JCO Interviews Dr. Rolf Behrents on Adult Craniofacial Growth

DR. WHITE Your two books regarding the aging craniofacial skeleton are causing orthodontists to re-evaluate their traditional views about the adult patient. Did you expect that would happen when you started the study?

DR. BEHRENTS We thought we might be able to document and describe some consistent minor morphological alterations in localized areas. In essence, our expectations were low because it was believed that growth more or less ceased in the adult.

DR. WHITE Instead, you found changes were more general and greater than you expected?

DR. BEHRENTS Yes. We found that craniofacial growth did not stop in young adulthood, but was a continuous process even into later ages. The units of change were smaller, of course, but change in the craniofacial skeleton became the operational concept rather than termination of the process.

DR. WHITE Your study examined patients who had participated in the Bolton study many years ago.

DR. BEHRENTS I tried to locate former participants who had been followed into young adulthood in the Bolton Study, and recalled them to the Bolton-Brush Growth Study Center for another examination, which included obtaining current cephalograms.

DR. WHITE And you compared them to those in the Bolton Study.

DR. BEHRENTS Yes. In the late '20s new study opportunities became available with the advent of clinical x-rays and, most important, the cephalostat developed by B. Holly Broadbent, Sr. The Bolton study gathered longitudinal data on participants from 1928 through the 1960s, and in some cases into the 1970s.

DR. WHITE How was the original study sample selected?

DR. BEHRENTS They were selected on the basis that they were well, normal children, and that they would be available to come in for examinations on a regular basis. Nearly 6,000 children participated.

DR. WHITE Up to what age were they followed in the Bolton Study?

DR. BEHRENTS Some were followed well into their 30s or beyond.

DR. WHITE With as wide an age range as there was originally and a study that began in 1928 and continued into the 1970s, your sample must have examined a wide range of older adults.

DR. BEHRENTS The ages ranged from the late teens into the 80s.

DR. WHITE How many of the original 6,000 participants were you able to find?

DR. BEHRENTS We were looking for orthodontically untreated individuals. Of the original 6,000 participants we were able to locate approximately 200 untreated individuals, and we ultimately examined 113. Most of them were still living in the Cleveland area.

DR. WHITE Did the recalled group have good dental health?

DR. BEHRENTS The group was very healthy dentally. They had very few missing teeth. In fact, excluding third molars, 90 of the 113 had intact dentitions.

DR. WHITE Since the original study was longitudinal, these people had more radiation than ordinary patients might have received. Did you see any ill effects in these patients?

DR. BEHRENTS By today's standards, these individuals were exposed to a considerable amount of radiation, and we will be following up that aspect of the study. But let me emphasize that the group remains generally healthy and disease free, and this could have an impact on our thinking about radiation sensitivity. It is a serious question, however, and I can only give you an impression at this time.

DR. WHITE It would be interesting to know how many of this sample had experienced TMJ problems.

DR. BEHRENTS A few of them had apparently had painful episodes that disappeared without treatment, but only 4 percent of the sample had any TMJ symptoms.

DR. WHITE Orthodontists tend to implicate occlusion as a major cause of TMJ problems. Were the occlusions in the sample better then "normal"?

DR. BEHRENTS There was a range of malocclusion, although most of the sample were Class I. However, none of the sample was what you would call textbook normal, and almost the entire sample had malocclusions with a substantial need for treatment.

DR. WHITE Were the maloccusions and interferences more severe in the 4% who had TMJ symptoms?

DR. BEHRENTS Not as a general rule.

DR. WHITE Do you draw any conclusions from that?

DR. BEHRENTS I would not be quick to adjust occlusions prophylactically with the idea of preventing TMJ problems.

DR. WHITE If growth was the rule rather than the exception in this group, did this affect the eruption of third molars?

DR. BEHRENTS It did for some. Some reported third molars erupting in their 30s and 40s, but some third molar positions worsened. It will be worth studying to see if conditions that favor later eruption can be identified early.

DR. WHITE Did you find any general differences in the growth of men and women?

DR. BEHRENTS Sexual dimorphism seemed easier to understand in this adult sample, as opposed to an adolescent group, because for the most part these people had "dimorphed"; they were more or less finished developing characteristics of "maleness" or "femaleness". Males, of course, were bigger to start with as adults, but they also grew more in later adulthood. Apart from size, male and female faces were different, and they grew differently. Males demonstrated a continuously decelerating curve of growth velocity. Females seemed to slow and then reaccelerate in their growth pattern. This seemed especially evident in their 20s and early 30s and may be related to other events in their lives, notably pregnancy. There is evidence to suggest that bone growth in pregnancy is a common occurrence, which seems to be seen in our study in the female craniofacial skeleton.

DR. WHITE Were there differences in the mandible between males and females?

DR. BEHRENTS The mandible increased in size in both males and females, but in the male the occlusal plane tended to flatten, the gonial angle became more acute, and-- with other dimensional changes-- the mandible appeared to continue on a downward and forward trajectory with a greater vertical component than during adolescence. The net effect was a tendency for a continued counterclockwise rotation of the mandible. In the female, more vertical change was evident, and the mandible appeared to be rotating clockwise.

DR. WHITE What do you make of that?

DR. BEHRENTS It might have a bearing on the long-term stability of treated cases. A treated Class II female might be more prone to relapse toward a Class II situation, and a treated Class III

male might be more prone to relapse to Class III.

DR. WHITE Were there differences in midfacial growth between males and females?

DR. BEHRENTS Males and females grew similarly in the midface. Most of the growth resulted in a vertical positional change, but there were horizontal dimensional increases as well.

DR. WHITE What was the net effect on the dentition?

DR. BEHRENTS With the substantial bony changes, one could easily expect that the dentition also adjusted, and this was the case.Uprighting of the upper incisors was very consistent in both sexes. The lower incisors showed a consistent inclination in the male, and a tendency for continued anterior inclination in the female.

DR. WHITE Did overbites deepen?

DR. BEHRENTS No, surprisingly, overbites did not change. This might be related to attrition of the anterior teeth, which was fairly generalized.

DR. WHITE Were there consistent changes in the soft tissues?

DR. BEHRENTS The changes seen in the soft tissue profile with age were more exaggerated than those seen in the skeleton, although the two seem to be related. The nose continues to grow, the chin is larger and located more inferiorly. The whole face appears longer and flatter.

DR. WHITE And you found growth changes in adults to be continual?

DR. BEHRENTS We kept restructuring our sample to test this. We took age spans from the sample that represented older and older age groups. We made several hundred linear and angular measurements in our study, and in these sub-groups-- even in the group past 40 years of age-- we found continued, significant changes.

DR. WHITE Will this continued growth make us rethink our conception of bimaxillary protrusion?

Untreated patient in childhood and adulthood. Child images printed in reverse. Profile view represents the right side of the face in both images. In the frontal view, the right side in the photo is the individual's left side in the adult and right side in the child. Note the similarity of

head posture even though there was more than 50 years between the sets of photographs. (From Behrents, R.G.: Growth in the Aging Craniofacial Skeleton , p. 86. Reprinted by permission.)

DR. BEHRENTS It might, because it would be reasonable to assume that individuals would appear less protrusive as they age, due to a number of factors. The maxillary incisors are continually uprighting during adulthood and with the continued growth of the nose, repositioning of the lips, and the vertical increases, one could easily envision that the adult would appear less protrusive over time.

DR. WHITE That might make us more conservative in our diagnosis of bimaxillary protrusion.

DR. BEHRENTS I would have to agree, and there are other instances in adolescent care in which our emphasis might have to be rethought. One example would be the nasolabial angle, which is of grave concern in the adolescent. One of the things that Mother Nature has in store for adolescents is that the nasolabial angle will correct itself to an extent if given enough time.

DR. WHITE How do you think continued growth is occurring in adults?

DR. BEHRENTS We know that remodeling is still going on, and this is growth. Some condylar growth may even be possible. Many of the supposedly closed facial sutures are still patent even into the later stages of life. The fact is that facial dimensions increase in adulthood, although less exuberantly than in adolescence. Explanations of why that occurs will not come so easily.

DR. WHITE What implications do you see in this study for orthodontic treatment?

DR. BEHRENTS I mentioned the possibility that continued growth differences in males and females might suggest a greater possibility of relapse of female Class II cases than male Class II cases, and of male Class III cases than female Class III cases. Conversely, male Class II and female Class III corrections might be enhanced. The very fact of continued growth should suggest that orthodontists have incomplete control of an orthodontic result and possibly should not accept indefinite responsibility for a perfect result. There are no biologic guarantees. We presently tend to use late adolescent standards to plan treatment for facial surgery for adults. That may have to change. For all purposes, we may have to develop an adult set of standards. At any rate, the likelihood of continued future growth will have to be taken into consideration.

DR. WHITE In light of growth in adulthood, do functional appliances have a use in adult orthodontics?

DR. BEHRENTS In brief, the answer is "no". The amount of growth we are talking about is large compared to a concept of no growth in the adult, but the amount of growth that is actually occurring on an annual basis is small and will not substantially alter the mechanotherapy we offer patients. If

orthodontists use this work as justification for using functional appliances, they will generally be disappointed. On the other hand, if orthodontists use this work to better comprehend the adult patient, then important aspects of orthodontics might be more easily understood. One example is relapse. Orthodontists should expect change subsequent to treatment as a natural event as opposed to expecting a forever static result.

DR. WHITE It would be interesting to repeat the study on a group of adults who did have orthodontic treatment in childhood or adolescence.

DR. BEHRENTS It is interesting that, quite inadvertently, we were able to gather long-term material on 28 additional individuals who had undergone orthodontic treatment before young adulthood.

DR. WHITE Were there differences between the orthodontically treated group and the untreated group?

DR. BEHRENTS The two groups were similar in that both involved individuals with malocclusions. The easiest way to envisage the differences between the two groups is to think of the orthodontically treated group as some sort of "malocclusion syndrome" group. They were generally different from the untreated group in that their facial configurations were quite abnormal in early adulthood, and they grew in an abnormal fashion during adulthood. In orthodontics, we tend to think our treatments may last a lifetime, but this study suggests that abnormally growing faces have little reverence for that thought. In fact, given enough time, some of the cases seemed to grow out of their corrections.

DR. WHITE Dr. Behrents, this work is one of the most significant and ambitious studies ever done on growth and development, and JCO thanks you immensely for sharing it with our readers.