30A
Letters to the editor
that once raised it to respectability gets "curiouser and curiouser"! Peter S. ViE Professor, Orthodontic Department The University of Michigan Ann Arbor, Mich.
More on the Clark Twin Block To the Editor: In a recent article, Orthopedic and Orthodontic Effects Resulting From the Use of a Functional Appliance With Different Amounts of Protrusive Activation (AM J ORTHOD DENTOFACORTHOP 1989;96:181-90.), John De Vincenzo and Michael W. Winn describe a functional appliance as "similar in some respects" to the Clark Twin Block. Some clarification is required. After 12 years of clinical experience in using the occlusal inclined plane as a full-time functional appliance, I wish to comment on the following points raised: 1. Activation and angulation of occlusal inclined planes. I agree with the authors' observation that a single large advancement of 5 to 6 mm is more effective in producing a significant orthopedic response than a series of small activations of 1 to 3 mm with no apparent difference in orthopedic or orthodontic variables. This finding is supported by my statistical analysis of 70 consecutively treated Twin Block cases. In teaching the Twin Block technique over the past 10 years, I have recommended a protrusive activation of 5 to 10 mm, depending on the ease with which the patient holds the jaw in a forward position. When I first used the technique in 1977, the occlusal bite blocks were constructed at 90 ° to the occlusal plane. This had the disadvantage in some cases that the patient did not make the effort to hold the jaw forward and produced a posterior open bite by closing together on the occlusal surfaces of the blocks. This difficulty was overcome by introducing an occlusal inclined plane to guide the mandible into a protrusive position. The inclined plane is at 45 ° to 70 ° , depending on the degree of vertical or horizontal activation required to correct overjet and overbite. A 70 ° angle applies a more horizontal component of force, which is appropriate in the majority of cases. 2. Adjustment and reactivation. My experience of reactivating the inclined planes is much simpler than the authors' description of activation, which was timed at 50 to 60 minutes. Activation of Twin Blocks takes 5 minutes on average, and the adjustment to the appliance is carried out by the chairside assistant. The clinician needs only to check the appliance in the mouth when the acrylic material is of the correct consistency to register a new protrusive bite. 3. Control of the vertical dimension. It was observed by the authors that at the termination of the functional
Am. J. Orthod. Dentofac. Orthop. March 1990
appliance phase, a posterior dental open bite was frequently present. The problem arises in this instance in the positioning and angulation of the vertical guide plane in the molar region, which leaves no possibility of adjusting the vertical dimension during treatment by encouraging molar eruption. Twin Block appliances are designed and adjusted to control molar eruption, and the posterior open bite is progressively reduced during Twin Block treatment. After the active phase, an anterior inclined plane is used to support the corrected occlusion while the buccal teeth erupt into full occlusion. The control of vertical dimension by encouraging selective eruption of posterior teeth is crucial in all functional treatment for correction of deep overbite if appliances with occlusal inclined planes are correctly designed, the problems encountered by the authors are easily overcome, and the Twin Block technique has been shown to have a wide application in dentofacial orthopedic correction. I congratulate the authors on their research on different amounts of protrusive activation. The reservations I express are confined to clinical management of the occlusal inclined plane as an effective functional mechanism. William J. Clark, BDS, DDO Kirkcaldy, Fife, Scotland
Reply to Ahlin's comments in August issue To the Editor: I wish to respond to the comments in the August issue made by Jeffrey H. Ahlin, Brading, Massachusetts, regarding my American Board case report, which was published in the May JOURNAL(1989;95:363-70). I thank Dr. Ahlin for his interest and appropriate comments regarding the treatment results. I would first like to say that this case was probably chosen for publication by the Diplomates of the American Board of Orthodontics because it contained most of the orthodontic problems that an individual can have in an orthodontic situation--i.e., negative facial esthetics, transverse skeletal problems, vertical skeletal problems, horizontally impacted teeth, severe crowding in both arches, overjet, and skeletal anterior openbite. Second, the treatment plan was originally presented to the patient as an orthognathic surgical correction. However, the patient and parents rejected the orthognathic surgical portion of the treatment on religous grounds and wished to have treatment pursued with conventional orthodontic treatment only, knowing the limitations, particularly in the facial esthetics area. Thus the case was basically a surgical case treated nonsurgically
Volume 97 ?,'umber 3
and therein lies the challenge for any of us. The best of my efforts was attempted in this particular case without the use of orthognathic surgical procedures because of the patient's choice. With the above in mind, I would suggest that one review the cephalometric numbers regarding control of the vertical dimension and other measurements regarding segmental shifts in the dentition that were necessary to achieve all the above objectives (with the exception of facial esthetics). I frankly could not have achieved that without much of Dr. Andy Haas's concepts involving very wide rapid palatal expansion (16 mm) and heavy vertical forces from orthopedic headgear to control the vertical dimension in this particular case along with the use of the deimpacting coils, which uprighted the horizontally impacted second molars. Last, with respect to the temporomandibular conditions of the patient, I would agree with Dr. Ahlin that more should be written regarding the general conditions, pre- and posttreatment, in all ABO reports. At the time 1 took my boards (1985), however, only significant pretreatment findings were to be included, and this patient had no significant TMJ problems. TMJ assessments were not mentioned in the report but were followed through treatment and, as none developed, nothing more was mentioned in the posttreatment results. I would like to mention that the patient was splinted with a neuromuscular (SRS) type of splint before diagnosis in an attempt to physiologically seat the condyles, and the case was also mounted on an articulator before diagnosis. There were no joint noises, limitations of function, or deviations of functional movements, and no discomfort was present before, during, or after treatment. This patient has recently been examined in our office and presently shows no TMJ problems. I would also like to mention that this patient began orthodontic treatment in January 1980 and completed treatment in March 1982, and I did not at that time have as complete a TMJ examination and orientation as I do today. Therefore I would like to thank Dr. Ahlin for his scrutiny of my American Board case and wish him and all others the greatest encouragement and success in completing their American Boards, as they were a great learning experience for me. Along these lines, I would also like to encourage our orthodontic membership to follow the learned advice of Drs. Roth, Williamson, Andrews, et al. to mount our cases with the joints in the
Letters to the editor
31A
fossa in some physiologically seated reference position prior to making our diagnoses and perhaps once again before we take the braces off to make sure that we are sound with regard to TMJ function. This would also apply to the use of the true hinge axis in constructing gnathologic positioners. Using these methods, we can, I believe, increase the quality of patient treatment and, as a profession, elevate the standard of care for our patients. That is what it's all about, is it not? Thank you. Jon C. Fisher, DMD, MSD Owensboro, Kentucky
Computer analysis of wire function: clarification To the Editor:
In our recently published article (Intrabracket Space and Interbracket Distance: Critical Factors in Clinical Orthodontics. 1989;96:281-94.), a computer analysis of wire function in various bracket arrangements was reported. The data collected were derived by asking the computer how far the wire could be deflected at a given bracket until it reached the inelastic or set point. While we feel that this strength and range information is meaningful and applicable under many circumstances in orthodontic treatment, it is not analogous to the forceper-unit analysis that Dr. Tom Creekmore did in an earlier paper. Consequently, our statement that Dr. Creekmore significantly overstated the impact that twin brackets have on wire stiffness was incorrect. When viewed from a force-per-unit basis, the computer data show that a wire in the elastic range will be from 1.7 to 3.0 times stiffer in intermediate twins than single brackets. Dr. Creekmore's figures were somewhat higher than this, but he used wider intermediate twins, and this would account for the difference. We apologize for this error in our conclusions relative to interbracket distance and stiffness. George F. Schudy, DDS, MS Fred F. Schudy, DDS Houston, Texas
Letters to the editor
that once raised it to respectability gets "curiouser and curiouser"! Peter S. ViE Professor, Orthodontic Department The University of Michigan Ann Arbor, Mich.
More on the Clark Twin Block To the Editor: In a recent article, Orthopedic and Orthodontic Effects Resulting From the Use of a Functional Appliance With Different Amounts of Protrusive Activation (AM J ORTHOD DENTOFACORTHOP 1989;96:181-90.), John De Vincenzo and Michael W. Winn describe a functional appliance as "similar in some respects" to the Clark Twin Block. Some clarification is required. After 12 years of clinical experience in using the occlusal inclined plane as a full-time functional appliance, I wish to comment on the following points raised: 1. Activation and angulation of occlusal inclined planes. I agree with the authors' observation that a single large advancement of 5 to 6 mm is more effective in producing a significant orthopedic response than a series of small activations of 1 to 3 mm with no apparent difference in orthopedic or orthodontic variables. This finding is supported by my statistical analysis of 70 consecutively treated Twin Block cases. In teaching the Twin Block technique over the past 10 years, I have recommended a protrusive activation of 5 to 10 mm, depending on the ease with which the patient holds the jaw in a forward position. When I first used the technique in 1977, the occlusal bite blocks were constructed at 90 ° to the occlusal plane. This had the disadvantage in some cases that the patient did not make the effort to hold the jaw forward and produced a posterior open bite by closing together on the occlusal surfaces of the blocks. This difficulty was overcome by introducing an occlusal inclined plane to guide the mandible into a protrusive position. The inclined plane is at 45 ° to 70 ° , depending on the degree of vertical or horizontal activation required to correct overjet and overbite. A 70 ° angle applies a more horizontal component of force, which is appropriate in the majority of cases. 2. Adjustment and reactivation. My experience of reactivating the inclined planes is much simpler than the authors' description of activation, which was timed at 50 to 60 minutes. Activation of Twin Blocks takes 5 minutes on average, and the adjustment to the appliance is carried out by the chairside assistant. The clinician needs only to check the appliance in the mouth when the acrylic material is of the correct consistency to register a new protrusive bite. 3. Control of the vertical dimension. It was observed by the authors that at the termination of the functional
Am. J. Orthod. Dentofac. Orthop. March 1990
appliance phase, a posterior dental open bite was frequently present. The problem arises in this instance in the positioning and angulation of the vertical guide plane in the molar region, which leaves no possibility of adjusting the vertical dimension during treatment by encouraging molar eruption. Twin Block appliances are designed and adjusted to control molar eruption, and the posterior open bite is progressively reduced during Twin Block treatment. After the active phase, an anterior inclined plane is used to support the corrected occlusion while the buccal teeth erupt into full occlusion. The control of vertical dimension by encouraging selective eruption of posterior teeth is crucial in all functional treatment for correction of deep overbite if appliances with occlusal inclined planes are correctly designed, the problems encountered by the authors are easily overcome, and the Twin Block technique has been shown to have a wide application in dentofacial orthopedic correction. I congratulate the authors on their research on different amounts of protrusive activation. The reservations I express are confined to clinical management of the occlusal inclined plane as an effective functional mechanism. William J. Clark, BDS, DDO Kirkcaldy, Fife, Scotland
Reply to Ahlin's comments in August issue To the Editor: I wish to respond to the comments in the August issue made by Jeffrey H. Ahlin, Brading, Massachusetts, regarding my American Board case report, which was published in the May JOURNAL(1989;95:363-70). I thank Dr. Ahlin for his interest and appropriate comments regarding the treatment results. I would first like to say that this case was probably chosen for publication by the Diplomates of the American Board of Orthodontics because it contained most of the orthodontic problems that an individual can have in an orthodontic situation--i.e., negative facial esthetics, transverse skeletal problems, vertical skeletal problems, horizontally impacted teeth, severe crowding in both arches, overjet, and skeletal anterior openbite. Second, the treatment plan was originally presented to the patient as an orthognathic surgical correction. However, the patient and parents rejected the orthognathic surgical portion of the treatment on religous grounds and wished to have treatment pursued with conventional orthodontic treatment only, knowing the limitations, particularly in the facial esthetics area. Thus the case was basically a surgical case treated nonsurgically
Volume 97 ?,'umber 3
and therein lies the challenge for any of us. The best of my efforts was attempted in this particular case without the use of orthognathic surgical procedures because of the patient's choice. With the above in mind, I would suggest that one review the cephalometric numbers regarding control of the vertical dimension and other measurements regarding segmental shifts in the dentition that were necessary to achieve all the above objectives (with the exception of facial esthetics). I frankly could not have achieved that without much of Dr. Andy Haas's concepts involving very wide rapid palatal expansion (16 mm) and heavy vertical forces from orthopedic headgear to control the vertical dimension in this particular case along with the use of the deimpacting coils, which uprighted the horizontally impacted second molars. Last, with respect to the temporomandibular conditions of the patient, I would agree with Dr. Ahlin that more should be written regarding the general conditions, pre- and posttreatment, in all ABO reports. At the time 1 took my boards (1985), however, only significant pretreatment findings were to be included, and this patient had no significant TMJ problems. TMJ assessments were not mentioned in the report but were followed through treatment and, as none developed, nothing more was mentioned in the posttreatment results. I would like to mention that the patient was splinted with a neuromuscular (SRS) type of splint before diagnosis in an attempt to physiologically seat the condyles, and the case was also mounted on an articulator before diagnosis. There were no joint noises, limitations of function, or deviations of functional movements, and no discomfort was present before, during, or after treatment. This patient has recently been examined in our office and presently shows no TMJ problems. I would also like to mention that this patient began orthodontic treatment in January 1980 and completed treatment in March 1982, and I did not at that time have as complete a TMJ examination and orientation as I do today. Therefore I would like to thank Dr. Ahlin for his scrutiny of my American Board case and wish him and all others the greatest encouragement and success in completing their American Boards, as they were a great learning experience for me. Along these lines, I would also like to encourage our orthodontic membership to follow the learned advice of Drs. Roth, Williamson, Andrews, et al. to mount our cases with the joints in the
Letters to the editor
31A
fossa in some physiologically seated reference position prior to making our diagnoses and perhaps once again before we take the braces off to make sure that we are sound with regard to TMJ function. This would also apply to the use of the true hinge axis in constructing gnathologic positioners. Using these methods, we can, I believe, increase the quality of patient treatment and, as a profession, elevate the standard of care for our patients. That is what it's all about, is it not? Thank you. Jon C. Fisher, DMD, MSD Owensboro, Kentucky
Computer analysis of wire function: clarification To the Editor:
In our recently published article (Intrabracket Space and Interbracket Distance: Critical Factors in Clinical Orthodontics. 1989;96:281-94.), a computer analysis of wire function in various bracket arrangements was reported. The data collected were derived by asking the computer how far the wire could be deflected at a given bracket until it reached the inelastic or set point. While we feel that this strength and range information is meaningful and applicable under many circumstances in orthodontic treatment, it is not analogous to the forceper-unit analysis that Dr. Tom Creekmore did in an earlier paper. Consequently, our statement that Dr. Creekmore significantly overstated the impact that twin brackets have on wire stiffness was incorrect. When viewed from a force-per-unit basis, the computer data show that a wire in the elastic range will be from 1.7 to 3.0 times stiffer in intermediate twins than single brackets. Dr. Creekmore's figures were somewhat higher than this, but he used wider intermediate twins, and this would account for the difference. We apologize for this error in our conclusions relative to interbracket distance and stiffness. George F. Schudy, DDS, MS Fred F. Schudy, DDS Houston, Texas
