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the dental and facial skeletal characteristics and growth of males and females with Class II, division 1 malocclusion between the ages of 10 and 14 (revisited)--Part II: Vertical and Anteroposterior  growth between the ages of 10 and 14       
[Back to Part I]

by Ted Rothstein DDS, PhDa and Xuan Lan Phan, DDSb, as it appears in the American Journal of Orthodontics and Dentofacial Orthopedics, November 2001, Vol. 120, No. 5, Pp. ?-?, and reproduced with permission from Mosby, Inc.,  Aug. 2nd 2000. This copyrighted material may be used for personal use only and may not be distributed further.

This article is based on research submitted by Dr. Ted Rothstein in partial fulfillment of the requirement for the PhD degree, Graduate School of Arts and Sciences, Department of Anthropology, University of Pennsylvania, 1971. This study was supported by NIDR grant 5T 01 DE 0001 0904.
a
In private practice, since 1976, Brooklyn, NY, and on faculty at St. Luke’s-Roosevelt Hospital, NY.
b Orthodontic resident, University of Illinois at Chicago.
Reprint requests to: Dr. Ted Rothstein, 133 Pacific St. Brooklyn, NY 11201: e-mail,
drted35@aol.com
Website:
www.drted.com
American Journal of Orthodontics and Dentofacial Orthopedics
Volume
120, Number 5, Page
?
Copyright C 2000 by the American Association of Orthodontists

Abstract

Introduction

Materials and Methods

Registration Point and Plane of Orientation

Measurements

Limitations and strengths of the study

Results

Circumpubertal growth visualized

Growth of the facial skeleton and dentition in males and females with Class II, Division 1

Discussion

Conclusions

Clinical Implications

References

 Tables:

I. Total growth from SA 10 – 14 of  FEMALES and MALES  with Class 11, Division 1 malocclusion compared with their female and male control groups, and the difference between them and the controls.  

Figures:

Fig 1.            Class I FEMALE composite, circumpubertal, visualized growth standard (magnification ≈ 6%): showing magnitude and direction of growth from SA 10 to 14.

Fig 2.            Class I MALE composite, circumpubertal, visualized growth standard (magnification ≈ 6%): showing magnitude and direction of growth from SA 10 to 14.

Fig 3.                 Measurements utilized to compare differences in magnitude and direction of growth of female and male samples having Class II, Division 1 malocclusion with matching samples of Class I normal controls.

Fig 4.                 FEMALE circumpubertal (SA 10-12-14) growth vectors of selected endpoints representing: 1. Cranial base, upper and mid-face (Ba, Nas and A), 2. Mandible (Ar, Go, Gn and B), 3. Upper dentition (DU6 and U1), 4. Lower dentition (DL6 and L1).

Fig 5.                 MALE circumpubertal (SA 10-12-14) growth vectors of selected endpoints representing: 1. Cranial base, upper and mid-face (Ba, Nas and A), 2. Mandible (Ar, Go, Gn and B), 3. Upper dentition (DU6 and U1), 4. Lower dentition (DL6 and L1).

Fig 6.                Total Growth, in millimeters age 10 to14, along the X- and Y-axes, of points (DU6, U1, DL6 and L1) representing the dentition (Nas and A), the upper and mid-face (Gn), the anterior mandible, and (Ar and Go) the posterior mandible.

Fig 7.                 The variables in FEMALES where the difference in the measurement between the Class II, Division 1 sample differed from the controls by a factor of ≥ 1.4 mm or degrees. (-) or (+) indicates whether the II,1 variable was greater or less than the control.

Fig 8.                The variables in MALES where the difference in the measurement between the Class II, Division 1 sample differed from the controls by a factor of ≥ 1.4 mm or degrees.  (-) or (+) indicates whether the II,1 variable was greater or less than the control.

CONTINUING EDUCATION ARTICLE

Dental and facial skeletal characteristics and growth of males and females with Class II, Division 1 malocclusion between the ages of 10 and 14 (revisited)—Part II: Vertical and AnteroPosterior Circumpubertal Growth

Ted Rothstein, DDS, PhD, and Xuan Lan  Phan, DDS.

Brooklyn, NY, and Chicago, Ill

ABSTRACT

A radiographic composite standard/template for Class I females and males showing the growth changes in the dentition and facial skeleton from ages 10 to 14 is presented.  The amount and direction of growth change of dental and facial skeletal parameters derived from the radiographs of 335 children with Class II, Division 1 malocclusion (II,1) were compared with 273 Class I controls and the differences described. Both II,1 and control groups were subdivided into three female and three male samples, skeletal ages 10, 12, 14 ±6 months, ranging in chronological age from 8.5 to 15.5 years.  Radiographs of like II,1 and control samples were converted to X- and Y-coordinate data from which fifty-two commonly used linear, angular and coordinate axis measurements were made.  The mean Class I plot from the coordinate data at age 14 was superimposed over the age-10 mean Class I plot, resulting in the creation of a circumpubertal growth standard.  The standards are supported by growth vector diagrams and other data that support the following conclusions: 1. Normal males differ distinctively from females in amount and direction of circumpubertal growth. 2. The radiographic composite standards are useful and accurate clinical tools to show mean dentofacial skeleton growth and change between age 10 and 14. 3. Compared to controls, II,1 females’ maxillary dentition grows more horizontally; upper incisors, but not lower incisors, procline farther; mandible grows more horizontally. 4. II,1 males’ mid-facial convexity markedly increased owing to some horizontal growth at point A and less horizontal growth than controls at Nasion and Pogonion; upper and lower anterior teeth procline farther. 5. Angular measurements involving S,N,A,B, and Pog are useful only when Nasion’s position is known. 6. Cranial base flexure bears no relationship to the development of II,1 malocclusions. (Am J Orthod Dentofacial Orthop 2001:120, ?-?)

This article is based on research submitted by Dr Ted Rothstein in partial fulfillment of the requirement for the PhD degree, Graduate school of Arts and sciences, Department of Anthropology, University of Pennsylvania, 1971. This study was supported by NIDR grant 5T 01 DE 000l 0904.

Special attention re correction of data omitted in Part I: V.117 n. 3, P. 324-5.  Please note them in Part II.

Re error/omission in Table II, (Mean and Standard deviation of each variable for the control sample): The entries for MANDIBLE (AP relationship to Sella:) Posterior mandible (Ar-S, diagram D12) and Anterior mandible (S-Pog diagram D13) should be:

            F10               F12             F14             M10             M12         M14

Ar-S 13.8±2.4    14.5±2.2    15.0±2.3    14.8±2.0    15.5±2.0   16.9±2.1

                                S-Pog    56.3±6.3    56.6±6.4    59.6±6.3    54.9±5.4    58.6±4.7    61.6±6.3

INTRODUCTION

“Find out the cause of this effect, Or rather say, the cause of this defect; For this effect defective comes by cause.”—Shakespeare, Hamlet II, ii, 101.   Seasoned practitioners are continuously alert to the size, form and position of the dentofacial skeleton, in all three dimensions, in the growing child.  They are constantly titrating the direction and magnitude of forces they apply against a growth force that may help or hinder treatment objectives. 

Fortunately, most of our patients present with Angle's Class I malocclusion, where the maxillary and mandibular first permanent molars are Class I and the maxilla and the mandible are in good relation to each other transversely, vertically, and sagitally to the anterior cranial base.  In such cases we are less concerned that our choice of mechano-therapy may not be justified, or even be deleterious.

However, the "moderate-severe" Class II and Class III cases i.e., those with an anterior-posterior dental (apical base) discrepancy greater than 4 mm, often alert us to the possibility that underlying the apparent dental malocclusion problem there may also be a jaw-size, jaw-form or position discrepancy.  The clinician can to a modest but meaningful extent restrict [or promote] growth of the maxilla and promote [or retard] growth in the mandible.1  This may warrant the use or avoidance of particular treatment modalities, or, indeed, may virtually mandate surgical intervention to produce an ideal treatment result.   For example, the use of class II elastic traction between the maxilla and the mandible is contraindicated in cases of skeletal open-bite attended by an excessive mandibular plane angle in a patient with a borderline long-face syndrome.

The Class II, Division 1 malocclusion (protruding upper anterior teeth and an apparent retrusive/retro-positioned mandible) is a frequently treated problem.

In Part I2 of this study, the research question was couched in terms intent on testing Angle's hypothesis that Class II, Division 1 malocclusion is characterized by an underdeveloped (size) or posteriorly positioned mandible or both.  The 52 parameters describing the face/dentition indicated that in both females and males at SA ages 10, 12 and 14 with Class II, Division 1 malocclusion, where a skeletal dysphasia may be present, the mandible/mandibular dentition is similar to controls in size, form and position, while the maxilla/maxillary dentition is forwardly/mesially positioned.  The palate was inclined superiorly, and no statistically significant vertical dysplasia was found.  The magnitude of the variable at 10,12, and 14 was given for the control and 11,1 groups.

In Part II, growth differences between children with Class II, Division 1 malocclusion and samples of normal occlusion are presented.  Most important, nowhere in the literature can one find a visual composite standard/template for craniofacial and dentofacial growth in males and females based on skeletal age that graphically shows the amount and direction of growth over the circumpubertal (ages 10-14) growth period.  Jacobson3 and Jacobson and Kilpatrick4 have shown how growth templates can be used for orthodontic diagnosis and other researchers have provided numerical standards for the annual increments in children with normal occlusion5, but few studies have attempted to compare Class II,1 children to controls with normal occlusion over that period of time in which the orthodontic clinician is most likely to commence and complete treatment of this problem.

Knowledge of the differences in magnitude and direction of growth in children with Class II, Division 1 malocclusion can in some instances enable the clinician to control the outcome of his or her plan of treatment.   Granted, we are far from being able uniformly and accurately to predict in a given individual the magnitude and direction of growth.  However, it behooves all clinicians to be familiar with the broad characteristics of normal and deviant growth of the maxilla, mandible and dentition during this circumpubertal growth period because major deviations from it, if not recognized sufficiently early, can result in a preventable treatment compromise or failure.

Part II, therefore, aims to (1) provide a graphic description / standard of normal growth for females and males from skeletal ages 10 through 14; (2) describe the similarities and differences in the magnitude and direction of growth of the dentition and facial skeleton of children with Class II, Division 1 malocclusion when compared with Class I control groups.  In essence the clinician will have “holistic” graphic templates of mean circumpubertal growth, one for each gender, describing reference points most often used by clinicians to measure and describe the growth of jaws and dentition.

MATERIAL AND METHODS

The radiographs for this study, drawn from the files of the W.M. Krogman Research Center for Child Growth and Development in Philadelphia, Pennsylvania, were reasonably representative of the white children in the City of Philadelphia during the 1950s and early 1960s.

Radiographs of the control group, n=273, representing children with "normal" occlusion were part of an ongoing longitudinal survey of normal growth;6 however, the samples were essentially described as cross-sectional.

The Class II, Division 1 series of radiographs, n=335, represented children referred to the Growth Center by the Orthodontic Department, School of Dental Medicine of the University of Pennsylvania for growth status and treatment plan evaluation.  The sample description of both groups was described in Part I.2

The conversion of a lateral head radiograph into a “mathematical model” and then a series of lateral head radiographs into a composite line drawing is briefly described in Part I, as is the error of the method; both are described in thorough detail in Rothstein’s doctoral dissertation.7,8

Registration Point and Plane of Orientation

Sella was taken as the point of origin (0.0, 0.0 in the Cartesian coordinate system) because growth of the cranial base is largely completed by ages seven to nine.   Thus the cranial base provides a relatively stable (i.e., unchanging) area to which middle and lower facial and dental growth changes can be related.  Point Sella is also used by most orthodontists and researchers in craniofacial growth analyses.  In addition, the vertical axis of the coordinate system passes through Sella in the cranial base and is centrally located.9,10  Moorrees9,10 observed that the degree of variation increases in general with the distance of the landmarks from the basic orientation axis both in the vertical and the horizontal directions.

The "Krogman-Walker" (K-W) horizontal plane of orientation, described in Part I, is defined by two highly reproducible endpoints, maxilla (Max) and occipitale (Occ), which are located in the mid-sagittal plane.  In addition, the K-W plane passes through the midface, consequently, one could expect a reduction in the magnitude of variability (standard deviation) of the endpoints in the middle and lower face.  Finally, the K-W plane closely parallels the Frankfort plane, which approximates natural head position, making it more reliable in the assessment of anterior-posterior deviations.10

Measurements

The schema in Fig 3 (A-G)  [Same as Fig. 4 in Part I]  will help the reader to organize and visualize the 52 measurements made at ages 10, 12, and 14 in II,1 and control samples of females and males.  The same schema is followed in Table I and in the review of the findings.

Limitations and strengths of the study

The samples are cross sectional not longitudinal.  Group and inter-group measurement and mean growth data and statistics for each of the 52 measurements for the six Class I and six Class II groups can be found in Appendix III of the dissertation.7  Table Is shows the change in size between ages 10 and 14 for the Class I and the Class II groups and the arithmetic difference between the two.  Parameters whose differences were 1.4 mm or greater (an arbitrarily chosen cut-off number) are presented in bold italics.  The authors extrapolated their findings from the combined analysis of Table I and the growth vector diagrams presented in Fig 4 (Female) and Fig 5 (Male).  The sample sizes are statistically adequate, and grouped by developmental age and gender.  Most important, X- and Y-coordinate data have been used to verify and interpret the purported significance of angular data.

RESULTS

Circumpubertal growth visualized

Fig 1 shows the radiographic composite norm/standard for the 10-year-old normal FEMALE sample (n=47).   Superimposed on it with Sella registered and the Krogman-Walker planes of orientation made parallel is the composite sample of 14-year-old females (n=48).  Fig 2 displays the same composites for normal MALES showing the magnitude amount and direction of growth between skeletal ages 10 (n=48) and 14 (n=45).  The 12-year-old composite is not shown lest it detract from visualizing the growth occurring between ages 12 and 14.  The measurements for the 12-year-olds can be seen in Figs 4 (F) and 5 (M).  The reader is encouraged to examine Figs 1 and 2 side by side to note the differences in amount and direction of growth between males and females.

Tables II and III, Part I,2  [Table II Part I][Table III Part I],   present the changes in size for each of 52 measurements made at ages 10, 12 and 14 for control and II, 1 males and females.  Fig 4 shows the vectors of growth of the major landmarks of the face and dentition during 10 to12 and 12 to14 years of age in FEMALES, both for the control and Class II,1 groups.  The vector path for Class II,1 samples is denoted by a double male or female sign.  Note that the figure also portrays the position of the Class II,1 landmark at 10 years old in relation to that same landmark in the control sample.   For example, the upper molar is represented by DU6.  One can clearly see that in the Class II,1 sample, it was positioned about 2 mm anterior to the control group and its vector of growth is more horizontal.  Fig 5 presents the MALE growth vectors for control and Class II,1 samples ages 10 to14.

Growth of the facial skeleton and dentition in males and females with Class II, Division 1

Fig 5 presents the growth-vectors of pertinent endpoints.  Vector diagrams were constructed from sample means obtained from the normal and Class II series females and males.  Fig 6 is a numerical summary of the vector diagrams of selected endpoints representative of the main skeletal and dental components, and gives the total horizontal and vertical growth between ages 10 and 14 years for both genders of both series.

In Class II, 1 females between ages 10 and 14, in the upper and middle facial profile, (Nas and A) and the upper molar (DU6), the magnitude of the X component of the growth vector was 0.5-1.4 mm larger (Fig 6), and the Y component (DU6) 1.4 mm smaller, At Ar, Go, Gn, in the mandible, the X-axis growth component averaged approximately 1.7 mm larger and the Y component 1.8 mm smaller (only at Gn).  Fig 4 growth vectors shows this vividly.  These observations imply that in Class II, 1 females, between ages 10 and 14 (note vector pattern of DU6 and Pog in Fig 4), growth forces were channeled in a more horizontal and less vertical direction than in normal females.  Moreover, it appeared that the mandibles of Class II females were mimicking a similar pattern of growth in the maxilla.  Thus the direction of mandibular growth vectors suggested that this horizontal movement was accomplished by an increasingly horizontal growth vector pari passu with a decreasing vertical component, or what is commonly described as a “counterclockwise” mandibular rotation.

In Class II,1 males, between ages 10 and 14 (Fig 6), superiorly at Nasion, the X component of the vector was approximately 1.5 mm less and the Y component almost 2 mm less.  At the midface (ANS, A, U1), the X component of the vectors averaged about .7 mm larger; whereas the Y component of growth was seen to differ from the controls only for the upper incisors, where it was found to be 1.6 mm (an effect of increasing labial proclination (see Table 1, C25 and Fig 5, U1).  Anteriorly, at Gnathion on the mandible, the X and Y components of the vector were approximately 2 mm less horizontally forward as a result of the vertically directed growth between 10 and 12, and 1.2 mm less vertically downward as a result of the more horizontally directed growth between 12 and 14.  Unlike the Class II,1 females, where the Y component of the upper molar (DU6) grew 1.4 mm less than controls, the II,1 males grew 0.8 mm more vertically than controls at DU6.  This finding was not reflected at point Gnathion, where vertical growth was 1.2 mm less than controls. 

These means suggest that in II,1 males, mid-facial convexity tends to increase more than in controls because of increased horizontal growth at A and decreased horizontal growth at Nas and Gn, coupled with decreased vertical growth at Gn, while vertically downward growth of the upper molar was not apparently a factor in downward and backward movement of the mandible.  Indeed, Table 1 shows that angle N-A-Pog (E27) in males showed the greatest difference of all the measurements, and total anterior facial height was 1.7o -2.0o less than controls in the female and male samples, respectively.  However, unlike II,1 females, in II,1 males no connection could be made to decreases vertical growth at DU6.  These observations suggested that in Class II,1 children the circumpubertal growth spurt sculpts the form of the II,1 female face differently than it does the male.

Table 1 presents a compilation of the total growth for each variable measured between ages 10 and 14 in females and males for the Class II,1 and control samples, and the difference between their growth magnitude/direction.  Differences equal to or greater than 1.4 mm or degrees are shown in bold italics.  The results are presented in the order they appear in the schema (See Fig 3A-G  [Same as Fig. 4 in Part I]  and Table 1).  The letter/number combination seen in parentheses (e.g., A1) refers to the diagrams in Fig 3, which define the measurement taken.  Figs 7 and 8 show at a glance those measurements that are equal to or greater than 1.4 mm or degrees for II,1 females and males.

·        Cranium: Frontal bone thickness at sinus: similar growth as controls.

·        Cranial Base: In Class II,1 males, A3, A4 and A5 all showed less growth.  Females II,1 showed no differences as compared to controls. The cranial base angle (A3) in II,1 females increased  0.3 degrees from 133.1, while in control females it increased 1.2 degrees.from 130.7  In II,1 males it decreased 1.4 degree down from 132.5, while in control males it increased 0.2 degrees from 130.0 degrees.

·        Mandible:  In Class II,1 females, Pogonion (D13) grew 1.7 mm more horizontally and Gnathion 1.9 mm less vertically (D15) than controls.  In males, Pog grew 1.9 mm less horizontally than controls (D13) while Gnathion, although showing less growth than controls, did not rise to the level of the 1.4 mm cut-off level.  The gonial angle (B10) decreased slightly in females and controls, but in II,1 males it decreased 2.1o more than controls.  Class II,1 males showed 1.9 mm less growth in overall length (B7) than controls.

·        Maxilla:  In II,1 females, the key ridge (C28) grew 1.4 mm more horizontally and the palato-mandibular plane angle (E32) decreased, differing from controls by 1.5o.

·             Increased mid-facial convexity in Class II,1 males is revealed by 1. the increase of angles S-N-A (C26) and ANB (C33), (note: Class II,1s increase and the controls decrease); 2. a decrease of angle N-A-Pog (E 27) (note that the large difference –4.8o is owed largely in part to angle N-A-Pog increasing in control males, and in part to its decreases in II,1 males.); and finally, 3. an increase of 1.7 mm (C34) in the magnitude of the horizontal distance between points A and B,.owing largely to the combination of point A growing .7 mm more forward (C25), and Pog growing 1.9 mm less horizontally (D13).

·        Maxilla / Key Ridge:  In Class II,1 males, horizontal growth between Sella and Maxillon (representing the key ridge), (C28), was 1.8 mm less than controls.  However, viewed in relation to the horizontal growth from Sella to A (C25), one could deduce that horizontal growth is exuberant (3.0 mm more than controls) across the area of the maxilla sinus (G30, Max – ANS) in Class II,1 males.

·        Maxilla / PalateIn II,1 males palatal slope (E31) remained almost the same while the mandibular plane angle relative to palatal plane (E32) decreased in both Class II,1 females, 1.1o, and in males, 2.7o, compared with their controls (females increased .4o mm and males decreased 1.0o).

·        Maxilla – Mandible: In II,I males the magnitude of discrepancy B–A (C34) increased .3 mm but in controls decreased 1.4 mm (total difference 1.7 mm).

·        Mandibular and Maxillary dentition:   In II,1 females both the upper and lower molars (F35 and F40) are growing more horizontally than controls (1.5 and 1.4 mm, respectively), while the upper incisor (F43, S-U1) and (F45, incisor inclination to S-N) increases its proclination 1.5 degrees i.e., .9 mm more than in controls (3.8 mm).  The lower incisors in both II,1 and control females, (F39), grow similarly, showing only a slight increase in proclination, 0.3 mm and 0.4 mm, respectively.

·             In II,1 males, in contrast to females, an unexpected pattern emerged: the distance between the molars and the incisors (B38 and F44), i.e., the distance between the UPPER molars and incisors, in control in II,1 males decreased .1 mm (F44) and the distance between the LOWER molars (B38) and incisors .4 mm., unlike the control male samples where the distance decreased 2.2 mm and 2.3 mm, respectively, most likely a consequence of the closure of the leeway space.

·             In both II,1 females and controls, unlike in the males, the distance between molars and incisors barely closed at all (F44, upper, approached 0.0 mm closure and B38, lower, closure averaged .7 mm).

·        One would have expected the molar incisor distance to decrease in control females since the decrease in male controls was attributed to closure of the leeway space as deciduous molars give way to the smaller permanent premolars.  The absence of molar-incisor closure in II,I males and females can be attributed to an anterior/horizontal shift of the dentition en masse.  No explanation is offered as to why the control female data do not show a diminution of molar-incisor distance similar to the control males.

·             In control females proclination of the upper incisor as represented by F43 and F45 (angle of the incisor to S-N remained about the same, while in II,1 females and males it out distanced controls 1.6o and 3.5o, respectively.  Thus, at 14, II,1 males incisor proclination has markedly increased, while in controls it decreased…the third largest difference in Table I, (F45).  Measurement F43 (S-U1 horizontally), however, does not corroborate well with  F45 since it shows that U1 in II,1s outdistanced controls by a mere .9 mm (F) and .6 mm in males. 

·             In Class II,1 females, the lower molar, DL6 (F35) grew horizontally / mesially 1.5 mm more than the controls.  In Class II,1 males, the increase of the lower incisor inclination (F39) was considerably more (difference of 4.1 degrees) and the lower molar-incisor separation (B38) barely closed (.4 mm) while in controls it closed 2.3 mm.,  (The en masse movement of the dentition in II,1s seems to prevent the leeway space from closing.)

·        Facial Depth:  In both Class II,1 females and control groups, upper middle and lower facial depth growth were similar (G46, G47 and G48). On the other hand, in Class II,1 males, point A was 1.4 mm more excessive while Nas (A5) and Pog (D13) exhibited 1.5 mm and 1.9 mm less growth, respectively, than the controls, thus again supporting the II,1 male showing of excess mid-facial growth as compared to controls.

·        Facial Height:  In both II,1 male and female samples, growth of anterior total facial height (G49) was 1.7 mm and 2 mm less than their respective control samples.  In II,1 females the diminished height was an apparent result of 1.9 mm less growth than controls in lower anterior facial height (G51).

DISCUSSION  

Of patterns – points – and place of teeth –

Of maxillae – and means –

And why the jaw grows out in front –

And how the palate swings.--- Pace Lewis Carroll 

Few studies did radiographic comparisons of the growth of children presenting Class II, Division 1 malocclusion.  Anderson and Popovich11 compared 68 children with Class II malocclusion to 148 children with Class I occlusion at ages 8, 12 and 16 years.  They found that in Class II children the jaws, especially mandibles were positioned more posteriorly in relation to the cranium, and there was more open flexure of the cranial base angle (Bolton-Sella-Nasion).  Bacon et al.12  reported that there was a relationship between cranial base flexure (Ba-S-Na) and Class II in some cases.  However, they stated that cranial base contribution was far from being decisive in most of the Class II cases.  The present study did not support the hypothesis that the flexure of the cranial base angle (see Part I, Tables II and III, (Ba-S-Na, A3)13 contributed in some systematic way to mandibular position.  The angle stays the same size in females or becomes 1.3o smaller in males, however, the mandible and its dentition in Class II, Division 1 samples were found to be identical to those of the control subjects in size, form, and position for both genders at the ages of 10, 12, and 14 years, except for symphyseal height (B11), which measured significantly larger in II,1 males,(see Table III, Part I).14

Buschang et al.15 compared 20 males (12 with Class II, Division 1 and 8 with Class II, Division 2 untreated malocclusion) to 20 control males with normal occlusion using longitudinal data over the period between 11 and 14 years of age.  They demonstrated the application of a polynomial regression technique that was used to describe differences in size, velocity, and acceleration of the variables based on fitted curves from which random variation has been removed.  They found that Class II,1 males had a decreased growth velocity in Ba – Na.  Mandibular length (Ar – Pog) was significantly shorter (approximately 2.5 mm) and ANB angle was larger in Class II, Division 1 group, but that the yearly reduction in this angle was comparable to controls.  In Class II, 1 males of the present study, Ba – Na and Ar – Gn grew 1.5 mm and 1.9 mm, respectively, less and angle ANB outdistanced controls 1.9o (C33); i.e., II,1s increase 1.0o, while controls decrease 0.9o.  Buschang, et al. concluded that since all other measurements were comparable in growth velocity and acceleration, size differences were established before 11 years of age and maintained during adolescence.

In a longitudinal cephalometric study, Ngan et al.16 compared the skeletal growth changes between Class II, Division 1 and Class I female subjects between ages 7 and 14.  Tensor analysis was used to determine the yearly growth rate and direction.  The maxilla (SNA) was found to be normally related to the cranial base while the mandible (SNB, SNPog) was significantly more retrusive in II,1 females..  Mandibular length (Ar – Gn) and corpus length (Go – Gn) were shorter in the Class II group.  In the present study, the mandibular overall length (Ar – Gn, B7) grew 1.9 mm less in II,1 males.  The increase of SNA angle (C 26) was greater in II,1 males while the increase of SNB angle (C 17) showed differences of only 0.5o and 0.9o, respectively, for females and males between two groups.  However, we must remind the reader that SNA(Pog), SNB(Pog) and ANB(Pog) angles must be evaluated with caution.  For example, N-A-Pog, facial convexity (E27), in II,1 males at age 14, differed from controls by 4.8o owing to a combination of increased growth at point A and decreased growth at Nas and Pog.  Part I17 revealed that angles E27 (N-A-Pog), C26 (S-N-A) and E16 (S-N-Pog) were in no way significantly different in relation to controls while S-N-B was.  In reality, point B was identical in IIs and controls, but was masked by Nas being more anteriorly positioned as well.  Consequently, without an age-sex standard for the position of Nasion, the above angles are likely to mislead clinicians and researchers.

Our findings agree with those of Gesch.18  In his longitudinal study of growth-related changes in an untreated II,1 sample. 40 untreated Swedish children were examined between ages 10.1 and 12.  He found the most frequent cause of a distal relationship between the two jaws was a disharmoniously anterior shift of the maxilla.

We believe Walker’s mathematical model warrants the attention of researchers, as it can examine the magnitude and direction of growth horizontally and vertically of every landmark in the dental and craniofacial complex allowing a more accurate interpretation of angular data. 19,20  For example, the data indicate that facial convexity and the maxillo – mandibular discrepancy worsen in Class II, 1 males.  The reason can be found by looking at the horizontal growth behavior of points Na, A, and Pog.  The N-A-Pog angle indicates that the difference in growth between the II,1 and control samples is 4.8o (E 27).  The explanation for this difference lies in the fact that horizontal growth at Nasion (upper face) and Pogonion (lower face) was less (A5 and D13) while point A (midface) (C 25) showed slightly more growth than controls.  A part of that diminished growth at Pog is owing to the fact that growth of the mandibular corpus length (B 9) was slightly less in II,1 males.  It must be recalled that except for symphyseal height in males, the mandible and its antero-posterior position in relation to Sella were not significantly smaller or posteriorly positioned as compared to the control samples of females and males at 10, 12, and 14 years of age.

CONCLUSIONS

1.       The magnitude and direction of circumpubertal growth differs for females and males.   A growth composite standard/template is now presented for each gender.

2.        II,1 females show more horizontal growth of pogonion, upper and lower molars and more proclination of upper incisors, but not lowers, and less growth in total and lower anterior facial height.  Both II,1 males and females demonstrated a decreased mandibular plane angle, less growth in total anterior height and more labial proclination of the upper anteriors.

3.       II,1 males showed a decreased gonial angle, pronounced increased proclination of upper and lower incisors, increased mid-facial convexity, and less growth in mandibular overall length and upper facial depth.

4.       The three female (age 10, 12 and 14) and three male composite standards resulting from the Cartesian coordinate system used in Part I and Part II of this study to  measure growth of the dentition and craniofacial skeleton were useful in the interpretation of such angular measurements as SNA, SNB, ANB, and NAB, which can be subject to serious misinterpretation.

5.       Growth changes in the cranial base angle in II,1 females and males were similar to controls.

CLINICAL IMPLICATIONS:
           
For clinicians the data suggest that in growing females normalization of the Class II, Division 1 malocclusion to a Class I molar relation may be more easily accomplished because of the exuberance of the horizontal growth in the mandible that seems to take place between ages 10 and 14. In II,1 males it is desirable to restrain forward/horizontal growth of the maxillary dentition since one can expect the growth of the male mandible to show a larger vertical component of growth

We gratefully acknowledge the assistance of Esther Lafair who participated in every phase of this research project since its inception in 1969, and the National Institute of Dental Research whose grant originally funded the work.

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