Adhesion to Bovine Dentin- Surface Characterization N.D. RUSE and D.C. SMITH Centre for Biomaterials, Faculty of Dentistry, University of Toronto, 124 Edward Street, Toronto, Ontario, Canada MSG 1G6
X-ray photo-electron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were used to characterize the dentin surface, to determine the effects of different pre-conditioning procedures on the elemental composition of the dentin surface, and to investigate the interaction between dentin and a dentin bonding agent (ScotchBond) by studying the changes in the elemental composition of dentin as a result of the interaction. Scanning electron microscopy (SEM) was used to characterize sample surface morphology, which was then correlated with surface elemental composition. The results showed that: (a) the elemental composition of the smear layer was similar to that of the underlying dentin; (b) cleaning with hydrogen-peroxide did not produce any modification in the elemental composition of the dentin surface; and (c) acid-etching led to an almost complete demineralization of the dentin, leaving behind an organic-rich surface. The results suggest that bonding systems that use acid-etching as a pre-conditioning procedure should be based on agents able to interact with the organic components of dentin, since bonding agents that rely on a chelation-to-calcium reaction are unlikely to be successful. The investigation of the interaction between the bonding agent and dentin led to a postulated adhesive-bonding reaction mechanism and suggested a partially cohesive failure in the bonding agent during fracturing of a dentin-bonding-agentbonded assembly. J Dent Res 70(6):1002-1008, June, 1991
Introduction. Attachment to tooth hard tissues in the oral cavity is a complex and difficult problem that has challenged many investigators and that has not yet been satisfactorily solved (Douglas, 1989). Important steps in dealing with this problem should be: (a) a thorough characterization of the substrate; (b) the development of a bonding agent able to interact with the main, if not with every, constituent of the substrate; and, finally, (c) the development of a pre-conditioning procedure to optimize and enhance the reaction between the bonding agent and the substrate. A good bonding system and the procedures involved should fulfill requirements such as biocompatibility, minimal tooth tissue loss, effective sealing for prevention of marginal microleakage, resistance in the harsh oral environment, practical applicability, and efficiency, to mention only the major ones (Matasa, 1989). Many bonding systems are presently on the market, but none of them offers a definitive solution to all the requirements involved. The aim of this study was to investigate attachment to dentin by spectroscopic surface analysis methods, used to characterize the dentin surface chemically, to determine the effects of difReceived for publication November 15, 1990 Accepted for publication March 1, 1991 This investigation was supported in part by a grant from the Medical Research Council of Canada. N.D.R. acknowledges the support of a fellowship from the Ontario Graduate Scholarship Program.
1002
ferent pre-conditioning procedures on the elemental composition of the dentin surface, and, finally, to investigate the interaction between dentin and a dentin bonding agent from the changes in the elemental composition of dentin as a result of the interaction. The results of the surface analysis were correlated with sample surface morphology as characterized by scanning electron microscopy (SEM).
Materials and methods. The surface analysis methods chosen were x-ray photo-elec-
tron spectroscopy (XPS) and secondary ion mass spectrometry
(SIMS). The XPS and SIMS analyses were performed at Surface Science Western, University of Western Ontario, London, Ontario. For the XPS analyses, a Surface Science Labs SSX100 spectrometer was operated under the following conditions: a vacuum reading of 10-6 - 10-7 Pa (10-8 - 10-9 Torr), resolution 2, spot size of 1000 pm, and a flood gun reading of between 2 and 8. A Mg Kc (1253.6 eV) monochromatic xray was used. The SIMS depth-profile analyses were obtained with a Cameca IMS 3f instrument under the following operating conditions: 0- ions as the primary beam, a primary accelerating voltage of 12.5 kV, and a secondary accelerating voltage of 4.5 kV. A Sloan Dektak II surface-profiling instrument was used to determine the depth of beam damage. From the primary current intensity, the time of exposure, and the total depth of etch, the rate of profiling could be calculated. Bovine teeth were used for this study as substitutes for human teeth. Although slightly different in composition and structure, bovine teeth can be used as substitutes for human teeth, and the rationale behind their use has been well-documented in several papers (Nakamichi, 1982; Nakamichi et al., 1983). The teeth were extracted by one of the authors (NDR) at a local abattoir. The roots were cut off, the pulp was removed, and any remaining soft tissue was scraped off with a scalpel. The teeth were stored in tap water at 40C until required, a period not exceeding eight weeks. For determination of the elemental compositon of dentin, a tooth was fractured through dentin, close to the dentino-enamel junction, creating a clean dentin surface. A small initial crack, produced with a diamond disc, was used to initiate the fracture at the desired level. The teeth were then fractured with a chisel and a mallet, and care was taken not to contaminate the dentin. The exposed dentin surface came into contact with no other surface, and thus, the only contamination that might have occurred was due to the adsorption of molecules from the environment. It is believed that in the high vacuum required by the XPS analysis, any such molecules would be desorbed, resulting in a surface free of contamination. The fractured dentin surface did not receive any additional treatment. The sample was dried under vacuum prior to the XPS investigation. For the investigation of the effects of different pre-conditioning procedures on the elemental composition of dentin, samples were prepared as shown in Table 1. The surfaces were dried under vacuum prior to the XPS investigation. So that the interaction between a dentin bonding agent and dentin could be studied, ScotchBond (3M Co., St. Paul, MN) was selected based on data obtained previously in our labo-
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on June 28, 2015 For personal use only. No other uses without permission.
Vol. 70 No. 6
ADHESION, DENTIN, SURFACE ANALYSIS
ratory (Smith and Ruse, 1986; Ruse, 1988). These data suggested that the ScotchBond system relies only on an adhesive bonding mechanism and has in the chemical composition of its bonding agent an element that could be used as an internal "marker" for ScotchBond, namely, chlorine (Cl) (Bunker, 1983). Three samples were prepared for surface analysis. The first one was obtained by application of a thin layer of lightcured ScotchBond over a dentin surface exposed by being ground and cleaned with hydrogen-peroxide (see sample preparation No. 2 in Table 1). The ScotchBond layer was then cured, and the sample vacuum-dried before XPS analysis. A second sample was obtained by following the same procedure up to the curing of the bonding agent. The applied ScotchBond layer was allowed to interact with the dentin surface for two min, after which the sample was rinsed twice for 60 s in absolute ethanol. The sample was then vacuum-dried prior to the XPS investigation. One last sample was obtained by fracturing a bonded assembly of dentin-ScotchBond-P30. The bonded assembly was obtained as follows: Dentin was exposed by being ground, rinsed, dried, cleaned with hydrogen-peroxide for 30 s, rinsed for 60 s, dried, ScotchBond applied in a thin layer, light-cured for 20 s, and P30 composite applied on top and light-cured for 40 s. After fracture in tension, the dentin sample was vacuum-dried prior to the XPS analysis. After the surface analyses of the specimens had been carried out, the samples were gold-coated, and their surface morphology was characterized by an ISO-60 scanning electron microscope (SEM) operated at an accelerating voltage of 10 kV.
Results and discussion. XPS is a highly selective and specific method of surface analysis (Briggs and Seah, 1990) that was referred to as "probably the most useful single tool for studying composition of surfaces" (Kasemo and Lausmaa, 1986). It not only allows for the identification and the quantitation of all elements, with the exception of hydrogen (H), present on a given surface, but it also provides information about the chemical environment of the identified elements. The method allows the upper 1 to TABLE 1 DENTIN PRE-CONDITIONING PROCEDURES
Steps 1 2
3 4
5
1 2 3 grind rinse* and dry** grind rinse and dry rinse H202 grind rinse and dry HCO 1 min rinse grind rinse and dry rinse H3PO4 1 min grind rinse and dry rinse H3PO4 2 min *All rinsing was done with distilled tap water for 60 s. **All drying was done with dry, oil-free compressed air.
4
and dry and dry and dry and dry
TABLE 2 XPS ELEMENTAL COMPOSITIONS IN ATOMIC PERCENTAGE 0 Surface N P C Ca Si Cl Fractured 51.5 8.0 25.9 6.7 6.5 Ground 54.4 4.7 24.7 7.2 6.9 55.2 2.7 25.1 8.0 6.6 H202 HCI 67.3 13.2 16.7 0.8 0.8 34.9 4.7 39.8 H3PO4 1 min 0.2 20.5 41.6 7.3 35.4 H3PO4 2 min 0.3 14.9 ScotchBond 73.2 19.6 0.6 4.5 2.2 S.B. washed 68.4 8.9 19.6 0.6 0.7 0.6 0.6 Dent-S.B. fract. 62.9 5.3 24.5 2.2 2.6 1.4 0.8 -
-
-
-
-
-
1003 spot
size 1000 Pm
Resolution 4
VERTICAL SCALE 4000 COUNTS/INCH
9 0
A
e1 c1
Sample
-
Dentin fractured
X-ray photo-electron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were used to characterize the dentin surface, to determine the effects of different pre-conditioning procedures on the elemental composition of the dentin surface, and to investigate the interaction between dentin and a dentin bonding agent (ScotchBond) by studying the changes in the elemental composition of dentin as a result of the interaction. Scanning electron microscopy (SEM) was used to characterize sample surface morphology, which was then correlated with surface elemental composition. The results showed that: (a) the elemental composition of the smear layer was similar to that of the underlying dentin; (b) cleaning with hydrogen-peroxide did not produce any modification in the elemental composition of the dentin surface; and (c) acid-etching led to an almost complete demineralization of the dentin, leaving behind an organic-rich surface. The results suggest that bonding systems that use acid-etching as a pre-conditioning procedure should be based on agents able to interact with the organic components of dentin, since bonding agents that rely on a chelation-to-calcium reaction are unlikely to be successful. The investigation of the interaction between the bonding agent and dentin led to a postulated adhesive-bonding reaction mechanism and suggested a partially cohesive failure in the bonding agent during fracturing of a dentin-bonding-agentbonded assembly. J Dent Res 70(6):1002-1008, June, 1991
Introduction. Attachment to tooth hard tissues in the oral cavity is a complex and difficult problem that has challenged many investigators and that has not yet been satisfactorily solved (Douglas, 1989). Important steps in dealing with this problem should be: (a) a thorough characterization of the substrate; (b) the development of a bonding agent able to interact with the main, if not with every, constituent of the substrate; and, finally, (c) the development of a pre-conditioning procedure to optimize and enhance the reaction between the bonding agent and the substrate. A good bonding system and the procedures involved should fulfill requirements such as biocompatibility, minimal tooth tissue loss, effective sealing for prevention of marginal microleakage, resistance in the harsh oral environment, practical applicability, and efficiency, to mention only the major ones (Matasa, 1989). Many bonding systems are presently on the market, but none of them offers a definitive solution to all the requirements involved. The aim of this study was to investigate attachment to dentin by spectroscopic surface analysis methods, used to characterize the dentin surface chemically, to determine the effects of difReceived for publication November 15, 1990 Accepted for publication March 1, 1991 This investigation was supported in part by a grant from the Medical Research Council of Canada. N.D.R. acknowledges the support of a fellowship from the Ontario Graduate Scholarship Program.
1002
ferent pre-conditioning procedures on the elemental composition of the dentin surface, and, finally, to investigate the interaction between dentin and a dentin bonding agent from the changes in the elemental composition of dentin as a result of the interaction. The results of the surface analysis were correlated with sample surface morphology as characterized by scanning electron microscopy (SEM).
Materials and methods. The surface analysis methods chosen were x-ray photo-elec-
tron spectroscopy (XPS) and secondary ion mass spectrometry
(SIMS). The XPS and SIMS analyses were performed at Surface Science Western, University of Western Ontario, London, Ontario. For the XPS analyses, a Surface Science Labs SSX100 spectrometer was operated under the following conditions: a vacuum reading of 10-6 - 10-7 Pa (10-8 - 10-9 Torr), resolution 2, spot size of 1000 pm, and a flood gun reading of between 2 and 8. A Mg Kc (1253.6 eV) monochromatic xray was used. The SIMS depth-profile analyses were obtained with a Cameca IMS 3f instrument under the following operating conditions: 0- ions as the primary beam, a primary accelerating voltage of 12.5 kV, and a secondary accelerating voltage of 4.5 kV. A Sloan Dektak II surface-profiling instrument was used to determine the depth of beam damage. From the primary current intensity, the time of exposure, and the total depth of etch, the rate of profiling could be calculated. Bovine teeth were used for this study as substitutes for human teeth. Although slightly different in composition and structure, bovine teeth can be used as substitutes for human teeth, and the rationale behind their use has been well-documented in several papers (Nakamichi, 1982; Nakamichi et al., 1983). The teeth were extracted by one of the authors (NDR) at a local abattoir. The roots were cut off, the pulp was removed, and any remaining soft tissue was scraped off with a scalpel. The teeth were stored in tap water at 40C until required, a period not exceeding eight weeks. For determination of the elemental compositon of dentin, a tooth was fractured through dentin, close to the dentino-enamel junction, creating a clean dentin surface. A small initial crack, produced with a diamond disc, was used to initiate the fracture at the desired level. The teeth were then fractured with a chisel and a mallet, and care was taken not to contaminate the dentin. The exposed dentin surface came into contact with no other surface, and thus, the only contamination that might have occurred was due to the adsorption of molecules from the environment. It is believed that in the high vacuum required by the XPS analysis, any such molecules would be desorbed, resulting in a surface free of contamination. The fractured dentin surface did not receive any additional treatment. The sample was dried under vacuum prior to the XPS investigation. For the investigation of the effects of different pre-conditioning procedures on the elemental composition of dentin, samples were prepared as shown in Table 1. The surfaces were dried under vacuum prior to the XPS investigation. So that the interaction between a dentin bonding agent and dentin could be studied, ScotchBond (3M Co., St. Paul, MN) was selected based on data obtained previously in our labo-
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on June 28, 2015 For personal use only. No other uses without permission.
Vol. 70 No. 6
ADHESION, DENTIN, SURFACE ANALYSIS
ratory (Smith and Ruse, 1986; Ruse, 1988). These data suggested that the ScotchBond system relies only on an adhesive bonding mechanism and has in the chemical composition of its bonding agent an element that could be used as an internal "marker" for ScotchBond, namely, chlorine (Cl) (Bunker, 1983). Three samples were prepared for surface analysis. The first one was obtained by application of a thin layer of lightcured ScotchBond over a dentin surface exposed by being ground and cleaned with hydrogen-peroxide (see sample preparation No. 2 in Table 1). The ScotchBond layer was then cured, and the sample vacuum-dried before XPS analysis. A second sample was obtained by following the same procedure up to the curing of the bonding agent. The applied ScotchBond layer was allowed to interact with the dentin surface for two min, after which the sample was rinsed twice for 60 s in absolute ethanol. The sample was then vacuum-dried prior to the XPS investigation. One last sample was obtained by fracturing a bonded assembly of dentin-ScotchBond-P30. The bonded assembly was obtained as follows: Dentin was exposed by being ground, rinsed, dried, cleaned with hydrogen-peroxide for 30 s, rinsed for 60 s, dried, ScotchBond applied in a thin layer, light-cured for 20 s, and P30 composite applied on top and light-cured for 40 s. After fracture in tension, the dentin sample was vacuum-dried prior to the XPS analysis. After the surface analyses of the specimens had been carried out, the samples were gold-coated, and their surface morphology was characterized by an ISO-60 scanning electron microscope (SEM) operated at an accelerating voltage of 10 kV.
Results and discussion. XPS is a highly selective and specific method of surface analysis (Briggs and Seah, 1990) that was referred to as "probably the most useful single tool for studying composition of surfaces" (Kasemo and Lausmaa, 1986). It not only allows for the identification and the quantitation of all elements, with the exception of hydrogen (H), present on a given surface, but it also provides information about the chemical environment of the identified elements. The method allows the upper 1 to TABLE 1 DENTIN PRE-CONDITIONING PROCEDURES
Steps 1 2
3 4
5
1 2 3 grind rinse* and dry** grind rinse and dry rinse H202 grind rinse and dry HCO 1 min rinse grind rinse and dry rinse H3PO4 1 min grind rinse and dry rinse H3PO4 2 min *All rinsing was done with distilled tap water for 60 s. **All drying was done with dry, oil-free compressed air.
4
and dry and dry and dry and dry
TABLE 2 XPS ELEMENTAL COMPOSITIONS IN ATOMIC PERCENTAGE 0 Surface N P C Ca Si Cl Fractured 51.5 8.0 25.9 6.7 6.5 Ground 54.4 4.7 24.7 7.2 6.9 55.2 2.7 25.1 8.0 6.6 H202 HCI 67.3 13.2 16.7 0.8 0.8 34.9 4.7 39.8 H3PO4 1 min 0.2 20.5 41.6 7.3 35.4 H3PO4 2 min 0.3 14.9 ScotchBond 73.2 19.6 0.6 4.5 2.2 S.B. washed 68.4 8.9 19.6 0.6 0.7 0.6 0.6 Dent-S.B. fract. 62.9 5.3 24.5 2.2 2.6 1.4 0.8 -
-
-
-
-
-
1003 spot
size 1000 Pm
Resolution 4
VERTICAL SCALE 4000 COUNTS/INCH
9 0
A
e1 c1
Sample
-
Dentin fractured
