An interview by Dr. Larry White
Dr. Tom Mulligan
Dr. Tom Mulligan came to the attention of the orthodontic community in 1980 when he published a series of articles in the Journal of Clinical Orthodontics entitled “Common Sense Mechanics,” which he subsequently published in a book that has undergone three editions. Common Sense Mechanics has been one of the most popular and useful books on orthodontic bio-mechanics ever written and is destined to be so for many years.
Tom, you finished dental school at Marquette and then studied orthodontics at Indiana University under Dr. Charles Burstone. Tell us something about that experience.
Following the completion of dental school at Marquette, I entered the graduate program in orthodontics at Indiana in 1960. I had no idea that such programs could differ significantly at various universities. Like my basic training in the military, I assumed the majority of schools would subject me to what essentially was basic training.
However, I was exposed to a program that was unique — something I did not fully realize until graduation. When I joined the Arizona Orthodontic Study Group following my graduation, as a new member I was required to give a summary of my Indiana Orthodontic Training under Dr. Charles Burstone. This was my very first experience in lecturing. When I finished, no one had any idea of what I was talking about, and this came as a complete shock to me — especially since the Arizona Orthodontic Study Group had a reputation of being one of the best at that time. Orthodontists throughout the world were familiar with the name, “Dr. Charles Tweed,” who practiced orthodontics in Tucson, Arizona. He was world famous for the Tweed Technique. It was now clearly time for Dr. Charles Burstone to thoroughly teach mechanics.
Had Dr. Burstone developed his concepts of orthodontic bio-mechanics when you started your residency? And was his segmented mechanics part of your training, and did you ever use it?
Dr. Burstone became famous worldwide for the Segmented Arch Technique, and our class was exposed to orthodontic mechanics that simply did not exist in any other orthodontic program. Many aspects of Burstone mechanics were contrary to generally taught orthodontic mechanics. At that time, Burstone mechanics were not widely applied throughout the world due to its presumed complexity. I felt fortunate to have entered this program, as I was raised in a large family of 10 children and always questioned everything because I was very “cause/effect” oriented. I wanted to understand every aspect of Burstone mechanics and constantly asked the question, “Why?” I am sure I drove people crazy, including Dr. Burstone, but he answered all of my questions patiently, thoroughly, and completely.
Dr. Burstone always provided the cause/effect relationships and the rationales for applying his mechanics. In 53-plus years of orthodontic practice, I never used the Segmented Arch Technique, but this is not to imply that I disagreed with Dr. Burstone’s concepts. I simply applied the mechanics in a different way that met my needs, but without violating the equilibrium concepts, etc., that apply to all tooth movements and were the basis of his mechanics. Many excellent orthodontists frequently violate these biomechanical fundamentals and simply don’t recognize them, but as a result, find it necessary to use various auxiliaries to overcome side effects that many clinicians consider common and unavoidable in orthodontics.
You illustrate in your book partial bonding, such as two molars and four incisors or two molars and six anterior teeth, rather than a complete bonding that includes all of the teeth. Why do you recommend that approach?
When I started my career, full appliances were considered an absolute requirement in order to obtain excellent results. I rarely began treatment with full appliances and applied mechanics based on cause/effect relationships. Most orthodontists were taught that second molars should always be banded. If they were in a normal position with a normal Curve of Wilson or a normal Curve of Monson, I did not place a tube on the second molars contained in the normal curve unless I intended to change the anterior/posterior positions of such molars.
Many individuals failed to appreciate the significance of these “functional curves,” and, as a result, unintentionally overlooked the stability intended by their long axis relationships during occlusal function. This in itself is often responsible for the prolonged need of retainers and therefore responsible for relapses that occurred with loss of retainer(s) or not wearing retainers as instructed.
Placing full orthodontic appliances routinely results in the creation of instability in various locations — just the opposite of what is intended. When a full appliance is placed and continuous archwires fully engaged, as clinicians frequently do, teeth that require no movement whatsoever frequently move undesirably, as they became “participants” in the total force system produced as a result of the requirements for static equilibrium.
A continuous archwire does not restrict itself to correction of only the malposed teeth. The requirements for static equilibrium must always be met without exception and the effects clearly recognized. When the orthodontist places archwires, three conditions create automatically for static equilibrium: 1)The sum of the vertical forces equals zero. 2) The sum of the horizontal forces equals zero. 3) The sum of the moments around a common point equals zero.
If we fail to recognize the forces and moments beyond the movements we are attempting, we can witness side effects that are totally unpredictable. Such failure to recognize the significance of these requirements has led to an unbelievable assortment of appliances intended to prevent undesirable side effects, such as lingual arches, palatal arches, elastics, removable appliances, functional appliances, etc.
All of these mentioned factors led me to begin the vast majority of my treatments with a partial appliance — usually a 2 x 4 or 2 x 6. The static requirements led me to avoid rectangular wire except in very rare situations. As a result, I became accustomed to the use of round archwires, partial appliances, etc., and avoided second molars unless they needed movement of one kind or another.
To give readers an idea of your edgewise appliances, could you tell us what type of brackets, bands, wires, etc., you typically use, and why you chose those instruments?
Many other so-called requirements involving bracket slots, torque, width, angulation, etc., as taught by various schools and courses, has become almost a necessity by most orthodontists. I was able to substitute these needs with the use of standard stainless steel brackets containing no angulated slots and stainless steel round wire, none of which were ever intended to fill the bracket slots.
Orthodontists claimed that round wire could not provide the torque required in many malocclusions. For example, if incisors intrude with a partial appliance using only round wire, the molars extrude. What would prevent the molars from moving lingually due to the eruptive forces acting through the molar tubes and buccal to the Center of Resistance, which results in lingual crown moments on the molars? The answer is so simple, and I did this throughout my orthodontic career. Forty-five degree bends, placed distal to the canines and acting in a buccal direction relative to the molars, produce molar buccal crown moments larger than the lingual crown moments produced by the vertical forces acting through the molar tubes. Remember that Force X Distance = Moment. This produces a net buccal force acting through the molar tube resulting in a buccal crown moment. This is where a partial appliance is so special. A full appliance would not direct the buccal force to the molars with the 45 degree bend. Now you can see that the use of round wire with partial appliances allows the operator to produce moments in different planes of space with the same archwire, at the same time, without suffering the various consequences of rectangular wire and the side effects that may occur with the higher magnitudes of force, including occlusal-plane tipping, etc.
To sum up this procedure, vertical forces with round wire can cause moments that can create a problem, but the addition of horizontal forces, as described, can correct or prevent such a problem. Why? Because the vertical forces acting through the molar tubes act at a shorter perpendicular distance to the Center of Resistance, while the horizontal forces act at a significantly longer perpendicular distance to this same Center of Resistance, thus creating a net moment in the horizontal plane, which eliminates the need for rectangular wires and tubes or brackets that permit the development of torque within the brackets.
You often use tip-back bends on Class II maxillary molars to achieve a Class I occlusion, but doesn’t the presence of a second molar limit the effect of the tip-back bend?
The question as to whether the presence of second molars limits the effect of tip-back bends in the correction of a Class II depends on a number of issues. First of all, the presence of a Class II malocclusion may exist at various ages. When the situation involves diminishing growth and the tip-back bends are being used to simply maintain the AP position of the molars as growth continues, there is no problem. If the molars involve a Class II with mesial tipping of the molars, the tip-back bends are very effective. The important thing to remember is that tip-back bends produce differential moments with relatively light vertical forces due to the large interbracket distances involved. Remember also that these vertical forces produce lingual crown moments that can be easily overcome with buccal crown moments if required, as previously explained. These vertical forces in a partial appliance do not increase the vertical dimension of the patient because of relatively low magnitudes, so “what you see is what you get.” One of the most significant aspects is that the tip-back bends do not require cooperation from the patient as does a headgear. Both produce distal crown moments, but only one requires patient compliance. This isn’t magic, but rather simplicity in which the orthodontist determines the outcome rather than the patient who must wear the headgear.
In the latest edition of Common Sense Mechanics, you don’t mention the use of headgears. Was that intentional, or did you evolve in your treatment mechanics to not need them?
I did use headgear minimally, but I didn’t use them for the past 25-30 years and have relied only on tip-back bends. There were times when I used Class II elastics knowing it would create instability in certain cases, but this typically had to do with facial profiles or some type of compromise.
You had practiced orthodontics about 10 years before Straight Wire Orthodontics was introduced. Did you ever use the SWO technique and, if not, why?
I have never used the Straight Wire technique in orthodontics because I was comfortable with the approach I used by applying Dr. Burstone’s teachings. I don’t mean to imply that one method is right and the other wrong, but as I have already said, I am very cause/effect oriented.
One of the most significant developments in orthodontics has been nitinol wire, but I have heard you mention that you have never felt the need to use it, nor do you use any loops to decrease the force of wires and increase the range of wire action. Why is that, and what is your alternative?
The answer is simply absolutely not. Keep in mind that because of 2 x 4 and 2 x 6 treatment — at least in the earlier stages of treatment — my patients experienced relatively light forces, since load-deflection rates involve significantly larger interbracket distances than full appliances. Also, keep in mind that load-deflection rates vary inversely to the cube of the length. Excessive force magnitudes were not a consideration in my practice, as I did not have to worry about an increase in vertical dimension due to excessive force magnitudes.
Over the past 30 years in orthodontics, so-called noncompliance bite correctors such as Herbst appliances, Forsus™, MPAs, Jasper Jumpers, and so on have had an enormous appeal. Have you ever used these appliances and, if not, why?
I understand the excitement so many orthodontists experience with Herbst appliances, Forsus, MPAs, Jasper Jumpers, etc. However, I am not one of them. I don’t mean that I think I am better or smarter. That is simply not the case. But because of my training under Dr. Burstone, I cannot help but look at the “entire mechanics” from the first day of treatment rather than deciding what appliance(s) I might choose “along the way.”
Most orthodontists rely on edgewise wires within the brackets to deliver maxillary incisor lingual root torque, but is this the most efficient or even the most desirable way of torquing anterior teeth?
Many orthodontists have asked me why I don’t use rectangular wire to torque teeth. It is because of a number of things. First of all, I don’t like high force magnitudes. Labial or lingual torque of the incisor segment can produce tipped occlusal planes because of the balancing forces. Lingual root torque of the incisor segment, for example, if left for a sufficient period of time, can result in posterior open bites, possible canting of the occlusal plane, not to mention increases in anterior overbite. With round wire, there are various ways to incorporate intrusive forces that lie anterior to the Center of Resistance in the incisor segment while avoiding posterior eruption of teeth due to the relatively long interbracket distances to the posterior segments. Remember that with partial appliances – rather than full appliances – the vertical forces reduce significantly, not to mention that one-half of that force goes to each side.
Currently, one of the most emphasized features of orthodontic therapy is the mini-screws for osseous anchorage. Did you ever make these a part of your armamentarium and, if not, why?
I have never used miniscrews for osseous anchorage because with partial appliances and round stainless steel wire, I can use differential moments to create the needed anchorage.
Can you explain how you prepare patients for retention and how you retain them long term?
When it comes time to retain a patient, I typically removed all archwires for a minimum of 6 weeks to check on stability. I frequently did this during treatment as well in order to predict the degree of retention one might expect, if any. Very often retention was not indicated although I usually provided nighttime retainers with the explanation that for many individuals, some mandibular crowding tends to develop with time — with or without orthodontic treatment. Retainers, when provided, are worn day and night for 6 weeks, then night only (usually up to 6 months), and then “try-in only each night” for the rest of their lives!
Why the latter? Somewhere liability must be transferred. I didn’t want any patients coming to my office 10 years later and saying they lost their retainer “several years ago.” Frankly, I really never had a problem with this approach, although I give credit to the partial appliances that, for the most part, preserved the normal position of teeth and therefore served as references for the correct position of the malposed teeth, thus increasing the odds of stability.
What advice would you offer young orthodontists just beginning their careers?
My strong advice, particularly for young orthodontists, is to become absolutely glued to cause/effect relationships. Always mentally “see” the entire force system associated with whatever tooth movement you attempt. If you are only rotating a bicuspid, do not allow yourself to simply “view” the moment required. Learn to always visualize the entire force system, as there will be other teeth affected. If you fail to make this approach, I can assure you that you will be making unnecessary orthodontic purchases throughout your career. An understanding of fundamental mechanics will help you avoid buying what you shouldn’t need.