9 1987by The Humana Press Inc. All rightsof any nature, whatsoever,reserved. 0163-4984/87/1300-0319502.60
Nuclear Corrosion Monitoring-NCM-Applied to Biornaterials DAG BRUNE
Dag Brune Consulting, Bakkehaugveien 16,0873 Osio 8, Norway ABSTRACT Nuclear corrosion technique has been developed for the assay of various heavy metals released through corrosion and abrasion into electrolytes from various biomaterials like amalgams, chromium- cobalt and gold alloys, steel, and titanium. Application of the technique in measurement of selective release rates under static or dynamic conditions, i.e., during cyclic loading, is discussed. The elements chromium, cobalt, copper, gold, iron, mercury, molybdenum, silver, titanium, and zinc have been quantitatively assessed. In vivo corrosion measurements are further included. By combining the present nuclear tracer technique with ESCA technique, knowledge about reaction mechanisms occurring at the interface solid/liquid is obtained. Exposure of humans to various heavy metals from biomaterials, e.g., dental materials, can be estimated using the NCM technique. The technique also has a potential for selective release measurements of several nuclides possessing suitable radioanalytical properties from other types of alloys immersed in various liquid environments. Index Entries: Neutron activation; trace analysis; biomaterials;
corrosion testing.
INTRODUCTION K n o w l e d g e about the m a g n i t u d e of release of various metals from dental alloys inserted in the oral cavity is essential in the evaluation of h u m a n ' s internal exposure to such elements, with regard to possible health hazards (1,2). F u r t h e r m o r e , corrosion m a y change the physical a n d esthetic properties of such materials (3). Usually, electrochemical m e t h o d s comprising, e.g, polarization technique (potentiokinetic), are Biological Trace Element Research
3 ]9
Vol. 13, 1987
320
Brune
used for the evaluation of corrosion resistance of biomaterials, i.e., materials like amalgams and gold alloys inserted in teeth as well as stainlesssteel and chromium-cobalt alloys used as orthopedic appliances (4). However, the assay of specific elemental release from such alloys is difficult to perform with the electrochemical technique. Generally, there is a lack of information in the literature pertinent to kinetics of selective elemental release at the interface alloy/liquid. In the analytical chemical assay of various heavy metals in various electrolyte solutions, e.g., body fluids, atomic absorption spectrophotometry, ICP-techniuque (inductively coupled plasma atomic emission spectrometry), neutron activation analysis, or polarographic techniques might in principle be suitably used. However, in the accomplishment of trace element analysis at the ng level, contamination of the sample might be a serious analytical problem. Furthermore, various biological tissues and fluids contain trace elements in a varying range of concentrations between different individuals. Consequently, a small amount of a specific element released under in vivo corrosion conditions might be difficult to render. Such difficulties could be avoided using the nuclear method, as presently described. Furthermore, using such technique in combination with the electron spectroscopy for chemical analysis (ESCA) technique, information about interactions at the border alloy surface and solution can be obtained (5). Laboratory tests may provide valuable information in the interpretation of release mechanisms in the oral cavity. Release conditions in the mouth may principally be simulated in model experiments in vitro in which chewing is simulated by cyclic loading experiments (dynamic conditions) and rest is simulated by static release measurements. Release rate or accumulated release pertinent to static or dynamic conditions could be studied for the following dental or orthopedic materials (Table 1): Amalgams, gold alloys, steel, chromium-cobalt alloys, and titanium.
METHOD The nuclear corrosion monitoring--NCM--technique comprises principally the following steps:
Sample Preparation For static release measurements, rectangular flats usually with a surface area of 1 cm 2 and a thickness of approximately 0.05-0.4 mm, were prepared. In certain cases a surface area of about 10 cm 2 was considered. It was especially necessary to prepare thin samples of gold in order to reduce the mass for safe handling purposes (high activity levels). Cyl indrical specimens 8 mm high and 4 mm in diameter were used for release measurements conducted under dynamic conditions, i.e., during Biological Trace Element Research
Vol. 13, 1987
Nuclear Corrosion Monitoring
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Nuclear Corrosion Monitoring-NCM-Applied to Biornaterials DAG BRUNE
Dag Brune Consulting, Bakkehaugveien 16,0873 Osio 8, Norway ABSTRACT Nuclear corrosion technique has been developed for the assay of various heavy metals released through corrosion and abrasion into electrolytes from various biomaterials like amalgams, chromium- cobalt and gold alloys, steel, and titanium. Application of the technique in measurement of selective release rates under static or dynamic conditions, i.e., during cyclic loading, is discussed. The elements chromium, cobalt, copper, gold, iron, mercury, molybdenum, silver, titanium, and zinc have been quantitatively assessed. In vivo corrosion measurements are further included. By combining the present nuclear tracer technique with ESCA technique, knowledge about reaction mechanisms occurring at the interface solid/liquid is obtained. Exposure of humans to various heavy metals from biomaterials, e.g., dental materials, can be estimated using the NCM technique. The technique also has a potential for selective release measurements of several nuclides possessing suitable radioanalytical properties from other types of alloys immersed in various liquid environments. Index Entries: Neutron activation; trace analysis; biomaterials;
corrosion testing.
INTRODUCTION K n o w l e d g e about the m a g n i t u d e of release of various metals from dental alloys inserted in the oral cavity is essential in the evaluation of h u m a n ' s internal exposure to such elements, with regard to possible health hazards (1,2). F u r t h e r m o r e , corrosion m a y change the physical a n d esthetic properties of such materials (3). Usually, electrochemical m e t h o d s comprising, e.g, polarization technique (potentiokinetic), are Biological Trace Element Research
3 ]9
Vol. 13, 1987
320
Brune
used for the evaluation of corrosion resistance of biomaterials, i.e., materials like amalgams and gold alloys inserted in teeth as well as stainlesssteel and chromium-cobalt alloys used as orthopedic appliances (4). However, the assay of specific elemental release from such alloys is difficult to perform with the electrochemical technique. Generally, there is a lack of information in the literature pertinent to kinetics of selective elemental release at the interface alloy/liquid. In the analytical chemical assay of various heavy metals in various electrolyte solutions, e.g., body fluids, atomic absorption spectrophotometry, ICP-techniuque (inductively coupled plasma atomic emission spectrometry), neutron activation analysis, or polarographic techniques might in principle be suitably used. However, in the accomplishment of trace element analysis at the ng level, contamination of the sample might be a serious analytical problem. Furthermore, various biological tissues and fluids contain trace elements in a varying range of concentrations between different individuals. Consequently, a small amount of a specific element released under in vivo corrosion conditions might be difficult to render. Such difficulties could be avoided using the nuclear method, as presently described. Furthermore, using such technique in combination with the electron spectroscopy for chemical analysis (ESCA) technique, information about interactions at the border alloy surface and solution can be obtained (5). Laboratory tests may provide valuable information in the interpretation of release mechanisms in the oral cavity. Release conditions in the mouth may principally be simulated in model experiments in vitro in which chewing is simulated by cyclic loading experiments (dynamic conditions) and rest is simulated by static release measurements. Release rate or accumulated release pertinent to static or dynamic conditions could be studied for the following dental or orthopedic materials (Table 1): Amalgams, gold alloys, steel, chromium-cobalt alloys, and titanium.
METHOD The nuclear corrosion monitoring--NCM--technique comprises principally the following steps:
Sample Preparation For static release measurements, rectangular flats usually with a surface area of 1 cm 2 and a thickness of approximately 0.05-0.4 mm, were prepared. In certain cases a surface area of about 10 cm 2 was considered. It was especially necessary to prepare thin samples of gold in order to reduce the mass for safe handling purposes (high activity levels). Cyl indrical specimens 8 mm high and 4 mm in diameter were used for release measurements conducted under dynamic conditions, i.e., during Biological Trace Element Research
Vol. 13, 1987
Nuclear Corrosion Monitoring
321
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