JCO Interviews Dr. Robert Shaye on Functional Appliances

DR. GOTTLIEB Bob, you have had the advantage of training and experience in functional appliances in Europe.

DR. SHAYE Yes, I lived in Europe for seven years, three of those as a general dentist, at which time I had many opportunities to observe patients treated by German orthodontists and general dentists. The most productive period was the four years I spent at the University of Zurich with a man whom I consider my first inspiration in orthodontics, Professor Rudolph Hotz. When I went to Zurich in 1967, Hotz had been working with functional appliances for more than 30 years. He had studied with Andresen in the early '30s, prior to the publication of the first Andresen-Haupl book in 1936. He was very meticulous in his record-keeping. He had very carefully documented his cases with photographs and cephalometrics, and kept long-term records. I was able to study this material and occasionally examine the patients themselves many years after treatment had ended. I learned removable appliances and functional appliances before I learned about fixed appliances. Functional appliances, of course, are only one type of removable appliance. The others are considered "active" plates. A.M. Schwartz of Vienna was instrumental in their development, and Hotz had also studied with him.

DR. GOTTLIEB What did you see clinically in Hotz's patients who came back years after treatment?

DR. SHAYE In the Zurich cases, as well as our cases at LSU, there is no doubt that when the appliances work the relapse tendency is minimal. Relapse can be traced to tooth movement rather than skeletal change. For example, post-treatment increase in overjet may occur. This can usually be shown cephalometrically as an uprighting of lower incisors and/or a flaring of upper incisors, often related to an uncorrected problem in lip activity. A long-term study on activators by Pancherz supports this observation.

DR. GOTTLIEB No dual bites?

DR. SHAYE One thing that Hotz taught me was that you always have to test for the dual bite. You have to try to manipulate the mandible back every time the patient comes in, because many patients will posture the mandible forward. In fact, that's the initial response to our treatment. I call it the "phantom activator phenomenon". But you certainly can't call a case corrected or successful if the mandible can still be pushed back to the Class II position at the termination of treatment. Dual bite or Sunday bite cases are failures.

DR. GOTTLIEB Do you see dual bite in patients who you think cooperated, as well as in those you think didn't?

DR. SHAYE In general, this appears to be a problem in postpubertal females, and this would be a caveat that I would have for people who use functional appliances. Physiologically, this agrees with the observation that after menarche, toward the end of puberty, the female growth rate drops precipitously.

DR. GOTTLIEB Where did the term "activator" come from?

DR. SHAYE The original Andresen activator was a loose fitting appliance. In fact, Andresen and Haupl felt that in order for the appliance to work it had to be loose fitting, so that when the mouth opened the appliance would drop down and cause the patient to reflexively close against the appliance to reposition it. They felt that this constant repositioning of the mandible was critical to the changes they desired. They felt that this "activated" the musculature and the blood supply,eliciting favorable skeletodental changes.

DR. GOTTLIEB What are the differences between the Andresen-Haupl activator and today's activator?

DR. SHAYE One of the problems I find today when I speak of activators is that many people think, "That's an old-fashioned appliance-- that's Andresen's appliance". Activators, physically and conceptually, differ throughout the world. If you stick to Andresen's and Haupl's definition of an activator and the activation of the musculature, all functional appliances are activators of a type, from Frankel's function regulator to the bionator and back to the original monobloc. Andresen'sactivator bears some resemblance to the type of appliance that we use or Herren uses or Harvold uses, but these modern derivatives have evolved and been modified. For example, the original activator was toothborne in both arches. The teeth contacted facets ground into the activator, which helped guide the upper teeth posteriorly and the lower teeth anteriorly. The activator material (vulcanite) would contact the lingual of the whole lower incisor area. Many European orthodontists are still using a close approximation of the original Andresen activator.

DR. GOTTLIEB A criticism of the results of Class II cases treated with such an appliance is that, quite often, the lower incisors would tip forward.

DR. SHAYE It stands to reason that, if you have a Class II malocclusion for which you construct an appliance that protrudes the mandible, and the appliance contacts the lingual of the lower incisors, then as the muscles pull the mandible back toward centric relation position, incisor flaring easily occurs. Even the labial extension of acrylic over the incisors, which is constructed on the bionator or the Andresen type of activator, is often not enough to prevent this labial tipping of the lower front teeth. In the appliance which we have developed, the plastic has been relieved from the lower teeth. Only the deep lingual flanges maintain the mandible in the forward position. This eliminates the possibility of the appliance forcing the lower teeth anteriorly, thereby amplifying the potential skeletal response.

Also, as I said before, Andresen and Haupl felt that the appliance had to be loose fitting to have its effect, so that when the mouth was opened the appliance would drop down and the patient would be constantly repositioning his mandible. A significant problem with functional appliances, at least during the initial weeks of treatment, is preventing appliance dislodgment during sleep. Most

children sleep with their mouths at least partially open, and the appliance is easily lost. A simple solution to this problem by us and others, the dogma of Andresen and Haupl notwithstanding, was to clasp the appliance to the upper molars. Later in treatment, when the patient has accommodated to the appliance, the clasps can be removed to allow for molar expansion if necessary.

DR. GOTTLIEB How does the tissue react to the lingual flanges?

DR. SHAYE There is really no significant soft tissue problem. Of course, a large rough area of plastic can cause some irritation, but this is easily remedied. I feel the main reason that there are very few soft tissue problems in the flange area is because the patient simply moves away from an uncomfortable area.

The LSU Activator

DR. SHAYE We make them as deep as possible. In other words, we'd rather overextend them and have to grind away a bit when we deliver the appliance, rather than make them too short. The longer the flange, the better the chance that the patient will be able to maintain the mandible in the appliance while sleeping at night.

DR. GOTTLIEB Does shortening of flanges on your appliance-- which a lot of American orthodontists seem to do-- change the appliance enough to affect its ability to do what you expect it to do?

DR. SHAYE In our appliance, the lingual flanges are of paramount importance. They maintain the mandible in the forward position. As they become shorter the effectiveness of the appliance diminishes. This also relates to the vertical dimension of the appliance. Our type of activator has a relatively high vertical dimension. Routinely we construct it with 8-12mm of plastic between the incisal edges of the teeth.

The long flanges and high vertical help to keep the mandible engaged in the appliance while the child sleeps. We consider the wearing of the appliance during sleep to be of the utmost importance. The interrelationship between sleep and growth has been well documented in human and animal studies. In fact, we do not ask our patients to wear the appliance at all during the day. The reason we can afford to use a bulky appliance is that we don't require daytime wear-- it is basically a nocturnal device. As we discussed previously, we do have a diurnal effect in the phantom activator phenomenon.

Appliances such as the bionator, Bimler, Frankel, kinetor, etc., which can be considered skeletonized derivatives of the activator, require full-time wear to be effective. These are appliances which have relatively low vertical dimensions and short lingual flanges. When patients sleep with these appliances in place, the mandible can easily disengage, dropping downward and backward. The mandible loses its protruded position. This is one explanation of why such devices are not as effective during sleep and require full-time wear.

On the other hand, there is evidence to show that if the vertical dimension is excessively high, the growth response can be inhibited.

DR. GOTTLIEB One of the points of controversy in functional jaw orthopedics is your advocacy of part-time wearing of the LSU activator, while other appliances are required to be worn full-time.

DR. SHAYE That is a problem that Alex Petrovic and I have discussed over the years. There is experimental evidence which suggests that the most important time in a 24-hour period for wearing appliances (orthodontic as well as orthopedic) may well be during sleep. It's well known that the peak level of growth hormone in the human is during sleep-- more specifically during slow-wave sleep. Through the studies of Petrovic and his associates, we know that growth hormone amplifies the effect of the functional appliance. In other words, if you have a functional appliance in one animal and you have a functional appliance plus increased growth hormone in another, you'll get significantly more growth with the functional appliance plus the growth hormone than with the functional appliance alone.

Studies on human alveolar bone have demonstrated that alveolar bone turnover rates are significantly higher at night than during the day, and that tooth movement rates are correlated to turnover rates. This suggests that the orthodontic movement of teeth may be more effective at night than during the day. Petrovic, Oudet, and I recently published a study in a German orthodontic journal indicating that, when experimental animals wore a simulated LSU activator 12 hours per day, the mandibular growth rate and amount were higher than when the appliance was worn 18 or 22.5 hours. Clinically, we find that our patients who wear their activators only at night respond at least as well and as fast to treatment as others wearing different types of functional appliances full-time.

DR. GOTTLIEB Where does function come in? We used to think that, as you said, it was the catching of that loose appliance that made it a functional appliance. Here you're talking about a slack jaw during sleep.

DR. SHAYE That's a good point, because the term "function" is bandied about throughout dentistry, not only orthodontics-- everyone talks about function. What does function mean? When we discuss functional jaw orthopedics, my interpretation of the term is that you are altering the functioning of various muscles to effect an ultimate change in the jaw relationship. Muscles have one primary function, and that is to contract. Placing a functional appliance affects many facial muscles. We emphasize the role of the lateral pterygoid, since it is important in the protrusion of the mandible and is intimately involved with the temporomandibular joint. There is experimental evidence to show that the functional appliance decreases the growth rate of this muscle, implying that as treatment progresses it will be shorter than it would have been without appliance therapy,

thus altering the position of the mandible in an anterior direction.

DR. GOTTLIEB Is this positioning not just an exercise?

DR. SHAYE The word "exercise" implies voluntary activity. For years clinicians have noticed that patients who wear activators posture their mandibles forward with no conscious effort, even during the daytime when the appliance is not worn. This is what I have referred to as the "phantom activator phenomenon", and it is an early response to treatment. Through Petrovic's experiments on the rats, we've seen that when the LSU activator is compared to other functional appliances (hyperpropulsor, Frankel), a more rapid decrease in the growth rate of the external pterygoid muscle occurs. At the end of a four-week experiment, the animals with appliances had significantly shorter muscles than the controls. If we extrapolate to humans, this may be at least a partial explanation of the phantom activator phenomenon. I should emphasize that this is an early response to treatment. The mandible can still be forced back toward the Class II position. As treatment progresses, however, the mandible increases in length and can no longer be retruded to Class II.

DR. GOTTLIEB If you use a bite plane and Class II elastics, are you doing the same thing?

DR. SHAYE Well, in a way, you are. The work of Petrovic has shown that Class II elastics can also elicit a condylar response. The weakness of Class II elastics, however, is the fact that they are toothborne. We're trying to emphasize the skeletal potential of the appliance and de-emphasize the dental effect.

DR. GOTTLIEB Is the interdigitation of the molars assisting the skeletal repositioning? Does a dental change affect the jaw change?

DR. SHAYE That's the idea behind using the functional appliance, as we use it, with no lower tooth contact. There's no way to drag the lower teeth forward, whether they are molars or incisors, because the only parts of the activator holding the mandible forward are the long lingual flanges, which don't contact the teeth or the alveolus. Years ago this design feature led me to think that there's more to Class II correction than a pure dentoalveolar response. I'm certainly not saying that there's no dentoalveolar input to this type of appliance therapy, but I believe-- again, based on our clinical findings as well as the animal experimentation-- that there's a significant skeletal effect. Almost all the functional appliances have a labial bow and do contact the upper teeth, so I think there's definitely a dentoalveolar effect in the upper arch. But in the type of appliance we use or in the Frankel appliance, we have perhaps not negated, but lessened, the dental effect. Our LSU activator study supports our contention that there is an increase in the growth rate and amount in the mandible, and the increase can be clinically significant.

DR. GOTTLIEB You've been talking about your work with Petrovic. The relationship you have with him has got to be the most interesting one in functional appliances.

DR. SHAYE I like to think that it is an interaction between the clinically oriented research scientist and the scientifically oriented clinician. I have always been a skeptic, but I became a much more critical thinker through my association with Petrovic. His research is conducted under very rigorous, experimental conditions, and both he and I try our best to present our material based upon

experimental findings. Of course, clinical experience is also important to the advancement of our knowledge. Insights derived from clinical experience act to provoke scientific investigation. Such insights become the basis for working hypotheses, which can be tested experimentally.

DR. GOTTLIEB How long have you been collaborating?

DR. SHAYE We have been working together since about 1976. Alex is a visiting professor at LSU. He's a very keen observer and a good listener, and he would try to elicit ideas and questions fromme about the mechanism of action underlying functional appliances.

To give you an example, one of the things that we did jointly, based upon clinical observations, was to investigate whether you would obtain an increased growth rate of the condylar cartilage if you brought the mandible farther forward. In other words, if you brought the mandible forward 2mm, would there be less of a skeletal response than if you brought the mandible forward 4mm? The hypothesis would be something like this: increased protrusion of the mandible results in an increased growth rate of the condylar cartilage. In Zurich, I had learned to take construction bites a few millimeters anterior to and open from postural rest position. As I gained more experience, I noticed that when the mandible was brought farther forward the case appeared to respond faster. By 1972, when I started at LSU, we routinely went to almost full protrusive position in our construction bites. An experiment was designed to test the "degree of protrusion" hypothesis. Varying degrees of mandibular protrusion were established in several groups of young rats through the use of a functional appliance, the "hyperpropulsor". The results were unequivocal. By measuring the mandibles themselves, and through the use of radioautography, it was shown that increased protrusion elicited increased growth of the rat mandibles.

DR. GOTTLIEB What is radioautography?

DR. SHAYE It is a laboratory technique whereby cells about to undergo mitosis can be radioactively labelled. This technique allows for a quantitative measurement of growth by counting the numbers of cells synthesizing DNA.

DR. GOTTLIEB When do you decide that this becomes clinically significant?

DR. SHAYE We have done parallel studies on our clinical patients-- not with radioautography, obviously. We measured how much the patient's jaw grew before treatment and compared that to how the jaw grew during treatment. We feel that the increased amount of growth we saw during the treatment period has clinical significance. Petrovic's results in the rats are similar to the work that'sbeen done in monkeys. In fact, looking at a sample of condylar cartilage under the microscope-- whether from a rat, a monkey, or a human-- a histologist would be hard put to tell which was which. If you read the work of Petrovic, McNamara, and others, you'd also find that the condylar response to functional appliances is similar. With such similar responses in rat and monkey,considering that these animals are farther apart on the phylogenetic scale than monkey and man, it wouldn't be illogical to assume that what you see happening in a rat and a monkey also could happen in a man. In our human material our approach is limited to cephalometrics, and we have seen similar findings in the increase of mandibular length through the use of our appliances.

DR. GOTTLIEB Getting back to the clinical aspects of your appliance, you were discussing what distinguishes it from other kinds of functional appliances.

DR. SHAYE I think we covered the clasps and the fact that the jaw is held forward not by the teeth, but by the long flanges, which are tissue-borne. Also, as opposed to the Frankel appliance or to the bionator, we bring the mandible almost to a full protrusive position, because we feel that you get a higher growth rate the farther forward you bring the mandible. Another thing I haven't talked about is the periodic forward repositioning, which I think is very important.

DR. GOTTLIEB If you come all the way forward in your bite registration to start with, what additional forward repositioning are you talking about?

DR. SHAYE As strange as it sounds, if the mandible is brought to full protrusive in the LSU activator, after the patient wears the appliance for, let's say, three months, he can protrude the mandible several millimeters beyond his original maximal protrusive position. Another way to look at it is this: On the day of appliance delivery there is obvious strain as the patient places his mandible in the protruded position. Two or three months later, in cooperative patients, the muscular effort in wearing the activator is significantly decreased. This is a result of muscular change and an increase in the length of the mandible.

The Reactivator

This ties in with our thoughts on "periodic forward repositioning", which means that after two to four months of treatment the mandible is caused to be positioned farther forward by the appliance. By doing this, we increase the rate of change from Class II to Class I. This clinical observation is again supported by experimental evidence. Petrovic has demonstrated that periodic forward repositioning does result in a greater increase in mandibular length than is seen in animals that have not undergone this procedure.

DR. GOTTLIEB For how many months do you have the patients wear the appliance?

DR. SHAYE Instead of having the patients wear the functional appliance for several years as they do in Europe, we usually have our patients wear them for 12 to 18 months. At that point we usually have enough improvement to go to the fixed appliance stage. Occasionally with just the activator phase we can finish the case, but it's very seldom that we just have one phase of treatment; 99 times out of 100 we'll move on to a second phase, with a fixed appliance for about a year.

DR. GOTTLIEB Is it always the patient's fault if you don't get the response you want?

DR. SHAYE I don't like to be dogmatic, but I do say this: If the patient has been wearing the appliance-- I don't care if it's an LSU activator or a Frankel or whatever-- for four months and you see no improvement in the intermaxillary relationship, there's something wrong. I'm not saying you have to see complete correction, but you should see some movement toward the Class I. Usually the problem is that the patient just hasn't been wearing the appliance enough. In some cases, though, it's not the patient's fault; we've constructed the appliance incorrectly. Perhaps we haven't made the flanges long enough, or we have not built sufficient vertical dimension into the appliance, so when the patient goes to sleep at night the mandible falls out of the appliance and drops back.

Usually, with periodic forward repositioning, in 12 to 18 months we're finished with the first phase of treatment. We find that with our activator we seem, at least initially, to get a faster response than with other functional appliances. This has been demonstrated on rats, comparing the LSU activator to the function regulator and the bionator. This may be due to positioning the mandible farther forward with our appliance than you would with the others. I emphasize that this is the initial response.

DR. GOTTLIEB Do you have to make a new appliance for every reactivation?

DR. SHAYE By "reactivation" you are referring to periodic forward repositioning. There are several ways this can be accomplished: 1. A new appliance can be fabricated with the mandible in a more advanced position. 2. The old appliance can be relined. 3. The original appliance can be sectioned horizontally and rejoined, with the mandibular half advanced. 4. The latest and easiest method is to use an appliance with the possibility for reactivation built in. We call this appliance the "Reactivator". It is essentially an old German design which has been modified by a former student of mine, Dr. David Hoffman. A screw is incorporated into the activator, which, when turned, slides the bottom half forward, resulting in a more anteriorly positioned mandible. The Reactivator is available through Professional Positioners, Inc.

DR. GOTTLIEB And what is your signal to reactivate?

DR. SHAYE After the patient has been in treatment for a few months, we ask him to protrude his mandible as far as possible, with the activator in place. If he can position the jaw 2-3mm beyond the original activator, it is time to reactivate.

DR. GOTTLIEB What happens when you put an expansion screw in these appliances? Does it change the nature of the appliance to do two things at once? Does it make it more toothborne?

DR. SHAYE Only in the upper. It doesn't affect its being toothborne in the lower, because in the lower we have all the plastic cleared from the teeth. But in virtually all Class II division 1 cases, some upper transverse expansion is necessary so the arches will be coordinated in the Class I position. In the classic approach to activator therapy, you grind Inclined planes into the plastic adjacent to the posterior teeth, which allows them to erupt buccally. This can result in several millimeters of expansion. If you feel you need more than that amount, an expansion screw can be built into the appliance. On the average, I usually say that without an expansion screw you're going to get about 4 or 5mm of expansion between the upper molars and about half that amount between the upper canines. If you put an expansion screw in, over a period of time you can get a few

millimeters more.

DR. GOTTLIEB Those who open the suture say they're moving the two sides bodily out and are therefore getting a more stable position. Do you get tipping of the teeth with the screw in an activator, or do you get bodily movement?

DR. SHAYE I don't feel that you get any more tipping with this kind of expansion than you do with a fast expansion. Don't forget, the activator is not only toothborne in the upper, but it also has good palatal support, especially in those patients who have a high palatal vault. We expand very slowly at the rate of one-quarter turn every 15 days.

DR. GOTTLIEB Do you think you grow mandibles?

DR. SHAYE in a word, yes. I think that the activator or some other functional appliances do elicit a significant skeletal effect upon the mandible. Let me make a point here. Most of the controversy about functional orthopedics revolves around your question. The question itself is primarily of academic interest. The fact of the matter is that functional appliances work. They are clinically effective. Whether they do or do not stimulate the growth of the mandible will remain a subject of debate for years to come.

DR. GOTTLIEB And is this growth proportionate to the growth that's occurring in the rest of the area?

DR. SHAYE Some investigators maintain that the increased growth you see when you use a functional appliance is dependent upon an overall growth spurt. I don't agree. Petrovic and his co-workers have tested many appliances, from the hyperpropulsor to the LSU activator to the Frankel appliance. They have shown that the response in the condylar cartilage is independent of the growth in the long-bone growth cartilages. In other words, the overall growth of the animal doesn't necessarily relate directly to growth in specific parts of the body. We have preliminary data in humans that suggest there is little interrelation between increase in mandibular length and increase in statural height.

DR. GOTTLIEB Those who do not believe you can grow mandibles beyond what they would normally be growing say that these are good growers and, while they grew more in that period, everything grew more in that period. Do you have any evidence on humans that shows a differential increase in mandibular growth with functional appliances?

DR. SHAYE In a clinical investigation, we evaluated the effect of the activator on 34 patients. When cephalometric tracings taken at treatment commencement were superimposed over tracings taken after approximately six months of treatment, virtually all the cases exhibited little facial change, except for the mandibles, which increased in length, on the average, 3.5mm.

DR. GOTTLIEB Can you predict which person will show a differential increase and which person will not?

DR. SHAYE This question is not easy to answer. We are limited by a major weakness inherent to clinical studies-- the cooperation factor. One relevant statement I will make concerning prediction

is this: the patient with the best chance for a favorable mandibular response is that patient with the most favorable mandibular morphology. Using Bjork's terminology, this would be the child with the potential for an anterior rotational type of growth.

DR. GOTTLIEB An additional question is raised whether, if you had two identical people and one grew more during the period, would the other fellow catch up? You may have artificially created a period of greater activity that does not give you a differential for life over what would have happened anyway in that individual.

DR. SHAYE I think that question would be extremely difficult to answer for humans because of a major problem with controls. The heterogeneity of the human population would, in my opinion, flaw a study to determine the effect of a functional appliance on the ultimate length of the mandible, if a supposedly "matched" set of controls were used for comparison. Cavalli-Sforza and his associates at Stanford concluded that genetic differences between "racial groups" account for only 10 percent of the total variation in the human gene pool. Most genetic variations, about 84 percent, arise from differences between individuals of the same race.

Petrovic has also investigated this problem of the final length of the mandible. In Sprague Dawley rats, a strain with a high degree of genetic similarity, the experimental findings indicate that the mandibles of animals treated with a functional appliance remain significantly longer than those of controls into adulthood. This discovery, in my opinion, is extremely important to our understanding of the biological effects of functional appliances. A point which bears emphasis is this: When we speak of increases in mandibular length through appliance therapy, we are discussing relatively small amounts-- perhaps 10 to 15 percent, not 50 or 60 percent. A possible increase of even 10 percent in the length of the human mandible by means of therapy, however, would have great clinical import.

DR. GOTTLIEB Apart from changes in the condylar area, is there that much change in the forward position of the mandible?

DR. SHAYE Recent studies concerning the effect of functional appliances on the mandible have concentrated on the temporomandibular joint. This includes not only the condyle, but also the disk, fossa, and retrodiskal pad. There is also evidence to show that wear of a functional appliance affects bone remodeling throughout the mandible. In our studies, we are concerned with measurements of mandibular length. Our operational definition of mandibular length in the human is the longest distance between the chin and the condyle. In rats it is the distance between the mental foramen and the condyle. The dynamics of condylar growth, therefore, is an important area for investigation.

Condylar growth does relate to changes in other parts of the mandible through what Enlow terms "area relocation". As development proceeds, part of the condyle is transformed to ramus, and part of the ramus to corpus. If you compare the rate of bone growth to cartilage growth, the difference is striking. Bone has been estimated to grow subperiostally at the rate of 7.5-10 microns per day. Cartilage, on the other hand, has been estimated to grow from 50-300 microns per day. If we use the figure of 100 microns per day, in 10 days one millimeter of condyle growth could be achieved. In short-term studies on condylar cartilage growth, differences due to treatment are relatively easy to detect.

DR. GOTTLIEB I think we're getting back to the argument that some people make-- that this growth ultimately happens anyway.

DR. SHAYE I have already touched on the animal experiments which showed that increase in mandibular length due to functional appliance therapy remained in the adult. An initial response to the functional appliance appears to be a more posterior orientation of the bone trabeculae in the condyle. This produces an opening of the angle between the condyle and the mandibular base (Stutzmann's angle). As treatment proceeds, this angle closes and no longer differs from the controls, but the mandible is longer.

The ultimate constancy of Stutzmann's angle, coupled with an increase in mandibular length, suggests that if morphogenetic predetermination predominates in growth (as some claim), it is in the form or shape of the bone, not in its size. This is supported by observations on monozygotic adult twins reared apart from each other. Although the shape of their long bones was similar, one of the twins was several inches taller than the other.

DR. GOTTLIEB Is there an application for functional appliances in adults?

DR. SHAYE Some clinicians advocate the use of functional appliances in adults. Our contention is that attempting to cause growth in an individual who has ceased to grow is physiologically untenable. It is true that viable cartilage cells have been demonstrated in condyles of humans of advanced age. These are cells which are necessary for tissue maintenance and turnover. However,when we speak of amplifying growth through appliance therapy, we must have enough cells to yield at least a detectable response.

Adultness means fully grown. Some studies on "young adults" have produced variable results relative to condylar growth stimulation. This is not surprising, since some young adults-- whether rat, monkey, or man, and depending on the individual's state of maturation-- could still be capable of some condylar response to a functional appliance. It should be emphasized that the attainment of sexual maturity does not mean that growth has ceased. A non-growth response to therapy could be due to a pure positional change of the mandible. You could compare this to the phantom activator phenomenon with no subsequent condylar growth.

Another non-growth response could be a pure dentoalveolar change where the upper teeth are moved back and the lower are pushed forward. Removable appliances can be designed to perform these actions. In my opinion, fixed appliances are better suited to dentoalveolar movements. Petrovic has demonstrated that neither the functional appliances he has tested nor Class II elastics elicit an increase in mandibular length when used in the adult.

DR. GOTTLIEB Is stimulation of increase in mandibular length necessary for the functional appliance to make some kind of change in the jaw relationship?

DR. SHAYE Not necessarily. But if I want dentoalveolar change, why do I have to use a functional appliance? I can do that much more effectively and efficiently with the fixed appliance. The reason I'm using a functional appliance is I'm trying to maximize the skeletal growth potential and minimize the dentoalveolar change.

DR. GOTTLIEB How about the case where you don't get as much measurable increase in

mandibular length as you might in some other cases? Do you not get a favorable change in the jaw relationship, in the profile, in the lip posture, and in the molar relationship?

DR. SHAYE Response to treatment is individualized. Factors which may influence the degree of skeletal change are cooperation, proximity to puberty and its hormonal ramifications, and the genetic potential for favorable growth. Patients in whom a positive interaction of these factors takes place should respond well, since the appliance is amplifying existing growth. More simply stated: good growers yield good results.

DR. GOTTLIEB How much of a headgear effect is there with the LSU activator?

DR. SHAYE There is a headgear effect in most functional appliances, and initially more so in the LSU activator, since the pronounced forward positioning is coupled with a reciprocal posterior pressure against the maxilla. This distalizing effect on the maxillary arch decreases as treatment progresses. To sustain and increase the effect we sometimes use a headgear coupled with the activator, especially in cases where, through our cephalometric analysis, we might feel that there is more maxillary component to the malocclusion than to the usual Class II division 1 malocclusion. We also use the headgear-activator combination in a child who's nearing the end of puberty-- a female, for example, who exhibits secondary sex characteristics, but has not yet achieved menarche. In such a case, we'll try to get as much maxillary dental movement as we possibly can, because we feel that there may not be sufficient growth left for the mandibular skeletal effect to correct the sagittal discrepancy.

DR. GOTTLIEB What are the best cases for functional appliance treatment?

DR. SHAYE I think the functional appliance finds its optimal application in Class II mixed dentition treatment. Most Class I and Class III cases can be treated more efficiently with active appliances such as headgears, face masks, expansion devices, etc. In general, my thoughts on indications for treatment are rather simple: Class II malocclusion in a child with a good potential for growth; in other words, more the anterior rotator as opposed to the severe posterior rotator. In a 9-year-old Class II mixed dentition case, you have the option of placing a headgear or saying, "Come back when the permanent teeth are in". The functional appliance is another alternative.

DR. GOTTLIEB Of course, we have edgewise practitioners who will say, "I can wait until the patient is older than mixed dentition, treat them with a fixed appliance, get whatever growth they're going to give me, get the dentoalveolar change, and wind up in the same place-- but I haven't subjected them to a functional appliance".

DR. SHAYE I agree with them. If I have a patient who's, let's say, a 14-year-old male, who has a favorable growth potential, I can also get a nice result with my Class II elastics and fixed appliance. If, however, I treat these patients at a younger age, with a functional appliance, by the time they are in the permanent dentition I can already be in Class I and thereby shorten the fixed appliance phase of treatment significantly. I can be in fixed appliances for 6 to 12 months instead of 18 to 24 months. I feel that's an advantage.

DR. GOTTLIEB Would you use a functional appliance on somebody who was younger than age 8?

DR. SHAYE Theoretically, you could use a functional appliance on an infant. In fact, Hotz treated very young children with a modified oral screen. The appliance was constructed with the mandible slightly advanced to get an activator effect. In extreme cases we might attempt treatment in very young children, age 4 to 7. But in-the routine Class II case, I find that if I wait until the late mixed dentition, let's say 9 or 10, there is still plenty of time to correct the problem. And I can usually communicate better with the older child than I can with the very young one. Another point is this: I don't like a long hiatus between my phases of treatment. If I start at 6 and correct him by 7, then I've got to wait perhaps three or four years until I finally see whether he's going to need a second phase of treatment. Then I have to start treatment over again. I like to blend from one phase to the next. If I begin at age 9 or 10, as treatment progresses the primary teeth are shedding. When this phase ends there are sufficient permanent teeth to begin fixed therapy.

DR. GOTTLIEB When you treat division 2, do you use fixed appliances to align the anterior teeth first?

DR. SHAYE No. As a matter of fact, I think some of the best responding cases to functional appliances are of the Class II division 2 variety. These cases are anterior rotators, the good growers, the forward growers, depending on whose terminology you use. I don't pretreat them. With the activator we insert protrusion springs into the acrylic behind the upper central incisors. These springs and the labial bow can then be adjusted to align the anteriors.

DR. GOTTLIEB And that pushing forward against resistance doesn't interfere with the activator effect?

DR. SHAYE No. As the protrusion springs act on the upper central incisors, the mandible is positioned downward and forward to elicit mandibular growth.

DR. GOTTLIEB Do you assign specific types of cases to specific types of appliances? Is it more appropriate to use a bionator on a certain case and a Frankel on another case and an activator on another case?

DR. SHAYE We employ functional appliances only in Class II malocclusions. The devices you mention all appear to be effective in such cases. I dislike comparing or rating one appliance against another. It is very difficult to be objective about such comparisons. Clinicians will use an appliance which is effective and easy to manipulate. My personal bias favors the activator. It is simple to construct, inexpensive, resistant to breakage, and has to be worn only at night. From the child'spoint of view, some prefer the activator, some the Frankel, some the bionator. Most prefer no appliance at all.

DR. GOTTLIEB Of the patients that you select for treatment, what percentage would you expect to be cooperative?

DR. SHAYE I still agree with the figures that my mentor taught me, that is, out of 10 patients, five to six will readily wear the appliance. With some coaxing, two or three more will take to the appliance. But the last one or two are not going to wear the activator, the Frankel, headgear-- they're not going to cooperate at all. Much depends on the motivational skills of the operator. A

negative attitude on the part of the dentist will be transmitted to the patient. A positive attitude will produce more positive results.

DR. GOTTLIEB Of the children who wear it reasonably well, what percentage of success do you have, if you measure success by achieving a Class I molar relationship and a more orthognathic profile?

DR. SHAYE If you follow the indications, and if the patient wears the appliance correctly, I would have to say that you get improvement in virtually 100 percent of the cases. That's my experience. As I said before, if a patient shows no improvement after three or four months, we can trace it back to the patient either not wearing the appliance enough or not having the mandible engaged in the appliance while he's sleeping.

DR. GOTTLIEB Is there a difference between the word "improvement" and accomplishment of your goals? Do you really achieve all the things that you want to achieve with it?

DR. SHAYE No, I can't say that in every full cusp Class II malocclusion you're going to go to a completely socked-in Class I occlusion-- at least not in the short 12 to 18 months that we have the patients wear the appliance. I hate to sound as though I'm evading the question, but remember that we feel the late mixed dentition period is optimal for the functional appliance. As this phase is ending, most of the permanent teeth have emerged and fixed therapy can begin. At times, after 12 or 18 months, we've gone from the Class II to perhaps not a perfect Class I. At this point, particularly if there are severe tooth malpositions, we will place the fixed appliance and complete the Class II correction with headgear and Class II elastics. In other words, at times we won't allow the functional appliance to achieve its full potential.

DR. GOTTLIEB What do you think is the future of functional appliances in the United States?

DR. SHAYE I believe that there is an important but limited role for functional appliances in orthodontic practice. It disturbs me to hear and read of the exaggerated claims and panacean cures attributed to this method of treatment.

In 1939, Hotz, in the Swiss Dental Journal, described the emotionally charged atmosphere at the annual meeting of the European Orthodontic Society in Bonn, Germany. The controversy centered on the recently introduced functional jaw orthopedics. He noted that the extremists among the proponents of this new concept were those with the least experience. He concluded by warning that it would be unfortunate if the positive aspects of the functional appliance were forgotten when the realization dawned that its effectiveness had been overstated and oversold.

DR. GOTTLIEB Thank you very much, Bob, for sharing your unique insights into functional appliances.