LETTERS TO THE EDITOR Comments on straight-wire appliances To The Editor: The October 1989 AJO-DO carried an article entitled "Three Biologic Variables Modifying Faciolingual Tooth Angulation by Straight-Wire Appliances" by Germane, Bentley, and Isaacson. Any research that furthers our knowledge of tooth structure is to be applauded. This article has good intent, but its clinical merit is suspect. It requires corrections, and the terminology is confusing. The study involved measuring 600 extracted teeth to learn the constancy of the angles between a line representing various sites on the face of the crown and the long axis and the constancy of the angle between the long axis of the crown and the long axis of the root for each tooth type. One purpose of the study was to assess the universality of crown inclination to learn the feasibility of an appliance with one set of such values for all patients. Their finding, like those of Dellinger' and Morrow, 2 was that a Customized appliance would be superior to one that is individualized. This comes as no surprise because everyone knows that all teeth of any one type are not exactly alike. My own data reflect a similar range for inclination; a lesser range was found for angulation and prominence? Why, then, has the individualized design of the straight-wire appliance been so successful in spite of the fact that the inclinations for all tooth types are not exactly alike? All of us encounter crown inclination variations such as those reported in the articles cited but not within one dentition unless the teeth are abnormal. The inclination of patient's teeth may vary from the average, but when that occurs, they do so in an orderly pattern throughout the arch. It is this factor that renders the Straight-Wire appliance effective for so many patients. Such a condition requires only the canting of the arch wire accordingly throughout--a wire-forming and not a wire-bending procedure, and one that is compatible with the straightwire concept. This is a factor the Germane study had to ignore because they used 600 extracted teeth from an unstated number of dentitions, and there was no mention as to whether these teeth were normal. Such a sample cannot be studied in relation to their same dentition kin, and that disqualifies them, for all practical purposes, for generalizing about the effects that their structures might have on the treatment of normal teeth within an arch or a dentition. The compelling fact is that the Straight-Wire appliance works. Any controversy about the efficacy of appliances with built-in features does not arise from tooth structure but from the less sophisticated appliances--the ones that are incorrectly designed, without specified siting instructions, and incorrectly la-

beled or categorized as straight-wire appliances. They do not work as well. I yearn for the day when clinicians, researchers, writers, and editors will distinguish between the nonprogrammed, partly programmed, and fully programmed edgewise appliances because they operate in significantly different ways. ~ The phrase straight-wire appliances, as it is used in this article, is incorrect and a serious oversight by the writers. The Straight-Wire appliance is not a category of edgewise appliances, it is the registered name of an appliance manufactured and sold by a specific company ("A"-Company, a Johnson & Johnson company). The fact that the authors used lower-case letters does not make the terminology correct because, at this time, the Straight-Wire appliance is the only fully programmed appliance. When there is another appliance that qualifies as a fully programmed appliance, then the lower case use would not be incorrect, so long as the intent is to mean a fully programmed appliance. If the AJO-DO is going to be our standard bearer for accuracy in reporting, then bracket design differences and how brackets are sited are as important to us as is the composition of a drug and how it is prescribed are to a physician. The New England "Journal of Medicine would not permit the use of penicillin to mean all antibiotics. In fact, the effects of the design differences of these appliances, even if they are sited at the FA point, can be illustrated to have a greater effect on tooth position than the variations in tooth structure reported in this article2 I would like to commend you on your job as our editor and at the same time recommend that a stronger effort be made by the Journal to rule out the use of jargon and to take a stand on using only the most correct terminology. We orthodontists are in such a sorry state concerning terminolo~.y (classification, too) that we have trouble communicating. A word that typifies the terminology problem is torque when it is used to mean inclination rather than a twisting force. Other examples are words or phrases used to mean the faciolingual cant of a crown, such as torque, faciolingual torque, axial positioning in the faciolingual plane, faciolingual angulation, faciolingual orientation, facial contour, faciolingual position, facial surface inclinations, lingual root torque, buccolingual inclination, and long axis orientation. The list is longer if all examples in the literature are added. However, all of these can be found in the Germane article, and it is confusing for the reader. It seems to me that the term inclination would suffice in all instances. It would be correct and would not be confusing. The article's title, "Three Biologic Variables Modifying Faciolingual Tooth Angulation by Straight-Wire Appliances," would be more correct if it were "Tooth Structure and Bracket Prescription." Biologic is not the most correct word; what the writers mean is tooth shape, or tooth structure. Faciolingual tooth angulation is not incorrect, but inclination is preferred; generally, angulation is mesiodistal, not faciolingual. 25A

Am. J. Orthod. Dentofac. Orthop.

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Letters to the editor

August 1990

I strongly disagree with the Germane findings that the FA point (formerly called the LA point) is no better than any other site for bracketing. The list of the advantages of the FA point for bracket siting is long2 -s.7At the top of that list is the site from which the measurements were made to design the Straight-Wire appliance. Placing the brackets elsewhere is counterproductive because the midtransverse plane and the FA point of each clinical crown are on the same plane (or surface) when the teeth are correctly positioned; the middle of the clinical crown (the FA point) is readily located without measuring instruments; and the inclination of a correctly positioned crown is more consistent for all tooth types, regardless of size, when measured from the FA point than from a site that is a measured distance from the cusp tip? -7This is true because there is not a correlation between change in tooth shape with a change in tooth size. A linear approach may be orderly, but it will not lead to bracketing sites that are geographically the same for all patients' crowns, regardless of size, as does the FA point. For example, 4 mm from the cusp tip or incisal edge may be at the equator on short crowns but in the northern or southern hemisphere on tall teeth, whereas the FA point is always at the equator. 3.4,7 This article also identifies variables in the angle formed by the crown axis and the root axis. We are told this angle must be a bracket-prescription consideration. However, we are not told how to determine this variable clinically or what the effects on occlusal interfacing might be. I do know that I have not found this angle to be a factor, even once, in my 30 years of practice. We are also told that another reason a customized appliance is needed is that optimal tooth position, when measured from the occlusal plane, must vary depending on the steepness of the occlusal plane. I would have appreciated it if the writers had explained why they think this is true; I don't think it is. Finally and pragmatically, variation in crown inclination does exist within tooth types from patient to patient. This factor may be a problem for those who use partly programmed appliances because the design of those appliances compounds the problem even when sited at the FA point? The Straight-Wire appliance deals with inclination variables simply by canting the arch wire throughout. The Straight-Wire appliance is being taught in virtually all North American orthodontic departments and is used by some 30% of all North American orthodontists. It has, I believe, brought a major improvement in occlusal treatment results, in the consistency of those results, and in the reduction of chairtime for both the orthodontist and the patient. Lawrence 1:. Andrews 2025 Chatsworth Blvd. San Diego, Calif.

REFERENCES 1. Dellinger EL. A scientific assessment of the straight-wire appliance. AM J ORTHOD1978;73:290-9. 2. Morrow JB. The angular variability of the facial surfaces of the morphological assumptions implicit in the various "straight-wire

3. 4.

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techniques" [Master's thesis]. St. Louis, Missouri: St. Louis University, 1978. Andrews LF. Straight wire, the concept and appliance. LA: Wells, 1989. Andrews LF. Straight-wire appliance: syllabus of philosophy and techniques, rev. ed. San Diego: Lawrence F. Andrews Foundation, 1975. Andrews LF. The straight-wire appliance: origin, controversy, commentary. J Clin Orthod 1976;10:99-114. Andrews LF. The straight-wire appliance: explained and compared. J Clin Orthod 1976;10:174-95. Andrews LF. The straight-wire appliance: arch form, wire bending, and an experiment. J Clin Orthod 1976;581-8.

Reply To the Editor:

Dr. Andrews' letter concerning our article, "Three Biologic Variables Modifying Faciolingual Tooth Angulation by Straight-Wire Appliances," (AM J ORTHOD DENTOFAC ORTHOP 1989;96:312-9) appears to offer dramatic evidence of different approaches to appliance therapy existing today. A line-by-line response is less appropriate than a definition of two basic fundamentals involved. One is the goal of treatment, and the other is the processes used to achieve these goals. First, the goal. Irrespective of the preadjustment present, all brackets are used to orient the facial surfaces of teeth. In the case of faciolingual cant (to use Dr. Andrews' terminology), the preadjustment in the bracket, by design, angulates the facial surface of the crown relative to the occlusal plane. When a patient has an average relationship between the occlusal plane and the cranial base (OP-SN = 14°), the central incisor is also positioned in an average relationship to SN (U1-SN = 102°). Variations in skeletal pattern normally exist, however, and patients commonly show OP-SN relationships with variation ranging over more than 200.1 If the relationship of U1-OP is fixed by the bracket design and the OP-SN increases, either the U1-SN angle or the OP-SN angle must change as a treatment goal. If either of these variations is not acceptable, the orthodontist must change the U1-OP angle by bending the arch wire. The anatomy forms a closed triangle, and changing one angle must change one or both of the others to maintain a total of 180 °. It is not a question of right and wrong, but simply a recognition that biologic variation exists normally in nature. Our article addressed one small subsection of this question. It demonstrated that biologic variation also exists normally in the relationship between the facial surface of teeth and the long axis of their crowns. This was true at all facial surface locations studied. If this is true, the attachment of any bracket at any of the sites reported must produce variation among patients in the relationships of the long axis of the crown to the occlusal plane. Our data showed variation ranging over more than 10 °