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Technical note: Resin-to-metal bonds mediated by adhesion promoters
Technical note: Resin-to-metalbonds mediated by adhesion promoters Y.E.Y. Aboush A. Mudassir R.J. Elderton
Department of Conservative Dentistry University of Bristol Lower Maudlin Street Bristol BS1 2LY, England Received November 16, 1990 Accepted July 8, 1991 This paper is based on a dissertation submitted by A.M. to the Faculty of Medicine, University of Bristol, in partial fulfilment of the requirements for the MSc Degree. Dent Mater 7:279-280, October, 1991
Abstract--This study aimed to establish whether the bonding between a composite cement (Comspan Opaque) and grit-blasted nickel-chromium alloy (Biobond Plus) could be enhanced by pre-treatment of the alloy surface with adhesion promoters. Six groups of metal adherends, of ten specimens each, were prepared. The specimens in each group were finished flat and blasted with 50 pm alumina. The first group was used without further treatment of the metal surface. A second group was electrolytically etched. Each of the remaining four groups was treated with an adhesion promoter. The resin cement was bonded to the adherend and, after 24 h in water at 37~, the tensile bond strengths were determined. ANOVA and the Scheff~ test at the 0.05 level showed that Scotchbond dual-cure dental adhesive enhanced the resin-to-metal bond significantly and produced a mean bond strength value (30.9 MPa) higher than that obtained with electrolytic etching (22.7 MPa) or grit-blasting (14.6 MPa). This would appear to be of considerable significance. The metal primers, ABC primer and GoldLink, and the ceramic primer, Scotchprime, were much less effective than Scotchbond dual-cure.
everal conventional composite cements are now available for the cementing of cast metal resinbonded restorations. The bonding of these cements to cast dental alloys has commonly been achieved through electrolytic etching of the alloy surface, a procedure which has been proven to be clinically successful (Thompson et al., 1989; Williams et al., 1989). However, etching of alloys is alloy-specific, technique-sensitive, and requires the handling and storage of potentially harmful acids. Therefore, suitable alternatives to the etching techniques warranted investigation. The aim of this study was to assess the effectiveness of various adhesion promoters in the bonding of a conventional resin composite cement to a base metal alloy.
S
MATERIALS AND M E T H O D S
The alloy used was Biobond Plus (Dentsply International, Inc., York, PA, USA), a beryllium-free,nickel-chromium alloy that is known to etch properly. The composite cement used was Comspan Opaque, with its accompanyingbonding agent (L.D. Caulk Co., Milford, DE, USA). The adhesion promoters evaluated are listed in Table 1. To prepare the adherends, we cast metal disks, 6 mm in diameter and 2 mm thick, from plastic patterns. Each disk was mounted in a cold-cure acrylic resin block. These were then lapped on abrasive papers so that flat bonding surfaces would be produced. After being cleaned in liquid detergent, the metal surfaces were blasted with 50 pm of aluminum oxide, washea ultrasonically with distilled water, and air-dried. Six test groups, of ten specimens each, were prepared for bonding. As a control, the first group was used without further treatment of the metal surface. A second group was electrolytically etched in a standard manner for five min in 0.5 N nitric acid at 250 (mA/cm~)2 followed by 20 rain of ultrasonic cleaning in 18% hydrochloric acid. Each of the remaining four groups was treated with a moderate layer of an adhesion
promoter (Table 1). Scotchbond dualcure was used without being light-cured. Bond test specimens were prepared by application of the resin cement to the prepared metal surfaces by use of an assembly described elsewhere (Aboush and Elderton, 1991). This apparatus enabled a truncated cone of adhesive, 2.5 ram in diameter at the bond surface and 3.5 mm in height, to be applied to the adherend. The resin cement, dispensed and mixed according to the manufacturer's instructions, was applied to the metal surface. Except for the Scotchbond group, a layer of the bonding agent was applied before the insertion of the composite cement. Ten min after bonding, the bonding assembly was dismantled and the test specimen transferred to a water bath at 37°C. After 24 h, the tensile bond tests were carried out on a Universal Testing Machine (Instron, Instron Ltd., Bucks, England) at a cross-head speed of 2 mm/ rain. On completion of the bond tests, the fracture surfaces were examined under a light microscope (X 40) so that the mode of bond failure could be assessed. The bond strength data were subjected to one-way analysis of variance (ANOVA), and multiple comparisons of means were made by use of the Scheffd test at the 0.05 level. RESULTS
The mean bond strengths achieved are presented in Table 2. ANOVA revealed that there was a highly significant difference among the six groups [F (5,54) = 16.44; P <0.001)]. The result of the Scheffd test is shown in Table 2 in the form of vertical lines connecting the means that were not significantly different. Specimens in the grit-blasted, ABC primer, GoldLink, and Scotchprime groups failed through the resin-metal interface (adhesive failure); those in the Scotchbond and etched groups failed partly through the interface and partly through the cement (adhesive/cohesive failure). In each Scotchbond specimen,
Dental Materials~October 1991 279
more than half of the bonding area was coveredwith a readily recognizable layer of resin. In the etched specimens, it appeared that the fracture surface had passed through the tips of the irregularities of the etched metal surface, leaving resin locked into the retention cavities.
TABLE 1 ADHESIONPROMOTERSUSED Adhesion Promoter
Description
Manufacturer
ABC primer
Metal primer
Vivadent,Schaan/Liechtenstein
GoldLink
Metal primer
Den-Mat, Santa Maria,CA
DISCUSSION
Scotchprime
Ceramic primer
3M, Dental ProductsDivision,St. Paul, MN
The results showed that the use of ABC primer, GoldLink, and Scotchprime had little effect on the resin-to-metal bond; the values obtained with these primers were not significantly different from those attained with grit-blasting alone. This finding is in line with that of Tjan et al. (1987), who reported that bond strengths achieved with the use ofmetal primers were, in general, not high. The ABC primer is supplied for use with the composite cement ABC, which is a urethane dimethacrylate-based resin, whereas the cement used in this study (Comspan Opaque) is based on the bisGMA system. The use of the dentin bonding agent, Scotchbond, produced a substantial improvement in the resin-to-metal bond, and this is believed to be of considerable importance. Furthermore, the value obtained with Scotchbond was significantly higher than that obtained with electrolytic etching. In resin-bonded bridgework, the bonding of conventional composite cements to the grit-blasted metal retainer surfaces via Scotchbond has many advantages over procedures such as electrolytic etching, tin-electroplating, or Silicoating of the metal surface, all of which require the use of specialized equipment and are technique-sensitive (Saunders, 1989). Scotchbond is also an effective adhesive on enamel; thus, there is no need for a separate bonding agent
Scotchbonddual-cure
Dentin bonding agent
3M, Dental ProductsDivision,St. Paul, MN
TABLE 2 TENSILE BOND STRENGTHSOF COMSPANOPAQUETO BIOBONDPLUS BondStrength (MPa) Alloy SurfaceTreatment
Mean"
SD
Grit-blasting
14.6
3.0
ABC primer
16.7
5.2
GoldLink
19.2
4.2
Scotchprime
19.8
3.9
Electrolyticetching
22.7
4.6
Scotchbonddual-cure
30.9
5.5
"Values joined by tie lines were not significantlydifferent.
(unfilled resin). Further, it would be possible for restorations to be bonded to teeth with exposed dentin at the bonding sites. Also, Scotchbond can be used for cementingRochette-type(perforated) restorations with restorative resins. REFERENCES
ABOUSH, Y.E.Y. and ELDERTON,R.J. (1991): Bonding of a Light-curing Glass-ionomer Cement to Dental Amalgam, Dent Mater 7:130-132. SAUNDERS,W.P. (1989): Resin Bonded Bridgework:AReview,J D e n t 17:255265.
280 Aboush et al. / Technical note: resin-to-metal bonds mediated by adhesion promoters
THOMPSON,V.P.; WOOD,M.; and DERIJK, W. (1989): Bonded Bridge Recalls and Weibull Distribution: Results Averaging Seven Years, J Dent Res 68:920, Abstr. No. 427. TJAN,A.H.L.;NEMETZ,H.; andTJAN,A.H. (1987): Bond Strength of Composite to Metal Mediated by Metal Adhesive Promoters, J Prosthet Dent 57:550554. WILLIAMS,V.D.; THAYER,K.E.; DENEHY, G.E.; and BOYER,D.B. (1989): Cast Metal, Resin-Bonded Prostheses: A 10-Year Retrospective Study, J Prosthet Dent 61:436-441.
Department of Conservative Dentistry University of Bristol Lower Maudlin Street Bristol BS1 2LY, England Received November 16, 1990 Accepted July 8, 1991 This paper is based on a dissertation submitted by A.M. to the Faculty of Medicine, University of Bristol, in partial fulfilment of the requirements for the MSc Degree. Dent Mater 7:279-280, October, 1991
Abstract--This study aimed to establish whether the bonding between a composite cement (Comspan Opaque) and grit-blasted nickel-chromium alloy (Biobond Plus) could be enhanced by pre-treatment of the alloy surface with adhesion promoters. Six groups of metal adherends, of ten specimens each, were prepared. The specimens in each group were finished flat and blasted with 50 pm alumina. The first group was used without further treatment of the metal surface. A second group was electrolytically etched. Each of the remaining four groups was treated with an adhesion promoter. The resin cement was bonded to the adherend and, after 24 h in water at 37~, the tensile bond strengths were determined. ANOVA and the Scheff~ test at the 0.05 level showed that Scotchbond dual-cure dental adhesive enhanced the resin-to-metal bond significantly and produced a mean bond strength value (30.9 MPa) higher than that obtained with electrolytic etching (22.7 MPa) or grit-blasting (14.6 MPa). This would appear to be of considerable significance. The metal primers, ABC primer and GoldLink, and the ceramic primer, Scotchprime, were much less effective than Scotchbond dual-cure.
everal conventional composite cements are now available for the cementing of cast metal resinbonded restorations. The bonding of these cements to cast dental alloys has commonly been achieved through electrolytic etching of the alloy surface, a procedure which has been proven to be clinically successful (Thompson et al., 1989; Williams et al., 1989). However, etching of alloys is alloy-specific, technique-sensitive, and requires the handling and storage of potentially harmful acids. Therefore, suitable alternatives to the etching techniques warranted investigation. The aim of this study was to assess the effectiveness of various adhesion promoters in the bonding of a conventional resin composite cement to a base metal alloy.
S
MATERIALS AND M E T H O D S
The alloy used was Biobond Plus (Dentsply International, Inc., York, PA, USA), a beryllium-free,nickel-chromium alloy that is known to etch properly. The composite cement used was Comspan Opaque, with its accompanyingbonding agent (L.D. Caulk Co., Milford, DE, USA). The adhesion promoters evaluated are listed in Table 1. To prepare the adherends, we cast metal disks, 6 mm in diameter and 2 mm thick, from plastic patterns. Each disk was mounted in a cold-cure acrylic resin block. These were then lapped on abrasive papers so that flat bonding surfaces would be produced. After being cleaned in liquid detergent, the metal surfaces were blasted with 50 pm of aluminum oxide, washea ultrasonically with distilled water, and air-dried. Six test groups, of ten specimens each, were prepared for bonding. As a control, the first group was used without further treatment of the metal surface. A second group was electrolytically etched in a standard manner for five min in 0.5 N nitric acid at 250 (mA/cm~)2 followed by 20 rain of ultrasonic cleaning in 18% hydrochloric acid. Each of the remaining four groups was treated with a moderate layer of an adhesion
promoter (Table 1). Scotchbond dualcure was used without being light-cured. Bond test specimens were prepared by application of the resin cement to the prepared metal surfaces by use of an assembly described elsewhere (Aboush and Elderton, 1991). This apparatus enabled a truncated cone of adhesive, 2.5 ram in diameter at the bond surface and 3.5 mm in height, to be applied to the adherend. The resin cement, dispensed and mixed according to the manufacturer's instructions, was applied to the metal surface. Except for the Scotchbond group, a layer of the bonding agent was applied before the insertion of the composite cement. Ten min after bonding, the bonding assembly was dismantled and the test specimen transferred to a water bath at 37°C. After 24 h, the tensile bond tests were carried out on a Universal Testing Machine (Instron, Instron Ltd., Bucks, England) at a cross-head speed of 2 mm/ rain. On completion of the bond tests, the fracture surfaces were examined under a light microscope (X 40) so that the mode of bond failure could be assessed. The bond strength data were subjected to one-way analysis of variance (ANOVA), and multiple comparisons of means were made by use of the Scheffd test at the 0.05 level. RESULTS
The mean bond strengths achieved are presented in Table 2. ANOVA revealed that there was a highly significant difference among the six groups [F (5,54) = 16.44; P <0.001)]. The result of the Scheffd test is shown in Table 2 in the form of vertical lines connecting the means that were not significantly different. Specimens in the grit-blasted, ABC primer, GoldLink, and Scotchprime groups failed through the resin-metal interface (adhesive failure); those in the Scotchbond and etched groups failed partly through the interface and partly through the cement (adhesive/cohesive failure). In each Scotchbond specimen,
Dental Materials~October 1991 279
more than half of the bonding area was coveredwith a readily recognizable layer of resin. In the etched specimens, it appeared that the fracture surface had passed through the tips of the irregularities of the etched metal surface, leaving resin locked into the retention cavities.
TABLE 1 ADHESIONPROMOTERSUSED Adhesion Promoter
Description
Manufacturer
ABC primer
Metal primer
Vivadent,Schaan/Liechtenstein
GoldLink
Metal primer
Den-Mat, Santa Maria,CA
DISCUSSION
Scotchprime
Ceramic primer
3M, Dental ProductsDivision,St. Paul, MN
The results showed that the use of ABC primer, GoldLink, and Scotchprime had little effect on the resin-to-metal bond; the values obtained with these primers were not significantly different from those attained with grit-blasting alone. This finding is in line with that of Tjan et al. (1987), who reported that bond strengths achieved with the use ofmetal primers were, in general, not high. The ABC primer is supplied for use with the composite cement ABC, which is a urethane dimethacrylate-based resin, whereas the cement used in this study (Comspan Opaque) is based on the bisGMA system. The use of the dentin bonding agent, Scotchbond, produced a substantial improvement in the resin-to-metal bond, and this is believed to be of considerable importance. Furthermore, the value obtained with Scotchbond was significantly higher than that obtained with electrolytic etching. In resin-bonded bridgework, the bonding of conventional composite cements to the grit-blasted metal retainer surfaces via Scotchbond has many advantages over procedures such as electrolytic etching, tin-electroplating, or Silicoating of the metal surface, all of which require the use of specialized equipment and are technique-sensitive (Saunders, 1989). Scotchbond is also an effective adhesive on enamel; thus, there is no need for a separate bonding agent
Scotchbonddual-cure
Dentin bonding agent
3M, Dental ProductsDivision,St. Paul, MN
TABLE 2 TENSILE BOND STRENGTHSOF COMSPANOPAQUETO BIOBONDPLUS BondStrength (MPa) Alloy SurfaceTreatment
Mean"
SD
Grit-blasting
14.6
3.0
ABC primer
16.7
5.2
GoldLink
19.2
4.2
Scotchprime
19.8
3.9
Electrolyticetching
22.7
4.6
Scotchbonddual-cure
30.9
5.5
"Values joined by tie lines were not significantlydifferent.
(unfilled resin). Further, it would be possible for restorations to be bonded to teeth with exposed dentin at the bonding sites. Also, Scotchbond can be used for cementingRochette-type(perforated) restorations with restorative resins. REFERENCES
ABOUSH, Y.E.Y. and ELDERTON,R.J. (1991): Bonding of a Light-curing Glass-ionomer Cement to Dental Amalgam, Dent Mater 7:130-132. SAUNDERS,W.P. (1989): Resin Bonded Bridgework:AReview,J D e n t 17:255265.
280 Aboush et al. / Technical note: resin-to-metal bonds mediated by adhesion promoters
THOMPSON,V.P.; WOOD,M.; and DERIJK, W. (1989): Bonded Bridge Recalls and Weibull Distribution: Results Averaging Seven Years, J Dent Res 68:920, Abstr. No. 427. TJAN,A.H.L.;NEMETZ,H.; andTJAN,A.H. (1987): Bond Strength of Composite to Metal Mediated by Metal Adhesive Promoters, J Prosthet Dent 57:550554. WILLIAMS,V.D.; THAYER,K.E.; DENEHY, G.E.; and BOYER,D.B. (1989): Cast Metal, Resin-Bonded Prostheses: A 10-Year Retrospective Study, J Prosthet Dent 61:436-441.