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Proplast-coated high-strength magnets as potential denture stabilization devices
Proplast-coated denture
high-strength
stabilization
magnets
as potential
devices
Robert J. Connor, D.D.S., M.S.,* and Carl W. Svare, D.D.S., Ph.D.** The University of Iowa, College of Dentistry, Iowa City, Iowa
M
ost edentulous patients can be fitted with dentures that are functional, comfortable, and esthetic. However, conventional prosthetic techniques are inadequate for a number of patients. To aid this group of patients, a number of retentive devices, suction cups, springs, repelling magnets, and adhesive powders, gums, and ointments have been devised. All of these have proved to be unsatisfactory. Physicians have been implanting nonviable substances into the human body since 1565. During the ensuing years, several fundamental principles of implantation were realized: ( 1) the implant must be made of material that the tissues will tolerate, (2) the implant must be completely covered by tissue, (3) load-bearing implants must be immobile, and (4) the implant must not interfere with the physiologic state of the adjacent tissue. The solution, it appears, would be to position in the jaw a substance which can be completely covered, that will not interfere with the physiologic state of the tissue, and yet which can transmit a retentive force to the denture. The only material which seemingly meets these criteria is a magnet. IMPLANTING
MAGNETS
TO RETAIN
DENTURES
The theory as it evolved was simple. Implant a magnet in the jaw, covering it completely with tissue, and place a magnet in the denture. The attractive force between the magnet in the jaw and the magnet in the denture would pass through the covering tissue and help hold the denture in place. This concept is not new. Behrman’ showed that magnets implanted in the mandible provided a simple, safe, and efficient aid to complete denture retention in those patients who were unable to wear dentures satisfactorily because of loss of bone in the lower ridge. He implanted magnets of a specific platinum-cobalt alloy which *Assistant Professor, Department School of Dentistry, Atlanta, Ga. **Associate Professor, University of Iowa.
Department
of Crown of
Fixed
and
Bridge
Prosthodontics,
Prosthodontics,
College
Emory of
University
Dentistry,
The
339
340
Connor
J. I’rosthct. March.
and Suare
Denr. 1977
were well tolerated by tissues. The authors, however, use a very powerful magnetic alloy of samarium-cobalt. The magnetic strength of this new alloy is approximately five times that of the previously used platinum-cobalt magnets. Thus, the implant can be one fifth as bulky as the platinum-cobalt magnet and still produce the same effect. This is an obvious surgical advantage in jaws which have minimum bone bulk. Some of the complications of the samarium-cobalt material become evident immediately. These are: (1) extreme difficulty in fabrication-the samarium-cobalt magnets must have a protective coating which can be applied at less than 3OW Cl., or the result will be demagnetization by extreme heat-and (2) the samarium-cobalt magnet is biodegradable and, therefore, needs a coating which separates it from the body’s environment. The coating we propose to use is the commercially available Proplast.” Proplast is composed of polytetrafluoroethylene and pyrolytic graphite. a pure molecular form of carbon that is pyrolytically derived from hydrocarbons such as rayon. These materials have been screened for biocompatibility in animal and clinical studies by Homsy and associates.‘-’ Proplast has also been utilized as a binding interface between metallic implants and hard or soft tissue.“, 4 Implantation of porous calcium-aluminate root forms indicated that the implant must be covered with mucosa and allowed to heal prior to loading.5 Most varieties of materials, including metals, plastics, ceramics, and combinations of these, have been implanted in the oral cavity, largely without success.“-” In light of the proved utility of magnets in stabilizing dentures and the surgical advantages of implanting the smaller-size magnet, the aim of this project was to determine whether a samarium-cobalt magnet could be effectively sealed from the in vivo environment with Proplast. Later, we will study the problem of its stability and location in bone upon application of simulated functional stress. TEST SUBJECTS The experimental animals used for this work were adult dogs weighing from 20 to 30 pounds. They were used because: (1) their oral cavities and teeth are large enough for surgical and prosthetic convenience; (2) all teeth are fully erupted, so the implant cannot be impinged upon by erupting teeth; and (3) they have an oral chemical environment similar to that of man so that the magnet’s pattern of chemical breakdown should be similar to that found in man. PROCEDURE Ten implants, consisting of a samarium-cobalt magnet about 6 mm. long and 3 mm. wide with an 0.5 mm. coating of Proplast, were placed in the oral cavities of the adult dogs. At the time of implantation, a median incision was made in the mucosa in the edentulous region and the mucosa was retracted. A hole was prepared to the dimensions of the implant midway between the remaining teeth, using a sharp bone bur and saline coolant. The sterilized implant was allowed to remain in a nonfunctional *Vitek
Incorporated,
Houston,
Texas.
Volume Numhrr
37 3
Magnets
for denture
stabilization
341
state for 1 month to allow for firm attachment to occur between the bone and the implant. The simulated functional state was achieved by implanting a magnet in the opposing tooth in a manner similar to that used for an inlay restoration. The polarity of the magnets was arranged so they would exert an attracting force toward one another. Such a force is similar to that created when magnets are placed in a mandible and then in a denture base to aid in denture retention, In the final analysis, we should be able to determine (1) if the coating sealed the magnet and also (2) the effectiveness of the Proplast in stabilizing the magnet in the bone. Using a pneumatically driven surgical saw, bone blocks containing the specimen were removed 5 months after implantation. They were then sectioned with a diamond saw at selected sites of potential high leakage, such as corners and edges. Following this, they were hand ground to a thickness suitable for examination by transmitted-light microscopy. The specimens were then used for both the nondestructive chemical and the histologic analyses. Based on these observations, a judgment was made on whether any samarium or cobalt had leaked and whether such leakage had elicited any untoward histologic effects on the tissue supporting the implant. The electron probe was employed in the nondestructive chemical analysis. The electron probe is an instrument which permits an essentially complete chemical analysis to be performed on thin sections prepared by standard histologic methods. The instrument accomplishes this highly localized analysis of a “microvolume” of material at the surface of a sample through spectrographic analysis of the characteristic x-ray spectrum generated by a finely focused beam of high-energy electrons. The probe detected leaks of samarium or cobalt, and then the location of the leak was examined under the microscope to determine if the leak was caused by a break in the coating or diffusion through the coating itself. After the ten sections were analyzed by use of the electron probe, they were examined histologically for the presence of fibroblastic and vascular changes. In chronic inflammation of this type, we looked for vascular fibroblastic proliferation and mononuclear cell reaction of lymphocytes, plasma cells, and macrophages. A low-power photomicrograph of a typical sample is shown in Fig. 1. RESULTS Seven of the ten samples showed no breaks in the protective coating within the limits of detection and no leakage of samarium or cobalt into the surrounding tissues. Three of the samples under microscopic examination showed breaks in the protective coating and, under chemical analysis, leaks of samarium into the tissues where the coating was broken. In samples in which the coating was broken, the break could be accounted for by either faulty coating in that particular region or disturbances of the coating during the surgical placement of the implant in these three samples, the results were consistent in that samarium was the only element that leached. Samarium obviously had a higher diffusion rate and was chemically more active than the cobalt in the magnet proper. Only one sample did not follow this general scheme. For this sample, there was evidence that cobalt had leaked into the surrounding tissues and cobalt was present in higher concentrations than samarium. A possible
342
Fig.
Connor
1. The
J. Pmsthet. March.
and Svare
samarium-cobalt
magnet
coated
with
Proplast
is encased
in bone
and
fibrous
Dent. 1977
tissue.
explanation for this finding is that fragments of the magnet were present in the surrounding tissue. In future experiments, the coated magnets can be pretested for leaks by placing them in Ringer’s solution for a designated period, Then, the coated magnets can be removed from the solution and chemical analysis used to determine if any of the elements have leaked out. By this method, we can be assured that the coating functions as a diffusion barrier. By eliminating leakage, the success rate should improve.
SUMMARY AND CONCLUSIONS This study was designed to determine if a samarium-cobalt magnet could be effectively sealed from the in vivo environment and be physically stabilized in bone under simulated functional stress. The following conclusions can be made from this study. (1) It is possible to effectively seal a samarium-cobalt magnet from the in vivo environment. Clinical observation, radiographs, and photomicrographs on all samples showed good healing and dense tissue over the surgical sites. The samples showed that connective tissue penetrated the Proplast, and clinically, the magnets appeared to be well stabilized in bone. (2) It follows that if magnets are properly coated and good surgical techniques are used, Proplast can be an effective sealant. Samarium or cobalt appeared in the surrounding tissues only where the coating was faulty. Further studies are being conducted which will cover a 2 year period as opposed to the original 5 month study. It is hoped that with specific tests, we will be able to demonstrate absolute fixation and no migration of the magnets.
References 1. 2.
Behrman, S. J.: Magnets Implanted in the Mandible: Dent. Assoc. 68: 206-215, 1964. Homsy, C. A., King, J. W., and Cain, T. E.: Dynamic J. Bone Joint Surg. (Am.) 52A: 604, 1970.
Aid
to Denture
Stabilization
Retention,
of Implanted
J. Am. Prosthesis,
y&mr 3. 4. 5.
6. 7. 8. 9.
Magnets
“3’
for
denture
stabilization
343
Homsy, C. A.: Bio-compatibility in Selection of Materials for Implantation, J. Biomed. Mater. Res. 4: 341-356, 1970. for Oral Implantation-Biological Homsy, C. A., Kent, J. N., and Hinds, E. C.: Materials and Functional Criteria, J. Am. Dent. Assoc. 86: 817-832, 1973. Svare, C. W., and Fritts, K. W.: Study of Porous Calcium Aluminate as a Functioning Hard Tissue Substitute, Iowa Section, Proceedings of the Fiftieth General Session of the IADR, Las Vegas, Nev., March, 1972. Studies on the Reaction of Alveolar Bone to Bernier, J. L., and Canby, C. D.: Histologic Vitallium Implants, J. Am. Dent. Assoc. 30: 188-197, 1943. Branemark, P. I., and Breine, U. A.: Intraosseous Anchorage of Dental Prostheses, Stand. J. Plast. Reconstr. Surg. 3: 81-100, 1969. Status of the Polymer Tooth Implant Hodosh, M., Povar, M., and Shklar, G.: Current Concept, Dent. Clin. North Am. 14: 103-115, 1970. Hodosh, M., Povar, M., and Shklar, G.: The Clinical Use of Polymer Coated Metal Pins as Endosteal Implants, J. PROSTHET. DENT. 25: 85-91, 1971. DR. CONNOR EMORY UNIVERSITY SCHOOL OF DENTISTRY ATLANTA, GA. 30322 DR. SVARE THE UNIVERSITY OF IOWA COLLEGE OF DENTISTRY IOWA CITY, IOWA 52242
ARTICLES
TO APPEAR IN FUTURE
lingual Melchor
Range Bocage,
Ecologic N. Brill,
changes Gerd Tryde,
Subiective
reactions
dentures Larry D. Campbell,
design Odont.Dr.,
in complete and Jaime
in the oral K. Stoltze, to
major
restoration Kai Chiu Ph.D.
electron
dentures Lehrhaupt,
Odont.Dr.
cavity caused by removable and E. A. El Ghamrawy connector
designs
for
partial
removable
dentures
partial
D.D.S.
Removable partial denture Bert T. Cecconi, D.D.S., M.S. Scanning
ISSUES
research
microscope
finishing Chan, D.D.S.,
techniques M.S., John
study W.
and
its clinical
of
marginal
Edie,
M.S.,
significance
adaptation Ph.D.,
and
of amalgam Carl
W.
Svare,
in D.D.S.,
high-strength
stabilization
magnets
as potential
devices
Robert J. Connor, D.D.S., M.S.,* and Carl W. Svare, D.D.S., Ph.D.** The University of Iowa, College of Dentistry, Iowa City, Iowa
M
ost edentulous patients can be fitted with dentures that are functional, comfortable, and esthetic. However, conventional prosthetic techniques are inadequate for a number of patients. To aid this group of patients, a number of retentive devices, suction cups, springs, repelling magnets, and adhesive powders, gums, and ointments have been devised. All of these have proved to be unsatisfactory. Physicians have been implanting nonviable substances into the human body since 1565. During the ensuing years, several fundamental principles of implantation were realized: ( 1) the implant must be made of material that the tissues will tolerate, (2) the implant must be completely covered by tissue, (3) load-bearing implants must be immobile, and (4) the implant must not interfere with the physiologic state of the adjacent tissue. The solution, it appears, would be to position in the jaw a substance which can be completely covered, that will not interfere with the physiologic state of the tissue, and yet which can transmit a retentive force to the denture. The only material which seemingly meets these criteria is a magnet. IMPLANTING
MAGNETS
TO RETAIN
DENTURES
The theory as it evolved was simple. Implant a magnet in the jaw, covering it completely with tissue, and place a magnet in the denture. The attractive force between the magnet in the jaw and the magnet in the denture would pass through the covering tissue and help hold the denture in place. This concept is not new. Behrman’ showed that magnets implanted in the mandible provided a simple, safe, and efficient aid to complete denture retention in those patients who were unable to wear dentures satisfactorily because of loss of bone in the lower ridge. He implanted magnets of a specific platinum-cobalt alloy which *Assistant Professor, Department School of Dentistry, Atlanta, Ga. **Associate Professor, University of Iowa.
Department
of Crown of
Fixed
and
Bridge
Prosthodontics,
Prosthodontics,
College
Emory of
University
Dentistry,
The
339
340
Connor
J. I’rosthct. March.
and Suare
Denr. 1977
were well tolerated by tissues. The authors, however, use a very powerful magnetic alloy of samarium-cobalt. The magnetic strength of this new alloy is approximately five times that of the previously used platinum-cobalt magnets. Thus, the implant can be one fifth as bulky as the platinum-cobalt magnet and still produce the same effect. This is an obvious surgical advantage in jaws which have minimum bone bulk. Some of the complications of the samarium-cobalt material become evident immediately. These are: (1) extreme difficulty in fabrication-the samarium-cobalt magnets must have a protective coating which can be applied at less than 3OW Cl., or the result will be demagnetization by extreme heat-and (2) the samarium-cobalt magnet is biodegradable and, therefore, needs a coating which separates it from the body’s environment. The coating we propose to use is the commercially available Proplast.” Proplast is composed of polytetrafluoroethylene and pyrolytic graphite. a pure molecular form of carbon that is pyrolytically derived from hydrocarbons such as rayon. These materials have been screened for biocompatibility in animal and clinical studies by Homsy and associates.‘-’ Proplast has also been utilized as a binding interface between metallic implants and hard or soft tissue.“, 4 Implantation of porous calcium-aluminate root forms indicated that the implant must be covered with mucosa and allowed to heal prior to loading.5 Most varieties of materials, including metals, plastics, ceramics, and combinations of these, have been implanted in the oral cavity, largely without success.“-” In light of the proved utility of magnets in stabilizing dentures and the surgical advantages of implanting the smaller-size magnet, the aim of this project was to determine whether a samarium-cobalt magnet could be effectively sealed from the in vivo environment with Proplast. Later, we will study the problem of its stability and location in bone upon application of simulated functional stress. TEST SUBJECTS The experimental animals used for this work were adult dogs weighing from 20 to 30 pounds. They were used because: (1) their oral cavities and teeth are large enough for surgical and prosthetic convenience; (2) all teeth are fully erupted, so the implant cannot be impinged upon by erupting teeth; and (3) they have an oral chemical environment similar to that of man so that the magnet’s pattern of chemical breakdown should be similar to that found in man. PROCEDURE Ten implants, consisting of a samarium-cobalt magnet about 6 mm. long and 3 mm. wide with an 0.5 mm. coating of Proplast, were placed in the oral cavities of the adult dogs. At the time of implantation, a median incision was made in the mucosa in the edentulous region and the mucosa was retracted. A hole was prepared to the dimensions of the implant midway between the remaining teeth, using a sharp bone bur and saline coolant. The sterilized implant was allowed to remain in a nonfunctional *Vitek
Incorporated,
Houston,
Texas.
Volume Numhrr
37 3
Magnets
for denture
stabilization
341
state for 1 month to allow for firm attachment to occur between the bone and the implant. The simulated functional state was achieved by implanting a magnet in the opposing tooth in a manner similar to that used for an inlay restoration. The polarity of the magnets was arranged so they would exert an attracting force toward one another. Such a force is similar to that created when magnets are placed in a mandible and then in a denture base to aid in denture retention, In the final analysis, we should be able to determine (1) if the coating sealed the magnet and also (2) the effectiveness of the Proplast in stabilizing the magnet in the bone. Using a pneumatically driven surgical saw, bone blocks containing the specimen were removed 5 months after implantation. They were then sectioned with a diamond saw at selected sites of potential high leakage, such as corners and edges. Following this, they were hand ground to a thickness suitable for examination by transmitted-light microscopy. The specimens were then used for both the nondestructive chemical and the histologic analyses. Based on these observations, a judgment was made on whether any samarium or cobalt had leaked and whether such leakage had elicited any untoward histologic effects on the tissue supporting the implant. The electron probe was employed in the nondestructive chemical analysis. The electron probe is an instrument which permits an essentially complete chemical analysis to be performed on thin sections prepared by standard histologic methods. The instrument accomplishes this highly localized analysis of a “microvolume” of material at the surface of a sample through spectrographic analysis of the characteristic x-ray spectrum generated by a finely focused beam of high-energy electrons. The probe detected leaks of samarium or cobalt, and then the location of the leak was examined under the microscope to determine if the leak was caused by a break in the coating or diffusion through the coating itself. After the ten sections were analyzed by use of the electron probe, they were examined histologically for the presence of fibroblastic and vascular changes. In chronic inflammation of this type, we looked for vascular fibroblastic proliferation and mononuclear cell reaction of lymphocytes, plasma cells, and macrophages. A low-power photomicrograph of a typical sample is shown in Fig. 1. RESULTS Seven of the ten samples showed no breaks in the protective coating within the limits of detection and no leakage of samarium or cobalt into the surrounding tissues. Three of the samples under microscopic examination showed breaks in the protective coating and, under chemical analysis, leaks of samarium into the tissues where the coating was broken. In samples in which the coating was broken, the break could be accounted for by either faulty coating in that particular region or disturbances of the coating during the surgical placement of the implant in these three samples, the results were consistent in that samarium was the only element that leached. Samarium obviously had a higher diffusion rate and was chemically more active than the cobalt in the magnet proper. Only one sample did not follow this general scheme. For this sample, there was evidence that cobalt had leaked into the surrounding tissues and cobalt was present in higher concentrations than samarium. A possible
342
Fig.
Connor
1. The
J. Pmsthet. March.
and Svare
samarium-cobalt
magnet
coated
with
Proplast
is encased
in bone
and
fibrous
Dent. 1977
tissue.
explanation for this finding is that fragments of the magnet were present in the surrounding tissue. In future experiments, the coated magnets can be pretested for leaks by placing them in Ringer’s solution for a designated period, Then, the coated magnets can be removed from the solution and chemical analysis used to determine if any of the elements have leaked out. By this method, we can be assured that the coating functions as a diffusion barrier. By eliminating leakage, the success rate should improve.
SUMMARY AND CONCLUSIONS This study was designed to determine if a samarium-cobalt magnet could be effectively sealed from the in vivo environment and be physically stabilized in bone under simulated functional stress. The following conclusions can be made from this study. (1) It is possible to effectively seal a samarium-cobalt magnet from the in vivo environment. Clinical observation, radiographs, and photomicrographs on all samples showed good healing and dense tissue over the surgical sites. The samples showed that connective tissue penetrated the Proplast, and clinically, the magnets appeared to be well stabilized in bone. (2) It follows that if magnets are properly coated and good surgical techniques are used, Proplast can be an effective sealant. Samarium or cobalt appeared in the surrounding tissues only where the coating was faulty. Further studies are being conducted which will cover a 2 year period as opposed to the original 5 month study. It is hoped that with specific tests, we will be able to demonstrate absolute fixation and no migration of the magnets.
References 1. 2.
Behrman, S. J.: Magnets Implanted in the Mandible: Dent. Assoc. 68: 206-215, 1964. Homsy, C. A., King, J. W., and Cain, T. E.: Dynamic J. Bone Joint Surg. (Am.) 52A: 604, 1970.
Aid
to Denture
Stabilization
Retention,
of Implanted
J. Am. Prosthesis,
y&mr 3. 4. 5.
6. 7. 8. 9.
Magnets
“3’
for
denture
stabilization
343
Homsy, C. A.: Bio-compatibility in Selection of Materials for Implantation, J. Biomed. Mater. Res. 4: 341-356, 1970. for Oral Implantation-Biological Homsy, C. A., Kent, J. N., and Hinds, E. C.: Materials and Functional Criteria, J. Am. Dent. Assoc. 86: 817-832, 1973. Svare, C. W., and Fritts, K. W.: Study of Porous Calcium Aluminate as a Functioning Hard Tissue Substitute, Iowa Section, Proceedings of the Fiftieth General Session of the IADR, Las Vegas, Nev., March, 1972. Studies on the Reaction of Alveolar Bone to Bernier, J. L., and Canby, C. D.: Histologic Vitallium Implants, J. Am. Dent. Assoc. 30: 188-197, 1943. Branemark, P. I., and Breine, U. A.: Intraosseous Anchorage of Dental Prostheses, Stand. J. Plast. Reconstr. Surg. 3: 81-100, 1969. Status of the Polymer Tooth Implant Hodosh, M., Povar, M., and Shklar, G.: Current Concept, Dent. Clin. North Am. 14: 103-115, 1970. Hodosh, M., Povar, M., and Shklar, G.: The Clinical Use of Polymer Coated Metal Pins as Endosteal Implants, J. PROSTHET. DENT. 25: 85-91, 1971. DR. CONNOR EMORY UNIVERSITY SCHOOL OF DENTISTRY ATLANTA, GA. 30322 DR. SVARE THE UNIVERSITY OF IOWA COLLEGE OF DENTISTRY IOWA CITY, IOWA 52242
ARTICLES
TO APPEAR IN FUTURE
lingual Melchor
Range Bocage,
Ecologic N. Brill,
changes Gerd Tryde,
Subiective
reactions
dentures Larry D. Campbell,
design Odont.Dr.,
in complete and Jaime
in the oral K. Stoltze, to
major
restoration Kai Chiu Ph.D.
electron
dentures Lehrhaupt,
Odont.Dr.
cavity caused by removable and E. A. El Ghamrawy connector
designs
for
partial
removable
dentures
partial
D.D.S.
Removable partial denture Bert T. Cecconi, D.D.S., M.S. Scanning
ISSUES
research
microscope
finishing Chan, D.D.S.,
techniques M.S., John
study W.
and
its clinical
of
marginal
Edie,
M.S.,
significance
adaptation Ph.D.,
and
of amalgam Carl
W.
Svare,
in D.D.S.,