LETTERS TO THE EDITOR The extraction/ nonextraction dilemma To the Editor:
I was very interested in reading Dr. Weintraub's article (AM J ORTHOO DENTOFAC ORTHOP 1989;96:462-6). I have often wondered what the frequency of extractions in orthodontic treatment is, and if there is a recent trend toward fewer extractions. At the most recent meeting of the Great Lakes Association of Orthodontists in October 1989, at Dearborn, Michigan, I was reviewing the cases presented for the ABO examination and again wondered how often extractions are recommended. I noted as I walked around the room that of the 52 cases displayed at the time, 26 had had either two or four premolars extracted as part of the treatment plan. Using my own practice as a measure, a 50% extraction rate seemed rather high. I realize that the cases presented by the ABO candidates were treatment planned at least 5 years ago and may have represented neither the practitioner's patient profile at the time nor his current extraction philosophy. In any case, a 50% extraction rate is not far off from the statewide average found by Dr. Weintraub. The extraction/nonextraction dilemma remains as lively a topic of discussion among orthodontists today as it was at the turn of the century or during the thirties. More time and more study still is needed before we can determine an extraction/nonextraction "standard of care" if ever we can. The epidemiologic data presented here are an important first step. John C. Ligas, DDS, MS Flushing, Mich.
Comment reference in intrabracket space and intrabracket distance article To the Editor:
Schudy and Schudy, in their article, "lntrabracket Space and Interbracket Distance: Critical Factors in Clinical Orthodontics" (AMERICANJOURNALOF ORTHODONTICS AND DENTOFACIAL ORTHOPEDICS 1989;96:281-94), calculated force (strength) and deflection (range) to permanent set. My article "The Importance of Interbracket Width in Orthodontic Tooth Movement" (J Clin Orthod 1976;10:530-4), calculated stiffness, which Thurow defines as the amount of force required to bend a wire a certain distance (within its elastic limit). For clarification of the differences between stiffness, strength, and range, Thurow states: "Stiffness is inversely proportional to the cube of the length, strength is inversely proportional to
length, and range is proportional to the square of the length." Double the length of a wire and its stiffness decreases by eight times; its strength decreases by half; its range increases four times. Schudy mistakenly compared the force values in his data, which he referred to as stiffness, directly with my stiffness values. He failed to compensate for the varying deflections. Had he computed stiffness (force/deflection) and the actual interbracket distances shown on his model, then his data would be essentially the same as that in my article. I wonder how many orthodontists will also make the same mistake and misinterpret Schudy's force values as stiffness rather than strength, since most archwire charts compare relative stiffness, not strength. Needless to say, I found it somewhat distressing to read in the Schudy article, "Creekmore credited a great deal more significance to interbracket distance than actually exists . . . . " "The increased force or stiffness that is directly attributable to the shorter span of wire between the twin brackets is drastically less than that calculated by Creekmore." Thomas D. Creekmore, DDS Houston, Texas
Response to Dr. Johnston's Viewpoint To the Editor:
I am writing in response to Dr. kysle Johnson's "View-
point" (AMJ ORTHOD DENTOFACORTHOP 1989;96:266-7), in which he expressed his concern that "resourceful entrepreneurs escape their rightful burden of proof." I share his sentiments and wish that intellectual debate on such issues was the rule rather than the exception. However, in the same vein I hope he is equally prepared to debate the views of the established schools. Although the nonextraction treatment promoted by some entrepreneurs may have a poor record of success, so it seems has long-term correction by other means. Could it be that we are not giving enough attention to the actual cause of malocclusion? It is still widely taught in dental schools that malshapen jaws are inherited, and yet this view is largely without scientific support and is in many respects illogical. Lysle concludes that "the schools are the solution (or at least part of the solution) rather than the problem." I think one has to accept that the schools themselves may also be part of the problem. As he points out, commercial courses are challenging the very survival of some schools. Why? I think he underestimates the deep unhappiness felt by many general dentists about some aspects of conventional orthodontic treatment. This problem is not new. Nearly 100 years ago Angle 33A
I was very interested in reading Dr. Weintraub's article (AM J ORTHOO DENTOFAC ORTHOP 1989;96:462-6). I have often wondered what the frequency of extractions in orthodontic treatment is, and if there is a recent trend toward fewer extractions. At the most recent meeting of the Great Lakes Association of Orthodontists in October 1989, at Dearborn, Michigan, I was reviewing the cases presented for the ABO examination and again wondered how often extractions are recommended. I noted as I walked around the room that of the 52 cases displayed at the time, 26 had had either two or four premolars extracted as part of the treatment plan. Using my own practice as a measure, a 50% extraction rate seemed rather high. I realize that the cases presented by the ABO candidates were treatment planned at least 5 years ago and may have represented neither the practitioner's patient profile at the time nor his current extraction philosophy. In any case, a 50% extraction rate is not far off from the statewide average found by Dr. Weintraub. The extraction/nonextraction dilemma remains as lively a topic of discussion among orthodontists today as it was at the turn of the century or during the thirties. More time and more study still is needed before we can determine an extraction/nonextraction "standard of care" if ever we can. The epidemiologic data presented here are an important first step. John C. Ligas, DDS, MS Flushing, Mich.
Comment reference in intrabracket space and intrabracket distance article To the Editor:
Schudy and Schudy, in their article, "lntrabracket Space and Interbracket Distance: Critical Factors in Clinical Orthodontics" (AMERICANJOURNALOF ORTHODONTICS AND DENTOFACIAL ORTHOPEDICS 1989;96:281-94), calculated force (strength) and deflection (range) to permanent set. My article "The Importance of Interbracket Width in Orthodontic Tooth Movement" (J Clin Orthod 1976;10:530-4), calculated stiffness, which Thurow defines as the amount of force required to bend a wire a certain distance (within its elastic limit). For clarification of the differences between stiffness, strength, and range, Thurow states: "Stiffness is inversely proportional to the cube of the length, strength is inversely proportional to
length, and range is proportional to the square of the length." Double the length of a wire and its stiffness decreases by eight times; its strength decreases by half; its range increases four times. Schudy mistakenly compared the force values in his data, which he referred to as stiffness, directly with my stiffness values. He failed to compensate for the varying deflections. Had he computed stiffness (force/deflection) and the actual interbracket distances shown on his model, then his data would be essentially the same as that in my article. I wonder how many orthodontists will also make the same mistake and misinterpret Schudy's force values as stiffness rather than strength, since most archwire charts compare relative stiffness, not strength. Needless to say, I found it somewhat distressing to read in the Schudy article, "Creekmore credited a great deal more significance to interbracket distance than actually exists . . . . " "The increased force or stiffness that is directly attributable to the shorter span of wire between the twin brackets is drastically less than that calculated by Creekmore." Thomas D. Creekmore, DDS Houston, Texas
Response to Dr. Johnston's Viewpoint To the Editor:
I am writing in response to Dr. kysle Johnson's "View-
point" (AMJ ORTHOD DENTOFACORTHOP 1989;96:266-7), in which he expressed his concern that "resourceful entrepreneurs escape their rightful burden of proof." I share his sentiments and wish that intellectual debate on such issues was the rule rather than the exception. However, in the same vein I hope he is equally prepared to debate the views of the established schools. Although the nonextraction treatment promoted by some entrepreneurs may have a poor record of success, so it seems has long-term correction by other means. Could it be that we are not giving enough attention to the actual cause of malocclusion? It is still widely taught in dental schools that malshapen jaws are inherited, and yet this view is largely without scientific support and is in many respects illogical. Lysle concludes that "the schools are the solution (or at least part of the solution) rather than the problem." I think one has to accept that the schools themselves may also be part of the problem. As he points out, commercial courses are challenging the very survival of some schools. Why? I think he underestimates the deep unhappiness felt by many general dentists about some aspects of conventional orthodontic treatment. This problem is not new. Nearly 100 years ago Angle 33A
