LETTERS TO THE EDITOR A word of caution To the Editor:
I am writing to present a "Case Report" for all practitioners of dentistry as follows: In a recent orthodontic debanding/debonding procedure, the use of an 1156 carbide bur at high speed produced a "shower of sparks" when inadvertently touched against the residual portion of a ceramic bracket on an adjacent tooth. Normally any portion of the ceramic bracket that will not come off with the usual special instrumentation is taken off with diamond burs at high speed with copious water. Therefore this "shower of sparks" phenomenon had not been noticed before. It would be advisable for practitioners using steel or carbide instruments on a patient with ceramic brackets be most careful to avoid this contact, or consider using only fine diamonds when removing any "flash" or when finishing the,tooth surface after ceramic bracket removal. The consequences for the patient or members of the staff may be serious if occurring in the vicinity of flammable anesthetics or gases and should reinforce the use of copious water to dampen any accidental contact and the use safety glasses for all concerned. Lart3, K. Aagesen, DDS, MS 1000 West University Suite 200 Rochester, M! 48307-1875
Comments on static magnetic fields To the Editor:
I would like to comment on an article that was published in the JOURNAL by Linder-Aronson and Lindskog entitled "A Morphometric Study of Bone Surfaces and Skin Reactions After Stimulation With Static Magnetic Fields in Rats." (AM J ORTHOD DENTOFAC ORTHOP 1991 ;99:44-8) The work reported in this article is difficult to interpret and would certainly not be easy to reproduce. For example, it is not clear whether the effects reported are actually due to the magnetic field. They may, in fact, be more related to mechanical and chemical factors or they may be nonexistent. Consequently, many questions arise to challenge the claims made in this study. Specifically, there is a serious lack of information about the magnet, the field parameters, and its orientation. Which Samarium-Cobalt (SmCo) alloy was used? What is the energy product? The dimensions of the SmCo magnet are given as 2 x 4 mm. What is the third dimension-this is critical, particularly for oral application? Is the 2 x 4 mm dimension the pole face? If so, how was it oriented with respect to the target epithelial and osseous 18A
tissues? The change in the magnetic field geometry as the aluminum rings are adjusted for growth should be described since this changes dosimetry and has a potential impact on the bioeffect. The lack of this information represents a serious deficiency in the article. These factors influence the magnetic field flux density at t h e epithelial and osseous interfaces. Consequently, there certainly is a critically varying dose at these different levels that is not given. Any potent!al bioeffect is certainly dependent on actual magnetic field flux level, particularly within the biologic window. What was the effect of the opposing magnet on this flux density? Did the aluminum rings perturb the field in any way? The experimental design should have included modelling and mapping of the flux density in gauss or tesla units as they varied with the field gradient. Furthermore, this research was inadequately controlled leading to faulty interpretation of the data. For example, sham magnets were not employed! Were the active magnets coated to prevent leach-out products, thereby avoiding potential chemical complications? Indeed, the magnets were probably contacting the skin, as stated on page 44: "to examine the soft tissue in immediate contact with the magnets." Were the magnets therefore positioned between the aluminum ring and the skin? Was there a cutout in the ring to accommodate the magnets? Were the corners of the magnets impinging on the skin? Also, were the legs shaved? Considering these factors, it is not clear whether sham magnets would not have had the same effect on the soft and hard tissue as was observed with the active ones. To further complicate the situation, another dosim-
Voh,me 99 Number 6
etry factor must be considered. Although there is a penetrating externally derived static magnetic field, internally there is an electromagnetic field, since ionic conductors (e.g., blood cells, ions) are moving through the externally applied magnetic flux density. These streaming potentials introduce an induced ionic current that may have different effects in the leg compared with the jaw. Most important, the use of static fields in this experiment does not simulate any known orthodontic application! None of the examples of clinical magnetic orthodontic use provided at the beginning of the article are pure static fields since they also possess some timevarying characteristics (dB/dt). These orthodontic ap-
plications also supply force simultaneously with a field. This combination is critical to the success of these magnetic devices and determines the soft and hard tissue response. None of the magnetic devices straddle the alveolar bone buccally and lingually with the field oriented across this bone, as the magnets apparently are intended to do in this research. The air gap between opposing or aiding magnets is much larger than any known orthodontic application, therefore the authors were again dealing with a dose response different from that encountered in clinical usage. Thus it is difficult to extrapolate evidence from this static experiment to the dynamic events in clinical orthodontic application. The use of Figs. 7 and 8 as evidence for bone resorption is particularly disturbing, since it is well established in the orthopedic literature that resorption always starts from the endosteal surface in the cortical bone. It then proceeds intracortically by creating lacunae. Holes of the size seen in these figures only appear after periods longer than 4 weeks when the bone is seriously weakened and about to collapse. Resorption in trabecular bone is always seen as a thinning of the trabeculae (particularly those oriented horizontally). Therefore, without any histologic correlates, these photographs offer no proof whatsoever of bone resorption, as would be expected in an osteopenic response. As a matter of interest, the enclosed photos show normal "holes" unequally distributed in human left and" right long bones. The holes
Letters to the editor
1 9A
present on the bone surface in the photos, as well as in the article, appear to be those for vascular penetration. In fact, the increased surface area of holes could conceivably be because of vascular dilatation, which could occur in response to the magnetic field. Further attempts to interpret the data lead to more questions and conjecture. To continue the discussion, let us temporarily accept the fact that Figs. 7 and 8 do demonstrate surface cortical resorption.. Since the control side showed possible resorption near the epiphysis, as well as the experimental side, normal movement of the rat may have been inhibited sufficiently to initiate some disuse porosis within 4 weeks. A bulging experimental side ring would augment this effect to be consistent with the claims. By introducing this unwanted variable, the results may be skewed. In addition, does the field on the active side have a bioeffect on the control side, which is then no longer static? The difficulty of not adequately characterizing the magnetic field geometry and the target tissues, is again evident because the rings and magnets were apparently positioned between the diaphysis and epiphyseal plate, according to the figures. Under these conditions, it would appear that the bone immediately under the magnet was the deposition (F) area and the resorptive (R) area was either at the border of the magnet or completely outside the field. For the ring (dimensions not given) and the magnet to lie directly over the resorptive site, the ring would have to flare to accommodate the wider bony anatomy in the metaphysis and epiphyseal area (distal fibula plus distal tibia). However, this is not confirmed by Figs. 1, 3, and 4, which appear to show parallel-sided rings resting above the epiphysis to prevent distal slipping. A certain amount of skin pressure from the rings must be present to completely immobilize them, otherwise the rats would try to remove them, or they would rotate around the leg confusing the results even further. The authors indicate that the rings were manually adjusted to accommodate for growth of the legs. Unfortunately, the skin pressure on either limb was not quantified and could have led to unequal amounts of pressure ischemia.
Am. J. Orthod. Dentofac. Orthop.
20A
Letters to the editor
Also, it is unfortunate that there were no controls showing sections of skin that were not subjected to ring pressure. The apparent thinning of the epithelial layer may have merely been because of a differential pressure effect. The histologic photos in Figs. 5 and 6 are apparently not at the same magnification, according to a pathologist. It is therefore difficult to really ascertain the amount of epithelial thinning, particularly if the sections were not taken from samples obtained at exactly the same position on the limb. If indeed there is epithelial thinning, it does not appear unlike that which would occur from constant pressure over a specific skin area. (This, of course, can ultimately lead to decubiti.) If direct skin pressure is a factor in these results, it should be pointed out that the orthodontic application of magnets does not require this type of pressure. In fact it is usually avoided for obvious reasons. If the epithelium is thinner, what is the significance of this finding? Is it temporary or permanent? Can it be compared with epithelial effects under removable appliances? Certainly clinical experience with magnets has not sh6wn any reported adverse epithelial effects. If we accept the bone surface changes, can the authors then extrapolate these changes to resorption that occurs inside the maxilla and mandible when teeth are undergoing orthodontic movement? In the clinical orthodontic example, it has been reported that more rapid movement seems to occur when magnets are used. It is important to note that this is usually accompanied by decreased mobility and less discomfort of the moving teeth than with conventional forces. If resorption alone was stimulated to account for more rapid movement, as was suggested in the article, then increased clinical mobility would be expected with concomitant increased discomfort compared with conventional forces. Clinical experience does not support this thesis and, in fact, suggests the opposite. Observed decreased mobility and discomfort, in spite of rapid movement, supports the hypothesis that the apposition rate was much more significantly accelerated. It is conceivable that some practitioners might miss these important clinical symptoms and signs (i.e., discomfort and mobility) because they are patient perceptions and may not necessarily be reported, and mobility is not checked since movement is occurring. The statistical design you have chosen can also be challenged. The fact that right tibias were always experimental and left tibias were always the control is a controversial subject since this does not demonstrate random distribution and may lead to faulty interpretation. Earlier in vitro and in vivo research seems to confirm the hypothesis that static magnetic fields will accelerate the physiologic process for which the cells have been programmed. With osteoblast progenitor cells, in vitro work has demonstrated a twofold increase in alkaline phosphatase (associated with deposition) and a threefold decrease in lysosomal enzymes (associated with resorption) with static magnetic fields of specific properties. 1 In vivo research with rats showed that when the cranial midsagittal suture was expanded with an orthodontic bihelical sprLng in the presence of specific orthodontic magnetic fields, there was a twofold increase in
June 1991
bone volume in the expanded suture (unpublished). Both of these experiments used sham magnets and no magnets as controls, and the magnets and their fields were carefully mapped to specify the gauss-dose at the target area. It is important to realize that both static and timevarying magnetic and electromagnetic fields have been used clinically in medicine and dentistry for almost 40 years. To my knowledge there has not b.een a single reported and documented adverse clinical effect because of these specifically therapeutic fields. I have been personally involved in this area of research for more than 25 years, and my personal clinical experience confirms this observation. Furthermore, for the past 10 years, there has been extensive research on the potential mechanism of action of both static and time-varying magnetic and electromagnetic fields in the medical and scientific literature; none of which has negated the successful efficacy of clinical devices using these modalities.z.3 Moreover, many of these devices have been approved for clinical use since the late 1970s and their mechanism of action still remains unclear. Indeed, the molecular mechanism of transduction of conventional mechanical forces in orthodontics and orthopedics into biochemical and bioelectric events also remains unclear. The past history of basic scientific research in magnetic and electromagnetic fields has been characterized by inconsistent and often contradictory results in spite of successful clinical use. Only recently have these investigations reached a level of sophistication, by providing sufficient data, where they are reproducible and more consistent. However, we should profit from similar inconsistent past experiences, particularly in orthope'dics, and attempt to avoid their mistakes. Sufficient data must be provided in our papers to enable reproducibility! I commend the authors for their interest in this subject. There is no question that further research is required. I would encourage the authors' interest and motivation in pursuing this research and plead with them to properly document the magnetic fields used in experiments of this type, and also consider more convincing experimental designs. It is only in this manner that we will be able to properly document the biologic effects of these and other magnetic and electric fields. Dr. Abraham M. Blechman 153 Lester Dr. Tappan, NY 10983
REFERENCES 1. Blank M. Findl E. Mechanistic approaches to interaction of electromagnetic fields v,'ith living systems. New York: Plenum Press, 1987:389-97. 2. Gandhi OP. Biological effects and medical applications of electromagnetic energy. Englewood Cliffs, N. J.: Prentice Hall, 1990. 3. Marino AA. Modem bioelectricity. New York: Marcel Dekker, 1988.
I am writing to present a "Case Report" for all practitioners of dentistry as follows: In a recent orthodontic debanding/debonding procedure, the use of an 1156 carbide bur at high speed produced a "shower of sparks" when inadvertently touched against the residual portion of a ceramic bracket on an adjacent tooth. Normally any portion of the ceramic bracket that will not come off with the usual special instrumentation is taken off with diamond burs at high speed with copious water. Therefore this "shower of sparks" phenomenon had not been noticed before. It would be advisable for practitioners using steel or carbide instruments on a patient with ceramic brackets be most careful to avoid this contact, or consider using only fine diamonds when removing any "flash" or when finishing the,tooth surface after ceramic bracket removal. The consequences for the patient or members of the staff may be serious if occurring in the vicinity of flammable anesthetics or gases and should reinforce the use of copious water to dampen any accidental contact and the use safety glasses for all concerned. Lart3, K. Aagesen, DDS, MS 1000 West University Suite 200 Rochester, M! 48307-1875
Comments on static magnetic fields To the Editor:
I would like to comment on an article that was published in the JOURNAL by Linder-Aronson and Lindskog entitled "A Morphometric Study of Bone Surfaces and Skin Reactions After Stimulation With Static Magnetic Fields in Rats." (AM J ORTHOD DENTOFAC ORTHOP 1991 ;99:44-8) The work reported in this article is difficult to interpret and would certainly not be easy to reproduce. For example, it is not clear whether the effects reported are actually due to the magnetic field. They may, in fact, be more related to mechanical and chemical factors or they may be nonexistent. Consequently, many questions arise to challenge the claims made in this study. Specifically, there is a serious lack of information about the magnet, the field parameters, and its orientation. Which Samarium-Cobalt (SmCo) alloy was used? What is the energy product? The dimensions of the SmCo magnet are given as 2 x 4 mm. What is the third dimension-this is critical, particularly for oral application? Is the 2 x 4 mm dimension the pole face? If so, how was it oriented with respect to the target epithelial and osseous 18A
tissues? The change in the magnetic field geometry as the aluminum rings are adjusted for growth should be described since this changes dosimetry and has a potential impact on the bioeffect. The lack of this information represents a serious deficiency in the article. These factors influence the magnetic field flux density at t h e epithelial and osseous interfaces. Consequently, there certainly is a critically varying dose at these different levels that is not given. Any potent!al bioeffect is certainly dependent on actual magnetic field flux level, particularly within the biologic window. What was the effect of the opposing magnet on this flux density? Did the aluminum rings perturb the field in any way? The experimental design should have included modelling and mapping of the flux density in gauss or tesla units as they varied with the field gradient. Furthermore, this research was inadequately controlled leading to faulty interpretation of the data. For example, sham magnets were not employed! Were the active magnets coated to prevent leach-out products, thereby avoiding potential chemical complications? Indeed, the magnets were probably contacting the skin, as stated on page 44: "to examine the soft tissue in immediate contact with the magnets." Were the magnets therefore positioned between the aluminum ring and the skin? Was there a cutout in the ring to accommodate the magnets? Were the corners of the magnets impinging on the skin? Also, were the legs shaved? Considering these factors, it is not clear whether sham magnets would not have had the same effect on the soft and hard tissue as was observed with the active ones. To further complicate the situation, another dosim-
Voh,me 99 Number 6
etry factor must be considered. Although there is a penetrating externally derived static magnetic field, internally there is an electromagnetic field, since ionic conductors (e.g., blood cells, ions) are moving through the externally applied magnetic flux density. These streaming potentials introduce an induced ionic current that may have different effects in the leg compared with the jaw. Most important, the use of static fields in this experiment does not simulate any known orthodontic application! None of the examples of clinical magnetic orthodontic use provided at the beginning of the article are pure static fields since they also possess some timevarying characteristics (dB/dt). These orthodontic ap-
plications also supply force simultaneously with a field. This combination is critical to the success of these magnetic devices and determines the soft and hard tissue response. None of the magnetic devices straddle the alveolar bone buccally and lingually with the field oriented across this bone, as the magnets apparently are intended to do in this research. The air gap between opposing or aiding magnets is much larger than any known orthodontic application, therefore the authors were again dealing with a dose response different from that encountered in clinical usage. Thus it is difficult to extrapolate evidence from this static experiment to the dynamic events in clinical orthodontic application. The use of Figs. 7 and 8 as evidence for bone resorption is particularly disturbing, since it is well established in the orthopedic literature that resorption always starts from the endosteal surface in the cortical bone. It then proceeds intracortically by creating lacunae. Holes of the size seen in these figures only appear after periods longer than 4 weeks when the bone is seriously weakened and about to collapse. Resorption in trabecular bone is always seen as a thinning of the trabeculae (particularly those oriented horizontally). Therefore, without any histologic correlates, these photographs offer no proof whatsoever of bone resorption, as would be expected in an osteopenic response. As a matter of interest, the enclosed photos show normal "holes" unequally distributed in human left and" right long bones. The holes
Letters to the editor
1 9A
present on the bone surface in the photos, as well as in the article, appear to be those for vascular penetration. In fact, the increased surface area of holes could conceivably be because of vascular dilatation, which could occur in response to the magnetic field. Further attempts to interpret the data lead to more questions and conjecture. To continue the discussion, let us temporarily accept the fact that Figs. 7 and 8 do demonstrate surface cortical resorption.. Since the control side showed possible resorption near the epiphysis, as well as the experimental side, normal movement of the rat may have been inhibited sufficiently to initiate some disuse porosis within 4 weeks. A bulging experimental side ring would augment this effect to be consistent with the claims. By introducing this unwanted variable, the results may be skewed. In addition, does the field on the active side have a bioeffect on the control side, which is then no longer static? The difficulty of not adequately characterizing the magnetic field geometry and the target tissues, is again evident because the rings and magnets were apparently positioned between the diaphysis and epiphyseal plate, according to the figures. Under these conditions, it would appear that the bone immediately under the magnet was the deposition (F) area and the resorptive (R) area was either at the border of the magnet or completely outside the field. For the ring (dimensions not given) and the magnet to lie directly over the resorptive site, the ring would have to flare to accommodate the wider bony anatomy in the metaphysis and epiphyseal area (distal fibula plus distal tibia). However, this is not confirmed by Figs. 1, 3, and 4, which appear to show parallel-sided rings resting above the epiphysis to prevent distal slipping. A certain amount of skin pressure from the rings must be present to completely immobilize them, otherwise the rats would try to remove them, or they would rotate around the leg confusing the results even further. The authors indicate that the rings were manually adjusted to accommodate for growth of the legs. Unfortunately, the skin pressure on either limb was not quantified and could have led to unequal amounts of pressure ischemia.
Am. J. Orthod. Dentofac. Orthop.
20A
Letters to the editor
Also, it is unfortunate that there were no controls showing sections of skin that were not subjected to ring pressure. The apparent thinning of the epithelial layer may have merely been because of a differential pressure effect. The histologic photos in Figs. 5 and 6 are apparently not at the same magnification, according to a pathologist. It is therefore difficult to really ascertain the amount of epithelial thinning, particularly if the sections were not taken from samples obtained at exactly the same position on the limb. If indeed there is epithelial thinning, it does not appear unlike that which would occur from constant pressure over a specific skin area. (This, of course, can ultimately lead to decubiti.) If direct skin pressure is a factor in these results, it should be pointed out that the orthodontic application of magnets does not require this type of pressure. In fact it is usually avoided for obvious reasons. If the epithelium is thinner, what is the significance of this finding? Is it temporary or permanent? Can it be compared with epithelial effects under removable appliances? Certainly clinical experience with magnets has not sh6wn any reported adverse epithelial effects. If we accept the bone surface changes, can the authors then extrapolate these changes to resorption that occurs inside the maxilla and mandible when teeth are undergoing orthodontic movement? In the clinical orthodontic example, it has been reported that more rapid movement seems to occur when magnets are used. It is important to note that this is usually accompanied by decreased mobility and less discomfort of the moving teeth than with conventional forces. If resorption alone was stimulated to account for more rapid movement, as was suggested in the article, then increased clinical mobility would be expected with concomitant increased discomfort compared with conventional forces. Clinical experience does not support this thesis and, in fact, suggests the opposite. Observed decreased mobility and discomfort, in spite of rapid movement, supports the hypothesis that the apposition rate was much more significantly accelerated. It is conceivable that some practitioners might miss these important clinical symptoms and signs (i.e., discomfort and mobility) because they are patient perceptions and may not necessarily be reported, and mobility is not checked since movement is occurring. The statistical design you have chosen can also be challenged. The fact that right tibias were always experimental and left tibias were always the control is a controversial subject since this does not demonstrate random distribution and may lead to faulty interpretation. Earlier in vitro and in vivo research seems to confirm the hypothesis that static magnetic fields will accelerate the physiologic process for which the cells have been programmed. With osteoblast progenitor cells, in vitro work has demonstrated a twofold increase in alkaline phosphatase (associated with deposition) and a threefold decrease in lysosomal enzymes (associated with resorption) with static magnetic fields of specific properties. 1 In vivo research with rats showed that when the cranial midsagittal suture was expanded with an orthodontic bihelical sprLng in the presence of specific orthodontic magnetic fields, there was a twofold increase in
June 1991
bone volume in the expanded suture (unpublished). Both of these experiments used sham magnets and no magnets as controls, and the magnets and their fields were carefully mapped to specify the gauss-dose at the target area. It is important to realize that both static and timevarying magnetic and electromagnetic fields have been used clinically in medicine and dentistry for almost 40 years. To my knowledge there has not b.een a single reported and documented adverse clinical effect because of these specifically therapeutic fields. I have been personally involved in this area of research for more than 25 years, and my personal clinical experience confirms this observation. Furthermore, for the past 10 years, there has been extensive research on the potential mechanism of action of both static and time-varying magnetic and electromagnetic fields in the medical and scientific literature; none of which has negated the successful efficacy of clinical devices using these modalities.z.3 Moreover, many of these devices have been approved for clinical use since the late 1970s and their mechanism of action still remains unclear. Indeed, the molecular mechanism of transduction of conventional mechanical forces in orthodontics and orthopedics into biochemical and bioelectric events also remains unclear. The past history of basic scientific research in magnetic and electromagnetic fields has been characterized by inconsistent and often contradictory results in spite of successful clinical use. Only recently have these investigations reached a level of sophistication, by providing sufficient data, where they are reproducible and more consistent. However, we should profit from similar inconsistent past experiences, particularly in orthope'dics, and attempt to avoid their mistakes. Sufficient data must be provided in our papers to enable reproducibility! I commend the authors for their interest in this subject. There is no question that further research is required. I would encourage the authors' interest and motivation in pursuing this research and plead with them to properly document the magnetic fields used in experiments of this type, and also consider more convincing experimental designs. It is only in this manner that we will be able to properly document the biologic effects of these and other magnetic and electric fields. Dr. Abraham M. Blechman 153 Lester Dr. Tappan, NY 10983
REFERENCES 1. Blank M. Findl E. Mechanistic approaches to interaction of electromagnetic fields v,'ith living systems. New York: Plenum Press, 1987:389-97. 2. Gandhi OP. Biological effects and medical applications of electromagnetic energy. Englewood Cliffs, N. J.: Prentice Hall, 1990. 3. Marino AA. Modem bioelectricity. New York: Marcel Dekker, 1988.
