The Alabama analysis

The Alabama analysis WENDELL H.

H.

PERRY

TAYLOR,

B.S.,

HITCHCOCK,

Birmingham,

D.M.D.,’

D.M.D.,

and

M.S.D.“”

Ala.

IT IS understood that there is very little that is truly new and that most seemingly new things are merely new applications of old ideas. With this in mind, we would like to explain the purpose and objectives of the Alabama analysis. It has been recognized by most clinicians that, in addition to being a useful tool for the research worker studying growth and development, cephalometrics is a valuable adjunct to diagnosis and treatment planning. If the clinicians of this area are to use cephalometrics as a vital part of their diagnosis, then we should first evaluate the rationale of using existing studies. The most questionable point of the existing analyses seems to be the location of the studies as related to the ethnic background of the samples studied. This idea seems to come from the realization of the numerous ethnic groups that have settled in this country. The South was settled predominantly by the Scottish, Irish, and English, with some Spanish and French influence. Even though the people of this area are heterogeneous, it stands to reason that it would be worth while to have a study based on samples from our area. Our hypothesis is that the ethnic background of Southern white children is different enough from that of children in other sections of the country to warrant a separate cephalometric standard and that this new standard probably might be used in this area for comparing children of Southern white ancestors. In turn, the statisticians apply the “null hypothesis” of no difference. Therefore, the burden of proof is up to the investigator. The idea of ethnic background differences is not original. It has been disPresented Ga., Oct.

at the annual 25, 1965.

This research Orthodontists. *Assistant Dentistry. **Professor of Dentistry.

was Professor, and

meeting

partially

of the supported

Orthodontic

Chairman,

Orthodontic

Southern by

Society

a grant

Department, Department,

of Orthodontists,

from

the

University University

of

Savannah,

Southern

Society

of

Alabama

School

of

of

Alabama

School

245

cussed by many, and it was brought ini o t ho discussion at I 1~ first. (‘tq)halomt:t ricd ?Vorkshop.‘!’ The next most questionable point sCtms to be which rrlca.sUI’eltltllts ant t,llch most, meaningful. This matter was also discussed at the first C%phalomctric Workshop, and a series of points, lines, and angles wcrc rceornmcndcd. Howcvclr, it was pointed out that the group could be a bit premature in their selection of these points and landmarks in that these ma.y not he t,he best ones to use. We agreed that from a clinical standpoint we should try to det,ermine which lines and points to measure and decide which will be more clinically meaningful, even if some so-called “standby measurements” are eliminated. Therefore, looking at our problem objectively, we decided that we should test a number of measurements and use those which were statistically validated. We realize, of course, that it would be difficult to not be influenced by points and measurements that we have become accustomed to using. We decided to attempt to report the facts as we found them, putt,ing the emphasis on reliability, validity, and usefulness rather than showing any favoritism for any of the measurements. In collecting samples for this study, we were trying to get a cross section which would be representative of the population of this area. Striving

Fig.

1. Facial

photographs

and

roentgenograms

of

representative

participants.

Volume Number

Alabama

52 4

analysis

24 7

B

D

Pig.

2. Study

models

of two

participants.

for a fair distribution according to sex, age, and sample size, with the realization that the clinician is primarily interested in the child usually from the ages of 8 to 15, we made a special attempt to select our sample from this age range. Fig. 1 shows photographs and cephalometric roentgenograms of two typical children in the study, and Fig. 2 shows models of two other children used in this study. The collection of data for such a project might appear simple, but it turns out to be quite a job. We started about 7 years ago. Our first objective was to find children to study. The Junior Chamber of Commerce and the Birmingham District Dental Society agreed to co-sponsor a smile contest each year in conjunction with National Children’s Dental Health Week. School children in grades 3 through 6 were to select one boy and one girl from each class to participate in the final contest at the University of Alabama School of Dentistry. At the School of Dentistry the children were carefully screened and selections were made from those who had normal occlusions, untreated orthodontically, with pleasing or at least acceptable facial development. These ultimate selections were made by orthodontists. The selected children were then subjected to a careful genealogical history which, of course, was obtained from the parents. The final samples were limited to those children whose families were of predominantly Southern extraction for at least two generations. The subjects (seventeen boys and twenty-three girls) were then called in, and records and model impressions were made in the Orthodontic Department of the University of Alabama. Cephalometric roentgenograms for this study were made

with a Margolis cephalostat. Tracings were made, and (!;1cAhone was III~~~S\IWC~ by at least two different orthodontists or graduate stntlmts, nGthc>r ol’ whom knew what the other had found. Differences of more than 1 dcgrcc or 1 mm. WPIY double checked and corrected. Differences of less tha,u 1 dcgrcc or .I mm. WV~V averaged. After many conferences with t,he Department of l3pidemiology and Kiometrics, the figures were turned over t,o the Computer Center for analysis. It has taken several years to complet,e this study, and we would likr to acknowledge the help that we received from Dr. Fayette Williams, Jr., and Dr. Jimi Metha, who gave a considerable amount of time to t,his project. .It is very appropriate that WC should present this material to t,ht? Sout,hern Society first, for it was some of their money that helped make this project possible. Much credit is due the personnel of the Computer Center at the University of Alaba,ma Medical Center for their helpful suggestions and efficiency. Also, WC would like to acknowledge the help received concerning statistics from Dr. Homer Jamison and Dr. Albert Wolff in the Department of Epidemiology and Riometrics. RESULTS

A total of thirty-two measurements were made from the tracing of each of the forty subjects. The means and standard deviations were calculated for every measurement (Table I j . What we have called the “spread” (or ‘(s-d,” using the first and last letters) gives us certain limits on either side of the average. These?limits include slightly more than a two thirds’ majority of the cases studied in the sample. This coincides with bhe statistician’s ‘(one standard deviation.” For purposes of cstablishing a sta,ndard, it, is more limiting or confining than thtr minimnm-to-mnximnm range. The data were analyzed separately for boys and girls. Only one measurement, the upper incisor to SN angle, showed a value large enough to indicate a questionable difference between boys and girls if the sample had been larger. We conclude from this that between the ages of 8 to 12 sex differences arc minimal for this cephalometric analysis. Intercorrelations were obtained from computer calculations. To be. more specific, each measurement was correlated with all of t,he other measurements. One purpose was to reduce the number of measurement,s from thirty-two and to justify t,he selection by statistical means. Many have voiced objections to the use of the Frankfort plane on the basis that it is difficult to find on the roentgenogram. This plane was borrowed from the anthropologists and is not necessarily the best reference line. Different investigators use different arbitrary points for porion. WC used a point 4 mm. above the center of the ear rod. Many relationships to the Frankfort pla.ne have also been taken to the sella nasion base line. In every instance we found that each relationship to the Frankfort plane shows a larger standard deviation or spread than the corresponding measurement to a plane other than the Frankfort. The following series of illustrations will show some of t,hese differences. The Frankfort plane will bc on the left : thr one which the statist,& showed we slmulcl

Table I. Alabama analysis

of forty

subjects Standard

Yeaausement 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32.

SNA (degrees) SNB (degrees) SNA minus SNB (degrees) Facial plane (NP) to Frankfort plane (degrees) Facial plane to SN (degrees) Angle of convexity (degrees) Frankfort-mandibular plane angle (degrees) Mandibular plane to SN angle (degrees) Y axis to Frankfort plane (degrees) Y axis to SN (degrees) Occlusal plane to SN (degrees) AB to SN (degrees) AB to occlusal plane (degrees) Facial plane to palatal plane (degrees) Upper incisor to lower incisor (degrees) Upper incisor to Frankfort plane (degrees) Upper incisor to SN (degrees) Upper incisor to NP (distance in mm.) Upper incisor to AP (distance in mm.) Upper incisor to NA angle (degrees) Upper incisor to AP angle (degrees) Upper incisor to occlusal plane (degrees) Upper incisor to palatal plane (degrees) Lower incisor to mandibular plane (degrees) Lower incisor to occlusal plane (degrees) Lower incisor to Frankfort plane (degrees) Lower incisor to SN (degrees) Lower incisor to SAR (degrees) Lower incisor to NB angle (degrees) Lower incisor to AP (distance in mm.) Lower incisor to AB (distance in mm.) Lower incisor to NB (distance in mm.)

Minimzlm

Maximum

Mean

deviation

74.25 70.75 -1.25

87.25 84.50 7.00

81.0 78.2 2.8

23.2 22.9 +2.0

78.0 71.5 -8.0

93.00 85.00 15.50

84.7 79.0 4.0

53.3 52.8 25.1

16.0

37.00

26.4

k4.6

22.75

41.00

32.0

24.5

51.00 61.00 9.50 66.00 80.75

68.75 73.00 23.25 83.00 96.00

60.4 66.1 16.7 73.8 90.1

53.5 22.8 t4.1 24.6 23.5

77.50

91.00

85.3

23.5

104.00

143.00

126.8

28.4

69.00 81.00

119.00 116.00

108.9 103.8

k8.8 k6.6

2.00

13.00

6.9

?2.7

2.00

9.50

5.9

22.0

13.25

35.00

23.2

55.0

16.00

37.25

27.2

T5.5

49.25

71.75

59.7

24.7

92.50

120.00

110.2

t5.0

83.00

110.00

97.3

26.3

54.70

79.75

67.2

25.5

40.50 34.00 -11.50

68.50 62.00 19.00

56.4 50.8 6.9

56.4 26.2 k7.1

17.50

39.50

27.3

25.8

-0.50

7.00

3.1

+1.8

1.50

7.50

4.1

IQ.4

2.70

9.50

5.4

41.6

ALABAMA

Fig.

3

Max. to 10&Q

Fig.

ANALYSIS

Incisor

Max

Incieor

- ShJ

Frankfort 4 8.8

I

4

came toa*

1

Fig. 3. A comparison of the standard deviation (dotted lines) between the facial and facial to 8N bases. The small angular differences of the standard deviations proportionally in vertical block form with dotted lines, showing “plus” above below the average. The average is represented by a diamond. Fig. 4. A comparison of the standard devia.tion Frankfort and maxillary incisor to SN bases. shown proportionally in vertical block form “minus” below the diamond-shaped average.

to Frankfort are shown and “minus”

(dotted linesj between the maxillary incisor to The differences in the standard deviations are with dotted lines, indicated r‘plus” above and

Volume Number

52 4

Alabama

analysis

25 1

use will be on the right (Fig. 3). The relationship to the Frankfort plane is shown on the left, and the relationship showing the smaller spread or standard deviation is on the right. The averages of the profile angles are represented by solid lines, and the spreads or standard deviations are by dotted lines on either side of the solid lines. Small differences between angular spreads or standard deviations are difficult to visualize. Therefore, we have symbolized proportionally the plus and minus angular standard deviations in block form, with a dotted line, showing plus above and minus below the average. The average is represented by a diamond. The case numbers at the bottom of the illustration refer to the fact that these are actual representations of the subjects within our sample who come closest to the average for this particular measurement. We found an average difference of 5.6 degrees between the facial plane to Frankfort plane5 and the facial plane to SN3 angles. The range, however, was from -1 to +15.5 degrees. It would seem that orbitale, which is located on different-sized orbits in different persons, and porion, which is mechanically determined from a machine, are not very satisfactory as landmarks for determining a base line. Again, we interpret the statistics as meaning that the measurement on the right is more nearly acceptable. Fig. 4 also shows the Frankfort plane relationship on the left. The relationship showing the smaller spread or standard deviation is on the right. Again, the small differences between angular spreads or standard deviations are proportionally symbolized as solid blocks, with dotted lines showing plus above and minus below the diamond-shaped average. Admittedly, every base line is variable. Nevertheless, we have reluctantly concluded that the Frankfort plane is not reliable enough to use. This study indicates that other lines are more valid, reliable, or meaningful than the Frankfort plane. On this basis, five angular measurements have been discarded (Fig. 5) : Frankfort to mandibular plane P axis to Frankfort plane Upper incisor to Frankfort Facial plane to Frankfort plane Lower incisor to Frankfort. Fig. 6 shows a comparison between the angle of convexity5 and the SNA-SNB difference.15 The average angle of convexity is shown in solid lines in the middle drawing on the left, with plus and minus standard deviations on either side of it. The angle of convexity has an exceptionally high coefficient of correlation (0.92) with the SNA-SNB difference. The numerical evaluation of the coefficient of correlation extends from +1 to -1. If we had a +1 coefficient of correlation between any two measurements, it would mean that for every unit increase in one of those measurements there would be a proportionate increase in the other measurement. If we had -1 coefficient of correlation between any two measurements, it would mean that as

Fig. 5. The Frankfort relationships plane angle; B, Y axis to Frankfort D, facial plane to Frankfort plane

Angle

which plane angle;

have been deleted. -4, The Frankfort angle; C, upper incisor to Frankfort E, lower incisor to Frankfort plane

of Convexity 4.0% 5.1

SNA

coeff.

mandibular plane angle; angle.

minus SNR 2.&t 2-o

of corr.

Fig. 6. The angle of convexity compared to the SNA-SNB difference. The coefficient tion, at 0.92, is so high that one measurement can readily be substituted for the SNA-SNB difference, with its smaller spread or standard deviation, is selected.

of correlaother. The

Volume Number

52 4

Fig. 7. The AB to SN measurement was dropped because high coefficients of correlation with other measurements. relationship was eliminated on the basis of difficulty in lack of widespread usage in this country.

Alabama

of a large The facial establishing

analysis

253

standard deviation and plane to palatal plane the palatal plane and

one measurement increased the other measurement would decrease by a proportionate amount. A high coefficient of correlation is not interpreted to mean a cause-and-effect relationship between two variables. Nevertheless, it can mean that one measurement may be substituted for the other in the evaluation of a particular criterion. The standard deviation or spread of the angle of convexity is 15.1, whereas the standard deviation of the SNA-SNB difference is only k2.0. For these reasons, the angle of convexity has been left out. In Fig. 7, the AB to SN angle was eliminated because it had high coefficients of correlation with other measurements and its standard deviation was larger than those of the other measurements. The facial plane to palatal plane angle, also shown in Fig. 7, is not widely used in other analyses in this country, and we dropped it from our final inclusions. Also, it is difficult to standardize a method for repeatedly designating the palatal plane. However, because of its low or only fair coefficient of correlation to the rest of the measurements, it seems to give us some different information, and it might stand further investigation. UPPER INCISOR RELATIONSHIPS. Considering upper incisor relationships, seven angular measurements and two linear relationships were studied. Fig. 8 represents the angular relationships of the maxillary incisor, in order of decreasing standard deviation or spreads, reading from left to right. The final selections are shown by cross-lined bars.

Fig. 8. Variations spreads above and eliminated. Angles Alabama analysis.

in maxillary incisor angular relationships below the diamond-shaped average. Angles indicated by cross-lined bars are included

as shown by plus and minus represented by solid bars were in the final composition of the

The upper incisor to occlusal plane angle,” at the right had the smallest spread from the average of any of t,he a.ngular measurements studied, so this was included. The upper incisor to palat.al plane angle I1 has the same spread or standard deviation as the upper incisor to NA angle. 8, I* The coefficient of correlation between the upper incisor to palatal plane angle and the upper incisor to occlusal plane angle is -0.81. This high correlation would indicate that we are getting similar information from this other source. Because we had already used the line NA, it was chosen in preference to the palatal plane for an incisor relationship. The upper incisor to AP line has a high coefficient of correlation with the upper incisor to occlusal plane angle. Therefore, the upper incisor t.o the A-pogonion line was left out on the basis of its being less reliable than some other measurements which give us nearly the same information and give it better. In our forty subjects, the upper incisor to sella-nasion angleI varies more from the average than the other measurements that were kept. However, it was included in order that we might have a measurement to a base which probably will not change position very much during growth or treatment. The upper incisor to lower incisor angle 5gI5 has next to the highest spread or standard deviation from the average of all measurements studied in our sample, Therefore, it was dropped. The upper incisor to Frankfort plane angleI had already been eliminated.

Volume Number

Alabama

52 4

MAXILLARY

INCISOR

*averages

RELATIONSHIPS

analyysis 2 5 5

(Ll.NEAR)

& spread(s.d.1

Fig. 9. Spreads and coefficients of variability The distance from the most anterior point has been selected.

of two linear measurements on the crown of the upper

of the upper incisor to the

incisor. AP line

Fig. 9 shows the upper incisor linear relationships. In the profile drawing at the left, the average position of the most labial point of the upper incisor to NP lineI is shown by a solid line. The standard deviations are shown on either side of it as dotted lines. On the right, the average position of the most labial point of the crown to the AP5 line is shown by a solid line. On either side of it are the dotted limits of one standard deviation or spread. The upper incisor to AP line has been selected on the basis of a smaller spread or standard deviation as well as a smaller coefficient of variability (C.V.) than the upper incisor to NP line. The coefficient of variability is the ratio of the standard deviation to the average, expressed as a percentage. It is particularly applicable to linear measurements. LOWER INCISOR. Fig. 10 represents the seven angular relationships of the mandibular incisor, in order of decreasing spread or standard deviation, reading from left to right. The final selections are indicated by cross-lined bars. Again, the occlusal plane relationship,15 at the right, shows the least spread or standard deviation. We have been somewhat arbitrary in eliminating the lower incisor to NB angle. It is a good measurement, but it seemed a superfluous measurement because of high coefficients of correlation to the occlusal planeincisor relationship (-0.9) and to the SN-incisor relationship (-0.89). Both the occlusal plane and point B may change as a result of treatment or

356

Taylor

and Hitchcock

MANDIBULAR

INCIS

veragas

OR

RELATIONSHIPS

and

spread

(ANGULAR)

(5.d.)

+6.4

Fig. 10. Variations in mandibular incisor angular relationships, spreads above and below the diamond-shaped average. Angles are included in the final composition of the Alabama analysis.

MANDIBULAR +averages

CM

584

INCISOR

by plus or minus by cross-lined bars

RELATIONSHlPSt

and

cu

as shown represented

LINEAR)

spread(s.da)

354

Fig. 11. Spreads and coefficients of variability of three linear incisor, as measured from the most anterior point on the crown. been selected on the basis of a smaller coefficient of variability

CY

3tb5

measurements of the lower The lower incisor to NB has (30.5).

Volume Number

Alabama

52 4

analysis

2 57

growth. Therefore, the relationships of the lower incisor to sella nasion and to the mandibular plane I3 have also been included in spite of slightly higher spreads. The lower incisor to Frankfort plane angle has already been relinquished. In our sample, parallelism between the lower incisor and sella-articulare” could not be determined. This has the second highest standard deviation of any lower incisor measurement studied. It was eliminated along with the previously mentioned upper incisor to lower incisor relationship. Fig. 11 shows the three lower incisor linear measurements. The solid line is drawn the average distance away from the most anterior portion of the crown of the lower incisor. The dotted lines show the limit of one standard deviation on either side of the average. The lower incisor to AB line has the smallest spread or standard deviation, but the lower incisor to NB line 8, I7 has the smallest coefficient of variability. We have been advised by the statisticians that when differences between standard deviations of linear measurements are small, the coefficient of variability may be a more critical determinant.g Linear

mea.wrement

Coeficient

of

1

to

API4

58.4

“1 1

to

NB

30.5

to

AB

35.1

-

variability

On this basis, the lower incisor to NB relationship has been selected as the linear measurement for the position of the lower incisor. DISCUSSION

After these processes of selection, what do we have left? We have half of the measurements we started with. SNA15 is an indication of the relation of the maxillary dental base to the cranial base. SNB15 is an indication of the relation of the mandibular dental base to the cranial base. The SNA-SNB15 difference gives a positional comparison of the dental bases to each other. Three relationships to sella nasion are shown in Fig. 12. The facial plane (NP) to sella nasion angle3 gives a relationship of the profile to the cranial base, as modified by the chin, and it also gives an indication of the degree of divergence of the profile-straight, forward diverging, or backward diverging. This angle has an extremely high coefficient of correlation with SNB (0.95). On this basis, one might be justified in recommending that the facial plane (NP) to SN angle be eliminated. However, we believe that because of the probability of some chin growth at a later age, the facial plane to SN angle would be useful for comparison at the end of treatment and out of retention. Thus, we have left it in the analysis, even though a person in the age group

Fig.

12

.*.*..................

..*-

. . .. . .. . .. .. . . .. . . ...e--‘*‘-*

AB to occtusal

pig. 13

octlusal

plane

to

Fig. 12. Three relationships to the cranial base. NP to SN gives a profile relationship as modified by the chin. The Y axis indicates a comparison between downward and forward growth of the mandible. The mandibular plane to SN indicates a relationship between posterior facial height and anterior facial height. Fig. 13. Two occlusal plane. (SN is projected

plane relationships-occlusal down as the parallel

dotted

plane line

to sella S’-N’.)

nasion

and

A3

to

occlusal

Volume Number

52 4

Alabama

analysis

259

at the initiation of treatment may not be crucially implicated regarding the position of pogonion as compared to the position of point B. It will be recognized that some of these averages are close to those already established through other studies. The Y axis to sella nasion angle,l also shown in Pig. 12, indicates a comparison between downward and forward growth of the mandible, and the mandibular plane to sella nasion angle15, I7 is an indication of the relationship between posterior facial height and anterior facial height. In actual tracings sometimes the base lines have to be projected downward for a particular measurement to be obtained within the confines of the tracing paper. Likewise, in Fig, 13, we have shown the SN line projected as the parallel dotted line, S’-N’. Two occlusal plane relationships are included. The occlusal plane to SN angle7 usually changes during treatment, but initially it may be used to compare anterior and posterior tooth eruption. The AB to occlusal plane angle4 seems to be a reliable indicator to reinforce the classification of the malocclusion. It may be a product of occlusal and muscular stimulation, which varies less than some of the anatomy surrounding it. Fig. 14 shows the three angular measurements and the one linear measurement of the upper incisor. The upper incisor to SN angleI is an indication of the procumbency or retrusion of the upper incisor to the cranial base. The upper incisor to the occlusal plane angle3 gives an initial functional relationship which probably changes during treatment, and perhaps after retention. The procumbency (or leaning) of the upper incisors is important from the standpoint of esthetics. Therefore, the upper incisor to NA angles, I7 has been included. The protrusion (or forwardness) of the upper incisors, regardless of angulation, is obtained from the upper incisor to AP line measurement5 shown on the right. Four mandibular incisor relationships are also included. The three angular measurements and one linear measurement are shown in Fig. 15. The lower incisor is related to the mandible,131 I5 its own anatomic base. It is also related to the occlusal planeI (its functional base) and to the SN line (as a cranial base). The protrusion or forwardness of the lower incisor is related to an esthetic base, NB,17 as shown in millimeters. These sixteen measurements form the Alabama Analysis. From a treatment standpoint, not all of them may be necessary. From a teaching standpoint, we are reluctant to discard any of them until they have been applied to our Class I, Class II, and Class III cases before treatment, after treatment, and out of retention. For now, we think that they are statistically reliable and clinically useful. The second purpose of our study-selection of the most meaningful measurements-is thus served before the first purpose. This has lessened the number of tests necessary to accomplish our first purpose, namely, determination of which measurements differ significantly in Southern white children as compared to these same measurements in other studies. Some problems arose in testing for significant differences between our

260

I’aylor

and

Hitchcock

Am

MAXILLARY

to

Fig.

INCISOR

a cranial

RELATIONSHtPS

base

14 sthetic

MANDIBULAR

INCISOR

to

to Fig.

a

cranial

a functional

bar

RELATIONSHIPS

base

base

v

15

anatomic=

Fig.

14. One

linegr

and

three

angular

relationships

of maxillary

Fig.

15. One

linear

and

three

angular

relationships

of

mandibular

incisors. incisors.

,I. fbthoclontics April 1966

Volume Number

52 4

Alabama

Table II. Six measurements which show statistically compared to available data from other samples Other Yeaszvrement

Average

significant

stzldy /

analysis

261

diflerences

when

“p

No.

Author

value

Probability

Occlusal plane to SN degrees) AB to occlusal plane (degrees) Upper incisor to occluSal plane (degrees) Upper incisor to AP

16.66 16.66

19.9 20.9

25 boys 25 girls

Higley

(1954)

3.32502 4.61584

0.00500 0.00100

90.05

87.5

40

Bushra

(1948)

3.17722

0.00500

59.68

58.0

322

(mm.) Lower incisor to mandibular plane (degrees) Lower incisor to occlusal plane (degrees)

5.94

2.7

20

97.25 97.25

90.0 93.5

100 24

67.18

71.8

24

Bjiirk

(1947)

2.02893

0.05000

Downs

(1948)

4.91787

0.00100

Margolis (1943) Riedel (1952)

9.17884 2.35286

0.00100 0.02500

Riedel

3.33126

0.00500

(1952)

measurements and those of other workers. For instance, some investigators did not give the number of persons in the sample, and their results could not be used. For some of the measurements, the other samples included malocclusions and normal occlusions. Certain lines have slightly different end points in different samples. Although some of these studies are not exactly comparable to our sample, there are six measurements which are significantly different on the basis of available data. Table II shows these six measurements and gives some information about the compared samples. Concerning the meaning of the term probability, our statistician friends say : “If you did an infinite number of experiments using these same criteria with random samples from the two test populations, and if the populations did actually have the same characteristics, then only five times out of one hundred would you observe differences this great or greater. Consequently, the probability is that you are dealing with two different populations.“g When the probability gets into the range of five times out of 1,ooO or one time in 1,000, then we can be even more nearly certain that we are dealing with two different populations. Nevertheless, what is statistically significant is not necessarily clinically important. As an example, the probability value for the upper incisor to occlusal plane angle is 0.050 or five times out of 100. The sample difference between the Alabama average and the average reported by Bjiirk is 1.7 degrees. It is doubtful that this difference would, or should, be considered important in comparing an individual to the standard. The size of BjBrk’s sample seems to be the overwhelming factor that barely gets this difference of the averages into the significant category.

2 62

Taylor

Table III.

and Hitchcock

Alabama Name Age l-4 Case

analysis iu

applicxblc~

form

#WI

ALABAMA

:-:a;-:a;ge,w,

ANALY

SI S (1965)

MEASUREMENT

MEAN

S. D.

12-15

mcl

1. SNA

81.0”

+3.2

16-19

mm

2. SNB

78.2”

k2.9

20-22

1m.n

27-29 30-32

40-42

SN

mu

5. ‘Y’

Axis

to

SN

UHJ

6.

1170

46-49

53-56

to

/l-jjn

43-45

cm0 1-rbr-j

jm.n

51-59

~--n--j

m.0 co.0

60-62 63-65

2. 8”

LNP)

rrru--1

36-39

- SNB

4. Fat

1130

33-35

50-52

3. SNA

mu

23-26

Mand

to

SN

*7.

Occl.

to

S.N

*8.

AB to Occlusal

*9.Ito

79.0”

Plane

Occlusal

Plane

66.1”

*Z. 8

32.0”

*4.5

16.7”

i4.1

90. 1”

*3.5

59.7”

*4.7

lo. Ito

NA

23.2”

i5.0

11. - 1 to

SN

103.8”

*6.6

*12.

Ito

AP (linear)

*13.

it0

Mand.

*14.

it0

occl.

Plane Plane

15.7

to

SN Plane

16. 1

to

NB (linear)

5.9mm.*2.0 97.3” 67.2”

*5.5 zt.6.2

5.4rnrnCtl.6

Racial Type of Mother: l-Nordic, 2-Mediterranean, 3-Alpine, 5-Negro, 6-Nordic-Medit, 7-Medit-Dinaric, 8-Other

4-Dinaric,

67 0

Racial Type of Father: l-Nordic, 2+Iediterranean, 3-Alpine, 5-Negro, 6-Nordic-Medit. ‘I-Medit-Dinaric, 8-Other

I-Dinaric,

Evaluation l-Good,

69

q

Evaluation l-Good,

70 0

26.3

50.8”

66 0

68 0

*2. 0 *2.8

of Skeletal Pattern 2-Fair, 3-Poor, 4-l ndeterminate of Upper Denture Area L-Fair, 3-Poor, 4-l ndeterminate

Evaluation of Lower Denture Area l-Good, 2-Fair, 3-Poor, 4-Indeterminate

CONCLUSIONS

Table III is derived from the actual data sheets that WC use. The numbered blocks on the left are where the patient’s readings are to be entered. The numbers are for the use of the key punch operator in entering the data on IBM cards. You will note that the skeletal relationships, numbered 1 through 6, are not significantly different from those found in studies done in other parts of the country. In the starred relationships, 7 to 9 and 12 to 14, which the orthodontist may change during treatment, the measurements are already chatiged as compared to those obtained in other samples.

Volume Number

52 4

Alabama

analysis

263

The lower incisor to SN relationship (No. 15) may be different from some other study, but we could not locate a previous work that would provide the sample size, mean, and standard deviation of this item, all of which are necessary for a statistical comparison. If it is thought that an angulation of 97.3 degrees is too high for the lower incisor-mandibular plane relationship, attention is directed to an article by Hallam Gresham’j which appeared in the Angle Orthodontist of April, 1963. In this study, Gresham compared New Zealand white children with North American white children whose records were obtained from the Orthodontic Department of the University of Washington. His value for the lower incisor to mandibular plane angle in the North American group is 97.045 degrees, nearly identical to ours. Gresham stated : “Broadly speaking, a figure of 90 degrees +5 degrees is considered the average and normal range for this component. It is surprising therefore to find a mean figure of 97.045 degrees for the North American sample in this study.” In the Northwest and Southeast, it should no longer be surprising to find this angulation of the lower incisor to the mandibular plane in white populations with normal occlusion. In spite of limitations and differences concerning the compared samples, we conclude that Southern white children do vary significantly in some of those relationships which the orthodontist is able to change. Therefore, the Alabama analysis is considered most nearly suitable as a cephalometric standard to which native white Southern children are to be compared. What are the practical implications of this study? First of all, from the standpoint of total facial to cranial relationships, it does not make much difference which North American study is used. However, some of the measurements involving the teeth and occlusal plane are statistically different from the compared samples (Table II) : 1. The occlusal plane to SN angle is smaller. In other words, the occlusal plane is not as steep. 2. The AB to occlusal plane angle, which we like because of its classification possibilities, shows a more nearly perpendicular relation to the occlusal plane. 3. The upper incisor to occlusal plane angle is different statistically, but it has already been pointed out that probably not much importance can be attached to that difference from a clinical standpoint. 4. The upper incisor to AP line measurement indicates that children with normal occlusion in our sample have more prominent upper incisors. 5. The significant difference of the lower incisor to occlusal plane relationship indicates that the lower incisor is leaning forward more than in the compared sample. Part of this, however, may be due to the fact that the occlusal plane itself is not as steep. 6. The lower incisor to mandibular plane angle indicates that the lower incisor is more procumbent.

Up to now we have tried to avoid st,atemcnts concorning treatrucnt. At this point, however, avoidance of the subject may be more noticeable t,han tackling the problem. The big treatment question which surrounds this item is not,: “L!wL we get the lower incisor to 90 degrees with the mandibular plane?” It is not: “Can we move the lower incisor to any particular angulation to any particular line or plane,” Rather, the important question is : “Should we 8” Treatment goals will va.ry from one orthodontist to another, and these goals will depend on background, training, ability, hero emulation, experience, ethics, and a sense of artistic rightness. A cephalometric standard furnishes an objective starting point. Beyond this starting point, whatever happens to the individual patient becomes a highly subjective matter as the orthodontist proceeds toward his treatment goals. It would seem reasonable to consider that an orthodontist is successful if, with his chosen appliance, he can approach those treatment goals, as judged by his peers, which are attainable within the framework of the philosophy which surrounds that appliance. Nevertheless, our study shows that it may be more difficult to justify the heroic measures necessary to force a Southern child to conform to an average measurement obtained from a different ethnic and geographic sample. If esthetics is a primary consideration, it should be pointed out that Southern girls are consistently in the top ten in the Miss America Pageant at Atlantic City. SUMMARY

Forty Alabama children whose parents also were born in the South were x-rayed by means of the Margolis cephalostat. Means, standard deviations, and coefficients of correlation were obtained for all measurements. Separate determinations showed no statistically significant difference bet,ween the profiles of boys and girls in the age range studied. Of thirty-two measurements analyzed, sixteen have been selected as statistically significant and clinically useful for the time being. Comparisons with other data from different samples were subjected to the “t” test for significance of differences of the means. Six measurements involving teeth and occlusal plane relationships showed significant differences. Therefore, something besides chance is operating, and we are dealing with a different population than has been used in previous studies. It is suggested that for Southern white children, treatment planning may be more nearly commensurate with the results achievable if based on a diagnosis which includes a comparison of the patient with the Alabama Analysis. REFERENCES 1. Baldridge, J. P.: A Study of the Relation of the Face in Class I and Class II Malocclusions, 2. Ballard, C. F.: Some Bases for Aetiology and 133-145, 1948. 3. BjGrk, A.: The Face in Profile, Svensk Tandl.

the Maxillary First Permanent Molars to Angle Orthodontist 11: 100-109, 1941. Diagnosis in Orthodontics, D. Record 68: Tidskr.

40:

Supp.

5 B, 1947.

Volume Number

52 4

Alabama

analysis

2 65

4. Bush+ E.: Variations in the Human Facial Pattern in Norma Lateralis, Angle Orthodontist 8: 100-102, 1948. Their Significance in Treatment and 5. Downs, W. B.: Variation in Facial Relationships: Prognosis, AM. J. ORTHODONTICS 34: 812-840, 1948. 6. Gresham, H.: A Cephalometric Comparison of Some Skeletal and Denture Pattern Components in Two Groups of Children With Acceptable Occlusions, Angle Orthodontist 33: 114-119, 1963. 7. Higley, L. B.: Cephalometric Standards for Children 4-8 Years of Age, AM. J. ORTHODONTICS 40: 51-59, 1954. 8. Holdaway, R. A.: Changes in Relationships of Points A and B, During Orthodontic Treatment, AM. J. ORTHOLWNTICS 42: 176-193, 1956. 9. Jamison, H. : Personal Communication. 10. Kaplan, H.: Cephalometric Study of a New Cranial Base Angle, Sella-Articulare-Mandibular Plane, AM. J. ORTHODONTICS 49: 785-786, 1963 (abst.). 11. Korkhaus, G.: Present Orthodontic Thought in Germany, Ax J. ORTHODONTICS 45: 881900, 1963. 12. Krogman, W. M., and Saesouni, V.: A Syllabus in Roentgenographic Cephalometry, Philadelphia, 1957, Philadelphia Center for Research in Child Growth. 13. Margolis, H.: The Axial Inclination of the Mandibular Incisors, AM. J. ORTHODONTICS 29: 571-594, 1943. 14. Ricketts, R. M.: A Foundation for Cephalometric Communication, AM. J. ORTHODONTICS 46: 330-357, 1960. 15. Riedel, R.: The Relation of Maxillary Structures to the Cranium in Malocclusion and iu Normal Occlusion, Angle Orthodontist 22: 142-145, 1952. 16. Steiner, C.: Cephalometrics for You and Me, AM. J. ORTHODONTICS 39: 729-755, 1953. 17. Schudy, F. F.: Cant of the Occlusal Plane and Axial Inclinations of Teeth, Angle Orthodontist 33: 69-82, 1963. 18. Tweed, C. H.: The Frankfort Mandibular Incisor Angle (FMIA) in Orthodontic Diagnosis, Treatment Planning, and Prognosis, Angle Orthodontist 24: 121-169, 1954. 19. Workshop on Roentgenographic Cephalometrics; Special Committee on Cephalometrics, A. A. O., March, 1957. (Mimeographed data.)