From Nordenström, B.E.W. (1983). Biologically Closed Electric Circuits: Clinical, Experimental and Theoretical Evidence for an Additional Circulatory System. Stockholm: Nordic Medical Publications/URSUS .
Used by permission
After the introduction of amalgams as dental filling materials over 100 years ago, the possible development of galvanic currents in the oral cavity has been discussed from time to time. The symptoms of burning mouth, oral pain or smart, and a taste of metal or salt (18 , 92 ) have been referred to as oral galvanism.
The secondary phenomena of oral corrosive processes have also been discussed in terms of local and general biologic reactions (3 , 4 , 8 , 15 , 22 , 23 , 33 ,34 , 35 , 37 , 44 , 55 , 60 , 61 , 62 , 68 , 69 , 74 , 78 , 80 , 81 , 82 , 83 , 85 , 86 , 87 , 93 ). Many attempts have been made to explain the symptoms as caused by electrochemical interaction of metals in the saliva (18 , 23 , 31 , 42 , 44 , 49 , 60 , 68 , 93 ). Galvanic currents in the oral cavity have been assumed to develop between relatively anodic and cathodic parts of one metal or on contact between two different restorations and the saliva. As a result of corrosion, different metals or metallic compounds should then appear in the saliva (11 , 12 , 31 , 32 , 36 , 42 , 63 , 65 , 66 , 67 , 94 ) or in the tissues adjacent to amalgam fillings (32 , 36 , 38 , 39 , 47 , 78 , 82 , 94 ). A large number of in vivo studies have been performed of electric potentials between different dental restorations (for references, see Nilner, 1981). Different surfaces of a restoration may present different degrees of polarization, indicating inhomogeneity of the material (11 , 12 , 47 , 49 , 51 , 56 , 65 ). Potential differences between different restorative materials may give rise to estimated galvanic currents of a magnitude of 1 – 36 μA (65  ). It has been judged that values about 5 μA could possibly explain clinically apparent galvanism. Surprisingly, however, some of the highest values of galvanic current measured were found in a control group of patients without symptoms. In a study of dissolving Ag [silver], Ca [calcium], Hg [mercury], Sn [tin] and Zn [zinc] in the saliva, no significant differences could be found between patients with symptoms and patients without symptoms in different control groups (65 ). Studies of this type are important and informative, but illustrate also clearly that the mechanism of oral galvanism is still in many respects unexplained. The possibility of overlying psychological factors has been suggested (38 , 39 ). Neurotoxic effects by retrograde axonal transports of dissolved metal (41 ) have also been suggested. The mechanism of retrograde axonal transports (30 , 84 ) is also not very well understood. All explanations of oral galvanism have been based on the assumption that an intraoral closed circuit is created when two metals of different electric potential make direct metal-to-metal “electronic” contact (for example, via a silver spoon). The “outer” part of the circuit is created by the electrically conducting saliva. Anodic dissolution of metal will then take place and may in some way produce symptoms. One might then expect that the amounts of dissolved metal in the saliva would correlate with the symptoms of oral galvanism, but no such results have been found. Some of the largest amounts of intraoral galvanic currents were found in patients without symptoms of galvanism (65 ).
The principle of BCEC [Biologically Closed Electrical Circuits] may overcome this dilemma (see also the description of in vivo corrosion, Chapter XII, page 112). As indicated in Fig. XVIII: 8, different branches of BCEC systems may combine with “accessory” or “temporary” conducting biological channels or materials.
Fig. XVIII: 8. Acupuncture: a driven electrical system is created by an external electric power source connecting needles in Tissues I and II. Current flow is induced over parallel vascular-interstitial branches or accessory BCEC branches, such as ductal channels. The conducting media include blood, intraductal secretions, and pleural, peritoneal, cerebrospinal and interstitial fluids. Self-driving and driven systems should interfere with tissue metabolism and nervous regulation of tissue functions. Associated metabolic modifications and levellings of tissue potentials may explain medical effects of acupuncture.
Thus, in oral galvanism the intraoral ionic conducting branch, formed over the saliva between two electron conductors, may combine with one or several parallel-coupled, biological conducting branches in surrounding tissues. These branches, for instance, may be represented by blood vessels and interstitial channels. Such a circuit is outlined in principle in Fig. XVIII: 9a.
Fig. XVIII: 9. Suggested explanation of oral galvanism. (a) So-called general corrosion slowly dissolves metal ions, which spread into adjoining tissues and saliva. Toxic injuries induce ionization of tissue. Metals I and II become joined electrically, “externally” by the saliva and “internally” by preferential biologic pathways for current, e.g., vascular and interstitial BCZEC branches. A minimum of four redox sites is included in the closed circuit. Differences of potential of metal may deliver the electromotive force.
Its different components represent a set of individual variables. A galvanic current through the circuit can now develop between metals of different electric potential even when these metals are separated by a distance. No direct contact, such as over a silver spoon, is therefore necessary. The interconnecting branch between the metals is created by the saliva.
“Injury reactions” at the interfaces between the gingival or root canals and the restoration metals provide connections to BCEC channels in the tissues. The “injury reactions” include many different processes which lead to ionization and separation of charges. Examples of such processes are local infection, degrading of tissue or foreign material in the gingival pockets, vascular thrombosis, and local toxic effects of dissolved metal from the restorations (from so-called general corrosion). Each of these processes should lead to closing of the intraoral and the vascular-interstitial channels of the circuit. Coinciding “injury reactions” at two metal-tissue interfaces combined with two metal-saliva interfaces should be sufficient to establish a galvanic current. This system may then be recognized to contain a minimum of four redox sites.
The driving electromotive force of this system need not necessarily be found in the potential difference between relatively anodic and cathodic parts of the metals. Locally degrading processes (injury potentials) adjacent to the metals may also drive the system (see Chapter XII, “complicated erosion,” page 115). Periodontitis or chronic periodontosis of different origins, leading to focal toxic or infectious injuries in the gingival pockets, should be able to induce transport of electric current in the described BCEC without the presence of any metal. The driving electromotive force in such systems may depend on differences in age of two polarizing processes in the circuit (Fig. XVIII:1).
Fig. XVIII:1. Illustration of fluctuating, attenuating, electric injury potential, comprising a summation of energies (SE) of different ionic collections (ionars, e.g., E1 and En) in relation to the summation of fluctuating physiologic potentials (R+ and R-) of surrounding normal tissue. Entropy of the system increases during healing. (F+)1, (F-)1, (F+)2 represent maxima and minima of fluctuations.
In the case of healthy (noninjured) tissue adjacent to the metals, the biological circuit is interrupted. Consequently, no current will flow even if the potential difference between the two metals is relatively “large,” as was the case in the control subjects reported by Bergman, Ginstrup and Nilner (12 ). The concept of BCEC makes it therefore possible to explain the seeming inconsistencies between clinical galvanism on one hand and the measured electric potential differences between intraoral metals and amount of dissolved metals in the saliva on the other.
Fig. XVIII: 9b illustrates some of the possible biologic reactions adjacent to one of the participating metals of the closed circuit.
Fig. XVIII: 9. Suggested explanation of oral galvanism. (b) The driving force of the closed circuit does not necessarily depend on difference of potential between two filling materials. A slow dissolving of metal, as in general corrosion, may induce toxic changes in tissue. These changes may initiate electric conduction between metal and vascular-interstitial channels and deliver a fluctuating electromotive force. Tissue injuries adjacent to two separate fillings are necessary for closing of the circuit. Injury is enhanced as current flow leads to liberation of tissue hormones, which spread by diffusion, migration in the electric field, tissue convection and possibly as retrograde axonal transports. For further explanation, see text.
Thus, redox reactions will take place at one interface against the saliva and at one against the injured tissue. Metal ions may dissolve when the metal is relatively anodic. Production of cathodic alkalinity and anodic acidity will influence metabolic reactions. Normal and pathological metabolic products will undergo electrophoretic transports. Direct current stimulation of nerve end-plates may directly or indirectly produce pain. Thus, several tissue hormones, e.g., substance P, histamine, serotonin and prostaglandins are known to be involved in inflammatory reactions (14 , 70 , 96 ) and may be distributed electrophoretically by the activated closed circuit.
If this proposed explanation of oral galvanism is correct, the conclusion can then be reached that the different causes leading to connection of BCEC branches of the closed circuit are the crucial targets for therapy. One of the difficult causes to treat is then probably the “allergic” reactions of tissue to metals in certain individuals. These reactions may even develop slowly, as in general corrosion at a tissue-metal interface. When the injury reaction is caused by superimposed infection, the condition should be fairly accessible to successful treatment.
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