Volume 99 Number 6
More on static magnetic fields To the Editor:
kinder-Aron$on and Lindskog' should be commended for investigating the possible biologic effects of static magnetic fields. However, I challenge their concluding statement that "static magnetic fields should be Used with care in orthodontic practice until a more complete understanding of their mechanism of action has been established." In addition to the obvious question of whether the observed effects are significant or detrimental, their method leaves too many questions to draw conclusions as to causes. For instance, the rings used on their controls lacked an object mounted and encased on them to simulate those on the experimental counterparts. Hence, only the experimental tibias carried the magnet bulges (see Figs. 1 and 4). These could have applied significant pressure to the underlying epithelium and bone on the experimental side (e.g., from the animal's own weight when lying down or from the weight of others lying next to or on top of these bulges). Could pressure sensitive biologic responses resulting from these extraneous forces have been a factor? If the authors had constructed acceptable control rings by taking a similar sized piece of samariumcobalt magnet, demagnetized it2, and embedded it the same way, then any observed difference between experimental and control tibias could not have been attributed to the structure of the ring or chemical factors from the samarium-cob&It material itself or by-products of magnetic material-aluminum interactions. In addition, to avoid possible right or left side biases, half the experimental rings should have been placed on the left tibias. The animals should have been housed in individual cages to minimize the impacts of social behavior on the bulging ring of the experimental tibia. Thus there were many uncontrolled variables within their experimental design that could have affected tissue changes. In Table I repelling magnetic rings were always about 0.5 mm closer together than the rings on the controls. Thus, when the data presented in Table II show that the mean number of cells constituting the epithelial thickness for the repelling magnets goes from 6.7 at 2 weeks to 5.4 at 3 weeks and 4.1 at 4 weeks, I wonder if this is a result of reduced ring clamp distance and therefore possible pressure influences on epithelial tissue. This is a particularly appealing hypothesis when I note that the epithelial thickness in the attracting magnetic mode, where the clamp distance was similar in experimental and control tibias, stays constant during the entire experiment (6.0, 6.7, 6.7). Furthermore, the data in Table I1 show that the epithelial thickness in the control tibias continues to increase dramatically over the observation interval (7.2, 8.2, 10.4). This is suspect. A 150 gm male rat is about 40 days old, is probably sexually active, and is at its maximum growth rate 3, and I am unaware of data that suggest that an almost 50% increase in epithelial
Letters to the editor
21A
thickness normally occurs at this age. The statistically significant change in epithelial thickness reported in Table II is largely the result of an increased thickness in the controls and not a decreased thickness (except for repelling at 4 weeks) among the experimentals. Why didn't the authors discuss this? However, even if there been epithelial changes attributed to the magnetic field and even if the responses of rat tibia epithelium mimicked those that would be found in human oral mucosa, would that have been justification to caution against the further clinical use of magnets at this time? That magnetic, electromagnetic, and electric fields have effects on biologic tissues has been known for some time, 2.'.s.6but it does not follow that these effects are detrimental in either the short or long term. Enhanced fracture healing, 2 more rapid collagen formation, and wound repair' are among some of the reported benefits of electromagnetic and magnetic fields. The authors might suggest that their magnetic fields were differefit from all previous ones, but Bassett 8would caution that one cannot easily divorce electric fields from magnetic fields because currents are induced in any conductor that moves through a static magnetic field. A recent workshop on the effects of magnetic fields on human cancer concluded that it is now difficult to establish a link, 9 and investigations are not finding unequivocal results at the basic molecular and cell structure levels. 1° Blechman" could find no literature suggesting detrimental effects. Likewise Sandler et al. I~ found no effects on cells in tissue culture. Why were the results of these and many other reports, dating back many years, not discussed? In the litigious climate of the United States, such an unjustified conclusion by the authors is in effect a death blow to the present clinical use of magnets. That "further investigation is warranted" would have been a more accurate concluding statement on the basis of the experimental design and information given in this report. Dr. John DeVincenzo San Luis Obispo, Calif. REFERENCES I. Linder-Aronson S, Lindsk~ S. A morphometric study of bone surfaces and skin reactions after stimulation with static magnetic fields in rats. AM J ORTttOD DEN'I'OFACORTIIOP 1991;99:44-8. 2. Bruce GK, Howlett CR, Huckstep RL. Effect of a static magnetic field on fracture healing in rabbit radius. Clin Orthop 1987;222:300-6. 3. DeVincenzo JP, Lyman GE, Lehman JK, Baugh GC, Franz CO, Duke BD. A longitudinal growth study of the male albino rat from weanling to adulthood. J S Calif Dent Assoc 1971;39:32734. 4. Ketchen EE, Porter WE, Bolton NE. The biol~ical effects of magnetic fields on man. Am Ind tlyg Assoc J 1978;39:1-11. 5. Esformes I, Kummer F, Livelli T. Biologic effects of magnetic fields generated with CoSm magnets. Bull Hosp Jt Dis Orthop Inst 1981;41:81-7. 6. Gerling JA, Sinclair PM, Roa RL. The effect of pulsating electromagnetic fields on condylar growth in guinea pigs. AM J ORa]too 1985;87:211-23.
22A
L e t t e r s to the editor
7. Ottani V, DePasquale V, Govani O, Franchi M, Zaniol P, Ruggeri A. Effect of pulsed extremely-low-frequency magnetic fields on skin wounds in the rat. Bioelectromagnetics 1988;9:53-62. 8. Basset CA. Letter in clinical orthopaedics and related research. Clin Orthop 1988;234:311-2. 9. Ad Hoc Working Group, Intemation Agency for Research on Cancer. Extremely low-frequency electric and magnetic fields and risk of human cancer. Bioelectromagnetics 1990;11:9 !-9." I0. Frazier ME, Reese JA, Morris JE,. Jostes RF, Miller DL. Exposure to mammalian cells to 60-Hz magnetic or electric fields: analysis of DNA repair of induced, single-strand break. Bioelectromagnetics 1990;11:229-34. I1. Blechman A. Magnetic force in orthodontics. AM J O ~ O D ! 978;74:435-43. 12. Sander PJ, Meghji S, Crow V. Magnets and orthodontics. Br J Orthod 1989;16:243-9.
Reply To the Editor: Thank you for the opportunity to respond to the letter from Dr. DeVincenzo's to the editor of the AMERICAN JOURNAL OF ORTHODONTICSAND DENTOFACIAL ORTHOPEDICS concerning our article on biologic effects of static orthodontic magnetic fields. Dr. DeVincenzo raises some interesting points, and it is evident that he has devoted much effort to the specific problems involving the use of magnets in orthodontics. The letter contains three main objections and criticisms. First, he challenges our conclusion that " . . . static magnetic fields should be used with care in orthodontic practice, until a more complete understanding of their mechanism of action has been established." From the observations described in our article, especially the effect on epithelium (as the first part of the cited sentence states), it appears to us not unjust to use orthodontic magnets with care, that is, recall the patients more frequently to observe the oral mucosa close to the magnets to discover any mucosal changes at an early stage. In fact, any new therapy should be used with care until its side effects and limitations have been investigated in a larger patient material. Furthermore, Dr. DeVincenzo asks the "obvious" question "whether the observed effects are significant or detrimental." In our article we have not stated whether the effects are to be regarded as significant or detrimental. It can not be excluded that they are, in fact, therapeutic. However, Dr. DeVincenzo seems to have interpreted them as detrimental. Until this question has been answered more in detail, it is, in our opinion, most prudent to use this new therapy with care. Second, the experimental design also concerns Dr. DeVincenzo, especially the design of rings carrying
Am. J. Orthod. Dentofac. Orthop. June 1991
the magnets and the possibility of a higher external pressure exerted on the tissue by the experimental rings. This seems unlikely since the rings were perfectly smooth on the inside and the magnets, covered by acrylic only showed on the external contour of the rings. It also seems unlikely that any metal interactions caused the effects since the magnets were completely encapsulated in acrylic. Furthermore, Dr. DeVincenzo has interpreted Table I to mean that the "repelling magnetic rings were always about 0.5 mm closer together than the rings on the controls." Table I gives no basis for this, in fact there are no significant differences between the distances week by week, not even between the beginning and the end of the experiment, although the rings were adjusted for growth of the legs. Consequently, his interpretation that the epithelium under the repelling magnets was exposed to a higher pressure is merely speculative. The data could just as well be interpreted as meaning that the legs under the repelling magnets grew slower in thickness. This, however, is far too speculative for us. Third, the epithelial thickness in the controls increased from 7.2 to 10.4 cells as measured in the central part of the epithelium under the rings. This increase is not significant and, consequently, the interpretation by Dr. DeVincenzo that the recorded difference of epithelial thickness between experiment and control "is largely a result of an increased thickness Jn the controls" appear erroneous. However, Dr. DeVincenzo acknowledges that the significance of the 4-week observations is the result of a decreased epithelial thickness under the repelling magnets. Dr. DeVincenzo, furthermore, cites a number of references where biologic tissues have been exposed to several different "electric phenomena" alluding to fheir beneficial effects. He also cites Bassett (letter in Clin Orthop Rel Res 1988;234:311-2) cautioning that "one can't easily divorce electric fields from magnetic fiel~ls because currents are induced in any conductor that moves through a static magnetic field." We are somewhat puzzled by these statements. It was never our intention to differentiate between electric and magnetic fields at tissue level, merely to record possible biologic effects of an external static magnetic field. Whether the static magnetic fields generated electric currents inside the biologic tissues was beyond the scope of our investigation. However, we agree with Dr. DeVincenzo that "it is presently difficult to establish a link, and investigations are not finding unequivocal results at the basic molecular and cell structure levels" after exposure to magnetic fields. Thus, until more data has been generated, a little caution would not be out of place. Sten Linder-Aronson
Sven Lindskog Httddinge, Sweden
More on static magnetic fields To the Editor:
kinder-Aron$on and Lindskog' should be commended for investigating the possible biologic effects of static magnetic fields. However, I challenge their concluding statement that "static magnetic fields should be Used with care in orthodontic practice until a more complete understanding of their mechanism of action has been established." In addition to the obvious question of whether the observed effects are significant or detrimental, their method leaves too many questions to draw conclusions as to causes. For instance, the rings used on their controls lacked an object mounted and encased on them to simulate those on the experimental counterparts. Hence, only the experimental tibias carried the magnet bulges (see Figs. 1 and 4). These could have applied significant pressure to the underlying epithelium and bone on the experimental side (e.g., from the animal's own weight when lying down or from the weight of others lying next to or on top of these bulges). Could pressure sensitive biologic responses resulting from these extraneous forces have been a factor? If the authors had constructed acceptable control rings by taking a similar sized piece of samariumcobalt magnet, demagnetized it2, and embedded it the same way, then any observed difference between experimental and control tibias could not have been attributed to the structure of the ring or chemical factors from the samarium-cob&It material itself or by-products of magnetic material-aluminum interactions. In addition, to avoid possible right or left side biases, half the experimental rings should have been placed on the left tibias. The animals should have been housed in individual cages to minimize the impacts of social behavior on the bulging ring of the experimental tibia. Thus there were many uncontrolled variables within their experimental design that could have affected tissue changes. In Table I repelling magnetic rings were always about 0.5 mm closer together than the rings on the controls. Thus, when the data presented in Table II show that the mean number of cells constituting the epithelial thickness for the repelling magnets goes from 6.7 at 2 weeks to 5.4 at 3 weeks and 4.1 at 4 weeks, I wonder if this is a result of reduced ring clamp distance and therefore possible pressure influences on epithelial tissue. This is a particularly appealing hypothesis when I note that the epithelial thickness in the attracting magnetic mode, where the clamp distance was similar in experimental and control tibias, stays constant during the entire experiment (6.0, 6.7, 6.7). Furthermore, the data in Table I1 show that the epithelial thickness in the control tibias continues to increase dramatically over the observation interval (7.2, 8.2, 10.4). This is suspect. A 150 gm male rat is about 40 days old, is probably sexually active, and is at its maximum growth rate 3, and I am unaware of data that suggest that an almost 50% increase in epithelial
Letters to the editor
21A
thickness normally occurs at this age. The statistically significant change in epithelial thickness reported in Table II is largely the result of an increased thickness in the controls and not a decreased thickness (except for repelling at 4 weeks) among the experimentals. Why didn't the authors discuss this? However, even if there been epithelial changes attributed to the magnetic field and even if the responses of rat tibia epithelium mimicked those that would be found in human oral mucosa, would that have been justification to caution against the further clinical use of magnets at this time? That magnetic, electromagnetic, and electric fields have effects on biologic tissues has been known for some time, 2.'.s.6but it does not follow that these effects are detrimental in either the short or long term. Enhanced fracture healing, 2 more rapid collagen formation, and wound repair' are among some of the reported benefits of electromagnetic and magnetic fields. The authors might suggest that their magnetic fields were differefit from all previous ones, but Bassett 8would caution that one cannot easily divorce electric fields from magnetic fields because currents are induced in any conductor that moves through a static magnetic field. A recent workshop on the effects of magnetic fields on human cancer concluded that it is now difficult to establish a link, 9 and investigations are not finding unequivocal results at the basic molecular and cell structure levels. 1° Blechman" could find no literature suggesting detrimental effects. Likewise Sandler et al. I~ found no effects on cells in tissue culture. Why were the results of these and many other reports, dating back many years, not discussed? In the litigious climate of the United States, such an unjustified conclusion by the authors is in effect a death blow to the present clinical use of magnets. That "further investigation is warranted" would have been a more accurate concluding statement on the basis of the experimental design and information given in this report. Dr. John DeVincenzo San Luis Obispo, Calif. REFERENCES I. Linder-Aronson S, Lindsk~ S. A morphometric study of bone surfaces and skin reactions after stimulation with static magnetic fields in rats. AM J ORTttOD DEN'I'OFACORTIIOP 1991;99:44-8. 2. Bruce GK, Howlett CR, Huckstep RL. Effect of a static magnetic field on fracture healing in rabbit radius. Clin Orthop 1987;222:300-6. 3. DeVincenzo JP, Lyman GE, Lehman JK, Baugh GC, Franz CO, Duke BD. A longitudinal growth study of the male albino rat from weanling to adulthood. J S Calif Dent Assoc 1971;39:32734. 4. Ketchen EE, Porter WE, Bolton NE. The biol~ical effects of magnetic fields on man. Am Ind tlyg Assoc J 1978;39:1-11. 5. Esformes I, Kummer F, Livelli T. Biologic effects of magnetic fields generated with CoSm magnets. Bull Hosp Jt Dis Orthop Inst 1981;41:81-7. 6. Gerling JA, Sinclair PM, Roa RL. The effect of pulsating electromagnetic fields on condylar growth in guinea pigs. AM J ORa]too 1985;87:211-23.
22A
L e t t e r s to the editor
7. Ottani V, DePasquale V, Govani O, Franchi M, Zaniol P, Ruggeri A. Effect of pulsed extremely-low-frequency magnetic fields on skin wounds in the rat. Bioelectromagnetics 1988;9:53-62. 8. Basset CA. Letter in clinical orthopaedics and related research. Clin Orthop 1988;234:311-2. 9. Ad Hoc Working Group, Intemation Agency for Research on Cancer. Extremely low-frequency electric and magnetic fields and risk of human cancer. Bioelectromagnetics 1990;11:9 !-9." I0. Frazier ME, Reese JA, Morris JE,. Jostes RF, Miller DL. Exposure to mammalian cells to 60-Hz magnetic or electric fields: analysis of DNA repair of induced, single-strand break. Bioelectromagnetics 1990;11:229-34. I1. Blechman A. Magnetic force in orthodontics. AM J O ~ O D ! 978;74:435-43. 12. Sander PJ, Meghji S, Crow V. Magnets and orthodontics. Br J Orthod 1989;16:243-9.
Reply To the Editor: Thank you for the opportunity to respond to the letter from Dr. DeVincenzo's to the editor of the AMERICAN JOURNAL OF ORTHODONTICSAND DENTOFACIAL ORTHOPEDICS concerning our article on biologic effects of static orthodontic magnetic fields. Dr. DeVincenzo raises some interesting points, and it is evident that he has devoted much effort to the specific problems involving the use of magnets in orthodontics. The letter contains three main objections and criticisms. First, he challenges our conclusion that " . . . static magnetic fields should be used with care in orthodontic practice, until a more complete understanding of their mechanism of action has been established." From the observations described in our article, especially the effect on epithelium (as the first part of the cited sentence states), it appears to us not unjust to use orthodontic magnets with care, that is, recall the patients more frequently to observe the oral mucosa close to the magnets to discover any mucosal changes at an early stage. In fact, any new therapy should be used with care until its side effects and limitations have been investigated in a larger patient material. Furthermore, Dr. DeVincenzo asks the "obvious" question "whether the observed effects are significant or detrimental." In our article we have not stated whether the effects are to be regarded as significant or detrimental. It can not be excluded that they are, in fact, therapeutic. However, Dr. DeVincenzo seems to have interpreted them as detrimental. Until this question has been answered more in detail, it is, in our opinion, most prudent to use this new therapy with care. Second, the experimental design also concerns Dr. DeVincenzo, especially the design of rings carrying
Am. J. Orthod. Dentofac. Orthop. June 1991
the magnets and the possibility of a higher external pressure exerted on the tissue by the experimental rings. This seems unlikely since the rings were perfectly smooth on the inside and the magnets, covered by acrylic only showed on the external contour of the rings. It also seems unlikely that any metal interactions caused the effects since the magnets were completely encapsulated in acrylic. Furthermore, Dr. DeVincenzo has interpreted Table I to mean that the "repelling magnetic rings were always about 0.5 mm closer together than the rings on the controls." Table I gives no basis for this, in fact there are no significant differences between the distances week by week, not even between the beginning and the end of the experiment, although the rings were adjusted for growth of the legs. Consequently, his interpretation that the epithelium under the repelling magnets was exposed to a higher pressure is merely speculative. The data could just as well be interpreted as meaning that the legs under the repelling magnets grew slower in thickness. This, however, is far too speculative for us. Third, the epithelial thickness in the controls increased from 7.2 to 10.4 cells as measured in the central part of the epithelium under the rings. This increase is not significant and, consequently, the interpretation by Dr. DeVincenzo that the recorded difference of epithelial thickness between experiment and control "is largely a result of an increased thickness Jn the controls" appear erroneous. However, Dr. DeVincenzo acknowledges that the significance of the 4-week observations is the result of a decreased epithelial thickness under the repelling magnets. Dr. DeVincenzo, furthermore, cites a number of references where biologic tissues have been exposed to several different "electric phenomena" alluding to fheir beneficial effects. He also cites Bassett (letter in Clin Orthop Rel Res 1988;234:311-2) cautioning that "one can't easily divorce electric fields from magnetic fiel~ls because currents are induced in any conductor that moves through a static magnetic field." We are somewhat puzzled by these statements. It was never our intention to differentiate between electric and magnetic fields at tissue level, merely to record possible biologic effects of an external static magnetic field. Whether the static magnetic fields generated electric currents inside the biologic tissues was beyond the scope of our investigation. However, we agree with Dr. DeVincenzo that "it is presently difficult to establish a link, and investigations are not finding unequivocal results at the basic molecular and cell structure levels" after exposure to magnetic fields. Thus, until more data has been generated, a little caution would not be out of place. Sten Linder-Aronson
Sven Lindskog Httddinge, Sweden
