LETTERS TO THE EDITOR The first direct bonding in orthodontia, a zother report To the Editor: Your F e b r u a r y i s s u e of t h e A J O / D O s t i m u l a t e d m e to write this article furthering t h e h i s t o r y of b o n d i n g .
This report is to provide some additional information on the history of direct bonding in orthodontia. Reference is made to the article by Cueto 1with the follow-up articles by MitcheIF and Newman 3 that appeared in the September 1990 and February 1991 issues, respectively, of this JOURNAL. In 1959 1 started my orthodontic training as a postgraduate student in the Department of Stomatology in the School of Medicine at Boston University. This unit subsequently became the Department of Orthodontics in the Boston University Goldman School of Graduate Dentistry. As a student, it was necessary for me to find and carry out a research project as a requirement for completing my training. On the basis of a report on the use of Eastman 910 by Buonacore,' I decided to do an in vitro study on bonding handmade stainless steel brackets embedded in acrylic and cure adapted to the buccal surfaces of extracted teeth. These tailored brackets were then bonded to the teeth with the Eastman 910. They were then set up in an arch form in plaster, and orthodontic wires were ligated to the set-up. For the same reasons as stated by Mitchell, 2 I also did not acid etch the teeth even though I, and others in the area, had used hooks embedded in the direct application of black copper cement to the facial surfaces of surgically exposed canines. The project was completed in 1961 and submitted to the department. In 1963 or 1964, I was invited to deliver a lecture on this project at the 1965 meeting of the Japan Research Society of Dental Materials and Appliances in Tokyo, Japan. This was a very interesting group, which shows in retrospect how the Japanese approached the problem of moving ideas from the research to the manufacturing stage. The meeting was a combination of researchers, academicians, practitioners, and industry people. This gave all the attendees the opportunity to communicate with one another, to discuss possible solutions to problems, and to network with each other. My lecture had to be basically translated into three levels of Japanese so that the differences in technical terms could be understood by the different disciplines represented. To my knowledge, this was the first exposure the Japanese had to the concept of direct bonding of orthodontic brackets to teeth. I like to think that it was my lecture at this meeting that started the Japanese working in this area, as it was not too long after that they presented their progress especially in the products that they began offering to the specialty. The manufacturers' interest was especially keen as evidenced in the time they spent with me after the lecture 14A
in talking with and entertaining me, and also having me visit their factories. When I returned home, I did write letters to a couple of our dental supply companies to open some contacts for them. My paper, entitled "Methods and Factors Involved in Bonding Orthodontic Attachments to Enamel," was published in the September 1965 issue of the Journal of Nihon University School of Dentistry2 It was then abstracted in the May 1966 issue of Dental Abstracts2 Leonard Bernstehz, DMD Clinical Professor of Orthodontics Boston University Goldman School of Graduate Dentistry REFERENCES I. Cueto HI. A little history: the first direct bonding in orthodontia. AM J ORTItOD DF=NTOFACORTIIOP 1990;98:276-7. 2. Mitchell DL. The first direct bonding in orthodontia, revisited. AM J ORnIOD DF.',,"rOFACORTItOP 1991 ;I 01 : 187-9. 3. Newman GV. First direct bonding in orthodontia. Ax~ J ORTIIOD Dr~',rrOVACORTIIOP 1991;101:190-1. 4. Buonacore MG. Evaluation of resin film-forming materials for use as bonding agents between resin filling materials and tooth structure (Abstract). 1955;34:749. 5. Bernstein L. Methods and factors in bonding orthodontic attachments to enamel. J Nihon Univ School of Dent 1965;17:96-102. 6. Bernstein L. Factors and methods involved in bonding orthodontic attachments to enamel. Dent Abstr 1966;1 !:308.
Superelastic wires To the Editor:
There is a definite need to critically assess the properties of the "new breed" nickel-titanium superelastic wires. Toward this goal, Khier, Brantley, and Fournelle in their article, "Bending Properties of Superelastic and Nonsuperelastic Nickel-titanium Orthodontic Wires" (AM J DENTOFACOFITHOP 1991 ;99:310-8), try to examine the differences between the new superelastic and the older nonsuperelastic nickel-titanium wires. Several deficiencies exist in their article that should be noted. The term, superelasticity, was used in the orthodontic literature by Miura et al.' to indicate a property of a wire that results in a constant stress despite changing strain. This was related to shape memory in that, as the wire recovered its original configuration at a temperature within the temperature transformation range, it displayed the superelastic property. Therefore these thermodynamic wires are temperature sensitive and should be tested at mouth temperature, 37 ~ C, not 22 ~ G as used by Khier et al. Second, Miura et al.' point out that the cantilever test used is deceiving because it tended to give lower values of stiffness and higher values of flexibility. Wires that were in fact not superelastic displayed superelastic properties with this test. A more clinically relevant test for Khier et al. to have used would have been a bending test with the wire supported at either end. The true residual deformation of the wire on unload-
Volume 102
Letters to the editor
15A
Number 1
ing was not determined in their study, because the pointers of the torque meter obscured the position of zero bending moment. This measure of springback is important to differentiate between the different wires and is a fault in the method. The property of superelasticity in arch wires is relatively new and as yet not completely investigated. Important properties that need to be characterized are the stiffness and range of deflection of these wires over the various sections of their force deflection curves. This is important for clinical use to estimate the forces being applied by the wire on unloading and to enable comparisons of various wires. These features are absent from the article. Simply quoting ranges of forces needed to produce an 80 ~ deflection is not sufficient, as most situations do not demand such extreme activation. Our knowledge of the behavior of these new superelastic wires is still in its infancy. Research into their laboratory and clinical behavior is necessary to elucidate how they may best be used. Jeff Lipshatz Postgraduate orthodontic student University of Melbourne REFERENCE 1. Miura F, M ~ i M, Ohura Y, Hamanka H. The super-elastic property of the Japanese NiTi alloy wire for use in orthodontics. A.~ J ORTHODDENTOFACORTIIOP 1986;90:1-10.
REPLY
To tlre Editor: The comments by Dr. Lipshatz offer us the opportunity to provide additional perspective to our recent article, "Bending Properties of Superelastic and Nonsuperelastic Nickel-titanium Orthodontic Wires," published in AM J ORTHOD DENTOFACORTHOP 1991 ;99:310-8. This article was based on a portion of the PhD dissertation (1988) from Dr. Khier at Marquette University entitled "Structural Characterization, Biomechanical Properties, and Potentiodynamic Polarization Behavior of Nickel-titanium Orthodontic Wire Alloys," which was reference 4 in our article. It was the purpose of Dr. Khier's engineering materials science dissertation to obtain fundamental information about the complex metallurgical structures of these NiTi alloys by x-ray diffraction and differential scanning calorimetry, and to determine relationships between these structures on atomic and microstructural levels and the important areas in orthodontics of bending properties and electrochemical corrosion. Cantilever bending with test spans appropriate to interbracket distances was selected since this test procedure can be performed with facility and yields excellent and highly reproducible plots. Activation of the test spans to 80 ~ angular deflection displayed essentially the complete nature of the loading and unloading behavior, and the wire response to smaller levels of activation in the range of clinical interest can easily be estimated by extrapolation from these bending plots. Although the torque meter pointer did obscure the position of zero bending moment, as we noted in our article, the bending plots in
the vicinity of the origin could easily be constructed by extrapolation. Moreover, the very large difference in values of springback for the superelastic and nonsuperelastic NiTi wires was both dramatic and unambiguous in our experiments. Our testing method largely followed that of Burstone et al. for evaluation of the Chinese NiTi wire in AM J OnTHOO 1985;87:445-52. We have always appreciated the voluminous dental scientific literature that exists on the selection of an appropriate bending test for orthodontic wires. Kusy and Dilley have provided an excellent summary for cantilever, three-point and four-point bending tests in their article "Elastic Modulus of a Triple-stranded Stainless Steel Arch Wire Via Threeand Four-point Bending" in J Dent Res 1984;63:123240. Recently Nikolai et al. have described a very interesting five-point bending test, simulating an arch wire segment supported by two brackets, in their article, "Structural Responses of Orthodontic Wires in Flexure From a Proposed Alternative to the Existing Specification Test," AM J ORTHOO DENTOFAC OFITHOP 1988;93:496504. We believe that any of these bending tests are inherently acceptable, provided that due attention in the analysis of results is directed to the relevant principles of solid mechanics. We certainly recognized the potential dependence of the bending properties of the superelastic NiTi wires for test temperatures of 22 ~ C and 37 ~ C. However, Burstone et al. found that the bending properties of Chinese NiTi were not greatly different for these two temperatures. Furthermore, the differential scanning calorimetry determinations in Dr. Khier's dissertation of the temperature ranges and activation enthalpies for the reversible austenite-martensite transformations suggested that the three brands of superelastic wires evaluated in our study were very similar. Consequently, we considered that 37 ~ C testing was probably not important for these wires, given the focus of her dissertation at the time, although this conclusion is certainly not the case for recently marketed NiTi wires with shape memory characteristics at mouth temperature (Fletcher et al., "DSC and Bending Studies of a New Shape-memory Orthodontic Wire" in J Dent Res 1992;71 (Special Issue):169, AADR Abstract #505). We plan to submit the extensive differential scanning calorimetry and x-ray diffraction results from Dr. Khier's dissertation and a subsequent master's thesis by Leu (reference 15 in our article) for publication in the near future. William A. Brantley, PhD Professor Section of Restorative and Prosthetic Dentistry College of Dentistry Tire Ohio State University Columbus, 011 43210-1241
C o m m e n t on m a n d i b u l a r growth To the Editor: I was interested to note the report of Ayoub and Mostafa in the March 1992 issue of the AJO/DO entitled
This report is to provide some additional information on the history of direct bonding in orthodontia. Reference is made to the article by Cueto 1with the follow-up articles by MitcheIF and Newman 3 that appeared in the September 1990 and February 1991 issues, respectively, of this JOURNAL. In 1959 1 started my orthodontic training as a postgraduate student in the Department of Stomatology in the School of Medicine at Boston University. This unit subsequently became the Department of Orthodontics in the Boston University Goldman School of Graduate Dentistry. As a student, it was necessary for me to find and carry out a research project as a requirement for completing my training. On the basis of a report on the use of Eastman 910 by Buonacore,' I decided to do an in vitro study on bonding handmade stainless steel brackets embedded in acrylic and cure adapted to the buccal surfaces of extracted teeth. These tailored brackets were then bonded to the teeth with the Eastman 910. They were then set up in an arch form in plaster, and orthodontic wires were ligated to the set-up. For the same reasons as stated by Mitchell, 2 I also did not acid etch the teeth even though I, and others in the area, had used hooks embedded in the direct application of black copper cement to the facial surfaces of surgically exposed canines. The project was completed in 1961 and submitted to the department. In 1963 or 1964, I was invited to deliver a lecture on this project at the 1965 meeting of the Japan Research Society of Dental Materials and Appliances in Tokyo, Japan. This was a very interesting group, which shows in retrospect how the Japanese approached the problem of moving ideas from the research to the manufacturing stage. The meeting was a combination of researchers, academicians, practitioners, and industry people. This gave all the attendees the opportunity to communicate with one another, to discuss possible solutions to problems, and to network with each other. My lecture had to be basically translated into three levels of Japanese so that the differences in technical terms could be understood by the different disciplines represented. To my knowledge, this was the first exposure the Japanese had to the concept of direct bonding of orthodontic brackets to teeth. I like to think that it was my lecture at this meeting that started the Japanese working in this area, as it was not too long after that they presented their progress especially in the products that they began offering to the specialty. The manufacturers' interest was especially keen as evidenced in the time they spent with me after the lecture 14A
in talking with and entertaining me, and also having me visit their factories. When I returned home, I did write letters to a couple of our dental supply companies to open some contacts for them. My paper, entitled "Methods and Factors Involved in Bonding Orthodontic Attachments to Enamel," was published in the September 1965 issue of the Journal of Nihon University School of Dentistry2 It was then abstracted in the May 1966 issue of Dental Abstracts2 Leonard Bernstehz, DMD Clinical Professor of Orthodontics Boston University Goldman School of Graduate Dentistry REFERENCES I. Cueto HI. A little history: the first direct bonding in orthodontia. AM J ORTItOD DF=NTOFACORTIIOP 1990;98:276-7. 2. Mitchell DL. The first direct bonding in orthodontia, revisited. AM J ORnIOD DF.',,"rOFACORTItOP 1991 ;I 01 : 187-9. 3. Newman GV. First direct bonding in orthodontia. Ax~ J ORTIIOD Dr~',rrOVACORTIIOP 1991;101:190-1. 4. Buonacore MG. Evaluation of resin film-forming materials for use as bonding agents between resin filling materials and tooth structure (Abstract). 1955;34:749. 5. Bernstein L. Methods and factors in bonding orthodontic attachments to enamel. J Nihon Univ School of Dent 1965;17:96-102. 6. Bernstein L. Factors and methods involved in bonding orthodontic attachments to enamel. Dent Abstr 1966;1 !:308.
Superelastic wires To the Editor:
There is a definite need to critically assess the properties of the "new breed" nickel-titanium superelastic wires. Toward this goal, Khier, Brantley, and Fournelle in their article, "Bending Properties of Superelastic and Nonsuperelastic Nickel-titanium Orthodontic Wires" (AM J DENTOFACOFITHOP 1991 ;99:310-8), try to examine the differences between the new superelastic and the older nonsuperelastic nickel-titanium wires. Several deficiencies exist in their article that should be noted. The term, superelasticity, was used in the orthodontic literature by Miura et al.' to indicate a property of a wire that results in a constant stress despite changing strain. This was related to shape memory in that, as the wire recovered its original configuration at a temperature within the temperature transformation range, it displayed the superelastic property. Therefore these thermodynamic wires are temperature sensitive and should be tested at mouth temperature, 37 ~ C, not 22 ~ G as used by Khier et al. Second, Miura et al.' point out that the cantilever test used is deceiving because it tended to give lower values of stiffness and higher values of flexibility. Wires that were in fact not superelastic displayed superelastic properties with this test. A more clinically relevant test for Khier et al. to have used would have been a bending test with the wire supported at either end. The true residual deformation of the wire on unload-
Volume 102
Letters to the editor
15A
Number 1
ing was not determined in their study, because the pointers of the torque meter obscured the position of zero bending moment. This measure of springback is important to differentiate between the different wires and is a fault in the method. The property of superelasticity in arch wires is relatively new and as yet not completely investigated. Important properties that need to be characterized are the stiffness and range of deflection of these wires over the various sections of their force deflection curves. This is important for clinical use to estimate the forces being applied by the wire on unloading and to enable comparisons of various wires. These features are absent from the article. Simply quoting ranges of forces needed to produce an 80 ~ deflection is not sufficient, as most situations do not demand such extreme activation. Our knowledge of the behavior of these new superelastic wires is still in its infancy. Research into their laboratory and clinical behavior is necessary to elucidate how they may best be used. Jeff Lipshatz Postgraduate orthodontic student University of Melbourne REFERENCE 1. Miura F, M ~ i M, Ohura Y, Hamanka H. The super-elastic property of the Japanese NiTi alloy wire for use in orthodontics. A.~ J ORTHODDENTOFACORTIIOP 1986;90:1-10.
REPLY
To tlre Editor: The comments by Dr. Lipshatz offer us the opportunity to provide additional perspective to our recent article, "Bending Properties of Superelastic and Nonsuperelastic Nickel-titanium Orthodontic Wires," published in AM J ORTHOD DENTOFACORTHOP 1991 ;99:310-8. This article was based on a portion of the PhD dissertation (1988) from Dr. Khier at Marquette University entitled "Structural Characterization, Biomechanical Properties, and Potentiodynamic Polarization Behavior of Nickel-titanium Orthodontic Wire Alloys," which was reference 4 in our article. It was the purpose of Dr. Khier's engineering materials science dissertation to obtain fundamental information about the complex metallurgical structures of these NiTi alloys by x-ray diffraction and differential scanning calorimetry, and to determine relationships between these structures on atomic and microstructural levels and the important areas in orthodontics of bending properties and electrochemical corrosion. Cantilever bending with test spans appropriate to interbracket distances was selected since this test procedure can be performed with facility and yields excellent and highly reproducible plots. Activation of the test spans to 80 ~ angular deflection displayed essentially the complete nature of the loading and unloading behavior, and the wire response to smaller levels of activation in the range of clinical interest can easily be estimated by extrapolation from these bending plots. Although the torque meter pointer did obscure the position of zero bending moment, as we noted in our article, the bending plots in
the vicinity of the origin could easily be constructed by extrapolation. Moreover, the very large difference in values of springback for the superelastic and nonsuperelastic NiTi wires was both dramatic and unambiguous in our experiments. Our testing method largely followed that of Burstone et al. for evaluation of the Chinese NiTi wire in AM J OnTHOO 1985;87:445-52. We have always appreciated the voluminous dental scientific literature that exists on the selection of an appropriate bending test for orthodontic wires. Kusy and Dilley have provided an excellent summary for cantilever, three-point and four-point bending tests in their article "Elastic Modulus of a Triple-stranded Stainless Steel Arch Wire Via Threeand Four-point Bending" in J Dent Res 1984;63:123240. Recently Nikolai et al. have described a very interesting five-point bending test, simulating an arch wire segment supported by two brackets, in their article, "Structural Responses of Orthodontic Wires in Flexure From a Proposed Alternative to the Existing Specification Test," AM J ORTHOO DENTOFAC OFITHOP 1988;93:496504. We believe that any of these bending tests are inherently acceptable, provided that due attention in the analysis of results is directed to the relevant principles of solid mechanics. We certainly recognized the potential dependence of the bending properties of the superelastic NiTi wires for test temperatures of 22 ~ C and 37 ~ C. However, Burstone et al. found that the bending properties of Chinese NiTi were not greatly different for these two temperatures. Furthermore, the differential scanning calorimetry determinations in Dr. Khier's dissertation of the temperature ranges and activation enthalpies for the reversible austenite-martensite transformations suggested that the three brands of superelastic wires evaluated in our study were very similar. Consequently, we considered that 37 ~ C testing was probably not important for these wires, given the focus of her dissertation at the time, although this conclusion is certainly not the case for recently marketed NiTi wires with shape memory characteristics at mouth temperature (Fletcher et al., "DSC and Bending Studies of a New Shape-memory Orthodontic Wire" in J Dent Res 1992;71 (Special Issue):169, AADR Abstract #505). We plan to submit the extensive differential scanning calorimetry and x-ray diffraction results from Dr. Khier's dissertation and a subsequent master's thesis by Leu (reference 15 in our article) for publication in the near future. William A. Brantley, PhD Professor Section of Restorative and Prosthetic Dentistry College of Dentistry Tire Ohio State University Columbus, 011 43210-1241
C o m m e n t on m a n d i b u l a r growth To the Editor: I was interested to note the report of Ayoub and Mostafa in the March 1992 issue of the AJO/DO entitled
