same time period. Even the acid-etched specimens show minimal adhesion or completely destroyed bonds after 30 days of thermocycling. The results of the cycling test give the same ranking for the decrease in the adhesive bond strength as those of the long-term isothermal storage studies. Therefore, ther-
mocycling is valuable as an accelerated procedure in predicting long-term performance of adhesive joints. All subsequent tensile adhesion tests were performed using the accelerated aging thermocycling test with 540 temperature cycles per day. Typical cross-linking agents were incorporated into the isobutyl 2-cyanoacrylate monomer so that, after curing, an insoluble, more hydrolytically stable polymeric adhesive might be formed. However, addition of potential cross-linking agents such as 20% diallyl phthalate, 10% ethylene glycol dimethacrylate, 1% maleic anhydride or 1% itaconic anhydride, to the isobutyl 2cyanoacrylate adhesive did not increase the strength of the dentin-poly(methyl methacrylate) joint (Table 4). Thirty-second pretreatments of the dentin with very dilute acid solutions are more promising than the incorporation of crosslinking agents into the monomer adhesive. Results of these tensile adhesion measurements for treated dentin surfaces are given in Table 5. Swabbing the dentin surface with diluted ethanol prior to bonding increases adhesion, due to the cleansing action of this pretreatment. Etching with 1% phosphoric acid prior to bonding the dentin to the acrylic rod yields a bond strength of 12.4 MPa (1800 PSI). Etching the dentin with 1% succinic, methacrylic or aconitic acid or maleic anhydride does not improve tensile adhesion. Best results are obtained using a 1% solution of citric acid in dilute alcohol (1:2 ETOH/H20 by volume). The bond strength after 30-second pretreatment of the dentin with this solution, and after curing
TABLE 2 TENSILE STRENGTH OF THE DENTIN-ACRYLIC JOINT BONDED WITH VARIOUS CYANOACRYLATES Tensile Strength, MPa Mean SD* 2-Cyanoacrylate Treatment Days in H20 1.67 0.97 Ethyl (Alpha Ace) DMPT 1 3.50 2.65 Isobutyl DMPT 1 7.23 2.86 Isobutyl 37% H3P04 1 1.89 0.56 Isobutyl 37% H3PO4 90 Did not cure n-Amyl DMPT 3.22 0.39 Isoamyl DMPT 1 2.65 0.70 Isoamyl, viscous DMPT 1 3.00 1.09 Isoamyl, viscous 37% H3PO4 1 0.25 0.38 Isoamyl, viscous 37% H3PO4 90 *SD -Standard deviation for 5 measurements Downloaded from jdr.sagepub.com at The University of Iowa Libraries on July 12, 2015 For personal use only. No other uses without permission.
1903
BONDING OFA CR YLIC TO DENTIN
Vol. 58 No. 9
TABLE 3 TENSILE STRENGTH OF THE DENTIN-ACRYLIC JOINT BONDED WITH VARIOUS CYANOACRYLATES
Temperature of water: 5 C and 55 C Frequency of cycles: 540 per day Tensile Strength in MPa after cycling 30 days 7 days 1 day
Surface 2-Cyanoacrylate
Treatment
Isobutyl Isobutyl Isoamyl Isoamyl, viscous Isoamyl, viscous
37% H3PO4 37% H3PO4
5.65 (2.40) --
37% H3PO4
2.38 ( .68)
0.12 ( .27)* 3.32 (2.71) -0.00 2.53 ( .43)
0.25 ( .56) 0.00 -0.00
*Standard deviations are given in parentheses TABLE 4 STRENGTH OF DENTIN-ACRYLIC RESIN JOINT BONDED WITH MODIFIED ISOBUTYL 2-CYANOACRYLATE
Joint was thermocycled in 5 C and 55 C water for one day (540 cycles) Modifier Added to Adhesive* ---
20% v/v Diallyl Phthalate 10% Ethylene Glycol Dimethacrylate 5% Poly(methyl methacrylate) + 10% Dibutyl Phthalate 1% w/v Itaconic Anhydride 1% w/v Maleic Anhydride
Tensile Strength, MPa SD** Mean
5.38 0 0.58 2.60*** 3.12 0
3.00 0 1.00 3.40 1.47 0
*Percentages given for solid modifiers dissolved in the monomer are in w/v; for liquid modifiers they are in v/v.
**Standard deviation. ***Mean determined on 10 specimens rather than 5.
and thermocycling for one day is 14.10 dition of copolymerizable allyl compounds MPa (2050 PSI). This value is considerably to the uncured adhesive, coupled with 1% higher than any adhesion to smooth dentin citric acid pretreatment of the dentin surfaces which has been previously reported. substrate, does not improve adhesion (Table The bond strength is slightly decreased when 6). Incorporation of a fluorinated 2-cyanomore dilute citric acid solutions are used. acrylate into the monomer or substitution of Pretreatment with solutions containing 0.5 n-amyl 2-cyanoacrylate for the uncured or 0.1% citric acid gives bond strength adhesive also does not increase the bond values of 13.4 MPa and 10.7 MPa, respec- strength. Increasing the length of storage of the tively. Other pretreatments yielding tensile adhesion values above 10 MPa include solu- joined (citric acid pretreated) specimens tions of 1% alcoholic (1:2) citraconic in the thermocycled water bath to one week anhydride, 1% alcoholic tetrahydrofuran or one month considerably decreases the -2,3 ,4,5-tetracarboxylic acid, and 1% aqueous tensile adhesion. Seven-day bond strength ethylenediaminetetraacetic acid tetrasodium values of 2.5 to 4.9 MPa are obtained with the pretreated specimens using the unmodsalt. Pretreatment of the dentin with allyl ified isobutyl 2-cyanoacrylate adhesive compounds potentially capable of copoly- (Table 7). Again, addition of 2-5% crossmerization with isobutyl 2-cyanoacrylate linking monomer such as diallyl maleate, has no beneficial effect on adhesion. Ad- triallyl phosphate or triallyl cyanurate does Downloaded from jdr.sagepub.com at The University of Iowa Libraries on July 12, 2015 For personal use only. No other uses without permission.
JDent Res September 1979
BRAUER ET AL.
1904
TABLE 5 STRENGTH OF PRETREATED DENTIN-ACRYLIC RESIN BOND AFTER THERMOCYCLING FOR ONE DAY
Adhesive: Isobutyl 2-Cyanoacrylate Tensile Strength, MPa Stand. Dev. Mean
Dentin Pretreatment* Aq. Ethanol (1:2) 1% Phosphoric Acid 1% Alc. (1:2) Succinic Acid 1% Alc. (1:2) Methacrylic Acid 1% Alc. (1:2) Aconitic Acid 1% Alc. Maleic Anhydride 1% Alc. Abietic Acid 1% Aq. Citric Acid 1% Alc. (1:2) Citric Acid 0.5% Alc. (1:2) Citric Acid 0.1% Alc. (1:2) Citric Acid 1% Alc. (1:2) Itaconic Acid 1% Alc. (1:2) Itaconic Anhydride 1% Alc. (1:2 Citraconic Anhydride 1% Alc. (1:2) Tetrahydrofuran 2,3,4,5tetracarboxylic acid 1% Alc. TriaUlyl Phosphate 1% Alc. Triallyl Cyanurate 0.5% Alc. Triallyl Cyanurate
7.79 12.38 2.83 3.68 2.75 4.94 4.28 12.60 14.10** 13.44 10.68 8.29*** 5.80 11.13 10.22
1.97 2.75 3.89 1.59 2.57 1.61 2.36 3.62 4.46 3.91 3.89 3.25 2.42 2.83 2.75
2.51
2.84 4.31
4.25 1.17
1.69 2.84 2.51 0.2% Alc. Triallyl Cyanurate 0.18 0.12 1% Aq. Calcium Hydroxide 2.54 11.66 1% Aq. EDTA Tetrasodium salt ethanol (1:2) or *Percentages given are weights of solids or volumes of liquids dissolved in volume of water. **Mean of 10 measurements ***Mean of 20 measurements
TABLE 6 STRENGTH OF DENTIN-ACRYLIC RESIN BOND AFTER THERMOCYCLING FOR ONE DAY
Dentin pretreated with 1% alc. (1:2) citric acid Adhesive: modified isobutyl 2-cyanoacrylate
Adhesive Modifier*
5% Triallyl Phosphate 5% Diallyl Maleate 5% Diallyl Phthalate 2% Triallyl Cyanurate 5% Alyl Methacrylate 10% Triethylene Glycol Dimethacrylate 20% Fluorinated 2-Cyanoacrylate 100% n-Amyl 2-Cyanoacrylate
Tensile Strength, MPa Stand. Dev. Mean
7.77 8.03 0 8.60 7.95 0 7.22 3.97
1.57 2.15 0 1.32 3.41 0 1.48 1.22
*Percentages given for solid modifiers dissolved in the monomer are in w/v; for liquid modifiers, they are v/v.
appreciably increase the hydrolytic stability. Addition of 3% to 30% poly(ethyl 2-cyanoacrylate) to the isobutyl 2-cyanoacrylate monomer, however, yields a bond with
greater resistance to water. Thus, the sevenday bond strength of adhesive containing 5% poly(ethyl 2-cyanoacrylate) is 8.7 MPa, compared to 3.7 MPa for the unmod-
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Vol. S8 No. 9
1905
BONDING OFACR YLIC TO DENTIN
TABLE 7 STRENGTH OF DENTIN-ACRYLIC RESIN JOINT BONDED WITH ISOBUTYL 2-CYANOACRYLATE AFTER THERMOCYCLING*
Adhesive Modifierl
Length of Thermocycling days
_2 -3 -4 -
5% Allyl Methacrylate 5% Allyl Methacrylate 5% Triallyl Phosphate 5% Diallyl Maleate 2% Triallyl Cyanurate 3% Poly(ethyl 2-cyanoacrylate) 5% Poly(ethyl 2-cyanoacrylate) 12% Poly(ethyl 2-cyanoacrylate) 20% Poly(ethyl 2-cyanoacrylate) 30% Poly(ethyl 2-cyanoacrylate) 40% Poly(ethyl 2-cyanoacrylate) 50% Poly(ethyl 2-cyanoacrylate)
7 7 30 7 7 7 7 30 7 7 7 7 7 7 7 7 7 7
Tensile Strength, MPa Stand. Dev. Mean 2.57 3.71 0.12 3.87 2.98 4.88 3.72 0 2.89 3.18 4.35 5.84 8.67 6.59 6.77 6.28 1.51 1.18
1.73 1.34 0.25 1.78 1.72 1.98 2.05 -
1.35 2.61 2.34 1.47 1.68 1.12 1.92 2.69 0.82 0.88
Percentages are given as weight of solids dissolved in volume of liquid and volume of liquid dissolved in liquid
2Dentin pretreatment: 0.5% alc. (1:2) citric acid
3Dentin pretreatment: 1% alc. (1:2) itaconic acid 4Dentin pretreatment: 1% alc. (1:2) citraconic acid *Dentin pretreated with 1% alc. (1:2) citric acid
ified adhesive. Formulations containing more than 30% of dissolved polymer become quite viscous, and their bond strength is quite low. Results of 30-day thermocycling tests employing isobutyl 2-cyanoacrylate with or without 5% allyl methacrylate are disappointing, giving a bond strength of 0.1 MPa for the unmodified adhesive. To reduce or eliminate debonding, a hydrophobic sealant, which was polymerized by a UV-light source, was placed around the dentin-methacrylate interface. The rationale for this procedure is that the coating would seal off the adhesive from contact with water, or at least the water permeation through the protective film to the adhesive surface would be reduced. Thus, it was hoped that hydrolytic degradation of the bond would be minimized. Suitable protective formulations should (1) cure within one minute, (2) be hydrophobic, (3) be compatible with the etched dentin and the cured cyanoacrylate adhesive, and (4) be storage stable for at least 24 hours. A number of
monomeric resin formulations were prepared (Table 8) which were capable of polymerization after irradiation with the Nuva-Lite UV light source for 30 seconds. Four compositions with contact angles varying from 54 degrees to 80 degrees were studied further. A thin film of these compositions was painted around the dentin-acrylate joint immediately after the adhesive had set. The protective coating was then cured with the UV light source and the joints were placed immediately into water. A significant improvement in the shorter-term stabilization of the bond was obtained with a composition containing 43% hexamethylene glycol dimethacrylate, 41% Bis-GMA, 12% 1H,1H,5H-octafluoropentyl acrylate,2% benzoin ethyl ether UV initiator and 2% of UV photo cross-linking agent (1 oxa-5-acryloxymethyl-3 ,7-dioxabicyclo[3,3 ,0J octane). After seven days of thermocycling, the bond strength of dentin-resin joints coated witlh a protective film of this composition averaged 8.9 MPa (1340 PSI). However, after 30
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1906
J Dent Res September 19 79
BRAUER ET AL.
TABLE 8 STRENGTH OF DENTIN-ACRYLIC RESIN JOINT COVERED WITH A PROTECTIVE COATING AFTER THERMOCYCLING
Adhesive: Isobutyl 2-cyanoacrylate Dentin pretreated with 1% alcoholic (1:2) citric acid Protective Coating
Curing Time
H20 Contact
sec.
Angle
Adhesive Tensile Strength, MPa 7 day 30 day
30
590
5.11 (2.00) 0.98 (0.68)
-
-
30
600
8.92 (3.88) 0.59 (0.63)
43% Urethane dimethacrylate 43% Hexamethylene glycol dimethacrylate 10% Pentadecafluorooctyl methacrylate 2% UV initiator; 2% photo crosslinking agent
30
540
3.58 (1.06)
70% Polyfluoropolyacrylate 30% Pentadecafluorooctyl methacrylate 2% UV initiator 0.3% Dimethylaminophenylacetic acid
30
800
4.40 (1.64)
days of thermocycling the adhesive strength reduced to 1 MPa. The other formulations containing a urethane dimethacrylate or the most hydrophobic composition, which contained a fluoropolyacrylate, gave coatings that resulted in only marginal improvement in stability of the bond. Addition of polymeric 2-cyanoacrylate to the adhesive prior to applying the coating did not yield a statistically significant increase in bond strength. The results indicate that, even after applying a protective coating, the adhesive compositions studied cannot be recommended for use where a long-term bond is required. Studies, especially by Stanley and coworkers,21 have shown that etching of dentin with rather concentrated acid solutions, such as 37% or 50% phosphoric acid, give an undesirable pulp response. If our present pretreatment of the dentin proves successful in in vitro studies, it will then
be necessary to determine whether or not very dilute solutions of citric acid (0.1 to 1%) can be tolerated clinically.
Composition 60% Bis-GMA 25% Trimethylolpropane trimethacrylate 10% 2,2,2-Trifluoroethyl methacrylate 2% UV initiator; 3% photo crosslinking agent Same as above but adhesive containing 5% poly(ethyl 2-cyanoacrylate) 41% Bis-GMA 43% Hexamethylene glycol dimethacrylate 12% lH,1H,5H-Octafluoropentyl acrylate 2% UV initiator, 2% photo crosslinking agent
was
5.27 (2.77)
It should be realized, however, that the abrupt temperature changes during the cycling procedure will result in considerable stress formation in the joined substrates which may not be encountered under clinical conditions; i.e., the accelerated test may be so excessively severe as not to be predictive of the clinical long-term applicability of this treatment. many
Conclusions. 1. The isobutyl ester is the most effective 2-cyanoacrylate for bonding dentin to acrylic resins. 2. Pretreatment of the dentin with dilute acids, such as 1% solution of citric acid in dilute alcohol (1:2), greatly increases bond strength.
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Vol. 58 No. 9
BONDING OFACR YLIC TO DENTIN
1907
3. The strength of the bond decreases on 10. BUCK, C. J.: Modified Cyanoacrylate Monoprolonged water exposure. mers, U.S. Patent 4,041,063, August 9, 1977. U.S. Patent 4,041,061, August 9, 1977. 4. Addition of a 2-cyanoacrylate polymer to the adhesive or application of a protec- 11. BUCK, C. J.: Blocked bis 2-cyanoacrylate Monomers, U.S. Patent 4,003,942, Jan. 18, tive coating to the bonded surface in1977. creases the hydrolytic stability of the 12. MATEEVA, K.; TSOLOVA, E.; and POPOV, bond. K.: Impregnation of Dental Surfaces by a 5. Isobutyl 2-cyanoacrylate may be useful 2-Cyanoacrylate Adhesive (Communication clinically as a short-term adhesive if it I), Stomatologiya (Sofia) 58:127-131, 1976, is found to be biocompatible. (Through CA 85:166597e, 1976). 13. ALEKSIEVA, K. and CHAKMAKOV, D.: REFERENCES 1. BRAUER, G. M.; KUMPULA, J. W.; TERMINI, D. J.; and DAVIDSON, K. M.: Durability of the Bond Between Bone and Various 2-Cyanoacrylates in an Aqueous Environment, J Biomed Mat Res (in press). 2. BEECH, D. R.: Bonding of Alkyl 2-Cyanoacrylates to Human Dentin and Enamel, JDentRes 51:1438-1442, 1972. 3. BAKLAND, T. and BAUM, L.: Cyanoacrylate in the Cementation of Threaded Retentive Pins, J Ga Dent Assoc 47:13-16, Summer, 1973. 4. DILTS, W.; COLLARD, E. W.; and DUNCANSON, M. G.: Retention of Pins with a Cyanoacrylate Bonding System, IADR Progr & Abst 53:47, 1973. 5. TRABERT, R. C. and CAPUTO, A. A.: Effects of Cement Type and Thickness upon Retention of Serrated Pins, IADR Progr & Abst 53:50, 1973. 6. STANFORD, J. S.: Cyanoacrylate Cements -Precautions, JADA 90:727, 1975. 7. LAMBERT, R. L.: Retentive Properties of Stainless Steel Pins Cemented with Ethyl Cyanoacrylate, J Prosthet Dent 34:187-
191, 1975. 8. BAUM, L.: Cementing Pins with Cyanoacrylate (An Appraisal of Biodegradability), Gen Dent 24:32-34, Jul-Aug 1976. 9. BEECH, D. R. and KURER, H. G.: An In vitro Study of a Cyanoacrylate as an Adhesive for Composite Restorations, IADR Progr & Abst 54:1356, 1974.
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In vitro Study of the Strength of Some Alkyl a-Cyanoacrylates with Hard Dental Tissues, Probi Stomatol 2:109-116, 1974. (Through CA 86:161266g, 1977). BOYANOV, B.; ALEKSIEVA, K.; CHAKMAKOV, D.; and RAICHEY, L.: Study of the Effect of Fluoride on the Insulation Properties of Some Alkyl 2-Cyanoacrylate Preparations for Caries Prevention, Probl Stomatol 4:9-10, 1976. (Through CA 88:83415, 1978). TAKEUCHI, M. and OTSUKI, A.: Adhesive Pit and Fissure Sealant, UfS. Patent 4,012,840, March 22, 1977. FUKUSHI, Y.: Treatment of Cavity Walls with Cyanoacrylates: I. The Effect on Adhesion of Composite Resins, Kokubyo Gakkai Zasshi 44:101-107, 1977. (Through CA 88: 27780h, 1978). OTSUKI, A. and TAKEUCHI, M.: Simple Fissure Sealant and its Tensile Bond Strength to Etched Bovine Enamel, Caries Res 10: 463472, 1976. COOVER, H. W. and McINTIRE, J. M.: Poly(Methyl 2-Cyanoacrylate) Macromolec Synth 5:51-54, 1974. BRAUER, G. M.; DULIK, D. M.; ANTONUCCI, J. M.; and ARGENTAR, H.: unpublished data. LEE, H. L.; SWARTZ, M. L.; and CULP, G.: Static Load Testing of Dental Adhesives, J Dent Res 48:211-216, 1969. STANLEY, H. R.; GOING, R. E.; and CHAUNCEY, H. H.: Human Pulp Response to Acid Pretreatment of Dentin and to Composite Restoration, JADA 91:817-825, 1975.
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