Primer for bonding resin to metal

Dent Mater 11:2-6, January, 1995

Primer for bonding resin to metal Yohsuke Tairal, Yohji ImaP

‘Department of Fixed Prosthodontics, School ‘Institute for Medical and Dental Engineering,

of Dentistr-y, Nagasaki University, Nagasaki, JAPM Tokyo Medical and Dental University, Tokyo, JAPAN

ABSTRACT Objectives. The purpose was to examine the effect on the bond strength and durability of a resin bond to metal of modification of a primer consisting of thiophosphoric methacrylate with phosphoric methacrylates and/or benzoyl peroxide. Methods. Acrylic rods were bonded with a luting resin consisting of poly(methyl methacrylate) powder and a mixture of methyl methacrylate and tributylborane initiator to silver-palladium alloy (Ag-Pd), goldsilver alloy (Au-AS), cobalt-chromium alloy (Co-Cr), and titanium (Ti) surfaces treated with various primers. The bonded samples were thermocycled for 2,000 cycles and the mean bond strengths were compared using one-way ANOVA and Duncan’s new multiple range test at p < 0.05. Results. Using primers of thiophosphoric methacrylate or phosphoric methacrylates alone, the bond strengths of Ag-Pd decreased significantly (p < 0.05) after thermocycling. The durability was significantly improved (p < 0.05) when thiophosphoric methocrylate was used in combination with the phosphate monomers. The additional use of benzoyl peroxide and heat treatment resulted in a significant increase (p < 0.05) in the durability of two groups; the mean bond strengths over 20 MPa and the lowest values remained unchanged even after 2,000 thermocycles. Significance. The highest level of bond strength and durability to dental noble metals was achieved using a mixture of thiophosphoric and phosphoric methacrylates and benzoyl peroxide. These bond strength results are comparable to values obtained for base metals. INTRODUCTION The clinical application of resin-bonded fixed partial dentures has the advantage of minimal tooth tissue loss in preparation, easy manipulation, and no occlusal change during construction. Perforated or etched cast retainers have improved mechanical retention between the metal framework and kiting resin (Rochette, 1973; Livaditis and Thompson, 1982). However, these prostheses have a substantial problem with debonding (Creugers and Van? Hof, 1991; Creugers et al., 2

Taira& Imai/Pnmer for bonding resin to metai

1992; Besimo, 1993; Boyer et al., 1993; Verzijden et al., 1994 ). Therefore, further improvement in bonding between metal and resin is still needed. It is well known that some methacrylates containing phosphoric acid or carboxylic acid groups promote adhesion to base metal alloys. These monomers, however, are not effective in promoting adhesion to noble alloys without some surface preparation such as tin plating (Yamashita et al.. 1984). high temperature oxidation (Tanaka et al., 1988a1, ion-coating (Tanaka et al., 1988b), or Ga-Sn alloy application (Ohno et al., 1992). Recently, new types of functional monomers containing sulfur have been synthesized and used successfully as primers for bonding to noble alloys. Kojima et al. (1987a J reported on 6-(4-vinylbenzylpropyl)amino-1,3,5triazine2,4-dithione WBATDT) and Atsuta et al. (1992) used this monomer for a composite-veneered prosthesis with good results. Another sulfur-containing monomer of lo-methacryloyloxydecyl dihyrogen thiophosphate (MIOP) has also been shown to be effective in bonding to noble alloys as well as base metal alloys (Kojima et al., 1987h). The methacrylate with thiophosphoric acid motiety WEB), commercially known as GC Metal Primer (GC Co., Tokyo, Japan), has also been reported to produce a durable bond with various dental metal alloys (Ikushima and Sakuma, 1993). However, this primer still appears to require further improvement in durability and reliability. The purpose of this study was to examine the effect of modfying the thiophosphoric methacrylate primer with phosphoric methacrylate monomers and/or benzoyl peroxide on bonding resin to dental metal alloys and on the durability of this primer against thermocycling stress.

MATERIALS AND METHODS The metals used in this study are listed in Table 1. Three types of dental alloys were cast in disk specimens (10 mm in diameter, 2 mm thick). The titanium specimens i 15 mm in diameter, 8 mm thick) were machined from a rod.

Type - MC.

Japan

Ag-Pd

New Au-Pd

J. Nlorita co., Suita, Osaka, Japan

Co-Cr

Metacast

Sun Medical Co., Moriyama, Shiga, Japan

Co 62, Cr 32, MO 4, trace elements 2

Ti

Titanium metal

Toho Tiianium Co., Tokyo, Japan

Ti > 99.9

A

0

EPiA

0

0

DPlA

0

S/MIA

0.2

SIMIAIB

0.2

0

SIMIAlB”*’

0.2

SlEPlMlA

0.2

SIEPIMIAIB

Pt3, Pd 3

0

111386

Ag 51, Fd 20, Cu 14.5, Au 72, trace elements 2.5

0

100

0

None

0

None

99.6

0

0

95

None

0

95

None

49.8

50

None

49.9

49.7

0.3

None

0

49.8

49.7

0.3

Yes

2.5

49.0

47.5

0

None

0

0.2

2.5

49.8

47.2

0.3

None

0.2

2.5

0

49.8

47.2

0.3

Yes

SlDPlMlA

0.2

0

2.5

49.0

47.5

0

None

SIDPiMiAlB

0.2

0

2.5

49.8

4732

0.3

Non

0

2.5

49.0

47.2

0.3

Yes

SIDPIMIAIBh**

The composition of pruners used is summarized inTable 2. Commercial GC Metal Primer (CC Co.), consisting of 0.4% thiophosphoric methacrylate (S) and methyl methacrylate CM), was used as a basic component of the primers. Four acetone (A) solutions with and without 0.6% benzoyl peroxide (B) were prepared. Some solutions were prepared containing 5% lo-methacryloyloxydecyl phosphate (DP) or 5% di(2-methacryloyloxyethyl) phosphate (EP) which was obtained from Nippon Kayaku Co., Tokyo, Japan. The same amounts of Metal Pruner and an acetone solution were mixed together just before priming. The lutingresin consisted of polymethyl methacrylate powder and a mixture of M and tributylborane (TBB) initiator, which is used commercially in Super-Bond C&B resin (Sun Medical Co., Moriyama, Shiga, Japan) and Amalgambond (Parke& Farmingdale, NY, USA). The surface of the metals was ground on a graded series of

silicon carbide papers (#200-#600), cleaned in acetone in an ultrasonic cleaner, air-dried, and then given an application of the primer with a brush and air-dried. In some experiments, the primed specimens were placed in an oven at 60°C for 1 min. The surface was washed for 5 s with acetone, blowdried for 10 s with cold air, and covered with adhesive masking tape 50 p thick with a hole (5 mm in diameter) cut to define the bonding area. The luting resin was applied to the treated metal surface using a brush-on technique, and an acrylic rod (8mm diameter, 3Q mm length) was affixed perpendicularly. The specimens were left undisturbed for 30 min and then stored in water at 37°C for 24 h. This condition was designated as 0 thermocycles. AtIer the specimens were thermocycled in a thermocychng test machine (R&a Kogyo, Hachioji, Tokyo, Japan) up to 2,000 times between water baths held 4°C and 60°C with a dwell time of 1 min, they were then tested for tensile bond strength on a universal

Dental Materials/January

7995 3

0.4 + 0.2d

-

SIM

24.4 rt 3.8&

18.8 ri 6.F

EPIA

11 .o + 1.4””

1.o +- 0.368

DPlA

20.6 zt 2.7”bA

SIMIA

A

-

-

-

4.7 2 3.3d”B

19.2

12.0

0.6

0.5 +_0.2eB

10.0

0.4

0.3

13.1 i 3.6cB

0.3 IO.2”C

18.5

6.0

0.1

20.7 + 2.3abA

19.3 I? 3.4abA

5.6 + 5.6dB

17.8

14.3

0.6

SIMINB

19.3 f 1.9bA

9.6 k 3.kicE

12.4 r 4.W’

16.4

9.1

6.1

SIMIAW

19.1 + 3.1bA

14.1 + 5.3bCA

13.9 f 2.0CA

SIEWMIA

23.1 f I&”

21.8 ct 3.5*

13.7 f 2.5CB

SIEPIMIAIB

22.1 +_2.8abA

21.2 +_1 .gaA

20.0 f 4.6abA

21 .o 5 3.0&

23.9 + 2.8&

21.6 i 2.6aA

14.4 ? 3.lCB

SIEPIMIAIW23.1 + 2fFA

0.2

SIDPIMIA

24.5 i 4.2”A

SlDPiMhv3

21.7 f 2.4abA

20.2 zk 1 .F

16.4 + 2.4*B

SIDPIMIAIBh

21 .O 5

20.0 Jtz 3.gaA

20.4 + 2.0abA

-

-

A

AAAAA

S/M

MMMMM

MMMMM

AMMMM

EPIA

MMMMM

AAAAM

AAAAA

DPIA

MMMMM

MMMMM

AAAAA

S/MIA

MMMMM

MMMMM

AMMMM

S/MIA/B

MMMMM

MMMMM

MMMMM

SIMIAIBh

MMMMM

MMMMM

MMMMM

S/E PiWA

MMMCC

MMMMM

MMMMM

SIEPIMIAIB

MMCCC

MMMMC

MMMMC

SIEPfMIAIBh

MCCCC

MMMMM

MMCCC

S/D PIMIA

MMMCC

MMMMM

MMMMM

SIDPIMttVB

MMCCC

MMMMM

MMMMM

testing machine (AGS-lOOOA, Shimadzu Co., Kyoto, Japan) at a crosshead speed of 2mmJmin. Five specimens were tested for each group. Data were analyzed with one-way analysis of variance (ANOVA). When the F-ratios were significant

4 Tara & lmai/Primer for bonding resin to metai

(p < 0.05), Duncan’s new multiple range test was used to compare mean values at p < 0.05. After the tensile testing, the fractured surfaces were examined through a magnifying glass (10x) to evaluate failure modes. The failure modes were classified into: resin-metal interface (adhesive. A). within king material (cohesive. C ),and a combination of these modes i mixed, M 1.

RESULTS

Table 3 shows the effects of metal surface treatments and thermocycling on tensile bond strengths 12.4 10.2 13.8 betweenAg-Pd alloy disks and acrylic 10.3 20.9 16.6 rods. When the metal surface was 13.7 18.6 18.3 primed with only acetone, the mean tensile bond strength was onI>, 19.1 15.9 20.1 0.4 MPa at 0 thermocycles. The, 18.3 9.1 19.8 number of thermocycles produced a 18.4 13.8 18.6 significant effect ip < 0.05) on the tensile bond strength observed in 17.3 14.9 17.6 eight of the twelve groups. The tensile bond strength for all three groups treated with the primers containing B and followed by heat treatment and for the SlEP/M/AlB group remained unchanged up to 2.000 cycles. Although the S/M group produced significantly higher ten-sile bond strength (24.4 f 3.8 MPa) (p < 0.05) before thermocycling when compared with group A (0.4 -t_0.2 MPa). a significant decrease (p < 0.05) in the S/M treated specimen bond strength (4.7 +_3.3 MPa) occurred after 2,000 cycles. Comparison of groups S/M, EPIA, and DP/A demonstrated the effect of using each functional monomer alone. While group EP/A showed significantly lower tensile bond strength than groups S/M and DP/A before and after 500 cycles, no significant tierence was found among these groups aRer 2,000 cycles. Dilution of the Metal Primer with acetone produced no signifkant di%erence (group S/M 2:s.S/M/A) Groups S/M/A, YEPLMIA, and S/DPIM/A compared the effects of S/M primers used together with phosphate monomers of EP and DP No signifkmt difference was found among the groups at 0 and 500 cycles. After 2,000 cycles. however. the effect of the phosphate monomers was a significant. increase in the mean tensile bond strength (p < 0.05) compared to the S/M group after 2,000 cycles. The use of SAWA, S/EP/M/A. or S/DP/MA together with B and heat treatment resulted in a further sign&ant increase (p < 0.05) in tensile bond strength after 2,000 cycles. The tensile bond strength measured after 2,000 cycles increased in this order: A<< DP/A, EP/A<
S/M

18.3 + 0.5&

4.7 + 3.3dB

0.4 * 0.3bC

0.4 f 0.4CC

0

0

EPlA

0.9 f. 0.3hA

0.5 f 0.2e*

DPIA

1.3 + 0.9”

0.3 f o.2eA

SIEPIMfA

17.4 zt 3.8*

SIEPIMIAIBh S/DP/M/A

17.8

0.6

0.1

0.1

23.0 2 3.2a8

22.1 f 1.7as

0.5

0.1

17.9

20.4

13.7 f 2.508

0.3 f 0.3fi

0.3 f OF

13.6

10.3

0.1

0.t

17.3 f 3.7&

23.9 f 2.8aB

0.3 + 0.2bC

0.4 f 0.2CC

11.0

20.1

0.1

0.1

21.0 zt 5.2”

14.4 t 3.1&

15.2

9.1

13.9

12.9

10.8

17.6

14.5

17.9

SIM

M-i M-i

EPIA

AAAAA

M

19.7 k 3.4&

A M ii--M M---- A A A M M

A A A AM

AAAAA

AAAAA

AAAAA

DPIA

AMMMM

AAAAA

MMCCC

MMMCC

SlEPlMlA

MMCCC

MMMMM

AAAAA

AAAAA

SIEPIMIAIBh

MM M C C

MM C C C

A A A A A

A A A A A

SIDPIMIA

MMMCC

MMMMM

AAACC

MCCCC

SIDPIMIAIBh

MMM C C

MMM C C

MMCCC

MCCCC

The SiM primer was effective in reducing adhesive failure after thermocycling when compared with EP/A and DP/A. The use of B and/or heat treatment resulted in an increase in cohesive failure in groups S/EP/M/A and S/DP/M/A. Table 5 compares the effect of surface treatments for four metals on the tensile bond strength atler 2,000 cycles. The difference in tensile bond strength among the four metals was significant for five treatment groups except groups S/DP/M/A and S/DPiM/mh. For the Au-Ag alloy, all the mean tensile bond strength values obtained with the primers containing S were significantly higher than those with EP or DP (p < 0.05i. For Co-Cr alloy and Ti, only the groups using the primers with DP showed significantly higher tensile bond strength than those without DP (p < 0.05). Table 6 shows the distribution of failure modes for each specimen after 2,000 cycles. The failure mode varied among the types of metals and treatment groups, with the exception of group EP/A in which adhesive failure always occurred. For Au-Ag alloy, while almost all specimens of groups S/M and DP/A showed mixture failure, four groups using mixed

18.8 f 4.5”

primers of S/M and EP/A or DP/A showed an increase in cohesive failure. For Co-Cr alloy as well as Ti metal, the failure mode of specimens primed with S/M and/or EP/A was mostly adhesive. In contrast, cohesive failure increased in all three groups using DP

DISCUSSION Adhesive bonding to precious alloys has been improved considerably by the use of some sulfur-containing functional monomers. However, before this study, the bonding was not as durable as bonding to base metal alloys. The present study reports on a major advancement in bonding of resin to metals, including noble alloys, by modification of the primer containing a thiophosphoric acid derivative monomer (S). It was difficult to obtain a durable bond with monomers of thiophosphoric or phosphoric acid derivatives alone (groups S/M, EP/A, DP/AJ The durability was significantly improved by the use of S monomer in combination with phosphate monomers (EP and DP) and further by B and heat treatment. The best bond durability was obtained with groups S/EP/M/ A/Bh and S/DP/M/A/Bh, in which the mean tensile bond strength over 20 MPa and the lowest values remained unchanged even after 2,000 cycles. The S primer was modif?ed based on the following expectations: 1) DP known to be effective for non-precious metals, might contribute to improving bonding to noble alloys as well as base metals; and 2) the addition of B might promote polymerization of the monomer primed on the metal surface. The effectiveness of B and heat treatment was greater than expected. The mechanism of the improved durability achieved by modikation of the S primer remained totally unclear and must be studied in the future. The S monomer was very effective for precious alloys. However, its effect was different between the alloys. In contrast to the results for Ag-Pd alloy, S alone was equally effective for Au-Ag alloy. No additional effects of the use of phosphate monomers and/or B together with S were observed

Dental Materials/January

1995 5

in the mean tensile bond strength (18.3 + 0.5 MPa US.17.3 + 3.7-21.0 f 5.2 MPa) (p > 0.05). Rather, the use of S alone produced a higher lowest tensile bond strength (17.8 MPa US. 10.8 - 15.2 MFa). However, as far as failure mode is concerned, the addition of modifiers to S seems desirable because it resulted in the reduction of mixed failure and an increase in cohesive failure. Table 5 shows that S alone was effective only for the Au-Ag alloy among the four metals tested. It has been demonstrated that MIOPS and S (assumed to have a structure analogous to MIOPS) produced a durable bond between the resin and various metals including Au-Ag, Ag-Pd, Co-Cr, and Ti (Kojima et al., 198713;Ikushima and Sakuma, 1993). Therefore, before the experiment, it was anticipated that the Metal Primer would be equally effective for noble as well as base metals. However, the results did not agree with the observations reported. This disagreement may be due to the difference in the experimental conditions or test specimens. The adherends and concentration of the fkctional monomers were different in each study. In one study, the same smooth metal surface was treated with acetone solution of 5%’MIOPS, and then bonded together with M-TBB resin. In another, the sandblasted metal surface was primed with M solution of 0.4% S and bonded to stainless steel with M-B/amine resin. The smooth metal surface was primed with M solution of 0.4% S and bonded to an acrylic rod with M-TBB resin. Among these three test specimens, thermal and aqueous environmental stresses imposed on the metal-resin bond would be more severe for the specimen in which a smooth metal surface was bonded to an acrylic rod having a considerably higher thermal expansion coefficient than metals. The use of a higher concentration of S alone may possibly improve the durability of bonding to various metals other than the Au-Ag alloy Surface treatment of the dental Au-Ag and Ag-Pd alloys with primers containing S, phosphate methacrylates, and B followed by heat treatment resulted in the highest bond strength values, comparable to those obtained for non-precious metals using DP. It can be said that the bond strength and durability obtained for Co-Cr alloy or Ti are among the highest achievable in metal-resin bonding at the present time. Therefore, the surface treatment described above was considered to be a big advance in noble metal-resin bonding and will be worthy of clinical evaluation. Without complicated surface preparation, this very simple treatment is applicable not only to the M-TBB resin used in this study, but also to various other luting resins including composite types. Addition of minimum retentive devices and sand-blasting prior to application of the primer to the surface of the metal frameworks will fkrther improve the durability

Received July 22,1994

6

/Accepted

December

20.1994

Taira& lmai/Primer for bonding resin to metal

Address

correspondence

and repnnt

requests

to:

Yohji Imai Institute

for Medical and Dental Engineering

Tokyo Medical and Dental Ilniversig 2-Z1-10. Kanda-Surugadai.

Chiyoda-ku.

Tok,vo, 10 1, .JAl’AS

REFERENCES Atsuta M, Matsumura H, Tanaka T ( 1992). Bonding fixed prosthodontics composite resin and precious metal alloys with the use of a vinyl&o1 primer and an adhesive opaque resin. d Pros&t Dent 67:296-300. Besimo CH (1993). Resin-bonded fixed partial denture technique. Results of a medium-term clinical follow-up invtlstigation. J Prosthet Dent 69:144-148. Boyer DB. Williams VD, Thayer KE, Denehy GE, Diaz-Arnold AM ( 1993). Analysis of debond rates of resin-bonded prostheses. J Dent Res 7211244-1248. Creugers NHJ, Van? Hof MA f 1991 J.An analysis of clinicai studies on resin-bonded bridges. ?I Dent Res 70:146-149. Creugers NHJ, &yserAF. Van? Hof MA ( 1992). A seven-anda-half-year survival study of resin-bonded bridges. -J Ikrr/ Rcjs 71:1822-1825. Ikushima K, Sakuma T ( 1993 1.Adhesive property of’primer for bonding metal to resin “GC Metal Primer”. AdIwsirv Dent&p 11:117-118. Kojima K Kadoma Y, Imai Y t 1987a). Adhesion to precious metal utilizing triazinedithione derivative monomer. rJ4x7 Dent Mater 6:702-707. Kojima K Kadoma Y, Imai Y ( 198713). Adhesion to precioub metal using new type functional monomer containing sufur ?JIJpn Dent Muter 6 (Special issue):112-113. Livaditis GJ, Thompson VP (19821. Etched castings: An improved retentive mechanism fbr resin-bonded retaincirs .J Prosthet Dent 47:52-58. Ohno H. Araki Y, Endo K ( 1992 1.A new method fbr promotmg adhesion between precious metal alloys and dental adhesives. J Dent Rw 71:1326-1331. BrochetteAL ( 1973 1.Attachment of a splint to enamel of lowet ‘anterior teeth. d Prostlwt Dent 30:418-423. Tanaka T Atsuta M, Nakabayashi N, Masuhara E I 1988a). Surface treatment of gold alloys for adhesion. .I Prostlw! Dcwt 60:271-279. Tanaka T, Hirano M, Kawahara H, Matsumura H, Atsuta M ( 198813J.A new ion-coating surface treatment of alloys for dental adhesive resins. ?JDent Rcs 67:1376-1380. Verzijden CWGJM. Creugers NHJ, Mulder J (1994). A multipractice clinical study on posterior resin-bonded bridges: A 25year interim report. -/Dent Res 73529-535. Yamashita A, Kondo Y. Fujita M (1984). Adhesive strength of adhesive resin Panavia EX to dental allovs. Part 2. Adhesive strength of precious alloys. J .J,prz Prosthodont Sock 28:1023-1033.