Process of maturation and growth prediction

T HROI;(;HOUT the history of orthodontics, the clinician has been interested in the growth and development of the bones of the skull. There have lxml numerous claims concerning the significance of this growth, or perhaps its lack of significance. Some orthodontists have predicated their treatment on the as- sumption that growth can be ignored as an integral part, of treatment planning. They have implied that if one aims at excellence of occlusion everything wit1 work out satisfactorily. Still others have assumed that if teeth are placed where they belong, according to a given standard, growth need not be considerctl or that, if favorable growth does occur, a better result will be produced.

At the other extreme are to be found those clinicians who believe that orthct- dontic treatment can alter the growth pattern of the maxilla7 the mandible, and the cranial base in either amount or direction.

Horn important is growth in the treatment of a malocclusion! What is its role in treatment planning? Cephalometric studies have shown that not only do dramatic changes occur in the position of teeth during orthodontic t,reatment but equally dramatic changes may occur spatially between the maxilla and the mandiblo. These latter changes are associated with the sum total of growth oc- curring throughout the skull. Fig. 1 demonstrates the growth direction of a Class II, Division 1 malocclusion treated by a nonestraction method. The convexity t,f the face has been reduced by mandibular growth occurring horizonta,lly at a faster rate than maxillary growth. This difftrential is further reflected in tlie improvement of the profile after treatment, (Fig. 2). On the other hand, the reduction in the deep overbite is associated primarily \vith vertical mandibular growth. The change in occlusion with the reduction of the distoclusion has brw produced primarily by the horizontal differential betwcn maxillary and mandib-.

Presented before the American Association of Orthodontists in Miami l3each, Fla.. May 6, 1963.

*Chairman, Department of Orthodontics, Indiana Uniwrsity School of Tlcntixtry

Fig. 1. Fig. 2.

Fig. 1. Anterior cranial base superposition of a 14-year-old boy. Treatment interval, 15 months. The mandible has grown horizontally more than the maxilla, resulting in partial correction of the Class II malocclusion.

Fig. 2. Profile change in patient represented in Fig. 1.

ular growth rates rather than by tooth movement itself. Horizontal and vertical changes in the position of maxilla to mandible, as demonstrated in this case, are not atypical and are commonly found in treated eases during the period of growth. Of course, the orthodontist would like to know how much of this change is associated with the growth that would have occurred without orthodontic treatment and how much might be associated with the treatment itself. Defini- tive answers to this last question are hard to obtain because of the great amount of variation in the pattern of growth among individuals. We may well have t,o wait for large controlled samples before the role of therapy is fully understood. It must be conceded, however, that growth-whether or not it is altered by ortho- dontic therapy-is important in the production of the final end result.

It is necessary for the orthodontist to attempt some type of growth predic- tion before beginning his treatment. It is not possible to know exactly where to position teeth unless it is known where the bony bases will be during and at the end of treatment. The proverbial round-trip ride of teeth is associated in part, with a lack of understanding of the role of growth in altering the occlusal relationship. A growth prediction is important not only in treatment planning and treatment; it becomes equally important in evaluating the prognosis of the case during the retention and the postretention period.

How accurately can we predict the growth of the skull? There are inherent, problems in any attempt to make an accurate prediction, since so many variables are involved. Every orthodontist, however, consciously or unconsciously makes an estimate of the growth potential of his patient. Some of these estimates are more elaborate than others. In any event, it is necessary for us to make this

estimate before starting treatment, even though all of the answers may not be yet known. We cannot declare a moratorium on treatment until more is known about growth prediction. In predicting growth, it is necessary to understand the normal process of growth as well as the possible effect of orthodontic treat- ment on the growth pattern. The starting point in H growth prediction is a con sideration of the normal growth process isolated from the effect,s produced b) treatment.

There are many factors involved in gron;t,h prediction, but in this article I shall consider only one namely, maturation. Any prediction concerning either the direction or the amount of growth must consider both the maturation level and the rate of maturation of the patient.

THE CONCEPT OF MBTURATION

Nntu&ion refers to the process of development toward completion of the skeleton and, in this particular instance, the completion of the dentofacial com- plex. There are two key concepts of maturation that are of considerable impor- tance : (1) the level of maturation and (2) the rate of maturation.

The level of maturation refers to the status of an individual relative to full completion of his pattern. In other words, it is a statement of how far along the individual is on the road to completion of his growth. The concept of maturat

9 10 Burstone Am. J. Olthodontics December 1963

Other terms that describe growth rate and are synonymous with rate are growth increment and growth velocity. In Fig. 3 t,he growth rate of the nasion-gnathion dimension of a boy is plotted against chronologic age (based on data from Nan- dal). There is a fairly characteristic pattern in which a period of deceleration is seen from 6 years to 12 years. This is the prep&era1 stage. The p&era1 stage, which begins at the point of inflection of the curve, is characterized by a period of rapid acceleration (a growth spurt). In this boy the peak relocity in the N-Gn dimension is reached at 1.4.5 years of age. Following the peak velocity, the postpuberal sta.ge is entered; this is characterized once again by a period of dc- celeration, up to the point of maturity. Thus it is that the rate of growth from birth to maturity is not a constant but raries from one time interval to the nest. The level of maturity of an individual can bc described not only by his chrono- logic age but, more accurately, by the stage of skeletal development which he has reached. It is useful to think of certain landmarks along the road to maturity for purposes of describing the maturational level. Convenient landmarks can be seen at the point of inflection on the curve when t,he child will be between the prepuberal and puberal stages or the point of completion when t,he rate of growth has dropped to zero, or perhaps the most useful landmark would be the point of peak velocity during which the growth rate has reached its circunapuberal mnxi- mmm.

Thus, if we are interested in predictin, n the increments of growth during an interval of time, it is rather meaningless to use arcrage rates. For example, we could areragc the rate of increase for thcl dimension Y-Gn. but we would lose the important information concernin g variation in growth increments that occur from one developmental stage to another. If WC arc interestZed in a more reasonable prediction of growth rate, it is necessary first to estimate the del-elop- mental lerel of the child, with an understanding of where that child stands in relation to the peak relocity or any other stage of development. Then we arc in a better position to estimate the possible growth that will occur during the time of treatment or thereafter. Still another question of clinical significance concerns the optimal time for treatment. In the evaluation of the optimal time to treat a malocclusion, a number of factors are involved beyond the growth potential of the patient. Considering only growth rate, ho~vcwr, it might seem logical, if the growth pattern were favorable, to treat many cxws during the time of peak velocity, that is, during the circnmpul~cral grolvth spurt.

The advantages of treating at the time of the peak velocity during the pn- bcral growth spurt is twofold. In the first place, growth increments arc at their maximum. This would minimize the amount of tooth movement required Co1 both correction of a distoclusion and deep owrbite, provided, of course, that the pattern of growth is favorable. In the second place, the possibility remains that ease of tooth movement may bc cnhanccd by the endocrine picture associated with these growth changes. The wlationship betjwen the androgen and estrogen levels and changes occurring within the periodontal membrane during tooth movement merits further investigation. Since there are other reasons to suggest that in many cases treatment should be carried out earlier than the time of the peak growth velocity, it is suggested that peak velocity is only one factor to bc

considered in evaluating the optimal time for treatment, The prediction of the time of maximal circumpuberal growth becomes significant, if the decision is made to treat during the permanent-dentition period.

The final reason for determining the developmental level of an orthodontic+ patient is to help in the estimation of how much growth will occur subscqucrrt, to orthodontic treatment. The prognosis for a Class 111 malocclusion may b(: quite different if treatment is completed before rat,her than after the peak gro\vth velocity. Understanding the developmental status of the pnticnt gives us a bet,1 VI opportunity to ensure a satisfactory prognosis for the CilSC.

In short, in order to estimate the rates of growth, tither on a long-term or a short-term basis, it is necessary to consider the maturity level of the vhiltl. Average rates of growth become meaningful only if c~:n~I~aral~lc l~cls of ma- tnrit.v are compared.

If all children reached a given developmental level at approximately the sallie age, estimating the level of maturation would be rclativelp simple. C:nfor- turiatel)-, there is a great amount of variation in the d(velolJmcntal stages 01

6 I 8 9 10 11 12 13 14 15 16 17 16

AGE, YEARS

Fig. 4. Variation in rate of maturation in body stature of three girls. A, Early matmw; B, average maturer; C, late maturer (based on the data of Shuttleworth).

9 12 Burstonc Am. J. Orthodontics December 1963

children of identical chronologic ages. Using the developmental level of peak velocity for demonstration, one can observe, in Fig. 4, the variat.ion in age at which the peak velocity has occurred in three girls. The measured increments represent total height or stature of the body according to the data of Shuttlc- worth.2 It should also be noted that there is considerable variation in the mag- nitude of the peak velocity (Fig. 5). This can be seen better if growth velocity

I -6 -5 -4 -3 -2 -1YAx. 1 2 3 4 5 6

VEL.

y&m BEFQRE AND AFTER TIME OF MAXJhlUM VELOCITY

Fig. 5. Curves of three girls in Fig. 4 superposed on the circumpuberal maximum. Enclosed area has been blackened for emphasis. Notice variation in magnitude of growth rate, par- ticularly at peak velocity (thickness of black line indicates amount of variation).

is plotted against years before and after the time of maximal velocity using the same data as found in Fig. 4. Most of the research dealing with rate of matura- tion has been carried on not in the area of the skull but, rather, in standing height. There is no reason to believe that similar phenomena cannot be observed during facial growth, namely, that there is considerable variation in the onset, of the peak velocity (as well as any other developmental level) and that varia- tion in the magnitude of the peak velocity or any other developmental level also exists.

Since many children mature at faster rates than others, it is convenient to classify the rate of maturation on the basis of the onset of the puberal growth

spurt or the occurrence of the peak growth velocit,y (Fig. 1). The a\rerage ma-, turer would he one 1~1~0 would reach his peak velocity at about the same t,irrw as other c~hildren in his own age group. The earl)- maturer would reach it earlier, and the late maturer would reach it later than a\(lap(l. Although this classif- cdation is wry useful, it should be remembered that thrlrc, is a gradual bI~xnd I)etTwen t,he eal*lv, average, and late matnrcrs and thilt thrtxe discrete (at cwiw cl0 not exist.

The concept of rat,e of maturation has a llumbc:r ot: clinical ;~l~pli~4ali~~ns. Lf one is int,erestcd in using the peak velocity in statlwc as a guide 10 \)t>ak velocity in the face (there seems to be some evidence that the two arc very trlosel>- I*elatcd), averages for boys and girls may appear superficially to 1~ hc~ll~f~~l. On the average, the peak velocity (body stature) is reached at ll$< pears of ag(s in girls and at around 14 years of age in boys. I The fallacy of losing a\-cragcs can be swn when the ranges are studied. The range in girls is from S;!l to 111 :! years of age, and in boys it is Srom lOI, to 16 ywrs of age. From a c*Linical viewpoint, it can be seen that chronologic age is not a gootl guitlc in cstinlatinc t,hc dc~clopmental status of the patient.

It was stated earlier that not only wre tliertr diffcw~ltws in ttw time of orwi of a given drrolopmental level, such as the peak vc1oc:it.y ilt puberty, I)ut t1Jn1 there ww also differences in the magnitude of t,he rate at this time. It is possibl~~ that ilSSPSSiIlg the developmental level of a patient in relation to other c~hiltlrcw of the SilJJlC! chronologic age may give some clues to the magnitutlc of the pwlc growth wlocitg. Studies in stature have demonstrated that, OJJ the avcragc~. o~II~!~ maturers tend to have increased rates of growth and late matlirrrs shop\- tlta creased rates of growth at puberty. It may be logical to espwt, similar cllang(:s within the region of the face. This hypothesis has not bwn atlqtatrly twttvl. but it, merits consideration as an aid in growth pwlict ion of snc~h structnrc,s as the mandible.

11 growth prediction of the face implies that not only have we gained a11 nndcrstantling of the developmental level of the child whom we arc treating but that we also have evaluated his rate of development in comparison to his peers. If w arc fortunate enough to graph the rates of growth of a given bone year by year up to the point of maturity, a positive statement can be made about thy developmental level of the child at each stage as well as about his rate of dwelop mcnt. From a clinical viewpoint, the orthodontist has a more difficult pnhlm~. since he must make a prediction of developmental level and rate of maturation before growth is completed-and many times with inadequate records of past growth. Some possible clinical guides to the evaluation of maturatioll lewl an(l

lXt,e of maturation level will now he considered.

DENTAL AGE

IIow good is the eruptive pattern of the teeth as a guide to the mat,uration level of the child? Do early erupters mature early in terms of skeletal growth? The correlation between dental age and skeletal age is very 10w.*-~ Clinically, this means that dental age is a very poor guide to the developmental level of the child skeletally or to his rate of maturation. This is not to imply that eruption

and skeletal growth are not related but only that predictability is poor. It ma3 be a mistake to use the erupbive pattern of the teeth in determining the optimal time for treatment,, even though it cannot bc denied that this may be a major factor mechanically in the handling of the case. It can also be seen that if one routinely waits for the eruption of second molars before the initiation of ortho- dontic treatment, the period of maximal growth may long have passed, par- ticularly in girls who are early maturers. One of the clinical problems faced by the orthodontist is this lack of correlation between skeletal development and dental dcvelopmcnt, since treatment planning is made more difficult if dental maturation proceeds at a slower rate than skeletal maturation.

A number of techniques have been devised for assessing the skeletal age of a patient. Most of these procedures rely on the interpretation of an x-ray picture of a bone or a group of bones and its comparison to a suitable group of standards representing norms for every age.7 Perhaps the most commonly used met,hod for evaluating skeletal age is the use of the wrist plate. To be sure, there are inherent problems in evaluating skeletal age bs this method. Different bones of the body may have different rates of maturation, and rates of maturation may vary from one time interval to the nest. 8 Nevertheless, skeletal age as evaluated by wrist plate may be one of the most useful and accurate adjuncts in evaluating the childs skeletal maturation level as well as his rate of matura- tion, An estimation of skeletal age is a recommended adjunct for an orthodontic growth prediction. An inherent problem, however, in employing the concept of skeletal age for all bones of the body is the fact that diffcrcnt, bones will have different developmental patterns. Thus, peak velocity, for instance, may vary from one growth area of the skull to another and may bc reached in a given facial structure at a different time than in the hand or wrist.

SEX OF THE CHILD

Girls, on the arcrage, tend to mature earlier than boys (Eig. 6). Typically, there is a 2 year different,ial between girls and boys with respect to the onset of the peak velocity. Not only do boys mature later than girls, but the magnitude of their peak velocity will be considerably greater than in girls. These changes ha~c been observed primarily in statural growth, but most likely a similar phe- nomenon will be observed in the growth of structures in the skull.

This may explain some of the clinical differences in response that can be observed in boys and girls treated durin g the early permanent dentition. One might expect that a male teen-ager would show a more favorable response to Class II treatment than the typical female teen-ager, assuming that the pattern of growth was fairly typical. Furthermore, this differential in the onset of the peak velocity sqggests that it may be desirable to start the treatment of many girls earlier than that of boys. This is not to suggest that all treatment of boys should wait until the time of peak velocity. It does suggest, however, that if earlier treatment is not indicated a more optimal time might be during the period of the circumpuberal maximum.

2

AGE (years)

Fig. 6. Comparison of typical rates of growth in stature of boys and girls. Curves royrescnt means of average maturers. (After Tanner, J. 31. : Growth at .~tlolcsct~nce, Springfield, Ill., 1955, Charles C Thomas.)

At about the time of pubert,p, profound hormonal changes arc occurring which are reflect,ed throughout the body. Rapid increases in statural height arc noticed. Likewise, the bones of the face (particularly the mandible) are rapidI\ increasing in size. The reproductive system is developing, and secondary ses characteristics begin to emerge.

Chanpcs in the reproductire system and the emrrgence of secondary ses characteristics may give clans to the onset of the puberal skeletal growth spurt. This is not too surprising, since these two phenomena are very closely related. 1 :I the male there are voice and beard changes, but these changes are very tlifficnlt to eraluatc, particularly during the early stages of puberty. In the female, breast, changes signal the dcrelopment of the reproductive system. Fundamentally, in both the male and the female, the devtlopmcnt of marked secondary sex charar- teristics suggrst,s that most likely the peak \-elocity at puberty has been paswl. From the point. of view of t.he ort,hodontist, evaluation of secondary sex chara+ teristics is either not a practical guide or is not definitive in e\-alnating t 110 status of the patient relative to his peak velocity.

On the other hand, an excellent guide to sexual development in the female is the time of mcnnrche. Fig. 7 shows the typical patterns of statural develop- ment in the earl-, average, and late maturers as well as the relationship betwvn the peak wlocity and the time of menarche. It can be noted that early maturers tend to have an earlier than average menarche. Even more important, it is

Maturity - early

---- Maturity - average

------ Maturity - late

1 8 9 10 11 12 13 14 15 16 17 AGE (years)

Fig. 7. Relation of peak velocity to menarche in early-, average-, and late-maturing girls. Ar- TOW points to time of menarche. (After Simmons and Greulich: J. Pediat. May, 1943, pub- lished by The C. V. Mosby Company.)

apparent that, in the early-maturing girl, menarche lies much closer to the peak velocity than in the girl who matures lat,er. This would suggest that if menarche has been reached, growth rates are beginning to decelerate and the peak growth velocities have already occurred. The early maturer has greater growth potential left after menarche than the late maturer. This means that the early maturer will experience more growth after menarche than the late maturer.

BODY TYPE

A crude guide to the rate of maturation is body type. Generally, persons who are particularly tall for their age are early maturers and those who tend to be particularly short for their age are late maturers.1

If body typing is based upon the relative height to width of an individual, as in the classification of ectomorph, mesomorph, and endomorph, it can be ob- served that the mesomorph tends to predispose to early maturation and the ecto- morph to late maturation.ll

Since there are numerous exceptions, generalizations of this type are not very reliable. However, an evaluation of body type may well add another facet to the prediction of growth.

CORRELSTING GROWTH IN HEIGHT WITH FACIAL GROWTH

Much of the foregoing discussion has been based upon the process of matura- tion, considering parameters of statural growth. The work of Nandal has sug-

gested that there is a close relationship between such developmental levels as the peak velocity in body stature and the peak velocity in certain facial st,ruc- tures. Nanda states t,hat the peak velocity in the facial region comes at nearly thcb same time as the peak velocity in stature or tends to occur slight,ly later.

The implication of this relationship is that much of Iv-hat is currently know11 about growth in stature may be applicable to the region of the skull. It also suggests that any information that the clinician may obtain concerning staturt, growth may be helpful in the prediction of the onset of the peak velocity in the face. In many areas, data on heights may be available on a yearly basis from the school system. In other situations height changes in a child may be available from family records. Observations, during and before treatment, concerning the rates of growth in height may also be suggestive ot where the child is in relation to his peak velocity. A history of previous height incrclases is an impor- tant adjunct to growth prediction, and, fortunately, it is if history that lllosi parents arc in a good position to give.

The limitation in using body-weight curves lies in the diffcrencc~s in ra tc: of maturation between facial structures and other bones in the body. As more is known about differential maturation among bones throughout the body. height curves will probably brcome more, rather than less, predictive.

GFSETI( EACTORS d 1

It has been established that there is a strong genetic basis for the morphol- ogy of the bones of the skull. The question arises: Is there a genetic basis for the rate of maturat,ion of an individual?

Once again, it is necessary to return to height studies if an answer to this question is to be found. As far as height is concerned, a familiar tendency in the rat,e of maturation has been observed between siblings and between the parent and child of the same sex.12

Children of broad-chested parents show more rapid maturation and greater increments of growth at the circumpuberal maximum. This information is highly suggestive that a good history and observation on mrmbers of the sarn( family may give some hint as to the rate of maturation that may be expectt4 in a child who requires orthodontic treatment. Thus, hcrcditary charact~crist,ics may be more useful in predicting rates of maturation than in cvalnating that skeletal morphology of the child, since skeletal configurat,ion ran be dircctl? obscr\-cd.

An understanding of growth processes and the ability to predict growth are an integral part of treatment planning. The orthodont,ist is not, only in- terested in the dentofacial configurations at the beginning of t,reatment, but hr must consider what these configurations will be at t,he end of treatrnent and. perhaps, at the completion of the growth process. A growth prediction involves an understanding of normal growth processes, upon which must be superposed the possible effects of orthodontic therapy. The starting place, therefore, fol a growth prediction is an estimation of the changes that might occur without orthodont,ic intervention.

9 18 Burstone

Fundamentally, a growth prediction resolves itself to the estimat,ion of rates of growth for a given structure or structures. h regional type of analysis, in which growth rates are estimated for individual bones or growth areas followed by summation of all of these individual areas to form a composite growth prcdic- tion of the face, offers the most promise in predictability.14 Since each growth site of the skull has its own patt,ern of maturation as well as its own rate of growth, the regional type of approach seems most logical.

This article has dealt with two &toys that can influence growth rates-the maturation level and the rate of maturation of a bone. It has been suggested that, averages based on age can be rcry misleading in efforts to estimate the amount of growth that will occur subsequently. In estimating the mnturatioa lcccl of bong development and by comparing children at idcnt,ical levels, wc are in a much better position to predict growth rates accurately.

On the other hand, if we are int,erested in establishing the time of onset of the puberty spurt or the time at which most of the growth will cease, it is neces- sary to estimate the rate of maturation of the bones of the skull. Once again, averages as to the onset of the peak relocity or the full cessaticn of growth are not particularly useful, since children show considerable variation in the rate of maturation throughout the bones of the body, including dclltofacial struc- tures.

It should be remembcrcd that gro\vth prediction of the face involves more than the measurement of angles and linear dimensions on lateral headplates. Cephalometric analyses become meaningful only if they arc corrclatcd with the over-all physiologic changes that occw in the child. It is for this reason that a growth prediction involving the craniofacial complex comprls thn orthoclontist to go beyond the measurements of the face and to consider the child not just as a head but as an integrated organism.

REFERESCES

1. Nanda, R. 5.: The Rates of Growth of Several Facial Components Measured From Serial Cephalometric Roentgenograms, An, .T. Am. Dent. A. 62: 161-167, 1961.

5. Sutom, W. W., Tcrasaki, T., and Onwada, 1~. : Comparison of Skclctal Maturation \Vith Dental Status in Japanese Children, Pediatrics 14: 3Zi-333, 1954.

6. DeMiseh, A., and Waterman, P.: Calcification of the Mandibular Third Molar and Tts Relation to Skeletal and Chronologic Age in Children, Child Develop. 27: 459, 1956.

7. Greulich, W. W., and Pyle, S. J.: Radiographic Atlas of Skeletal Dwrlopmcnt of Hand and Wrist, Stanford, Calif., 1959, Stanford University Press.

8. Hewitt, David, and Acheson, R. M.: Some Aspects of Skeletal Developmcbnt Through Adolescence, Am. J. Phys. Anthropol. 19: 321-344, 1961.

9. Shuttleworth, F. K.: Sexual Maturation and the Skeletal Growth of Girls ,%ge Sis to Nineteen, Monographs of the Society for Research in Child Development, Vol. ITT, ~0. 3, Washington, D. C., 1938, National Research Council, pp. l-56.

I (1. Simmons, I